Field Studies

Ainley, David G., Grant Ballard, and Silvia Olmastroni. 2009. An Apparent Decrease in the Prevalence of "Ross Sea Killer Whales" in the Southern Ross Sea. Aquatic Mammals 2009, 35(3), 335-347.

ABSTRACT
Killer whales (Orcinus orca), both ecotype-B and -C, are important to the Ross Sea, Antarctic ecosystem. The ecotype-C is referred to as "Ross Sea [RS] killer whale." Herein, we review data on occurrence patterns and diet of RS killer whales and present new information on numbers observed in the southwestern Ross Sea, 2002-2003 to 2008-2009 austral summers. These "resident" whales appear to feed principally on fish, including the large Antarctic toothfish (Dissostichus mawsoni). On the basis of sea watches from Cape Crozier, Ross Island, sighting frequency and average group size appears to have decreased; prevalence as indicated by casual observations from helicopter pilots flying over the area on a daily basis has also decreased in nearby McMurdo Sound. Consistent with a decrease in the catch-per-unit-effort of scientific fishing for toothfish in McMurdo Sound, we suggest and review evidence that the change in RS killer whale numbers in the southern Ross Sea is related to an industrial fishery-driven, density-dependent northward contraction of the toothfish stock and not to changes in the physical (and, in turn, biological) environment. We surmise that in this closely coupled foodweb, composed of very abundant penguin, seal, and whale components, loss of the toothfish option for RS killer whales would force more direct competition with other predators for capture of the smaller-fish prey. Therefore, we propose, the RS killer whales have opted to move elsewhere, in a scenario consistent with that of the Pacific coast of Canada, where numbers of resident killer whales have decreased following the loss of large fish as a prey choice.

Full paper HERE (870kb).

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Alava, Juan José, Pedro J. Jiménez, Patricia A. Fair, and Lance Barrett-Lennard. 2019. First Record of a Live-Stranded Killer Whale (Orcinus orca) in Coastal Ecuador and Insights on Killer Whale Occurrence in Ecuadorian Waters. Journal of Mammalogy, 92(2):275–282, 2011.

EXCERPTS:
While the species is commonly found in waters off Ecuador and the Galapagos Islands (Merlen, 1999; Alava et al., 2011, 2013; Alarcón et al., 2012; Smith, 2012; Denkinger et al., 2013; Bublichenko, 2015; O’Hern et al., 2017), information is incomplete about the abundance and distribution of killer whales in the marine coastal waters of Ecuador (Alava et al., 2011; O’Hern et al., 2017). This cetacean is considered “Near Threatened” in Ecuadorian waters, including the Galápagos waters (Alava et al., 2011), yet data providing insights into its population dynamics, behavior, and foraging ecology in the marine-coastal areas of Ecuador are sparse.

More data exist for Galapagos waters, where killer whale predation events and interactions with other marine animals suggest that this species exhibits at least two kinds of predatory habits: one focused on bony fish, sharks, and manta rays, and the other on large whales (i.e., sperm whales [Physeter macrocephalus] and baleen whales), small-toothed cetaceans (e.g., bottlenose dolphins [Tursiops truncatus] and short-beaked common dolphins [Delphinus delphis]), and Galapagos otariids (Merlen, 1999; Sonnino Sorisio et al., 2006; Alava & Merlen, 2009; Alava et al., 2013). Additionally, a pod of killer whales was video-documented interacting/playing with and presumably hunting, a Galapagos green sea turtle (Chelonia agassizii) in waters off Isabela Island, Galapagos Islands, in September 2018 (Roth, 2018).
...
Thus, the aim of this note is to describe the first live-stranding of a killer whale calf along the mainland coast of Ecuador and its rescue by the local community.

Full paper HERE.

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Allen SJ, Bryant KA, Kraus RHS, Loneragan NR, Kopps AM, Brown AM, Gerber L, Krützen (2016). Genetic isolation between coastal and fishery-impacted, offshore bottlenose dolphin (Tursiops spp.) populations.. Molecular Ecology doi: 10.1111/mec.13622.

ABSTRACT
The identification of species and population boundaries is important in both evolutionary and conservation biology. In recent years, new population genetic and computational methods for estimating population parameters and testing hypotheses in a quantitative manner have emerged. Using a Bayesian framework and a quantitative model-testing approach, we evaluated the species status and genetic connectedness of bottlenose dolphin (Tursiops spp.) populations off remote northwestern Australia, with a focus on pelagic ‘offshore’ dolphins subject to incidental capture in a trawl fishery. We analysed 71 dolphin samples from three sites beyond the 50 m depth contour (the inshore boundary of the fishery) and up to 170 km offshore, including incidentally caught and free-ranging individuals associating with trawl vessels, and 273 dolphins sampled at 12 coastal sites inshore of the 50 m depth contour and within 10 km of the coast. Results from 19 nuclear microsatellite markers showed significant population structure between dolphins from within the fishery and coastal sites, but also among dolphins from coastal sites, identifying three coastal populations. Moreover, we found no current or historic gene flow into the offshore population in the region of the fishery, indicating a complete lack of recruitment from coastal sites. Mitochondrial DNA corroborated our findings of genetic isolation between dolphins from the offshore population and coastal sites. Most offshore individuals formed a monophyletic clade with common bottlenose dolphins (T. truncatus), while all 273 individuals sampled coastally formed a well-supported clade of Indo-Pacific bottlenose dolphins (T. aduncus). By including a quantitative modelling approach, our study explicitly took evolutionary processes into account for informing the conservation and management of protected species. As such, it may serve as a template for other, similarly inaccessible study populations.

Full paper HERE.

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Amano Masao, Tadasu K. Yamada, Robert L. Borwness, Jr., and Yoshikazu Uni. 2011. Age determination and reproductive traits of killer whales entrapped in ice off Aidomari, Hokkaido, Japan. Journal of Mammalogy, 92(2):275–282, 2011.

ABSTRACT
On 7 February 2005 a group of 9 killer whales (Orcinus orca) were trapped in drifting sea ice and died at Aidomari, Hokkaido, Japan. We carried out age determination based on tooth growth layers and examined the reproductive organs of these whales. Growth layer groups (GLGs) in the dentine and cementum were readable, even in the old specimens, and complementary to each other in decalcified and stained thin sections of lower teeth. Reliable age determination of killer whales is feasible, and GLGs are accumulated annually. The longitudinal growth of the teeth continued until about 20 years of age, which is much longer than for the corresponding age in other delphinids. Counts of corpora lutea and albicantia increased linearly with age from 3 to 7 in whales 13–34 years old, but the oldest female (59 years old) had only 8 corpora albicantia, which could indicate a decline in the ovulation rate in old females. Photographs of the original group trapped in the ice confirmed that at least 2 whales escaped or died and did not strand with the others. Therefore, this group was composed originally of a mature male, 1 possibly postreproductive female, 5 reproductively active females, 3 calves, and 2 or 3 unidentified individuals.

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Andrews, Russel D., Robert L. Pitman, Lisa T. Ballance. 2008. Satellite tracking reveals distinct movement patterns for Type B and Type C killer whales in the southern Ross Sea, Antarctica. Polar Biol (2008) 31:1461:1468.

ABSTRACT
During January/February 2006, we satellitetracked two different ecotypes of killer whales (Orcinus orca) in McMurdo Sound, Ross Sea, Antarctica, using surface-mounted tags attached with sub-dermal darts. A single Type B whale (pinniped prey specialist), tracked for 27 days, traveled an average net distance of 56.8 ± 32.8 km day, a maximum of 114 km day, and covered an estimated area of 49,351 km². It spent several days near two large emperor penguin (Aptenodytes forsteri) colonies, a potential prey item for this form. By contrast, four Type C killer whales (fish prey specialists) tracked for 7 - 65 days, traveled an average net distance of 20 ± 8.3 km day, a maximum of 56 net km day, and covered an estimated area of only 5,223 km². These movement patterns are consistent with those of killer whale ecotypes in the eastern North Pacific where mammal-eating "transients" travel widely and are less predictable in their movements, and fish-eating "residents" have a more localized distribution and more predictable occurrence, at least during the summer months.

INTRODUCTION
Long-term research on killer whales (Orcinus orca) in the Northeast Pacific and Antarctica has revealed that they can comprise populations of up to three sympatric, largely noninterbreeding ecotypes that specialize on different prey types (Ford et al. 1998; Baird 2000; Pitman and Ensor 2003). Furthermore, specific prey preferences among these ecotypes appear to be linked to different foraging habitats and movement patterns (Ford et al. 2000). In the eastern North Pacific, for example, the relationship between feeding and movement patterns has led to three ecotypes being referred to as "transients", a marine mammal-eating form; "residents", a fish-eating form that specializes on salmonids, and "offshores", a less well-known form that spends little time in coastal areas and whose food habits are largely unknown but do include fish (Bigg 1982; Ford et al. 2000; Baird 2000; Jones 2006). All three North Pacific killer whale ecotypes have overlapping geographic ranges (at least during summer), but residents occupy smaller ranges and are more predictably located than either transients or offshores. Recently, three different killer whale ecotypes were described from Antarctica based on field observations of color pattern differences, apparent prey specialization, habitat and herd size differences (Pitman and Ensor 2003), as well as differences in body length for at least two of the forms (Pitman et al. 2007). The three ecotypes were designated Types A, B and C, and it was suggested that they might represent different species. Type A, apparently the nominate form, lives in open water and preys mainly on Antarctic minke whales (Balaenoptera bonaerensis); Type B lives in loose pack ice where it preys mainly on seals (see also Visser et al. 2008), and Type C forages deep in the pack ice and among leads in the fast ice, and fish is its only known prey (see also Krahn et al. 2008).

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Árnason, Úlfur, Fritjof Lammers, Vikas Kumar, Maria A. Nilsson, Axel Janke, 2018. Whole-genome sequencing of the blue whale and other rorquals finds signatures for introgressive gene flow. Sci. Adv. 2018;4: eaap9873 4 April 2018

ABSTRACT
Reconstructing the evolution of baleen whales (Mysticeti) has been problematic because morphological and genetic analyses have produced different scenarios. This might be caused by genomic admixture that may have taken place among some rorquals. We present the genomes of six whales, including the blue whale (Balaenoptera musculus), to reconstruct a species tree of baleen whales and to identify phylogenetic conflicts. Evolutionary multilocus analyses of 34,192 genome fragments reveal a fast radiation of rorquals at 10.5 to 7.5 million years ago coinciding with oceanic circulation shifts. The evolutionarily enigmatic gray whale (Eschrichtius robustus) is placed among rorquals, and the blue whale genome shows a high degree of heterozygosity. The nearly equal frequency of conflicting gene trees suggests that speciation of rorqual evolution occurred under gene flow, which is best depicted by evolutionary networks. Especially in marine environments, sympatric speciation might be common; our results raise questions about how genetic divergence can be established.

PDF copies are available.

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Aschettino, Jessica M., Robin W. Baird, Daniel J. McSweeney, Daniel L. Webster, Gregory S. Schorr, Jessica L. Huggins, Karen K. Martien, Sabre D. Mahaffy, Kristi L. West, 2011. Population structure of melon-headed whales (Peponocephala electra) in the Hawaiian Archipelago: Evidence of multiple populations based on photo identification. Marine Mammal Science doi: 10.1111/j.1748-7692.2011.00517.x.

ABSTRACT
Despite the presence of melon-headed whales in tropical and subtropical waters worldwide, little is known about this species. To assess population structure in Hawai'i, dedicated field efforts were undertaken from 2000 to 2009. Using only good quality photographs, there were 1,433 unique photo-identified individuals, of which 1,046 were distinctive. Of these, 31.5% were seen more than once. Resighting data combined with social network analyses showed evidence of two populations—a smaller, resident population, seen exclusively off the northwest region of the island of Hawai'i, and a larger population, seen throughout all the main Hawaiian Islands (hereafter the “main Hawaiian Islands” population). A Bayesian analysis examining the probability of movements of individuals between populations provided a posterior median dispersal rate of 0.0009/yr (95% CI = 0–0.0041), indicating the populations are likely demographically independent. Depth of encounters with the Hawai'i Island resident population was significantly shallower (median = 381 m) than those with the main Hawaiian Islands population (median = 1,662 m). Resightings of individuals have occurred up to 22 yr apart for the Hawai'i Island resident population and up to 13 yr apart for the main Hawaiian Islands population, suggesting long-term residency to the islands for both populations.

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Ayres, Katherine L., Rebecca K. Booth, Jennifer A. Hempelmann, Kari L. Koski, Candice K. Emmons, Robin W. Baird, Kelley Balcomb-Bartok, M. Bradley Hanson, Michael J. Ford, Samuel K. Wasser. 2012. Distinguishing the Impacts of Inadequate Prey and Vessel Traffic on an Endangered Killer Whale (Orcinus orca) Population. PLoS ONE 7(6): e36842. doi:10.1371/journal.pone.0036842.

ABSTRACT
Managing endangered species often involves evaluating the relative impacts of multiple anthropogenic and ecological pressures. This challenge is particularly formidable for cetaceans, which spend the majority of their time underwater. Noninvasive physiological approaches can be especially informative in this regard. We used a combination of fecal thyroid (T3) and glucocorticoid (GC) hormone measures to assess two threats influencing the endangered southern resident killer whales (SRKW; Orcinus orca) that frequent the inland waters of British Columbia, Canada and Washington, U.S.A. Glucocorticoids increase in response to nutritional and psychological stress, whereas thyroid hormone declines in response to nutritional stress but is unaffected by psychological stress. The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha). The vessel impact hypothesis argues that high numbers of vessels in close proximity to the whales cause disturbance via psychological stress and/or impaired foraging ability. The GC and T3 measures supported the inadequate prey hypothesis. In particular, GC concentrations were negatively correlated with short-term changes in prey availability. Whereas, T3 concentrations varied by date and year in a manner that corresponded with more long-term prey availability. Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability. Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.

Full paper HERE.

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Baird, R.W., 2009. A review of false killer whales in Hawaiian waters: biology, status, and risk factors. Report prepared for the U.S. Marine Mammal Commission under Order No. E40475499.

ABSTRACT
Recent management and conservation issues have arisen concerning false killer whales in Hawaiian waters. Two demographically isolated populations have been identified, a small (estimated 123 individuals) island-associated population around the main Hawaiian Islands (hereafter Hawai'i insular stock) and a larger (estimated 484 individuals) offshore population (hereafter Hawai'i pelagic stock). Individuals within the Hawai'i insular stock regularly move among islands and have been documented at distances of 110 km offshore. Less is known of movements/range of individuals from the Hawai'i pelagic stock; one group has been documented 42 km offshore and individuals likely move beyond the Hawaiian Exclusive Economic Zone. No information is available to assess trends in the Hawai'i pelagic stock. For the Hawai'i insular stock, a significant decline in sighting rates from aerial surveys conducted between 1993 and 2003 suggests a large decline in population size. Other available evidence also supports a decline in population size for the insular stock: a reduction in sighting rates from boat-based surveys since the mid-1980s, lower than expected survival based on photo-identification data, and much higher sighting rates and larger group sizes in a 1989 aerial survey compared to boat-based surveys since 2000. False killer whales in Hawai'i feed primarily on large game fish that are also the target of commercial and recreational fisheries. A number of potential conservation threats have been identified. Individuals from the Hawai'i insular stock have elevated levels of persistent organic pollutants. Three of nine individuals sampled had levels high enough to potentially influence health. Because of the overlap between false killer whale diet and commercially harvested fish, reduced prey size or abundance could influence false killer whale foraging success or nutritional levels. Significant declines in body size and/or catch per unit effort have been documented for several false killer whale prey species in Hawaiian waters. False killer whales have been documented taking fish off lines in both nearshore and offshore fisheries. Depredation of caught fish may lead to retaliatory shooting by fishermen although, given potential fines and penalties, such shooting is not likely to occur where it may be witnessed; thus there is no information available to assess the potential for this to influence population dynamics. With the overlap in diet with commercially and recreationally harvested fish, the potential for hook ingestion, either from depredation or from free-swimming hooked fish, is relatively high. Based on studies elsewhere, hook ingestion would have a high likelihood of leading to mortality. Bycatch may occur in nearshore kaka line or shortline fisheries that use similar, but shorter gear to offshore longline fisheries, but there is no observer coverage of nearshore fisheries. False killer whales are the most frequently recorded bycaught cetacean in the Hawai'i-based offshore longline fishery. Rates of serious injury and mortality have exceeded the potential biological removal (PBR) levels since bycatch rates and population levels were first available in 2000. Bycatch rates are underestimated as they do not take into account individuals that are not positively classified as to species or individuals that may break free with gear attached before being documented by observers. A number of research recommendations are presented to help reduce uncertainty and to clarify factors that may be influencing the population trajectories of both the Hawai'i insular and Hawai'i pelagic stocks, as well as to provide information that could be used to reduce bycatch rates or otherwise mitigate anthropogenic impacts on these populations.

A pdf copy can be downloaded from Cascadia Research.

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Baird, R.W., D.J. McSweeney, C. Bane, J. Barlow, D.R. Salden, L.K. Antoine, R.G. LeDuc and D.L. Webster. 2006. Killer whales in Hawaiian waters: information on population identity and feeding habits. Pacific Science 60:523-530.

ABSTRACT
Killer whales (Orcinus orca) have only infrequently been reported from Hawaiian waters, and most of what is known about killer whales world-wide comes from studies in coastal temperate waters. Here we document 24 records of killer whales from within the Hawaiian Exclusive Economic Zone between 1994 and 2005. Killer whales were recorded 10 months of the year, most around the main Hawaiian Islands. While there were slightly more records than expected during the period when humpback whales are abundant around the islands, there is likely an increase in sighting effort during this period. Killer whales were documented feeding on both a humpback whale and cephalopods, and two species of small cetaceans were observed fleeing from killer whales. Although it is possible there are both marine mammal-eating and cephalopod-eating populations within Hawaiian waters, it seems more likely that Hawaiian killer whales may not exhibit foraging specializations as documented for coastal temperate populations, given the lower productivity and thus reduced selective pressure for specialization in tropical waters. Saddle patch pigmentation patterns were generally fainter and narrower than for those seen in killer whales from the temperate coastal North Pacific, though were most similar to the mammal-eating form of killer whale from those areas. Analysis of skin samples from two animals indicated two mitochondrial haplotypes, one identical to the "Gulf of Alaska transient 2" haplotype (a mammal-eating form), and the other a new haplotype one base different from haplotypes found for mammal-eating killer whales in coastal Alaskan waters. While more samples are needed, including samples from intervening areas, we suggest that killer whales around the Hawaiian Islands are likely isolated from populations in coastal temperate areas.

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Baird, Robin W. and Lawrence M. Dill (1995). Occurrence and behaviour of transient killer whales: seasonal and pod-specific variability, foraging behaviour, and prey handling. Can. J. Zool. 73(7): 1300-1311 (1995).

ABSTRACT
We studied the occurrence and behaviour of so-called transient killer whales (Orcinus orca) around southern Vancouver Island from 1986 to 1993. Occurrence and behaviour varied seasonally and among pods; some pods foraged almost entirely in open water and were recorded in the study area throughout the year, while others spent much of their time foraging around pinniped haulouts and other nearshore sites, and used the study area primarily during the harbour seal (Phoca vitulina) weaning-postweaning period. Overall use of the area was greatest during that period, and energy intake at that time was significantly greater than at other times of the year, probably because of the high encounter rates and ease of capture of harbour seal pups. Multipod groups of transients were frequently observed, as has been reported for "residents," but associations were biased towards those between pods that exhibited similar foraging tactics. Despite the occurrence of transients and residents within several kilometres of each other on nine occasions, mixed groups were never observed and transients appeared to avoid residents. Combined with previous studies on behavioural, ecological, and morphological differences, such avoidance behaviour supports the supposition that these populations are reproductively isolated.

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Baird, Robin W. and Hal Whitehead (2000). Social organization of mammal-eating killer whales: group stability and dispersal patterns. Canadian Journal of Zoology 78:2096-2105.

ABSTRACT
The social organization of mammal-eating "transient" killer whales (Orcinus orca) was studied off southern Vancouver Island from 1985 through 1996. Strong and long-term associations exist between individual transients, so sets of individuals with consistently high association levels, termed pods, can be delineated. Pods consist of individuals of mixed ages and sexes, and typically contain an adult female and one or two offspring (averaging 2.4 individuals). The mother-offspring bond remains strong into adulthood for some male (and less often for female) offspring. Other males disperse from their maternal pod and appear to become "roving" males, spending some of their time alone, and occasionally associating with groups that contain potentially reproductive females. These males appear to have no strong or long-term relationships with any individuals, and adult male - adult male associations occur significantly less often than expected by chance. Females that disperse from their natal pod appear to be gregarious (having high average association rates) but socially mobile (having low maximum association rates). Differences in social organization from the sympatric fish-eating "resident" killer whales (where no dispersal of either sex occurs) likely relate to differences in foraging ecology. Transient killer whales maximize per capita energy intake by foraging in groups of three individuals, whereas no such relationship has been documented for resident killer whales.

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Barrett-Lennard, Lance G., Craig O. Matkin, John W. Durban, 5, Eva L. Saulitis, David Ellifrit (2011). Predation on gray whales and prolonged feeding on submerged carcasses by transient killer whales at Unimak Island, Alaska. Mar Ecol Prog Ser, Vol. 421: 229–241.

ABSTRACT
As apex predators, killer whales Orcinus orca are expected to strongly influence the structure of marine communities by impacting the abundance, distribution, behavior, and evolution of their prey. Empirical assessments of these impacts are difficult, however, because killer whales are sparsely distributed, highly mobile, and difficult to observe. We present a 4 yr time series of observations of foraging and feeding behavior of >150 transient killer whales that aggregate annually during the northbound migration of gray whales past Unimak Island, Alaska. Most predatory attacks were on gray whale Eschrichtius robustus calves or yearlings and were quickly abandoned if calves were aggressively defended by their mothers. Attacks were conducted by groups of 3 to 4 killer whales, which attempted to drown their prey. Gray whales generally tried to move into shallow water along the shoreline when attacked; if they succeeded in reaching depths of 3 m or less, attacks were abandoned. Kills occurred in waters from 15 to 75 m deep or were moved into such areas after death. After some hours of feeding, the carcasses were usually left, but were re-visited and fed on by killer whales over several days. Carcasses or pieces of prey that floated onshore were actively consumed by brown bears Ursus arctos, and carcasses on the bottom were fed on by sleeper sharks Somniosus pacificus, apparently increasing the local density of both species.

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Bearzi, Maddalena, Craig B. Stanford (2007). Dolphins and African apes: comparisons of sympatric socio-ecology. Contributions to Zoology, 76 (4) 235-254.

ABSTRACT
Dolphins and African apes are distantly related mammalian taxa that exhibit striking convergences in their socioecology. In both cetaceans and African apes, two or more closely related species sometimes occur in sympatry. However, detailed reviews of the ways in which sympatric associations of dolphins and apes are similar have not been done. As field studies of dolphins and apes have accumulated, comparisons of how the two groups avoid direct food competition when in sympatry have become possible. In this paper we review sympatric ecology among dolphins and African apes, and examine convergences in species-associations in each taxa. We review evidence for hypotheses that seek to explain avoidance of food competition, and consider whether ape-dolphin similarities in this area may be related to the way in which social groups in both taxa optimally exploit their food resources.

Free PDF copy or send requests to: mbearzi@earthlink.net.

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Bender, Courtney E., Denise L. Herzing and David F. Bjorklund (2008). Evidence of Teaching In Atlantic Spotted Dolphins (Stenella frontalis) by Mother Dolphins Foraging in the Presence of their Calves. Animal Cognition [Epub ahead of print]. Published Online: July 29, 2008 DOI: 10.1007/s10071-008-0169-9

ABSTRACT
Teaching is a powerful form of social learning, but there is little systematic evidence that it occurs in species other than humans. Using long-term video archives the foraging behaviors by mother Atlantic spotted dolphins (Stenella frontalis) were observed when their calves were present and when their calves were not present, including in the presence of non-calf conspecifics. The nine mothers we observed chased prey significantly longer and made significantly more referential body-orienting movements in the direction of the prey during foraging events when their calves were present than when their calves were not present, regardless of whether they were foraging alone or with another non-calf dolphin. Although further research into the potential consequences for the naïve calves is still warranted, these data based on the maternal foraging behavior are suggestive of teaching as a social-learning mechanism in nonhuman animals. Electronic supplementary material. The online version of this article (doi:10.1007/s10071-008-0169-9) contains supplementary material, which is available to authorized users.

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Best, Peter B., MA Meÿer, M Thornton, PGH Kotze, SM Seakamela, GJG Hofmeyr, S Wintner, CD Weland and D Steinke (2014). Confirmation of the occurrence of a second killer whale morphotype in South African waters. African Journal of Marine Science 2014, 36(2): 215–224.

ABSTRACT
Killer whales Orcinus orca occur worldwide in a number of morphotypes that differ in size, pigmentation, acoustic behaviour, food type and genetics – some may indeed warrant subspecific or even specific status. Until recently, all killer whales in South African waters were referred to a single morphotype, Type A, but three individuals (two males and one female) that have stranded since 1969 differ in several respects from other killer whales examined from the region. Adult length is some 1–1.5 m smaller, appendages such as dorsal fin and flippers tend to be relatively larger, and tooth wear is excessive. Although dietary information is scant, one stomach contained the remains of several elasmobranchs, identified from a DNA subsample as blue sharks Prionace glauca, a dietary item that, if habitual, might account for the tooth wear. This morphotype, referred to here as ‘flat-toothed’ and which in several respects resembles the offshore form in the North Pacific and the Type 1 form in the North Atlantic, does not seem to have been recorded previously from the Southern Hemisphere.

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BOLAÑOS-JIMÉNEZ, Jaime, Antonio A. MIGNUCCI-GIANNONI, Janice BLUMENTHAL, Andrea BOGOMOLNI, José Julio CASAS, Angiolina HENRÍQUEZ, Miguel IÑÍGUEZ BESSEGA, Jalaludin KHAN, Nelmarie LANDRAU-GIOVANNETTI, Caroline RINALDI, Renato RINALDI, Grisel RODRÍGUEZ-FERRER, Lesley SUTTY, Jolanda Andrea LUKSENBURG (2014). Distribution, feeding habits and morphology of killer whales Orcinus orca in the Caribbean Sea. SC/59/SM4.

ABSTRACT
1. Killer whales Orcinus orca are found in all oceans of the world, but most of our knowledge on the species comes from studies conducted at higher latitudes. Studies on killer whales in the Caribbean have been scarce.
2. We compiled 176 records of killer whales from the Caribbean, including 95 previously unreported records and 81 records recovered from the literature, consisting of 27 capture or kill records, 4 stranding records and 145 sighting records.
3. Our results indicate that killer whales are widespread in the Caribbean Sea and can be found year-round in the region. Mean group size was 3.7 animals. A diversity of prey items was recorded, including sea turtles and marine mammals and possibly fish. We cannot exclude ecotype or morphotype-specific dietary specialization in the Caribbean population. A preliminary morphological analysis of 10 characters in 52 individuals from 21 different groups suggests that Caribbean killer whales do not represent any of the four Antarctic and subantarctic types, type 1 from the northwest Atlantic, or ‘resident’ and ‘transient’ killer whales from the northwest Pacific. Some Caribbean killer whales share a combination of characters typical of type 2 in the North Atlantic, whereas others share those typical of ‘offshore’ killer whales in the northwest Pacific. The significance of this is unclear. Comparison of Caribbean killer whales to previously described morphotypes and ecotypes is hampered by the lack of detailed, quantitative data on variation within other types, as well as by the lack of comparisons of genetic diversity.
4. Our study adds to the growing knowledge of the diversity of killer whales worldwide but underscores that additional research is warranted in the tropics.

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Brent, Lauren J.N., Daniel W. Franks, Emma A. Foster, Kenneth C. Balcomb, Michael A. Cant, Darren P. Croft (2015). Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales. Current Biology, Volume 25, Issue 6, 746 - 750.

ABSTRACT
Classic life-history theory predicts that menopause should not occur because there should be no selection for survival after the cessation of reproduction [1]. Yet, human females routinely live 30 years after they have stopped reproducing [2]. Only two other species—killer whales (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus) [3, 4]—have comparable postreproductive lifespans. In theory, menopause can evolve via inclusive fitness benefits [5, 6], but the mechanisms by which postreproductive females help their kin remain enigmatic. One hypothesis is that postreproductive females act as repositories of ecological knowledge and thereby buffer kin against environmenta hardships [7, 8]. We provide the first test of this hypothesis using a unique long-term dataset on wild resident killer whales. We show three key results. First, postreproductively aged females lead groups during collective movement in salmon foraging grounds. Second, leadership by postreproductively aged females is especially prominent in difficult years when salmon abundance is low. This finding is critical because salmon abundance drives both mortality and reproductive success in resident killer whales [9, 10]. Third, females are more likely to lead their sons than they are to lead their daughters, supporting predictions of recent models [5] of the evolution of menopause based on kinship dynamics. Our results show that postreproductive females may boost the fitness of kin through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female resident killer whales and humans continue to live long after they have stopped reproducing.

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Christine M. Bubac Amy C. Johnson1 Robert Otis. Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population. Marine Ecology. Marine Ecology. 2020;00:e12626 https://doi.org/10.1111/maec.12626

ABSTRACT
Southern Resident killer whales (SRKWs) (Orcinus orca) are an endangered population in the United States and Canada, partly due to declines of their primary prey species, Chinook salmon. Prey availability influences various aspects of SRKW behavior, including distribution patterns and social structure. Yet, it is unclear to what extent a limited prey source influences the frequency of surface-active behaviors (SABs), behaviors with important ecological implications. Here, we used long-term datasets (1996–2019) to examine the relationships between the abundance of Chinook salmon, vessel presence, and the frequency with which SRKWs perform SABs. Salmon abundance was a significant predictor of SAB frequency, with fewer SABs performed in times of lower salmon abundance. SRKWs displayed more SABs when more whale watching vessels were present, and the whales spent a greater amount of time in the study area, performing more milling as opposed to traveling behavior, when vessel numbers were higher. Lastly, we found pod-specific differences, such that K pod displayed significantly fewer SABs than either J or L pods. The observed relationships between SRKW behavior and both salmon abundance and vessel presence have implications for social network cohesion and foraging success. Our study adds to a growing body of literature highlighting factors affecting SRKW behavior as they experience increased threats from decreased prey availability, habitat loss, and anthropogenic disturbance, with implications for trans-boundary management and conservation efforts.

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Burdin, Alexander M., Erich Hoyt, Hal Sato, Karina Tarasyan and Olga A. Filatova. Resident and Transient-type Killer Whales, Orcinus orca, in Southeast Kamchatka, Russia. SC/59/SM4.

ABSTRACT
Killer whales, Orcinus orca, were studied in Avacha Gulf, southeast Kamchatka, in the Russian Far East (RFE) from 1999-2003 using land- and boat-based photo-identification and sound recordings. A total of 121 photographically identified killer whales in the area have been determined to be residents based on (1) site fidelity with frequent re-sightings, (2) observations of predation on fish and (3) the recording of stable, resident-type dialects. The study has also documented transient-type marine mammal hunting killer whales in the RFE through morphological observations and biopsy documentation of contaminant levels and genetic characteristics. On 26 September 2003, some 32-37 resident-type killer whales were captured by the Utrish Dolphinarium Ltd, six of which had been photo-identified in previous years. One young female drowned in the nets; another young female was removed and sent to the Utrish Dolphinarium where she subsequently died. No more captures should be permitted until more is known about the population structure and population sizes of RFE killer whales.

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Burdin, Alexander M., Erich Hoyt, Olga A. Filatova, Tatyana Ivkovich, Karina Tarasyan and Hal Sato (2007). Status of Killer Whales (Orcinus orca) in Eastern Kamchatka (Russian Far East) Based on Photo-Identification and Acoustic Studies. Preliminary Results. SC/59/SM4.

ABSTRACT
From 1999-2006, a long-term study of killer whales (Orcinus orca) off eastern Kamchatka has conducted photoidentification and acoustic studies from a field station in Avacha Gulf. From 2002-2005, wide-area large ship surveys have expanded the study to other regions in the Russian Far East (RFE) including: northeast Kamchatka, Commander Islands, Chukotka, Kuril Islands and northeast Sakhalin. In this paper we mainly discuss the killer whale status on the eastern coast of Kamchatka, and give a brief review of available information regarding the killer whale status in other areas of the RFE. During the field seasons 2005-2006, a total of 434 individuals were identified in Avacha Gulf in at least three acoustic clans with different dialects. Most are resident-type fish-eating whales. Some transient-type marine mammal eating whales have also been recorded in Avacha Gulf and in other areas of the RFE. Transients as well as some residents show bites from the cookie cutter shark (Isistius brasiliensis) which may indicate long distance travel along the Asian coast or out to sea. To date, live captures have removed at least two subadult females from the Avacha Gulf residents. A live-capture quota of 6-10 killer whales in the RFE has been granted every year since 2002 (8 for 2007) although data remain inadequate to support this. The conflict between whales and fishermen in the Sea of Okhotsk due to killer whale depredation merits further study.

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Cosentino, Mel (2015). First record of Norwegian killer whales attacking and feeding on a harbour porpoise. Marine Biodiversity Records, page 1 of 5. # Marine Biological Association of the United Kingdom, 2015 doi:10.1017/S1755267215000895; Vol. 8; e108; 2015 Published online.

ABSTRACT
Orcinus orca is a cosmopolitan species and the most widely distributed marine mammal. Its diet includes over 140 species of fish, cephalopods, sea birds and marine mammals. However, many populations are specialised on certain specific prey items. Three genetically distinct populations have been described in the North Atlantic. Population A (that includes the Icelandic and Norwegian sub-populations) is believed to be piscivorous, as is population C, which includes fish-eating killer whales from the Strait of Gibraltar. In contrast, population B feeds on both fish and marine mammals. Norwegian killer whales follow the Norwegian spring spawning herring stock. The only description in the literature of Norwegian killer whales feeding on another cetacean species is a predation event on northern bottlenose whales in 1968. Daily land-based surveys targeting sperm whales were conducted from the Andenes lighthouse using BigEyesw binoculars (25×, 80 mm). The location of animals at sea was approximated through the use of an internal reticule system and a graduated wheel. On 24 June 2012 at 3:12 am, an opportunistic sighting of 11 killer whales was made off Andenes harbour. The whales hunted and fed on a harbour porpoise. Despite these species having overlapping distributions in Norwegian waters, this is the first predatory event reported in the literature.

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Couture, Fanny, Greig Oldford, Villy Christensen, Lance Barrett-Lennard, Carl Walters (2022). Requirements and availability of prey for northeastern pacific southern resident killer whales. Plos One

ABSTRACT
The salmon-eating Southern Resident killer whale (SRKW) (Orcinus orca) population currently comprises only 73 individuals, and is listed as ‘endangered’ under the Species at Risk Act in Canada. Recent evidence suggests that the growth of this population may be limited by food resources, especially Chinook salmon (Oncorhynchus tshawytscha). We present spatio-temporal bioenergetics model for SRKW in the Salish Sea and the West Coast of Vancouver Island from 1979–2020 with the objective of evaluating how changes in the abundance, age-structure, and length-at-age of Chinook salmon populations has influenced the daily food consumption of the SRKW population. Our model showed that the SRKW population has been in energetic deficit for six of the last 40 years. Our results also suggested that the abundance of age-4 and age-5 Chinook salmon are significant predictors of energy intake for SRKW. We estimated that the annual consumption (April-October) of Chinook salmon by the whales between 1979 and 2020 ranged from 166,000 216,300. Over the past 40 years, the model estimated that the contribution in the predicted SRKW diet of Chinook salmon originating from the Columbia River has increased by about 34%, and decreased by about 15% for Chinook salmon stocks originating from Puget Sound. Overall, our study provides an overview of the requirements and availability of prey for SRKW over the last 40 years, while supporting the hypothesis that SRKW were limited by prey abundance in the study period.

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Croft, Darren P., Rufus A. Johnstone, Samuel Ellis, Stuart Nattrass, Daniel W. Franks, Lauren J.N. Brent, Sonia Mazzi, Kenneth C. Balcomb, John K.B. Ford, Michael A. Cant (2017). Reproductive Conflict and the Evolution of Menopause in Killer Whales. Current Biology, http://dx.doi.org/10.1016/j.cub.2016.12.015.

SUMMARY
Why females of some species cease ovulation prior to the end of their natural lifespan is a long-standing evolutionary puzzle [1, 2, 3, 4]. The fitness benefits of post-reproductive helping could in principle select for menopause [1, 2, 5], but the magnitude of these benefits appears insufficient to explain the timing of menopause [6, 7, 8]. Recent theory suggests that the cost of inter-generational reproductive conflict between younger and older females of the same social unit is a critical missing term in classical inclusive fitness calculations (the “reproductive conflict hypothesis” [6, 9]). Using a unique long-term dataset on wild resident killer whales, where females can live decades after their final parturition, we provide the first test of this hypothesis in a non-human animal. First, we confirm previous theoretical predictions that local relatedness increases with female age up to the end of reproduction. Second, we construct a new evolutionary model and show that given these kinship dynamics, selection will favor younger females that invest more in competition, and thus have greater reproductive success, than older females (their mothers) when breeding at the same time. Third, we test this prediction using 43 years of individual-based demographic data in resident killer whales and show that when mothers and daughters co-breed, the mortality hazard of calves from older-generation females is 1.7 times that of calves from younger-generation females. Intergenerational conflict combined with the known benefits conveyed to kin by post-reproductive females can explain why killer whales have evolved the longest post-reproductive lifespan of all non-human animals.

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Greg O’Corry-Crowe, Robert Suydam, Lori Quakenbush, Brooke Potgieter, Lois Harwood, Dennis Litovka, Tatiana Ferrer, John Citta, Vladimir Burkanov, Kathy Frost, Barbara Mahoney (2018). Migratory culture, population structure and stock identity in North Pacific beluga whales (Delphinapterus leucas). PLoS ONE 13(3): e0194201. https://doi.org/10.1371/journal.pone.0194201

The annual return of beluga whales, Delphinapterus leucas, to traditional seasonal locations across the Arctic may involve migratory culture, while the convergence of discrete summering aggregations on common wintering grounds may facilitate outbreeding. Natal philopatry and cultural inheritance, however, has been difficult to assess as earlier studies were of too short a duration, while genetic analyses of breeding patterns, especially across the beluga’s Pacific range, have been hampered by inadequate sampling and sparse information on wintering areas. Using a much expanded sample and genetic marker set comprising 1,647 whales, spanning more than two decades and encompassing all major coastal summering aggregations in the Pacific Ocean, we found evolutionary-level divergence among three geographic regions: the Gulf of Alaska, the Bering-Chukchi-Beaufort Seas, and the Sea of Okhotsk (Fst = 0.11–0.32, Rst = 0.09–0.13), and likely demographic independence of (Fst-mtDNA = 0.02–0.66), and in many cases limited gene flow (Fst-nDNA = 0.0–0.02; K = 5–6) among, summering groups within regions. Assignment tests identified few immigrants within summering aggregations, linked migrating groups to specific summering areas, and found that some migratory corridors comprise whales from multiple subpopulations (PBAYES = 0.31:0.69). Further, dispersal is male-biased and substantial numbers of closely related whales congregate together at coastal summering areas. Stable patterns of heterogeneity between areas and consistently high proportions (~20%) of close kin (including parent-offspring) sampled up to 20 years apart within areas (G = 0.2–2.9, p>0.5) is the first direct evidence of natal philopatry to migration destinations in belugas. Using recent satellite telemetry findings on belugas we found that the spatial proximity of winter ranges has a greater influence on the degree of both individual and genetic exchange than summer ranges (rwinter-Fst-mtDNA = 0.9, rsummer-Fst-nDNA = 0.1). These findings indicate widespread natal philopatry to summering aggregation and entire migratory circuits, and provide compelling evidence that migratory culture and kinship helps maintain demographically discrete beluga stocks that can overlap in time and space.

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Dalheim, Marilyn, Paula A. White (2010). Ecological aspects of transient killer whales (Orcinus orca) as predators in southeastern Alaska. Wildlife Biology, Volume 6, No. 3: 308-322.

ABSTRACT
In this study we present empirical data on predator numbers, movements and area usage, and predation obtained from tracking transient killer whales (Orcinus orca) throughout the inland waters of southeastern Alaska, USA. During 1991-2007, we documented 155 transient killer whales via photo-identification methodology within this large study area (27,808 km2). Transient killer whales were distributed throughout southeastern Alaska and were present during all seasons, although not all individuals were seen each year. Resighting data suggested that within southeastern Alaska, maternal groups may partition area usage of their environment. By following whales for 1,467 km, we calculated a mean travel speed of 7.2 km/h with mean daily movements of 134 km ± 88 km/24 hours and ranging within 59-240 km/24 hours. Photographic matches demonstrated that most (86%) of the transient killer whales identified in southeastern Alaska also utilized British Columbia and Washington State waters. In contrast, photographic matches between whales in southeastern Alaska and whales seen off of California, USA, were rare, suggesting that different transient killer whale stocks occupy these two regions. Transient killer whales preyed upon Dall's porpoise (Phocoenoides dalli), Pacific white-sided dolphins (Lagenoryhncus obliquidens), harbor porpoise (Phocoena phocoena), minke whales (Balaenoptera acutorostrata), Steller sea lions (Eumetopias jubatus), harbor seals (Phoca vitulina), and seabirds. Potential prey species available, but not targeted, included humpback whales (Megaptera novaeangliae), elephant seals (Mirounga angustirostris), and sea otters (Enhydra lutris). Prey-handling techniques varied depending upon the prey being targeted with no evidence of prey specialization. During 114 encounters totaling 332.5 hours of direct observations of transient killer whales, we documented 36 predation events for a calculated kill rate of 0.62 prey items/24-hour period/whale. The data we present in this article provide a foundation of transient killer whale ecology aimed at improving our ability to understand the impact of transient killer whale predation on southeastern Alaska prey populations.

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Dalheim, Marilyn, Alisa Schulman-Janiger, Nancy Black, Richard Tenullo, Dave Ellifrit, Kenneth C. Balcomb, III (2008). Eastern temperate North Pacific offshore killer whales (Orcinus orca): Occurrence, movements, and insights into feeding ecology. MARINE MAMMAL SCIENCE, 24(3): 719-729 (July 2008).

No abstract.

PDF of paper HERE (5.2 meg .pdf file.)

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de Bruyn, P. J. Nico, Cheryl A. Tosh1 and Aleks Terauds (2012). Killer whale ecotypes: is there a global model? Biol. Rev. (2012), pp. 000–000.

ABSTRACT
Killer whales, Orcinus orca, are top predators occupying key ecological roles in a variety of ecosystems and are one of the most widely distributed mammals on the planet. In consequence, there has been significant interest in understanding their basic biology and ecology. Long-term studies of Northern Hemisphere killer whales, particularly in the eastern North Pacific (ENP), have identified three ecologically distinct communities or ecotypes in that region. The success of these prominent ENP studies has led to similar efforts at clarifying the role of killer whale ecology in other regions, including Antarctica. In the Southern Hemisphere, killer whales present a range of behavioural, social and morphological characteristics to biologists, who often interpret this as evidence to categorize individuals or groups, and draw general ecological conclusions about these super-predators. Morphologically distinct forms (Type A, B, C, and D) occur in the Southern Ocean and studies of these different forms are often presented in conjunction with evidence for specialised ecology and behaviours. Here we review current knowledge of killer whale ecology and ecotyping globally and present a synthesis of existing knowledge. In particular, we highlight the complexity of killer whale ecology in the Southern Hemisphere and examine this in the context of comparatively well-studied Northern Hemisphere populations. We suggest that assigning erroneous or prefatory ecotypic status in the Southern Hemisphere could be detrimental to subsequent killer whale studies, because unsubstantiated characteristics may be assumed as a result of such classification. On this basis, we also recommend that ecotypic status classification for Southern Ocean killer whale morphotypes be reserved until more evidence-based ecological and taxonomic data are obtained.

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Deecke, Volker B., Milaja Nykänen, Andrew D. Foote, Vincent M. Janik (2011). Vocal behaviour and feeding ecology of killer whales Orcinus orca around Shetland, UK. Aquatic Biology 13:79-88.

ABSTRACT
Killer whales Orcinus orca are sighted regularly off Shetland, UK, but little is known about their numbers, diet and population identity. We aimed to relate vocal behaviour to diet of killer whales around Shetland in order to investigate population structure and differences in feeding strategies. Fieldwork was conducted in the summers of 2008 and 2009. We located killer whales through a sightings network and shore-based scans and collected photo-ID data, behavioural information, feeding data and acoustic recordings from a small boat. The majority of encounters (n = 14) were of small groups (1 to 15 individuals) travelling close to shore and feeding on marine mammals. Two encounters were with large groups (20+ individuals) feeding on herring Clupea harengus farther offshore. Seal-hunting groups vocalised rarely, producing pulsed calls, echolocation clicks and whistles almost exclusively when surface-active or milling after a kill. Herring-eating groups were largely silent during one encounter, but very vocal during the other. Analysis of pulsed calls identified 6 stereotyped call types for seal-hunting groups and 7 for herring-eating groups. No call types were shared between both kinds of groups. The vocal behaviour of seal-hunting groups showed striking parallels to that of Pacific marine mammal specialists and presumably evolved to decrease detection by acoustically sensitive prey. One call type produced by Shetland herring-eating killer whales matched a vocalisation that a previous study had described from Iceland and identified as a possible herding call that may function to concentrate herring during feeding. These findings point to behavioural and dietary specialisation among Shetland killer whales, which should be taken into account when making management decisions affecting these animals.

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Deecke, Volker B., Janice M. Straley, Dena R. Matkin and Christine M. Gabriele (2006). The Mammal-Eating Killer Whales of Glacier Bay National Park and Preserve: Hunting with the Strong Silent Types.

EXCERPT
Like two tribes inhabiting the same home range but keeping out of each other’s way, two distinct forms, or ecotypes, of killer whales inhabit the coastal waters of the northeastern Pacific. Resident killer whales, one ecotype, live in large stable groups and feed exclusively on fish, predominantly on salmon (Oncorhynchus spp.), while the second ecotype, transient killer whales, feed exclusively on warm-blooded animals. Their primary prey are marine mammals (Ford et al. 1998, Saulitis et al. 2000), although they also take sea birds on occasion. Resident killer whales can be found frequently and predictably in the straits and inlets of southeastern Alaska and Prince William Sound in the summer months because they follow salmon on their annual migration through these coastal waters. By comparison, members of the transient ecotype are stealthy nomads. Presumably because of the lower density of their prey populations and the fact that their prey would quickly cue in on their presence, transients rarely linger for long in the same area. They often cover large distances in a single day, making them difficult to study.

FULL ARTICLE.

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Durban, J. W., H. Fearnbach, D. G. Burrows, G. M. Ylitalo, R. L. Pitman. (2017). Morphological and ecological evidence for two sympatric forms of Type B killer whale around the Antarctic Peninsula Polar Biol (2017) 40: 231.

ABSTRACT
Killer whales (Orcinus orca) are apex marine predators in Antarctica, but uncertainty over their taxonomic and ecological diversity constrains evaluations of their trophic interactions. We describe two distinct, sympatric forms sharing the characteristic pigmentation of Type B, the most common around the Antarctic Peninsula. Laser photogrammetry revealed nonoverlapping size differences among adults: Based on a body length index (BLI: blowhole to dorsal fin) adult females of the larger form (“B1”) were 20 % longer than the smaller form (“B2”), and adult males were 24 % longer on average. Dorsal fins of B1 adult females were 19 % taller than B2 females, and adult males 32 % taller. Both types were strongly sexually dimorphic, but B1 more so, including for BLI (B1 males = 1.07× females; B2 = 1.05×) and especially for dorsal fin height (B1 male fins = 2.33× female; B2 = 2.10×). The characteristically large Type B eye patch was more extensive for B1 than B2, comprising 41 and 37 % of BLI, respectively. Average group size was also significantly different, with B1s in smaller groups (mean 7, range 1–14) and B2s more gregarious (mean 36, range 8–75). Stable isotope analysis of skin biopsies indicated dietary differences: a significantly lower nitrogen 15N/14N ratio in B2s supported observations of feeding primarily on krill consumers (e.g., pygoscelid penguins), while B1s prey mainly on predators of krill consumers (e.g., Weddell seals Leptonychotes weddellii). These differences likely represent adaptations to distinct foraging niches, which has led to genetic divergence; their ecology now needs further study.

Full paper HERE: HERE

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Durban, J. W., and R. L. Pitman. (2011). Antarctic killer whales make rapid, round-trip movements to subtropical waters: evidence for physiological maintenance migrations? Biological Letters doi: 10.1098/rsbl.2011.0875

ABSTRACT
Killer whales (Orcinus orca) are important predators in high latitudes, where their ecological impact is mediated through their movements. We used satellite telemetry to provide the first evidence of migration for killer whales, characterized by fast (more than 12 km/h, 6.5 knots) and direct movements away from Antarctic waters by six of 12 type B killer whales tagged when foraging near the Antarctic Peninsula, including all tags transmitting for more than three weeks. Tags on five of these whales revealed consistent movements to subtropical waters (30–37° S) off Uruguay and Brazil, in surface water temperatures ranging from -1.9°C to 24.2°C; one 109 day track documented a nonstop round trip of almost 9400 km (5075 nmi) in just 42 days. Although whales traveled slower in the warmest waters, there was no obvious interruption in swim speed or direction to indicate calving or prolonged feeding. Furthermore, these movements were aseasonal, initiating over 80 days between February and April; one whale returned to within 40 km of the tagging site at the onset of the austral winter in June. We suggest that these movements may represent periodic maintenance migrations, with warmer waters allowing skin regeneration without the high cost of heat loss: a physiological constraint that may also affect other whales.

An open access PDF is available.

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Durban, J., D. Ellifrit, M. Dahlheim, J. Waite, C. Matkin, L. Barrett-Lennard, G. Ellis, R. Pitman, R. LeDuc and P. Wade (2010). Photographic mark-recapture analysis of clustered mammal-eating killer whales around the Aleutian Islands and Gulf of Alaska. Marine Biology Volume 157, Number 7, 1591-1604, DOI: 10.1007/s00227-010-1432-6

ABSTRACT
We used photographic mark-recapture methods to estimate the number of mammal-eating “transient” killer whales using the coastal waters from the central Gulf of Alaska to the central Aleutian Islands, around breeding rookeries of endangered Steller sea lions. We identified 154 individual killer whales from 6,489 photographs collected between July 2001 and August 2003. A Bayesian mixture model estimated seven distinct clusters (95% probability interval = 7–10) of individuals that were differentially covered by 14 boat-based surveys exhibiting varying degrees of association in space and time. Markov Chain Monte Carlo methods were used to sample identification probabilities across the distribution of clusters to estimate a total of 345 identified and undetected whales (95% probability interval = 255–487). Estimates of covariance between surveys, in terms of their coverage of these clusters, indicated spatial population structure and seasonal movements from these near-shore waters, suggesting spatial and temporal variation in the predation pressure on coastal marine mammals.

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Ellis, Samuel, Daniel W. Franks, Mia Lybkær Kronborg Nielsen, Michael N. Weiss & Darren P. Croft (2024) The evolution of menopause in toothed whales

ABSTRACT
Understanding how and why menopause has evolved is a long-standing challenge across disciplines. Females can typically maximize their reproductive success by reproducing for the whole of their adult life. In humans, however, women cease reproduction several decades before the end of their natural lifespan1,2. Although progress has been made in understanding the adaptive value of menopause in humans3,4, the generality of these findings remains unclear. Toothed whales are the only mammal taxon in which menopause has evolved several times5, providing a unique opportunity to test the theories of how and why menopause evolves in a comparative context. Here, we assemble and analyse a comparative database to test competing evolutionary hypotheses. We find that menopause evolved in toothed whales by females extending their lifespan without increasing their reproductive lifespan, as predicted by the ‘live-long’ hypotheses. We further show that menopause results in females increasing their opportunity for intergenerational help by increasing their lifespan overlap with their grandoffspring and offspring without increasing their reproductive overlap with their daughters. Our results provide an informative comparison for the evolution of human life history and demonstrate that the same pathway that led to menopause in humans can also explain the evolution of menopause in toothed whales.

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Esteban, R., P. Verborgh, P. Gauffier, J. Giménez, A. D. Foote, R. de Stephanis. (2015). Maternal kinship and fisheries interaction influence killer whale social structure. Behavioral Ecology and Sociobiology, pp 1-12, First online: 31 October 2015

ABSTRACT
The primary prey of killer whales (Orcinus orca) in the Strait of Gibraltar is the bluefin tuna (Thunnus thynnus). All killer whales observed in this area hunt tuna by chasing individual fish until they become exhausted and can be overcome. However, a subset of pods also interact with a dropline tuna fishery which has developed since 1995. Here, we investigated the social structure within and among social units (pods). Our data suggested that social structure was shaped by maternal kinship, which appears to be a species-specific trait, but also by foraging behavior, which is less common at the intra-population level. At the start of the study, only one cohesive pod interacted with the fishery, which during the course of the study underwent fission into two socially differentiated pods. Social structure within these two fishery-interacting pods was more compact and homogenous with stronger associations between individuals than in the rest of the population. Three other pods were never seen interacting with the fishery, despite one of these pods being regularly sighted in the area of the fishery during the summer. Sociality can influence the spread of the novel foraging behaviors and may drive population fragmentation, which, in this example, is already a critically small community. Observations of social changes in relation to changes in foraging at the earliest stages of diversification in foraging behavior and social segregation may provide insights into the processes that ultimately result in the formation of socially isolated discrete ecotypes in killer whales.
Full paper can be downloaded HERE.

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Esteban, R., Verborgh, P., Gauffier, P. Giménez, J., Guinet, C. and de Stephanis R. (2015). Dynamics of killer whale, bluefin tuna and human fisheries in the Strait of Gibrlatar. Biological Conservation, Volume 194, February 2016, Pages 31-38.

ABSTRACT
A complex balance has arisen between the bluefin tuna, killer whales, and human activities in the Strait of Gibraltar. Recent changes in fishing effort have dramatically decreased tuna stocks, breaking this balance. Killer whales exhibit two strategies for feeding on tuna: active hunting and depredation on a drop-line fishery. From 1999 to 2011, a small community of 39 individuals was observed in the Strait in spring and summer. All individuals displayed active hunting and 18 of them also depredated on the fishery. These differences in foraging behaviour influenced life-history parameters. Adult survival for interacting and non-interacting individuals was estimated at 0.991 (SE=0.011) and 0.901 (SE=0.050), respectively. Juvenile survival could only be estimated for interacting individuals as 0.966 (SE = 0.024), because only one juvenile and one calf were observed among non-interacting individuals. None of the interacting calves survived after 2005, following the decrease in drop-line fishery catches. Calving rate was estimated at 0.22 (SE = 0. 02) for interacting individuals and 0.02 (SE = 0. 01) for non-interacting. Calving interval, which could only be calculated for interacting groups, was 7 years. The population growth rate was positive at 4% for interacting individuals, and no growth was observed for non-interacting individuals. These differences in demographic parameters could be explained by access to larger tuna through depredation. Consequently, we found that whales would need more tuna to cover their daily energy requirements while actively hunting. Therefore, our findings suggest an effect of artificial food provisioning on their survival and reproductive output. Urgent actions are needed to ensure the conservation of this, already small, community of killer whales. These include its declaration as Endangered, the implementation of a conservation plan, the creation of a seasonal management area where activities producing underwater noise (i.e. military exercise, seismic surveys or even whale watching activities) are forbidden from March to August, and the promotion of bluefin tuna conservation. Additionally, energetic requirements of this whale community should be taken into account when undertaking ecosystem-based fishery management for the Atlantic bluefin tuna stock. In the meantime, as marine predators are most sensitive to changes in fish abundance when prey abundance is low, we suggest an urgent short-term action. Artisanal fisheries, such as drop-lines, should be promoted instead of purse seiners in the Mediterranean Sea. This will help to maintain the survival and reproductive output of the whale community until showing clear signs of recovery and stability, and/or their prey stock recovers.

Full paper can be downloaded HERE:

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Fearnbach, Holly, John W. Durban, Dave K. Ellifrit, Janice M. Waite, Craig O. Matkin, Chris R. Lunsford, Megan J. Peterson, Jay Barlow, Paul R. Wade. (2013). Spatial and social connectivity of fish-eating “Resident” killer whales (Orcinus orca) in the northern North Pacific. Mar Biol (2014) 161:459–472.

ABSTRACT
The productive North Pacific waters of the Gulf of Alaska, Aleutian Islands and Bering Sea support a high density of fish-eating “Resident” type killer whales (Orcinus orca), which overlap in distribution with commercial fisheries, producing both direct and indirect interactions. To provide a spatial context for these interactions, we analyzed a 10-year dataset of 3,058 whale photoidentifications from 331 encounters within a large (linear ~4,000 km) coastal study area to investigate the ranging and social patterns of 532 individually identifiable whales photographed in more than one encounter. Although capable of large-scale movements (maximum 1,443 km), we documented ranges generally <200 km, with high site fidelity across summer sampling intervals and also re-sightings during a winter survey. Bayesian analysis of pair-wise associations identified four defined clusters, likely representing groupings of stable matrilines, with distinct ranging patterns, that combined to form a large network of associated whales that ranged across most of the study area. This provides evidence of structure within the Alaska stock of Resident killer whales, important for evaluating ecosystem and fisheries impacts. This network included whales known to depredate groundfish from longline fisheries, and we suggest that such large-scale connectivity has facilitated the spread of depredation.

Full paper HERE.

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Fearnbach, Holly, John W. Durban, Dave K. Ellifrit, Ken C. Balcomb III. (2011). Size and long-term growth trends of Endangered fish-eating killer whales. Endang Species Res Vol. 13: 173–180.

ABSTRACT
The Endangered southern resident population of killer whales Orcinus orca has been shown to be food-limited, and the availability of their primary prey, Chinook salmon Oncorhynchus tshawytscha, has been identified as a key covariate for the whales’ individual survival and reproduction. We collected aerial photogrammetry data on individual whale size, which will help to better inform energetic calculations of food requirements, and we compared size-at-age data to make inferences about long-term growth trends. A helicopter was used to conduct 10 flights in September 2008, resulting in 2803 images from which useable measurements were possible for 66 individually identifiable whales, representing more than three-quarters of the population. Estimated whale lengths ranged from 2.7 m for a neonate whale in its first year of life, to a maximum of 7.2 m for a 31 yr old adult male. Adult males reached an average (asymptotic) size estimate (± SE) of 6.9 ± 0.2 m, with growth slowing notably after the age of 18 yr; this was significantly larger than the asymptotic size of 6.0 ± 0.1 m for females, which was reached after the earlier age of 15 yr. Notably, there was no overlap between the ranges of estimated sizes of adult males (6.5 to 7.2 m) and females (5.5 to 6.4 m). On average, older adults (> 30 yr) were 0.3 m (n = 14, p = 0.03) and 0.3 m (n = 5, p = 0.23) longer than the younger whales of adult age, for females and males, respectively; we hypothesize that a long-term reduction in food availability may have reduced early growth rates and subsequent adult size in recent decades.

Full paper HERE.

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Filatova O.A., Fedutin I.D., Burdin A.M., Hoyt E. (2007). The structure of the discrete call repertoire of killer whales Orcinus orca from Southeast Kamchatka. Bioacoustics V 16(3): 261-280.

ABSTRACT
The problem of categorization arises in any classification system because classes should be discrete while the characteristics of most natural objects and aspects of nature are more or less gradual. In systematics, this problem usually is solved by creating several levels of categories, such as class, order, family, genus and species.
In the existing killer whale discrete call classification, only two levels occur - call type and call subtype. In this paper we describe structural categories at a broader level than call type in the discrete sounds of killer whales and compare these categories between and within vocal clans in a community of resident killer whales from Southeast Kamchatka, Russian Far East, and also with killer whales outside this community. We found four main classes of discrete calls in the repertoire of resident killer whales from Southeast Kamchatka. The calls of Southeast Kamchatka transient killer whales and Sakhalin killer whales do not fall into these classes. This suggests that the resident killer whale community from Southeast Kamchatka has some rules defining the structure of calls which are typical for this community. Consequently, all resident killer whales from Southeast Kamchatka can be said to share the same vocal tradition.

A pdf copy is available upon request from alazor@rambler.ru

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Foote, Andrew D., Michael D. Martin, Marie Louis, George Pacheco, Kelly M. Robertson, Mikkel-Holger S. Sinding, Ana R. Amara, Robin W. Baird, C. Scott Baker, Lisa Ballance, Jay Barlow, Andrew Brownlow, Tim Collins, Rochelle Constantine, Willy Dabin, Luciano Dalla Rosa, Nicholas J. Davison, John W. Durban, Ruth Esteban, Steven H. Ferguson, Tim Gerrodette, Christophe Guinet, M. Bradley Hanson, Wayne Hoggard, Cory J. D. Matthews, Filipa I. P. Samarra, Renaud de Stephanis, Sara B. Tavares, Paul Tixier, John A. Totterdell, Paul Wade, M. Thomas P. Gilbert, Jochen B.W. Wolf, Phillip A. Morin (2019). Killer whale genomes reveal a complex history of recurrent admixture and vicariance. Jan. 16, 2019; doi: http://dx.doi.org/10.1101/520718.

ABSTRACT
Reconstruction of the demographic and evolutionary history of populations assuming a consensus tree-like relationship can mask more complex scenarios, which are prevalent in nature. An emerging genomic toolset, which has been most comprehensively harnessed in the reconstruction of human evolutionary history, enables molecular ecologists to elucidate complex population histories. Killer whales have limited extrinsic barriers to dispersal and have radiated globally, and are therefore a good candidate model for the application of such tools. Here, we analyse a global dataset of killer whale genomes in a rare attempt to elucidate global population structure in a non-human species. We identify a pattern of genetic homogenisation at lower latitudes and the greatest differentiation at high latitudes, even between currently sympatric lineages. The processes underlying the major axis of structure include high drift at the edge of species’ range, likely associated with founder effects and allelic surfing during post-glacial range expansion. Divergence between Antarctic and non-Antarctic lineages is further driven by ancestry segments with up to four-fold older coalescence time than the genome-wide average; relicts of a previous vicariance during an earlier glacial cycle. Our study further underpins that episodic gene flow is ubiquitous in natural populations, and can occur across great distances and after substantial periods of isolation between populations. Thus, understanding the evolutionary history of a species requires comprehensive geographic sampling and genome-wide data to sample the variation in ancestry within individuals.

Full paper HERE.

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Foote, Andrew D., Phillip A. Morin (2016). Genome-wide SNP data suggest complex ancestry of sympatric North Pacific killer whale ecotypes. Heredity (3 August 2016) | doi:10.1038/hdy.2016.54.

ABSTRACT
Three ecotypes of killer whale occur in partial sympatry in the North Pacific. Individuals assortatively mate within the same ecotype, resulting in correlated ecological and genetic differentiation. A key question is whether this pattern of evolutionary divergence is an example of incipient sympatric speciation from a single panmictic ancestral population, or whether sympatry could have resulted from multiple colonisations of the North Pacific and secondary contact between ecotypes. Here, we infer multilocus coalescent trees from >1000 nuclear single-nucleotide polymorphisms (SNPs) and find evidence of incomplete lineage sorting so that the genealogies of SNPs do not all conform to a single topology. To disentangle whether uncertainty in the phylogenetic inference of the relationships among ecotypes could also result from ancestral admixture events we reconstructed the relationship among the ecotypes as an admixture graph and estimated f4-statistics using TreeMix. The results were consistent with episodes of admixture between two of the North Pacific ecotypes and the two outgroups (populations from the Southern Ocean and the North Atlantic). Gene flow may have occurred via unsampled ‘ghost’ populations rather than directly between the populations sampled here. Our results indicate that because of ancestral admixture events and incomplete lineage sorting, a single bifurcating tree does not fully describe the relationship among these populations. The data are therefore most consistent with the genomic variation among North Pacific killer whale ecotypes resulting from multiple colonisation events, and secondary contact may have facilitated evolutionary divergence. Thus, the present-day populations of North Pacific killer whale ecotypes have a complex ancestry, confounding the tree-based inference of ancestral geography.

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Foote, Andrew D., Nagarjun Vijay, María C. Ávila-Arcos, Robin W. Baird, John W. Durban, Matteo Fumagalli, Richard A. Gibbs, M. Bradley Hanson, Thorfinn S. Korneliussen, Michael D. Martin, Kelly M. Robertson, Vitor C. Sousa, Filipe G. Vieira, Tomáš Vinar, Paul Wade, Kim C. Worley, Laurent Excoffier, Phillip A. Morin, M. Thomas P. Gilbert & Jochen B.W. Wolf (2016). Genome-culture coevolution promotes rapid divergence of killer whale ecotypes. Nature Communications 7, Article number: 11693 doi:10.1038/ncomms11693.

ABSTRACT
Analysing population genomic data from killer whale ecotypes, which we estimate have globally radiated within less than 250,000 years, we show that genetic structuring including the segregation of potentially functional alleles is associated with socially inherited ecological niche. Reconstruction of ancestral demographic history revealed bottlenecks during founder events, likely promoting ecological divergence and genetic drift resulting in a wide range of genome-wide differentiation between pairs of allopatric and sympatric ecotypes. Functional enrichment analyses provided evidence for regional genomic divergence associated with habitat, dietary preferences and post-zygotic reproductive isolation. Our findings are consistent with expansion of small founder groups into novel niches by an initial plastic behavioural response, perpetuated by social learning imposing an altered natural selection regime. The study constitutes an important step towards an understanding of the complex interaction between demographic history, culture, ecological adaptation and evolution at the genomic level.

Full paper HERE.

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Foote, Andrew D., Phillip A. Morin, John W. Durban, Eske Willerslev, Ludovic Orlando, M. Thomas P. Gilbert; (2011). Out of the Pacific and Back Again: Insights into the Matrilineal History of Pacific Killer Whale Ecotypes. PLoS ONE 6(9): e24980. doi:10.1371/journal.pone.0024980.

ABSTRACT
Killer whales (Orcinus orca) are the most widely distributed marine mammals and have radiated to occupy a range of ecological niches. Disparate sympatric types are found in the North Atlantic, Antarctic and North Pacific oceans, however, little is known about the underlying mechanisms driving divergence. Previous phylogeographic analysis using complete mitogenomes yielded a bifurcating tree of clades corresponding to described ecotypes. However, there was low support at two nodes at which two Pacific and two Atlantic clades diverged. Here we apply further phylogenetic and coalescent analyses to partitioned mitochondrial genome sequences to better resolve the pattern of past radiations in this species. Our phylogenetic reconstructions indicate that in the North Pacific, sympatry between the maternal lineages that make up each ecotype arises from secondary contact. Both the phylogenetic reconstructions and a clinal decrease in diversity suggest a North Pacific to North Atlantic founding event, and the later return of killer whales to the North Pacific. Therefore, ecological divergence could have occurred during the allopatric phase through drift or selection and/or may have either commenced or have been consolidated upon secondary contact due to resource competition. The estimated timing of bidirectional migration between the North Pacific and North Atlantic coincided with the previous inter-glacial when the leakage of fauna from the Indo-Pacific into the Atlantic via the Agulhas current was particularly vigorous.

Full paper HERE.

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Foote, Andrew D., Jason Newton, Stuart B. Pierteney, Eske Willerslev and M. Thomas P. Gilbert; (2009). Ecological, morphological and genetic divergence of sympatric North Atlantic killer whale populations. Molecular Ecology (2009) 18, 5207-5217

ABSTRACT
Ecological divergence has a central role in speciation and is therefore an important source of biodiversity. Studying the micro-evolutionary processes of ecological diversification at its early stages provides an opportunity for investigating the causative mechanisms and ecological conditions promoting divergence. Here we use morphological traits, nitrogen stable isotope ratios and tooth wear to characterize two disparate types of North Atlantic killer whale. We find a highly specialist type, which reaches up to 8.5 m in length and a generalist type which reaches up to 6.6 m in length. There is a single fixed genetic difference in the mtDNA control region between these types, indicating integrity of groupings and a shallow divergence. Phylogenetic analysis indicates this divergence is independent of similar ecological divergences in the Pacific and Antarctic. Niche-width in the generalist type is more strongly influenced by between-individual variation rather than within-individual variation in the composition of the diet. This first step to divergent specialization on different ecological resources provides a rare example of the ecological conditions at the early stages of adaptive radiation.

Full paper available HERE.

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Foote, Andrew (2008). Mortality rate acceleration and post-reproductive lifespan in matrilineal whale species. Biol. Lett. 4, 189-191

ABSTRACT
The strength of selection to increase the span of a life stage is dependent upon individuals at that stage being able to contribute towards individual fitness and the probability of their surviving to that stage. Complete reproductive cessation and a long post-reproductive female lifespan as found in humans are also found in killer whale (Orcinus orca) and short-finned pilot whale (Globicephala macrorhynchus), but not in the long-finned pilot whale (Globicephala melaena). Each species forms kin-based, stable matrilineal groups and exhibits kin-directed behaviours that could increase inclusive fitness. Here, the initial mortality rate and mortality rate-doubling time of females of these three closely related whale species are compared. The initial mortality rate shows little variation among pilot whale species; however mortality rate accelerates almost twice as fast in the long-finned pilot whale as it does in killer whale and short-finned pilot whale. Selection for a long post-reproductive female lifespan in matrilineal whales may therefore be determined by the proportion of females surviving past the point of reproductive cessation.

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John K.B. Ford, James F. Pilkington, Amalis Reira, Mayuko Otsuki, Brian Gisborne, Robin M. Abernethy, Eva H. Stredulinsky, Jared R. Towers, and Graeme M. Ellis (2017). Habitats of Special Importance to Resident Killer Whales (Orcinus orca) off the West Coast of Canada. DFO Can. Sci. Advis. Sec. Res. Doc. 2017/035. viii + 57 p.

ABSTRACT
Two populations of fish-eating Killer Whales, Northern Resident and Southern Resident, inhabit waters off Canada’s west coast. The populations were listed under the Species at Risk Act (SARA) as Threatened and Endangered, respectively, in 2003. As required by the SARA, efforts have since been underway to identify critical habitat for these populations. Partial critical habitat was identified for each of the two populations in the 2011 Resident Killer Whale Recovery Strategy, which included a schedule of future studies to identify additional areas of critical habitat. In this report, we identify two new areas of special importance to Resident Killer Whales that potentially meet the criteria for designation as critical habitat under the SARA. One area includes waters on the continental shelf off southwestern Vancouver Island, including Swiftsure and La Perouse Banks. The other area includes waters of west Dixon Entrance, along the north coast of Graham Island from Langara Island to Rose Spit. Long-term vesselbased field studies and remote passive underwater acoustic monitoring show that both areas are important year-round habitat for Resident Killer Whales, especially for feeding on the whales’ primary prey, Chinook Salmon. The biophysical functions, features and attributes of these habitats of special importance are described, and examples of activities likely to result in the destruction of these components of critical habitat are summarized.

Full paper HERE.

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Ford, John K. B., Graeme M. Ellis (2014). You Are What You Eat: Foraging Specializations and Their Influence on the Social Organization and Behavior of Killer Whales. DOI: 10.1007/978-4-431-54523-1_4. In book: Primates and Cetaceans, pp.75-98.

ABSTRACT
The feeding ecology of predators can have a profound effect on their life history and behaviour. The killer whale—the apex marine predator—has a cosmopolitan distribution throughout the world’s oceans. Globally, it is a generalist predator with a diverse diet, but regionally, different socially and genetically isolated killer whale populations can have highly specialized foraging strategies involving only a few types of prey. In the eastern North Pacific, the three sympatric killer whale lineages have distinct dietary specializations: one feeds primarily on marine mammals, another on salmon, and the third appears to specialize on sharks. These ecological specializations are associated with distinct patterns of seasonal distribution, group size, social organization, foraging behavior, and acoustic activity. Divergent foraging strategies may have played a major role in the social isolation and genetic divergence of killer whale populations.

Full paper HERE.

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Ford, John K. B., Graeme M. Ellis, Craig O. Matkin, Michael H. Wetklo, Lance G. Barrett-Lennard, Ruth E. Withler (2011). Shark predation and tooth wear in a population of northeastern Pacific killer whales. Aquatic Biology 11:213-224.

ABSTRACT
The cosmopolitan killer whale Orcinus orca feeds on a wide variety of prey types over its global range, but in at least some regions, genetically distinct and ecologically specialised lineages of killer whales coexist sympatrically. In coastal waters of the northeastern Pacific, 2 such lineages have been well described: the so-called ‘residents’ prey on teleost fish, especially salmonids and the other (‘transients’) on marine mammals. A third lineage in this region (‘offshores’) appears from chemical tracers to be ecologically distinct from residents and transients, but its diet is very poorly known. Here we describe 2 encounters with offshore killer whales during which multiple predation events involving sharks were observed. Using DNA analysis of tissue samples collected from these predation events, we identified the prey species as Pacific sleeper shark Somniosus pacificus and determined that a minimum of 16 individuals were consumed over the 2 encounters. This represents the first confirmed prey species of offshore killer whales based on field observations of foraging and the first record of any Somniosus species in the prey of Orcinus. We also show quantitatively that apical tooth wear is far greater in offshores than in resident and transient killer whales, and propose that such wear is at least in part due to abrasion from dermal denticles embedded in shark skin. Further studies are needed to determine whether offshore killer whales are as specialised ecologically as resident and transient killer whales, and whether sharks play a dominant role in their diet.

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Ford, John K.B., Graeme M. Ellis, Peter F. Olesiuk and Kenneth C. Balcomb (2009). Linking killer whale survival and prey abundance: food limitation in the oceans' apex predator?

ABSTRACT
Killer whales (Orcinus orca) are large predators that occupy the top trophic position in the world's oceans and as such may have important roles in marine ecosystem dynamics. Although the possible top-down effects of killer whale predation on populations of their prey have received much recent attention, little is known of how the abundance of these predators may be limited by bottom-up processes. Here we show, using 25 years of demographic data from two populations of fish-eating killer whales in the northeastern Pacific Ocean, that population trends are driven largely by changes in survival, and that survival rates are strongly correlated with the availability of their principal prey species, Chinook salmon (Oncorhynchus tshawytscha). Our results suggest that, although these killer whales may consume a variety of fish species, they are highly specialized and dependent on this single salmonid species to an extent that it is a limiting factor in their population dynamics. Other ecologically specialized killer whale populations may be similarly constrained to a narrow range of prey species by culturally inherited foraging strategies, and thus are limited in their ability to adapt rapidly to changing prey availability.

Full paper HERE.

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Ford, John K.B., Graeme M. Ellis (2005). Selective foraging by fish-eating killer whales Orcinus orca in British Columbia. MARINE ECOLOGY PROGRESS SERIES Vol. 316: 185-199, 2006.

ABSTRACT

As the apex non-human marine predator, the killer whale Orcinus orca feeds on a wide diversity of marine fauna. Different ecotypic forms of the species, which often exist in sympatry, may have distinct foraging specialisations. One form found in coastal waters of the temperate NE Pacific Ocean, known as the 'resident' ecotype, feeds predominantly on salmonid prey. An earlier study that used opportunistic collection of prey remains from kill sites as an indicator of predation rates suggested that resident killer whales may forage selectively for chinook salmon Oncorhynchus tshawytscha, the largest but one of the least abundant Pacific salmon species. Potential biases in the prey fragment sampling technique, however, made the validity of this finding uncertain. We under-took field studies of foraging behaviour of resident killer whales to resolve this uncertainty and to examine potential variation in prey selection by season, geographical area, group membership and prey availability. Foraging by resident killer whales was found to frequently involve sharing by 2 or more whales. Prey fragments left at kill sites resulted mostly from handling and breaking up of prey for sharing, and all species and sizes of salmonids were shared. Resident killer whale groups in all parts of the study area foraged selectively for chinook salmon, probably because of the species' large size, high lipid content, and year-round availability in the whales' range. Chum salmon Oncorhynchus keta, the second largest salmonid, were also taken when available, but smaller sock-eye O. nerka and pink O. gorbuscha salmon were not significant prey despite far greater seasonal abundance. Strong selectivity for chinook salmon by resident killer whales probably has a significant influence on foraging tactics and seasonal movements, and also may have important implications for the conservation and management of both predator and prey.

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Ford, John K.B., Graeme M. Ellis (2005). Prey selection and food sharing by fish-eating 'resident' killer whales (Orcinus orca) in British-Columbia. Canadian Science Advisory Secretariat Research Document - 2005/041.

ABSTRACT
Three distinct, socially-isolated forms, or ecotypes, of killer whales (Orcinus orca), inhabit coastal waters of British-Columbia, Washington State, and southeastern Alaska. The so-called transient ecotype feeds primarily on marine mammal prey, the resident ecotype feeds primarily on fish, and the diet of the offshore ecotype is not known. A previous study of the diet of the resident and transient ecotypes using opportunistic collection of prey remains from kill sites as a primary measure of prey selection found that resident killer whales feed predominantly on salmonids, particularly on chinook salmon (Oncorhynchus tshawytscha). To address uncertainties concerning potential biases in the prey fragment sampling technique and questions regarding seasonal and geographic variability in diet, we conducted field studies of foraging behaviour during 1997-2004. Foraging by resident killer whales often involves cooperation among kin-related group members, and prey items are frequently shared by two or more whales. Adult males share prey less often than do females and subadults. Prey sharing does not appear to be related to prey size. Prey fragments left at kill sites result mostly from prey handling and sharing, and are reliable indicators of selection for different salmonid species by resident killer whales. Chinook is the predominant prey species taken by both northern and southern resident communities during May-August, but chum salmon (O. keta) is more prevalent in September-October, at least in northern residents. Coho salmon (O. kisutch) are taken in low numbers in June-October, but sockeye (O. nerka) and pink (O. gorbuscha) salmon are not significant prey species despite their high seasonal abundance. Non-salmonid fishes do not appear to represent an important component of resident whale diet during May-October. Their strong preference for chinook salmon may influence the year-round distribution patterns of resident killer whales in coastal British-Columbia and adjacent waters.

Full paper here.

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Ford, J.K.B., Graeme. M. Ellis, Peter Olesiuk (2005). Linking prey to population dynamics: did food limitation cause recent declines of 'resident' killer whales (Orcinus orca) in British Columbia? Fisheries and Oceans Canada Research Document 2005/042 (www.dfo-mpo.gc.ca/csas). Not to be cited without permission of the authors.

ABSTRACT
Two populations of fish-eating killer whales (Orcinus orca) in British Columbia, known as residents, are listed under the Canadian Species-at-Risk Act due to thier small population size and recent unexplained declines in abundance. Threats considered to potentially affect survival and recovery of these populations include environmental pollutants, physical and acoustic disturbance, and reductions in the availability or quality of salmonids, their primary prey. Recent studies have shown that chinook salmon and, to a lesser degree, chum salmon, are important prey for resident killer whales, but other smaller salmonid species are not. In this report, we assess whether food limitation was potentially a significant factor in recent declines of these whale populations. We examined the relationship between trends in killer whale population dynamics based on long-term photo-identification data, and abundance levels of chinook and chum salmon off the British Columbia coast over the the past 25 years. Resident killer whale population productivity is regulated primarily by changes in survival. Periods of decline were primarily due to unusually high mortality rates that were experienced by all age- and sex-classes of whales and were synchronous in the socially-isolated two resident communities. Fluctuations in observed versus expected mortality rates showed a strong correlation with changes in chinook salmon abundance, but no relationship to chum salmon abundance. A sharp drop in coast-wide chinook abundance during the late 1990s was closely associated with a significant decline in resident whale surivial. The whales' preference for chinook salmon is likely due to the species' relatively large size, high lipid content and, unlike other salmonids, its year-round presence in the whales' range. Resident killer whales may be especially dependent on chinook during winter, when this species is the primary salmonid available in coastal waters, and the whales may be subject to nutritional stress leading to increased mortality if the quantity and/or quality of this prey resource declines. Chinook salmon is clearly of great importance to resident killer whales, but determining whether the species is the principal factor limiting whale productivity will require on-going monitoring of both salmon and whale population trends.

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Ford, J.K.B., G.M. Ellis, L.G. Barrett-Lennard, A.B. Morton, R.S. Palm, and K.C. Balcomb III (1999). Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in coastal British Columbia and adjacent waters. Canadian Journal of Zoology, Vol. 76, p. 1456-1471

ABSTRACT

Two forms of killer whale (Orcinus orca), resident and transient, occur sympatrically in coastal waters of British Columbia, Washington State, and southeastern Alaska. The two forms do not mix, and differ in seasonal distribution, social structure, and behaviour. These distinctions have been attributed to apparent differences in diet, although no comprehensive comparative analysis of the diets of the two forms has been undertaken. Here we present such an analysis, based on field observations of predation and on the stomach contents of stranded killer whales collected over a 20-year period. In total, 22 species of fish and 1 species of squid were documented in the diet of resident-type killer whales; 12 of these are previously unrecorded as prey of O. orca. Despite the diversity of fish species taken, resident whales have a clear preference for salmon prey. In field observations of feeding, 96% of fish taken were salmonids. Six species of salmonids were identified from prey fragments, with chinook salmon (Oncorhynchus tshawytscha) being the most common. The stomach contents of stranded residents also indicated a preference for chinook salmon. On rare occasions, resident whales were seen to harass marine mammals, but no kills were confirmed and no mammalian remains were found in the stomachs of stranded residents.
Transient killer whales were observed to prey only on pinnipeds, cetaceans, and seabirds. Six mammal species were taken, with over half of observed attacks involving harbour seals (Phoca vitulina). Seabirds do not appear to represent a significant prey resource. This study thus reveals the existence of strikingly divergent prey preferences of resident and transient killer whales, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations.

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Ford, Michael J., Jennifer Hempelmann, M. Bradley Hanson, Katherine L. Ayres, Robin W. Baird, Candice K. Emmons, Jessica I. Lundin, Gregory S. Schorr, Samuel K. Wasser, Linda K. Park (2016). Estimation of a Killer Whale (Orcinus orca) Population's Diet Using Sequencing Analysis of DNA from Feces. PLOS, Published: January 6, 2016, DOI: 10.1371/journal.pone.0144956

ABSTRACT
Estimating diet composition is important for understanding interactions between predators and prey and thus illuminating ecosystem function. The diet of many species, however, is difficult to observe directly. Genetic analysis of fecal material collected in the field is therefore a useful tool for gaining insight into wild animal diets. In this study, we used high-throughput DNA sequencing to quantitatively estimate the diet composition of an endangered population of wild killer whales (Orcinus orca) in their summer range in the Salish Sea. We combined 175 fecal samples collected between May and September from five years between 2006 and 2011 into 13 sample groups. Two known DNA composition control groups were also created. Each group was sequenced at a ~330bp segment of the 16s gene in the mitochondrial genome using an Illumina MiSeq sequencing system. After several quality controls steps, 4,987,107 individual sequences were aligned to a custom sequence database containing 19 potential fish prey species and the most likely species of each fecal-derived sequence was determined. Based on these alignments, salmonids made up >98.6% of the total sequences and thus of the inferred diet. Of the six salmonid species, Chinook salmon made up 79.5% of the sequences, followed by coho salmon (15%). Over all years, a clear pattern emerged with Chinook salmon dominating the estimated diet early in the summer, and coho salmon contributing an average of >40% of the diet in late summer. Sockeye salmon appeared to be occasionally important, at >18% in some sample groups. Non-salmonids were rarely observed. Our results are consistent with earlier results based on surface prey remains, and confirm the importance of Chinook salmon in this population’s summer diet.

Full paper HERE.

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Ford MJ, Hanson MB, Hempelmann JA, Ayres KL, Emmons CK, Schorr GS, Baird RW, Balcomb KC, Wasser SK, Parsons KM, Balcomb-Bartok K. Inferred Paternity and Male Reproductive Success in a Killer Whale (Orcinus orca) Population. The Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, WA 98112.

ABSTRACT
We used data from 78 individuals at 26 microsatellite loci to infer parental and sibling relationships within a community of fish-eating ("resident") eastern North Pacific killer whales (Orcinus orca). Paternity analysis involving 15 mother/calf pairs and 8 potential fathers and whole-pedigree analysis of the entire sample produced consistent results. The variance in male reproductive success was greater than expected by chance and similar to that of other aquatic mammals. Although the number of confirmed paternities was small, reproductive success appeared to increase with male age and size. We found no evidence that males from outside this small population sired any of the sampled individuals. In contrast to previous results in a different population, many offspring were the result of matings within the same "pod" (long-term social group). Despite this pattern of breeding within social groups, we found no evidence of offspring produced by matings between close relatives, and the average internal relatedness of individuals was significantly less than expected if mating were random. The population's estimated effective size was <30 or about 1/3 of the current census size. Patterns of allele frequency variation were consistent with a population bottleneck.

Full paper HERE.

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Foster, Emma A., Daniel W. Franks, Sonia Mazzi, Safi K. Darden, Ken C. Balcomb, John K. B. Ford, Darren P. Croft. Adaptive Prolonged Postreproductive Life Span in Killer Whales. Science Vol. 337 14 September 2012.

ABSTRACT
Prolonged life after reproduction is difficult to explain evolutionarily unless it arises as a physiological side effect of increased longevity or it benefits related individuals (i.e., increases inclusive fitness). There is little evidence that postreproductive life spans are adaptive in nonhuman animals. By using multigenerational records for two killer whale (Orcinus orca) populations in which females can live for decades after their final parturition, we show that postreproductive mothers increase the survival of offspring, particularly their older male offspring. This finding may explain why female killer whales have evolved the longest postreproductive life span of all nonhuman animals.

Full paper HERE.

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Foster, Emma A., Daniel W. Franks, Lesley J. Morrell, Ken C. Balcomb, Kim M. Parsons, Astrid van Ginneken, Darren P. Croft Social network correlates of food availability in an endangered population of killer whales, Orcinus orca. Animal Behaviour 83 (2012) 731e736.

ABSTRACT
For the majority of social species, group composition is dynamic, and individuals are interconnected in a heterogeneous social network. Social network structure has far-reaching implications for the ecology of individuals and populations. However, we have little understanding of how ecological variables shape this structure. We used a long-term data set (1984e2007) to examine the relationship between food availability and social network structure in the endangered southern resident killer whales. During the summer months individuals in this population feed primarily on chinook salmon, Oncorhynchus tshawytscha, which show annual variation in abundance. We tested the hypothesis that temporal variation in chinook salmon will correlate with variation in social network structure. Using a null model that controlled for population demography, group size and sampling effort, we found a significant relationship between the connectivity of the social network and salmon abundance, with a more interconnected social network in years of high salmon abundance. Our results demonstrate that resource availability may be an important determinant of social network structure. Given the central importance of the social network for population processes such as the maintenance of cooperation and the transmission of information and disease, a change in social network structure caused by a change in food availability may have significant ecological and evolutionary consequences.

Full paper HERE.

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Garrett, H. (2002) Do Orcas Use Symbols?

ABSTRACT
Recent theoretical studies of culture in whales and dolphins have reviewed experimental research on captive animals and patterns of behavioral variation found in wild populations. Captive studies of cognitive processes in dolphins, such as imitation, teaching, and use of gestures and other symbolic representations, have provided indications of the capacity for culture in dolphins. The ethnographic approach, based on evolutionary ecology, has found evidence that the vocal and behavioral traditions of killer whales (Orcinus orca) appear to have no parallel outside humans. To date, however, no published theory has provided a synthesis that accommodates both the experimental findings and the ethnographic evidence. The theory of symbolic interactionism, borrowed and adapted from sociology, provides a conceptual framework for integrating the experimental "process-oriented" and the ethnographic "product-oriented" perspectives. Symbolic interactionism may help account for the divergent and complex cultural traditions found in sympatric orca populations.

Full paper. Poster presentation (10.5 mg .pdf).

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Goley, P. D., and J. M. Straley. 1994. Attack on gray whales (Eschrichtius robustus) in Monterey Bay, California, by killer whales (Orcinus orca) previously identified in Glacier Bay, Alaska. Can. J. Zool. 72:1528-1530.

ABSTRACT

A group of at least 17 killer whales (Orcinus orca) were observed attacking a gray whale (Eschrichtius robustus) mother and calf on 2 May 1992 in Monterey Bay, California, U.S.A. (36°47.90′N, 122°00.17′W). Small groups of killer whales took turns harassing the gray whales and prevented them from leaving the area. Three of the killer whales participating in this attack previously had been photographed on 6 August 1989 in Glacier Bay, Alaska, U.S.A. (58°41′N, 136°04′W). This linear distance nearly doubles the maximum range of movement previously reported for killer whales.

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Groskreutz, Molly J., John W. Durban, Holly Fearnbach, Lance G. Barrett-Lennard, Jared R. Towers, John K. B. Ford 2019. Decadal changes in adult size of salmon-eating killer whales in the eastern North Pacific. Endangered Species Research, December 2018. Vol. 40: 183–188, 2019.

ABSTRACT
Two populations of killer whales aggregate around Vancouver Island to feed primarily on Chinook salmon. Aerial photogrammetry of endangered southern residents has documented some adults growing to smaller lengths in recent decades, suggesting that early growth may have been constrained by low Chinook availability in the 1990s. We investigated whether growth and adult length were also constrained in the more abundant northern residents. Photographs were collected from an unmanned hexacopter at altitudes of 30 to 37 m over 4 yr, 2014 to 2017. Images were linked to 78 individuals of known age and sex based on distinctive saddle patch pigmentation. The length of each whale was estimated by measuring pixel dimensions between both the snout and dorsal fin and the dorsal fin and fluke; these were scaled to real size using camera lens focal length and altitude, determined by a laser or pressure altimeter. Total length, derived by summing the longest (flattest) of each measure, ranged from 2.42 m for a first year calf to 7.45 m for the largest adult male. A Bayesian change point analysis revealed that adult whales <40 yr old were on average shorter by 0.44 m than older adults, which grew to typical lengths of 6.28 and 7.14 m for females and males, respectively. This mirrors the growth trends reported for southern residents, supporting demographic evidence of correlated prey limitation in both populations. The growth data suggest that the effects of nutritional stress are not only acutely lethal but also have long-term consequences for the condition of whales in both populations.

Full paper HERE.

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Grimes, Charli; Lauren J. N. Brent; Michael N. Weiss; Daniel W. Frank; Kenneth C. Balcomb; David K. Ellifrit; Samuel Ellis; Darren P. Croft. 2022. The effect of age, sex, and resource abundance on patterns of rake markings in resident killer whales (Orcinus orca). Mar Mam Sci. 2022;1–18.

ABSTRACT
Fluctuations in aggressive behavior of group-living species can reflect social conflict and competition for resources faced by individuals throughout their lifespan and can negatively impact survival and reproduction. In marine mammals, where social interactions are difficult to observe, tooth rake marks can be used as an indicator of received aggression. Using 38 years of photographic data, we quantified the occurrence of tooth rake marks on wild resident killer whales (Orcinus orca), examining the effects of age, sex, and prey abundance on rake density. Our analysis revealed sex and age effects, with males exhibiting higher rake density than females and rake density declining significantly with age. Contrary to predictions, we observed an increase in rake density across the population as the abundance of their primary food resource, Chinook salmon (Oncorhynchus tshawytscha), increased. These results provide indirect evidence of fluctuations in received aggression from conspecifics across the lifespan of an individual, possibly reflecting changes in patterns of social conflict which may be mediated by resource abundance. Our findings highlight the need for further research to examine the fitness consequences of aggression in killer whales and to understand the proximate mechanisms by which resource abundance influences rates of aggression in the population.

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Guerrero-Ruiz, Mercedes; Pérez-Cortés M., Héctor; Salinas Z., Mario; Urbán R., Jorge 2006. First Mass Stranding of Killer Whales (Orcinus orca) in the Gulf of California, Mexico. Aquatic Mammals, Volume 32, Number 3, September 2006 , pp. 265-272

ABSTRACT
We present the first report of a mass stranding of killer whales (Orcinus orca) in Mexican waters. This species is a temporal inhabitant of the region. On 31 July 2000, eight killer whales stranded alive at the southern tip of Isla San José in Bahía de La Paz (24° 54′ N, 110° 35′ W). All the individuals died despite the attempts performed by local fishermen to return them to sea. The group consisted of an undetermined number of females, immature males, and two calves. Skin and blubber samples were collected, as well as a skull on 2 August from a 4.6-m immature male. A second skull was collected on 19 August, which belonged to an individual of undetermined sex that measured 5 m in length. The teeth from both individuals were completely worn down. A couple of months later, two other skulls were collected. Individual strandings of killer whales are rare, and six records have been documented in the Mexican Pacific and Gulf of California. This report represents the first mass stranding of killer whales in Mexico. Since 1972, more than 160 killer whale sightings have been collected in the Gulf of California, with more than 90 photo-identified killer whales; nevertheless, no matches with the stranded individuals were found. There are few cases of killer whales found stranded live, probably as a result of whales chasing or following prey, or as a result of an outgoing tide. Causes of this stranding remain unknown.

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Guimaraes, P.R. Jr., M.A. de Menezes, R.W. Baird, D. Lusseau, P. Guimaraes, and S.F. dos Reis. 2007. Vulnerability of a killer whale social network to disease outbreaks. Physical Review E 76, 042901.

ABSTRACT
Emerging infectious diseases are among the main threats to conservation of biological diversity. A cruicial task facing epidemiologists is to predict the vulnerability of populations of endangered animals to disease outbreaks. In this context, the network structure of social interactions within animal populations may affect disease spreading. However, endangered animal populations are often small and to investigate the dynamics of small networks is a difficult task. Using network theory, we show that the social structure of an endangered population of mammal-eating killer whales is vulnerable to disease outbreaks. This feature was found to be a consequence of the combined effects of the toplogy and strength of social links among individuals. Our results uncover a serious challenge for conservation of the species and its ecosystem. In addition, this study shows that the network approach can be useful to study dynamical processes in very small networks.

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Guinet, C. , P. Domenici, R. de Stephanis, L. Barrett-Lennard, J. K. B. Ford , P. Verborgh. 2007. Killer whale predation on bluefin tuna: exploring the hypothesis of the endurance-exhaustion technique. Mar Ecol Prog Ser. Vol. 347: 111–119.

ABSTRACT
Killer whales Orcinus orca occur in the area of the Strait of Gibraltar, where they prey on migrating bluefin tuna Thunnus thynnus. In the spring, killer whales were observed to chase tuna for up to 30 min at a relatively high sustained speed (3.7 ± 0.2 m s-1) until they captured them. Using simple models based on previous locomotor performance data on killer whales and thunnids, we investigated the hypothesis that killer whales push tuna beyond their aerobic limits to exhaust and capture them. To test this hypothesis, the endurance of bluefin tuna was estimated from data on maximum burst and aerobic swimming available for bluefin and yellowfin tuna T. albacares. The endurance performance of killer whales was evaluated on the basis of the maximal rate of oxygen uptake during exercise (VO2max). We modelled the maximum aerobic power output for a killer whale according to swimming speed using a VO2max ranging between 20 and 30 ml O2 kg-1) min-1). The output of this model was compared to the observed sustained swimming speed of killer whales chasing prey over long durations. Our results support the hypothesis that killer whales may use an endurance-exhaustion technique to catch small to medium sized (up to 0.8 to 1.5 m) bluefin tuna, while larger tuna may be inaccessible to killer whales unless they use cooperative hunting techniques or benefit through depredation of fish caught on long lines, drop lines or trap nets.

Full paper HERE.

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Hanson, M. Bradley, Candice K. Emmons,Michael J. Ford, Meredith Everett1 Kim Parsons, Linda K. Park, Jennifer Hempelmann, Donald M. Van Doornik, Gregory S. Schorr, Jeffrey K. Jacobsen, Mark F. Sears, Maya S. Sears, John G. Sneva, Robin W. Baird, Lynne Barre. Endangered predators and endangered prey: Seasonal diet of Southern Resident killer whales. Hanson, Bradley, et al. (2021). PLOS ONE | https://doi.org/10.1371/journal.pone.0247031 March 3, 2021.

ABSTRACT
Understanding diet is critical for conservation of endangered predators. Southern Resident killer whales (SRKW) (Orcinus orca) are an endangered population occurring primarily along the outer coast and inland waters of Washington and British Columbia. Insufficient prey has been identified as a factor limiting their recovery, so a clear understanding of their seasonal diet is a high conservation priority. Previous studies have shown that their summer diet in inland waters consists primarily of Chinook salmon (Oncorhynchus tshawytscha), despite that species’ rarity compared to some other salmonids. During other times of the year, when occurrence patterns include other portions of their range, their diet remains largely unknown. To address this data gap, we collected feces and prey remains from October to May 2004–2017 in both the Salish Sea and outer coast waters. Using visual and genetic species identification for prey remains and genetic approaches for fecal samples, we characterized the diet of the SRKWs in fall, winter, and spring. Chinook salmon were identified as an important prey item yearround, averaging ~50% of their diet in the fall, increasing to 70–80% in the mid-winter/early spring, and increasing to nearly 100% in the spring. Other salmon species and nonsalmonid fishes, also made substantial dietary contributions. The relatively high species diversity in winter suggested a possible lack of Chinook salmon, probably due to seasonally lower densities, based on SRKW’s proclivity to selectively consume this species in other seasons. A wide diversity of Chinook salmon stocks were consumed, many of which are also at risk. Although outer coast Chinook samples included 14 stocks, four rivers systems accounted for over 90% of samples, predominantly the Columbia River.
FULL PAPER HERE

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Hanson, M. Bradley, Candice K. Emmons, Eric J. Ward, Jeffrey A. Nystuen, and Marc O. Lammers (2013). Assessing the coastal occurrence of endangered killer whales using autonomous passive acoustic recorders. J. Acoust. Soc. Am. 134 (5), November 2013.

ABSTRACT
Using moored autonomous acoustic recorders to detect and record the vocalizations of social odonotocetes to determine their occurrence patterns is a non-invasive tool in the study of these species in remote locations. Acoustic recorders were deployed in seven locations on the continental shelf of the U.S. west coast from Cape Flattery, WA to Pt. Reyes, CA to detect and record endangered southern resident killer whales between January and June of 2006–2011. Detection rates of these whales were greater in 2009 and 2011 than in 2006–2008, were most common in the month of March, and occurred with the greatest frequency off the Columbia River and Westport, which was likely related to the presence of their most commonly consumed prey, Chinook salmon. The observed patterns of annual and monthly killer whale occurrence may be related to run strength and run timing, respectively, for spring Chinook returning to the Columbia River, the largest run in this region at this time of year. Acoustic recorders provided a unique, long-term, dataset that will be important to inform future consideration of Critical Habitat designation for this U.S. Endangered Species Act listed species.

Full paper HERE.

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Hanson, M. Bradley, Jennifer Hempelmann-Halos, Donald M. Van Doornik (2010). Species and stock identification of scale/tissue samples from southern resident killer whale predation events collected off the Washington coast during PODs 2009 cruise on the McArthur II. NOAA Doc # BB0149

INTRODUCTION
In order to improve the Critical Habitat designation for SRKW and determine prey selection during the winter and spring, the NWFSC has undertaken 5 survey cruises on the McArthur II in the coastal waters of Washington Oregon and British Columbia between 2004 and 2009 to locate pods from this population.
Quote: "...on 26 March 2010 near Gray's Canyon, L pod was sighted traveling northeast just offshore of Ocean Shores, Washington...Two predation event samples were collected as the whales travel parallel to the coast between the entrances to Gray's Harbor and Willapa Bay...both of the samples were Chinook salmon, and the most likely regions of origin for these samples were in the Columbia River; one from the Upper Columbia, the other from the Snake River."

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Hanson, M. Bradley, Robin W. Baird, John K. B. Ford, Jennifer Hempelmann-Halos, Donald M. Van Doornik, John R. Candy, Candice K. Emmons, Gregory S. Schorr, Brian Gisborne, Katherine L. Ayres, Samuel K. Wasser, Kenneth C. Balcomb, Kelley Balcomb-Bartok, John G. Sneva, Michael J. Ford (2010). Species and stock identification of prey consumed by endangered southern resident killer whales in their summer range. Endang Species Res Vol. 11: 69-82, 2010

ABSTRACT
Recovery plans for endangered southern resident killer whales Orcinus orca have identified reduced prey availability as a risk to the population. In order to better assess this risk, we studied prey selection from 2004 to 2008 in 2 regions of the whales' summer range: San Juan Islands, Washington and the western Strait of Juan de Fuca, British Columbia. Following the whales in a small boat, we collected fish scales and tissue remains from predation events, and feces, using a fine mesh net. Visual fish scale analysis and molecular genetic methods were used to identify the species consumed. Chinook salmon, a relatively rare species, was by far the most frequent prey item, confirming previous studies. For Chinook salmon prey, we used genetic identification methods to estimate the spawning region of origin. Of the Chinook salmon sampled, 80 to 90% were inferred to have originated from the Fraser River, and only 6 to 14% were inferred to have originated from Puget Sound area rivers. Within the Fraser River, the Upper Fraser, Middle Fraser, South Thompson River and Lower Fraser stocks were inferred to currently be sequentially important sources of Chinook salmon prey through the summer. This information will be of significant value in guiding management actions to recover the southern resident killer whale population.

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Heimlich-Boran, James R. (1987) Behavioral ecology of killer whales (Orcinus orca) in the Pacific Northwest. Can. J. Zool 66:565 -578.

ABSTRACT
Killer whales (Orcinus orca) were found to use different physiographic regions of their habitat in unique ways. Resident whales fed more in areas of high relief subsurface topography along salmon migratory routes, and may use these geographic features to increase feeding efficiency. Transient whales fed in shallow protected areas around concentrations of their prey, harbor seals (Phoca vitulina). Whales traveled across deep, featureless areas in moving from one feeding area to another. Whales rested depending on the previous sequence of behaviors and played in open water areas or adjacent to feeding areas. The location of food resources and habitats suitable for prey capture appears to be the prime determining factor in the behavioral ecology of these whales. These patterns of behavior most likely represent cultural mechanisms that have been learned through trial and error experiences leading to successful foraging strategies.

Full paper HERE.

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Herman, David P., Craig O. Matkin, Gina M.Ylitalo, John W. Durban, M. Bradley Hanson, Marilyn E. Dahlheim, Janice M. Straley, Paul R. Wade, Karen L. Tilbury, Richard H. Boyer, Ronald W. Pearce, Margaret M. Krahn (2008). Assessing age distributions of killer whale Orcinus orca populations from the composition of endogenous fatty acids in their outer blubber layers. Mar Ecol Prog Ser Vol. 372: 289-302, 2008

ABSTRACT
Knowledge of the age distributions of killer whale Orcinus orca populations is critical to assess their status and long-term viability. Except for accessible, well-studied populations for which historical sighting data have been collected, currently there is no reliable benign method to determine the specific age of live animals for remote populations. To fill this gap in our knowledge of age structure, we describe new methods by which age can be deduced from measurements of specific lipids, endogenous fatty acids (FAs) and FA ratios present in their outer blubber layers. Whereas correlation of wax and sterol esters with age was reasonable for female "resident" killer whales, it was less well-defined for males and "transients." Individual short-, branched-, and odd-chain FAs correlated better with age for transients and residents of both sexes, but these single parameter relationships were population specific and seemingly varied with long-term diet. Alternatively, a simple, empirical multi-linear model derived from the combination of 2 specific FA ratios enabled the ages of individual eastern North Pacific killer whales to be predicted with good precision (σ = ±3.8 yr), appeared to be independent of individual diet and was applicable to both genders and ecotypes. The model was applied to several less well-studied killer whale populations to predict their age distributions from their blubber FA compositions, and these distributions were compared with a population of known age structure. Most interestingly, these results provide evidence for the first time that adult male transient killer whales appear to have lower life expectancies than do their resident counterparts in Alaska.

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Hill, Marie C., Andrea R. Bendlin, Amy M. Van Cise, Aliza Milette-Winfree, Allan D. Ligon, Adam C. Ü, Mark H. Deakos, Erin M. Oleson. (2018). Short-finned pilot whales (Globicephala macrorhynchus) of the Mariana Archipelago: Individual affiliations, movements, and spatial use. Marine Mammal Science https://doi.org/10.1111/mms.12567.

ABSTRACT
Little is known about short-finned pilot whales (Globicephala macrorhynchus) in the western North Pacific outside of Japanese coastal waters. To expand understanding of short-finned pilot whale ecology in the region, we conducted small-boat surveys in 2010-2016 within the Mariana Archipelago to investigate individual associations, movements, spatial use, and dive behavior of short-finned pilot whales. We collected genetic, photo-identification, and satellite-tag data and identified 191 distinctive individuals. A preliminary social network diagram of photo-cataloged individuals revealed a main cluster that comprised 82% of individuals, representing all five mitochondrial DNA haplotypes identified within the population. Kernel density estimates for tagged short-finned pilot whales (n = 11) during summer were used to identify areas with the highest probability of use (10% probability density contour), core area (50%) and home range (95%). The area with highest probability of use by short-finned pilot whales was off the northwest side of Guam. Satellite tag data also suggest that some individuals are island-associated year-round. Data from five location-dive tags demonstrated that the short-finned pilot whales dove more often to intermediate depths at twilight and night, suggesting they may target prey that forage on the deep scattering layer as it migrates to and from the surface.

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Hoelzel, A. Rus, Hey J, Dahlheim ME, Nicholson C, Burkanov V, Black N. (2007). Evolution of population structure in a highly social top predator, the killer whale. Mol Biol Evol. 2007 Jun;24(6):1407-15.

ABSTRACT
Intraspecific resource partitioning and social affiliations both have the potential to structure populations, though it is rarely possible to directly assess the impact of these mechanisms on genetic diversity and population divergence. Here, we address this for killer whales (Orcinus orca), which specialize on prey species and hunting strategy and have long-term social affiliations involving both males and females. We used genetic markers to assess the structure and demographic history of regional populations and test the hypothesis that known foraging specializations and matrifocal sociality contributed significantly to the evolution of population structure. We find genetic structure in sympatry between populations of foraging specialists (ecotypes) and evidence for isolation by distance within an ecotype. Fitting of an isolation with migration model suggested ongoing, low-level migration between regional populations (within and between ecotypes) and small effective sizes for extant local populations. The founding of local populations by matrifocal social groups was indicated by the pattern of fixed mtDNA haplotypes in regional populations. Simulations indicate that this occurred within the last 20,000 years (after the last glacial maximum). Our data indicate a key role for social and foraging behavior in the evolution of genetic structure among conspecific populations of the killer whale.

On line.

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Hoelzel, A. Rus, Ada Natoli, Marilyn E. Dahlheim, Carlos Olavarria, Robin W. Baird and Nancy A. Black (2002). Low worldwide genetic diversity in the killer whale (Orcinus orca): implications for demographic history. Proc. Royal Soc. B 269: 1467-1475.

ABSTRACT
A low level of genetic variation in mammalian populations where the census population size is relatively large has been attributed to various factors, such as a naturally small effective population size, historical bottlenecks and social behaviour. The killer whale (Orcinus orca) is an abundant, highly social species with reduced genetic variation. We find no consistent geographical pattern of global diversity and no mtDNA variation within some regional populations. The regional lack of variation is likely to be due to the strict matrilineal expansion of local populations. The worldwide pattern and paucity of diversity may indicate a historical bottleneck as an additional factor.

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Houghton, Juliana, Robin W. Baird, Candice K. Emmons, M. Bradley Hanson (2015). Changes in the Occurrence and Behavior of Mammal-eating Killer Whales in Southern British Columbia and Washington State, 1987–2010. Northwest Science, Vol. 89, No. 2, 2015.

ABSTRACT
The primary prey species of mammal-eating killer whales in the Salish Sea, the inland waters of southern British Columbia and Washington state, have experienced dramatic increases in population abundances in the last 25 years. It is possible that changes in prey abundance over time have resulted in changes in predator spatial use, occurrence and group size. Focused studies of mammal-eating killer whale behavior in the area were undertaken from 1987–1993, and an extensive record of sightings with confirmed identifications was available from 2004–2010. Changes in occurrence across years, months, and subareas of the Salish Sea were examined as well as changes in group size and in the identity of specific matrilines using the area. Occurrence of mammal-eating whales increased significantly from 2004–2010 with different seasonal peaks compared to 1987–1993. Different matrilines occurred in different seasons, time periods, and subareas. Group size was larger in 2004–2010 than in 1987–1993. The whales may be increasing use of the area due to increasing prey abundance or an overall increase in the whale population size. Changes in seasonal patterns of occurrence and the increase in group size between the two periods could be due to increased prey diversity.

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Ivkovicha, Tatiana, Olga A. Filatovab, Alexandr M. Burdinc, Hal Satoe and Erich Hoyt (2009). The social organization of resident-type killer whales (Orcinus orca) in Avacha Gulf, Northwest Pacific, as revealed through association patterns and acoustic similarity. Mammalian Biology.

ABSTRACT
Northeast Pacific resident-type killer whales (Orcinus orca) are known to form stable associations based on kinship between maternal relatives (matrilines) with a system of vocal dialects thought to reflect kinship relationships. We analyzed association patterns and acoustic similarity to study the social organization of killer whales in Avacha Gulf (Kamchatka, Russia), in the Northwest Pacific. The resident-type killer whales of Avacha Gulf formed temporally stable units that included maternal relatives with no dispersal observed. Acoustically, the killer whale community of Avacha Gulf was characterized by a system of dialects comparable to the communities of Northeast Pacific resident-type killer whales. Different units rarely associated with each other and these associations were nonrandom. Associations at different spatial levels did not always coincide with each other and with the patterns of acoustic similarity. Associations between units could change quickly irrespective of kinship relationships. The vocal dialect of a unit, which is more stable than the association patterns between units, might better reflect the overall kinship relationships. The stability and frequency of associations between units depended on the number of mature males in a unit, which could contribute to differences in the speed of change in vocal dialects and association patterns.

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Johnstone, Rufus A., and Michael A. Cant (2010). The evolution of menopause in cetaceans and humans: the role of demography. Proc. R. Soc. B published online before print June 30, 2010, doi:10.1098/rspb.2010.0988

ABSTRACT
Human females stop reproducing long before they die. Among other mammals, only pilot and killer whales exhibit a comparable period of post-reproductive life. The grandmother hypothesis suggests that kin selection can favour post-reproductive survival when older females help their relatives to reproduce. But although there is an evidence that grandmothers can provide such assistance, it is puzzling why menopause should have evolved only among the great apes and toothed whales. We have previously suggested (Cant & Johnstone 2008 Proc. Natl Acad. Sci. USA 105, 5332-5336 (doi:10.1073/pnas.0711911105)) that relatedness asymmetries owing to female-biased dispersal in ancestral humans would have favoured younger females in reproductive competition with older females, predisposing our species to the evolution of menopause. But this argument appears inapplicable to menopausal cetaceans, which exhibit philopatry of both sexes combined with extra-group mating. Here, we derive general formulae for "kinship dynamics," the age-related changes in local relatedness that occur in long-lived social organisms as a consequence of dispersal and mortality. We show that the very different social structures of great apes and menopausal whales both give rise to an increase in local relatedness with female age, favouring late-life helping. Our analysis can therefore help to explain why, of all long-lived, social mammals, it is specifically among the great apes and toothed whales that menopause and post-reproductive helping have evolved.

Full paper HERE.

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Jourdain, Eve, Dag Vongraven, Anna Bisther, Richard Karoliussen (2017). First longitudinal study of seal-feeding killer whales (Orcinus orca) in Norwegian coastal waters. PLoS ONE 12(6): e0180099.

ABSTRACT
Killer whales (Orcinus orca) have been documented preying on either fish or marine mammals in several regions, suggesting that this odontocete species has the ability to specialize on different types of prey. Off Norway, killer whales have been shown to rely on the Atlantic herring (Clupea harengus) as a main prey resource. Infrequent observations have revealed seals as an additional component of their diet, yet the extent of predation on marine mammals has remained largely unknown. Here, we present the findings of 29 years of photographic and observational data on seal-feeding killer whale groups identified in Norwegian coastal waters. Four groups have been observed preying and feeding on seals over several years, taking both harbor (Phoca vitulina) and grey (Halichoerus grypus) seals. These stable groups are shown to adopt small group sizes, were typically observed in near-shore areas and were not encountered on herring wintering grounds. Behavioral and social traits adopted by these groups are similar to those of pinniped-feeding killer whales from other regions. The potential ecological reasons and the extent of such prey specializations are discussed.

Full paper HERE.

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Kiszka, Jeremy J., Michelle Caputo, Paula Méndez-Fernandez and Russell Fielding (2021). Feeding Ecology of Elusive Caribbean Killer Whales Inferred From Bayesian Stable Isotope Mixing Models and Whalers’ Ecological Knowledge. Front. Mar. Sci., 30 April 2021 | https://doi.org/10.3389/fmars.2021.648421.

ABSTRACT
Investigating the feeding ecology of marine predators is critical for understanding their roles and functional importance in ecosystems. However, assessing the diet of large and wide-ranging predators can be challenging, particularly in the case of rare and elusive species. Killer whales (Orcinus orca) are large apex predators in global oceans, but very little is known about their feeding ecology in tropical ecosystems, particularly in the Caribbean Sea. Killer whales are distributed throughout the Caribbean, and are a regular target of artisanal whalers in St. Vincent and the Grenadines (West Indies). Here we investigate the feeding ecology of Caribbean killer whales using a combination of stable isotope analysis (?15N, ?13C) and traditional ecological knowledge (TEK) data from whalers operating from St. Vincent. Potential prey data from the Caribbean region included large pelagic teleosts, sea turtles, oceanic sharks, cetaceans, and oceanic cephalopods. Mixing models suggest that the contribution of odontocete cetaceans to the diet of killer whales is the most important (overall mean contribution: 60.4%), particularly mesopelagic delphinids (Lagenodelphis hosei; 26.4%, SD = 0.14), large teuthophageous odontocetes (Physeter macrocephalus, Globicephala macrorhynchus; 20.0%, SD = 0.14), and epipelagic delphinids (Stenella attenuata; 14%, SD = 0.14). Oceanic sharks (Carcharhinus longimanus) had a contribution of 17.0% of the diet of killer whales (SD = 0.13), and other potential prey had a relatively marginal contribution. TEK data suggest that whalers believe killer whales feed almost exclusively on cetaceans, particularly odontocete species that they hunt (e.g., G. macrorhynchus). Stable isotope and TEK data were consistent to some extent, although TEK data are qualitative and based on a limited number of observations. Despite some limitations (including sample size for both methods), this study highlights the value of combining independent data sources and methodologies to investigate the ecological roles of marine predators in data-poor regions.

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Krahn, Margaret M., M. Bradley Hanson, Gregory S. Schorr, Candice K. Emmons, Douglas G. Burrows, Jennie L. Bolton, Robin W. Baird, Gina M. Ylitalo (2009). Effects of age, sex and reproductive status on persistent organic pollutant concentrations in "Southern Resident" killer whales. Mar. Pollut. Bull. (2009), doi:10.1016/j.marpolbul.2009.05.014.

ABSTRACT
"Southern Resident" killer whales (Orcinus orca) that comprise three fish-eating "pods" (J, K and L) were listed as "endangered" in the US and Canada following a 20% population decline between 1996 and 2001. Blubber biopsy samples from Southern Resident juveniles had statistically higher concentrations of certain persistent organic pollutants than were found for adults. Most Southern Resident killer whales, including the four juveniles, exceeded the health-effects threshold for total PCBs in marine mammal blubber. Maternal transfer of contaminants to the juveniles during rapid development of their biological systems may put these young whales at greater risk than adults for adverse health effects (e.g., immune and endocrine system dysfunction). Pollutant ratios and field observations established that two of the pods (K- and L-pod) travel to California to forage. Nitrogen stable isotope values, supported by field observations, indicated possible changes in the diet of L-pod over the last decade.
FULL PAPER

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Krützen, Michael, Janet Mann, Michael R. Heithaus, Richard C. Connor, Lars Bejder, and William B. Sherwin (2005). Cultural transmission of tool use in bottlenose dolphins. PNAS, June 21, 2005, vol. 102, no. 25, 8939-8943.

ABSTRACT
In Shark Bay, wild bottlenose dolphins (Tursiops sp.) apparently use marine sponges as foraging tools. We demonstrate that genetic and ecological explanations for this behavior are inadequate; thus, "sponging" classifies as the first case of an existing material culture in a marine mammal species. Using mitochondrial DNA analyses, we show that sponging shows an almost exclusive vertical social transmission within a single matriline from mother to female offspring. Moreover, significant genetic relatedness among all adult spongers at the nuclear level indicates very recent coancestry, suggesting that all spongers are descendents of one recent "Sponging Eve." Unlike in apes, tool use in this population is almost exclusively limited to a single matriline that is part of a large albeit open social network of frequently interacting individuals, adding a new dimension to charting cultural phenomena among animals.

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Kuczaj, Stan A., Radhika Makecha, Marie Trone, Robin D. Paulos, and Joana A. Ramos (2006). Role of Peers in Cultural Innovation and Cultural Transmission: Evidence from the Play of Dolphin Calves. International Journal of Comparative Psychology, 2006, 19, 223-240.

ABSTRACT
Observations of the spontaneous play behaviors of a group of captive bottlenose dolphins (Tursiops truncatus) revealed that each individual calf's play became more complex with increasing age, suggesting that dolphin play may facilitate the ontogeny and maintenance of flexible problem solving skills. If this is so, play may have evolved to help young dolphins learn to adapt to novel situations. Novel play behaviors were more likely to be produced by dolphin calves than by adults, demonstrating that calves were the main source of innovative play behaviors in the group. Calves were also more likely to imitate novel play behaviors first produced by another dolphin, suggesting that calves contribute significantly to the spread of novel behaviors within a group. All in all, these data suggest that peers may be important catalysts for both cultural innovation and cultural transmission, and that the opportunity to interact with peers may enhance the effect play has on the emergence of flexible problem solving skills.

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Lacy, Robert C., Rob Williams, Erin Ashe, Kenneth C. Balcomb III, Lauren J. N. Brent, Christopher W. Clark, Darren P. Croft, Deborah A. Giles, Misty MacDuffee & Paul C. Paquet (2017). Evaluating anthropogenic threats to endangered killer whales to inform effective recovery plans . Scientific Reports 7, Article number: 14119.

ABSTRACT
Understanding cumulative effects of multiple threats is key to guidingeffective management to conserve endangered species. The critically endangered, Southern Resident killer whale population of the northeastern Pacific Ocean provides a data-rich case to explore anthropogenic threats on population viability. Primary threats include: limitation of preferred prey, Chinook salmon; anthropogenic noise and disturbance, which reduce foraging efficiency; and high levels of stored contaminants, including PCBs. We constructed a population viability analysis to explore possible demographic trajectories and the relative importance of anthropogenic stressors. The population is fragile, with no growth projected under current conditions, and decline expected if new or increased threats are imposed. Improvements in fecundity and calf survival are needed to reach a conservation objective of 2.3% annual population growth. Prey limitation is the most important factor affecting population growth. However, to meet recovery targets through prey management alone, Chinook abundance would have to be sustained near the highest levels since the 1970s. The most optimistic mitigation of noise and contaminants would make the difference between a declining and increasing population, but would be insufficient to reach recovery targets. Reducing acoustic disturbance by 50% combined with increasing Chinook by 15% would allow the population to reach 2.3% growth.

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LeDuc, Richard G., Kelly M. Robertson, and Robert L. Pitman (2008). Mitochondrial sequence divergence among Antarctic killer whale ecotypes is consistent with multiple species. Biol. Lett. (2008) 4, 426-429.

ABSTRACT
Recently, three visually distinct forms of killer whales (Orcinus orca) were described from Antarctic waters and designated as types A, B and C. Based on consistent differences in prey selection and habitat preferences, morphological divergence and apparent lack of interbreeding among these broadly sympatric forms, it was suggested that they may represent separate species. To evaluate this hypothesis, we compared complete sequences of the mitochondrial control region from 81 Antarctic killer whale samples, including 9 type A, 18 type B, 47 type C and 7 typeundetermined individuals. We found three fixed differences that separated type A from B and C, and a single fixed difference that separated type C from A and B. These results are consistent with reproductive isolation among the different forms, although caution is needed in drawing further conclusions. Despite dramatic differences in morphology and ecology, the relatively low levels of sequence divergence in Antarctic killer whales indicate that these evolutionary changes occurred relatively rapidly and recently.

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Mate, B. (1989a). Satellite-Monitored Radio Tracking as a Method for Studying Cetacean Movements and Behaviour. Sci. Rep Int. Whale Commn. Vol. 40, p. 389-391.

Note: In summer 1987, a pilot whale tagged with an Argos satellite-monitored radio tag was tracked for 95 days in the western North Atlantic. The whale was located 479 times by satellite during movements of at least 7,588 km and sighted from an aircraft several times in the company of other pilot whales. Duration of dive data were collected on 187,866 dives. Transmitter temperature information was also sent and indicated that virtually all deep dives occurred at night, when the whale was likely feeding on squid. Surface resting occurred most often immediately after sunrise on a four-to seven-day cycle. Future movement and dive information in conjunction with oceanographic data will be important in identifying the critical habitats of whales and understanding their behavior. Satellites offer an important new cost-effective tool for studying whales.

The technology existed as of 1989 to satellite tag released whales and track them over long distances for significantly long periods of time. Dr. Mate has also satellite tagged bowhead whales and bottlenosed dolphins with good success. Two other pilot whales attached with radio tags in 1991 were sighted in February 1994 with harnesses still attached.

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Matkin, Craig O., (contact author), Janice M. Straley, John W. Durban, Dena R. Matkin, Eva L. Saulitis, Graeme M. Ellis, Russel D. Andrews. 2012. Contrasting abundance and residency patterns of two sympatric populations of transient killer whales (Orcinus orca) in the northern Gulf of Alaska. Fish. Bull. 110:143–155 (2012)

ABSTRACT
Two sympatric populations of “transient” (mammal-eating) killer whales were photo-identified over 27 years (1984–2010) in Prince William Sound and Kenai Fjords, coastal waters of the northern Gulf of Alaska (GOA). A total of 88 individuals were identified during 203 encounters with “AT1” transients (22 individuals) and 91 encounters with “GOA” transients (66 individuals). The median number of individuals identified annually was similar for both populations (AT1=7; GOA=8), but mark-recapture estimates showed the AT1 whales to have much higher fidelity to the study area, whereas the GOA whales had a higher exchange of individuals. Apparent survival estimates were generally high for both populations, but there was a significant reduction in the survival of AT1 transients after the Exxon Valdez oil spill in 1989, with an abrupt decline in estimated abundance from a high of 22 in 1989 to a low of seven whales at the end of 2010. There was no detectable decline in GOA population abundance or survival over the same period, but abundance ranged from just 6 to 18 whales annually. Resighting data from adjacent coastal waters and movement tracks from satellite tags further indicated that the GOA whales are part of a larger population with a more extensive range, whereas AT1 whales are resident to the study area.

Full paper here.

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Matkin, C. O., E. L. Saulitis, G. M. Ellis, P. Olesiuk, S. D. Rice 2008. Ongoing population-level impacts on killer whales Orcinus orca following the "Exxon Valdez" oil spill in Prince William Sound, Alaska. Mar Ecol Prog Ser., Vol. 356: 269-281, 2008

ABSTRACT
Killer whales were photographed in oil after the 1989 "Exxon Valdez" oil spill, but preliminary damage assessments did not definitively link mortalities to the spill and could not evaluate recovery. In this study, photo-identification methods were used to monitor 2 killer whale populations 5 yr prior to and for 16 yr after the spill. One resident pod, the AB Pod, and one transient population, the AT1 Group, suffered losses of 33 and 41%, respectively, in the year following the spill. Sixteen years after 1989, AB Pod had not recovered to pre-spill numbers. Moreover, its rate of increase was significantly less than that of other resident pods that did not decline at the time of the spill. The AT1 Group, which lost 9 members following the spill, continued to decline and is now listed as depleted under the Marine Mammal Protection Act. Although there may be other contributing factors, the loss of AT1 individuals, including reproductive-age females, accelerated the population's trajectory toward extinction. The synchronous losses of unprecedented numbers of killer whales from 2 ecologically and genetically separate groups and the absence of other obvious perturbations strengthens the link between the mortalities and lack of recovery, and the "Exxon Valdez" oil spill.

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Matkin, Craig O., Lance G. Barrett-Lennard, Harald Yurk, David Ellifrit, Andrew W. Trites. Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska.. Fish. Bull. 105:74–87 (2007).

ABSTRACT
From 2001 to 2004 in the eastern Aleutian Islands, Alaska, killer whales (Orcinus orca) were encountered 250 times during 421 days of surveys that covered a total of 22,491 miles. Three killer whale groups (resident, transient, and off-shore) were identified acoustically and genetically. Resident killer whales were found 12 times more frequently than transient killer whales, and offshore killer whales were encountered only once. A minimum of 901 photographically identified resident whales used the region during our study. A total of 165 mammal-eating transient killer whales were identi-fied, and the majority (70%) were encountered during spring (May and June). The diet of transient killer whales in spring was primarily gray whales (Eschrichtius robustus), and in summer primarily northern fur seals (Callorhinus ursinus). Steller sea lions (Eumetopias jubatus) did not appear to be a preferred prey or major prey item during spring and summer. The majority of killer whales in the eastern Aleutian Islands are the resident ecotype, which does not consume marine mammals.

The three known ecotypes of killer whales inhabiting waters off British Columbia and southern Alaska (resident, transient, and offshore) are acoustically distinguishable by 1) vocalization rate; 2) the occurrence of different discrete calls; 3) the syllables used in calls; and 4) the production rate and characteristics of echolocation clicks. Transient killer whales, which appear to rely on passive listening to catch their marine mammal prey, vocalize less frequently than resident killer whales (Deecke et al., 2005). Transients rarely use echolocation clicks, in contrast to resident and offshore killer whales (Deecke et al., 2005). All calls of transient killer whales are distinct from the calls of resident whales by 1) an audible quavering of the fundamental sound frequencies (instead of a crisp appearance of these sound frequencies that is typical of calls from resident killer whales), and 2) a distinctively lower amount of different call syl-lables and a distinct order of these syllables compared to those in calls of resident killer whales (Yurk, 2005). Transient and resident killer whales are distinguishable from offshore killer whales by their use of unique call types (Yurk, 2005). We determined whether the encountered whales fell into discrete acoustic groups and, if so, whether those acoustic groups were similar to any of the acoustic groups observed in British Columbia and southern Alaska. Analysis was completed by Yurk (2005), independent of knowledge of genetic differences and social associations among groups. Call rates were estimated from field estimates of killer whale group sizes for each encounter.

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McAuliffe, Katherine and Hal Whitehead. 2005. Eusociality, menopause and information in matrilineal whales. TRENDS in Ecology and Evolution Vol.20 No.12 December 2005

ARTICLE
In their recent article in TREE, Foster and Ratnieks make the interesting proposal that humans should be considered 'eusocial' on the grounds that females spend a substantial part of their adult life reproductively sterile and help their close relatives. The authors consider that menopause, in this sense of the term, is unique among vertebrates to humans. However, female shortfinned pilot whales Globicephala macrorhynchus, killer whales Orcinus orca, and probably a few other species of cetacean, such as sperm whales Physeter macrocephalus, have menopause with similar attributes to human females. In all these species, reproduction ceases at approximately 40 years of age, although females routinely live on for several more decades. Thus, cetaceans can also be considered eusocial if the term can be used in the context of within-individual classes of reproductives and sterile helpers.
The cetacean species in which menopause is known or probable all have matrilineal social systems in the sense that most of the females spend their lives grouped with their mothers when both are alive. This correlation, and the presence of menopause in these cetaceans which (unlike modern humans) have not faced a dramatic recent change in their living conditions, strongly indicate that menopause is adaptive, and results from the tradeoff between continued reproduction and assisting kin. Given that menopause invariably occurs in these species, the benefits of assisting kin must outweigh the costs of reproductive cessation. What is not clear, however, is how these menopausal grandmothers help. Among menopausal cetaceans, assistance in foraging is not seen, and at least in killer whales, defence against predators is rare. Similar to human grandmothers, menopausal cetacean females have experience that might benefit other members of their matrilines. The value of this information could explain why females in these species live about a third of their lives as post-reproductive members of their social groups.
The informative role of cetacean grandmothers is consistent with an emerging body of information indicating cultures in matrilineal cetacean species. Thus, in both cetaceans and humans, the storage and provision of information might be the primary function of menopausal females and, thus, the driver of eusociality.

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McGowen, Michael R., Michelle Spaulding, John Gatesy. 2009. Divergence date estimation and a comprehensive molecular tree of extant cetaceans. Molecular Phylogenetics and Evolution 53 (2009) 891-906

ABSTRACT
Cetaceans are remarkable among mammals for their numerous adaptations to an entirely aquatic existence, yet many aspects of their phylogeny remain unresolved. Here we merged 37 new sequences from the nuclear genes RAG1 and PRM1 with most published molecular data for the group (45 nuclear loci, transposons, mitochondrial genomes), and generated a supermatrix consisting of 42,335 characters. The great majority of these data have never been combined. Model-based analyses of the supermatrix produced a solid, consistent phylogenetic hypothesis for 87 cetacean species. Bayesian analyses corroborated odontocete (toothed whale) monophyly, stabilized basal odontocete relationships, and completely resolved branching events within Mysticeti (baleen whales) as well as the problematic speciose clade Delphinidae (oceanic dolphins). Only limited conflicts relative to maximum likelihood results were recorded, and discrepancies found in parsimony trees were very weakly supported. We utilized the Bayesian supermatrix tree to estimate divergence dates among lineages using relaxed-clock methods. Divergence estimates revealed rapid branching of basal odontocete lineages near the Eocene–Oligocene boundary, the antiquity of river dolphin lineages, a Late Miocene radiation of balaenopteroid mysticetes, and a recent rapid radiation of Delphinidae beginning 10 million years ago. Our comprehensive, timecalibrated tree provides a powerful evolutionary tool for broad-scale comparative studies of Cetacea.
"Here Orcinus orca (killer whale), the largest delphinid, and Leucopleurus acutus (Atlantic white-sided dolphin) were basal delphinids in all model-based analyses"

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Morin, Phillip A., Kim M. Parsons, Frederick I Archer, Maria C. Avila-Arcos, Lance G Barrett-Lennard, Luciano Dalla Rosa, Sebastian Duchene, John Durban, Graeme M. Ellis, Steven H. Ferguson, John K Ford, Michael J. Ford, Cristina Garilao, M. Thomas Pl. Gilbert, Kristin Kaschner, Craig O. Matkin, Stephen D. Petersen, Kelly M. Robertson, Ingrid N. Visser, Paul R. Wade, Simon Y. W. Ho and Andrew D. Foote. Geographic and temporal dynamics of a global radiation and diversification in the killer whale. Molecular Ecology (2015) 24, 3964–3979 doi: 10.1111/mec.13284

ABSTRACT
Global climate change during the Late Pleistocene periodically encroached and then released habitat during the glacial cycles, causing range expansions and contractions in some species. These dynamics have played a major role in geographic radiations, diversification and speciation. We investigate these dynamics in the most widely distributed of marine mammals, the killer whale (Orcinus orca), using a global data set of over 450 samples. This marine top predator inhabits coastal and pelagic ecosystems ranging from the ice edge to the tropics, often exhibiting ecological, behavioural and morphological variation suggestive of local adaptation accompanied by reproductive isolation. Results suggest a rapid global radiation occurred over the last 350 000 years. Based on habitat models, we estimated there was only a 15% global contraction of core suitable habitat during the last glacial maximum, and the resources appeared to sustain a constant global effective female population size throughout the Late Pleistocene. Reconstruction of the ancestral phylogeography highlighted the high mobility of this species, identifying 22 strongly supported long-range dispersal events including interoceanic and interhemispheric movement. Despite this propensity for geographic dispersal, the increased sampling of this study uncovered very few potential examples of ancestral dispersal among ecotypes. Concordance of nuclear and mitochondrial data further confirms genetic cohesiveness, with little or no current gene flow among sympatric ecotypes. Taken as a whole, our data suggest that the glacial cycles influenced local populations in different ways, with no clear global pattern, but with secondary contact among lineages following long-range dispersal as a potential mechanism driving ecological diversification. Full paper HERE.

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Morin, Phillip A., Frederick I Archer, Andrew D Foote, Julie Vilstrup, Eric E Allen, Paul Wade, John Durban, Kim Parsons, Robert Pitman, Lewyn Li, Pascal Bouffard, Sandra C Abel Nielsen, Morten Rasmussen, Eske Willerslev, M. Thomas P Gilbert and Timothy Harkins Complete mitochondrial genome phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species. Genome Research April 2010, 20 (4)

ABSTRACT
Killer whales (Orcinus orca) currently comprise a single, cosmopolitan species with a diverse diet. However, studies over the last 30 years have revealed populations of sympatric "ecotypes" with discrete prey preferences, morphology and behaviors. Although these ecotypes avoid social interactions and are not known to interbreed, genetic studies to date have found extremely low levels of diversity in the mitochondrial control region, and few clear phylogeographic patterns worldwide. This low level of diversity is likely due to low mitochondrial mutation rates that are common to cetaceans. Using killer whales as a case study, we have developed a method to readily sequence, assemble, and analyze complete mitochondrial genomes from large numbers of samples to more accurately assess phylogeography and estimate divergence times. This represents an important tool for wildlife management, not only for killer whales but for many marine taxa. We used high-throughput sequencing to survey whole mitochondrial genome variation of 139 samples from the North Pacific, North Atlantic and southern oceans. Phylogenetic analysis indicated that each of the known ecotypes represents a strongly supported clade with divergence times ranging from approximately 150,000 to 700,000 years ago. We recommend that three named ecotypes be elevated to full species, and that the remaining types be recognized as subspecies pending additional data. Establishing appropriate taxonomic designations will greatly aid in understanding the ecological impacts and conservation needs of these important marine predators. We predict that phylogeographic mitogenomics will become an important tool for improved statistical phylogeography and more precise estimates of divergence times. Full paper.

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Morin, Phillip A., Richard G. LeDuc, Kelly M. Robertson, Nicole M. Hedrick, William F. Perrin, Michael Etnier, Paul Wade, Barbara L. Taylor 2006. Genetic analysis of killer whale (Orcinus Orca) historical bone and tooth samples to identify western U.S. ecotypes. Marine Mammal Science, Volume 22 Issue 4 Page 897 - October

ABSTRACT
Little is known about the historical range of killer whale ecotypes in the eastern North Pacific (ENP). It is possible that ranges have shifted in the last few decades because of changes in availability of food. In particular, the southern resident ecotype, currently found primarily in the inland waters of Washington State, is known to prey extensively on salmon, which have declined in recent decades along the outer coasts of Washington, Oregon, and California. To investigate historical distributions of this and the other ENP ecotypes, samples of teeth and bones were obtained from NMFS and museum collections. We amplified a short section of the mitochondrial DNA control region that contains four diagnostic sites that differentiate between haplotypes found in ecotypes of ENP killer whales. Results did not show any southern resident haplotypes in samples from south of the Washington State inland waterways. One whale genetically identified as a northern resident extends the known southernmost distribution of the population from Oregon to California. Items of diet identified from stomach contents of six of the whales genetically identified to ecotype conformed with what is known of the feeding habits of the various ecotypes.

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Moura, A E , J G Kenny, R R Chaudhuri, M A Hughes, R R Reisinger, P J N de Bruyn, M E Dahlheim, N Hall and A R Hoelzel. Phylogenomics of the killer whale indicates ecotype divergence in sympatry. Heredity (2015) 114, 48–55.

ABSTRACT
For many highly mobile species, the marine environment presents few obvious barriers to gene flow. Even so, there is considerable diversity within and among species, referred to by some as the ‘marine speciation paradox’. The recent and diverse radiation of delphinid cetaceans (dolphins) represents a good example of this. Delphinids are capable of extensive dispersion and yet many show fine-scale genetic differentiation among populations. Proposed mechanisms include the division and isolation of populations based on habitat dependence and resource specializations, and habitat release or changing dispersal corridors during glacial cycles. Here we use a phylogenomic approach to investigate the origin of differentiated sympatric populations of killer whales (Orcinus orca). Killer whales show strong specialization on prey choice in populations of stable matrifocal social groups (ecotypes), associated with genetic and phenotypic differentiation. Our data suggest evolution in sympatry among populations of resource specialists.

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Nattrass, Stuart, Darren P. Croft, Samuel Ellis, Michael A. Cant, Michael N. Weiss, Brianna M. Wright, Eva Stredulinsky, Thomas Doniol-Valcroze, John K. B. Ford, Kenneth C. Balcomb, and Daniel W. Franks. (2019) Postreproductive killer whale grandmothers improve the survival of their grandoffspring. Proceedings of the National Academy of Sciences Dec 2019, 201903844; DOI: 10.1073/pnas.1903844116

ABSTRACT
Understanding why females of some mammalian species cease ovulation prior to the end of life is a long-standing interdisciplinary and evolutionary challenge. In humans and some species of toothed whales, females can live for decades after stopping reproduction. This unusual life history trait is thought to have evolved, in part, due to the inclusive fitness benefits that postreproductive females gain by helping kin. In humans, grandmothers gain inclusive fitness benefits by increasing their number of surviving grandoffspring, referred to as the grandmother effect. Among toothed whales, the grandmother effect has not been rigorously tested. Here, we test for the grandmother effect in killer whales, by quantifying grandoffspring survival with living or recently deceased reproductive and postreproductive grandmothers, and show that postreproductive grandmothers provide significant survival benefits to their grandoffspring above that provided by reproductive grandmothers. This provides evidence of the grandmother effect in a nonhuman menopausal species. By stopping reproduction, grandmothers avoid reproductive conflict with their daughters, and offer increased benefits to their grandoffspring. The benefits postreproductive grandmothers provide to their grandoffspring are shown to be most important in difficult times where the salmon abundance is low to moderate. The postreproductive grandmother effect we report, together with the known costs of late-life reproduction in killer whales, can help explain the long postreproductive life spans of resident killer whales.

Full paper here.

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Nielsen, Mia Lybkær Kronborg, Samuel Ellis, Michael N. Weiss, Jared R. Towers, Thomas Doniol-Valcroze, Daniel W. Franks, Michael A. Cant, Graeme M. Ellis, John K. B. Ford, Mark Malleson, Gary J. Sutton, Tasli J. H. Shaw, Kenneth C. Balcomb, David K. Ellifrit and Darren P. Croft. Temporal dynamics of mother–offspring relationships in Bigg's killer whales: opportunities for kin-directed help by post-reproductive females. Proc. R. Soc. B. 2902023013920230139 http://doi.org/10.1098/rspb.2023.0139

ABSTRACT
Age-related changes in the patterns of local relatedness (kinship dynamics) can be a significant selective force shaping the evolution of life history and social behaviour. In humans and some species of toothed whales, average female relatedness increases with age, which can select for a prolonged post-reproductive lifespan in older females due to both costs of reproductive conflict and benefits of late-life helping of kin. Killer whales (Orcinus orca) provide a valuable system for exploring social dynamics related to such costs and benefits in a mammal with an extended post-reproductive female lifespan. We use more than 40 years of demographic and association data on the mammal-eating Bigg's killer whale to quantify how mother–offspring social relationships change with offspring age and identify opportunities for late-life helping and the potential for an intergenerational reproductive conflict. Our results suggest a high degree of male philopatry and female-biased budding dispersal in Bigg's killer whales, with some variability in the dispersal rate for both sexes. These patterns of dispersal provide opportunities for late-life helping particularly between mothers and their adult sons, while partly mitigating the costs of mother–daughter reproductive conflict. Our results provide an important step towards understanding why and how menopause has evolved in Bigg's killer whales. Full paper HERE.

PDF of Killer Whales - The Top, Top Predator

Nielsen, Mia Lybkær Kronborg, Samuel Ellis, Jared R. Towers, Thomas Doniol-Valcroze, Daniel W. Franks, Michael A. Cant, Michael N. Weiss, Rufus A. Johnstone, Kenneth C. Balcomb III, David K. Ellifrit, Darren P. Croft. A long postreproductive life span is a shared trait among genetically distinct killer whale populations. Ecology and Evolution, Volume 11, Issue 13, July 2021.

ABSTRACT
The extended female postreproductive life span found in humans and some toothed whales remains an evolutionary puzzle. Theory predicts demographic patterns resulting in increased female relatedness with age (kinship dynamics) can select for a prolonged postreproductive life span due to the combined costs of intergenerational reproductive conflict and benefits of late-life helping. Here, we test this prediction using >40 years of longitudinal demographic data from the sympatric yet genetically distinct killer whale ecotypes: resident and Bigg's killer whales. The female relatedness with age is predicted to increase in both ecotypes, but with a less steep increase in Bigg's due to their different social structure. Here, we show that there is a significant postreproductive life span in both ecotypes with >30% of adult female years being lived as postreproductive, supporting the general prediction that an increase in local relatedness with age predisposes the evolution of a postreproductive life span. Differences in the magnitude of kinship dynamics however did not influence the timing or duration of the postreproductive life span with females in both ecotypes terminating reproduction before their mid-40s followed by an expected postreproductive period of about 20 years. Our results highlight the important role of kinship dynamics in the evolution of a long postreproductive life span in long-lived mammals, while further implying that the timing of menopause may be a robust trait that is persistent despite substantial variation in demographic patterns among populations. Full paper here.

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Noad, Michael J; Douglas H. Cato and M.M. Bryden. Cultural displacement and replacement in the songs of Australian humpback whales. Nature 408, 537 2000.

ABSTRACT
Song was recorded from Australian east coast humpback whales, Megaptera novaeangliae, during migration in 1995 - 1998. Over 1000 hours of song were used to determine the song pattern in 252 song sessions. While the pattern of the song was initially highly stereotyped, in 1996 two singers were recorded with a completely different song type. During the 1997 migrations the use of the 'new' song type increased dramatically and completely replaced the 'old' song by 1998. The 'new' song type was identical to song from Australian west coast humpback whales recorded in 1996 but identical to song from Australian west coast humpback whales recorded in 1996 but different to that from 1995 or 1997. These results demonstrate that the introduction of west coast song at a very low initial prevalence was able to completely displace the vocal cultural tradition of the east coast population. The process of change in humpback whale song and bird song has been described as 'cultural evolution' whereby changes in songs are passed among individuals by learning and accumulate over time. The song changes described here were cultural, but were revolutionary rather than evolutionary, the cultural vocal pattern of one population displacing and replacing completely that of another population.

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Nousek, Anna E., Peter J.B. Slater, Chao Wang, Patrick J.O. Miller. 2006. The influence of social affiliation on individual vocal signatures of northern resident killer whales (Orcinus orca). Royal Society Journal

ABSTRACT
Northern resident killer whales (Orcinus orca) live in highly stable groups and use group-specific vocal signals, but individual variation in calls has not been described previously. A towed beam-forming array was used to ascribe stereotyped pulsed calls with two independently modulated frequency contours to visually identified individual killer whales in Johnstone Strait, British Columbia. Overall, call similarity determined using neural networks differed significantly between different affiliation levels for both frequency components of all the call types analysed. This method distinguished calls from individuals within the same matriline better than different calls produced by a single individual and than chance. The calls of individuals from different matrilines were more distinctive than those within the same matriline, confirming previous studies based on group recordings. These results show that frequency contours of stereotyped calls differ among the individuals that are constantly associated with each other and use group-specific vocalizations, though across-group differences were substantially more pronounced.

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Olesiuk, P.F., G.M. Ellis and J.K.B Ford (2005). Life History and Population Dynamics of Northern Resident Killer Whales (Orcinus orca) in British Columbia.

ABSTRACT
Annual photo-identification surveys conducted between 1973-75 and 2004 were used to estimate life history parameters and develop a population model for the northern resident population of killer whales that inhabits coastal waters of British Columbia. During the 1970's, 80's and early 90's, the population grew exponentially (r2=0.986; F1,22=1,568.5; P 0.001) at an annual rate of 2.6% (95% CI 2.48-2.76%). Although the population almost doubled in size from about 125 to 217 animals, there was no evidence of a slowing of the growth rate (F1,21=0.25; P=0.622), suggesting the population was unrestrained and increasing at its maximum intrinsic rate. The population peaked abruptly in the mid-1990s, declined by 7-9%, and then exhibited a small increase, resulting in no discernible trend over the last decade (F1,10=1.36; P=0.271), indicating that something was restraining its growth. Life history and population parameters were thus estimated separately for 1973-96, a period of unrestrained growth; and 1996-2004, a period of no net change. During the period of unrestrained growth, females had a mean life expectancy of 46 years and maximum longevity was on the order of 80 years. Females typically gave birth to their first viable calf at 14.1 years of age (SE=0.050; range 10-21 years) and those that survived produced a total of 4.7 calves at mean intervals of 4.9 years (SE=0.18; range 2-11 years) over a reproductive lifespan typically lasting about 24 years. Older females exhibited reproductive senescence, with about 50% being post-reproductive by 38 years of age, and none reproducing after 46 years of age. Based on development of the dorsal fin - a secondary sexual characteristic - males typically attained sexual maturity at 13.0 years of age (SE=0.046; range 9-18 years) and the fin continued to develop for an average of 5.5 years (SE=0.113; range 3-7 years), such that males had typically attained physical maturity by 18.5 years of age. Males had a mean life expectancy of 31 years and maximum longevity was probably on the order of 60-70 years. Mortality curves were U-shaped for both sexes, indicating most mortality occurred early and late in life, but the right limb was steeper for males, resulting in a sex ratio that was progressively skewed toward females with increasing age (1:1 at age 15, 2:1 by age 34, and 3:1 by age 41 years). A sex- and age-structured model incorporating these parameters predicted that a population would increase at a rate of 2.4% per annum and be comprised of 46% juveniles, 22% reproductive females, 10% post-reproductive females, and 22% adult males. During 1973-96, the study population actually increased at 2.6% and was comprised, on average, of 46% juveniles, 21% reproductive females, 11% post-reproductive females and 22% adult males, indicating a good fit with the model predictions. Surprisingly, there were no major changes in reproductive parameters as the population stabilized during 1996-2004. Mean age at first birth increased slightly but significantly from 14.1 to 15.4 years (t49=3.23; P=0.002), mean age of onset of post-reproductive senescence increased from 38.4 to 40.6 years (t61=2.84; P=0.006), and calving intervals were marginally longer (5.5 versus 4.9 years; t97=2.92; P=0.091). The overall effect was a slight drop in the estimated reproductive potential of females from 4.7 to 4.5 calves. The recent decline in productivity was due almost entirely to increases in mortality, which were evident and statistically significant (7.63 X2 8.14; P 0.01) across all sex- and age-categories. Survival of viable calves to age 15 (about the age they are recruited to the adult population) dropped from 80% to 61%, and mean life expectancy declined from 46 to 30 years for females and from 31 to 19 years for males. Because the increase in mortality was broadly distributed across all sex- and age-classes, the predicted sex and age structure of the stable population remained almost unchanged at 47% juveniles, 24% reproductive females, 11% post-reproductive females, and 18% adult males. The life history parameters for neighbouring resident killer whale populations in Alaska and Washington appear to fall within the range of our unrestrained and stable models for northern BC residents, suggesting the models represent the general population biology of the resident ecotype of killer whale. We believe such models provide a useful construct for exploring and developing a better understanding of the factors that may regulate or impact killer whale populations.
Note: "Since most births occurred outside our field season, calves were generally first encountered when they were about 6 months of age. Although this makes it impossible to estimate neonate mortality from the summer survey data, we suspect mortality at birth and in the first few months of life is high. Olesiuk et al. (1990) inferred it could be as high as 37-50%, although in retrospect that is probably on the high side."
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Olesiuk, P.F., M.A. Bigg and G.M. Ellis (Dept. of Fisheries and Oceans, Pacific Biological Station, Nanaimo, B.C., Canada V9R 5K6) (1990). Life history and population dynamics of resident killer whales (Orcinus orca) in the coastal waters of British Columbia and Washington State. In: P.S. Hammond, S.A. Mizroch and G.P. Donovan (eds.): Individual recognition of cetaceans: Use of photo-identification and other techniques to estimate population parameters. Special Report #12, International Whaling Commission, Cambridge, p. 209-243

ABSTRACT
Life history parameters are derived for the resident form of killer whale in the coastal waters of British Columbia and Washington State based on the demographic changes observed in two communities (closed to immigration and emigration) that were monitored between 1973-4 and 1987. Females have a mean life expectancy of 50.2 years, typically give birth to their first viable calf at 14.9 years of age, produce an average of 5.35 viable calves over a 25.2 year reproductive lifespan and have a maximum longevity ofabout 80-90 years. Calving is diffusely seasonal with most births occurring in October-March. Neonate mortality is approximately 43%. The estimated proportion of mature females pregnant varies from 0.274 in April to 0.411 in September. Males have a mean life expectancy of 29.2 years, typically attain sexual maturity at 15.0 years and physical maturity at 21.0 years of age, and have a maximum longevity of about 50-60 years. Mortality curves are U-shaped for both females and males, but the curve is narrower for males. There is no evidence of density dependence in the life history parameters as a result of cropping prior to the start of the study or as the populations increased during the study.

The derived life history parameters are used to develop a sex-and age-specific matrix population model and to calculate life tables. The model accurately emulates the demographic changes observed during the study. Population projections indicate that both communities represent stable populations below their carrying capacity. These populations had a finite annual rate of increase of 2.92% and were composed of 50% juveniles, 19% mature males, 21% reproductive females and 10% post-reproductive females. Discrepancies between the sex- and age-structure of the study populations and those of a stable population can be largely attributed to the selective cropping of pods prior to the start of the study. (...)

Note: 261 Pacific Northwest killer whales were alive in 1987 in two resident communities. A community comprises individuals that share a common range and associate with one another; a pod is a group of individuals within a community that travels together the majority of the time; a subpod is a group of individuals that temporarily fragments from its pod to travel separately; an intra-pod group consists of a cohesive group of individuals within a subpod that always travels in close proximity. The genealogical trees indicate that intra-pod groups are matrilines. A matrilineal group typically comprises 2-4 generations. Pod-specific dialects suggest that related pods associate randomly. The lack of dispersal of the resident form of killer whale from their natal groups appears to be unique among mammalian social systems. This species has the potential to have developed many local races over its cosmopolitan range, with each race having unique social and behavioral characteristics.

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Olson, Paula A., Paul Ensor and Sanna Kuninga Observations of killer whales off East Antarctica, 82°-95°E, in 2009. (2012) J. CETACEAN RES. MANAGE. 12(1): 61–64, 2012

ABSTRACT
Observations of killer whales (Orcinus orca) during a survey off East Antarctica, 82°–95°E revealed previously undescribed variations in pigmentation and group associations. During the survey 24 killer whale groups were sighted south of 60°S and classified, when possible, to Types A, B, or C based on their external morphology. Sufficient observation was available for nine groups to be classified: 2 groups of Type A; 1 mixed group of Type A and Type B; 3 groups of Type C; and 3 groups with eyepatch pigmentation intermediate in size between Types B and C. These whales may represent an intergrade between Types B and C or a previously unrecognised form. One of the ‘intermediate’ groups was observed feeding in a multi-species aggregation with other cetaceans in deep water. Clearly distinguishable Type A and Type B whales were observed feeding together in a mixed aggregation, the first time that this has been documented.

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Pain, Stephanie Culture Shock .New Scientist magazine (24 March, 2001)

ABSTRACT
They don't have orchestras or art galleries, tools or technology, but whales still have a rich and varied cultural life. The notion that cetaceans have any sort of culture, popular or otherwise, is hotly disputed by some. Most social scientists stubbornly resist the idea that animals, even the great apes, have culture. After all, isn't it our languages and folklore, religion, music and all those other sophisticated strands of human culture that set us apart from the beasts? Clearly, whales and dolphins don't have art or literature; they have no architecture, agriculture or fancy cuisine. But patient observation over many years has begun to reveal behaviours that can only have been learned from other whales. And that, say whale biologists, constitutes culture.

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Parsons, K.M., Kim M. Parsons, John W. Durban, Alexander M. Burdin, Vladimir N. Burkanov, Robert L. Pitman, Jay Barlow, Lance G. Barrett-Lennard, Richard G. LeDuc, Kelly M. Robertson, Craig O. Matkin, and Paul R. Wade Geographic Patterns of Genetic Differentiation among Killer Whales in the Northern North Pacific. J Hered (2013) doi: 10.1093/jhered/est037.

ABSTRACT
The difficulties associated with detecting population boundaries have long constrained the conservation and management of highly mobile, wide-ranging marine species, such as killer whales (Orcinus orca). In this study, we use data from 26 nuclear microsatellite loci and mitochondrial DNA sequences (988bp) to test a priori hypotheses about population subdivisions generated from a decade of killer whale surveys across the northern North Pacific. A total of 462 remote skin biopsies were collected from wild killer whales primarily between 2001 and 2010 from the northern Gulf of Alaska to the Sea of Okhotsk, representing both the piscivorous "resident" and the mammal-eating "transient" (or Bigg's) killer whales. Divergence of the 2 ecotypes was supported by both mtDNA and microsatellites. Geographic patterns of genetic differentiation were supported by significant regions of genetic discontinuity, providing evidence of population structuring within both ecotypes and corroborating direct observations of restricted movements of individual whales. In the Aleutian Islands (Alaska), subpopulations, or groups with significantly different mtDNA and microsatellite allele frequencies, were largely delimited by major oceanographic boundaries for resident killer whales. Although Amchitka Pass represented a major subdivision for transient killer whales between the central and western Aleutian Islands, several smaller subpopulations were evident throughout the eastern Aleutians and Bering Sea. Support for seasonally sympatric transient subpopulations around Unimak Island suggests isolating mechanisms other than geographic distance within this highly mobile top predator.

Full paper HERE.

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Parsons, K.M., K.C. Balcomb III, J.K.B. Ford, and J.W. Durban The social dynamics of southern resident killer whales and conservation implications for this endangered population, Animal Behaviour, Volume 77, Issue 4, April 2009, Pages 963-971.

EXCERPT
Quantitatively characterizing the social structure of a population provides important insight into the forces shaping key population processes. Moreover, long-term social dynamics provide an avenue for understanding population-level responses to changes in socioecological conditions. This is particularly true for species that show natal philopatry and highly stable hierarchically structured social units, such as the piscivorous resident killer whales of the northeast Pacific. The southern resident killer whale population is a small, demographically closed population, comprising three commonly recognized pods (J, K and L pods), that has recently been listed as endangered throughout its range in both Canadian and U.S.A. waters. In this study, we quantitatively assessed social structure in this population from 29 years of photo-identification data to characterize significant temporal changes in sociality. Preferential affiliation among killer whales within both genealogical matrilines and pods was supported by two different analytical methods and, despite interannual variability, these social clusters persisted throughout the study. All three pods experienced fluctuations in social cohesion over time, but the overall rate of intrapod affiliation was consistently lowest within L pod, the largest of the southern resident pods. The most recent increase in fluidity within social units, occurring in the mid to late 1990s, was coincident with a significant decline in population size, suggesting a possible common response to external stressors. Quantifying these trends in social structure is the first step towards understanding the causes and consequences of long-term changes in killer whale social structure.

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Photopoulou, Theoni, Ines M. Ferreira, Peter B. Best (Deceased), Toshio Kasuya and Helene Marsh Evidence for a postreproductive phase in female false killer whales Pseudorca crassidens. Frontiers in Zoology2017.

ABSTRACT
Background
A substantial period of life after reproduction ends, known as postreproductive lifespan (PRLS), is at odds with classical life history theory and its causes and mechanisms have puzzled evolutionary biologists for decades. Prolonged PRLS has been confirmed in only two non-human mammals, both odontocete cetaceans in the family Delphinidae. We investigate the evidence for PRLS in a third species, the false killer whale, Pseudorca crassidens, using a quantitative measure of PRLS and morphological evidence from reproductive tissues.
Results
We examined specimens from false killer whales from combined strandings (South Africa, 1981) and harvest (Japan 1979-80) and found morphological evidence of changes in the activity of the ovaries in relation to age. Ovulation had ceased in 50% of whales over 45 years, and all whales over 55 years old had ovaries classified as postreproductive. We also calculated a measure of PRLS, known as postreproductive representation (PrR) as an indication of the effect of inter-population demographic variability. PrR for the combined sample was 0.14, whereas the mean of the simulated distribution for PrR under the null hypothesis of no PRLS was 0.02. The 99th percentile of the simulated distribution was 0.08 and no simulated value exceeded 0.13. These results suggest that PrR was convincingly different from the measures simulated under the null hypothesis.
Conclusions
We found morphological and statistical evidence for PRLS in South African and Japanese pods of false killer whales, suggesting that this species is the third non-human mammal in which this phenomenon has been demonstrated in wild populations. Nonetheless, our estimate for PrR in false killer whales (0.14) is lower than the single values available for the short-finned pilot whale (0.28) and the killer whale (0.22) and is more similar to working Asian elephants (0.13).

Full paper HERE.

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M. Pilot, M. E. Dahlheim & A. R. Hoelzel. Social cohesion among kin, gene flow without dispersal and the evolution of population genetic structure in the killer whale (Orcinus orca). J . EVOL. BIOL. 23 (2010) 20-31.

ABSTRACT
In social species, breeding system and gregarious behavior are key factors influencing the evolution of large-scale population genetic structure. The killer whale is a highly social apex predator showing genetic differentiation in sympatry between populations of foraging specialists (ecotypes), and low levels of genetic diversity overall. Our comparative assessments of kinship, parentage and dispersal reveal high levels of kinship within local populations and ongoing male-mediated gene flow among them, including among ecotypes that are maximally divergent within the mtDNA phylogeny. Dispersal from natal populations was rare, implying that gene flow occurs without dispersal, as a result of reproduction during temporary interactions. Discordance between nuclear and mitochondrial phylogenies was consistent with earlier studies suggesting a stochastic basis for the magnitude of mtDNA differentiation between matrilines. Taken together our results show how the killer whale breeding system, coupled with social, dispersal and foraging behaviour, contributes to the evolution of population genetic structure.

Full paper HERE.

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Pitman, Robert L., editor, (2011) Killer Whales - The Top, Top Predator. JOURNAL OF THE AMERICAN CETACEAN SOCIETY Spring 2011 Volume 40, Number 1

INTRODUCTION
Thirty-five years ago, when I first started going to sea, a quite different killer whale roamed the world’s oceans. It was a single, worldwide species and the ultimate omnivore, capable of preying upon any large vertebrate that swam into its purview, including fish, birds, mammals or reptiles. Social behavior revolved around dominant adult males, which used their much larger size and aggressive behavior to take command of harems of females and young - rather like a lion with his pride. Since that time, armadas of dedicated researchers working from small boats have spent countless thousands of hours following killer whales, studying their behavior and learning their ways. Their diligence, aided by burgeoning technologies – satellite tagging, digital photography, and genetic analyses, to name a few – has radically altered our understanding of this animal, and what has emerged is a completely different killer whale – in fact, several.

Contents
An Introduction to the World’s Premier Predator – by Robert Pitman...2
How Do We Study Killer Whales? – by John Durban and Volker Deecke...6
Killer Whales Around the World
Killer Whales of the Pacific Northwest Coast: From Pest to Paragon – by John K.B. Ford...15
Killer Whales in Alaskan Waters – by Craig Matkin and John Durban...24
North Atlantic Killer Whales – by Andy Foote...30
Crozet: Killer Whales in a Remote But Changing Environment – by Christophe Guinet and Paul Tixier...33
Centerfold: Ecotypes and Forms Drawn to Scale – by Uko Gorter...34
Antarctic Killer Whales: Top of the Food Chain at the Bottom of the World – by Robert Pitman...39
Killer Whales of California – by Alisa Schulman-Janiger, Nancy Black, and Richard Ternullo...46
Killer Whale Evolution: Populations, Ecotypes, Species, Oh My! – by Lance Barrett-Lennard...48
Predators, Prey, and Play: Killer Whales and Other Marine Mammals – by Robin W. Baird...54
Killer Whale Conservation: The Perils of Life at the Top of the Food Chain – by Lance Barrett-Lennard and Kathy Heise..58
About Our authors...63
Selected References...65

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Pitman, Robert L., J. W. Durban, (2011) Cooperative hunting behavior, prey selectivity and prey handling by pack ice killer whales (Orcinus orca), type B, in Antarctic Peninsula waters. MARINE MAMMAL SCIENCE, VOL. **, NO. **, 2011. Article first published online: 1 MAR 2011

ABSTRACT
Currently, there are three recognized ecotypes (or species) of killer whales (Orcinus orca) in Antarctic waters, including type B, a putative prey specialist on seals, which we refer to as “pack ice killer whale” (PI killer whale). During January 2009, we spent a total of 75.4 h observing three different groups of PI killer whales hunting off the western Antarctic Peninsula. Observed prey taken included 16 seals and 1 Antarctic minke whale (Balaenoptera bonaerensis). Weddell seals (Leptonychotes weddellii) were taken almost exclusively (14/15 identified seal kills), despite the fact that they represented only 15% of 365 seals identified on ice floes; thewhales entirely avoided taking crabeater seals (Lobodon carcinophaga; 82% relative abundance) and leopard seals (Hydrurga leptonyx; 3%). Of the seals killed, the whales took 12/14 (86%) off ice floes using a cooperative wave-washing behavior; they produced 120 waves during 22 separate attacks and successfully took 12/16 (75%) of the Weddell seals attacked. The mean number of waves produced per successful attack was 4.1 (range 1–10) and the mean attack duration was 30.4 min (range 15–62). Seal remains that we examined from one of the kills provided evidence of meticulous postmortem prey processing perhaps best termed "butchering."

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Pitman, Robert L., J. W. Durban, M. Greenfelder, C. Guinet, M. Jorgensen, P. A. Olson, J. Plana, P. Tixier, J. R. Towers (2010) Observations of a distinctive morphotype of killer whale (Orcinus orca), type D, from subantarctic waters. Polar Biology: DOI 10.1007/s00300-010-0871-3

ABSTRACT
Studies have shown that killer whale (Orcinus orca) communities in high latitudes regularly comprise assemblages of sympatric 'ecotypes'-forms that differ in morphology, behavior, and prey preferences. Although they can appear superficially similar, recent genetic evidence suggests that breeding is assortative among ecotypes within individual communities, and species-level divergences are inferred in some cases. Here, we provide information on a recently recognized 'type D' killer whale based on photographs of a 1955 mass stranding in New Zealand and our own six at-sea sightings since 2004. It is the most distinctive-looking form of killer whale that we know of, immediately recognizable by its extremely small white eye patch. Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. School sizes are relatively large (mean 17.6; range 9-35; n = 7), and although nothing is known about the type D diet, it is suspected to include fish because groups have been photographed around longline vessels where they reportedly depredate Patagonian toothfish (Dissostichus eleginoides).

PDF available from robert.pitman@noaa.gov.

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Pitman, Robert L., Wayne L. Perryman, Don Leroi, and Erik Eilers (2007) A dwarf form of killer whale in Antarctica. Journal of Mammalogy, 88(1):43-48

ABSTRACT
In the early 1980s, 2 groups of Soviet scientists independently described 1, possibly 2 new dwarf species of killer whales (Orcinus) from Antarctica. We used aerial photogrammetry to determine total length (TL) of 221 individual Type C killer whales-a fish-eating ecotype that inhabits dense pack ice-in the southern Ross Sea in January 2005. We confirmed it as one of the smallest killer whales known: TL of adult females (with calves) averaged 5.2 m ± 0.23 SD (n = 33); adult males averaged 5.6 ± 0.32 m (n = 65), with the largest measuring 6.1 m. Female Type A killer whales-offshore mammal-eaters-from Soviet whaling data in the Southern Ocean were approximately 1-2 m longer, and males were 2-3 m (up to 50%) longer (maximum length 9.2 m). Killer whale communities from the North Atlantic and in waters around Japan also appear to support both a smaller, inshore, fish-eating form and a larger, offshore, mammal-eating form. We suggest that, at least in Antarctica, this degree of size dimorphism could result in reproductive isolation between sympatric ecotypes, which is consistent with hypotheses of multiple species of killer whales in the Southern Ocean.

Full paper here:

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Pitman, Robert L. Good whale hunting: two tantalizing Russian reports take the author on a quest to the Antarctic, in search of two previously unrecognized kinds of killer whale. Natural History, December 2003.

EXCERPT
After three seasons in Antarctica, I am convinced that in addition to the familiar killer whale from around the world, at least one and probably two additional species of killer whale lurk in the icy waters around the cold continent. What I have seen are three quite different-looking forms, which have different, but at times overlapping, ranges and habitats. The three forms also prefer different prey and travel together in herds of different size (the latter behavior suggests their social structure is probably different, too). And though there are no discernible physical barriers to prevent intermingling or interbreeding, I have never seen mixed herds or any individual that looks like an intermediate form, or hybrid. The failure to find any social mixing or apparent hybrids is highly significant in itself.
Like the earlier reports of the Soviets, these conclusions will be met with healthy skepticism by other marine-mammal scientists. To meet this challenge I have already begun some collaborative studies on the genetics, vocalizations, and morphology of Antarctic killer whales that will bring additional evidence to bear on these issues. The preliminary analysis of the tissue samples I have collected, for instance, already suggests that the three forms may not interbreed, but the results are still preliminary and verification will take a while. There are no simple answers.

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Raverty, Stephen, Judy St. Leger, Dawn P. Noren, Kathy Burek Huntington, David S. Rotstein, Frances M. D. Gulland, John K. B. Ford, M. Bradley Hanson, Dyanna M. Lambourn, Jessie Huggins, Martha A. Delaney, Lisa Spaven, Teri Rowles, Lynne Barre, Paul Cottrell, Graeme Ellis, Tracey Goldstein, Karen Terio, Debbie Duffield, Jim Rice, Joseph K. Gaydos. Pathology findings and correlation with body condition index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013. PLOS - Published: December 2, 2020 - https://doi.org/10.1371/journal.pone.0242505

ABSTRACT
Understanding health and mortality in killer whales (Orcinus orca) is crucial for management and conservation actions. We reviewed pathology reports from 53 animals that stranded in the eastern Pacific Ocean and Hawaii between 2004 and 2013 and used data from 35 animals that stranded from 2001 to 2017 to assess association with morphometrics, blubber thickness, body condition and cause of death. Of the 53 cases, cause of death was determined for 22 (42%) and nine additional animals demonstrated findings of significant importance for population health. Causes of calf mortalities included infectious disease, nutritional, and congenital malformations. Mortalities in sub-adults were due to trauma, malnutrition, and infectious disease and in adults due to bacterial infections, emaciation and blunt force trauma. Death related to human interaction was found in every age class. Important incidental findings included concurrent sarcocystosis and toxoplasmosis, uterine leiomyoma, vertebral periosteal proliferations, cookiecutter shark (Isistius sp.) bite wounds, excessive tooth wear and an ingested fish hook. Blubber thickness increased significantly with body length (all p < 0.001). In contrast, there was no relationship between body length and an index of body condition (BCI). BCI was higher in animals that died from trauma. This study establishes a baseline for understanding health, nutritional status and causes of mortality in stranded killer whales. Given the evidence of direct human interactions on all age classes, in order to be most successful recovery efforts should address the threat of human interactions, especially for small endangered groups of killer whales that occur in close proximity to large human populations, interact with recreational and commercial fishers and transit established shipping lanes.

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Reggente, Melissa A. L., Filipe Alves, Cátia Nicolau, Luís Freitas, Daniele Cagnazzi, Robin W. Baird, Paolo Galli Nurturant behavior toward dead conspecifics in free-ranging mammals: new records for odontocetes and a general review.. J Mammal (2016) 97 (5): 1428-1434.

EXCERPT
Nurturant behavior toward dead conspecifics has been documented in several free-ranging marine and terrestrial mammals but still remains undocumented and poorly understood for most species. This study describes observations of adults carrying dead calves and juveniles in 7 odontocetes (toothed cetaceans) species and discusses the subject in mammals in general. Observations are based on 14 events from 3 oceans and constitute the 1st records for Indo-Pacific bottlenose dolphins (Tursiops aduncus), spinner dolphins (Stenella longirostris), killer whales (Orcinus orca), Australian humpback dolphins (Sousa sahulensis), and sperm whales (Physeter macrocephalus), as well as presenting additional records for Risso’s dolphins (Grampus griseus) and short-finned pilot whales (Globicephala macrorhynchus). Information on how the adults supported and carried the dead conspecifics, on the gender of both adults and dead young, and on the age class of the dead young, is presented. Moreover, a comparison with terrestrial mammals, including a compilation of published literature, and a discussion on possible hypotheses to explain this particular type of behavior are given. The present study helps to corroborate that adults mourning their dead young is a common and globally widespread behavior in long-lived and highly sociable/cohesive species of mammals.

Full paper here

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Rendell, Luke, Cantor M, Gero S, Whitehead H, Mann J., (2019) Causes and consequences of female centrality in cetacean societies.. Phil. Trans. R. Soc. B 374: 20180066

ABSTRACT
Cetaceans are fully aquatic predatory mammals that have successfully colonized virtually all marine habitats. Their adaptation to these habitats, so radically different from those of their terrestrial ancestors, can give us comparative insights into the evolution of female roles and kinship in mammalian societies. We provide a review of the diversity of such roles across the Cetacea, which are unified by some key and apparently invariable life-history features. Mothers are uniparous, while paternal care is completely absent as far as we currently know. Maternal input is extensive, lasting months to many years. Hence, female reproductive rates are low, every cetacean calf is a significant investment, and offspring care is central to female fitness. Here strategies diverge, especially between toothed and baleen whales, in terms of mother-calf association and related social structures, which range from ephemeral grouping patterns to stable, multi-level, societies in which social groups are strongly organized around female kinship. Some species exhibit social and/or spatial philopatry in both sexes, a rare phenomenon in vertebrates. Communal care can be vital, especially among deep-diving species, and can be supported by female kinship. Female-based sociality, in its diverse forms, is therefore a prevailing feature of cetacean societies. Beyond the key role in offspring survival, it provides the substrate for significant vertical and horizontal cultural transmission, as well as the only definitive non-human examples of menopause.
This is one contribution of 17 to a theme issue 'The evolution of female-biased kinship in humans and other mammals'.

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Rendell, Luke & Hal Whitehead, (2001) Culture in whales and dolphins. Behav. Brain. Sci. v24(2): 309-382

ABSTRACT
Studies of animal culture have not normally included a consideration of cetaceans. However, with several long-term field studies now maturing, this situation should change. Animal culture is generally studied by either investigating transmission mechanisms experimentally, or observing patterns of behavioural variation in wild populations which cannot be explained by either genetic or environmental factors. Taking this second, ethnographic, approach, there is good evidence for cultural transmission in several cetacean species. However, only the bottlenose dolphin (Tursiops spp.) has been shown experimentally to possess sophisticated social learning abilities, including vocal and motor imitation; other species have not been studied. There is observational evidence for imitation and teaching in killer whales. For cetaceans, and other large wide-ranging animals, excessive reliance on experimental data for evidence of culture is not productive, we favour the ethnographic approach. The complex and stable vocal and behavioural cultures of sympatric groups of killer whales (Orcinus orca) appear to have no parallel outside humans and represent an independent evolution of cultural faculties. (Emphasis mine.) The wide movements of cetaceans, the greater variability of the marine environment over large temporal scales relative to that on land, and the stable matrilineal social groups of some species are potentially important factors in the evolution of cetacean culture. There have been suggestions of gene-culture coevolution in cetaceans, and culture may be implicated in some unusual behavioural and life-history traits of the whales and dolphins. We hope to stimulate both discussion and research on culture in these animals.

Find the article, (with commentaries and responses) at Culture in whales and dolphins

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Riesch, Rüdiger, Lance G. Barrett-Lennard, Graeme M. Ellis, John K. B. Ford, and Volker B. Deecke (2012) Cultural traditions and the evolution of reproductive isolation: ecological speciation in killer whales? © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 1–17.

ABSTRACT
Human evolution has clearly been shaped by gene/culture interactions, and there is growing evidence that similar processes also act on populations of non-human animals. Recent theoretical studies have shown that culture can be an important evolutionary mechanism because of the ability of cultural traits to spread rapidly both vertically, obliquely, and horizontally, resulting in decreased within-group variance and increased between-group variance. Here, we collate the extensive literature on population divergence in killer whales (Orcinus orca), and argue that they are undergoing ecological speciation as a result of dietary specializations. Although we cannot exclude the possibility that cultural divergence pre-dates ecological divergence, we propose that cultural differences in the form of learned behaviours between ecologically divergent killer whale populations have resulted in sufficient reproductive isolation even in sympatry to lead to incipient speciation.

Full paper HERE.

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Sentiel A. Rommel, D. Ann Pabst, William A. McLellan, James G. Mead, Charles W. Potter (1991) Anatomical evidence for a countercurrent heat exchanger associated with dolphin testes

ABSTRACT
Cetaceans possess cryptic testes that lie within the abdominal cavity, that are surrounded by primary locomotor muscles, and that are presumably exposed to core or above core body temperatures. It has remained a question as to how cetaceans produce and store viable sperm at these high temperatures. We offer anatomical evidence for a two layer arterio-venous countercurrent heat exchanger at the cetacean testis. Subcutaneous veins from the peripheral surfaces of the dorsal fin and flukes carry cool blood from the fins to the lumbo-caudal venous plexus. The lumbo-caudal venous plexus is juxtaposed to the spermatic arterial plexus, which supplies the testis. Venous plexus flow is from the ventro-lateral margins of the visceral cavity towards the vena cava. Arterial plexus flow is from the aorta towards the ventro-lateral margins of the visceral cavity and into the testis. The existence of a countercurrent heat exchanger suggests that cetaceans potentially compensate for detrimental effects of core temperatures on sperm viability and storage by regulating the temperature of blood flow to the testis.

Available On-line

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Salvadeo, Christian J., Daniel Lluch-Belda, Alejandro Gómez-Gallardo, Jorge Urbán-Ramírez, Colin D. MacLeod. 2010. Climate change and a poleward shift in the distribution of the Pacific white-sided dolphin in the northeastern Pacific. Endang Species Res Vol. 11: 13-19, 2010.

ABSTRACT
Increasing water temperatures due to global warming mean that specific isotherms are shifting polewards. This may cause the poleward shifts in the range limits of species that are only found in specific thermal habitats. Such range shifts have been recorded in a number of plant and animal species. In the last 3 decades, we observed a decline in the presence of Pacific white-sided dolphin Lagenorhynchus obliquidens in the southwest Gulf of California (GOC), which is considered the southern boundary of their distribution. Considering that the thermal environment is physiologically important to animals, we believe that this poleward shift in the usual geographic range of the Pacific white-sided dolphin is due to long-term changes in the local climate. To obtain the conceptual framework needed to discuss such a hypothesis, we summarize and analyze current knowledge about Pacific white-sided dolphins in the southwest GOC, and sea surface temperature variability at a regional scale.

Full paper HERE.

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Samarra FI, Deecke VB, Vinding K, Rasmussen MH, Swift RJ, Miller PJ. 2010. Killer whales (Orcinus orca) produce ultrasonic whistles. J Acoust Soc Am. 2010 Nov;128(5):EL205-10.

ABSTRACT
This study reports that killer whales, the largest dolphin, produce whistles with the highest fundamental frequencies ever reported in a delphinid. Using wide-band acoustic sampling from both animal-attached (Dtag) and remotely deployed hydrophone arrays, ultrasonic whistles were detected in three Northeast Atlantic populations but not in two Northeast Pacific populations. These results are inconsistent with analyses suggesting a correlation of maximum frequency of whistles with body size in delphinids, indicate substantial intraspecific variation in whistle production in killer whales, and highlight the importance of appropriate acoustic sampling techniques when conducting comparative analyses of sound repertoires.

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Saulitis, Eva, Lance Barrett-Lennard, Kathy Heise, Graeme Ellis. 2000. Foraging strategies of sympatric killer whale (Orcinus orca) populations in Prince William Sound, Alaska. Marine Mammal Science 16 (1), 94-109.

ABSTRACT
Killer whales (Orcinus orca) feed on a wide variety of fish, cephalopods, and marine mammals throughout their cosmopolitan range; however, the dietary breadth that characterizes the species is not reflected in all populations. Here, we present the findings of a 14-yr study of the diet and feeding habits of killer whales in Prince William Sound, Alaska. Two non-associating forms of killer whale, termed resident and transient (Bigg et al. 1987), were identified. All prey seen taken by transients were marine mammals, including harbor seals (Phoca vitulina), Dall's porpoises (Phocoenoides dalli), Steller sea lions (Eumetopias jubatus), and harbor porpoises (Phocoena phocoena). Resident killer whales appeared to prey principally on salmon (Oncorhynchus spp.), preferring coho salmon (O. kisutch) over other, more abundant salmon species. Pacific herring (Clupea pallasi) and Pacific halibut (Hippocampus stenolepis) were also taken. Resident killer whales frequently were seen to interact in non-predatory ways with Steller sea lions and Dall's porpoises, while transients were not. Differences in the social organization and behavior of the resident and transient killer whales in Prince William Sound are discussed in the light of the dietary differences documented here.

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Scheel, D.; Craig O. Matkin and Eva Saulitis. 2001. Distribution of killer whale (Orcinus orca) pods in Prince William Sound, Alaska 1984-1996. Marine Mammal Science 17(3):555-569.

ABSTRACT
Thirteen years of encounter data (1984-1996) were used to examine killer whale distribution within Prince William Sound, Alaska. Four patterns of area use were found, which comprised differences between resident pods and transient groups and differences among resident groups. Resident pods frequented large open passages, while transient groups used the narrow passages and bays in the southwest. This dichotomy likely reflects resident use of salmon and transient use of pinniped prey resources, as well as the different foraging strategies required for these prey types. Four resident pods (AB, AI, AJ, and AN) used Knight Island Passage more than other areas of the Sound; two (AE and AK) used all areas of the Sound more evenly. Use of the Sound by the AT1 transient whales declined in the latter part of the study. Nearshore foraging for pinniped prey by the AT1 transient whales was more common in areas where these whales spend a disproportionate amount of time, suggesting that these areas were critical foraging habitat for them.
No similar pattern emerged for Open-water Foraging for cetaceans by AT1 whales, nor for foraging by the resident whales.
Keywords: killer whale, Orcinus orca, habitat use, distribution, Alaska, Prince William Sound, foraging behavior.

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Schorr, Gregory S, M. Bradley Hanson, Erin A. Falcone, Candice K. Emmons, Susan M. Jarvis, Russel D. Andrews and Eric M. Keen (2022) Movements and Diving Behavior of the Eastern North Pacific Offshore Killer Whale (Orcinus orca)

ABSTRACT

The Pacific Offshore killer whale population is currently listed as data deficient on the IUCN Red List and Threatened in Canada. The population is estimated at 300 individuals with a range extending from Southern California to the Aleutian Islands in Alaska. Only 157 encounters with this ecotype have been photo-documented between 1988 and 2014; consequently, movement and behavioral data are limited and restricted to areas commonly surveyed. To better understand movements, habitat use, and diving behavior, we deployed seven dart-attached satellite tags during two encounters with Offshores off California and one encounter off Washington State in 2013. Group size estimates were 6, 9, and 30 whales, respectively. Transmission durations ranged from 6.3 to 147.4 days providing a combined 2,469 location estimates. Whales tagged in Southern California travelled from 30.7°N to 59.3°N degrees latitude, covering a larger latitudinal range in 75 days than all previous sightings (33.5°N to 60.0°N). Within most of the California Current (southern extent of locations up to 48.5°N), Offshores typically used waters deeper than the 200 m isobath. As they approached the northern extent of the California Current and travelled into British Columbia and Alaska, locations were more common near or inside the 200 m isobath. Individuals tagged in the same group disassociated and re-associated within the tracking duration, with animals tagged together separating by as much 1,339 km. Two of the tags also reported summarized diving behavior, and tags captured 1,110 total dives with median dive depths of 41 m and 100 m for each tagged whale; the maximum dive depth was 480 m. Dives were typically short (median = 3.9 and 4.1 min respectively, max = 12.3). A comparison of dive depths and bathymetry suggests that whales typically dove to or near the seafloor in continental shelf habitat. Despite the small number of tag deployments, these data provide new information on social structure, individual ranges, diving behavior, and habitat use of this seldom encountered killer whale ecotype. Full paper HERE.

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Schorr, Greg S, Falcone Erin A, Moretti DJ, Andrews RD (2014) First Long-Term Behavioral Records from Cuvier’s Beaked Whales (Ziphius cavirostris) Reveal Record-Breaking Dives. PLoS ONE 9(3): e92633. doi:10.1371/journal.pone.0092633.

ABSTRACT
Cuvier’s beaked whales (Ziphius cavirostris) are known as extreme divers, though behavioral data from this difficult-to-study species have been limited. They are also the species most often stranded in association with Mid-Frequency Active (MFA) sonar use, a relationship that remains poorly understood. We used satellite-linked tags to record the diving behavior and locations of eight Ziphius off the Southern California coast for periods up to three months. The effort resulted in 3732 hr of dive data with associated regional movements – the first dataset of its kind for any beaked whale – and included dives to 2992 m depth and lasting 137.5 min, both new mammalian dive records. Deep dives had a group mean depth of 1401 m (s.d. = 137.8, n = 1142) and duration of 67.4 min (s.d. = 6.9). The group mean time between deep dives was 102.3 min (s.d. = 30.8, n = 783). While the previously described stereotypic pattern of deep and shallow dives was apparent, there was considerable inter- and intra-individual variability in most parameters. There was significant diel behavioral variation, including increased time near the surface and decreased shallow diving at night. However, maximum depth and the proportion of time spent on deep dives (presumed foraging), varied little from day to night. Surprisingly, tagged whales were present within an MFA sonar training range for 38% of days locations were received, and though comprehensive records of sonar use during tag deployments were not available, we discuss the effects frequent acoustic disturbance may have had on the observed behaviors. These data better characterize the true behavioral range of this species, and suggest caution should be exercised when drawing conclusions about behavior using short-term datasets.

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Selbmann, Anna, Charla J. Basran, Chiara G. Bertulli, Tess Hudson, Marie-Thérèse Mrusczok, Marianne H. Rasmussen, Jonathan N. Rempel, Judith Scott, Jörundur Svavarsson, Paul J. Wensveen, Megan Whittaker & Filipa I. P. Samarra (2022). Occurrence of long-finned pilot whales (Globicephala melas) and killer whales (Orcinus orca) in Icelandic coastal waters and their interspecific interactions. acta ethol (2022). https://doi.org/10.1007/s10211-022-00394-1.

ABSTRACT
Long-finned pilot whales and killer whales are widely distributed across the North Atlantic, but few studies have reported their occurrence in Icelandic coastal waters. Here, we use sightings data from research platforms and whale watching tours in six regions of Iceland from 2007 to 2020 to show that the occurrence of long-finned pilot and killer whales varied with region and season. Killer whales were regularly encountered in the south of Iceland during summer and west of Iceland during winter/spring. Long-finned pilot whales were only seen during the summer and were most often encountered in the south, west, and northwest of Iceland. Long-finned pilot whale occurrence in the south of Iceland appeared to increase during the study period but killer whale occurrence showed no noticeable changes. Long-finned pilot whales were sighted often in the areas that were also frequented by killer whales and interspecific interactions were commonly observed when both species co-occurred. Interactions appeared to be antagonistic, with killer whales often avoiding long-finned pilot whales and sometimes fleeing at high speed, similar to what has been described elsewhere in the North Atlantic. In the majority of interactions observed (68%), killer whales avoided long-finned pilot whales by moving away, but in 28% avoidance was at high speed with both species porpoising. This variability in the type of behavioural responses indicates that interactions may be more complex than previously described. We discuss regional trends in long-finned pilot whale and killer whale sightings and potential drivers of the observed interactions.
Full paper HERE.

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Shields, Monika W., Jimmie Lindell and Julie Woodruff. (2018). Declining spring usage of core habitat by endangered fish-eating killer whales reflects decreased availability of their primary prey. Pacific Conservation Biology - Published online: 15 May 2018 - https://doi.org/10.1071/PC17041

ABSTRACT
The salmon-eating Southern Resident killer whales (Orcinus orca) of the north-eastern Pacific Ocean are listed as endangered both in the United States and Canada. Their critical habitat has been defined as the region of the inland waters of Washington State and British Columbia known as the Salish Sea, where they have traditionally spent much of their time from spring through fall. Using reports from experienced observers to sightings networks, we tracked the daily presence of the Southern Residents in these waters from 1 April to 30 June from 1994 through 2016. We found that the escapement estimates of spring Chinook salmon (Oncorhynchus tshawytscha) on the Fraser River in British Columbia were a significant predictor of the cumulative presence/absence of the whales throughout the spring season. There was also a difference in both whale presence and salmon abundance before and after 2005, suggesting that the crash in Chinook salmon numbers has fallen below threshold where it is worthwhile for the whales to spend as much time in the Salish Sea. The use of the Salish Sea by the Southern Residents has declined in the spring months as they are either foraging for Chinook salmon elsewhere or are shifting to another prey species. In order to continue providing necessary protections to this endangered species, critical habitat designations must be re-evaluated as this population of killer whales shifts its range in response to prey availability.

Full paper HERE.

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Steiger, G.H., J. Calambokidis, J.M. Straley, L.M. Herman, S. Cerchio, D.R. Salden, J. Urbán-R, J.K. Jacobsen, O. von Ziegesar, K.C. Balcomb, C.M. Gabriele, M.E. Dahlheim, S. Uchida, J.K.B. Ford, P. Ladron de Guevara-P, M. Yamaguchi and J. Barlow. (2008). Geographic variation in killer whale attacks on humpback whales in the North Pacific: implications for predation pressure. Endangered Species Research 4:247-256.

ABSTRACT
We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geographic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14% at others) and feeding areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial portion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsistent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high-latitude feeding areas in the North Pacific.

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Stephanis, R. de, P. Verborgh, S. Pérez, R. Esteban, L. Minvielle-Sebastia and C. Guinet (2008). Long-term social structure of long-finned pilot whales (Globicephala melas) in the Strait of Gibraltar. Acta ethologica Volume 11, Number 2, September, 2008.

ABSTRACT
The Strait of Gibraltar is inhabited by around 216 pilot whales, which are present all year round, and nothing is known about their social structure. The aim of this study is to analyse the inter-individual association patterns within this pilot whales community to (1) provide an insight on their long-term social system and (2) to assess the relationship between sexes within this social system. Between 1999 and 2006, 23,004 km was sampled in the Strait of Gibraltar, and 4,887 images of dorsal fins of pilot whales were taken from 226 groups. The sex of 56 of the individuals could be determined genetically. The strength of the behavioural relationships between dyads of individuals was calculated, and the temporal aspects of the social structure were evaluated, showing in a non-random social structure made by constant companions. The preferred associations between individuals consisted in associations of males-females. Eight long-term units could be found with different degrees of association rates. Consequently, we propose that, in the Strait, the pilot whales exhibit a hierarchical social system composed of a population encompassing several clans of pilot whales each containing several pods. Pods will then be formed by several line units, similar to killer whale matrilineal units.

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Stredulinsky, Eva H, Chris T. Darimont, Lance Barrett-Lennard, Graeme M. Ellis, John K. B. Ford6(2021). Family feud: permanent group splitting in a highly philopatric mammal, the killer whale (Orcinus orca). Behavioral Ecology and Sociobiology (2021) 75:56

ABSTRACT
For animals that tend to remain with their natal group rather than individually disperse, group sizes may become too large to benefit individual fitness. In such cases, group splitting (or fission) allows philopatric animals to form more optimal group sizes without sacrificing all familiar social relationships. Although permanent group splitting is observed in many mammals, it occurs relatively infrequently. Here, we use combined generalized modeling and machine learning approaches to provide a comprehensive examination of group splitting in a population of killer whales (Orcinus orca) that occurred over three decades. Fission occurred both along and across maternal lines, where animals dispersed in parallel with their closest maternal kin. Group splitting was more common: (1) in larger natal groups, (2) when the common maternal ancestor was no longer alive, and (3) among groups with greater substructuring. The death of a matriarch did not appear to immediately trigger splitting. Our data suggest intragroup competition for food, leadership experience and kinship are important factors that influence group splitting in this population. Our approach provides a foundation for future studies to examine the dynamics and consequences of matrilineal fission in killer whales and other taxa.

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Tavares, Sara B., Filipa I.P. Samarra; Sonia Pascoal; Jeff A. Graves; Patrick J.O. Miller (2018). A multilevel society of herring-eating killer whales indicates adaptation to prey characteristics. Ecology and Evolution Article DOI: 10.1002/ece3.4646..

ABSTRACT
Local adaption through ecological niche specialization can lead to genetic structure between and within populations. In the Northeast Pacific, killer whales (Orcinus orca) of the same population have uniform specialized diets that are non-overlapping with other sympatric, genetically divergent, and socially isolated killer whale ecotypes. However, killer whales in Iceland show intrapopulation variation of isotopic niches and observed movement patterns: some individuals appear to specialize on herring and follow it year-round while others feed upon herring only seasonally or opportunistically. We investigated genetic differentiation among Icelandic killer whales with different isotopic signatures and observed movement patterns. This information is key for management and conservation purposes but also for better understanding how niche specialization drives genetic differentiation. Photo-identified individuals (N = 61) were genotyped for 22 microsatellites and a 611 bp portion of the mitochondrial DNA (mtDNA) control region. Photo-identification of individuals allowed linkage of genetic data to existing data on individual isotopic niche, observed movement patterns, and social associations. Population subdivision into three genetic units was supported by a discriminant analysis of principal components (DAPC). Genetic clustering corresponded to the distribution of isotopic signatures, mtDNA haplotypes, and observed movement patterns, but genetic units were not socially segregated Genetic differentiation was weak (FST < 0.1), suggesting ongoing gene flow or recent separation of the genetic units. Our results show that killer whales in Iceland are not as genetically differentiated, ecologically discrete, or socially isolated as the Northeast Pacific prey-specialized killer whales. If any process of ecological divergence and niche specialization is taking place among killer whales in Iceland, it is likely at a very early stage and has not led to the patterns observed in the Northeast Pacific.

Available online.

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Tavares, Sara B., Filipa I.P. Samarra, Patrick J.O. Miller. (2016). A multilevel society of herring-eating killer whales indicates adaptation to prey characteristics. Behavioral Ecology (2016) arw179.

ABSTRACT
Non-social factors can influence animal social structure. In killer whales (Orcinus orca), fish- versus mammal-eating ecological differences are regarded as key ecological drivers of their multilevel society, including group size, but the potential importance of specific target prey remains unclear. Here, we investigate the social structure of herring-eating killer whales in Iceland and compare it to the described social structures of primarily salmon- and seal-eating populations in the Northeast Pacific, which form stable coherent basic units nested within a hierarchical multilevel society. Using 29023 photographs collected over 6 years, we examined the association patterns of 198 individuals combining clustering, social network structure, and temporal patterns of association analysis. The Icelandic population had largely weak but non-random associations, which were not completely assorted by known ranging patterns. A fission–fusion dynamic of constant and temporary associations was observed but this was not due to permanent units joining. The population-level society was significantly structured but not in a clear hierarchical tier system. Social clusters were highly diverse in complexity and there were indications of subsclusters. There was no indication of dispersal nor strong sex differences in associations. These results indicate that the Icelandic herring-eating killer whale population has a multilevel social structure without clear hierarchical tiers or nested coherent social units, different from other populations of killer whales. We suggest that local ecological context, such as the characteristics of the specific target prey (e.g., predictability, biomass, and density) and subsequent foraging strategies may strongly influence killer whale social association patterns.

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Tennessen, Jennifer B., Marla M. Holt, M. Bradley Hanson, Candice K. Emmons, Deborah A. Giles, Jeffrey T. Hogan (2019). Kinematic signatures of prey capture from archival tags reveal sex differences in killer whale foraging activity. Journal of Experimental Biology 2019 222: jeb191874 doi: 10.1242/jeb.191874 Published 4 February 2019.

ABSTRACT
Studies of odontocete foraging ecology have been limited by the challenges of observing prey capture events and outcomes underwater. We sought to determine whether subsurface movement behavior recorded from archival tags could accurately identify foraging events by fish-eating killer whales. We used multisensor bio-logging tags attached by suction cups to Southern Resident killer whales (Orcinus orca) to: (1) identify a stereotyped movement signature that co-occurred with visually confirmed prey capture dives; (2) construct a prey capture dive detector and validate it against acoustically confirmed prey capture dives; and (3) demonstrate the utility of the detector by testing hypotheses about foraging ecology. Predation events were significantly predicted by peaks in the rate of change of acceleration (‘jerk peak’), roll angle and heading variance. Detection of prey capture dives by movement signatures enabled substantially more dives to be included in subsequent analyses compared with previous surface or acoustic detection methods. Males made significantly more prey capture dives than females and more dives to the depth of their preferred prey, Chinook salmon. Additionally, only half of the tag deployments on females (5 out of 10) included a prey capture dive, whereas all tag deployments on males exhibited at least one prey capture dive (12 out of 12). This dual approach of kinematic detection of prey capture coupled with hypothesis testing can be applied across odontocetes and other marine predators to investigate the impacts of social, environmental and anthropogenic factors on foraging ecology.

Full paper HERE.

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Terrapon, M., Kiszka, J. J., & Wagner, J. (2021). Observations of Killer Whale (Orcinus orca) Feeding Behavior in the Tropical Waters of the Northern Mozambique Channel Island of Mayotte, Southwest Indian Ocean. Aquatic Mammals, 47(2), 196-205. DOI: 10.1578/AM.47.2.2021.196.

ABSTRACT:
Very little is known about the foraging ecology of killer whales (Orcinus orca) in tropical oceans and on how these large apex predators affect prey communities. In most tropical waters, the presence of killer whales is unpredictable, and most information on their ecology is inferred from opportunistic records. This is particularly the case in the Indian Ocean where limited information is available. Between 2002 and 2017, killer whales were opportunistically encountered around the Mozambique Channel island of Mayotte in the eastern Comoros Archipelago (southwest Indian Ocean). A total of 15 killer whale sightings collected by various local experts were compiled and used to describe observed feeding events. Twenty-seven distinct individuals from four separate groups were identified by photo-identification, highlighting short-term site fidelity (minimum 7 days) to this area. Feeding was observed on seven occasions, and recorded prey included two species of elasmobranchs (Centroscymnus coelolepi and Mobula spp.) and two species of cetaceans: a humpback whale (Megaptera novaeangliae) calf and a pantropical spotted dolphin (Stenella attenuata). This study represents the first account of killer whales foraging on a combination of marine mammals and elasmobranchs in tropical waters, and describes the first presumed predation on a humpback whale calf in the southwest Indian Ocean.

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Thewissen, J. G. M.; E. M. Williams; L. J. Roe and S. T. Hussain. (2001). Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature (London) 413(6853):277-281. 2001.

ABSTRACT
Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having flippers, flukes, and a streamlined body. Eocene fossils document much of cetaceans' land-to-water transition, but, until now, the most primitive representative for which a skeleton was known was clearly amphibious and lived in coastal environments. Here we report on the skeletons of two early Eocene pakicetid cetaceans, the fox-sized Ichthyolestes pinfoldi, and the wolf-sized Pakicetus attocki. Their skeletons also elucidate the relationships of cetaceans to other mammals. Morphological cladistic analyses have shown cetaceans to be most closely related to one or more mesonychians, a group of extinct, archaic ungulates, but molecular analyses have indicated that they are the sister group to hippopotamids. Our cladistic analysis indicates that cetaceans are more closely related to artiodactyls than to any mesonychian. Cetaceans are not the sister group to (any) mesonychians, nor to hippopotamids. Our analysis stops short of identifying any particular artiodactyl family as the cetacean sister group and supports monophyly of artiodactyls.

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Tosh, Cheryl A., P.J. Nico de Bruyn, Marth'an N. Bester (2008). Preliminary analysis of the social structure of killer whales, Orcinus orca, at subantarctic Marion Island. MARINE MAMMAL SCIENCE, 24(4): 929–940 (October 2008).

ABSTRACT
Studies of social differentiation between populations of killer whales (Orcinus orca) are important due to the cosmopolitan nature of the species, both in terms of distribution and feeding habits. The following research provides preliminary findings describing the social structure of the killer whale, Orcinus orca, population at subantarctic Marion Island. We provide evidence for consistent, observable patterns of social interactions with animals associating and disassociating in nonrandom patterns. We show that the social structure of this population may follow a new pattern of association, displaying a blend of the traditional resident/transient model displayed in the Northern Hemisphere. However, we emphasize the critical need for further studies related to the sociality, biology, and life history of Southern Ocean killer whales.

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Towers, J. R., Paul Tixier, Katherine A Ross, John Bennett, John P Y Arnould, Robert L Pitman, John W Durban (2018). Movements and dive behaviour of a toothfish-depredating killer and sperm whale. ICES Journal of Marine Science, fsy118, 19 September 2018.

ABSTRACT
Depredation of demersal longlines by killer and sperm whales is a widespread behaviour that impacts fisheries and whale populations. To better understand how depredating whales behave in response to fishing activity, we deployed satellite-linked location and dive-profile tags on a sperm and killer whale that were depredating Patagonian toothfish from commercial longlines off South Georgia. The sperm and killer whale followed one fishing vessel for >180km and >300km and repeatedly depredated when longlines were being retrieved over periods of 6 and 7d, respectively. Their behaviours were also sometimes correlated with the depths and locations of deployed gear. They both dove significantly deeper and faster when depredating compared with when foraging naturally. The killer whale dove >750m on five occasions while depredating (maximum: 1087m), but these deep dives were always followed by long periods (3.9–4.6h) of shallow (<100m) diving. We hypothesize that energetically and physiologically costly dive behaviour while depredating is driven by intra- and inter-specific competition due to the limited availability of this abundant resource. Full article HERE.

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Towers, J. R., Muriel J. Hallé, Helena K. Symonds, Gary J. Sutton, Alexandra B. Morton, Paul Spong, James P. Borrowman & John K. B. Ford (2018). Infanticide in a mammal-eating killer whale population. Scientific Reports volume 8, Article number: 4366.

ABSTRACT
Infanticide can be an extreme result of sexual conflict that drives selection in species in which it occurs. It is a rarely observed behaviour but some evidence for its occurrence in cetaceans exists in three species of dolphin. Here we describe observations of an adult male killer whale (Orcinus orca) and his post-reproductive mother killing a neonate belonging to an unrelated female from the same population in the North Pacific. This is the first account of infanticide reported in killer whales and the only case committed jointly by an adult male and his mother outside of humans. Consistent with findings in other social mammals, we suggest that infanticide is a sexually selected behaviour in killer whales that could provide subsequent mating opportunities for the infanticidal male and thereby provide inclusive fitness benefits for his mother. Available On-line.

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Urian, K. W., D.A. Duffield, A. J. Read, R. S. Wells, E. D. Shell (1996). Seasonality of reproduction in bottlenose dolphins, Tursiops truncatus. Journal of Mammalogy, Vol. 77:2, p. 394-403.

Quote: Bottlenose dolphins showed diffuse peaks and considerable flexibility in their seasonality of reproduction. There was no relationship between latitude and seasonality of reproduction or synchrony of births. However, there was a correlation between origin of population and seasonality of reproduction in both wild and captive dolphins. We suggest that adaptations to local environmental conditions have the strongest influence on seasonality of reproduction in these populations of bottlenose dolphins.

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Van Cise, Amy M., Karen. K. Martien, Sabre D. Mahaffy, Robin W. Baird, Daniel L. Webster, James H. Fowler, Erin M. Oleson, Phillip A. Morin (2017). Familial social structure and socially driven genetic differentiation in Hawaiian short-finned pilot whales. Molecular Biology, Volume 26, Issue 23 December 2017.

ABSTRACT
Social structure can have a significant impact on divergence and evolution within species, especially in the marine environment, which has few environmental boundaries to dispersal. On the other hand, genetic structure can affect social structure in many species, through an individual preference towards associating with relatives. One social species, the short-finned pilot whale (Globicephala macrorhynchus), has been shown to live in stable social groups for periods of at least a decade. Using mitochondrial control sequences from 242 individuals and single nucleotide polymorphisms from 106 individuals, we examine population structure among geographic and social groups of short-finned pilot whales in the Hawaiian Islands, and test for links between social and genetic structure. Our results show that there are at least two geographic populations in the Hawaiian Islands: a Main Hawaiian Islands (MHI) population and a Northwestern Hawaiian Islands/Pelagic population (FST and FST p < .001), as well as an eastern MHI community and a western MHI community (FST p = .009). We find genetically driven social structure, or high relatedness among social units and clusters (p < .001), and a positive relationship between relatedness and association between individuals (p < .0001). Further, socially organized clusters are genetically distinct, indicating that social structure drives genetic divergence within the population, likely through restricted mate selection (FST p = .05). This genetic divergence among social groups can make the species less resilient to anthropogenic or ecological disturbance. Conservation of this species therefore depends on understanding links among social structure, genetic structure and ecological variability within the species.

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Vester, Heike and Kurt Hammerschmidt. (2013). First record of killer whales (Orcinus orca) feeding on Atlantic salmon (Salmo salar) in northern Norway suggest a multi-prey feeding type. Marine Biodiversity Records, page 1 of 5. # Marine Biological Association of the United Kingdom, 2013, Vol. 6; e9; 2013 Published online.

ABSTRACT
Occurrence of killer whales in Norway is linked to the migration of the herring population with most sightings during wintertime. Here we describe the first record of North Atlantic killer whales feeding on Atlantic salmon inside a fjord in northern Norway during summertime, thus adding an important factor in understanding the feeding ecology of North Atlantic killer whales.

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Vilstrup, Julia T., Simon YW Ho, Andrew D Foote, Phillip A Morin, Danielle Kreb, Michael Krützen, Guido J Parra, Kelly M Robertson, Renaud de Stephanis, Philippe Verborgh, Eske Willerslev, Ludovic Orlando & M Thomas P Gilbert (2011). Mitogenomic phylogenetic analyses of the Delphinidae with an emphasis on the Globicephalinae. BMC Evolutionary Biology volume 11, Article number: 65 (2011)

ABSTRACT
Previous DNA-based phylogenetic studies of the Delphinidae family suggest it has undergone rapid diversification, as characterised by unresolved and poorly supported taxonomic relationships (polytomies) for some of the species within this group. Using an increased amount of sequence data we test between alternative hypotheses of soft polytomies caused by rapid speciation, slow evolutionary rate and/or insufficient sequence data, and hard polytomies caused by simultaneous speciation within this family. Combining the mitogenome sequences of five new and 12 previously published species within the Delphinidae, we used Bayesian and maximum-likelihood methods to estimate the phylogeny from partitioned and unpartitioned mitogenome sequences. Further ad hoc tests were then conducted to estimate the support for alternative topologies.
Note: Figure 1 shows the origin of Orcinus orca to have occurred 8 million years ago.

Full paper HERE.

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Viricel, Amélia, Allan E. Strand, Patricia E. Rose, Vincent Ridoux and Pascale Garcia (2008). Insights on common dolphin (Delphinus delphis) social organization from genetic analysis of a mass-stranded pod. Behavioral Ecology and Sociobiology, Vol. 63, Number 2 / December, 2008

ABSTRACT
Compared to terrestrial mammals, little is known of cetacean social systems as they are generally less accessible to behavioral investigations due to their aquatic environment. The present study investigates group structure of the pelagic common dolphin, Delphinus delphis, using genetic markers. Tissue samples from 52 individuals representing a recent live mass-stranding event were compared to 42 single strandings taken from presumably different groups. The mass-stranding event occurred in 2002 on the French coast of the English Channel, whereas the single strandings were collected between 1993 and 2003 along the western coast of France (Bay of Biscay and English Channel). Analysis of mitochondrial DNA control region sequences indicated that genetic variability within the mass-stranded pod was similar to variability observed in single strandings. The mass-stranded group was composed of 41 different mitochondrial haplotypes or matrilines while the single strandings revealed 29 different haplotypes. Analysis of 11 microsatellite loci revealed that average relatedness of the mass-stranded pod was not different from average relatedness among all single strandings suggesting that individuals within the group had no closer kin relationships than animals taken from presumably different groups. These results do not support a matriarchal system and suggest that common dolphins constituting a pod are not necessarily genetically related.

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Visser, Ingrid N. and Frank J. Bonoccorso (2003). New observations and a review of killer whale (Orcinus orca) sightings in Papua New Guinea waters. Aquatic Mammals 2003, 29.1, 150–172.

ABSTRACT
Although typically considered a temperate to coldwater species, killer whales (or orca) (Orcinus orca) have been reported intermittently in tropical waters. While the IUCN (IUCN, 2000) does not list the species as present in Papua New Guinea waters, the records presented here indicate it is found in the area for at least 10 months of the year. A total of 94 sightings of killer whales in Papua New Guinea waters were compiled. Thirty-seven sightings from April 1987 to July 2002 were recorded with an exact date and location, with a further 57 sightings of unknown date or exact location. Twenty-seven of all records had either photographs or videotape to confirm species identication. The earliest reference to killer whales in this region was from 1956, when they were recorded taking fish off long-lines. Killer whales from Papua New Guinea waters have been observed feeding on four species of elasmobranchs (scalloped-hammerhead shark, Sphyrna lewini; grey reef shark, Carcharhinus amblyrhynchos; manta ray, Manta birostris; and blue-spotted ray, Dasyatis kuhlii) and four species of fin-fish (yellow-fin tuna, Thunnus albacares; big-eye tuna, Thunnus Obesus; Indo-Pacific sailfish, Istiophorus platypterus; and sunfish, Mola mola). These are the first records, worldwide, of killer whales feeding on scalloped-hammerhead sharks, grey reef sharks and blue-spotted rays. Killer whales in these waters have been reported in association with two species of cetaceans (sperm whales, Physeter macrocephalus and spinner dolphins, Stenella longirostris). Photo-identification images were collected for 14 individuals and a catalogue established. Matches were made for two animals—a female sighted approximately 30 n mi and two days apart and a sub-adult male sighted in the same region 16 months apart. Some individual killer whales from these waters have been observed with grey under-flukes, in contrast to white, which is typically described for this species.

FULL PAPER HERE.

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Ward, Eric J., Kim Parsons, Elizabeth E Holmes, Ken C Balcomb III and John KB Ford (2009). The role of menopause and reproductive senescence in a long-lived social mammal. Frontiers in Zoology 2009, 6:4.

ABSTRACT
Background: Menopause is a seemingly maladaptive life-history trait that is found in many longlived mammals. There are two competing evolutionary hypotheses for this phenomenon; in the adaptive view of menopause, the cessation of reproduction may increase the fitness of older females; in the non-adaptive view, menopause may be explained by physiological deterioration with age. The decline and eventual cessation of reproduction has been documented in a number of mammalian species, however the evolutionary cause of this trait is unknown.
Results: We examined a unique 30-year time series of killer whales, tracking the reproductive performance of individuals through time. Killer whales are extremely long-lived, and may have the longest documented post-reproductive lifespan of any mammal, including humans. We found no strong support for either of the adaptive hypotheses of menopause; there was little support for the presence of post-reproductive females benefitting their daughter's reproductive performance (interbirth interval and reproductive lifespan of daughters), or the number of mature recruits to the population. Oldest mothers (> 35) did appear to have a small positive impact on calf survival, suggesting that females may gain experience with age. There was mixed support for the grandmother hypothesis - grandoffspring survival probabilities were not influenced by living grandmothers, but grandmothers may positively influence survival of juveniles at a critical life stage.
Conclusion: Although existing data do not allow us to examine evolutionary tradeoffs between survival and reproduction for this species, we were able to examine the effect of maternal age on offspring survival. Our results are consistent with similar studies of other mammals - oldest mothers appear to be better mothers, producing calves with higher survival rates. Studies of juvenile survival in humans have reported positive benefits of grandmothers on newly weaned infants; our results indicate that 3-year old killer whales may experience a positive benefit from helpful grandmothers. While our research provides little support for menopause evolving to provide fitness benefits to mothers or grandmothers, our work supports previous research showing that menopause and long post-reproductive lifespans are not a human phenomenon.

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Ward, Eric J., Elizabeth E Holmes and Ken C Balcomb III (2009). Quantifying the effects of prey abundance on killer whale reproduction. Frontiers in Zoology 2009, 6:4.

ABSTRACT
Summary
1. Management decisions for threatened and endangered species require risks to be identified and prioritized, based on the degree to which they influence population dynamics. The potential for recovery of small populations at risk may be determined by multiple factors, including intrinsic population characteristics (inbreeding, sex ratios) and extrinsic variables (prey availability, disease, human disturbance). Using Bayesian statistical methods, the impact of each of these risk factors on demographic rates can be quantified and assigned probabilities to express uncertainty.
2. We assessed the impact of a wide range of factors on the fecundity of two threatened populations of killer whales Orcinus orca, specifically whether killer whale production is limited by availability of Chinook salmon Oncorhynchus tshawytscha. Additional variables included anthropogenic factors, climate variables, temporal effects, and population variables (population size, number of males, female age).
3. Our results indicate that killer whale fecundity is highly correlated with the abundance of Chinook salmon. For example, the probability of a female calving differed by 50% between years of low salmon abundance and high salmon abundance. Weak evidence exists for linking fecundity to other variables, such as sea surface temperature.
4. There was strong data support for reproductive senescence in female killer whales. This pattern of rapid maturity and gradual decline of fecundity with age commonly seen in terrestrial mammals has been documented in few marine mammal species. Maximum production for this species occurs between ages 20-22, and reproductive performance declines gradually to menopause over a period of 25 years.
5. Synthesis and applications. Our results provide strong evidence for reproductive senescence in killer whales, and more importantly, that killer whale fecundity is strongly tied to the abundance of Chinook salmon, a species that is susceptible to environmental variation and has high commercial value to fisheries. This strong predator-prey relationship highlights the importance of understanding which salmon populations overlap with killer whales seasonally and spatially, so that those salmon populations important as prey for killer whales can be identified and targeted for conservation efforts.

Full paper HERE.

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Wasser, Samuel K., Jessica I. Lundin, Katherine Ayres, Elizabeth Seely, Deborah Giles, Kenneth Balcomb, Jennifer Hempelmann, Kim Parsons, Rebecca Booth (2017). Population growth is limited by nutritional impacts on pregnancy success in endangered Southern Resident killer whales (Orcinus orca). Frontiers in Zoology 2009, 6:4.

ABSTRACT
The Southern Resident killer whale population (Orcinus orca) was listed as endangered in 2005 and shows little sign of recovery. These fish eating whales feed primarily on endangered Chinook salmon. Population growth is constrained by low offspring production for the number of reproductive females in the population. Lack of prey, increased toxins and vessel disturbance have been listed as potential causes of the whale’s decline, but partitioning these pressures has been difficult. We validated and applied temporal measures of progesterone and testosterone metabolites to assess occurrence, stage and health of pregnancy from genotyped killer whale feces collected using detection dogs. Thyroid and glucocorticoid hormone metabolites were measured from these same samples to assess physiological stress. These methods enabled us to assess pregnancy occurrence and failure as well as how pregnancy success was temporally impacted by nutritional and other stressors, between 2008 and 2014. Up to 69% of all detectable pregnancies were unsuccessful; of these, up to 33% failed relatively late in gestation or immediately post-partum, when the cost is especially high. Low availability of Chinook salmon appears to be an important stressor among these fish-eating whales as well as a significant cause of late pregnancy failure, including unobserved perinatal loss. However, release of lipophilic toxicants during fat metabolism in the nutritionally deprived animals may also provide a contributor to these cumulative effects. Results point to the importance of promoting Chinook salmon recovery to enhance population growth of Southern Resident killer whales. The physiological measures used in this study can also be used to monitor the success of actions aimed at promoting adaptive management of this important apex predator to the Pacific Northwest.

Full paper HERE.

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Whitehead, Hal. (2020). Cultural specialization and genetic diversity: Killer whales and beyond. Journal of Theoretical Biology. Available online 15 January 2020.

ABSTRACT
Culturally-transmitted ecological specialization can reduce niche breadths with demographic and ecological consequences. I use agent-based models, grounded in killer whale biology, to investigate the potential consequences of cultural specialization for genetic diversity. In these models, cultural specialization typically reduces the number of mitochondrial haplotypes, mitochondrial haplotype diversity, mitochondrial nucleotide diversity, and heterozygosity at nuclear loci. The causal route of this decline is mostly indirect, being ascribed to a reduction in absolute population size resulting from cultural specialization. However, small group size exacerbates the decline in genetic diversity, presumably because of increased founder effects at the initiation of each cultural ecotype. These results are concordant with measures of low genetic diversity in the killer whale, although culturally-transmitted ecological specialization alone might not be sufficient to fully account for the species’ very low mitochondrial diversity. The process may also operate in other species.

Full paper HERE.

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Whitehead, Hal. (2017). Gene–culture coevolution in whales and dolphins. PNAS | July 25, 2017 | vol. 114 | no. 3. | 7814–7821

ABSTRACT
Whales and dolphins (Cetacea) have excellent social learning skills as well as a long and strong mother–calf bond. These features produce stable cultures, and, in some species, sympatric groups with different cultures. There is evidence and speculation that this cultural transmission of behavior has affected gene distributions. Culture seems to have driven killer whales into distinct ecotypes, which may be incipient species or subspecies. There are ecotypespecific signals of selection in functional genes that correspond to cultural foraging behavior and habitat use by the different ecotypes. The five species of whale with matrilineal social systems have remarkably low diversity of mtDNA. Cultural hitchhiking, the transmission of functionally neutral genes in parallel with selective cultural traits, is a plausible hypothesis for this low diversity, especially in sperm whales. In killer whales the ecotype divisions, together with founding bottlenecks, selection, and cultural hitchhiking, likely explain the low mtDNA diversity. Several cetacean species show habitat-specific distributions of mtDNA haplotypes, probablythe result of mother–offspringcultural transmission of migration routes or destinations. In bottlenose dolphins, remarkable small-scale differences in haplotype distribution result from maternal cultural transmission of foraging methods, and large scale redistributions of sperm whale cultural clans in the Pacific have likely changed mitochondrial genetic geography. With the acceleration of genomics new results should come fast, but understanding gene–culture coevolution will be hampered by the measured pace of research on the socio-cultural side of cetacean biology.

Full paper HERE.

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Whitehead, Hal & Rendell, L. (2014). The Cultural Live of Whales and Dolphins. Univ. Chicago Press, Chicago.

SUMMARY
In the songs and bubble feeding of humpback whales; in young killer whales learning to knock a seal from an ice floe in the same way their mother does; and in the use of sea sponges by the dolphins of Shark Bay, Australia, to protect their beaks while foraging for fish, we find clear examples of the transmission of information among cetaceans. Just as human cultures pass on languages and turns of phrase, tastes in food (and in how it is acquired), and modes of dress, could whales and dolphins have developed a culture of their very own?
Unequivocally: yes. In The Cultural Lives of Whales and Dolphins, cetacean biologists Hal Whitehead, who has spent much of his life on the ocean trying to understand whales, and Luke Rendell, whose research focuses on the evolution of social learning, open an astounding porthole onto the fascinating culture beneath the waves. As Whitehead and Rendell show, cetacean culture and its transmission are shaped by a blend of adaptations, innate sociality, and the unique environment in which whales and dolphins live: a watery world in which a hundred-and-fifty-ton blue whale can move with utter grace, and where the vertical expanse is as vital, and almost as vast, as the horizontal.

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Whitehead, Hal, Mary Dillon, Susan Dufault, Linda Weilgart & Jonathan Wright. (1998). Non-geographically based population structure of South Pacific sperm whales: dialects, fluke-markings and genetics. Journal of Animal Ecology 67 253-262.

ABSTRACT
1. This study addresses the issue of structure in sperm whale (Physeter macrocephalus Linnaeus) populations and whether it is geographically based.
2. During a survey around the South Pacific Ocean, we collected sloughed skin for genetic analyses, recorded coda vocalizations, and photographed fluke markings.
3. Groups of female and immature sperm whales had characteristic mitochondrial haplotypes, coda repertoires, and fluke-mark patterns, but there was no clear geographical structure in any of these attributes.
4. However, similarities of coda repertoire and mitochondrial haplotype distribution were significantly correlated among pairs of groups in a manner that was not geographically based. There was also a significant canonical correlation coefficient between coda repertoire and fluke-mark patterns.
5. These results suggest that attributes (such as vocal repertoire and techniques of predator defence) which are acquired matrilineally, and probably culturally, are conserved during the fission and dispersal of groups.

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Whitehead, H., Luke Rendell, Richard W. Osborne, Bernd Würsig (2004). Culture and conservation of non-humans with reference to whales and dolphins: review and new directions. Biological Conservation Vol. 120, No. 3, December 2004, Pages 427-437

ABSTRACT
There is increasing evidence that culture is an important determinant of behavior in some non-human species including great apes and cetaceans (whales and dolphins). In some cases, there may be repercussions for population biology and conservation. Rapidly evolving "horizontal" cultures, transmitted largely within generations, may help animals deal with anthropogenic change and even allow them to exploit it, sometimes with negative consequences for both the animals and humans. In contrast, stable "vertical" or "oblique" cultures, transmitted principally between generations, may impede adaptation to environmental change, and confound range recovery, reintroductions and translocations. Conformist stable cultures can lead to maladaptive behavior, which may be mistaken for the results of anthropogenic threats. They can also structure populations into sympatric sub-populations with distinctive cultura variants. Such structuring is common among cetaceans, among which sympatric sub-populations may face different anthropogenic threats or respond to the same threat in different ways. We suggest that non-human culture should be integrated into conservation biology when considering populations with such attributes, and also more generally by refining definitions of evolutionarily significant units and considering how cultural attributes may change our perspectives of non-humans.

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Whitehead, H.(Dalhousie Univ., Halifax Nova Scotia) (1998). Cultural Selection and Genetic Diversity in Matrilineal Whales. Science, Vol. 282, p. 1708-1711.

ABSTRACT
Low diversities of mitochondrial DNA (mtDNA) have recently been found in four species of matrilineal whale [Sperm whales, orcas, long-finned pilot whales and short-finned pilot whales]. No satisfactory explanation for this apparent anomaly has been previously suggested. Culture seems to be an important part of the lives of matrilineal whales. The selection of matrilineally transmitted cultural traits, upon which neutral mtDNA alleles "hitchhike," has the potential to strongly reduce genetic variation. Thus, in contrast to other nonhuman mammals, culture may be an important evolutionary force for the matrilineal whales.

From accompanying article: "...suggests that in sperm whales and some other species, cultural traits-learned behaviors passed on to family members-are affecting the course of genetic evolution, a situation thus far documented only in humans."

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Wild, Sonja, William J.E. Hoppitt, Simon J. Allen, and Michael Krutzen. (2020). Integrating Genetic, Environmental, and Social Networks to Reveal Transmission Pathways of a Dolphin Foraging Innovation. Current Biology 30, 1–7.

ABSTRACT
Cultural behavior, which is transmitted among conspecifics through social learning[1], is found across various taxa [2–6]. Vertical social transmission from parent to offspring [7] is thought to be adaptive because of the parental generation being more skilled than maturing individuals. It is found throughout the animal kingdom, particularly in species with prolonged parental care, e.g.,[8,9]. Social learning can also occur among members of the same generation [4, 10, 11] or between older, non-parental individuals and younger generations [7] via horizontal or oblique transmission, respectively. Extensive work on primate culture has shown that horizontal transmission of foraging behavior is biased toward species with broad cultural repertoires [12] and those with increased levels of social tolerance [13, 14], such as great apes. Vertical social transmission has been established as the primary transmission mechanism of foraging behaviors in the Indo-Pacific bottlenose dolphin (Tursiops aduncus) population of Shark Bay, Western Australia [6, 9, 15, 16]. Here, we investigated the spread of another foraging strategy, ‘‘shelling’’ [17], whereby some dolphins in this population feed on prey trapped inside large marine gastropod shells. Using a multi-network version of ‘‘network-based diffusion analysis’’ (NBDA), we show that shelling behavior spreads primarily through non-vertical social transmission. By statistically accounting for both environmental and genetic influences, our findings thus represent the first evidence of non-vertical transmission of a foraging tactic in toothed whales. This research suggests there are multiple transmission pathways of foraging behaviors in dolphins, highlighting the similarities between cetaceans and great apes in the nature of the transmission of cultural behaviors.

Full paper HERE.

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