February 9th, 2011 by Joshua S Hill
Researchers from the University of Alberta have shown a linkage between declining polar bear litter sizes and the declining sea ice.
Using data collected since the 1990s, University of Alberta researchers Péter Molnár, from the Department of Biological Sciences and colleagues Andrew Derocher and Mark Lewis analysed how long the Hudson Bay is frozen over during the polar bear’s hunting season, and the amount of energy pregnant females can store up before denning and birthing.
“An early spring-ice break up reduces the hunting season, making it difficult for pregnant females to even support themselves, let alone give birth to and raise cubs,” said Derocher.
“Projected reductions in the number of newborn cubs are a significant threat to the western Hudson Bay polar-bear population,” said Molnár. “If climate change continues unabated the viability of the species across much of the Arctic will be in question.”
For pregnant polar bears, the question of food is utterly vital, for they will retire to a maternity den for up to eight months and not eat for the entire time, surviving solely on their fat stores. If there is not enough food for a pregnant polar bear to build up her fat stores, she might not even make it to her maternity den, let alone make it through eight months without food or be able to provide food for any cubs she can birth.
The researchers used mathematical models to estimate the energetic impacts of shortened hunting seasons, and calculated that if spring break up of ice in Hudson Bay comes one month earlier than in the 1990s, 40 to 73 percent of pregnant female polar bears will not reproduce. If the ice breaks up two months earlier, a full 55 to 100 percent of all pregnant female polar bears in the western Hudson Bay will not birth.
The current population of polar bears in the Hudson Bay is currently estimated to be around 900, down from 1,200 in the past decade.
“Because the Hudson Bay polar bears are the most southerly population, they are the first to be affected by the global-warming trend,” said Molnar. “However, if temperatures across the Arctic continue to rise, much of the global population of polar bears will be at risk.”
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