Thanks to the efforts of Canadian Wildlife Service biologists, the Western Hudson Bay population is one of the best-studied populations of polar bears in the world. Some of the results of those studies are troubling. A warming trend has been observed in the Arctic that has resulted in a three-percent loss to the extent of the pack ice every decade since 1970. Coupled with a spring break-up that is now occurring roughly three weeks earlier than historical records indicate, these changes have serious implications for polar bears.
Hudson Bay’s bears live on the ice hunting seals through the winter and into the summer. When the ice melts, they move ashore and survive on stored fat until the following winter when they can hunt seals on the ice once again. Most bears fast for about four months, however, pregnant females remain on land to give birth and fast for about eight months. Early ice break-up cuts short their time to hunt and build up their body condition, and longer ice-free periods extend the time that the bears fast on shore. Studies have shown that for each early week that break-up occurs, the bears come ashore ten kilograms lighter and thus in poorer condition.
Warmer weather for Hudson Bay can have other catastrophic impacts on polar bears. Spring rains can collapse maternity dens before mother and cub have departed and can impact the maternity dens of ringed seals, the primary prey species for Manitoba's polar bears. If the ringed seal population declines as a result, the polar bear population would decline in turn.
Warmer weather can also lead to an increase in the number of forest and brush fires in areas where polar bears dig maternity dens in peat. Fires melt the permafrost and without roots and other plant debris to hold the roofs together, dens often collapse. It can take 70 years after a fire for enough trees and shrubs to grow back to allow the denning sites to be used again.
It is possible, that if our society does nothing to reduce the emission of greenhouse gases, that the resulting global warming may some day produce ice conditions in Hudson Bay that could not support a population of polar bears.