Polar bears are capable of swimming vast distances, a potential survival skill needed in an Arctic environment where summer sea ice is vanishing, a study led by the US Geological Survey showed on Tuesday.

Polar bears are capable of swimming vast distances, a potential survival skill needed in an Arctic environment where summer sea ice is vanishing. [File photo]

The study, published in the Canadian Journal of Zoology, tracked 52 female polar bears in the southern Beaufort Sea off Alaska. Between 2004 and 2009, a period of extreme summer-ice retreat, about a third of those bears made swims exceeding 48 km in distance, according to the study results.

The 50 recorded ultra-marathon swims averaged 155 km, and one bear was able to swim nearly 354 km, according to the study results. The duration of the long-distance swims lasted from most of a day to nearly 10 days, according to the study.

The bears' movements were tracked using global positioning system collars. All the animals in the study were females because male polar bear necks are too thick for GPS-equipped collars, said Karen Oakley, a supervising biologist at the USGS Alaska Science Center.

Many of the polar bears in the study had young cubs with them, and it appears that at least some cubs might have been able to keep up with their mothers in the water.

The scientists were able to track 10 of the studied bears within a year of collaring and found that six still had their cubs, the lead scientist said in a statement.

"These observations suggest that some cubs are also capable of swimming long distances. For the other four females with cubs, we don't know if they lost their cubs before, during, or at some point after their long swims," Anthony Pagano, a scientist and lead author of the study, said in the statement.

Oakley said the study sample was too small to allow the scientists to draw conclusions about the fate of the entire polar bear population, which in 2008 was granted Endangered Species Act protections because of rapid warming in their Arctic habitat.

The study simply describes behavior that was observed, Oakley said. "It's just very interesting that in fact they can swim long distances, and cubs can swim long distances," she said. "Do all the cubs that attempt to swim these long distances survive? We don't know."

Polar bears probably lacked the need to make such long swims in that part of the Arctic in the past.

In past decades, polar bears were always able to rest on available floating summer sea ice, she said.

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