Turn south, and head straight for 400 miles: GPS trackers reveal polar bears can swim non-stop for up to 10 days



Polar bears are swimming more than 400 miles without stopping as they hunt for ice caps that have not melted, researchers said yesterday.

Bears fitted with GPS trackers swam non-stop for as long as ten days while searching for sea ice platforms in the Arctic.

More than 50 female polar bears in the southern Beaufort Sea off Alaska wore collars to record their movements over five years.

English Channel? No problem: Polar bears in the study were seen swimming distances of 90 miles without any problems - and some bears went a lot further

Scientists discovered that during the summer months, when sea ice is at its minimum, the bears were swimming farther and for longer periods of time than ever before in search of new hunting grounds.

A total of 20 bears tracked from 2004 to 2009 repeatedly embarked on long-distance journeys, with an average length of 96 miles.

One bear was able to swim 220 miles, while another covered an astonishing 420 miles non-stop over the course of ten days.

The findings, collated by the US Geological Survey and published in the Canadian Journal of Zoology, found a third of the 52 bears tracked swam more than 30 miles.

Researcher Oakley said that the bears would not have needed such a long swim in the past, as sea ice would have provided a float for them

The extraordinary results shed new light on how polar bears are having to adapt to the rapidly changing Arctic environment.

So great are fears over their survival that the bears are now classified as a threatened species by the US government. But while some claim swimming vast distances will make the bears weaker and compromise their ‘reproductive fitness’, others insist it shows they are capable of surviving the changes in their habitat.

‘That these bears can swim such long distances might mean that they are not as vulnerable to being stranded at sea,’ said the USGS in a statement.

‘However, long-distance swimming appears to have higher energetic demands than moving over sea ice.’

One bear was found to have lost 20 per cent of her body weight after a mammoth swim. The USGS said it could not be sure if the long- distance swimming was new to polar bears, but concluded that it had emerged as a result of declining summer sea ice.

Karen Oakley, of the USGS Alaska Science Center, said: ‘Historically, there had not been enough open water for polar bears in this region to swim the long distances we observed in these recent summers of extreme sea ice retreat.’

Scientists also noted that on average the polar bears moved 2.3 times more in the water than on sea ice. ‘Presumably this is because they’re not able to rest or hunt when they’re swimming,’ said Anthony Pagano, lead author of the study.

‘They appear to be moving continuously. But whether that’s affecting survival, we don’t know.’