Monday, July 7, 2008

Threats To Polar Bears Survival

Polar bears, top predators in their arctic habitat, face growing threats to their survival.

Global Warming

Polar bears are highly adapted to their Arctic habitat. Recent declines in their numbers can be linked to the melting of sea ice and its formation later in the year. The Artic Climate Impact Assessment polar bear crossingreported in 2004 that the covering of summer ice in the Arctic shrunk by 15 to 20 percent in the past 30 years, and the decline was expected to accelerate. Further predicted reductions of 10 to 50 percent of annual sea ice and 50 to 100 percent of summer sea ice in the next 50 to 100 years present a considerable threat. Ice is breaking up earlier in some areas and is predicted to do so in other areas, forcing bears ashore before they build up sufficient fat stores or forcing them to swim longer distances, which may exhaust them, leading to drowning. Not only is the Arctic warming forcing the bears to feed for a shorter time, but it is also decreasing their prey base. The consequences are thinner, stressed bears, decreased female reproductive rates, and lower juvenile survival rates.

Although a broad consensus has emerged that human activities are contributing to global warming, greenhouse gas emissions continue to increase in the United States and abroad. The United States has refused to sign the kyoto protocal, an international agreement intended to decrease the human production of greenhouse gases. Without the participation of the United States, the protocol is unlikely to meet its 2012 goal of reduced emissions of 5 percent of 1990 values in developed countries. Even if this goal is met, it is not stringent enough to preserve the polar bears' habitat.

Environmental Contaminant

The Arctic is considered a "sink" for environmental contaminants. Mercury, organochlorines such as PCBs and DDT, and other toxins are carried northward in rivers, ocean currents, and the wind. These toxins accumulate at higher levels along the food chain. Researchers have found extremely high amounts of chemical pollutants in polar bears, the top Arctic predator, putting the bears in danger of bone mineral density loss, hormonal imbalance, physiological damage, and compromised immune systems. Bone mineral density loss is especially devastating in female polar bears, which must mobilize large amounts of calcium and phosphate during pregnancy and nursing. As an additional blow, the harmful effects of pollutants can interact negatively with the nutritional stress caused by global warming.


Melting sea ice has resulted in the opening of the Arctic to tourism and mineral and energy development. As more people visit the Arctic, noise pollution and interactions with polar bears increase. Polar bears are harassed by photographers and tourists wanting to come closer. Yet when the bears are attracted to human camps by the smell of food, they may be perceived as a threat and killed.Oil and gas exploration is a growing threat to polar bears as well. Companies are eager to exploit the mineral reserves in the Arctic, but it comes at a great cost to the environment.


Because of their long lives and slow reproduction, polar bears rely on high adult survival rates to maintain their numbers. Over-hunting of adults can cause a catastrophic crash in population. Half of the 20 hunted polar bearrecognized populations of polar bears are currently threatened by potential over-hunting. The remainder may be over-hunted in the near future if hunting quotas are not reduced. Subsistence hunting is permitted in Canada, Greenland and Alaska, and sport hunting is permitted in Canada and recently Greenland. The World Conservation Union Red List of Threatened Species cites "a potential risk of over-harvest due to increased quotas, excessive quotas or no quotas in Canada and Greenland and poaching in Russia."

Although the United States prohibits non-subsistence hunting of polar bears under the Marine Mammal Protection Act and trophy hunting is arguably illegal under the International Agreement on the Conservation of Polar Bears, U.S. hunters are permitted to import the trophies from sport hunted polar bears from six Canadian populations—Southern Beaufort Sea, Northern Beaufort Sea, Western Hudson Bay, Lancaster Sound, Viscount Melville Sound, and Norwegian Bay. Declining populations in some areas have spurred the U.S. Fish and Wildlife Service to review the sustainability of hunting in these areas. Unfortunately, polar bears continue to be killed and imported into the United States while the Fish and Wildlife Service considers whether to lift its approvals for any of the six targeted populations.

No comments: