The International Whaling Commission’s Scientific Committee conducts regular Implementation Reviews (IRs) of the biology, threats and status of whale species subject to aboriginal subsistence whaling. The last IR of plans for hunting eastern North Pacific (ENP) gray whales by the Chukotka Natives of the Russian Federation and the Makah Tribe of the United States of America occurred in 2020. This paper presents a review of new scientific findings on gray whales to assess whether the current status of the stock(s) is within the parameter space tested in the 2020 IR. Updated information on gray whale stock structure hypotheses, abundance and calf productivity, health and strandings, human removals by hunting and non‐hunting sources, population growth rates, immigration into the Pacific Coast Feeding Group, parameterisation of the Makah hunt, and future episodic mortality events (EMEs) were reviewed for this assessment. For almost all factors, it appears that the current dynamics of the ENP gray whale population are within the parameter space evaluated in 2020 IR. The exception is that EMEs affecting whales in the ENP are occurring more frequently and at a greater magnitude than previously evaluated. However, preliminary evaluations suggest that the performances of the Gray Whale Strike Limit Algorithm (SLA) and Makah Management Plan are robust to recent and future EMEs of Northern Feeding Group gray whales and reductions of productivity of the Pacific Coast Feeding Group, at least under the initial parameterisations. We therefore conclude that there is no compelling need for a Special IR prior to the next scheduled IR in 2026, while noting that additional abundance data for 2022/23 and 2023/24 analysed after drafting this paper could strengthen or weaken the evidence for this conclusion.

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.

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.

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.

AbstractGray whale sexual behavior and copulation are observed throughout their range. The most prominent period for reproductive behavior is during the southward migration from summer feeding areas to wintering areas where some breeding occurs and calves of the year are reared. The seasonal migrations of gray whales are believed to function, in part, to bring together individuals that are otherwise widely distributed during the period of estrus to facilitate mating and reproduction. Sexual behaviors and sexual strategies for this species appear to align closely with those of balaenid (not rorqual) whales, although such comparisons need further investigation. Gray whales are polygynandrous (multi-mate) breeders. There does not appear to be female choice of mates, as groups of numerous females and males aggregate, and multiple copulations occur. Female estrus begins in mid-November and continues to early December; females may undergo a second estrus, extending into February, if they fail to conceive during their first cycle. Male gray whales have large testes and concomitantly produce large volumes of sperm, so they are believed to be sperm competitors; that is, they rely on multiple copulations (and sperm volume) to produce offspring. Multiple copulations with different males during the female estrus period may increase the likelihood that the timing of conception results in the birth of a calf approximately 13 months later near or in the wintering area(s). Mating bouts can last for minutes to hours, interspersed with surface-active-social-sexual behavior. Some all-male groups have been observed with erect penises engaged in social-sexual behavior in the absence of any females. Instances of male aggression toward postpartum females with calves of the year, sometimes resulting in injury or death, have been reported. As a result of dedicated long-term research in the past several decades, the state of knowledge on gray whale reproduction has greatly expanded and updated information on this topic is summarized in this chapter.

Humpback whales Megaptera novaeangliae undertake extensive annual migrations, have complex migratory patterns, and have held several mammalian long-distance movement records. Here, we report on a whale known to feed in the Russian Far East that was sighted in breeding areas on either side of the North Pacific, the Mariana Islands and Mexico, in less than 1 yr (357 d apart). This is the longest published distance (11261 km great-circle route) between 2 unique sightings of a photo-identified humpback whale to date. To understand the context of this movement, we investigated records of whales that had been sighted in Russian feeding areas and Mexican breeding areas using historic and newly available photo-identification data. We found 117 humpback whales documented in both countries between 1998 and 2021, revealing a substantial increase from the only 11 matches that were previously known. These whales exhibited high site fidelity to Mexico, with one-third seen in multiple years, and up to 10 yr. However, we also found that they changed breeding areas more frequently than Mexico whales matched to other feeding areas, illustrating how the Mariana Islands-Mexico movement may have occurred. We document the first complete round-trip migrations between Mexico and Russia, a journey of >16400 km, the longest known migration of Northern Hemisphere humpback whales. Our data demonstrate regular trans-Pacific movements of humpback whales in the North Pacific, highlighting the importance of Mexico for the species ocean-basin-wide and the need for effective local management to aid in the conservation of multiple at-risk distinct population segments.

Cetacean species are highly mobile, most of them regularly travelling over long distances, thereby presenting complex obstacles to their conservation. Identification of their critical habitats, specifically those parts of a cetacean's range that are essential for day-to-day survival and for maintaining a healthy population growth rate, is necessary for their effective protection. This study presents a summary of the data on cetacean sightings during surveys that covered substantial parts of the Russian Far East coastal waters from the Okhotsk Sea to Chukotka in order to determine important areas for particular cetacean species. Sixteen cetacean species were registered during the surveys, and for 12 of them with sufficient numbers of sightings, zones with maximum sighting rates were identified. Only 13% of all cetacean sightings and 22% of sightings of protected species occurred within marine protected areas (MPAs). The highest sighting rates for protected species were concentrated off north-eastern Sakhalin Island, in the Shantar Area, in Anadyr Gulf, in Kresta Bay and in the waters off eastern Chukotka. The analysis of the distribution patterns of various cetacean species in Russian Far East seas provides a solid base for future conservation planning. Lack of specific MPAs for protection of cetaceans and associated biodiversity hinders marine conservation in Russian Far East seas. The study highlights the specific zones important for various cetacean species and suggests the extension of some existing MPAs and the creation of new MPAs for future spatial habitat protection measures.

Steller’s sea cow, an extinct sirenian and one of the largest Quaternary mammals, was described by Georg Steller in 1741 and eradicated by humans within 27 years. Here, we complement Steller’s descriptions with paleogenomic data from 12 individuals. We identified convergent evolution between Steller’s sea cow and cetaceans but not extant sirenians, suggesting a role of several genes in adaptation to cold aquatic (or marine) environments. Among these are inactivations of lipoxygenase genes, which in humans and mouse models cause ichthyosis, a skin disease characterized by a thick, hyperkeratotic epidermis that recapitulates Steller’s sea cows’ reportedly bark-like skin. We also found that Steller’s sea cows’ abundance was continuously declining for tens of thousands of years before their description, implying that environmental changes also contributed to their extinction.

Recent findings that some gray whales that feed off Sakhalin Island (SI), Russia, in the western North Pacific (WNP) overwinter in the eastern North Pacific (ENP) indicate that population structure in this species is more complex than originally thought. We generated mitochondrial DNA (mtDNA) control region sequences and microsatellite genotypes (n = 12 loci) from 156 whales sampled off SI and compared them to available data from 106 ENP whales. Significant mitochondrial and nuclear genetic differentiation between the SI and ENP whales was found. Genetic cluster analysis identified two groups among the SI whales, one of which was genetically similar to ENP whales. Photographs collected from the biopsied SI whales showed that both groups comprised whales known to migrate to the ENP, suggesting that the clustering pattern was not reflective of some SI whales interbreeding while overwintering in the WNP. Instead, the genetic differentiation observed between the SI and ENP whales may be due to assortative mating of SI whales while west of eastern migratory routes. The rare but continued reports of gray whales off the coasts of Japan and China, however, confirm that some gray whales overwinter in the WNP and highlight the need to collect additional data from these whales.

Sea otter (Enhydra lutris) populations in southwest Alaska declined substantially between about 1990 and the most recent set of surveys in 2015. Here we report changes in the distribution and abundance of sea otters, and covarying patterns in reproduction, mortality, body size and condition, diet and foraging behavior, food availability, health profiles, and exposure to environmental contaminants over this 25-yr period. The population decline, which resulted in densities on the order of 5% of environmental carrying capacity, ranged from Attu Island in the west to about Castle Cape (on the south side of the Alaska Peninsula) in the east. Remaining sea otters moved closer to shore and into shallow, protected habitats. Reproductive rates appeared unchanged with the decline. Although the demographic cause of the decline was clearly elevated mortality, stranded carcasses were rare or absent. The net rate of energy gain by foraging sea otters, body length and condition, and prey biomass density, all increased after the decline and varied inversely with sea otter population density beyond the area of decline. Sea otters within the area of decline showed no increases in health anomalies, disease, contaminant exposure, or abnormal gene transcription patterns as compared to animals outside the area of decline. These collective findings are inconsistent with nutritional limitation, disease, or environmental contaminants, and consistent with predation (or possibly some other density-independent factor) as the reason for the sea otter population decline. Our approach and analyses provide a broad conceptual template for thinking about and assessing the causes of wildlife population declines.

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 < 0.001). No significant difference was observed between sexes. Notable disparities in contaminant levels between ecotypes support the major toxicological theories of contaminant bioaccumulation and dietary impacts on individual contaminant load.

Mitochondrial DNA (mtDNA) differences between humpback whales on different feeding grounds can reflect the cultural transmission of migration destinations over generations, and therefore represent 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 interchange between 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 single Russian feeding ground. Here, we assessed whether genetic differentiation exists between these 2 groups of humpback whales. We discovered a strong mtDNA differentiation between the 2 feeding 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 results with those from a previous ocean-basin study reinforced the differences between the 2 feeding sites. Humpback whales from the Commanders appeared most similar to those of the western Gulf of Alaska and the Aleutian feeding grounds, whereas Karaginsky differed from all other North Pacific feeding grounds. Comparison to breeding grounds suggests mixed origins for the 2 feeding sites; there are likely connections between Karaginsky and the Philippines and to a lesser extent to Okinawa, Japan, whereas the Commanders are linked to the Mexican breeding grounds. The mtDNA differentiation between the Commander Islands and Karaginsky Gulf suggests a case of gene-culture coevolution, correlated to fidelity to a specific feeding site within a particular feeding ground. From a conservation perspective, our findings emphasize the importance of considering these 2 feeding sites as separate management units.

The population assessment of gray whales Eschrichtius robustus feeding off Sakhalin and Kamchatka is updated, using a population model that alows for multiple feeding and breeding areas. The model is fit to photo-id data collected of Sakhalin during 1995-2015 (Burdin et al. 2015), tracking of whales from Sakhalin to the eastern North Pacific (Mate et al. 2015), photo-id matches of gray whales between the Sakhalin and Mexico catalogues (Urbán et al. 2013) and reported photo-id results from Kamchatka collected during 2004-12 (Yakovlev et al. 2013),. The results show that the Sakhalin and Kamchatka feeding populations have been increasing at 2-5% per year over the 10 or 20 years to 2015. The number of non-calf whales in 2016 is estimated to be 320−410, of which 130−170 are predominantly Sakhalinfeeding whales or 180−220 are whales that feed at least occasionally off Sakhalin. A test of the population model output against the results of a paternity analysis by Lang (2010) just rejects the hypothesis of genetic closure of the Sakhalin feeding population (p < 0.05) but does not reject the hypothesis of genetic closure of the Sakhalin and Kamchatka feeding populations combined. Of the predominantly Sakhalin-feeding whales, an estimated 0-50 belong to a possible relict western North Pacific breeding population (which may or may not be genetically closed). Using the IUCN Red List criteria, the Sakhalin and Kamchatka populations, if assessed as a subpopulation, either separately or together, would be classified as Endangered, on the basis of there being between 50 and 250 mature individuals (i.e. ~100-500 individuals when juveniles but not calves are included). If the relict western North Pacific breeding population were assessed as a subpopulation, it would be classified as Critically Endangered, on the basis of there being less than 50 mature individuals.

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.

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.

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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 showthat 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.

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.