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Polar Bears Swim Longer Distances As Sea Ice Melts Faster

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Polar bears in the Arctic Basin are now forced to swim longer distances as sea ice in the region continues to retreat faster, marking an evidence of climate change's "fingerprint," a new study in Canada revealed.

Past research has shown that swimming is a costly activity for polar bears in terms of their body's energy expenditure. With that, a team of scientists led by Nicholas Pilfold sought out to understand polar bears' swimming behavior.

The researchers found that polar bears are swimming more frequently and in longer distances as a result of the changes in the location and quantity of summer sea ice. This, in turn, is caused by climate change.

Pilfold and his colleagues tracked populations of polar bears in Hudson Bay and the Beaufort Sea through satellite-linked telemetry. Factors such as swimming frequency were different between individual polar bears, depending on body size, sex, age, and the region's geographic features.

How Swimming Longer Negatively Impacts Polar Bears

In 2012, the same year in which the quantity of Arctic sea ice dropped to a record-low, about 69 percent of the telemetry-tracked female polar bears in the Beaufort Sea had swam more than 50 kilometers or 31 miles at least once, the team found.

Female polar bears with young cubs often swam less to prevent submersion of their youngsters in frigid waters, while single subadults swam as often as lone adults, researchers said.

The longest recorded swim ever in the research was done by a subadult female polar bear, travelling for more than 687 kilometers or 427 miles over the course of nine days in 2011. The female polar bear lost 22 percent of her body weight. Her cub died along the way.

"These bears are going for days without stopping," said Pilford.

Pilfold, a postdoc fellow at San Diego Zoo Global, also found that swimming occurred more frequently in the Beaufort Sea than in Hudson Bay.

Biologist Andrew Derocher, a co-author of the study, said more and more polar bears are caught in places that they just can't stay. The ice they are on keeps breaking up, the floes are too small, and the animals have to swim longer distances to find better habitat.

What's more, the polar bear population in the Beaufort Sea has dropped to more than 50 percent in the past decade, Derocher said.

Although the study did not find any direct link to the population decline, Derocher and the team were unable to track survival of any cubs who may have been with female polar bears.

The study, which is a collaboration that involved experts from Environment and Climate Change Canada (ECCC) and the University of Alberta, is published in the journal Ecography.

Photo: Anita Ritenour | Flickr

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