Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity

The effects of declining Arctic sea ice on local ecosystem productivity are not well understood but have been shown to vary inter‐specifically, spatially, and temporally. Because marine mammals occupy upper trophic levels in Arctic food webs, they may be useful indicators for understanding variation in ecosystem productivity. Polar bears (Ursus maritimus) are apex predators that primarily consume benthic and pelagic‐feeding ice‐associated seals. As such, their productivity integrates sea ice conditions and the ecosystem supporting them. Declining sea ice availability has been linked to negative population effects for polar bears but does not fully explain observed population changes. We examined relationships between spring foraging success of polar bears and sea ice conditions, prey productivity, and general patterns of ecosystem productivity in the Beaufort and Chukchi Seas (CSs). Fasting status (≥7 days) was estimated using serum urea and creatinine levels of 1,448 samples collected from 1,177 adult and subadult bears across three subpopulations. Fasting increased in the Beaufort Sea between 1983–1999 and 2000–2016 and was related to an index of ringed seal body condition. This change was concurrent with declines in body condition of polar bears and observed changes in the diet, condition and/or reproduction of four other vertebrate consumers within the food chain. In contrast, fasting declined in CS polar bears between periods and was less common than in the two Beaufort Sea subpopulations consistent with studies demonstrating higher primary productivity and maintenance or improved body condition in polar bears, ringed seals, and bearded seals despite recent sea ice loss in this region. Consistency between regional and temporal variation in spring polar bear fasting and food web productivity suggests that polar bears may be a useful indicator species. Furthermore, our results suggest that spatial and temporal ecological variation is important in affecting upper trophic‐level productivity in these marine ecosystems.     

Climate change impacts on wildlife in a High Arctic archipelago – Svalbard,Norway

The Arctic is warming more rapidly than other region on the planet, and the northern Barents Sea, including the Svalbard Archipelago, is experiencing the fastest temperature increases within the circumpolar Arctic, along with the highest rate of sea ice loss. These physical changes are affecting a broad array of resident Arctic organisms as well as some migrants that occupy the region seasonally. Herein, evidence of climate change impacts on terrestrial and marine wildlife in Svalbard is reviewed, with a focus on bird and mammal species. In the terrestrial ecosystem, increased winter air temperatures and concomitant increases in the frequency of ‘rain‐on‐snow’ events are one of the most important facets of climate change with respect to impacts on flora and fauna. Winter rain creates ice that blocks access to food for herbivores and synchronizes the population dynamics of the herbivore–predator guild. In the marine ecosystem, increases in sea temperature and reductions in sea ice are influencing the entire food web. These changes are affecting the foraging and breeding ecology of most marine birds and mammals and are associated with an increase in abundance of several temperate fish, seabird and marine mammal species. Our review indicates that even though a few species are benefiting from a warming climate, most Arctic endemic species in Svalbard are experiencing negative consequences induced by the warming environment. Our review emphasizes the tight relationships between the marine and terrestrial ecosystems in this High Arctic archipelago. Detecting changes in trophic relationships within and between these ecosystems requires long‐term (multidecadal) demographic, population‐ and ecosystem‐based monitoring, the results of which are necessary to set appropriate conservation priorities in relation to climate warming.     

Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes

Polar bears (Ursus maritimus) in the northern Alaska region den in coastal areas and on offshore drifting ice. We evaluated changes in the distribution of polar bear maternal dens between 1985 and 2005, using satellite telemetry. We determined the distribution of maternal dens occupied by 89 satellite collared female polar bears between 137°W and 167°W longitude. The proportion of dens on pack ice declined from 62% in 1985–1994 to 37% in 1998–2004 (P = 0.044) and among pack ice dens fewer occurred in the western Beaufort Sea after 1998. We evaluated whether hunting, attraction to bowhead whale remains, or changes in sea ice could explain changes in den distribution. We concluded that denning distribution changed in response to reductions in stable old ice, increases in unconsolidated ice, and lengthening of the melt season. In consort, these changes have likely reduced the availability and quality of pack ice denning habitat. Further declines in sea ice availability are predicted. Therefore, we expect the proportion of polar bears denning in coastal areas will continue to increase, until such time as the autumn ice retreats far enough from shore that it precludes offshore pregnant females from reaching the Alaska coast in advance of denning.     

Cooperative hunting roles among taï chimpanzees

All known chimpanzee populations have been observed to hunt small mammals for meat. Detailed observations have shown, however, that hunting strategies differ considerably between populations, with some merely collecting prey that happens to pass by while others hunt in coordinated groups to chase fast-moving prey. Of all known populations, Taï chimpanzees exhibit the highest level of cooperation when hunting. Some of the group hunting roles require elaborate coordination with other hunters as well as precise anticipation of the movements of the prey. The meat-sharing rules observed in this community guarantee the largest share of the meat to hunters who perform the most important roles leading to a capture. The learning time of such hunting roles is sometimes especially long. Taï chimpanzee males begin hunting monkeys at about age 10. The hunters’ progress in learning the more sophisticated hunting roles is clearly correlated with age; only after 20 years of practice are they able to perform them reliably. This lengthy learning period has also been shown in some hunter-gatherer societies and confirms the special challenge that hunting represents.     

Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell-Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Ni?o-Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.     

The optimal foraging theory, crowding and Swedish grouse hunters

Hunters that have options to hunt in different areas should evaluate their previous hunting success when they decide where to hunt. Following optimal foraging theory for non-human predators, we investigated if hunting success and density of other hunters on the hunting area will affect the probability of return to the same area, and if such behavioural changes will result in a higher hunting success compared to hunters that change to a new area. For this purpose, we used detailed information about willow grouse (Lagopus lagopus) hunters on state-owned land in Sweden. We found support for the optimal foraging theory application on grouse hunters’ behavioural changes according to hunting success. The return rate increased with increasing hunting success, and hunters that returned to the same area also increased their success compared to hunters that changed to a new area. Only one third of the hunters returned to the same area the subsequent year. We also found a negative effect of density of hunters in an area on hunters’ return rates and their hunting success, suggesting crowding among Swedish grouse hunters.     

Prey items and predation behavior of killer whales (Orcinus orca) in Nunavut, Canada based on Inuit hunter interviews

Background

Killer whales (Orcinus orca) are the most widely distributed cetacean, occurring in all oceans worldwide, and within ocean regions different ecotypes are defined based on prey preferences. Prey items are largely unknown in the eastern Canadian Arctic and therefore we conducted a survey of Inuit Traditional Ecological Knowledge (TEK) to provide information on the feeding ecology of killer whales. We compiled Inuit observations on killer whales and their prey items via 105 semi-directed interviews conducted in 11 eastern Nunavut communities (Kivalliq and Qikiqtaaluk regions) from 2007-2010.

Results

Results detail local knowledge of killer whale prey items, hunting behaviour, prey responses, distribution of predation events, and prey capture techniques. Inuit TEK and published literature agree that killer whales at times eat only certain parts of prey, particularly of large whales, that attacks on large whales entail relatively small groups of killer whales, and that they hunt cooperatively. Inuit observations suggest that there is little prey specialization beyond marine mammals and there are no definitive observations of fish in the diet. Inuit hunters and elders also documented the use of sea ice and shallow water as prey refugia.

Conclusions

By combining TEK and scientific approaches we provide a more holistic view of killer whale predation in the eastern Canadian Arctic relevant to management and policy. Continuing the long-term relationship between scientists and hunters will provide for successful knowledge integration and has resulted in considerable improvement in understanding of killer whale ecology relevant to management of prey species. Combining scientists and Inuit knowledge will assist in northerners adapting to the restructuring of the Arctic marine ecosystem associated with warming and loss of sea ice.     

Temporal variability in arctic fox diet as reflected in stable-carbon isotopes; the importance of sea ice

Consumption of marine foods by terrestrial predators can lead to increased predator densities, potentially impacting their terrestrial resources. For arctic foxes (Alopex lagopus), access to such marine foods in winter depends on sea ice, which is threatened by global climate change. To quantify the importance of marine foods (seal carrion and seal pups) and document temporal variation in arctic fox diet I measured the ratios of the stable isotopes of carbon (¹³C/¹²C) in hair of arctic foxes near Cape Churchill, Manitoba, from 1994 to 1997. These hair samples were compared to the stable carbon isotope ratios of several prey species. Isotopic differences between seasonally dimorphic pelage types indicated a diet with a greater marine content in winter when sea ice provided access to seal carrion. Annual variation in arctic fox diet in both summer and winter was correlated with lemming abundance. Marine food sources became much more important in winters with low lemming populations, accounting for nearly half of the winter protein intake following a lemming decline. Potential alternative summer foods with isotopic signatures differing from lemmings included goose eggs and caribou, but these were unavailable in winter. Reliance on marine food sources in winter during periods of low lemming density demonstrates the importance of the sea ice as a potential habitat for this arctic fox population and suggests that a continued decline in sea ice extent will disrupt an important link between the marine and terrestrial ecosystems.     

Antibodies to marine caliciviruses in the Pacific walrus (Odobenus rosmarus divergens Illiger)

Sera from 155 Pacific walruses (Odobenus rosmarus divergens Illiger), sampled in the Chukchi Sea during the summer of 1983, were tested for serum neutralizing (SN) antibodies to six marine calicivirus serotypes. Serotypes tested included San Miguel sea lion virus (SMSV) types 1, 5, 8, and 10, previously isolated from northern fur seals (Callorhinus ursinus Linné) in the Bering Sea; walrus calicivirus (WCV), previously isolated from walrus feces collected off sea ice in the Chukchi Sea; and Tillamook calicivirus (TCV), a bovine isolate from Oregon of suspected marine origin. No antibodies were found to SMSV-1, SMSV-10, or TCV. Antibodies to SMSV-5 were found in two animals (titers 1:20 and 1:160); antibodies to SMSV-8 were found in four animals (all 1:20); and antibodies to WCV were found in one animal (titer 1:40). Antibodies to WCV have been found in the Pacific walrus previously; however, this represents the first report of antibodies to any of the SMSV serotypes in this marine mammal.     

Evolutionary Implications of Persistence Hunting: An Examination of Energy Return on Investment for !Kung Hunting

Hominins are smaller, slower, and weaker than most large mammals, yet they have been eating meat from freshly killed large mammals since before the invention of sophisticated weaponry. It is thought that they could have achieved this seemingly impossible feat through persistence hunting, a practice powered by endurance running. Essentially, one or more hunters pursue a prey animal in the heat of the day until it reaches the point of hyperthermia. This allows a hunter to safely kill the weakened animal at close range using methods such as beating, strangling, or spearing. The energy balance of this approach to getting food is controversial and has not been calculated previously. We examined the energy costs and gains of persistence hunting through several energy returned on investment (EROI) calculations based on synthesizing available field and laboratory data on the energy used by the hunters and the energy returned from the greater kudu (Tragelaphus strepsiceros). We estimate that the EROI of these hunter-gatherers hunting a kudu ranged from 26:1 to 69:1. The net energy gained from such an effort would sustain an average sized !Kung family for 6.7 to 11.2 days. The “profit” energy within these ranges would have supported the early human societies that practiced persistence hunting, contributing to the often-noted “leisure” characterizing many foraging societies (Sahlins 1974).     

Effects of climate warming on polar bears: a review of the evidence

Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze‐up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long‐term survival. To maintain viable subpopulations, polar bears depend on sea ice as a platform from which to hunt seals for long enough each year to accumulate sufficient energy (fat) to survive periods when seals are unavailable. Less time to access to prey, because of progressively earlier breakup in spring, when newly weaned ringed seal (Pusa hispida) young are available, results in longer periods of fasting, lower body condition, decreased access to denning areas, fewer and smaller cubs, lower survival of cubs as well as bears of other age classes and, finally, subpopulation decline toward eventual extirpation. The chronology of climate‐driven changes will vary between subpopulations, with quantifiable negative effects being documented first in the more southerly subpopulations, such as those in Hudson Bay or the southern Beaufort Sea. As the bears' body condition declines, more seek alternate food resources so the frequency of conflicts between bears and humans increases. In the most northerly areas, thick multiyear ice, through which little light penetrates to stimulate biological growth on the underside, will be replaced by annual ice, which facilitates greater productivity and may create habitat more favorable to polar bears over continental shelf areas in the short term. If the climate continues to warm and eliminate sea ice as predicted, polar bears will largely disappear from the southern portions of their range by mid‐century. They may persist in the northern Canadian Arctic Islands and northern Greenland for the foreseeable future, but their long‐term viability, with a much reduced global population size in a remnant of their former range, is uncertain.     

Decadal shifts in autumn migration timing by Pacific Arctic beluga whales are related to delayed annual sea ice formation

Migrations are often influenced by seasonal environmental gradients that are increasingly being altered by climate change. The consequences of rapid changes in Arctic sea ice have the potential to affect migrations of a number of marine species whose timing is temporally matched to seasonal sea ice cover. This topic has not been investigated for Pacific Arctic beluga whales (Delphinapterus leucas) that follow matrilineally maintained autumn migrations in the waters around Alaska and Russia. For the sympatric Eastern Chukchi Sea (‘Chukchi’) and Eastern Beaufort Sea (‘Beaufort’) beluga populations, we examined changes in autumn migration timing as related to delayed regional sea ice freeze‐up since the 1990s, using two independent data sources (satellite telemetry data and passive acoustics) for both populations. We compared dates of migration between ‘early’ (1993–2002) and ‘late’ (2004–2012) tagging periods. During the late tagging period, Chukchi belugas had significantly delayed migrations (by 2 to >4 weeks, depending on location) from the Beaufort and Chukchi seas. Spatial analyses also revealed that departure from Beaufort Sea foraging regions by Chukchi whales was postponed in the late period. Chukchi beluga autumn migration timing occurred significantly later as regional sea ice freeze‐up timing became later in the Beaufort, Chukchi, and Bering seas. In contrast, Beaufort belugas did not shift migration timing between periods, nor was migration timing related to freeze‐up timing, other than for southward migration at the Bering Strait. Passive acoustic data from 2008 to 2014 provided independent and supplementary support for delayed migration from the Beaufort Sea (4 day yr^?1) by Chukchi belugas. Here, we report the first phenological study examining beluga whale migrations within the context of their rapidly transforming Pacific Arctic ecosystem, suggesting flexible responses that may enable their persistence yet also complicate predictions of how belugas may fare in the future.     

Promoting hunting tourism in north Sweden: opinions of local hunters

Hunting tourism can help to diversify local economies in rural areas. In northern Sweden, hunting tourism has the potential to counteract outmigration and unemployment, but may entail ecological and social risks. I used a mail survey of 2,110 hunters in rural northern Sweden to assess attitudes toward hunting tourism. Respondents emphasized the importance of hunting to maintain economical, social, and cultural values in the rural areas. Most hunters estimated that game contributed equal or larger amount of meat to their household than meat bought commercially. Few respondents had first hand experience of hunting tourism and they were divided on their attitude towards promoting hunting tourism. Many (46%) were uncertain about their attitude towards hunting tourism; 36% were positive and 18% were negative. Ethical values on using wildlife in hunting tourism and the attitude towards new hunters coming to hunt influenced attitudes on development of hunting tourism. Hunters that were positive to hunting tourism believed that it would create new jobs. Because hunting in Sweden is highly organized and collective, there are no models of hunting tourism adapted to the hunting culture in northern Sweden. The uncertainty of the potential local benefits from a development of hunting tourism should be placed within a research framework, especially in the northernmost parts where governmental undertakings are large and the state can influence land use.     

Marine pelagic ecosystems: the west Antarctic Peninsula

The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2 degrees C increase in the annual mean temperature and a 6 degrees C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6 degrees C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along the WAP and the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response.     

Arctic Ocean microbial community structure before and after the 2007 record sea ice minimum

Increasing global temperatures are having a profound impact in the Arctic, including the dramatic loss of multiyear sea ice in 2007 that has continued to the present. The majority of life in the Arctic is microbial and the consequences of climate-mediated changes on microbial marine food webs, which are responsible for biogeochemical cycling and support higher trophic levels, are unknown. We examined microbial communities over time by using high-throughput sequencing of microbial DNA collected between 2003 and 2010 from the subsurface chlorophyll maximum (SCM) layer of the Beaufort Sea (Canadian Arctic). We found that overall this layer has freshened and concentrations of nitrate, the limiting nutrient for photosynthetic production in Arctic seas, have decreased. We compared microbial communities from before and after the record September 2007 sea ice minimum and detected significant differences in communities from all three domains of life. In particular, there were significant changes in species composition of Eukarya, with ciliates becoming more common and heterotrophic marine stramenopiles (MASTs) accounting for a smaller proportion of sequences retrieved after 2007. Within the Archaea, Marine Group I Thaumarchaeota, which earlier represented up to 60% of the Archaea sequences in this layer, have declined to <10%. Bacterial communities overall were less diverse after 2007, with a significant decrease of the Bacteroidetes. These significant shifts suggest that the microbial food webs are sensitive to physical oceanographic changes such as those occurring in the Canadian Arctic over the past decade.     

Retention of ice-associated amphipods: possible consequences for an ice-free Arctic Ocean

Recent studies predict that the Arctic Ocean will have ice-free summers within the next 30 years. This poses a significant challenge for the marine organisms associated with the Arctic sea ice, such as marine mammals and, not least, the ice-associated crustaceans generally considered to spend their entire life on the underside of the Arctic sea ice. Based upon unique samples collected within the Arctic Ocean during the polar night, we provide a new conceptual understanding of an intimate connection between these under-ice crustaceans and the deep Arctic Ocean currents. We suggest that downwards vertical migrations, followed by polewards transport in deep ocean currents, are an adaptive trait of ice fauna that both increases survival during ice-free periods of the year and enables re-colonization of sea ice when they ascend within the Arctic Ocean. From an evolutionary perspective, this may have been an adaptation allowing success in a seasonally ice-covered Arctic. Our findings may ultimately change the perception of ice fauna as a biota imminently threatened by the predicted disappearance of perennial sea ice.     

Subsistence hunting and bushmeat exploitation in central-western Tanzania

An ethnozoological research was carried out in the Tabora District (central-western Tanzania) from December '95 to February '96, to gather information on the sustainable exploitation of wildlife there and to outline the zoological culture of the native people (the Banyamwezi). The objective was to describe the hunting activity and the techniques employed in capturing wild mammals and to gather quantitative data on game harvest. An inventory of the mammal species living in the study area was conducted by three different methods: (1) direct field observation of animals and their tracks; (2) identification of animals captured by the villagers; (3) interviews with the hunters. The activities of 10 local hunters from seven villages were followed during a nine week period. The number of mammals killed and the techniques used for each species were recorded. Other data were collected through interviews of the villagers and concerned (1) the use of every species as food or for other purposes; (2) the species considered as pests; (3) the best places and time for hunting the different species; (4) the time spent hunting them; (5) the food restrictions and taboos; (6) the extent of the bushmeat market (quantity, price, etc.). A total of 236 animals belonging to 37 species were killed during the study period with the following breakdown into taxonomic groups: Bovidae (44.06%), Carnivora (22.88%), Lagomorpha (8.05%), Rodentia (7.2%), diurnal Primates (5.93%), Insectivora (4.23%), Hyracoidea (0.84%), nocturnal Primates (0.84%), Hippopotamidae (0.42%) and Pholidota (0.42%). Four different techniques were used by local hunters in the study area: guns (53.81%), traps (19.06%), spears (11.01%) and dogs (16.01%). Poaching is rampant because of the scarcity of ranger staff and vehicles for patrolling.     

Isotope evidence for the intensive use of marine foods by Late Upper Palaeolithic humans

We report here on direct evidence for the intensive consumption of marine foods by anatomically modern humans at approximately 12,000 years ago. We undertook isotopic analysis of bone collagen from three humans, dating to the late Palaeolithic, from the site of Kendrick's Cave in North Wales, UK. The isotopic measurements of their bone collagen indicated that ca. 30% of their dietary protein was from marine sources, which we interpret as likely being high trophic level marine organisms such as marine mammals. This indicates that towards the end of the Pleistocene modern humans were pursuing a hunting strategy that incorporated both marine and terrestrial mammals. This is the first occurrence of the intensive use of marine resources, specifically marine mammals, that becomes even more pronounced in the subsequent Mesolithic period.     

Environmental determinants of top predator distribution within the dynamic winter pack ice zone of the northern Antarctic Peninsula

Global warming is predicted to reduce the amount of sea ice concentration in polar environments, thus presenting profound changes for populations of seabirds and marine mammals dependent on sea ice. Using data from a shipboard survey during August 2012, I test the hypothesis that relative abundance of seabird and marine mammals reflects environmental variability associated with the dynamic pack ice zone. Using environmental data and observations of sea ice concentration, I quantified an environmental gradient that describes the spatial organization of the dynamic pack ice zone. The relationship of top predators to this environmental gradient revealed three important aspects: (1) an open water and pack ice community is present with some top predator species exhibiting higher abundance associated with moderate sea ice concentration (40–60 %) as opposed to the pack ice edge (10 %), (2) Antarctic fur seals (Arctocephalus gazella) were the most abundant pinniped and they were observed resting on ice floes and foraging within leads and polynyas, and (3) for the most abundant species, spatial regression models indicate that latitude and sea ice concentration (a principal north/south gradient) are the most important environmental determinants. Winter ocean conditions may strongly influence population dynamics of top predators; therefore, information regarding their habitat use during winter is needed for understanding ecosystem dynamics.     

Pre-partum diet of adult female bearded seals in years of contrasting ice conditions

Changing patterns of sea-ice distribution and extent have measurable effects on polar marine systems. Beyond the obvious impacts of key-habitat loss, it is unclear how such changes will influence ice-associated marine mammals in part because of the logistical difficulties of studying foraging behaviour or other aspects of the ecology of large, mobile animals at sea during the polar winter. This study investigated the diet of pregnant bearded seals (Erignathus barbatus) during three spring breeding periods (2005, 2006 and 2007) with markedly contrasting ice conditions in Svalbard using stable isotopes (δ(13)C and δ(15)N) measured in whiskers collected from their newborn pups. The δ(15)N values in the whiskers of individual seals ranged from 11.95 to 17.45 ‰, spanning almost 2 full trophic levels. Some seals were clearly dietary specialists, despite the species being characterised overall as a generalist predator. This may buffer bearded seal populations from the changes in prey distributions lower in the marine food web which seems to accompany continued changes in temperature and ice cover. Comparisons with isotopic signatures of known prey, suggested that benthic gastropods and decapods were the most common prey. Bayesian isotopic mixing models indicated that diet varied considerably among years. In the year with most fast-ice (2005), the seals had the greatest proportion of pelagic fish and lowest benthic invertebrate content, and during the year with the least ice (2006), the seals ate more benthic invertebrates and less pelagic fish. This suggests that the seals fed further offshore in years with greater ice cover, but moved in to the fjords when ice-cover was minimal, giving them access to different types of prey. Long-term trends of sea ice decline, earlier ice melt, and increased water temperatures in the Arctic are likely to have ecosystem-wide effects, including impacts on the forage bases of pagophilic seals.