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 percent 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 in December 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 Association 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.
The difference between "threatened" and the more serious "endangered" status is crucial in this case. Attorneys for the Center for Biological Diversity, Greenpeace and the Natural Resources Defense Council argue that an endangered finding will require the government to impose new controls on greenhouse gases across the country to protect the bears. In any case, they say, the bears are imperiled.
Republican Alaska Gov. Sean Parnell, who is leading the charge against the Endangered Species Act protections, has said the critical-habitat designation will cost the state hundreds of millions of dollars in lost economic development and tax revenue.
Plans to develop major stockpiles of offshore oil and gas resources are potentially threatened by the polar bear protection zones.