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The Chukchi Sea environment changes considerably in physical and biological conditions, driven by the expanding volume of warm Pacific summer water. These environmental changes can affect the migration timing of baleen whales in the southern Chukchi Sea. However, few studies have been conducted in this area to determine the migration timing of bowhead whales (Balaena mysticetus), the only baleen whale species endemic to the Arctic region. In this study, we conducted a fixed passive acoustic monitoring of bowhead whales in the southern Chukchi Sea from July 2012 to October 2015 and compared the occurrence patterns of vocalizations to physical and biological environmental factors. Bowhead whale calls were detected in fall/winter and spring during the ice-freezing and retreating periods, respectively. The fall migration timing of bowhead whales through the southern Chukchi Sea was delayed in the years when the timing of sea ice formation was late, and it formed increasingly later in the years 2013, 2014, and 2012, in that sequence. Moreover, the sea surface temperature decreased before freeze-up, which affected the timing of fall migration of bowhead whales. There was no clear relationship between the occurrence of bowhead whale calls and the abundance of prey, especially in spring, suggesting that most bowhead whales use the southern Chukchi Sea as a corridor during their spring northward migrations. However, the occurrence of bowhead whales and high abundance of zooplankton in October–November present the possibility that bowhead whales expand their feeding area in the southern Chukchi Sea.

An ice-based visual survey of the Bering-Chukchi-Beaufort Seas stock of bowhead whales (Balaena mysticetus) was conducted in spring 2019 near Utqiaġvik (formerly Barrow), Alaska. A Horvitz-Thompson-type estimator is used to estimate population abundance from the resulting data, correcting for detection probabilities, whale availability within visual range, and whale passage during periods of missed effort. Analytical methods mirror those used by Givens et al. (2016) for the 2011 survey as much as possible; however, unlike 2011, no simultaneous acoustic monitoring was conducted in 2019, so the availability correction factor had to be estimated from past years. The estimated abundance was 12,505 with 95% confidence interval of (7,994, 19,560) and a CV of 0.228. This estimated abundance is markedly lower than the 2011 estimate of 16,820, but the 2019 confidence interval wholly encompasses the 2011 interval. We do not interpret this finding as evidence of a decline for many reasons including: highly unusual ice conditions, an unusual migration route that was sometimes too distant from observers to detect whales, failure to conduct watch because of closed leads during the early weeks of the migration when numerous whales likely passed, an unusually short perch, and hunters’ heavy use of powered skiffs near the observation perch which likely disturbed the whales during the survey. Furthermore, bowhead health assessment information for 2019 suggests that harvested bowheads did not exhibit obvious reductions in health condition, and aerial surveys in summer 2019 indicated high calf production (Stimmelmayr et al. 2020). Despite the challenges of the 2019 survey, the estimate is adequate for use with the International Whaling Commission’s management procedure and complies with the survey requirements of the Aboriginal Whaling Scheme.

In a species of baleen whale, we identify olfactory epithelium that suggests a functional sense of smell and document the ontogeny of the surrounding olfactory anatomy. Whales must surface to breathe, thereby providing an opportunity to detect airborne odorants. Although many toothed whales (odontocetes) lack olfactory anatomy, baleen whales (mysticetes) have retained theirs. Here, we investigate fetal and postnatal specimens of bowhead whales (Balaena mysticetus). Computed tomography (CT) reveals the presence of nasal passages and nasal chambers with simple ethmoturbinates through ontogeny. Additionally, we describe the dorsal nasal meatuses and olfactory bulb chambers. The cribriform plate has foramina that communicate with the nasal chambers. We show this anatomy within the context of the whole prenatal and postnatal skull. We document the tunnel for the ethmoidal nerve (ethmoid foramen) and the rostrolateral recess of the nasal chamber, which appears postnatally. Bilateral symmetry was apparent in the postnatal nasal chambers. No such symmetry was found prenatally, possibly due to tissue deformation. No nasal air sacs were found in fetal development. Olfactory epithelium, identified histologically, covers at least part of the ethmoturbinates. We identify olfactory epithelium using six explicit criteria of mammalian olfactory epithelium. Immunohistochemistry revealed the presence of olfactory marker protein (OMP), which is only found in mature olfactory sensory neurons. Although it seems that these neurons are scarce in bowhead whales compared to typical terrestrial mammals, our results suggest that bowhead whales have a functional sense of smell, which they may use to find prey.

Full mitochondrial genomes were assembled for 12 recently sampled animals from the Svalbard bowhead whale (Balaena mysticetus) stock via high-throughput sequencing data, facilitating analysis of the demographic history of the population for the first time. The Svalbard population has retained noticeable amounts of mitochondrial genome diversity despite extreme historical harvest levels. Haplotype and nucleotide diversities were similar to those estimated earlier for other bowhead whale populations. The reconstructed demographic history was in accordance with a boom–bust scenario, combining a slight Pleistocene population growth 25 000–35 000 years ago and a Holocene decline. Employing a mutation rate of 3.418 × 10–8 substitutions per site per year, the time to the most recent common ancestor for the mitochondrial genomes of the contemporary Svalbard bowhead whales was estimated to be 68 782 (54 353–83 216) years before the present. Based on 370 bp fragments of the D-loop region, significant genetic differentiation was detected between all extant bowhead whale populations across the circumpolar Arctic. Thus, the Svalbard bowhead whales can be regarded as a population with its own genetic legacy.

We used satellite telemetry to examine bowhead whale movement behavior, residence times, and dive behavior in the Alaskan Beaufort Sea, 2006 – 18. We explored the timing and duration of use of three subregions (western, central, eastern) within the Alaskan Beaufort Sea and applied a two-state switching state-space model to infer bowhead whale behavior state as either transiting or lingering. Transiting whales made direct movements whereas lingering whales changed direction frequently and were presumably feeding. In spring, whales migrated across the Alaskan Beaufort Sea in 7.17 ± 0.41 days, primarily off the continental shelf over deep water. During the autumn migration, whales spent over twice as much time crossing the Alaskan Beaufort Sea than in spring, averaging 18.66 ± 2.30 days, spending 10.05 ± 1.22 days in the western subregion near Point Barrow. Most whales remained on the shelf during the autumn migration and frequently dove to the seafloor, where they spent 45% of their time regardless of behavioral state. Consistent dive behavior in autumn suggests that the whales were looking for food while migrating, and the identification of lingering locations likely reflects feeding. The lack of lingering locations in the eastern and central subregions suggests that prey densities are rarely sufficient to warrant whales pausing their migration for multiple days, unlike in the western subregion near Point Barrow, where bowhead whales regularly lingered for long periods of time.

Imagery and sighting data on bowhead whale (Balaena mysticetus) carcasses documented from 2009 to 2018 during aerial surveys in the eastern Chukchi and western Beaufort seas have provided evidence for killer whale (Orcinus orca) predation on bowhead whales of the Bering–Chukchi–Beaufort Seas stock. The Aerial Surveys of Arctic Marine Mammals (ASAMM) project provides information on distribution, behavior, and relative density of marine mammals. ASAMM surveys large areas of bowhead whale and killer whale summer and autumn habitat and offers consistent information on bowhead whale carcasses. Thirty-three bowhead whale carcasses were documented in July–October, from 2009 to 2018. Carcasses were distributed across the eastern Chukchi and western Beaufort seas from 141.6° W to 168.1° W and 68.9° N to 72.0° N. Carcass sighting rates (carcasses/1000 km) varied by month, year, and region. Statistical results suggest an alternating series of high and low annual carcass sighting rates. Eighteen bowhead whale carcasses having injuries consistent with probable killer whale predation were photo-documented: four each in 2016 and 2018, three each in 2013 and 2015, two in 2012, and one each in 2010 and 2017. Four carcasses, two in 2015 and one each in 2013 and 2018, were likely whales struck and lost during aboriginal subsistence hunting. Cause of death could not be determined for 11 carcasses. This study is the first systematic inquiry into non-harvest related mortality of bowhead whales in the U.S. Pacific Arctic and provides multi-year evidence for killer whale predation on bowhead whales in this portion of their range.

Bowhead whales are among the longest-lived mammals with an extreme lifespan of about 211 years. During the first 25 years of their lives, rib bones increase in mineral density and the medulla transitions from compact to trabecular bone. Molecular drivers associated with these phenotypic changes in bone remain unknown. This study assessed expression levels of osteogenic genes from samples of rib bones of bowheads. Samples were harvested from prenatal to 86-year-old whales, representing the first third of the bowhead lifespan. Fetal to 2-year-old bowheads showed expression levels consistent with the rapid deposition of the bone extracellular matrix. Sexually mature animals showed expression levels associated with low rates of osteogenesis and increased osteoclastogenesis. After the first 25 years of life, declines in osteogenesis corresponded with increased expression of EZH2, an epigenetic regulator of osteogenesis. These findings suggest EZH2 may be at least one epigenetic modifier that contributes to the age-related changes in the rib bone phenotype along with the transition from compact to trabecular bone. Ancient cetaceans and their fossil relatives also display these phenotypes, suggesting EZH2 may have shaped the skeleton of whales in evolutionary history.

This paper examines Neo-Inuit (ca. AD 1250 to present) responses to the decreased temperatures of the Little Ice Age (LIA) climate change episode (ca. AD 1300–1900) in the Foxe Basin region of central Nunavut, Arctic Canada. Cooler temperatures (and increased sea ice) would be expected to have reduced both bowhead whale (Balaena mysticetus) and Atlantic walrus (Odobenus rosmarus rosmarus) habitats, forcing Neo-Inuit to refocus their hunting activities on landfast-ice-dwelling small seals (e.g., Pusa hispida) during winter months. However, an analysis of faunal remains from Foxe Basin's largest-known Neo-Inuit (Thule, historic and modern Inuit) archaeological site, Pingiqqalik (NgHd-1), reveals a long-term subsistence economy based largely on multi-seasonal walrus hunting. Two interrelated factors may explain these results: (1) a system of recurring polynyas provided a degree of ecological stability for local walrus populations, and (2) the development of a distinctive walrus caching regime—a form of which continues among the region's contemporary Inuit—allowed residents to adeptly exploit an ecological niche, thereby ensuring food security. Together, these factors likely insulated northern Foxe Basin Neo-Inuit from the worst effects of the LIA.

Baleen, a unique oral α-keratin, has flat cortical layers enclosing hollow horn tubules. Baleen grows continuously to replace erosive loss from feeding-related wear. This is essential for maintaining efficient filtration over a whale’s long life history. Baleen fragments are seen in stomach contents and feces. We focused on fin (Balaenoptera physalus) and bowhead whales (Balaena mysticetus), but examined eleven mysticete species. Histological features including variably sized tubules plus differential growth along plate axes (growing faster along the medial fringed edge) and between plates of a rack (central plates growing faster than others) relate to baleen strength and flexibility. Sheet-like cortical layers provide strength and probably hinder erosive shedding, whereas medullary (tubular/intertubular) keratin provides flexibility and likely promotes shedding. To calculate amounts of grown/lost baleen, we considered both erosive wear and basal growth, recognizing that each plate represents several years of growth. We estimate average annual loss of 70–100,000 cm2 (20–40,000 cm3) of baleen in balaenids and 25–50,000 cm2 (7–14,000 cm3) in balaenopterids. Baleen growth rates depend on age, size, and other life history parameters; the most reliable calculations come from morphometric data with plate dimensions measured along full racks. We argue that baleen turnover has been under-rated and baleen growth rates underestimated in the published literature. Baleen turnover maintains filter integrity/porosity, while gut passage possibly clears gastrointestinal tracts of endoparasites. Large volumes of shed keratin hold potential ecological consequences by providing food for microbial decomposers and detritivores throughout ocean ecosystems, especially in polar regions where most mysticete feeding occurs.

—The bay waters of the Sea of Okhotsk near the Shantar Islands are the most important summer grazing areas for bowhead whales (Balaena mysticetus) of the Okhotsk population. A hydrobiological survey during the period from July 12–28th, 2016, demonstrated that waters around the Shantar archipelago are characterized by high concentrations of humic substance supplied by the peat-laden banks of rivers flowing into the bays. The average chlorophyll concentrations in bottom waters of Uda and Academy bays were 1.1 and 4.3 mg/m3, respectively. Uda and Academy bays are mainly considered heterotrophic and autotrophic basins, respectively. The measured zooplankton biomass in Uda Bay ranged from 9.5 to 2513 mg/m3, averaging 736 mg/m3; the corresponding characteristics in Academy Bay were 0.38 to 3620 mg/m3, averaging 458 mg/m3. In the Shantar water area, copepods of the species Calanus glacialis were the dominant contributor in terms of zooplankton biomass and species abundance. During early summer, nine bowhead whales were sighted south off Feklistov Island and lone whales were recorded in the North Strait and at the mouth of Nikolai Bay. The low density of polar whales in the Shantar water area in early summer may be due to the low zooplankton biomass after spring bloom and the last spawning.

The external acoustic meatus (EAM) of most baleen whales accumulates cellular debris annually in the lumen as whales age, forming a lamellated ear plug. The bowhead whale ear plug is formed from annually molting lining of the EAM as the entire epithelium releases at the level of the stratum basale during the spring migration. Epithelial regeneration is mostly completed by the fall migration, remaining intact for 6-7 months before being torn off the following spring. Desmosomes are integral to cell-cell adhesion with connecting desmosomal cadherins desmoglein (dsg) and desmocollin (dsc). Paraffin sections of the oral cavity and EAM lining of spring and fall adult bowhead whales, as well as the EAM of spring-caught juvenile, were immunohistochemically examined for the presence of these cadherins. In all fall specimens, both cadherins occurred in all layers except the superficial keratinous layer of the oral cavity. In spring, three different conditions existed: (a) oral cavity of spring-caught adults had reduced cadherins, with superficial fissuring in its keratinized layer and vacuolation in the upper stratum spinosum; (b) EAM of juvenile spring-caught whales displayed fissuring with accompanying reduction of both cadherins in its superficial lining; and (c) EAM lining of spring-caught adults displayed deep fissures, reduced cadherins, and absence of dsc1 in the fissuring zone. These results suggest that shedding of skin layers in mammals, whether normal molting, pathological, or the result of injury and wound repair all revolve around desmosome function. The specific role, structure, and location of these two cadherins need to be further addressed.

The availability of a food subsidy has the potential to influence the condition, behavior, fitness, and population dynamics of a species. Since the early 2000s, monitoring efforts along the coast of northern Alaska have indicated a higher proportion of polar bears (Ursus maritimus) of the southern Beaufort Sea (SB) subpopulation coming onshore to feed on subsistence-harvested bowhead whale (Balaena mysticetus) carcasses during the fall and early winter seasons. Concurrently, Indigenous communities annually hunt bowhead whale and deposit the unused remains at localized “bone piles,” creating the potential for human-bear interactions. Our objective was to determine the annual number of polar bears feeding at the bone pile near Kaktovik, Alaska. Using a hair snag surrounding the bone pile, we collected hair samples to identify individual bears via microsatellite genotypes during 2011 – 14. We used capture-mark-recapture data in the POPAN open-population model to estimate the number of bears visiting the bone pile. We estimated that as many as 72 (SE = 9) and 76 (SE = 10) male and female polar bears, respectively, used the bone pile located at Kaktovik, Alaska, in 2012, which represents approximately 16% of the SB polar bear subpopulation. It will be important to monitor the number of bears using the bone pile and subsequent human-bear interactions and conflicts along the northern coast of Alaska, if sea ice continues to recede.

Domoic acid (DA), the toxin causing amnesic shellfish poisoning (ASP), is produced globally by some diatoms in the genus Pseudo-nitzschia. DA has been detected in several marine mammal species in the Alaskan Arctic, raising health concerns for marine mammals and subsistence communities dependent upon them. Gastrointestinal matrices are routinely used to detect Harmful Algal Bloom (HAB) toxin presence in marine mammals, yet DA stability has only been studied extensively in shellfish-related matrices. To address this knowledge gap, we quantified DA in bowhead whale fecal samples at multiple time points for two groups: (1) 50% methanol extracts from feces, and (2) raw feces stored in several conditions. DA concentrations decreased to 70 ± 7.1% of time zero (T0) in the 50% methanol extracts after 2 weeks, but remained steady until the final time point at 5 weeks (66 ± 5.7% T0). In contrast, DA concentrations were stable or increased in raw fecal material after 8 weeks of freezer storage (−20 °C), at room temperature (RT) in the dark, or refrigerated at 1 °C. DA concentrations in raw feces stored in an incubator (37 °C) or at RT in the light decreased to 77 ± 2.8% and 90 ± 15.0% T0 at 8 weeks, respectively. Evaporation during storage of raw fecal material is a likely cause of the increased DA concentrations observed over time with the highest increase to 126 ± 7.6% T0 after 3.2 years of frozen storage. These results provide valuable information for developing appropriate sample storage procedures for marine mammal fecal samples.

We describe a case series of encapsulated fat necrosis with subcutaneous, abdominal, and thoracic locations in 7 subsistence-harvested bowhead whales Balaena mysticetus. Masses had a variably-dense fibrous capsule surrounding necrotic adipocytes and calcium salts (saponification). One animal also had prior concussive injury, pleural fibrosis, and hepatic lipoma; the other animals had no significant findings. The described condition is uncommon in bowhead whales, with 7/575 (1.2%) observed from 1996 to 2015. The exact mechanisms of development of encapsulated fat necrosis in bowhead whales remain to be determined. Encapsulated fat necrosis has been reported in other baleen whales, humans, and cows. It is usually an incidental finding during post-mortem examination that needs to be differentiated from neoplastic and inflammatory lesions, as the latter may have public health implications. Assessment of further cases in bowhead whales and other baleen whales is warranted to better understand their pathogenesis.

Funding for the ASAMM project is from Bureau of Ocean Energy Management (BOEM) Interagency Agreements M07RG13260 and M11PG00033 (C. Monnett, R. Denton, and C. Fairfield). Funding for the NOAA mooring and analysis is from BOEM: CHAOZ–M09PG00016 (C. Monnett and H. Crowley) and ARCWEST–M12PG00021 (C. Monnett, J. Denton, and H. Crowley). Funding for the UW mooring and analysis is from National Oceanographic Partnership Program (NOPP) Grant No. N00014-08-1-0311 and National Science Foundation (NSF) Grant Nos. ARC-0856244 and ARC-855828 to K.M.S. from the Office of Polar Programs of the NSF. T.A.M.’s time was covered by the Living Marine Resources (LMR) ACCURATE project (Contract No. N3943019C2176) and partial support by the Center of Statistics and its Applications (CEAUL) (funded by FCT–Fundação para a Ciência e a Tecnologia, Portugal, through Project No. UIDB/00006/2020). Eight years of passive acoustic data (2007–2014) from the Beaufort Sea were used to estimate the mean cue rate (calling rate) of individual bowhead whales (Balaena mysticetus) during their fall migration along the North Slope of Alaska. Calls detected on directional acoustic recorders (DASARs) were triangulated to provide estimates of locations at times of call production, which were then translated into call densities (calls/h/km2). Various assumptions were used to convert call density into animal cue rates, including the time for whales to cross the arrays of acoustic recorders, the population size, the fraction of the migration corridor missed by the localizing array system, and the fraction of the seasonal migration missed because recorders were retrieved before the end of the migration. Taking these uncertainties into account in various combinations yielded up to 351 cue rate estimates, which summarize to a median of 1.3 calls/whale/h and an interquartile range of 0.5–5.4 calls/whale/h. Publisher PDF

This study established the first baseline of changing elemental concentrations in bowhead whale baleen over time (1958–1999). From previously published stable isotope data, year, season (summer or winter), and location (Beaufort or Bering/Chukchi seas) were attributed to each sample. Thirteen elements (Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V, Zn) in baleen from nine subsistence-harvested bowhead whales (n = 138) were detected. Al, Cu, and Fe were the highest concentrations while Cd and V were among the lowest. Our data supports absorption as the main route of exposure to environmental elements rather than biomagnification due to bowhead whales’ low trophic position. A linear mixed-effects model confirmed most elements’ concentrations increased with time, while location and sex were insignificant explanatory factors. These temporal fluctuations were most likely a product of environmental changes due to a warming climate and human activities.

Bowhead whales (Balaena mysticetus) visit Disko Bay, West Greenland in winter and early spring to feed on Calanus spp., at a time of year when the copepods are still mostly in diapause and concentrated in near-bottom patches. Combining past observations of copepod abundance and distribution with detailed observations of bowhead whale foraging behaviour from telemetry suggests that if the whales target the highest-density patches, they likely consume 26–75% of the Calanus standing stock annually. A parallel bioenergetic calculation further suggests that the whales' patch selection must be close to optimally efficient at finding hotspots of high density copepods near the sea floor in order for foraging in Disko Bay to be a net energetic gain. Annual Calanus consumption by bowhead whales is similar to median estimates of consumption by each of three zooplankton taxa (jellies, chaetognaths, and predatory copepods), and much greater than the median estimate of consumption by fish larvae, as derived from seasonal abundance and specific ingestion rates from the literature. The copepods' self-concentration during diapause, far from providing a refuge from predation, is the behaviour that makes this strong trophic link possible. Because the grazing impact of the whales comes 6–10 months later than the annual peak in primary production, and because Disko Bay sits at the end of rapid advective pathways (here delineated by a simple numerical particle-tracking experiment), it is likely that these Calanus populations act in part as a long-distance energetic bridge between the whales and primary production hundreds or thousands of km away.

Bowhead whales (Balaena mysticetus) in the western Beaufort Sea (west of 140°W, south of 72°N) exhibit considerable spatiotemporal variability in distribution, density, and behavior that can be largely explained by variability in feeding opportunities, both local and remote. Bowhead whale feeding opportunities are dynamic and ephemeral, dependent on interannual variability driven by biological and physical forces. These insights were made possible by multidisciplinary investigations centered around the Aerial Surveys of Arctic Marine Mammals (ASAMM, https://www.fisheries.noaa.gov/alaska/marine-mammal-protection/aerial-surveys-arctic-marine-mammals ) time series, a long-term (1979–2019) dataset of line-transect surveys in the western Beaufort and eastern Chukchi Seas conducted during summer (July–August) and autumn (September–October). Seasonal patterns of bowhead whale distribution and density in the western Beaufort Sea during two time periods, prior to 2000 and since 2000, are evident in spatially explicit models of relative density that were created using ASAMM data. These models illustrate a general transition in bowhead distribution toward shallower waters as the open-water season (July–October) progresses. Notably, however, the location and number of high-density areas and the timing of the spatial transition have shifted between the two periods. The association between bowhead whales and sea ice in the western Beaufort Sea is rather enigmatic, as exemplified by the similarities in bowhead whale distribution in autumn 2019 (when sea ice retreat was extensive) with the distribution observed when sea ice extent was heavy in the 1980s and 1990s. Anthropogenic factors also affect bowhead whale distribution and density. The effects of anthropogenic and environmental factors on bowheads may be confounded, especially lacking sufficient understanding of the underlying environmental variability inherent in the ecosystem. Variability is a defining characteristic of the Arctic, but the parameters appear to be changing, sometimes in unexpected ways. Improving our understanding and capacity to predict arctic variability is fundamentally important to sound natural resource management. It follows that sound natural resource management is founded on continued monitoring of the ecosystem so that our understanding of the ecological linkages that shape animal distributions and densities tracks the changes occurring, and expected to continue to occur, in the Arctic.

The current subsistence harvest of bowhead whales (Balaena mysticetus) allows Inuit from Greenland, Canada, Alaska, and Chukotka to help fill important nutritional and cultural needs. Greenland and Canada primarily hunt from the East Canada–West Greenland stock and Alaska and Chukotka hunt from the Bering–Chukchi–Beaufort (BCB) Seas stock. There is no hunting on the Spitzbergen and Sea of Okhotsk stocks. The hunts for bowheads in Greenland, Canada, and Chukotka are small, numbering only one or two per year. The hunts on the BCB stock are considerably larger with a landed quota of 56 whales per year. The quota is established by the International Whaling Commission based on the cultural and nutritional needs of Inuit communities and on the population size and trend of bowheads. Data on harvested BCB whales have been collected since the mid-1970s. Between 1974 and 2018, hunters from 12 villages in Alaska, extending from the Bering Sea to the eastern Alaskan Beaufort Sea, harvested 1493 bowheads. Hunters at Barrow landed the most whales (n=748), while Shaktoolik only landed one and Little Diomede landed two. Some villages hunt only in the spring, some only in the autumn, while Barrow, Wainwright, and the Saint Lawrence Island villages (Gambell and Savoonga) hunt in both the spring and autumn/winter. The average size of whales differs among the villages. Gambell, Savoonga, and Wainwright harvest larger whales than do Point Hope and Barrow. It is not clear whether these differences are due to hunter selectivity, whale availability, or both. The size of landed whales changes during the migration in at least some villages. During the spring, larger whales tend to be taken more frequently near the end of the migration. The opposite is true for the autumn whereby larger whales tend to be taken early while small whales tend to be taken later. Overall, the sex ratio is equal. Generally, males and females do not appear to segregate during the spring or autumn migration. However, large females appear to comprise much of the tail end of the migration as they tend to be more common in late May in northern Chukchi Sea. The efficiency (no. of whales landed/no. of whales struck) of the hunt has increased markedly over this period. Currently, the efficiency is about 0.80. The bowhead harvests in West Greenland, Canada, Chukotka, and Alaska represent only a fraction of the estimated population size, indicating that the hunts are sustainable.

Bowhead whales (Balaena mysticetus) are divided into four stocks: the Okhotsk (OKH) Sea stock, the Bering-Chukchi-Beaufort (BCB) Seas stock, the East Canada-West Greenland (ECWG) stock, and the East Greenland-Svalbard-Barents (EGSB) Sea stock. Genetic data have contributed to the understanding of the differentiation among these stocks, rates of migration between them, and have been used to test hypotheses of stock substructure. Moreover, historical and recent demography of the BCB stock has been investigated using multiple genetic markers. No evidence of a genetic bottleneck from commercial whaling has been found, and models of recent population expansion are supported. Population genetic data is one source of data used by the International Whaling Commission (IWC) to issue an aboriginal whaling quota for the BCB stock.

The phylogenetic history of the bowhead whale (Balaena mysticetus) has been investigated intensively using ever-increasing samples of molecular data. By integrating this genomic information with evidence from the fossil record, divergence times can be estimated using “molecular clock” models. Recent hypotheses of cetacean phylogeny place the bowhead within Mysticeti (baleen whales), sister to the genus Eubalaena (North Atlantic, North Pacific, and southern right whales) in the family Balaenidae. The pygmy right whale (Caperea; Neobalaenidae) does not cluster with the skim-feeding balaenids and is instead positioned sister to Balaenopteroidea (rorquals and gray whale). Although a consensus has emerged regarding the divergence time between Mysticeti and Odontoceti (toothed whales) at ~36–39 Ma in the latest Eocene, the timing of evolutionary splits within Mysticeti remain contentious. Accurate dating of the baleen whale tree is complicated by lineage-specific rates of molecular evolution, gene flow among distantly related mysticete taxa, as well as contradictory results when different data and methodological approaches are applied.

Stable Isotope Analysis (SIA) has provided information on ocean productivity, and ecological aspects related to whales’ habitat use and feeding ecology, stock structure, physiology, and evolution. We reviewed published studies using SIA on whales worldwide from November 1979 to June 2017. Gaps in geographical areas and heterogeneity amongst species studied using this methodology were assessed. We also investigated which tissue was most frequently analysed, sources of variation in stable isotope values, how this methodology has been combined with other techniques, and how it can be useful for the conservation of the taxon and marine ecosystems. A total of 63 publications were found, and it was possible to detect a general increase in the number of publications along time, as 49% of the studies were from the last 7.5 years of the period analyzed. Almost 55% of studies focused on foraging ecology and habitat use. The baleen plate was the main tissue analyzed. Studies were related to 14 species, the most common being the fi n whale, Balaenoptera physalus (N=19) and the bowhead whale, Balaena mysticetus (N=18). Telemetry and SIA methodologies combined were helpful to understand geographical variations in stable isotope values. The methodology can also be valuable under the current scenario of climate change, for example providing information on feeding plasticity and changes in niche amplitude of diff erent species. Despite uncertainties related with stable isotopes distribution in the ocean, and with its incorporation rates for whales, for example, SIA provides primordial ecological information for effi cient management and conservation of this group. RESUMO A analise de isotopos estaveis (AIE) fornece informacoes sobre a produtividade do oceano e aspectos ecologicos de baleias relacionados ao uso do habitat e ecologia alimentar, estrutura de estoque, fi siologia e evolucao. Foram revisados estudos publicados usando a AIE em baleias em todo o mundo entre novembro de 1979 e junho de 2017. Foram avaliadas lacunas nas areas geografi cas e heterogeneidade entre as especies estudadas usando essa metodologia. Tambem investigamos quais tecidos foram mais utilizados para analise, as fontes de variacao em valores de isotopos estaveis, a combinacao desta metodologia com outras tecnicas e como pode ser util para a conservacao deste taxon e dos ecossistemas marinhos. Um total de 63 publicacoes foi encontrado e foi possivel detectar aumento no numero de publicacoes, uma vez que 49% dos estudos foram realizados nos ultimos 7 anos e meio do periodo analisado. Quase 55% dos estudos concentraram-se na ecologia de forrageio e no uso do habitat. As cerdas bucais foram o principal tecido analisado. Os estudos investigaram 14 especies, sendo mais comuns aqueles relacionados a baleia-fi n, Balaenoptera physalus (N=19) e a baleia-da-Groenlândia, Balaena mysticetus (N=18). As metodologias de telemetria e AIE combinadas foram uteis para entender as variacoes geografi cas em valores de isotopos estaveis. A metodologia pode tambem ter valor no cenario de mudancas climaticas fornecendo informacoes sobre plasticidade alimentar e amplitude de nicho de diferentes especies, por exemplo. Apesar das incertezas relacionadas a distribuicao dos valores de isotopos estaveis no mar e as taxas de incorporacao em baleias, por exemplo, a AIE fornece informacoes ecologicas primordiais para o manejo e conservacao desse grupo. Palavras-chave: Balaenopteridae; Balaenidae; Analise de isotopos estaveis; Ecologia da conservacao.

The hunting of bowhead whales (Balaena mysticetus) is an integral part of Inuit culture. An up-to-date abundance estimate of the entire Eastern Canada – West Greenland (EC-WG) bowhead population is necessary to support sustainable management of this harvest. The High Arctic Cetacean Survey (HACS) was conducted in August 2013, primarily to update abundance estimates for known stocks of Baffin Bay narwhal (Monodon monoceros). As the ranges of narwhal and bowhead largely overlap, the survey area was expanded to cover the summer range of bowhead whales. Bowhead whale abundance was estimated using 3 aircraft to cover the large survey area within a short time frame. Distance sampling methods were used to estimate detection probability away from the track line. Double platform with mark-recapture methods were used to correct for the proportion of whales missed by visual observers on the track line (perception bias). Abundance in Isabella Bay, an area known for high bowhead density, was estimated using density surface modelling to account for its complex shape and uneven coverage. Estimates were corrected for availability bias (whales that were not available for detection because they were submerged when the aircraft passed overhead) using a recent analysis of satellite-linked time depth recorders transmitting information on the diving behaviour of bowhead whales in the study area in August of the same survey year. The fully corrected abundance estimate for the EC-WG bowhead whale population was 6,446 (95% CI: 3,838–10,827). Possible sources of uncertainty include incomplete coverage and the diving behaviour of bowhead whales. These results confirm earlier indications that the EC-WG stock is continuing to recover from past overexploitation.

As zooplanktivorous predators, bowhead whales (Balaena mysticetus) must routinely locate patches of prey that are energy-rich enough to meet their metabolic needs. However, little is known about how the quality and quantity of prey might influence their feeding behaviours. We addressed this question using a new approach that included: (1) multi-scale biologging and unmanned aerial system observations of bowhead whales in Cumberland Sound, Nunavut (Canada), and (2) an optical plankton counter (OPC) and net collections to identify and enumerate copepod prey species through the water column. The OPC data revealed two prey layers comprised almost exclusively of lipid-rich calanoid copepods. The deep layer contained fewer, but larger, particles (10% greater overall biomass) than the shallow prey layer. Dive data indicated that the whales conducted long deep Square-shaped dives (80% of dives; averaging depth of 260.4 m) and short shallow Square-shaped dives (16%; averaging depth of 22.5 m) to feed. The whales tended to dive proportionally more to the greater biomass of zooplankton that occurred at depth. Combining behavioural recordings with prey sampling showed a more complex feeding ecology than previously understood, and provides a means to evaluate the energetic balance of individuals under current environmental conditions.

Adenoviruses are common pathogens infecting a wide range of vertebrates. Few cetacean adenoviruses have been described in the literature, and their pathogenicity is still unclear. Using PCR-based viral and bacterial pathogen surveillance in Bering-Chukchi-Beaufort seas bowhead whales (Balaena mysticetus) legally harvested 2012-15 during Alaskan aboriginal subsistence hunts, six of 59 bowhead whales (10%) tested positive for adenovirus DNA in the spleen. We found a high degree of sequence divergence from other mastadenoviruses, suggesting these may represent a novel species, tentatively named bowhead whale adenovirus. The sequences detected are distinct from adenoviruses previously identified in bottlenose dolphins (Tursiops truncatus) and harbor porpoises (Phocoena phocoena), forming two distinct clades in the cetacean hosts. The clinical impact is unclear, since no histopathologic evidence of adenovirus-associated disease was found. Furthermore, detection of adenovirus DNA in the spleen, contrary to other cetacean adenoviruses detected in the intestinal tract, may suggest a broader tissue tropism. Our study demonstrates adenovirus infection in bowhead whales and the usefulness of molecular diagnostics to discover and genetically characterize novel viruses in marine mammals.

The present study aims at an improved understanding of the origin and distribution of bowhead whales (Balaena mysticetus) along the Norwegian coast during Late Pleistocene/Holocene. We used ancient DNA methodology to identify the species of 52 large whale bones found along the coast of the Norwegian mainland. Nucleotide sequence variation of the mitochondrial control region (CR) was determined and subsequently screened against GenBank for species identification. Thirty-one bones (60%) yielded informative nucleotide sequences for the targeted mitochondrial CR. Of these, 24 matched with bowhead whale. Two additional bones were identified to bowhead whale based on morphology. Thus, 26 of the bones were identified to be from bowhead whales. The ages of the bowhead bones ranged from 15,084 cal years BP to present, with most bones older than 10,000 cal years BP. We suggest that our results show a change in distribution of bowhead whales from the very southern Norwegian Sea in the Heinrich Stadial 1 (19,000–14,600 years BP) to a distribution reaching 64°N in the Bolling–Allerod Interstadial (14,600–12,900 years BP), while the species probably was absent along the Norwegian coast during the cold Younger Dryas (12,900–11,700 years BP). During the Holocene, the species most likely has had only a northern distribution. The present study does not contribute new knowledge to solve the question if North Atlantic bowhead whales originated from a refugium in the southeast Atlantic during the Last Glacial Maximum or originate from the Pacific.

The subpopulation of the bowhead whale Balaena mysticetus in the East Greenland-Svalbard-Barents Sea is endangered and until recently was believed to number in the tens. Recent studies have suggested that this subpopulation appears to be increasing. Here, we report on unusual aggregations of bowhead whales within the Fram Strait. We present opportunistic and effort-corrected observations of bowhead whales made from a small expedition vessel during cruises in June (2015-2018). Bowhead whales were sighted on 85 occasions (220-227 whales). An aggregation in 2015 (n = 84 whales) and high numbers in 2018 (n = 104-110) exceeded all previous records. The index of whale abundance was significantly higher in open water-leads (1.08-1.14 whales km-1 of survey effort) compared to areas with drift-ice (0.51-0.53 whales km-1). The highest abundance index was measured in deep waters where the bottom slope was relatively steep. Our findings highlight the temporal and spatial consistency of this species in areas with relatively loose ice cover (open water-leads) and steep slopes. It is unknown how global warming and resultant changes in ice-extent are going to affect bowhead whales within the Strait and whether they will find new feeding grounds due to an expanding open-ocean habitat. These slopes may become increasingly important to bowhead whales and Arctic top predators as a spring/early summer feeding ground. These relatively large numbers of bowhead whales are encouraging and can help direct future research monitoring programs to study the population ecology of these endangered whales.

Few studies exist of the bowhead whale brain and virtually nothing is known about its cortical cytoarchitecture or how it compares to other cetaceans. Bowhead whales are one of the least encephalized cetaceans and occupy a basal phylogenetic position among mysticetes. Therefore, the bowhead whale is an important specimen for understanding the evolutionary specializations of cetacean brains. Here, we present an overview of the structure and cytoarchitecture of the bowhead whale cerebral cortex gleaned from Nissl-stained sections and magnetic resonance imaging (MRI) in comparison with other mysticetes and odontocetes. In general, the cytoarchitecture of cetacean cortex is consistent in displaying a thin cortex, a thick, prominent layer I, and absence of a granular layer IV. Cell density, composition, and width of layers III, V, and VI vary among cortical regions, and cetacean cortex is cell-sparse relative to that of terrestrial mammals. Notably, all regions of the bowhead cortex possess high numbers of von Economo neurons and fork neurons, with the highest numbers observed at the apex of gyri. The bowhead whale is also distinctive in having a significantly reduced hippocampus that occupies a space below the corpus callosum within the lateral ventricle. Consistent with other balaenids, bowhead whales possess what appears to be a blunted temporal lobe, which is in contrast to the expansive temporal lobes that characterize most odontocetes. The present report demonstrates that many morphological and cytoarchitectural characteristics are conserved among cetaceans, while other features, such as a reduced temporal lobe, may characterize balaenids among mysticetes. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:745-760, 2019. © 2018 Wiley Periodicals, Inc.

The range of the Bering-Chukchi-Beaufort (BCB) population of bowhead whales (Balaena mysticetus) extends across the seasonally ice-covered waters of the Pacific Arctic region. The majority of whales summer in the eastern Beaufort Sea and winter in the Bering Sea, migrating across the Chukchi Sea in fall and spring. As arctic sea-ice extent rapidly diminishes, the increasing length and variability of the open water season is changing bowhead habitat substantially, with many areas now regularly ice-free when whales are present. This study examines changes in the number of open water days (OWD) between 1979 and 2014 within annual bowhead whale core-use areas as defined by satellite tagging data, and within the western Beaufort Sea (140–157°W; to 72°N) sampled by fall aerial surveys. Ice cover has decreased more in the core-use areas in the northern extent of the range than in core-use areas in the southern extent. The numbers of OWD within the core-use areas near Point Barrow and along the northern Chukotka Coast during peak use have increased by 13 and 10 days/decade, respectively. The most dramatic reductions in sea-ice cover have taken place in the western Beaufort Sea where the number of OWD on the shelf and slope have increased by 20 and 25 days/decade, respectively. In contrast, sea-ice cover has not significantly changed within the winter core-use area near the Gulf of Anadyr. Using aerial survey data, we found that bowheads in the Beaufort Sea during the fall migration have a preference for being closer to shore than to the ice edge, and that their distance to shore decreases as the fraction of open water increases. This distribution may be due to increased feeding opportunities closer to shore as a result of greater upwelling along the shelf break when the ice cover is farther from shore. Furthermore, the aerial survey data also revealed a substantial shift westward toward Point Barrow in the whales’ use of the western Beaufort Sea during fall in the period 1997–2014 compared to 1982–1996. The extent and timing of sea-ice coverage has changed relatively little over time in the Bering Sea. Bowheads typically migrate north prior to spring ice melt and retreat; therefore, large changes in the timing of the spring migration are not expected. We anticipate that bowheads will spend increasingly more time within summer and fall feeding areas, delaying their arrival to wintering areas in the Bering Sea. Reduced ice coverage and thickness in the southern Chukchi Sea may make wintering there more common in the future. Summer and fall movements may be more variable as productivity and zooplankton aggregations in existing feeding areas are altered in response to sea ice thinning and retreat, and as new areas become available.

We collated available satellite telemetry data for six species of ice-associated marine mammals in the Pacific Arctic: ringed seals (Pusa hispida; n = 118), bearded seals (Erignathus barbatus, n = 51), spotted seals (Phoca largha, n = 72), Pacific walruses (Odobenus rosmarus divergens, n = 389); bowhead whales (Balaena mysticetus, n = 46), and five Arctic and sub-arctic stocks of beluga whales (Delphinapterus leucas, n = 103). We also included one seasonal resident, eastern North Pacific gray whales (Eschrichtius robustus, n = 12). This review summarized the distribution of daily locations from satellite-linked transmitters during two analysis periods, summer (May–November) and winter (December–April), and then examined the overlap among species. Six multi-species core use areas were identified during the summer period: 1) Chukotka/Bering Strait; 2) Norton Sound; 3) Kotzebue Sound; 4) the northeastern Chukchi Sea; 5) Mackenzie River Delta/Amundsen Gulf; and 6) Viscount Melville Sound. During the winter period, we identified four multi-species core use areas: 1) Anadyr Gulf/Strait; 2) central Bering Sea; 3) Nunivak Island; and 4) Bristol Bay. During the summer period, four of the six areas were centered on the greater Bering Strait region and the northwestern coast of Alaska and included most of the species we examined. The two remaining summer areas were in the western Canadian Arctic and were largely defined by the seasonal presence of Bering-Chukchi-Beaufort stock bowhead whales and Eastern Beaufort Sea stock beluga whales, whose distribution overlapped during both summer and winter periods. During the winter period, the main multi-species core use area was located near the Gulf of Anadyr and extended northwards through Anadyr and Bering Straits. This area is contained within the Bering Sea “green belt”, an area of enhanced primary and secondary productivity in the Bering Sea. We also described available telemetry data and where they can be found as of 2017. These data are important for understanding ice-associated marine mammal movements and habitat use in the Pacific Arctic and should be archived, with appropriate metadata, to ensure they are available for future retrospective analyses.

The acoustic environment of two focal Arctic species, bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales, varied among the three core-use regions of the Pacific Arctic examined during the months in which both species occur: (1) January-March in the St. Lawrence Island/Anadyr Strait region, (2) November-January in the Bering Strait region, and (3) August-October in the Barrow Canyon region. Biological noise (consisting of the signals of bowhead whales, walrus and bearded seals) dominated the acoustic environment for the focal species in the St. Lawrence Island/Anadyr Strait region, which was covered with ice throughout the months studied. In the Bering Strait region whales were exposed primarily to environmental noise (in the form of wind noise) during November, before the region was ice-covered in December, and biological noise (from bowhead and walrus) again was prevalent. Anthropogenic noise dominated the Barrow Canyon region for the focal species in late summer and fall (August through October); this was also the only region in which the two species did not overlap with sea ice. Under open water conditions both near Barrow Canyon and in Bering Strait, noise levels were tightly correlated with wind. However, with climate-change driven increases in open water leading to rising noise levels across multiple fronts (atmospheric, biological, anthropogenic), the relatively pristine acoustic environment of Arctic cetaceans is changing rapidly. Characterizing the acoustic habitat of these regions before they are further altered should be considered a management and conservation priority in the Arctic.

Aerial surveys for bowhead whales have been conducted with a relatively consistent methodology over the Alaskan Beaufort Sea since 1989. Sightings of bowhead whales in the central Alaskan Beaufort Sea in September 1997 and September 2014 were unusual in that hundreds of whales were observed within a few kilometers of local barrier islands. We compare bowhead whale sightings, river discharge data, wind records, and satellite imagery to argue that the large numbers of bowhead whales observed nearshore in September 1997 and 2014 resulted from favorable feeding conditions established by high river discharges and prior upwelling events. These results are then generalized in a simple binary-based mechanistic framework that links the relevant physics to occurrences of observed and potential feeding opportunities for bowhead whales in the central Alaskan Beaufort Sea and in other locales along the Beaufort coast.

The data on sightings of the bowhead whale (Balaena mysticetus Linnaeus, 1758) in the western Sea of Okhotsk collected during eight field seasons, as well as information obtained from interviews with local residents in the study region, are presented. The major areas of concentration of the bowhead whale population in the ice-free period are determined; the whale behavior in bays is described. Data on sea surface temperature, salinity, and depth measurements at the sites of bowhead whale sightings are provided. The possible causes of whale concentrations close to the shoreline and in apical parts of mainland shallow-water bays, as well as the potential threats to the population associated, inter alia, with this pattern of distribution, are discussed.

Previous studies have demonstrated that the analysis of biogeochemical tracers along baleen can provide seasonal, annual, and longer term insights into whale movements, habitat use, diet, and ecosystem processes. We measured the mercury (Hg) concentration and stable carbon (δ13C) and nitrogen (δ15N) isotope compositions along baleen plates of bowhead whales (Balaena mysticetus) harvested between 1988 and 1996 from the Bering–Chukchi–Beaufort (BCB) and the Eastern Canada–West Greenland (EC–WG) populations. These measurements were compared among individuals and between populations to assess seasonal cycling and to determine if bowhead whales forage year-round rather than fasting in winter. Individuals from the BCB population had synchronous cycles with higher Hg concentrations and lower δ13C values in summer and lower Hg concentrations and higher δ13C values in winter. EC–WG individuals also had synchronized periodic variations with peak values in isotopic ratios during summer. These results reflect an annual cycle of seasonal migration between distinct food webs in both populations. Spring and fall feeding activity was indicated in the intra-annual Hg and δ13C cycles along the baleen plates of all whales in our study. These shorter periods, spanning about half the annual growth, have not been previously described in the baleen of these populations, and are consistent with separate foraging areas along the migration routes. The results of this study provide further support for year-round foraging in a species previously thought to fast during winter. Future monitoring of seasonal foraging patterns in baleen would help to determine whether bowhead whales alter their foraging patterns in response to shifts in zooplankton community availability, composition, and phenology.

Each spring, most Bowhead Whales (Balaena mysticetus) of the Bering-Chukchi-Beaufort (BCB) population migrate to the Canadian Beaufort Sea and Amundsen Gulf for summer feeding. Occasionally, Inuvialuit hunters and others observe beachcast (stranded) or adrift Bowhead Whale carcasses. From 1987 to 2016, 26 such occurrences were recorded. Most (65%) were found by Inuvialuit hunters travelling on the land, with the majority (54%) reported during 2000–2006. Bowhead Whale carcasses were found widely distributed throughout the region, with twice as many in Amundsen Gulf (65%) compared with the southeastern Beaufort Sea (35%). It was possible to measure or estimate standard length for 17 of 26 specimens, and all were either provisional ‘subadults’ (7–9.5 m; n = 10; 59%) or provisional ‘mature adults’ (13–16 m; n = 7; 41%). The cause(s) of mortality was not determined for any of the specimens. Whales in the ‘subadult’ group were likely 1–4 years old, while the ‘mature adult’ group were likely mostly mature animals (~25 y), including some potentially very old (>100 y). There was evidence or direct observation of Polar Bears (Ursus maritimus) and/or Grizzly Bears (U. arctos) scavenging at 60% of the carcasses for which presence or absence of bears or bear sign (scats and/or tracks) was reported. It is important to continue to record incidental observations of beachcast Bowhead Whales, as this may enable stranding rates to be evaluated.