A female polar bear swam continuously for more than nine days in just-above-freezing water -- travelling almost 700 kilometres -- in search of Arctic sea ice, researchers have found.
Scientists from the U.S. Geological Survey studying the bears in the Beaufort Sea, north of Alaska, worry it's an example of the effect of climate change on the animals.
The bear lost 22 per cent of its body mass and her yearling cub died on the journey.
"The extraordinary long distance swimming ability of polar bears, which we confirm here, may help them cope with reduced Arctic sea ice. Our observation, however, indicates that long distance swimming in Arctic waters, and travel over deep water pack ice, may result in high energetic costs and compromise reproductive fitness," says the report in the journal Polar Biology.
The bear was originally captured in late Aug. 2008 to be fitted with a radio-collar and then again in Oct. 2008.
Although polar bears have been observed in open waters before, it's the first time such a long-distance journey has been tracked.
Polar bears prefer to live on Arctic sea ice, but swim between ice floes or sea and land for hunting. They have a calorie-rich diet mostly consisting of ringed seals.
The bears are the world's largest land carnivores.
