Polar Bears Endangered by Warming Trend
December 1, 1999
Copyright 1999 Discovery Communications Inc.
By Maryalice Yakutchik, Discovery News Brief
A long-term warming trend is wiping out the ice from under the feet of Hudson Bay polar bears, says a recently released study.
Co-author Ian Stirling, a zoologist with the University of Alberta, writes in the journal Arctic that the declining condition of adults as well as cubs in that region is related directly to rising spring temperatures that have cut short the animals' spring hunting season by two weeks over the past two decades.
Polar bears shed anywhere from 220 to 440 pounds during the eight months they spend fasting in their winter dens. The bears' survival depends largely on replenishing their bodies during the spring hunting season when they head out to pack ice to stalk ringed seal pups, according to Stirling.
But the warmer spring season is causing earlier break-ups of the sea ice platforms, which is forcing the bears ashore earlier. And as a result of the curtailed hunting season, the bears are coming ashore with less fat.
Stirling doesn't say whether he believes the warming trend is a manmade or naturally occurring event. "I keep out of the debate about what's making the climate change," he says. "What is clear is that it's changing. There's a strong correlation between the break-up time of the ice and the weights of the bear."
Over a period of 19 years, the Canadian Wildlife Service researchers studied the bears' movements using satellite telemetry and captured and recorded their weight.
Of more than 25,000 polar bears worldwide, about 1,200 polar bears live in the study area. Early breakups of ice on the bay mean that more hungry bears are likely to forage inland for berries and food in populated areas such as Churchill, Manitoba.
As top predators in the arctic, polar bears are particularly sensitive indicators of the health of that ecosystem, says Sara Iverson, an associate professor of biology at Dalhousie University in Halifax, Nova Scotia.
"He's been working on bears for so long," Iverson says. "The results of his research are alarming to all of us. I think it'll be important to follow this."