Chukchi Sea Polar Bears Faring Well Despite Declining Sea Ice

Polar bears in other locations not so lucky

By Kendra Pierre-Louis on November 18, 2013 9:13 AM EST

NOAA's National Ocean Service

Perhaps no other animal has become such a recognizable symbol of climate change as the polar bear. The large, nimble, and incredibly photogenic ursine is imperiled because unlike its kin — the Kodiak brown bear, the inland grizzly bear,  and the forest-dwelling black bear — the polar bear is a marine mammal that depends on Arctic sea ice for its survival. This is why a recent study on polar bear populations, which states that some bear populations are less sensitive to sea ice decline than previously thought, is raising some eyebrows.

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Polar bears spend eight months of the year at sea. They use the frozen sea, and ice flows, to bring them close to their prey of choice: the ringed seal. Their hunt is slow and steady; polar bears patiently wait for the seals to surface for air at breathing holes called aglus. The fatty flesh of a ringed seal's blubber provides enough nutrition to sustain a polar bear, whereas most land sources of food fail to provide the needed fat. Polar bears need to hunt on the ice because they are not adept enough to hunt the seals in open water.

Consequently, the traditional wisdom — and most evidence — has indicated that as the sea ice declines so too do polar bear populations. But this recent study published in Global Change Biology conducted by researchers from the U.S. Geological Survey, the U.S. Fish and Wildlife Service, and other institutions, on the effect of declines in sea ice habitat on polar bear populations has found that the picture might be more complex.

The study analyzes the health of polar bear populations based on size, condition, and the number of polar bears the researchers were able to successfully capture (a concept the researchers call "recruitment"), in the Bering and Chukchi sea, between two periods (1986-1994 and 2008-2011) when declines in sea ice habitat occurred. What they found was that on the Chukchi Sea, a marginal sea of the Arctic Ocean, polar bear populations remained steady despite an average reduction of sea ice of 44 days (sea ice is measured in days; for most of the year the sea is not frozen enough to provide the bears with stable hunting platforms).

The polar bears on the Bering Sea, a marginal sea of the Pacific Ocean, however, did not fare so well. They suffered declines in population as well as in overall wellbeing. As the researchers themselves point out, these geographic differences in the ways polar bears respond to climate change has broader applications to population forecasts not just in regards to polar bears but also to ice-dependent species more broadly. 

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