The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate change‐related concerns. While the ...population was known to be declining in the 1980s and 1990s, its recent status has not been determined. We developed Bayesian models of walrus population dynamics to assess the population by synthesizing information on population sizes, age structures, reproductive rates, and harvests for 1974–2015. Candidate models allowed for temporal variation in some or all vital rates, as well as density dependence or density independence in reproduction and calf survival. All selected models indicated that the population underwent a multidecade decline, which began moderating in the 1990s, and that annual reproductive rate and natural calf survival rates rose over time in a density‐dependent manner. However, selected models were equivocal regarding whether the natural juvenile survival rate was constant or decreasing over time. Depending on whether juvenile survival decreased after 1998, the population growth rate either increased during 1999–2015 or stabilized at a lesser level of decline than seen in the 1980s. The probability that the population was still declining in 2015 ranged from 45% to 87%.
Each spring, most bowhead whales of the Bering-Chukchi-Beaufort (BCB) population migrate to the southeast Beaufort Sea and summer in Canadian waters. In August and September, they form aggregations, ...which are known to occur mainly in the shallow, shelf waters when oceanographic conditions promote concentration of their zooplankton prey. The movements of individual bowheads while they occupy these late summer habitats are less well known; our knowledge is based on photographic evidence and limited tagging studies conducted from 1982 to 2000. In this study, 85% (17) of the 20 satellite-tagged whales that could have spent some time in the Canadian portion of the Beaufort Sea during late summer 2006 to 2012 spent all or part of August and September there. We analyzed location data for 16 whales, using a two-state switching correlated random walk (CRW) behavioural model, and classified locations in the Canadian waters as associated with lingering behaviour (inferred foraging) or directed travel. We found that these whales spent the greatest proportion of their time lingering (59%), followed by traveling (22%), and transitioning between lingering and traveling (19%). Using only lingering locations for these tagged whales in all study years pooled, we calculated kernel densities and defined five areas within the 75% density contour as aggregation areas. Together, the five aggregation areas we defined comprised 25 341 km2, 14.1% of the total area used by these tagged whales in Canadian waters during August and September of the deployment years. Three aggregation areas were located in shallow waters of the Beaufort Sea Shelf and were used almost exclusively by immature tagged whales in our sample. Two other aggregation areas were observed, one in Darnley Bay and one in Viscount Melville Sound in the Canadian Arctic Archipelago. Each of these was used by one mature whale. Tagged whales were observed to use one or two aggregation areas in a single season, and rarely more. The proportion of lingering time spent in each aggregation area was highly variable among individuals. The largest aggregation area (10 877 km2), located over the Beaufort Shelf north of the Tuktoyaktuk Peninsula (5–52 m depth), was used by 13 of the 16 tagged whales, almost exclusively by the immature whales, including three of four that were tracked in two consecutive summers. The Beaufort Shelf overall (and possibly the Tuktoyaktuk Shelf, including the Outer Shelf, in particular) was especially important for immature bowhead whales, while mature whales used habitats beyond the Beaufort Shelf during late summer. Findings may be important to inform both decisions on management and mitigative actions relating to bowhead whale use of the Beaufort Shelf and studies that aim to improve our understanding of the prey base of BCB bowhead whales in the Canadian Beaufort Sea region. Tous les printemps, la plupart des baleines boréales de la population de Béring-Tchouktches-Beaufort (BCB) migrent vers le sud-est de la mer de Beaufort et passent l'été dans les eaux canadiennes. En août et en septembre, elles forment des agrégations, principalement dans les eaux de plateau peu profondes lorsque les conditions océanographiques favorisent la concentration du zooplancton, qui leur sert de proie. Individuellement, les déplacements des baleines boréales qui occupent ces habitats en fin d'été sont moins connus. Nos connaissances sont fondées sur des preuves photographiques ainsi que sur des études de marquage restreint réalisées entre 1982 et 2000. Dans le cadre de la présente étude, 85 % (17) des 20 baleines pistées par satellite qui auraient pu passer du temps dans la partie canadienne de la mer de Beaufort vers la fin de l'été de 2006 à 2012 y ont passé les mois d'août et de septembre, en totalité ou en partie. Nous avons analysé les données de localisation de 16 baleines à l'aide d'un modèle de comportement de marche aléatoire corrélée à commutation binaire, et classé les localisations dans les eaux canadiennes comme relevant d'un comportement de traînage (présupposition de comportement d'alimentation) ou comme relevant de déplacements orientés. Nous avons constaté que ces baleines passaient la plus grande partie de leur temps à traîner (59 %), à se déplacer (22 %), et à faire la transition entre traîner et se déplacer (19 %). En n'utilisant que les localisations de traînage des baleines pistées pour toutes les années à l'étude, nous avons calculé les noyaux de densité et défini cinq zones à l'intérieur du contour de la densité de 75 % à titre de zones d'agrégation. Ensemble, les cinq zones d'agrégation que nous avons définies s'étendent sur 25 341 km2, soit 14,1 % de la zone totale utilisée par ces baleines pistées dans les eaux canadiennes en août et en septembre des années de déploiement. Trois zones d'agrégation étaient situées dans les eaux peu profondes du plateau de la mer de Beaufort, et ces zones étaient principalement utilisées par les baleines immatures pistées dans notre échantillon. Deux autres agrégations ont été observées, une dans la baie Darnley et l'autre dans le détroit du Vicomte de Melville situés dans la partie canadienne de l'archipel Arctique. Chacun de ces endroits était utilisé par une baleine adulte. Des baleines pistées ont été aperçues dans une ou deux zones d'agrégation au cours d'une même saison, rarement plus. La proportion du temps passé à traîner dans chaque zone d'agrégation variait beaucoup d'un individu à l'autre. La plus grande zone d'agrégation (10 877 km2), située sur le plateau de la mer de Beaufort au nord de la péninsule de Tuktoyaktuk (d'une profondeur de 5 à 52 m), était utilisée par 13 des 16 baleines pistées, presque toujours des baleines immatures, dont trois sur quatre ont été repérées pendant deux étés consécutifs. Dans l'ensemble, le plateau de la mer de Beaufort (et peut-être le plateau de Tuktoyaktuk, y compris la zone externe du plateau, en particulier) revêtait une importance particulière pour les baleines boréales immatures, tandis que les baleines adultes se servaient des habitats situés au-delà du plateau de la mer de Beaufort vers la fin de l'été. Ces constatations pourraient jouer un rôle important quand vient le temps d'éclairer tant les décisions en matière de gestion et de mesures d'atténuation se rapportant à l'utilisation que fait la baleine boréale du plateau de la mer de Beaufort que les études visant à améliorer notre compréhension de la composition des proies des baleines boréales de BCB dans la région canadienne de la mer de Beaufort.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Alaska Beluga Whale Committee co-manages three western Alaska beluga whale Delphinapterus leucas, stocks with the National Marine Fisheries Service, NOAA, and has conducted studies on stock ...identity, distribution, abundance, and subsistence harvests. Studies of mitochondrial DNA revealed substantial differentiation among belugas that use summering areas in Bristol Bay, the eastern Bering Sea, and the eastern Chukchi Sea, and there is little overlap in their seasonal distributions. The Bristol Bay stock summers in bays in inner Bristol Bay and winters in outer Bristol Bay. Abundance estimates from aerial surveys increased by more than 4% per year during 1994-2005. Survey counts in 2016 were similar to 20042005 indicating that the population may now be stable. Survey results and a genetics mark-recapture study indicate a population of approximately 2,000 whales. The average annual Alaska Native subsistence harvest over the past decade (23) is below the calculated potential biological removal (PBR; 39-43). The eastern Bering Sea beluga stock concentrates in summer off the Yukon River Delta and in Norton Sound and in winter moves offshore in the eastern Bering Sea. Abundance has been estimated at approximately 9,242 based on aerial survey data collected in 2017. The average annual subsistence harvest, plus the estimated number of struck and lost belugas, is 215 and exceeds the PBR calculated from this abundance estimate (201), but the abundance estimate is thought to be biased low and local and traditional knowledge does not indicate any decrease in abundance or availability. The eastern Chukchi Sea stock is migratory, wintering in the northern Bering Sea, moving north through the eastern Chukchi Sea in spring, and summering in the Beaufort Sea and Arctic Ocean. It is large, estimated at approximately 20,000 animals based on 2012 aerial surveys. The average annual subsistence harvest (57) is well below PBR (293). Few significant threats to persistence of western Alaska beluga stocks have been identified, although climate warming and declines in sea ice and industrial activities related to resource development and increases in commercial shipping are of concern and could pose challenges in the future. Continued monitoring of population size and trend, subsistence harvest, and health of western Alaska belugas is warranted.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Diving mammals use blubber for a variety of structural and physiological functions, including buoyancy, streamlining, thermoregulation, and energy storage. Estimating blubber stores provides proxies ...for body condition, nutritional status, and health. Blubber stores may vary topographically within individuals, across seasons, and with age, sex, and reproductive status; therefore, a single full-depth blubber biopsy does not provide an accurate measure of blubber depth, and additional biopsies are limited because they result in open wounds. We examined high-resolution ultrasound as a noninvasive method for assessing blubber stores by sampling blubber depth at 11 locations on beluga whales in Alaska. Blubber mass was estimated as a proportion of body mass (40% from the literature) and compared to a function of volume calculated using ultrasound blubber depth measurements in a truncated cone. Blubber volume was converted to total and mass-specific blubber mass estimates based on the density of beluga blubber. There was no significant difference in mean total blubber mass between the 2 estimates (R2 = 0.88); however, body mass alone predicted only 68% of the variation in mass-specific blubber stores in juveniles, 7% for adults in the fall, and 33% for adults in the spring. Mass-specific blubber stores calculated from ultrasound measurements were highly variable. Adults had significantly greater blubber stores in the fall (0.48 ± 0.02 kg/kgMB) than in the spring (0.33 ± 0.02 kg/kgMB). There was no seasonal effect in juveniles. High-resolution ultrasound is a more powerful, noninvasive method for assessing blubber stores in wild belugas, allowing for precise measurements at multiple locations.
Arctic marine mammals face many challenges linked to climate change, including increasing anthropogenic noise from vessel traffic. The bowhead whale ( Balaena mysticetus Linnaeus, 1758), an Arctic ...endemic cetacean, relies on acoustic communication, with documented overlapping frequencies between communication and vessel noise. Bering–Chukchi–Beaufort (BCB) bowhead whales migrate through areas with the highest levels of vessel traffic in the Pacific Arctic. Here, we document the spatial and temporal overlap between 25 satellite-tagged BCB bowhead whales and vessels during July–December, 2012–2018. We report 1332 occasions when a vessel was within 125 km of a tagged whale, and where possible, quantified changes in swim speed to investigate individual behavioural responses to vessel approaches within a 50 km radius ( n = 18 encounters). In the quantitative analysis, bowhead whales were not observed to alter swim speed within 8–50 km of vessels (we could not assess distances <8 km). Our results suggest that bowhead whales did not exhibit detectable long-range (i.e., up to 50 km) behavioural responses to vessels, consistent with observations of closely related North Atlantic right whales ( Eubalaena glacialis (Muller, 1776)), for which vessel strikes are a leading cause of mortality. More work is required to assess how bowhead whales react to vessels at closer distances.
We report on a method of visually classifying Pacific walruses (Odobenus rosmarus) to sex and age class with the goal of estimating calf:cow ratios. Development of this method began in 1958 by Dr. F. ...H. Fay and was used during six surveys in the Chukchi Sea between 1981 and 1999. We estimate calf:cow ratios using beta‐binomial models to allow for overdispersion and use Monte Carlo simulations to assess the reliability of prior surveys and quantify sample sizes required for future surveys. Calf:cow ratios did not vary by region, date, or by the number of cows in a group. However, higher ratios were observed in the morning and evening than during the day, indicating haul out behavior of cows varies by reproductive status. Adjusted for solar noon, few calves were observed in 1981 (3:100), 1984 (6:100), and 1998 (5:100), while substantially more were observed in 1982 (15:100) and 1999 (13:100). Classifying between 200 and 300 groups with cows (~1,600–2,300 individual cows) will yield calf:cow ratios with ~20%–30% relative precision. Tagging studies that examine hauling‐out behavior of cows with and without calves relative to time‐of‐day are necessary to better understand how to interpret calf:cow ratios.
Climate-related shifts in marine mammal range and distribution have been observed in some populations; however, the nature and magnitude of future responses are uncertain in novel environments ...projected under climate change. This poses a challenge for agencies charged with management and conservation of these species. Specialized diets, restricted ranges, or reliance on specific substrates or sites (eg for pupping) make many marine mammal populations particularly vulnerable to climate change. High-latitude, predominantly ice-obligate, species have experienced some of the largest changes in habitat and distribution and these are expected to continue. Efforts to predict and project marine mammal distributions to date have emphasized data-driven statistical habitat models. These have proven successful for short time-scale (eg seasonal) management activities, but confidence that such relationships will hold for multi-decade projections and novel environments is limited. Recent advances in mechanistic modeling of marine mammals (ie models that rely on robust physiological and ecological principles expected to hold under climate change) may address this limitation. The success of such approaches rests on continued advances in marine mammal ecology, behavior, and physiology together with improved regional climate projections. The broad scope of this challenge suggests initial priorities be placed on vulnerable species or populations (those already experiencing declines or projected to experience large climate changes that are consistent across climate projections) and species or populations for which ample data already exists (with the hope that these may inform climate change sensitivities in less well observed species or populations elsewhere). The sustained monitoring networks, novel observations, and modeling advances required to more confidently project marine mammal distributions in a changing climate will ultimately benefit management decisions across time-scales, further promoting the resilience of marine mammal populations.
Working with subsistence whale hunters, we tagged bowhead whales (Balaena mysticetus) with satellite-linked transmitters and documented their movements in the Bering Sea during two winters. We ...followed 11 whales through the winter of 2008—09 and 10 whales in 2009—10. The average date that bowhead whales entered the Bering Sea was 14 December in 2008 and 26 November in 2009. All but one tagged whale entered the Bering Sea west of Big Diomede Island. In the winter of 2008—09, whales were distributed in a line extending from the Bering Strait to Cape Navarin, whereas in 2009—10, the distribution shifted south of St. Lawrence Island, extending from Cape Navarin to St. Matthew Island. Bowhead whales were most likely to be found in areas with 90%—100% sea-ice concentration and were generally located far from the ice edge and polynyas. The average date whales left the Bering Sea was 12 April in 2009 and 22 April in 2010. During the spring migration, all whales but one traveled north along the Alaska coast to summering grounds in the Canadian Beaufort. The remaining whale migrated a month later and traveled up the northern coast of Chukotka, where it was located when the tag stopped transmitting in August. It is unlikely that this whale migrated to the Beaufort Sea before returning south to winter within the Bering Sea, indicating the movements of bowhead whales are more complex than generally believed. Declining sea ice in the Bering Sea may result in the expansion of commercial fisheries and shipping; areas where such activities may overlap the winter range of bowhead whales include the Bering and Anadyr straits, the eastern edge of Anadyr Bay, and St. Matthew Island. Avec l'aide de pêcheurs de baleine de subsistance, nous avons marqué des baleines boréales (Balaena mysticetus) au moyen de transmetteurs en liaison avec un satellite et répertorié leurs mouvements au cours de deux hivers dans la mer de Béring. Nous avons suivi 11 baleines pendant l'hiver 2008-2009 et dix baleines en 2009-2010. En 2008, les baleines boréales sont entrées dans la mer de Béring le 14 décembre en moyenne, tandis qu'en 2009, elles sont arrivées le 26 novembre. À l'exception d'une baleine, toutes les baleines marquées ayant pénétré dans la mer de Béring sont passées par l'ouest de la grande île Diomède. À l'hiver 2008-2009, le parcours des baleines s'étendait en ligne depuis le détroit de Béring jusqu'au cap Navarin, tandis qu'en 2009-2010, le parcours s'est déplacé vers le sud de l'île Saint-Laurent, s'étendant ainsi du cap Navarin jusqu'à l'île Saint-Mathieu. Les baleines boréales étaient plus susceptibles de se retrouver dans les endroits dont la glace de mer a une concentration allant de 90 à 100 %. Généralement, elles se tiennent loin des lisières de glace et des polynies. En 2009, la date moyenne à laquelle les baleines ont quitté la mer de Beaufort était le 12 avril, tandis qu'en 2010, cette date était le 22 avril. Pendant la migration printanière, toutes les baleines, sauf une, se sont déplacées vers le nord le long de la côte de l'Alaska pour se rendre à leur aire d'estivage dans la partie canadienne de Beaufort. L'autre baleine a fait sa migration un mois plus tard et s'est déplacée le long de la côte nord de Tchoukotka, là où elle avait été repérée lorsque son marqueur a cessé ses transmissions en août. Il est improbable que cette baleine ait migré dans la mer de Beaufort avant de revenir vers le sud pour passer l'hiver dans la mer de Béring, ce qui indique que les mouvements des baleines boréales sont plus complexes qu'on ne le croyait antérieurement. La perte de glace de mer dans la mer de Béring pourrait se traduire par l'intensification des activités de pêche commerciale et d'expédition de marchandises. Les endroits où ces activités pourraient chevaucher le parcours d'hiver des baleines boréales comprennent les détroits de Béring et d'Anadyr, le côté est de la baie d'Anadyr et l'île Saint-Mathieu.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Working with subsistence whale hunters, we tagged 19 mostly immature bowhead whales (Balaena mysticetus) with satellite-linked transmitters between May 2006 and September 2008 and documented their ...movements in the Chukchi Sea from late August through December. From Point Barrow, Alaska, most whales moved west through the Chukchi Sea between 71° and 74° N latitude; nine whales crossed in six to nine days. Three whales returned to Point Barrow for 13 to 33 days, two after traveling 300 km west and one after traveling ∼725 km west to Wrangel Island, Russia; two then crossed the Chukchi Sea again while the other was the only whale to travel south along the Alaskan side of the Chukchi Sea. Seven whales spent from one to 21 days near Wrangel Island before moving south to northern Chukotka. Whales spent an average of 59 days following the Chukotka coast southeastward. Kernel density analysis identified Point Barrow, Wrangel Island, and the northern coast of Chukotka as areas of greater use by bowhead whales that might be important for feeding. All whales traveled through a potential petroleum development area at least once. Most whales crossed the development area in less than a week; however, one whale remained there for 30 days. De concert avec les pêcheurs de baleines de subsistance, nous avons apposé des transmetteurs satellitaires sur 19 baleines boréales (Balaena mysticetus) pour la plupart immatures entre les mois de mai 2006 et septembre 2008, puis nous avons tenu compte de leurs mouvements dans la mer de Tchoukotka de la fin août jusqu'au mois de décembre. À partir de Point Barrow, en Alaska, la plupart des baleines se déplaçaient vers l'ouest dans la mer de Tchoukotka entre 71° et 74° N de latitude; neuf baleines ont fait la traversée en six à neuf jours. Trois baleines ont regagné Point Barrow pendant 13 à 33 jours, dont deux après avoir franchi 300 kilomètres en direction ouest et une après avoir franchi environ 725 kilomètres en direction ouest jusqu'à l'île Wrangel, en Russie; ensuite, deux baleines ont traversé la mer de Tchoukotka de nouveau tandis que l'autre était la seule baleine à se déplacer vers le sud le long du côté de la mer de Tchoukotka situé en Alaska. Sept baleines ont passé de un à 21 jours près de l'île Wrangel avant d'aller au sud du côté nord de Tchoukotka. Les baleines ont passé, en moyenne, 59 jours à suivre la côte de Tchoukotka vers le sud-est. L'analyse de la densité des noyaux a permis de déterminer que Point Barrow, l'île Wrangel et la côte nord de Tchoukotka sont des régions plus grandement utilisées par les baleines boréales, régions qui peuvent être importantes aux fins de l'alimentation. Toutes les baleines ont traversé une zone de mise en valeur éventuelle du pétrole au moins une fois. La plupart des baleines ont traversé la zone de mise en valeur en moins d'une semaine. Cela dit, une baleine est restée à cet endroit pendant 30 jours.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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