Public Release:  For polar bears, it's survival of the fattest

University of Alberta

(Edmonton) University of Alberta led polar bear research shows that in western Hudson Bay, changes to the seasonal sea ice break-up and freeze-up, brought on by climate change is forcing the animals to take to the shore earlier in the summer and delay their departure until later in the fall.

Lead researcher, U of A biologist Seth Cherry compiled more than 10 years of data measuring polar bear movement patterns and sea ice data. Cherry says the information helps explain results from other studies of the western Hudson Bay polar bear population that show falling levels of health and reduced cub production.

It's been known for some time that polar bears have adapted to the summer loss of sea ice in western Hudson Bay by moving onto land until late November or early December. Cherry's research reveals that the timing of polar bears' migration can be predicted by how fast the sea ice melts and freezes, and by when specific sea ice concentrations occur within a given area of Hudson Bay.

"These are precisely the kind of changes one would expect to see as a result of a warming climate, "said Cherry. "The data may help explain some other studies that are showing declines in body condition and cub production."

Recent estimates put the western Hudson Bay polar bear population at around 900 individuals. The population has declined since the 1990s, as has the bears' body condition and the number of cubs surviving to adulthood. Because polar bears' main food source is seals, and these are hunted almost exclusively on sea ice, the longer bears spend on land, the longer they must go without energy-rich seals.

"Climate-induced changes that cause sea ice to melt earlier, form later, or both, likely affect the overall health of polar bears in the area. Ultimately, for polar bears, it's survival of the fattest," said Cherry.

The research was published Mar. 19 in the British Ecological Society's Journal of Animal Ecology.

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