Polar bears are found only in the Arctic, where they are the largest land carnivores. Polar bears prefer multiyear ice for protective cover and for a platform to hunt their favorite food, ringed seals. During the summer, they eat very little while they wait for the ocean to freeze. In areas such as eastern Baffin Island and Hudson Bay, where most or all of the pack ice melts by mid- to late summer, the entire bear population must come ashore for two to four months in summer and early fall to wait for the ice to freeze again (Norris, Rosentrater, and Eid 2002).
Polar bears are moving to land earlier in the season as sea ice melts earlier in the spring, which means they don't have enough fat reserves to survive the ice-free season (Norris, Rosentrater, and Eid 2002). A polar bear's reproductive system is also strongly linked to their fat stores, which in turn are linked to finding food on the ice. If the bears are forced to move to land too early, they become unusually thin by the end of the summer. This affects their ability to reproduce and weakens future generations that are born.
Between 1981 and 1998, scientists in Hudson Bay observed that the weight and number of polar bear cubs born declined by 15 percent. If female bears fall below a certain weight threshold, they will not conceive (ENN 2002). For every week a bear has not been hunting, it becomes 10 kilograms (22 pounds) lighter (Kerr 2002). As Seymour Laxon of University College London put it, "No ice means no bears" (Laxon et al. 2003).
A 2002 World Wildlife Federation report claims that rapid changes in the northern ecosystem may be incapable of supporting polar bears within 100 years (Norris, Rosentrater, and Martin Eid 2002). Changing ice conditions in Hudson Bay have already reduced the number of polar bears over the last 20 years, and the number of live births and the health of adult bears have declined (Johansen, in press).
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