Forecasting the Range-wide Status of Polar Bears at Selected Times in the 21st Century

Abstract

To inform the U.S. Fish and Wildlife Service decision whether or not to list polar bears as threatened under the Endangered Species Act (ESA), we forecast the status of the world's polar bear (Ursus maritimus) populations 45, 75 and 100 years into the future. We applied the best available information about predicted changes in sea ice in the 21st century to current knowledge of polar bear populations and their ecological relationships to the sea ice to understand how the range-wide population of polar bears might change. We combined the world's 19 polar bear subpopulations into 4 ecological regions and projected sea ice conditions. These "ecoregions" are (1) the Seasonal Ice Ecoregion which includes Hudson Bay, and occurs mainly at the southern extreme of the polar bear range (2) the Archipelago Ecoregion of the Canadian Arctic, (3) the Polar Basin Divergent Ecoregion where ice is formed and then advected away from near-shore areas, and (4) the Polar Basin Convergent Ecoregion where sea ice formed elsewhere tends to collect against the shore. We incorporated projections of future sea ice in each ecoregion, based on 10 general circulation models (GCMs), into two models of polar bear habitat and potential population response.

Citation

Amstrup, Steven C.; Marcot, Bruce G.; Douglas, David C. 2007. Forecasting the Range-wide Status of Polar Bears at Selected Times in the 21st Century. In: USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision, U. S. Department of the Interior, p. 1-126