Early Ice Breakup Leads to Polar Bear Deaths

Scientists have linked a recent twenty percent decline in the number of polar bears living near the southern edge of their range to the earlier breakup of sea ice in spring.

The Western Hudson Bay polar bear population of an estimated 1,194 bears in 1987 dropped to 935 bears in 2004.

With the Arctic climate warming during this period, the 2004 breakup of sea ice occurred three weeks earlier than in 1987.

A solid ice pack is essential for polar bear survival as it provides the bears access to their main staple, seals. When ice over Hudson Bay disintegrates each spring, polar bears are forced ashore where they find little to eat.

During the 17-year study near Churchill, Manitoba, the date that sea ice broke apart varied from year to year. Researchers from Canada and the United States found that in years when sea ice broke up early, young bears and aging adults were more likely to die. However, the timing of breakup did not affect survival of adult male and female bears in their prime.

The study's authors warn that as climatic warming forecasted for the Arctic progresses, bear populations farther north will suffer in the same way these southernmost polar bears are in Hudson Bay.


Eric V. Regehr, Nicholas J. Lunn, Steven C. Amstrup and Ian Stirling. 2007. Effects of Earlier Sea Ice Breakup on Survival and Population Size of Polar Bears in Western Hudson Bay. Journal of Wildlife Management. 71(8): 2673-2683.

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