Article content continued

Using data from 900 bear captures between 1984 to 2009, he found the average weight of males had dropped by 45 kilograms and females by 31 kilograms.

The number of bears had remained stable, so the weight loss wasn’t from increased competition.

But when Obbard compared the drops in bear weight to the number of days with the minimum amount of sea ice the bears need for a hunting platform, he found the two changes moved in parallel. He had found the answer.

“Take the simplest explanation — these dramatic changes in sea ice. Now that we have bears that are spending 30 days longer on land, they have 30 days shorter to hunt.”

Some scientists suggest bears can replace those nice, fat seals with meals found on land — geese, eggs or moose calves. But Obbard said those resources have always been available and didn’t stop the slide in weight.

Obbard points out that at about 250 kilograms, female bears are half the size of males, so the weight loss is much more significant for them. He believes that’s because the females have to nurse cubs as well as maintain themselves.

That suggests this is going to pose even greater difficulty for these females in the future

“That suggests this is going to pose even greater difficulty for these females in the future,” Obbard said.

Sea ice decline is expected to continue. That, said Obbard, raises a crucial question:

“If we assume these declines in body condition are going to continue, when will we see greatly increased mortality and reproductive failure?

“In the future, there will be some years with good ice conditions. But we expect that there will be increasing numbers of years when there will be really poor ice conditions and ultimately, there are going to be years when we do have increased mortality.

“It’s another red flag about changes that are happening in that system.”