ECOLOGY AND WILDLIFE: Climate Change and the Arctic Diet

Each spring, female polar bears and their cubs emerge from hibernation after months without food, and their survival depends on having good sea ice for hunting seals, their almost exclusive food. Also in spring, the Arctic sea ice begins to melt and break apart. Over the past 25 years, the timing of this melting has become less predictable as a consequence of warming in the Arctic, varying by more than a month. Researchers in Canada now report the first evidence that changes in the timing of the annual sea ice breakup have contributed to a dietary shift for polar bears from western Hudson Bay in the Canadian sub-Arctic. This shift may be accelerating the bears' bioaccum-ulation of some classes of persistent contaminants , and people who consume these animals as part of a traditional subsistence diet could face greater exposure to contaminants that are passed up the food chain. the team measured levels of pollutants including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ether (PBDE) flame retardants in western Hudson Bay polar bears between 1991 and 2007. They also measured fatty acids and carbon isotopes in the bears' fatty tissues to determine what types of seals the bears were eating. Ice-associated seals, which eat from the sea floor, leave a different carbon signature than open-water seals, which eat higher on the food chain and thus accumulate higher contaminant levels. In the years the sea ice broke up earlier, polar bears ate more open-water species such as harbor and harp seals instead of ice-associated species such as bearded seals, perhaps because the former are more abundant in light ice conditions. As evidenced by carbon isotope analyses, the timing of spring ice breakup explained 84% of the variation in the polar bears' diet from year to year. The researchers say the effects of the bears' dietary shift are large enough in the case of PCBs to offset an apparent trend of decreasing concentrations in western Hudson Bay bears over the study period and to significantly accelerate an increasing trend in PBDEs. Letcher notes, however, that levels of PCBs, PBDEs, and other pollutants such as perfluorooctane sulfonate (PFOS) vary considerably among other northern bear populations and that time trend data are lacking in many regions. Climate change could also increase long-distance transport of pollutants to the Arctic by changing atmospheric circulation and hydrology, according to Climate Change 2007: Impacts, Adaptation and Vul ner ability, …