Amstrup, who has researched polar bears for nearly 30 years, told USINFO: As far as rescuing polar bears before their habitat disappears, there is really no rescue. As sea ice declines, he said, so does their capacity to hunt for their primary food, the ring seal. Polar bears are entirely dependent upon the sea ice because it is only from that platform that they are able to harvest the bounty from the sea, Amstrup said.
The quality of ice appears to matter, too. Not all ice is equal in the eyes of polar bears, said George Durner, research zoologist with the USGS Alaska Science Center. Durner studies how bears use the habitat. Although they adapt readily on the harsh ice fields, polar bears do not thrive on land. Of the 19 polar bear populations that live in the Arctic, those on the Hudson Bay have been forced to spend part of the year on the shore, but they do not significantly feed there. To survive summers on land, they bulk up on high-energy seal and walrus diets during the winters, but shorter winters reduce their ability to feed sufficiently. Food sources available on shore do not offer the rich nourishment these giant bears require.
Less ice and less time to feed leave the bears malnourished and vulnerable. Low reproduction and high mortality rates for cubs further reduce their numbers. Since 2004, several incidents of polar-bear cannibalism have been documented, something not seen previously, according to Amstrup.
Polar bears have drowned while trying to swim the increasing distances from one ice platform to another also a disturbing trend. Although strong swimmers, polar bears are not aquatic mammals, Armstrup said.