2/9/2011 2:56:36 PM

Cub Losses Threaten Churchill's Polar Bears

A new study by University of Alberta biologists, including PBI Advisory Council Scientist Andrew Derocher, predicts that Western Hudson Bay polar bears will be unable to reproduce at the level needed to sustain the population if current warming trends continue.

The study, published in the journal Nature Communications, predicts that up to 73% of pregnant female polar bears in the Western Hudson Bay population will not give birth to cubs if the sea ice breaks up one month earlier in summer.

According to biologist Peter Molner, the paper's lead author, the viability of the species across much of the Arctic will be in question if climate change continues unabated.

The Western Hudson Bay population of polar bears, which includes those bears that gather near the town of Churchill each fall, is forced ashore each summer when the sea ice melts. This leaves the bears without access to seals, the mainstay of their diet, until the bay freezes again in the fall.

During the ice-free season, the bears enter a prolonged fasting state. But the sea ice has been breaking up earlier each year—and freeze-up has been coming later—leaving the bears with a shorter hunting season.

Longer ice-free seasons have a direct impact on pregnant female polar bears, who must build up fat reserves to sustain them during the denning period. If their fat stores are inadequate, they reabsorb the embryos and fail to give birth.

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