Harp Seals Research Articles

Source levels and communication-range models for harp seal (Pagophilus groenlandicus) underwater calls in the Gulf of St. Lawrence, Canada

Harp seals ( Pagophilus groenlandicus (Erxleben, 1777)) produce underwater call types during the breeding season that are thought to be important for reproductive behaviours and herd formation. Underwater calls were recorded in the Gulf of St. Lawrence, Canada, in March 2007. A four hydrophone array system determined the locations of nearby calling seals and call source levels (amplitudes at 1 m from the seal). Source levels ranged from 103 to 180 dB re 1 µPa-m and mean values per call type ranged from 129 to 151 dB re 1 µPa-m with considerable overlap between call types. Short-range sound transmission losses under the ice were variable. Theoretical communication-range models were constructed under quiet (0 sea state, transmission-loss pattern of 20 log range) and noisy (herd noise, transmission-loss patterns of 15, 17.5, or 20 log range) conditions. Monte Carlo models for the calls for a quiet sea indicated median distances of 0.5–5.5 km (maximum 80 km). Communication distances in the presence of other calling seals dropped to 0.03–0.5 km (maximum 15 km) for dB loss = 20 log range but were longer under different spreading-loss patterns. Communication ranges are significantly influenced by call source levels, background noise, and in situ sound transmission patterns.

ECOLOGY AND WILDLIFE: Climate Change and the Arctic Diet

Each spring, female polar bears and their cubs emerge from hibernation after months without food, and their survival depends on having good sea ice for hunting seals, their almost exclusive food. Also in spring, the Arctic sea ice begins to melt and break apart. Over the past 25 years, the timing of this melting has become less predictable as a consequence of warming in the Arctic, varying by more than a month. Researchers in Canada now report the first evidence that changes in the timing of the annual sea ice breakup have contributed to a dietary shift for polar bears from western Hudson Bay in the Canadian sub-Arctic. This shift may be accelerating the bears’ bioaccumulation of some classes of persistent contaminants, and people who consume these animals as part of a traditional subsistence diet could face greater exposure to contaminants that are passed up the food chain.

Development of myoglobin concentration and acid buffering capacity in harp (Pagophilus groenlandicus) and hooded (Cystophora cristata) seals from birth to maturity

Pinnipeds rely on muscle oxygen stores to help support aerobic diving, therefore muscle maturation may influence the behavioral ecology of young pinnipeds. To investigate the pattern of muscle development, myoglobin concentration ([Mb]) and acid buffering ability (beta) was measured in ten muscles from 23 harp and 40 hooded seals of various ages. Adult [Mb] ranged from 28-97 to 35-104 mg g tissue(-1) in harp and hooded seals, respectively, with values increasing from the cervical, non-swimming muscles to the main swimming muscles of the lumbar region. Neonatal and weaned pup muscles exhibited lower (approximately 30% adult values) and less variable [Mb] across the body than adults. In contrast, adult beta showed little regional variation (60-90 slykes), while high pup values (approximately 75% adult values) indicate significant in utero development. These findings suggest that intra-uterine conditions are sufficiently hypoxic to stimulate prenatal beta development, but that [Mb] development requires additional postnatal signal such as exercise, and/or growth factors. However, because of limited development in both beta and [Mb] during the nursing period, pups are weaned with muscles with lower aerobic and anaerobic capacities than those of adults.

Harp seal heart valves being tested for human use

Researchers in Quebec will soon begin testing heart valves from harp seals to determine if they are suitable for use in humans. Animal rights groups say the research is unnecessary and will serve only as a government propaganda tool to promote Canada’s sealing industry, which received a major

Geographic variation in vocalizations of pups and mother-pup behavior of harp seals Pagophilus groenlandicus

All harp seal populations form breeding aggregations on the Arctic pack ice. However, pack ice conditions vary spatially and temporally among these aggregations with variation in envi- ronmental and oceanographic conditions, which may affect the behavioral interactions between mothers and their newborn pups. We investigated the variation in mother-pup behavior between harp seal breeding aggregations in the NE (Greenland Sea) and NW Atlantic coastal shelf region (Front). Acoustic cues provided by the pups are thought to be important in facilitating reunions with their mothers. Consequently, we measured variation in vocal parameters among seals to investigate geographic differences in pup vocalizations. Classification trees showed a distinctive split between Front and Greenland Sea pup vocalizations. There were no clear differences between male and female pups at the Front, where 42% of male and 38% of female pup calls could be attributed to a given individual. This contrasts with the Greenland Sea, where 55% of vocalizations of female pups were attributed to individuals compared with only 8% for males. Analyses of behavioral observations of mother-pup pairs made in the afternoon and evening showed that pups in the Greenland Sea suck- led more and were more alert than pups in the Front. Further, mother-pup attendance patterns dif- fered between sites. Mothers at the Front attended their pups 85.1% of the time, whereas mothers in the Greenland Sea attended their pups 52.2% of the time. These substantial differences between sites might be related to evolutionary changes in behavior resulting from commercial hunting or vari- able environmental conditions.

Septicemia, Endocarditis, and Cerebral Infarction Due to Staphylococcus aureus in a Harp seal (phoca groenlandica)

An adult, wild-collected, male harp seal (Phoca groenlandica) was transferred from a rehabilitation center to a display facility because of unilateral phthisis bulbi and decreased use of the right forelimb, which precluded its release. In quarantine, the animal demonstrated limited use of the right forelimb, which acutely progressed to complete disuse of the limb accompanied by intermittent lethargy. One month after transfer, the animal was found dead on exhibit. Necropsy showed septic arthritis of the right scapulohumeral joint, valvular endocarditis with systemic bacterial thromboembolism, and infarction of the cerebrum and myocardium. Culture of the blood and affected joint space revealed Staphylococcus aureus. Bacterial polymerase chain reaction of formalin-fixed tissues from the heart and brain were also positive for S. aureus. Staphylococcus aureus infection should be considered as an additional cause of endocarditis and embolic encephalitis in seals.

Sources of variation in diets of harp and hooded seals estimated from quantitative fatty acid signature analysis (QFASA)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 384:287-302 (2009) - DOI: https://doi.org/10.3354/meps08000 Sources of variation in diets of harp and hooded seals estimated from quantitative fatty acid signature analysis (QFASA) Strahan Tucker1,5,*, W. Don Bowen2, Sara J. Iverson1, Wade Blanchard3, Garry B. Stenson4 1Department of Biology, Dalhousie University, 355 Oxford Street, Halifax, Nova Scotia B3H 4J1, Canada 2Population Ecology Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, 1 Challenger Drive, Dartmouth, Nova Scotia B2Y 4A2, Canada 3Department of Mathematics and Statistics, Dalhousie University, 355 Oxford Street, Halifax, Nova Scotia B3H 4J1, Canada 4Northwest Atlantic Fisheries Centre, Department of Fisheries and Oceans, PO Box 5667, St John’s, Newfoundland A1C 5X1, Canada 5Present address: Pacific Biological Station, Department of Fisheries and Oceans, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada *Email: stucker2@dal.ca ABSTRACT: Inter-specific competition for prey is thought to influence the structure of ecological communities and species niche breadth. Harp seals Pagophilus groenlandicus and hooded seals Cystophora cristata are geographically overlapping and highly migratory predators in the North Atlantic ocean. Hooded seals are known to dive deeper and longer than harp seals and are more closely associated with the continental shelf edge and deep ocean. Quantitative fatty acid (FA) signature analysis (QFASA) was recently developed to estimate the species composition of diets by statistically comparing FA signatures of predator adipose tissue with that of potential prey. Using QFASA, we estimated diets for harp (adults, n = 294; juveniles, n = 232) and hooded (adults, n = 115; juveniles, n = 38) seals from the pre- and post-breeding periods between 1994 and 2004. We found evidence of inter- and intra-specific variation in diets, diet quality and breadth, reflecting different foraging tactics. Harp seal diets were comprised predominantly of amphipods, Arctic cod, capelin, herring, sand lance and redfish. Hooded seal diets were composed primarily of amphipods, Atlantic argentine, capelin, euphausiids and redfish. Relative to the other species, harp seals consumed twice the proportion of amphipods, while hooded seals consumed 3 times the proportion of redfish; percentages of capelin were similar. QFASA provided new evidence of the importance of amphipods in the diets of both species and of the pronounced differences in the proportions of pelagic forage fish between demographic groups. KEY WORDS: Harp seal · Pagophilus groenlandicus · Hooded seal · Cystophora cristata · Diet segregation · Quantitative fatty acid signature analysis · QFASA Full text in pdf format Supplementary material PreviousNextCite this article as: Tucker S, Bowen WD, Iverson SJ, Blanchard W, Stenson GB (2009) Sources of variation in diets of harp and hooded seals estimated from quantitative fatty acid signature analysis (QFASA). Mar Ecol Prog Ser 384:287-302. https://doi.org/10.3354/meps08000Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 384. Online publication date: May 29, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

The economics of ending Canada's commercial harp seal hunt

The roots of the Canadian harp seal hunt can be traced to the 16th Century. But in the mid-20th century, opposition to the commercial hunt became widespread after television images of seal pups being killed with clubs on the pack ice off the coast of Newfoundland were broadcast around the world. International conservation groups, animal welfare groups, animal rights groups, and foreign governments have been calling for the Canadian government to end the commercial seal hunt on the grounds that it is inhumane and that harvest levels are unsustainable. The Canadian government defends the traditional practices of hunting harp seals, argues that seal pelts are an important source of income for sealers, and insists that the killing methods are humane and that harvest levels are sustainable. Emotions run high on both sides of the debate. The purpose of this paper is to evaluate whether or not there is a purely economic argument for ending Canada's commercial seal hunt. The paper finds that the benefits of ending the commercial hunt exceed the costs, but not unequivocally. However, the paper argues there should be a higher criterion—the Pareto criterion—for ending the commercial hunt; that is the hunt should end only if winners compensate the losers. The paper goes on to argue that an effective way to satisfy this criterion is to introduce a system of individual transferable quotas (ITQs) and let the market reveal the value of the commercial seal hunt. In addition to many other advantages such as improving the safety and efficiency of the hunt, the ITQ market could provide a mechanism by which those willing to pay to end the hunt could do so directly to sealers thereby ensuring that the hunt is scaled back or ultimately ended only when it is economically efficient and unambiguously welfare-improving.

Estimation of seal pup production from aerial surveys using generalized additive models

In this paper, we estimate the pup production of harp seals ( Pagophilus groenlandicus ) using generalized additive models (GAMs) based on thin-plate regression splines. The spatial distribution of seal pups in a patch is modelled using GAMs, and the pup production is estimated by numerically integrating the model over a fine grid area of the patch. Closed form expression for estimation of the the standard error of the pup production estimate is derived. The estimators are applied to simulated seal populations to investigate their properties. The results show that the proposed pup production estimator is comparable with the conventional pup production estimator. However, the bias of the standard error estimator of the proposed method is much lower than the bias of the conventional standard error estimator. The decrease of standard error bias results in a considerable reduction of the coefficient of variation estimate using the proposed GAM-based method. The proposed method is also applied to real survey data of harp seals obtained from aerial surveys in the Greenland Sea pack ice in 2002. We show that the number of pups counted from aerial photographs possess a good fit to the negative binomial distribution when a logarithmic link function is applied. The approach described here is applicable to many situations where georeferenced counts or measurements are available.

Ecology of harp seal (Phoca groenlandica) pups on ices in the White Sea

The harp seal ( Phoca groenlandica ) is the most abundant species of the true seals inhabiting the northern hemisphere. Depending on breeding area location, three populations (Newfoundland, White-Sea, and Jan Mayen) of harp seals are distinguished [1, 2]. Owing to the high total abundance, the harp seal remains the key commercial animal whose herds in Russia, Norway, Canada, and Greenland (Denmark) are extensively harvested every year. The current size of the White-Sea population of harp seals is 1.8‐2 million animals [3]. The range of the harp seal is wide: during summer migrations, the seals inhabit the Barents Sea and other Northern Atlantic areas and occur in the Kara Sea [4‐6]. In winter, harp seals congregate in the White Sea for mating and breeding; they live in large herds on ice floes from December to May. The abundance of offspring annually born in spring on ice reaches more than 300 thousand pups [7]. The hydrometeorological conditions of the White Sea ensure gradual drift of ice floes with adult seals and pups from the central areas of the sea to the northeast areas and then to the Barents Sea. Harp seal pups live in the White Sea from February to May. Postnatal development of pups (suckling, moult, and transition to independent nutrition) takes place on drifting ice floes; at this time, young seals adapt to leaving in water. The short breeding (pupping) period, high breeding rate, and sufficient fatness of pups at the end of the suckling period are the key adaptation components. However, published data regarding these issues are scanty. It is known that body weight of pups increases after birth, the suckling period lasts for two weeks, and the postembryonic moult lasts for 25‐ 30 days [8, 9]. In the White Sea, the pupping period of harp seals continues for approximately four weeks [8‐11]. The pupping period of harp seals in 1925‐1935 began

Role of predation by harp seals Pagophilus groenlandicus in the collapse and non-recovery of northern Gulf of St. Lawrence cod Gadus morhua

A statistical catch-at-age model was developed to assess the effects of predation by the northwest Atlantic harp seal population on northern Gulf of St. Lawrence cod by estimating the rela- tive importance of different sources of mortality that affected the stock during a period of collapse and non-recovery. Cod recruitment at age 1 is modeled via a non-linear stock-recruitment relation- ship based on total egg production and accounts for changes in female length-at-maturity and cod condition. Natural mortality other than seal predation also depends on cod condition used as an inte- grative index of changes in environmental conditions. The linkage between seals and cod is modeled through a multi-age functional response that was derived from the reconstruction of the seal diet using morphometric relationships and stomach contents of more than 200 seals collected between 1998 and 2001. The model was fitted following a maximum likelihood estimation approach to a sci- entific survey abundance index (1984 to 2006). Model results show that the collapse of the northern Gulf of St. Lawrence cod stock was mainly due to the combination of high fishing mortality rates and poor environmental conditions in the early to mid-1990s contributing to the current state of recruit- ment overfishing. The increase in harp seal abundance during 1984 to 2006 was reflected by an increase in predation mortality for the young cod age-groups targeted by seals. Although current levels of predation mortality affect cod spawning biomass, the lack of recovery of the NGSL cod stock seems mainly due to the very poor recruitment.

Dorset Palaeoeskimo Skin Processing at Phillip's Garden, Port au Choix, Northwestern Newfoundland

This paper examines artifactual and palaeo-limnological evidence of sealskin processing associated with Phillip’s Garden, a Dorset Palaeoeskimo site at Port au Choix in northwestern Newfoundland. We propose that harp seals were hunted from Phillip’s Garden as much for skins as for meat and fat, and that processing sealskins was the first step in the important activity of making clothes, boots, and other items. We outline the steps and tools involved in sealskin processing throughout the northern circumpolar world, and we identify specialized skin-processing tools in the Phillip’s Garden tool assemblage. Sealskin processing is also inferred from pollen and chironomid data from Bass Pond, adjacent to Phillip’s Garden. Disturbance across pollen taxa is evident at 2200– 1400 cal BP, and anomalous salinity values are evident at 2000–1400 cal BP. We argue that these are connected to Palaeoeskimo activities at the pond, in particular Dorset sealskin soaking and tanning. This study shifts our perception of Dorset activities at Phillip’s Garden away from a narrow focus on seal hunting and the site itself and broadens our view to include more of the multiplicity of day-to-day human activities that took place within a larger cultural landscape that included Phillip’s Garden and Bass Pond.

Intrinsic and extrinsic sources of variation in the diets of harp and hooded seals revealed by fatty acid profiles

Individuals of different age, sex, and morphology are expected to exhibit differences in dietary niches largely owing to sexual dimorphism, ontogenetic niche shifts, and resource polymorphism. Harp ( Pagophilus groenlandicus (Erxleben, 1777)) and hooded ( Cystophora cristata (Erxleben, 1777)) seals are geographically overlapping and highly migratory predators in the North Atlantic Ocean. These species differ in their diving behaviour, with hooded seals diving deeper, longer, and more associated with the continental shelf edge and deep ocean than harp seals. We examined blubber fatty acid (FA) composition (N = 37; 93% of total FA by mass) of harp (adults N = 294; juveniles N = 232) and hooded (adults N = 118; juveniles N = 38) seals to test hypotheses about sources of intrinsic (age and sex) and extrinsic (geographic location, season, year) variations in diets. A significant difference in FA profiles suggested dietary segregation between species. We found significant effects of sex and age class on FA profiles, with these being more pronounced in the highly size-dimorphic hooded seals than in harp seals. FA profiles of both species also varied between inshore and offshore sampling locations and between prebreeding and postbreeding periods. Finally, FA profiles of harp seals differed among years, which was coincident with large changes in prey distribution and availability in the mid-1990s.

Gas Bubbles in Seals, Dolphins, and Porpoises Entangled and Drowned at Depth in Gillnets

Gas bubbles were found in 15 of 23 gillnet-drowned bycaught harp (Pagophilus groenlandicus), harbor (Phoca vitulina) and gray (Halichoerus grypus) seals, common (Delphinus delphis) and white-sided (Lagenorhyncus acutus) dolphins, and harbor porpoises (Phocaena phocaena) but in only 1 of 41 stranded marine mammals. Cases with minimal scavenging and bloating were chilled as practical and necropsied within 24 to 72 hours of collection. Bubbles were commonly visible grossly and histologically in bycaught cases. Affected tissues included lung, liver, heart, brain, skeletal muscle, gonad, lymph nodes, blood, intestine, pancreas, spleen, and eye. Computed tomography performed on 4 animals also identified gas bubbles in various tissues. Mean +/- SD net lead line depths (m) were 92 +/- 44 and ascent rates (ms(-1)) 0.3 +/- 0.2 for affected animals and 76 +/- 33 and 0.2 +/- 0.1, respectively, for unaffected animals. The relatively good carcass condition of these cases, comparable to 2 stranded cases that showed no gas formation on computed tomography (even after 3 days of refrigeration in one case), along with the histologic absence of bacteria and autolytic changes, indicate that peri- or postmortem phase change of supersaturated blood and tissues is most likely. Studies have suggested that under some circumstances, diving mammals are routinely supersaturated and that these mammals presumably manage gas exchange and decompression anatomically and behaviorally. This study provides a unique illustration of such supersaturated tissues. We suggest that greater attention be paid to the radiology and pathology of bycatch mortality as a possible model to better understand gas bubble disease in marine mammals.

Seals and Sea Ice in Medieval Greenland

Abstract Multidisciplinary approaches are used to examine possible changes in North Atlantic sea-ice cover, in the context of seal hunting, during the period of the Norse occupation of Greenland (ca. 985–1500). Information from Iceland is also used in order to amplify and illuminate the situation in Greenland. Data are drawn mainly from zooarchaeological analyses, but written records of climate and sea-ice variations, as well as paleoclimatic data sets are also discussed. Although it should be noted that any use of seal bones from excavated archaeofauna (animal bone collections from archaeological sites) must recognize the filtering effects of past human economic organization, technology, and seal-hunting strategies, it is suggested that differing biological requirements of the six seal species most commonly found in Arctic/North Atlantic regions may provide a potential proxy for past climate, in particular sea-ice conditions. It is concluded that an increase in the taking of harp seals, as opposed to com...

Ecosystem effects of the three capelin stock collapses in the Barents Sea

The Barents Sea capelin stock underwent drastic changes in stock size during the last three decades. Three stock collapses occurred in 1985–1989, 1993–1997, and 2003–2006. The collapses had effects both downwards and upwards in the food web. The release in predation pressure from the capelin stock led to increased amounts of zooplankton during the collapse periods. When capelin biomass was drastically reduced, its predators were affected in various ways. Cod experienced increased cannibalism, growth was reduced and maturation delayed. Sea birds experienced increased rates of mortality and total recruitment failures, and breeding colonies were abandoned for several years. Harp seals experienced food shortage, increased mortality because they invaded the coastal areas and were caught in fishing gears, and recruitment failures. There is evidence for differences in how the three capelin collapses affected the predators. The effects were most serious during the 1985–1989 collapse and can hardly be traced during the ongoing collapse. We conclude that these differences likely result from increased availability of alternative food sources during the two last periods of collapse.

Transfer of lipids from plankton to blubber of harp and hooded seals off East Greenland

Sub-Arctic marine ecosystems are some of the most productive ecosystems in the world's oceans. The capacity of herbivorous zooplankton, such as Calanus, to biosynthesize and store large amounts of lipids during the short and intense spring bloom is a fundamental adaptation which facilitates the large production in these ecosystems. These energy-rich lipids are rapidly transferred through the food chain to Arctic seals. The fatty acids and stable isotopes from harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) off East Greenland as well as their potential prey, were analysed. The results were used to describe the lipid dynamics and energy transfer in parts of the East Greenland ecosystem. Even if the two seal species showed considerable overlap in diet and occurred at relatively similar trophic levels, the fatty acid profiles indicated that the bases of the food chains of harp and hooded seals were different. The fatty acids of harp seals originate from diatom-based food chain, whereas the fatty acids of hooded seals originate from dinoflagellate and the prymnesiophyte Phaeocystis pouchetii-based food chain. Stable isotope analyses showed that both species are true carnivores on the top of their food chains, with hooded seal being slightly higher on the food chain than harp seal.

Distribution Patterns Suggest Biomagnification of Halogenated 1′-Methyl-1,2′-Bipyrroles (MBPs)

The halogenated 1'-methyl-1,2'-bipyrroles (MBPs) are a suite of marine natural products that have been detected in marine mammals worldwide. Although their concentrations are similar to persistent organic pollutants that biomagnify, such as 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153), it is notyet clearthat these natural products also biomagnify. Here we analyze MBPs and CB-153 isolated from the blubber and liver of marine mammals stranded on the eastern coast of Massachusetts. Four odontocete species (Delphinus delphis, Lagenorhynchus acutus, Phocoena phocoena, and Globicephala melas) and two pinniped species (Halichoerus grypus and Phoca groenlandica) were sampled. MBPs were present in all odontocetes, but not detected in pinnipeds; CB-153 was detected in every species. MBP patterns indicative of biomagnification were found, including age-dependent concentration increases and reduced concentrations in adult females. Also explored were the similarities and differences with CB-153, the effects of nutritional state on contaminant distribution, and the maternal transfer of blubber-based organic contaminants.

Seasonal energetics of northern phocid seals

The metabolic rate of harp ( Pagophilus groenlandicus), harbor ( Phoca vitulina), and ringed seals ( Pusa hispida) was measured at various temperatures in air and water to estimate basal metabolic rates (BMRs) in these species. The basal rate and body composition of three harp seals were also measured throughout the year to examine the extent to which they vary seasonally. Marine mammalian carnivores generally have BMRs that are over three times the rates expected from body mass in mammals generally, both as a response to a cold-water distribution and to carnivorous food habits with the basal rates of terrestrial carnivores averaging about 1.8 times the mean of mammals. Phocid seals, however, have basal rates of metabolism that are 30% lower than other marine carnivores. Captive seals undergo profound changes in body mass and food consumption throughout the year, and after accounting for changes in body mass, the lowest rate of food intake occurs in summer. Contrary to earlier observations, harp seals also have lower basal rates during summer than during winter, but the variation in BMR, relative to mass expectations, was not associated with changes in the size of fat deposits. The summer reduction in energy expenditure and food consumption correlated with a reduction in BMR. That is, changes in BMR account for a significant portion of the seasonal variation in energy expenditure in the harp seal. Changes in body mass of harp seals throughout the year were due not only to changes in the size of body fat deposits, but also to changes in lean body mass. These results suggest that bioenergetics models used to predict prey consumption by seals should include time-variant energy requirements.

POLAR BEAR DIETS AND ARCTIC MARINE FOOD WEBS: INSIGHTS FROM FATTY ACID ANALYSIS

We used quantitative fatty acid signature analysis (QFASA) to examine the diets of 1738 individual polar bears (Ursus maritimus) sampled across the Canadian Arctic over a 30‐year span. Polar bear foraging varied over large and small spatial and temporal scales, and between demographic groups. Diets in every subpopulation were dominated by ringed seals (Phoca hispida) and, in the eastern Arctic, secondarily by harp seals (Pagophilus groenlandica). Beluga whales (Delphinapterus leucas) were an important food source for bears in the High Arctic, which is consistent with previous anecdotal reports. Foraging patterns were most similar among neighboring subpopulations with similar prey assemblages, but also differed geographically within Western Hudson Bay. The sexual size dimorphism of polar bears had an important effect on foraging, as large bearded seals (Erignathus barbatus) and walruses (Odobenus rosmarus) were consumed most often by older, male bears, whereas ringed seals and, where available, harbor seals (P. vitulina) were most important to younger age classes. Larger, older bears also had the greatest dietary diversity, apparently because of their ability to include larger‐bodied prey. During spring and summer, polar bears in some areas increased predation on migratory harp seals and beluga whales. In Western Hudson Bay, bearded seal consumption declined between 1995 and 2001 for both male and female bears and continued to decline among females up to the most recent sampling (2004). Ringed seal consumption in Western Hudson Bay increased between 1998 and 2001, perhaps in response to increased ringed seal productivity, but was not significantly affected by date of sea‐ice breakup. Overall, our data indicate that polar bears are capable of opportunistically altering their foraging to take advantage of locally abundant prey, or to some degree compensating for a decline in a dominant prey species. However, in other areas polar bears are dependent on the availability of ringed and bearded seals. Recent population data suggest that polar bears with the most specialized diets may be most vulnerable to climate‐related changes in ice conditions. The results of this large‐scale, ecosystem‐based study indicate a complex relationship between sea‐ice conditions, prey population dynamics, and polar bear foraging.