Polar bears in the Hudson Bay area of Canada are likely to die out in the next three decades, and possibly sooner, as global warming melts more Arctic ice.
The animals in western Hudson Bay, one of 19 discrete sub-populations of the species around the Arctic, are losing fat and body mass as their time on the floating sea ice gets shorter and shorter, according to University of Alberta researchers.
The sea ice is where the bears hunt ringed and bearded seals, their main prey, and they have to build up enough fat in the winter, when the ice is at its greatest, to get through the summer, when the ice retreats from the shoreline and the bears can find no food.
Bears are now spending on average three more weeks on land per year, without food, than they did three decades ago, the researchers say.
As a consequence, their body weight in that time has dropped by 60lb, females have lost 10pc of their body length, and the west Hudson Bay population has declined from 1,200 animals to 900.
If the decline in the sea ice continues -- as predictions of global warming suggest it will -- it is feared that the bears could die out in 25 to 30 years, or perhaps in as few as 10, if there are a succession of years with very low sea ice cover.
Arctic sea ice reached its lowest-ever recorded extent in September 2007. In the last two years it has recovered, but is once again declining rapidly.