Researchers fear less ice cover will reduce mating choices

Groups of polar bears in southern Hudson Bay may be cut off from potential mates during their breeding season if shorter periods of ice cover mean they can't move around the region as easily as they do now.

If these groups of polar bears become isolated, the resulting inbreeding could affect their health, suggests a recently published study by scientists from Trent University in Peterborough, Ont.

By analyzing tissue samples collected from three polar bear groups in southern Hudson Bay, scientists found climate change may alter the genetic structure of polar bears.

Their study, which appeared in the October 2008 issue of the scientific journal Biological Conservation, says polar bear groups breed on-ice, according to predictable annual freeze-thaw patterns.

Summer's ice-free period forces the polar bears ashore until ice forms again in fall. During the winter, the polar bears generally travel widely along ice corridors, some stretching from western Hudson Bay to the Hudson Strait, a distance of 1,000 kilometres.

Changes to the distribution and duration of sea ice in Hudson Bay could reduce or change their movements and breeding patterns in the future, the study suggests.

A shorter ice season could further isolate polar bears in southern Hudson Bay, where the population on the James Bay islands appears already to be genetically distinct from the two other polar bear groups in southern Hudson Bay.

"As the ice timing shifts, we may be seeing less of those bears moving between those breeding groups, and that's when we would start getting concerned," said Paul Wilson, an associate professor of biology at Trent University.

Wilson said similar population splits have already occurred within caribou populations from regions that are divided by roads.