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Polar bear’s long swim illustrates ice melt

February 3, 2011

Searching for food, one female bear was tracked as she swam for 9 days across the Beaufort Sea before reaching an ice floe. Litigation continues over protection of bear habitat.

In one of the most dramatic signs ever documented of how shrinking Arctic sea ice impacts polar bears, researchers at the U.S. Geological Survey in Alaska have tracked a female bear that swam nine days across the deep, frigid Beaufort Sea before reaching an ice floe 426 miles offshore.

The marathon swim came at a cost: With little food likely available once she arrived, the bear lost 22% of her body weight and her year-old female cub, who set off on the journey but did not survive, the researchers said.

“Our activity data suggests that she swam constantly for nine days, without any rest. Which is pretty incredible,” said George M. Durner, a USGS zoologist and a lead author of the study, published last month in the journal Polar Biology.

“We have observed other long-distance swimming events. I don’t believe any of them have been as long in time and distance as what we observed with her,” he said. “How often does this happen? We’re trying to get a handle on that.”

Polar bears spend much of their waking lives on the shifting Arctic sea ice floes. They survive mainly on the ringed seals that are also dependent on sea ice and swim in abundance in the relatively shallow coastal waters of the continental shelf.

But sea ice has been melting dramatically in recent years, forcing polar bears during the fall open-water periods to either forage from shore or swim longer distances in search of sea ice.

Bears that retreat to land usually find little or no food there, and “typically … spend the duration fasting while they await the re-formation of ice needed to access and hunt seals,” according to a 2008 government study.

Conservation groups, the state of Alaska, the Alaska Oil and Gas Assn. and several other groups are locked in litigation in Washington, D.C., over polar bear protections and how much needs to be done to slow the pace of climate change to prevent further shrinking of their habitat.

In November, the Obama administration designated more than 187,000 square miles along the north coast of Alaska as “critical habitat” for the polar bear, but since the federal government considers the bears threatened, not endangered, there are no provisions to take dramatic steps to halt further deaths in the Beaufort and Chukchi seas.

But U.S. District Judge Emmet G. Sullivan ruled that the federal government erred in its presumptive standard that bears must be in “imminent” danger of extinction before being considered endangered. The parties are due back in court on Feb. 23.

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