The Alaska polar bear of the Southern Beaufort Sea
Diverging from their ancient grizzly bear ancestors roughly 150 000 years ago, polar bears are truly an “Alaska bear”. Scientific research shows that the species Ursus maritimus, the Sea bear, or polar bear, diverged from a particularly specific subspecies of grizzly bear or brown bear found only on Admiralty Island, off the coast of southeast Alaska, near what is now the city of Juneau.
Polar bears are now circumpolar, travelling widely around the subpolar regions of the globe. There are considered to be 19 subpopulations of polar bears around these northern climes, and though they do intermingle, its not common. Polar bears generally have a home range, not a territory, like, say, wolves might. The size of these areas they call home varies widely, depending on food population densities and sometimes a bears’ own individual inclinations. Some female polar bears, known as sows, have been known to traverse a home range as great as 230 000 square miles. Others have kept to much smaller areas, with a home range as (relatively) small as 1100 square miles. That’s an incredibly disparate difference.
The average home range for a female polar bear in the Alaskan Southern Beaufort Sea (one of 2 currently identified Alaska polar bear populations) is roughly 55 000 square miles. Within such a range, polar bears travel along the sea ice and pack ice, hunting seal, their favored and primary prey. High calorie, fat-rich foods are needed in the arctic, and polar bears can put on an enormous amount of weight in good times. Raising her cubs, a polar bear sow will breast feed the cubs thick, fat-rich milk, sometimes until the cubs reach 2 and 1/2 years of age. A female polar bear’s milk is usually around 33% fat, and some samples have been recorded as high as 45% fat; typically the younger the cub, the higher the fat content of the milk.
Known as the largest present-day land carnivore, adult male polar bears can weigh as much as 1400lbs, and some massive individuals have been recorded even larger. Pregnant females weighing as much as 1100lb have also been recorded, making the polar bear an intimidating creature for most animals they encounter.
There are 2 subpopulations identified within Alaska, the Chukchi Sea population and the Southern Beaufort Sea population. Of the 2, the polar bears of the Southern Beaufort Sea are studied most closely, and little is known of the bears of the Chukchi Sea. The polar bears of the Southern Beaufort Sea typically live within 200 miles of the shore, ranging over the pack ice that lies over the shallower waters of the continental shelf; the deeper water further out to sea is less productive water, with less algae forming under the ice, which means less krill and other smaller organisms that eat the algae, which means fewer fish that eat the krill, which means fewer seals and whales (esp. Belugas) that eat the fish, which means fewer polar bears. Nearer shore, the biologically rich waters provide a bountiful habitat for the marine mammals that live in the arctic.
The primary threat facing polar bears today is loss of habitat due to global climate change. Ever decreasing pack ice near shore means the polar bears must travel further from land to reach the pack ice, but more seriously means the ice they do hunt on, further offshore, lies over less productive habitat for their own primary prey, the seals. Polar bears face a serious food shortage as they travel on pack ice that contains fewer numbers of their prey.
Hopefully, we humans will begin to lower our own energy usage, lower our energy output, and lessen those influences driving current climate change; and that the polar bear will find, in its own resourceful manner, alternative possibilities for food and habitat to continue their existence.