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201204May16:27

Can Polar Bears avoid extinc­tion by swim­ming long distances?

Infor­ma­tion
pub­lished 04 May 2012 | mod­i­fied 04 May 2012
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Polar bears spend much of their lives in and around water, and they are well adapted for swim­ming. But recent find­ings of US Geo­log­i­cal Sur­vey (USGS) sci­en­tists demon­strate that they are even bet­ter swim­mers than many imagined:

In years of extreme sea-​ice retreat in the south­ern Beau­fort Sea region of Alaska, polar bears have been doc­u­mented tak­ing very long swims, in excess of 30 miles. Some Polar bears in the Arc­tic can swim in excess of 200 miles.

In addi­tion to being an impres­sive feat, this pro­vides some tan­ta­liz­ing clues into the polar bear’s future in an Arc­tic with less sea ice. That these bears can swim such long dis­tances might mean that they are not as vul­ner­a­ble to being stranded at sea as has been depicted by the media. Sci­en­tists won­der, how­ever, if polar bears might be expend­ing essen­tial energy in swim­ming long distances.

polar bear

A USGS-​led study tracked 52 adult female polar bears out­fit­ted with global posi­tion­ing sys­tem col­lars from 2004 to 2009. Get­ting a satel­lite teleme­try col­lar on a polar bear is no sim­ple mat­ter. Sci­en­tists use heli­copters to fly over the sea ice to find and tran­quil­ize bears. While the bear is tran­quil­ized, sci­en­tists attach a radio col­lar with mul­ti­ple anten­nae and give the bear a small iden­ti­fy­ing tat­too on the inside of the upper lip.

Later, when the bears are swim­ming, one of the anten­nae is sub­merged so that the swims appear as gaps in the data that is trans­mit­ted. Over­lay­ing this data onto maps of sea ice shows sci­en­tists approx­i­mately where the bears are swim­ming. Researchers doc­u­mented 50 swims with an aver­age length of 96 miles. While long-​distance swims were rel­a­tively uncom­mon, 38 per­cent of the col­lared bears took at least one long swim. Results from the study appear in the cur­rent issue of the Cana­dian Jour­nal of Zool­ogy.

Sci­en­tists have no way of know­ing if long-​distance swims are a new fea­ture of polar bear life. “We did not have the GPS tech­nol­ogy on col­lars to doc­u­ment this type of swim­ming behav­ior in polar bears in prior decades,” explains Karen Oak­ley, of the USGS Alaska Sci­ence Cen­ter . “How­ever, sum­mer sea ice con­di­tions in the south­ern Beau­fort Sea have changed con­sid­er­ably over the last 20 to 30 years, such that there is much more open water dur­ing sum­mer and fall. 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.”

While it is encour­ag­ing that polar bears can swim that far, it is also a poten­tial risk for the bears, the researchers noted. The energy and phys­i­cal costs of such long-​distance swim­ming are unknown, but sci­en­tists did note polar bears moved, on aver­age, 2.3 times more than when the same indi­vid­u­als were on sea ice. The move­ment data also sug­gest the bears were not paus­ing to rest or feed dur­ing long-​distance swims. Twelve of the twenty doc­u­mented swim­ming bears were adult females that had year­lings or cubs-​of-​the-​year at the time they were out­fit­ted with the GPS collar.

We were able to recap­ture or observe 10 of these females within a year of col­lar­ing, and 6 of these females still had their cubs,” said Anthony Pagano, a USGS sci­en­tist and lead author of the study. “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 above news item is reprinted from mate­ri­als avail­able at US Geo­log­i­cal Sur­vey. Orig­i­nal text may be edited for con­tent and length.

(Source: web­site USGS, 01.05.2012)

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