The Polar Bear

Polar bears are the closest relatives of brown bears. They must have diverged from an ancestral population of brown bears that became isolated away from the mainland, and other brown bears, about one million years ago. We can imagine that the ancestral polar bears were brown bears that lived in northern Siberia, perhaps along the coast of the Arctic Ocean or on Wrangell Island. They discovered an abundant source of food in the form of marine mammals; seals, walruses, and even whales, and learned to prey upon them. As they were doing this, the group of bears became isolated. It may have been a relatively small group to begin with, and they may even have been stranded on the ice when it receded away from shore during a period of warm climate. We will probably never know the whole story. Somehow, perhaps improbably, they managed to survive and reproduce. Adaptations that favored their new environment would have been rapidly selected for, and they developed white coats and thick layers of fat. In a relatively short period of evolutionary time, they became the polar bears that we know today.

Polar bears are marine carnivores. They feed exclusively on a diet of meat, primarily seals, and many polar bears spend their lives on the ice without ever setting foot on land. To survive, and thrive, on the polar ice pack requires many extreme adaptations. To provide camouflage on the ice their fur appears white. It is more than white, however, each hair is translucent and it conducts sunlight, like fiber optic cables, down to the skin where heat is absorbed. The skin is black to absorb the maximum amount of heat from sunlight. The thick fur then acts as an insulating blanket to preserve the heat.

Polar bears are legally hunted throughout most of their range today. They are not considered rare or endangered at present by the Convention on International Trade in Endangered Species (CITES). Hunting quotas are enforced by law in Alaska, and by agreement in parts of Canada. There are no legal limits for eskimos in Quebec, Greenland, and Alaska. Hunting is prohibited in Russia and the Svalbard Archipelago, but enforcement is difficult. In Russia especially, the current economic conditions have encouraged poaching and the extent of it is unknown. An international Agreement on the Conservation of Polar Bears was signed in 1973 by Canada, Denmark, Norway, the United States, and the former USSR which regulates hunting and guides the management of polar bear populations. The use of set guns and hunting from ships and aircraft are prohibited. Overharvesting and illegal killing are considered to be the greatest threat to polar bear populations today. However, human activities are becoming more of a threat as oil and gas development in particular begins to encroach on the Arctic. Human developments displace polar bears from important habitat, create conflicts that result in bear deaths, create disturbance and stress that affects their behavior and survival, and can introduce toxic substances that impact polar bears and their prey in direct and indirect ways.

Picture courtesy of Harriet Corbett, Rox Graphics, 866 Rd. 7RP, Powell, WY 82435, 307 645 3202, crowhart@wtp.net