Polar bears experiencing low levels of Arctic sea ice are swimming hundreds of kilometres nonstop to find food, scientists say.
Research led by the U.S. Geological Survey used collars equipped with GPS to track 52 adult female polar bears in the Beaufort Sea near Alaska from 2004 to 2009.
The scientists recorded 50 swims with an average distance of more than 154 kilometres. The speeds of the swims suggest the bears did not stop to feed or rest during their journeys.
The long swims require significant energy for the non-aquatic mammals, and the bears and their cubs risk drowning from exhaustion or rough water.
One case studied by the researchers tracked a female polar bear as she swam continuously for more than nine days, covering a distance of more than 687 kilometres. The bear lost 22 per cent of her body mass during the trip. Her cub died during the journey.
However, many cubs do survive the long swims, says Anthony Pagano, a lead author of the study.
“We were able to recapture or observe 10 of these females within a year of collaring, and six of these females still had their cubs,” Pagano said in a press release. “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.”
The study, published in the latest issue of the Canadian Journal of Zoology, is the first to use GPS to track polar bears’ long-distance swims. With declining levels of Arctic ice, these long swims could become more and more common.
There are about 25,000 polar bears in the Arctic. A 2004 survey of the Barents Sea polar bear population found about 3,000 polar bears in the region.
