Humans kill polar bears for aboriginal subsistence, sport, and defense of human life and property. In some areas, monitoring of polar bear kills is effective (in Norway and the United States), but in other areas there is little reliable information (Russia and Greenland). Concerns have recently been expressed about the threat posed by trophy hunting (currently allowed only in Canada and Greenland). Quotas are often based on poor population data. Approximately 80 trophies are imported into the United States each year from Canada.
Arctic marine mammals can accumulate high concentrations of pollutants in their blubber. As top predators, polar bears accumulate the highest concentrations, and in some areas there is concern about pollution effects on the bears' health. Polar bears with abnormal genitalia and other defects have been recorded, and there have been suggestions that these are caused by exposure to certain contaminants. Development in the Arctic is also an issue. The Arctic is rich in natural resources, especially oil and gas. Exploration for and extraction of these resources involve construction that could potentially reduce habitat, produce pollution, or cause disturbance.
Because of their exclusively Arctic habitat and their charismatic nature, polar bears have become the "poster child" for the impacts of climate change. The primary concern is the loss of sea ice. This would remove essential habitat, for both the bears and their marine mammal prey. Increasing numbers of drowned polar bears have been reported, the result of increasing areas of open water between ice floes, presumably leading to overexertion during swimming. The loss of ice cover could also reduce the ability to access prey and mates, disrupt migration routes, and increase distances animals have to travel to find food (exacting an energetic cost). Many females also construct their birthing dens on ice. In the past 20 years, the proportion of dens located on sea ice has halved.
Habitat loss and prey reduction may force bears closer to human habitation to find food. Sightings of animals near Arctic towns and villages are occurring with greater frequency. This increases the likelihood of negative human/polar bear interactions. In addition, researchers have reported a significant decrease in polar bear body condition over the past 20 years, and such a decline is likely to have impacts on reproduction and survival.
Climate change may also cause chronic overheating in the highly cold-adapted bear. Finally, rising temperatures are likely to cause a shift in the distributions of other bear species; for example, brown bear populations may shift farther north and could compete, or hybridize, with polar bears.
conservation OF POLAR BEARs
In 1965, the "polar bear" nations met and agreed that each country should take whatever steps were necessary to conserve the species. Cubs, and females accompanied by cubs, should be protected throughout the year; each nation should, to the best of its ability, conduct research on polar bears within its territory; and each nation should exchange information on polar bears freely. This eventually led to the signing of the International Agreement on the Conservation of Polar Bears in May 1973 in Oslo, Norway. This agreement is currently the major international polar bear treaty.
In 1982, largely due to declines resulting from hunting pressure, the World Conservation Union (IUCN) listed the polar bear as Vulnerable. This rating was reduced to Lower Risk in 1996. However, in May 2006, polar bears were relisted as Vulnerable due to a predicted population reduction of more than 30 percent within three generations (45 years), and a decline in area of occupancy, extent of occurrence, and habitat quality resulting from climate change.
In the United States, polar bears are managed by the Fish and Wildlife Service and are protected by the Marine Mammal Protection Act (MMPA), which prohibits harassment, hunting, capture, or killing, or attempts to do any of these. There are exemptions for Alaska Native subsistence hunting, as well as scientific research and "incidental harassment" from activities such as oil and gas exploration. However, a controversial amendment in 1994 permitted the import of sport-hunted polar bear trophies into the United States from some Canadian populations. A legislative attempt is ongoing to repeal this amendment.
In February 2005, the Center for Biological Diversity and Greenpeace USA petitioned the U.S. government to list polar bears as threatened (that is, likely to become endangered within the foreseeable future throughout all or a significant portion of its range) under the U.S. Endangered Species Act. Such a listing would obligate the U.S. government to reduce anthropogenic impacts on polar bears and to devise a plan to aid their recovery. In December 2006, the U.S. Secretary of the Interior announced a proposal to list the polar bear as threatened. The deadline for deciding on the listing was January 2008.
sEE ALsO: Impacts of Global Warming; Marine Mammals; Sea Ice.
BIBLIOGRAPHY. A.E. Derocher, et al., "Polar Bears in a Warming Climate," Integrative and Comparative Biology (v.44, 2004); A.S. Fischbach, et al., "Landward and Eastward Shift of Alaskan Polar Bear Denning Associated with Recent Sea Ice Changes," Polar Biology (in press); Charles Mon-nett and J.S. Gleason, "Observations of Mortality Associated with Extended Open-Water Swimming by Polar Bears in the Alaskan Beaufort Sea," Polar Biology (v.29, 2006); M.E. Obbard, et al., "Temporal Trends in Body Condition of Southern Hudson Bay Polar Bears," Climate Change Research Information Note (v.3, 2006); Aqqalu Rosing-Asvid, "The Influence of Climate Variability on Polar Bear (Ursus maritimus) and Ringed Seal (Pusa hispida) Population Dynamics," Canadian Journal of Zoology (v.84/3, 2006); Ian Stirling and A.E. Derocher, "Possible Impacts of Climatic Warming on Polar Bears," Arctic (v.46/3, 1993); Ian Stirling and C.L. Parkinson, "Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic," Arctic (v.59/3, 2006); Ian Stirling, et al., "Long Term Trends in the Population
Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change," Arctic (v.52/3, 1999).
E.C.M. Parsons B.J. Milmoe George Mason University Naomi A. Rose Humane Society International
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