Polar bear's 9-day swim shows impact of ice melt

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 Beaufort Sea before reaching an ice floe 426 miles offshore.

By Kim Murphy

Los Angeles Times

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 (USGS) in Alaska have tracked a female bear that swam nine days across the 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, which set off on the journey but did not survive, researchers said.

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

"How often does this happen? We're trying to get a handle on that," Durner said.

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

But sea ice has been melting dramatically, 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 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, 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.

The Obama administration in November designated more than 187,000 square miles along Alaska's north coast as "critical habitat" for the polar bear. Yet, because the 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.

However, U.S. District Judge Emmet Sullivan ruled 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 Feb. 23.

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 to protect the bears.

In any case, they say, the bears are imperiled.

"They're drowning and starving now, and all the scientific studies show an incredibly high likelihood of extinction of two-thirds of the world's polar bears in the next 40 years ... and that includes all the bears in Alaska," said Kassie Siegel, who is arguing the case for the Center for Biological Diversity.

Alaska Republican Gov. Sean Parnell is leading the charge against the Endangered Species Act protections, saying the critical-habitat designation will cost the state hundreds of millions of dollars in lost economic development, including oil and gas drilling, and tax revenue.

Durner said polar bears clearly are spending more time in open water, and possibly on land, looking for food.

"We speculate that mortalities due to offshore swimming during late-ice or mild-ice years may be an important and unaccounted source of natural mortality, given energetic demands placed on individual bears engaged in long-distance swimming," that study said.

In the case of the marathon bear, whose swim began Aug. 26, 2008, several miles east of Barrow, Alaska, researchers had fitted the bear with a GPS-equipped radio collar, along with body-temperature monitoring equipment and motion sensors. She was recaptured on shore near the Canadian border Oct. 26.

"What we have for this bear is actually a very beautiful profile of data that is very rare for any sort of wildlife, including polar bears," Durner said.

She appears to have swum in an arc north and then northeast from the Beaufort Sea coast for nine days before reaching an ice floe. "She was able to get on the surface of the sea ice for a couple of days and then she went swimming again for another day. So really, she swam for 10 days, but nine days of it was sequentially," Durner said.

The problem, he said, was that she was in waters 9,800 feet deep by then. "These waters ... are relatively unproductive biologically when you compare them to the continental shelf, and it's believed that seals do not use them as much as the waters of the continental shelf, which are by comparison maybe 300 feet deep."

The bear traveled across the far-northern ice and then made a beeline for the Alaska coast. By that time, she had lost 107 pounds — and her cub.

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