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Polar Bear

The polar bear, scientific name Ursus maritimus, is the largest land carnivore, the largest bear and the most northerly bear. Polar bears can live up to 25 years. Males weigh up to 800kg (1,700 pounds) and are up to 250 centimetres (eight to ten feet) from tip to tail. Females weigh up to 300kg (700 pounds) and are 180 to 250 centimetres (six to eight feet) long. Their feet are big and furry enough to act as snow shoes and paddles. Their thick fur is water-repellent.

Polar bears live in the Arctic, including Alaska (USA), Canada (more than half of them), Greenland, Norway and Russia. They have a thick layer of fat (blubber) under their skin to keep warm in temperatures as low as minus 55 degrees Celsius plus wind chill. The fatter they are, the warmer they can keep. They are warm blooded, with black skin for soaking up the sun's heat. They migrate seasonally with changes in the ice pack, so climate change affects their range and the degree to which they encounter humans.

Polar bears will actually hunt humans for food. They spend a lot of time on ice floes, or on shore. They are strong swimmers. They mostly eat ringed and bearded seals, which they catch by waiting quietly near breathing holes in the ice, then breaking through the snow. They can smell a seal one metre under the ice. They only catch about one in 50, though, or one every 4 to 5 days. They may eat 45 kilograms at a sitting. Occasionally they get beluga, fish, narwhal, walrus, reindeer, seabirds and carrion (which they can smell from 32km (20 miles) away), as well as berries etc. in summer. They do not need to drink as there is enough liquid in their food.

Polar bears spend most of their time alone, though they congregate for the breeding season or when there is a large supply of food. Their ranges can extend up to 300,000 square km, depending on the terrain. Pregnant females spend winters (November to January) in dens with their cubs (usually 1 to 3), which weigh approximately 600 grams, or 1.3 pounds.. Otherwise polar bears remain active, particularly at night. The cubs are helpless, blind and toothless when they are born. They remain with their mother for about 2.5 years. Being smaller and thinner than their mother, they lose heat more rapidly. Polar bears have a very slow reproductive rate, with a female producing perhaps 5 litters in her lifetime.

Polar bears are included in CITES Appendix II. This means that although they are not currently threatened with extinction, they might become so if trade was not regulated; any trade must be done under licence. Threats include hunting for meat and fur, and oil spills.

As they have such huge ranges, it is difficult to estimate how many there are, but biologists work on a figure of 22,000 to 25,000 bears, and think that the overall number is not currently changing much. They were under such pressure in the 1960s and 1970s, however, that Canada, Denmark (for Greenland), Norway, the U.S., and the former U.S.S.R. signed the International Agreement on the Conservation of Polar Bears in Oslo, November 15, 1973, during the Cold War. The agreement banned hunting from aircraft and icebreakers, protected dens, and introduced research. The Polar Bear Specialist Group meets every 3 or 4 years under the auspices of the IUCN World Conservation Union. The bears' numbers recovered after the agreement was signed.

Polar bears are top of the food chain in the Arctic, so if they are having problems, then much of the ecosystem probably is too. They are affected by a variety of problems caused by humans, including climate change, drilling, fishing, hunting, mining, pollution, and interaction in general. Humans are by far their greatest enemy. Polar bear livers contain so much Vitamin A that they are toxic to humans. If, as predicted, global warming makes the Arctic Ocean ice-free by the end of the century, then polar bears could die out in the wild. The Arctic is warming faster than other parts of the world. Tests show that a wide range of toxic chemicals have made their way to the Arctic one way or another, and it appears that polar bears are contaminated by PCBs (polychlorinated biphenyls) and pesticides.

Polar Bears Photo: U.S. Fish & Wildlife Service

Polar bear makes huge 74 km one-day Arctic swim

A polar bear called "Skadi" wearing a tracking device has been monitored swimming at least 74 km in a single day, and probably 100km since she was unikely to have swum in a straight line. It is thought unlikely that her cubs could have swum so far since they lose heat more rapidly, so they probably died earlier in the season. Retreating ice due to global warming is likely to cause more problems for young polar bears than for adult polar bears. Track Skadi here.

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