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Monday, November 26, 2007

Ice-melt causing death of Polar bears

Biologists have predicted that polar bears will struggle to survive as summer comes sooner to the Arctic. Less time spent on icy hunting platforms means the bears are slimming down before winter sets in, they said. A study of the polar bear population in Canada's Hudson Bay revealed that these animals rely on ice shelves as hunting grounds before winter sets in.

Anecdotal reports in 2005 say bears were found swimming far out at sea; a few were found floating dead, presumably drowned. So far no evidence has directly linked the trend of melting sea ice associated with climate change to bear deaths.

Now, looking at 20 years of data from bears captured along the coast of Hudson Bay, a team of scientists from the United States and Canada has found that fewer of the youngest and oldest bears survived in years when the ice broke early. Although the timing of ice break-up varies from year to year, the trend has been towards more days of open water. Historically, ice has filled Hudson Bay for eight months each year. Now the ice is clearing nearly three weeks earlier than it did 30 years ago.

Since 1984, wildlife managers have captured some bears that spend their summers on the western shore of the bay, releasing them with ear tags and lip tattoos. The marks allow biologists to recognize individual bears, track their fate and estimate how many survive each winter. It was found that over a period of two decades, this population has declined by more than 20 percent.

Polar bears fast through their summer by stocking up on weanling ring seals. In early spring, the bears feast on unwary seal pups until the ice breaks up, storing up much of the energy they'll need to get by. In years when the ice breaks early, the less able hunters catch fewer seals than they need. The United States is considering listing polar bears as threatened under the Endangered Species Act; a decision on this is expected early next year.

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