Levels Of Toxic Chemicals In Polar Bears example essay topic

Polar bears are big, white bears (sometimes darker fur) that live in very cold regions like around the art ic poles. There are 21,000 to 28,000 Polar bears alive that are known. Polar bears swim in water and are carnivores, they eat fish. Polar bears feed mainly on ringed seals and bearded seals. Depending upon their location, they also eat harp and hooded seals and eat carcasses of beluga whales, walruses, narwhals, and Bowhead whales. A polar bears's to mach can hold up to 15% to 20% of its body weight.

It can use 84% of the protein and 97% of the fat it eats. Polar bears need about 2 kg (4.4 lb.) of fat per day to survive. A ringed seal weighing 55 kg (121 lb.) could provide up to eight days of energy for a polar bear. On cold days polar bears curl up and cover their muzzle area. During the winter, some polar bears leave their dens and find other places to stay warm. They may use these shelters for several months at a time.

Polar bears generally walk with a steady, clumsy walk. The front paws swing towards the sides with each step, landing slightly pigeon-toed. The head swings from side to side. The walk has a four-beat pattern, first the right front foot touches the ground, then the left back foot, then the left front foot, and lastly, the right back foot. Humans may encounter polar bears wherever human and polar bear habitats come together. Polar bear attacks occur most often at sites of human camp where they fish and hunt or in towns close by polar's' habitat.

Compared to other bears, polar bears are more willing to consider humans as prey. Most likely the person attacked is killed, unless the polar bear is killed first. Polar bears can live up to 20 to 30 years, but only a few of the polar bears live past 15 to 18 years. The oldest known polar bear in the Arctic lived 32 years.

And the oldest polar bear in a zoo lived 41 years. Adult polar bears have no natural predators. Males sometimes kill other males competing for mates. Males rarely kill females protecting cubs. Cubs less than one year old sometimes are prey to adult male polar bears and other meat eaters, such as wolves. Newborn cubs may be killed by mothers that are hungry.

Polar bears have been hunted for thousands of years. Evidence of human polar bear hunts have been found in 2,500- to 3,000-year-old ruins. Arctic people have hunted polar bears for food, clothing, bedding, and religious-sacrifice purposes. Hunting of polar bears for hides began as early as the 1500's.

Kills increased a lot in the 1950's and 1960's when hunters began using snowmobiles, boats, and airplanes to hunt polar bears. Public concern about this type of hunting led to an international agreement in 1973 banning the use of aircraft or large motor boats for polar bear hunts. Hunting is the greatest single cause of polar bear deaths. Today, polar bears are hunted by native Arctic people mostly for food, clothing, souvenirs and sale of furs. Polar bears are also killed in defense of people or their land. Hunting is government-regulated in Canada, Greenland, and the United States.

Though hunting is now illegal in Norway and Russia. There are environmental factors, too. Oil spills from tankers threaten polar bears. A polar bear's fur loses its insulation when covered with oil. And oil spills could contaminate polar bear food sources. The presence of toxic chemicals in polar bears may have long-term effects on their health.

Toxic chemicals from worldwide industrial businesses are carried to the Arctic by air, rivers, and oceans. Arctic animals in higher food chain levels get larger amounts of toxic chemicals in their tissues than those below them. Polar bears, at the top of the food chain, develop the highest levels of all. Human-made toxic chemicals such as poly chlorinated biphenyl's (PCBs), dichlorodiphenyltrichloroethane (DDT), and chlordane's are present in the Arctic. These chemicals have been found in really high levels in the tissues of polar bears. Scientists continue to watch the levels of toxic chemicals in polar bears to determine their long-term effects.

Radionuclides, from nuclear waste dumping in the Russian Arctic, may have effects on polar bears, and the Arctic ecosystem as a whole. Starvation is the greatest threat to young polar bears. Babies are not good enough at hunting, and often are chased from prey by larger adults. Older, weaker bears also are vulnerable to starvation. As in any animal population, a variety of diseases and parasites can be responsible for polar bear illnesses. Polar bears are especially unprotected to the parasitic worm Trichinella, which they contract by feeding on infected seals.

Trichinella larvae are in various parts of the polar bear's body, usually muscle tissue. If enough larvae is in one area, such as the heart, the tissue becomes very damaged. Death may occur. The scientific classification of polar bears is: Order = Carnivora The scientific order Carnivora includes bears, dogs, cats, raccoons, otters, weasels, and their relatives. All carnivores have well developed claws and a pair of cheek teeth for cutting hard foods.

Family = UrsidaeAll bears belong to this family. The family is divided into three subfamilies, Ursine (black bears, brown bears, polar bears, sloth bears, and sun bears), Tremarctinae (spectacled bears), and Ailuropodinae (giant pandas). Genus species = Ursus maritimes. There are five other species in the genus Ursus: brown bears, American black bears, Asiatic black bears, sun bears, and sloth bears.

Species can be distinguished by size, build, color, and habitat. Fossil Record The oldest known polar bear fossil is less than 100,000 years old. Polar bears probably developed during the Pleistocene era from an ancestral brown bear. Polar bears and brown bears are still closely related; when cross-bred, they make fertile offspring..