Feeding Ecology

• Variation in winter feeding ecology of southern Beaufort Sea polar bears inferred from stable isotope analysis
• Dietary biomagnification of organochlorine contaminants in Alaskan polar bears
• Stable isotope and mercury profiles in polar bears from Northern Alaska

Variation in winter feeding ecology of Southern Beaufort Sea polar bears inferred from stable isotope analysis

Polar bears are the top carnivore in the arctic marine ecosystem. Ringed seals represent the majority of their annual diet. This dependency on ringed seal likely varies temporally and spatially based on availability of sea ice, ringed seals and other prey sources. Polar bears also feed on bearded seals, beluga whales, and walrus. They also scavenge beach cast carcasses of gray whales, and on remains of bowheads landed by native subsistence hunters. Bowhead and gray whales, as well as walrus and bearded seal, represent food sources lower in trophic level than ringed seals. We used stable isotopes of nitrogen and carbon to help determine the importance of low trophic level prey in the diet of 139 free ranging polar bears sampled along Alaska’s Beaufort Sea coast in spring 2003 and 2004.

Ben Meyer¹, Katrina Knott¹, Cassandra Kirk¹, Geoff York², Steve Amstrup², Todd O’Hara¹

¹Wildlife Toxicology Laboratory, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks Alaska 99775
²US Geological Survey, Anchorage, Alaska 99503

Mercury is both a naturally occurring and anthropogenic element that bioaccumulates and biomagnifies in apex predators, such as polar bear and their prey.  Increasing observational and chemical data potentially indicates that polar bears have a diverse source of prey to hunt and scavenge (variety of pinnipeds and cetaceans).  The magnitude of this “variation” and its impact on polar bears is still in early debate. This emerging issue requires clarification with respect to exposure to contaminants.  Blood and hair samples from captured polar bears offer the opportunity to assess spatial, temporal, and feeding ecology related variations in exposure to mercury.  Samples available from captures in 2005 (n=62) were analyzed for mercury content as well as stable isotopes of C and N to examine correlations between trophic level and mercury bioaccumulation with respect to other biological variables (i.e. age, sex).

Stable isotope signatures of polar bears offer preliminary insight into factors that may affect contaminant exposure in wildlife populations.

Poster Presentation at Wildlife Society Meeting, Anchorage, Alaska 2006.