March 20, 2013
Climate Change Affecting Polar Bears, Only Those With The Most Fat Thrive
Brett Smith for redOrbit.com - Your Universe Online
Recent climate induced changes to Arctic polar bears´ environment is affecting their habits and ability to survive, with the bears having to rely more and more on internal fat reserves, according to a new paper in the Journal of Animal Ecology.
The bears are having particular difficulty adjusting to the shifting sea ice dynamics. In the past, sea ice has remained throughout the Arctic summer months, but now it is almost completely melting and refreezing each year.
"This poses an interesting challenge for a species that has evolved as a highly efficient predator of ice-associated seals," explained the report´s lead author Seth G. Cherry, from the University of Alberta. "Because although polar bears are excellent swimmers compared with other bear species, they use the sea ice to travel, hunt, mate and rest."
In the study, over 100 female polar bears were fitted with satellite tracking collars. Males could not be fitted with the collars as their necks are bigger than their heads, making the collars slip off easily.
The movements of these females were tracked between 1991-97 and 2004-09. During the same time periods, the researchers also monitored the makeup of sea ice using satellite imagery.
"Defining precisely what aspects of sea ice break-up and freeze-up affect polar bear migration, and when these conditions occur, is a vital part of monitoring how potential climate-induced changes to sea ice freeze-thaw cycles may affect the bears," said Cherry.
"At first glance, sea ice may look like a barren, uniform environment, but in reality, it's remarkably complex and polar bears manage to cope, and even thrive, in a habitat that moves beneath their feet and even disappears for part of the year,” he added. “This is an extraordinary biological feat and biologists still don't fully understand it.”
Now that sea ice is less prevalent than it was in the past, polar bears in the study were seen migrating to land each summer and depending on their fat reserves to sustain them. The researchers found a direct connection between melting sea ice patterns around Hudson Bay and the bears´ migratory activities.
"The data suggest that in recent years, polar bears are arriving on shore earlier in the summer and leaving later in the autumn,” Cherry said in a statement. “These are precisely the kind of changes one would expect to see as a result of a warming climate and may help explain some other studies that are showing declines in body condition and cub production."
According to the researchers, the relationship between polar bears and their main food source, the Arctic seal, is being impacted the most by melting sea ice. As the bears hunt less seals in the summer months, they must learn to adapt in order to survive.
"Climate-induced changes that cause sea ice to melt earlier, form later, or both, likely affect the overall health of polar bears in the area," Cherry said. “Ultimately, for polar bears, it's survival of the fattest.”
Cherry said he hopes his study´s findings will enable other scientists and policy makers to predict how potential climate-induced changes to sea ice impact the ecosystem.