DEROCHER, A.E.*; LUNN, N.J.; STIRLING, I.; University of Alberta, Edmonton; Canadian Wildlife Service, Edmonton; Canadian Wildlife Service, Edmonton: Polar bears in a changing climate

Polar bears (Ursus maritimus) live throughout the Arctic circumpolar ice-covered waters, particularly in nearshore annual ice with high biological productivity. However, under scenarios predicted by climate change models, their habitat may be severely altered. Spatial and temporal sea ice changes will lead to shifts in trophic interactions involving polar bears through reduced access to their main prey: seals. Climatic warming impacts can be studied by measuring the dynamics of energy intake relative to energy use. Altered space-use patterns will affect energy expenditure, prey intake and, consequently, body size. Altered sea ice formation and break-up may reduce habitat access and result in large-scale distribution shifts of polar bears. In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves. A cascade of impacts from reduced sea ice will be observed in reduced fat stores leading to lowered reproductive rates because females will have inadequate fat stores to fast through winter when cubs are born and nursed, or, in some areas, fast on land though progressively longer periods of open water in summer. As sea ice thins, becoming more labile, polar bear energy use will increase to maintain contact with preferred habitats. A northward shift in sea ice may result in reduced primary productivity and could result in key parts of the arctic marine ecosystem being moved off the continental shelf, over deeper waters, where benthic community linkages would be lost. Climate change may also impact species composition in Arctic marine ecosystems and while this may result in new prey species for polar bears (e.g., expansion of southern seals), there are risks associated with disease and parasite exposure.