A new study is painting a worrisome picture for polar bear populations on Hudson Bay, noting that a loss of sea ice is leading to a rapid decline in the number of bear cubs born every year.
Researchers at the University of Alberta say if climate change continues unabated and if the number of newborn western Hudson Bay polar bear cubs continues to fall, the species across much of the Arctic could possibly be wiped out.
Hudson Bay polar bears typically hunt for food through the late spring, swimming between ice floes and sea ice, hunting for seals.
When the ice floes melt off in the fall and the bears can no longer hunt, the pregnant females return to land to dig a maternity den to give birth. The bears spend up to eight months in the den during which time, no food is available.
An early spring ice breakup reduces the hunting season for pregnant females, making it difficult for them to support themselves through the winter, let alone give birth to cubs.
For this study, the researchers looked at the changing length of time the Hudson Bay is frozen during the polar bear's hunting season, using data collected since the 1990s. They also noted the amount of energy pregnant females can store before hibernation and birthing.
The researchers estimate that in the early 1990s, 28 per cent of energy-deprived pregnant polar bears in the Hudson Bay region failed to give birth to a live cub. Energy-deprived pregnant females will either not enter a maternity den or will naturally abort the birth.
Using mathematical modeling to estimate the energetic impacts of a shortened hunting season, the research team calculated the following scenarios:
If spring break up in Hudson Bay comes one month earlier than in the 1990s, 40 to 73 per cent of pregnant female polar bears will not reproduce.
If the ice breaks up two months earlier than in the 1990s, 55 to a full 100 per cent of all pregnant female polar bears in western Hudson Bay will not have a cub.
The number of polar bears across the Arctic is estimated to be between 20,000 and 25,000. The polar-bear population of western Hudson Bay is currently estimated to be around 900, down from 1,200 bears in the past decade.
The research team says because the polar bears of Hudson Bay are the most southerly population, they will be the first to be affected by the global-warming trend.
However, they say that if temperatures across the Arctic continue to rise, much of the global population of polar bears will be at risk.
