Saturday, 7 May 2011
newspaper article from January 2011 on a tracked polar bear's search for food and her loss of her cub on the journey
Polar bear swims 426 miles in nine days in search of food and scientists blame global warming
By Daily Mail Reporter
Last updated at 9:26 AM on 26th January 2011
A polar bear swam continuously for over nine days, covering 426 miles, animal researchers were astonished to discover.
And the scientists studying bears around the Beaufort Sea, north of Alaska and Canada, claim this endurance feat could be a result of climate change.
Polar bears are known to swim between land and sea ice floes to hunt seals.
But the researchers say that increased sea ice melts push polar bears to swim greater distances, risking their own health and the survival of the species.
In their findings, published in the journal Polar Biology, researchers from the US Geological Survey reveal the first evidence of long distance swimming by polar bears.
One of the bears they fitted with a tracking collar made an epic journey in search of food between an initial capture in late August and a recapture in late October 2008.
'This bear swam continuously for 232 hours and 687 km and through waters that were 2-6 degrees C,' says research zoologist George M. Durner.
'We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold. It is truly an amazing feat.'
The study found that, in addition, the bear then intermittently swam and walked on the sea ice surface another 1200 miles.
Although bears have been observed in open water, this is the first time one's entire journey has been followed.
By fitting a GPS collar to a female bear, researchers were able to accurately plot its movements for two months as it sought out hunting grounds.
The scientists were able to determine when the bear was in the water by the collar data and a temperature logger implanted beneath the bear's skin.
A polar bear is seen in the water during an aerial survey off the Alaska coast in August 2008
Unfortunately for the bear, the feat came at a high cost. Not only did the polar bear lose body mass, she also lost her yearling cub along the way.
The baby bear simply could not survive the swim across the increasingly perilous Beaufort Sea in Alaska.
Polar bears swim from ice floe to ice floe in search of their main prey, ringed seals, but the warming global temperature has made the journey a bit harder.
'This individual lost 22 per cent of her body fat in two months and her yearling cub,' said Mr Durner.
"It was simply more energetically costly for the yearling than the adult to make this long distance swim.'
Mr Durner told the BBC that conditions in the Beaufort sea have become increasingly difficult for polar bears.
'In prior decades, before 1995, low-concentration sea ice persisted during summers over the continental shelf in the Beaufort Sea.
'This means that the distances, and costs to bears, to swim between isolated ice floes or between sea ice and land was relatively small.
'The extensive summer melt that appears to be typical now in the Beaufort Sea has likely increased the cost of swimming by polar bears.'
Polar bears (Ursus maritimus) live within the Arctic circle and eat a calorie-rich diet of ringed seals ( Pusa hispida ) to survive the frozen conditions.
The bears hunt their prey on frozen sea ice: a habitat that changes according to temperature.
'This dependency on sea ice potentially makes polar bears one of the most at-risk large mammals to climate change,' says Mr Durner.
His paper: 'Consequences of long-distance swimming and travel over deep-water pack ice for a female polar bear during a year of extreme sea ice retreat' is in the current issue of Polar Biology.
The International Union for Conservation of Nature identifies polar bears as a vulnerable species, citing global climate change as a 'substantial threat' to their habitat.
View of ice and the Prince Leopold Island cliffs in the Actic Ocean