Polar bear habitat preferences and prey availability in a changing sea ice environment:
In the Beaufort Sea, polar bears (Ursus maritimus), ringed seals (Phoca hispida), and bearded seals (Eriginathus barbatus), inhabit a seasonably dynamic environment that has experienced climate-induced changes. During most seasons polar bears prefer mixed ice habitats near ice edges in shallow waters over the continental shelf. In past decades, polar bears could maintain this habitat preference for nearshore ice, but in recent years, extensive ice melt has forced most polar bears to summer in deepwater ice habitat more than 200 km from the mainland coast. A smaller segment of the population is forced to use shoreline habitat. Other research suggests that prey resources may be diminished for polar bears force to occupy land and the deep water pack ice during summer. For example, the winter and spring distribution of ringed seals, the most important prey for polar bears, reflects the general distribution of polar bears. During summer, while some ringed seals may track the ice edge as it retreats north, others may have an open water life style and thus would be unavailable to polar bears. Bearded seals, due to their bottom-feeding habits, have not been available to polar bears summering over deep-water habitats during recent summers. In addition, a changing sea ice environment may affect reproduction of both predator and prey. Many pregnant polar bears in Alaska den on the active sea ice, the thinning of which brings into question whether winter ice has the stability necessary for successful denning. Seals also depend on sea ice for birth and hence are also susceptible to changes in the composition of sea ice. George Durner and Steven Amstrup, Session 33, Tuesday, Sept. 26, 8:40-9:00 a.m.
Survival and population size of polar bears in western Hudson Bay in relation to earlier sea ice breakup: