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Three aerial surveys were conducted along a portion of the northeastern coast of Sakhalin Island, Russia between August and September 1998. They were conducted to examine the spatial distribution of western gray whales on their feeding grounds, and in relation to current and planned industrial activity. A total of 32 gray whale groups, consisting of 38 whales, was sighted during the surveys. Group sizes ranged from 1-3 individuals (mean = 1.2, SD = 0.54), with 87.5% (n = 28) composed of single whales. All groups detected were within 5km of the shore and 93.8% (n = 30) were sighted inside 4km. Sighting locations ranged from 0.6-4.8km offshore, with an overall mean distance from shore of 2.5km (SD = 1.11). These data suggest that western gray whales feed primarily in waters less than 20m deep and relatively close to shore. The nutrient-rich effluent from a large coastal lagoon is believed to significantly enrich the near-shore benthic environment of the northeastern Sakhalin Island coast, creating an area of particularly high food availability, and in turn contributing to the near-shore affinity of gray whales observed during this study.

Gray whales (Eschrichtius robustus) occur along the eastern and western coastlines of the North Pacific as two geographically isolated populations and have traditionally been divided into the eastern (California-Chukchi) and western (Korean-Okhotsk) populations. Recent molecular comparisons confirm, based on differences in haplotypic frequencies, that these populations are genetically separated at the population-level. Both populations were commercially hunted, but only the eastern gray whale has returned to near pre-exploitation numbers. In contrast, the western population remains highly depleted, shows no apparent signs of recovery and its future survival remains uncertain. Research off Sakhalin Island, Russia between 1995 and 1999 has produced important new information on the present day conservation status of western gray whales and provided the basis for the World Conservation Union (IUCN) to list the population as ‘Critically Endangered’ in 2000. The information presented here, in combination with potential impacts from anthropogenic threats throughout the range of this population, raises strong concerns about the recovery and continued survival of the western gray whale.

Between 2005 and 2007, four female western gray whales were accidentally entrapped and died in Japanese set nets while migrating along the Pacific coast of Honshu, Japan. Photographs of these animals were compared to a photo-identification catalogue of western gray whales from their feeding ground off Sakhalin Island, Russia, to look for matches of individuals between the two areas. Although useable quality photographs were available for only one of the four whales from Japan, a confirmed match was made to a whale photographed off Sakhalin Island. This match represents the first link between the feeding ground and a migratory corridor and highlights the importance of multinational research collaboration in the formation of range-wide conservation measures to protect this critically endangered population.

This study provides the first description of the feeding aggregation recently formed by humpback whales in the Senyavin Strait, off eastern Chukotka. A total of 143 individuals were identified during the two summer and fall seasons of 2017 and 2018. More than half of the whales recorded in the first year were encountered again in the following year. The spatial distribution of feeding whales varied substantially between years, which may be explained by a shift in prey use. The structure of the feeding aggregation remained relatively stable, with a slightly higher number of new animals observed in the 2018 season. The estimated size of the aggregation was from 84 (±1.5) to 90 (±6.4) individuals in 2017 and from 105 (±3.7) to 109 (±6.2) individuals in 2018. A comparison of the whale photographs we took with the catalogues from other feeding grounds yielded matches with individuals recorded from the Chukchi Sea, Gulf of Anadyr, and waters off the Commander Islands and the eastern Aleutian Islands. Among the breeding grounds, matches were found only with catalogues of images collected from the waters off the Hawaiian Islands. Thus, we hypothesize that the feeding aggregation in the Senyavin Strait is relatively stable between seasons and within one season. There is some exchange of individuals with some other feeding grounds. This aggregation is formed mainly by whales of the Hawaiian subpopulation.

Until recently, it has been believed that only one cetacean species of the genus Berardius, the Baird’s beaked whale (Berardius bairdii Stejneger, 1883), inhabits the northern Pacific Ocean. However, a genetic analysis of tissue samples and morphometric data provide convincing evidence for the existence of a previously undescribed Berardius species sympatric to Baird’s beaked whale, which is referred to as “black” beaked whale. The high probability of occurrence of the black beaked whale in Russian waters is established and its possible range is described in the present study. A genetic analysis of the mitochondrial DNA control region was carried out for 28 new specimens of the genus Berardius from four Far Eastern regions. According to the results, all specimens from the Commander Islands and Kamchatka Gulf belonged to the phylogroup of the Baird’s beaked whale. Of the two dead animals stranded on the Kunashir Island coast, one was identified as Baird’s beaked whale and the other as black beaked whale. Another two black beaked whales were found on the eastern coast of Sakhalin Island. These are the first records of the new Berardius species from the Russian territory confirmed by genetic analysis.

Top predators strongly impact the structure of ecosystems through the top-down cascading effects on prey species. Killer whales (Orcinus orca), the top predators in marine ecosystems, are increasing their presence in the Arctic following the ice cover loss. The impact of killer whales on marine ecosystems differs dramatically across ecotypes: ‘resident’ R-type killer whales feed mostly on large fish, while ‘transient’ T-type whales feed mostly on marine mammals. We analyze the differences in geographical distribution of killer whale ecotypes in the western North Pacific in order to predict the potential effects of climate change on their range and the consequential impact on Arctic ecosystems. We show that R-type whales prevail in the coastal waters of eastern Kamchatka, Commander and Kuril Islands and in the central Okhotsk Sea, while T-type whales dominate the coastal waters of Chukotka and the coastal Okhotsk Sea. The most prominent difference between these areas is depth: in the regions where R-type whales prevail, deep waters occur close to shore, while the regions dominated by T-type whales are represented by wide shallows covered with ice in winter. We propose several hypotheses to explain this large-scale segregation, including distribution of prey species and ice cover. Habitat preferences suggest that range expansion in the Arctic induced by climate change will likely involve mostly T-type killer whales and consequently increase the predation pressure on marine mammals to a greater extent than on fish stocks. This should be considered in further studies and prediction models highlighting Arctic marine ecosystems change.

Exposure to persistent organic pollutants (POPs) is a key factor in predicting the collapse of global killer whale (Orcinus orca) populations due to reproductive and immune impacts. Blubber biopsies from killer whales (n = 25) were collected in the Russian Far East in 2002–2004. Biopsies were analyzed for ΣDDT, ΣPCB, and HCB concentrations. A subset of biopsies was further examined for additional contaminants, ΣPBDE, ΣHCH, ΣCHLD, mirex, and dieldrin. Mean concentrations were compared across resident (fish-eating) and transient (mammal-eating) ecotypes and between sexes. ΣPCB analytes (resident males 18,000, resident females 1200, and transient males 420,000 ng g−1 lw) and HCB (resident males 750, resident females 81, and transient males 6200 ng g−1 lw) differed significantly (p

International audience; Mitochondrial DNA (mtDNA) differences between humpback whales on different feeding groundscan reflect the cultural transmission of migration destinations over generations, and thereforerepresent one of the very few cases of gene-culture coevolution identified in the animal kingdom.In Russian Pacific waters, photo-identification (photo-ID) studies have shown minimal interchangebetween whales feeding off the Commander Islands and those feeding in the Karaginsky Gulf,regions that are separated by only 500 km and have previously been lumped together as a singleRussian feeding ground. Here, we assessed whether genetic differentiation exists between these2 groups of humpback whales. We discovered a strong mtDNA differentiation between the 2feeding sites (FST = 0.18, ΦST = 0.14, P < 0.001). In contrast, nuclear DNA (nuDNA) polymorphisms,determined at 8 microsatellite loci, did not reveal any differentiation. Comparing our mtDNA resultswith those from a previous ocean-basin study reinforced the differences between the 2 feedingsites. Humpback whales from the Commanders appeared most similar to those of the westernGulf of Alaska and the Aleutian feeding grounds, whereas Karaginsky differed from all other NorthPacific feeding grounds. Comparison to breeding grounds suggests mixed origins for the 2 feedingsites; there are likely connections between Karaginsky and the Philippines and to a lesser extentto Okinawa, Japan, whereas the Commanders are linked to the Mexican breeding grounds. ThemtDNA differentiation between the Commander Islands and Karaginsky Gulf suggests a case ofgene-culture coevolution, correlated to fidelity to a specific feeding site within a particular feedingground. From a conservation perspective, our findings emphasize the importance of consideringthese 2 feeding sites as separate management units.

Two ecotypes of killer whales—fish-eating and mammal-eating—have been found in the seas of the Russian Far East, but confirmation of their status required genetic studies of animals with known phenotype and foraging specialization. In this paper we combine the results of the analysis of nuclear genetic markers, isotopic composition of tissues and phenetic feature (shape of the saddle patch) of killer whales from different regions of Far Eastern seas. Analysis of allelic composition of 9 microsatellite loci of the nuclear DNA divided the samples into two distinct clusters with the divergence between them high enough to indicate reproductive isolation. The content of nitrogen stable isotope 15N in tissues of whales from the first cluster was significantly lower than that of the second cluster. The difference of δ15N values between individuals from different clusters was about 3‰, which corresponds to the difference between adjacent trophic levels. Apparently, the first cluster comprised fish-eating, and the second—mammal-eating animals. The ratio of saddle patch shape types also differed between the clusters. Whales from the first cluster had five types of patch shape in different proportions, while whales from the second cluster had only “smooth” saddle patches. The differences between the clusters were statistically significant. Thus, killer whales from the seas of the Russian Far East comprise at least two reproductively isolated clusters with stable ecological and morphological differences, that is, two different ecotypes—fish-eating and mammal-eating. Different ecotypes of killer whales should be managed separately during abundance surveys, monitoring, evaluation of human impact and estimates of total allowed takes from the wild populations.

Infection with Brucella spp., long known as a cause of abortion, infertility, and reproductive loss in domestic livestock, has increasingly been documented in marine mammals over the past two decades. We report molecular evidence of Brucella infection in Asian sea otters (Enhydra lutris lutris). Brucella DNA was detected in 3 of 78 (4%) rectal swab samples collected between 2004 and 2006 on Bering Island, Russia. These 78 animals had previously been documented to have a Brucella seroprevalence of 28%, markedly higher than the prevalence documented in sea otters (Enhydra lutris) in North America. All of the DNA sequences amplified were identical to one or more previously isolated Brucella spp. including strains from both terrestrial and marine hosts. Phylogenetic analysis of this sequence suggested that one animal was shedding Brucella spp. DNA with a sequence matching a Brucella abortus strain, whereas two animals yielded a sequence matching a group of strains including isolates classified as Brucella pinnipedialis and Brucella melitensis. Our results highlight the diversity of Brucella spp. within a single sea otter population.

We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds on the population structure of humpback whales Megaptera novae - angliae based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions dur- ing the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall FST = 0.121, ΦST = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall FST = 0.093, ΦST = 0.106, p < 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migra- tory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat.

We investigated the influence of the type of activity and the social context on the proportion of four different structural categories of stereotyped calls in the acoustic communication of Kamchatkan killer whales. Using generalized linear models, we described the dependence of each sound category on the type of activity, the number of killer whale pods and the presence of mixed-pod groups. We found that the proportion of different sound categories depended on the number of pods and the presence of mixed-pod groups, while the type of activity did not affect the proportion of sounds of different categories. Based on the observed differences we suggest that biphonic and high-frequency monophonic calls are mainly used as family and pod markers, and help to track the position of family members at long ranges, and low-frequency monophonic calls are used as close-range intra-group signals to maintain contact between pod members in the conditions of limited underwater visibility.

Ultrasonic whistles were previously found in North Atlantic killer whales and were suggested to occur in eastern North Pacific killer whales based on the data from autonomous recorders. In this study ultrasonic whistles were found in the recordings from two encounters with the eastern North Pacific offshore ecotype killer whales and one encounter with the western North Pacific killer whales of unknown ecotype. All ultrasonic whistles were highly stereotyped and all but two had downsweep contours. These results demonstrate that specific sound categories can be shared by killer whales from different ocean basins.

There are two recognized species in the genus Berardius, Baird’s and Arnoux’s beaked whales. In Japan, whalers have traditionally recognized two forms of Baird’s beaked whales, the common “slate-gray” form and a smaller, rare “black” form. Previous comparison of mtDNA control region sequences from three black specimens to gray specimens around Japan indicated that the two forms comprise different stocks and potentially different species. We have expanded sampling to include control region haplotypes of 178 Baird’s beaked whales from across their range in the North Pacific. We identified five additional specimens of the black form from the Aleutian Islands and Bering Sea, for a total of eight “black” specimens. The divergence between mtDNA haplotypes of the black and gray forms of Baird’s beaked whale was greater than their divergence from the congeneric Arnoux’s beaked whale found in the Southern Ocean, and similar to that observed among other congeneric beaked whale species. Taken together, genetic evidence from specimens in Japan and across the North Pacific, combined with evidence of smaller adult body size, indicate presence of an unnamed species of Berardius in the North Pacific.

Humpback whales feed on a variety of prey, but significant differences likely occur between regional feeding grounds. In this study, the diets of humpback whales were analyzed by comparing stable isotope ratios in animal tissues at three humpback whale feeding grounds in the Russian Far East: Karaginsky Gulf, Anadyr Gulf, and the Commander Islands. Anadyr Gulf is a neritic zone far from a shelf break, Karaginsky Gulf is a neritic zone close to a shelf break, and the Commander Islands represent an open oceanic ecosystem where whales feed off the shelf break. Samples

Genetic analysis of 49 biopsy samples from North Pacific right whales Eubalaena japonica in the eastern (48) and western (1) North Pacific revealed 24 individual whales with 7 mitochondrial haplotypes. Three pairs of large and small individuals were identified in the field; genotype analysis indicated that 2 of these could represent motheroffspring pairs; for the third small individual, no sampled female genetically qualified as a potential mother. In aggregate, the population appears to have lost some genetic diversity, though not to the degree of North Atlantic right whales E. glacialis, and males outnumber females 2:1. A comparison of the eastern Pacific samples to a single Russian sample suggested that the 2 populations are isolated to some degree. The effective population size for the eastern North Pacific was calculated to be 11.6 (95% CI: 2.9�75.0), based on the estimated linkage disequilibrium. These results further indicate that this population is at immediate risk of extirpation.

The role of environmental limitation and density-dependent regulation in shaping populations is debated in ecology. Populations at low densities may offer an unobstructed view of basic environmental and physiological interactions that impact individual fitness and thus population productivity. The energy reserves of an organism are reflected in its body condition, a measure linking individual fitness and the environment. From 1997 to 2007, we monitored the critically endangered western gray whale (Eschrichtius robustus) population on its primary summer feeding ground off the northeastern coast of Sakhalin Island, Russia. This effort resulted in a large data set of photo-identification images from 5,007 sightings of 168 individual whales that we used to visually assess western gray whale body condition. We quantified temporal variation in the resulting 1,539 monthly body condition determinations with respect to observations of reproductive status and sex. Western gray whale body condition varied annually, and we identified years of significantly better (2004) and worse (1999, 2006, and 2007) body condition. This study is the 1st to track the within-season body condition of individual whales. Body condition improved significantly as the summer progressed, although results suggest that not all whales replenish their energy stores by the end of the season. The body condition of lactating females was significantly worse than that of other whales at all times and was most often determined to be compromised. The body condition of their weaning calves exhibited no temporal variation and was consistently good. It is possible lactating females provide an energetic buffer to their offspring at the expense of their own body condition and future reproductive success. Findings from the analysis establish a foundation for quantifying links between western gray whale body condition, demographic parameters, and environmental conditions; and provide a baseline for monitoring individual and population condition of an ecosystem sentinel species in a changing environment. Overall, this study highlights the presence of density-independent environmental and physiological mechanisms that affect the abundance and growth of populations.

Northern sea otter (Enhydra lutris kenyoni) abundance has decreased dramatically over portions of southwest Alaska, USA, since the mid-1980s, and this stock is currently listed as threatened under the Endangered Species Act. In contrast, adjacent populations in south central Alaska, USA, and Russia have been stable to increasing during the same period. Sea otters bordering the area classified in the recent decline were live-captured during 2004-2006 at Bering Island, Russia, and the Kodiak Archipelago, Alaska, USA, to evaluate differences in general health and current exposure status to marine and terrestrial pathogens. Although body condition was lower in animals captured at Bering Island, Russia, than it was at Kodiak, USA, clinical pathology values did not reveal differences in general health between the two regions. Low prevalences of antibodies (5%) were found in Kodiak, USA, and on Bering Island, Russia, to Toxoplasma gondii, Sarcocystis neurona, and Leptospira interrogans. Exposure to phocine herpesvirus-1 was found in both Kodiak, USA (15.2%), and Bering Island, Russia (2.3%). Antibodies to Brucella spp. were found in 28% of the otters tested on Bering Island, Russia, compared with only 2.7% of the samples from Kodiak, USA. Prevalence of exposure to Phocine distemper virus (PDV) was 41% in Kodiak, USA, but 0% on Bering Island, Russia. Archived sera from southwest and south-central Alaska dating back to 1989 were negative for PDV, indicating exposure occurred in sea otters in Kodiak, USA, in recent years. Because PDV can be highly pathogenic in naïve and susceptible marine mammal populations, tissues should be examined to explore the contribution of this virus to otter deaths. Our results reveal an increase in exposure to pathogens in sea otters in Kodiak, Alaska, USA, since the 1990 s.

We estimated the abundance of humpback whales in the North Pacific by capture-recapture methods using over 18,000 fluke identification photographs collected in 2004–2006. Our best estimate of abundance was 21,808 (CV = 0.04). We estimated the biases in this value using a simulation model. Births and deaths, which violate the assumption of a closed population, resulted in a bias of +5.2%, exclusion of calves in samples resulted in a bias of −10.5%, failure to achieve random geographic sampling resulted in a bias of −0.4%, and missed matches resulted in a bias of +9.3%. Known sex-biased sampling favoring males in breeding areas did not add significant bias if both sexes are proportionately sampled in the feeding areas. Our best estimate of abundance was 21,063 after accounting for a net bias of +3.5%. This estimate is likely to be lower than the true abundance due to two additional sources of bias: individual heterogeneity in the probability of being sampled (unquantified) and the likely existence of an unknown and unsampled breeding area (−8.7%). Results confirm that the overall humpback whale population in the North Pacific has continued to increase and is now greater than some prior estimates of prewhaling abundance.

Killer whales produce repertoires of stereotyped call types that are primarily transmitted vertically through social learning, leading to dialects between sympatric pods. The potential function of these call repertoires remains untested. In this study, we compared the reaction of Kamchatkan fish-eating killer whales to the playbacks of calls from the same and different pods. After the playback of recordings from a different pod, in three cases whales changed the direction of their movement toward the boat, and in three cases no changes in direction were observed. After the playback of recordings from the same pod (either from the same or a different unit within the pod), in seven cases whales changed the direction of their movement toward the boat, and in only one case no change in direction was observed. Whales remained silent after all six playbacks of recordings from a different pod, even when they changed direction toward the boat. After the playback of recordings from the same pod, however, in all eight cases whales started calling in response. Our playback study shows that killer whales may react to playbacks of conspecific sounds and that reactions are dependent on the type of playback stimuli.

Gray whales (Eschrichtius robustus) are extant only in the North Pacific Ocean, where they exist as an abundant eastern and a critically endangered western population. Long-term monitoring of individual gray whales, including young of the year (calves), is conducted in several localities and has produced important results on the distribution, abundance, and demography of both populations (e.g., Weller et al. 1999, Calambokidis et al. 2002, Urban R. et al. 2003). Many of these studies use photo-identification methods, as all gray whales are individually identifiable

Steller sea lions (Eumetopias jubatus) have experienced a decline in Russia as well as the United States. The causes for the decline of the Russian population may or may not overlap the causes of the decline in Alaska. The demographics of the Russian population are not well understood and are an area of interest for scientists wishing to compare and contrast the Alaskan and Russian stocks. This study uses a unique observational system to assess survival by age at a small rookery on the Kamchatka Peninsula, Kozlova Cape. We proceeded under the hypothesis that changes in environmental conditions between years would produce noticeable differences in survival of pups born in those years. We found no evidence to support our hypothesis, but did find some differences from the Alaskan population in estimated survival for the juvenile stage class. This study also provides some of the history of Steller sea lions in Russia for context.

Western gray whales (Eschrichtius robustus) are critically endangered and anthropogenic threats, such as entanglement in fishing gear and collisions with vessels, may be acting to limit recovery of the population. Thus, examining the magnitude of such anthropogenic interactions using a scar-based approach is warranted. A multi-year (1995-2005) photo-identification study of western gray whales on their feeding ground off northeastern Sakhalin Island, Russia, has resulted in a large data set of digital and film images of 150 individuals. These images were reviewed and scored for anthropogenic scarring by recording the presence of visible scars resulting from fishing gear entanglement and vessel collisions in 21 defined body regions. In total, 20.0% (n = 30) of whales identified during the study period had detectable anthropogenic scarring, with 18.7% (n = 28) determined to have been previously entangled in fishing gear at least once and 2.0% (n = 3) to have survived at least one vessel collision. These estimates are likely to be conservative given the nature of the photo-identification data set, but indicate that male and female western gray whales are subject to anthropogenic interactions. Future studies designed to systematically estimate the frequency and rates of anthropogenic events are needed and would have direct conservation and management implications.

The western population of gray whales Eschrichtius robustus is one of the most endan- gered whale populations in the world. Recent studies of this population off the northeastern coast of Sakhalin Island, Russia, have produced a photographic dataset that was utilized for the first mark- recapture assessment of western gray whale abundance. Given encounter histories of 129 individu- ally identified whales spanning 25 monthly capture occasions from 1997 to 2003, a closed capture estimator was employed to estimate the number of individuals using the study area in each year. Temporary emigration probabilities were then applied to the closed capture estimates to enumerate the total population size of whales off northeastern Sakhalin Island. Total abundances from 1997 to 2003 were estimated as 64 ± 5.1 (SE), 55 to 75 (95% CI); 75 ± 4.9, 66 to 85; 86 ± 3.1, 80 to 93; 77 ± 4.7, 68 to 87; 91 ± 3.4, 84 to 98; 98 ± 4.1, 90 to 106; and 99 ± 4.9, 90 to 109, respectively. These abundance estimates, particularly the last values in the series, most likely approximate the size of the entire west- ern gray whale population. For comparison to the trend in the abundance estimates, life history data were used to estimate the growth rate of the population. Depending on the range of potential fecundity values incorporated, the resulting growth rate estimates indicate an annual population increase that is between 2.5 and 3.2%. The extremely small population size and slow rate of increase documented here further highlight concern about the viability of this critically endangered population.

Springer et al. (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using a regional approach, we reexamined whale catch data, killer whale predation observations, and the current biomass and trends of potential prey, and found little support for the prey-switching hypothesis. Large whale biomass in the Bering Sea did not decline as much as suggested by Springer et al., and much of the reduction occurred 50–100 yr ago, well before the declines of pinnipeds and sea otters began; thus, the need to switch prey starting in the 1970s is doubtful. With the sole exception that the sea otter decline followed the decline of pinnipeds, the reported declines were not in fact sequential. Given this, it is unlikely that a sequential megafaunal collapse from whales to sea otters occurred. The spatial and temporal patterns of pinniped and sea otter population trends are more complex than Springer et al. suggest, and are often inconsistent with their hypothesis. Populations remained stable or increased in many areas, despite extensive historical whaling and high killer whale abundance. Furthermore, observed killer whale predation has largely involved pinnipeds and small cetaceans; there is little evidence that large whales were ever a major prey item in high latitudes. Small cetaceans (ignored by Springer et al.) were likely abundant throughout the period. Overall, we suggest that the Springer et al. hypothesis represents a misleading and simplistic view of events and trophic relationships within this complex marine ecosystem.

The late Pleistocene extinction of so many large-bodied vertebrates has been variously attributed to two general causes: rapid climate change and the effects of humans as they spread from the Old World to previously uninhabited continents and islands. Many large-bodied vertebrates, especially large apex predators, maintain their associated ecosystems through top-down forcing processes, especially trophic cascades, and megaherbivores also exert an array of strong indirect effects on their communities. Thus, a third possibility for at least some of the Pleistocene extinctions is that they occurred through habitat changes resulting from the loss of these other keystone species. Here we explore the plausibility of this mechanism, using information on sea otters, kelp forests, and the recent extinction of Steller's sea cows from the Commander Islands. Large numbers of sea cows occurred in the Commander Islands at the time of their discovery by Europeans in 1741. Although extinction of these last remaining sea cows during early years of the Pacific maritime fur trade is widely thought to be a consequence of direct human overkill, we show that it is also a probable consequence of the loss of sea otters and the co-occurring loss of kelp, even if not a single sea cow had been killed directly by humans. This example supports the hypothesis that the directly caused extinctions of a few large vertebrates in the late Pleistocene may have resulted in the coextinction of numerous other species.

Gray whales Eschrichtius robustus exist as 2 geographically and genetically distinct pop- ulations in the eastern and western North Pacific. Subjected to intensive commercial whaling during the 19th and 20th centuries, the western population presently numbers approximately 100 individuals and is regarded as one of the most endangered baleen whale populations in the world. Since 1997, ongoing studies of western gray whales have resulted in a photographic dataset that can be used for mark-recapture survival estimation. Pollock's robust design was applied to 129 individual whale encounter histories spanning 25 monthly capture occasions from 1997 to 2003. Using Akaike's Infor- mation Criterion (AICc) model selection, models incorporating individual heterogeneity in residency patterns and higher temporary emigration probabilities for younger whales provided better fits to the data. Non-calf and calf (1st year post-weaning) survival were estimated as 0.951 (SE = 0.0135, 95% CI = 0.917 to 0.972) and 0.701 (SE = 0.0944, 95% CI = 0.492 to 0.850), respectively, averaging across the best models (n = 13) in order to account for model uncertainty. The non-calf survival point estimate is similar to mark-recapture estimates for Gulf of Maine humpback whales, but lower than an indirect estimate for the eastern gray whale population. Although no statistically robust direct estimates of baleen whale calf survival exist for comparison to the current study, the calf survival estimate is markedly lower than a value suggested for Gulf of Maine humpback whales. Estimation of survival is necessary for assessing the status of western gray whales, which can contribute to increased protec- tion, conservation, and management planning for this critically endangered population.

Skulls and canines of 460 sea otters from Lopatka Cape, Kamchatka, were examined to assess development patterns, individual variation and sexual differences. An allometric formula was applied to morphometrical data, and the relative growth of each character to total length of skull was analyzed. In both sexes, most morphometrical characters ceased growth at about 2 years of age. Canine root length increased rapidly during the first year of life, while crown length decreased due to remarkable wear. There was large individual variation in the feeding and breathing/sniffing apparatus, while there was little variation in braincase size. There were sexual differences in most characteristics, although males and females showed similar growth patterns. The coronoid process of the mandible showed positive allometry in both sexes, and we attributed this finding to feeding habits. The fact that only male mastoids showed positive allometry may be due to the need for male otters to maintain a passing territory.

Historical specimens of sea otters (Enhydra lutris) provide valuable information about the pre-bottleneck population. However, the sex of these specimens is often not known. We attempted to determine the sex of sea otters by means of polymerase chain reaction (PCR) amplification of the amelogenin and the zinc finger (ZFX/ZFY) regions. The PCR fragments of amelogenin amplified were same size regardless of the sex. On the other hand, we were able to distinguish the sex accurately by means of the sea otter-specific restriction enzyme (NlaIII) to digest a polymorphic site in the ZFX/ZFY region. This method was applicable to dental pulp from skull specimens with the use of novel inner primers (KH1/KH2). We suggest that with some modification, the ZFX/ZFY system can be applied to other species and to a variety of archaeological specimens.

We used 742 beach-cast carcasses to characterize age- and sex-specific sea otter mortality during the winter of 1990-1991 at Bering Island, Russia. We also examined 363 carcasses recovered after the 1989 grounding of the T/V Exxon Valdez, to characterize age and sex composition in the living western Prince William Sound (WPWS) sea otter population. At Bering Island, mortality was male-biased (81%), and 75% were adults. The WPWS population was female-biased (59%) and most animals were subadult (79% of the males and 45% of the females). In the decade prior to 1990-1991 we found increasing sea otter densities (particularly among males), declining prey resources, and declining weights in adult male sea otters at Bering Island. Our findings suggest the increased mortality at Bering Island in 1990-1991 was a density-dependent population response. We propose male-maintained breeding territories and exclusion of juvenile females by adult females, providing a mechanism for maintaining densities in female areas below densities in male areas and for potentially moderating the effects of prey reductions on the female population. Increased adult male mortality at Bering Island in 1990-1991 likely modified the sex and age class structure there toward that observed in Prince William Sound.

The annual return, seasonal occurrence, and site fidelity of Korean-Okhotsk or western gray whales on their feeding grounds off northeastern Sakhalin Island, Russia, were assessed by boat-based photo-identification studies in 1994-1998. A total of 262 pods were observed, ranging in size from 1 to 9 whales with an overall mean of 2.0. Sixty-nine whales were individually identified, and a majority of all whales (71.0%) were observed in multiple years. Annual sighting frequencies ranged from 1 to 18 d, with a mean of 5. 4 d. The percentage of whales reidentified from previous years showed a continuous annual increase, reaching 87.0% by the end of the study. Time between first and last sighting of identified individuals within a given year was 1-85 d, with an overall mean of 40.6 d. Annual calf proportions ranged from 4.3% (1997) to 13.2% (1998), and mother-calf separations generally occurred between July and September. The seasonal site fidelity and annual return of whales to this part of the Okhotsk Sea emphasize its importance as a primary feeding ground for this endangered population.

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 (988 bp) 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.

Univariate and multivariate analyses of 20 skull characters of 304 adult sea otters from throughout the geographic range strongly suggest that three subspecies should be recognized. The nominate form, Enhydra lutris lutris , occurs from the Kuril Islands north to the Commander Islands in the western Pacific Ocean. Individuals of E. l. lutris are characterized by large size and wide skulls with short nasal bones. E. l. nereis is found along the California coast and off San Nicolas Island, where the species recently has been reintroduced from coastal California. Specimens of E. l. nereis have narrow skulls with a long rostrum and small teeth, and usually lack the characteristic notch in the postorbital region found in most specimens of the other two subspecies. A new subspecies described by Don E. Wilson in this report, occurs throughout the Aleutian Islands and southward in the eastern Pacific to Washington. Specimens of the new subspecies are intermediate in size in most, but not all, characters and have longer mandibles than either of the other two subspecies.

Skulls and canines of 460 sea otters from Lopatka Cape, Kamchatka, were examined to assess development patterns, individual variation and sexual differences. An allometric formula was applied to morphometrical data, and the relative growth of each character to total length of skull was analyzed. In both sexes, most morphometrical characters ceased growth at about 2 years of age. Canine root length increased rapidly during the first year of life, while crown length decreased due to remarkable wear. There was large individual variation in the feeding and breathing/sniffing apparatus, while there was little variation in braincase size. There were sexual differences in most characteristics, although males and females showed similar growth patterns. The coronoid process of the mandible showed positive allometry in both sexes, and we attributed this finding to feeding habits. The fact that only male mastoids showed positive allometry may be due to the need for male otters to maintain a passing territory.