By DeGange, Anthony R.
Endangered Species Bulletin , Vol. 33, No. 3
What do polar bears, Pacific walrus, spectacled eiders, and Kittlitz's murrelets have in common? In a word--ice! Although the effects of climate change can now be observed almost anywhere in the United States, nowhere are the effects more prominent than in Alaska, where unprecedented rates of sea ice loss, tidewater glacier recession, coastal erosion, permafrost degradation, and other landscape changes presage major changes to Alaska wildlife populations.
Climate change will play an increasingly significant role in future decisions related to the Endangered Species Act (ESA), and research is critical to understand how wildlife and their habitats will change as the climate continues to warm. These four ice-related species exemplify the diverse approaches to research undertaken by biologists in the U.S. Geological Survey's Alaska Science Center (ASC) to help unravel the mysteries associated with climate change and wildlife in Alaska.
The summer of 2007 set another record in sea ice loss in the Arctic since satellite measurements began in 1979. Two species are emblematic of Arctic sea ice: the polar bear (Ursus maritimus) and the Pacific walrus (Odobenus rosemarus). The Secretary of the Interior announced the listing of polar bears as threatened under the ESA on May 14, 2008. Polar bears depend on sea ice for much of their life history needs. They mate and den on sea ice, travel on sea ice, and feed almost exclusively on seals captured from the sea ice surface. Pacific walrus are currently the subject of a petition to list under the ESA.
The ASC's polar bear research team, under the direction of Steve Amstrup and George Durner, has been studying polar bears in Alaska for several decades. This extensive research record now enables comparisons of denning behavior, size and condition, and survival between periods when sea ice was abundant over the productive continental shelf and recent years, when it has been absent for increasingly longer periods of time. ASC biologists have documented a shift in the proportion of dens on sea ice to land in response to changing sea ice conditions, as well as declines in some measurements of body size and condition. Perhaps one of the most critical findings was the ability to link survival of polar bears to sea ice. In other words, survival of polar bears was higher in years when sea ice covered the continental shelf for longer periods of time, presumably because bears continued to have access to ice seals, their preferred prey. A similar relationship between sea ice and survival was also documented by ASC biologists, in collaboration with their Canadian colleagues, for polar bears in Western Hudson Bay, Canada.
In 2007, in response to requests from the Fish and Wildlife Service (FWS) and the Secretary of the Interior, the ASC assembled an international, interdisciplinary team of polar bear scientists, sea ice experts, and computer modelers to conduct analyses to help inform the listing decision on polar bears. In addition to understanding the current status of several polar bear subpopulations in Alaska and Canada, the team developed population and habitat models using sea ice forecasts from climate models to understand how the Southern Beaufort Sea polar bear population and polar bear sea ice habitat will change with future declines in sea ice.
The results of this study suggest a bleak outlook for polar bears. Polar bears were forecasted to decline throughout all of their range during this century, but the severity of the decline will depend upon the status of sea ice where they reside. In areas of seasonal sea ice, or where sea ice is receding far north of the continental shelf each summer and fall, extirpation was forecast as the most likely outcome for polar bears by mid-century. Polar bears were predicted to persist longer in areas of northern Canada and Greenland where sea is expected to be more stable. …