Polar bears evolved from brown bears and are the largest member of the bear family. Male polar bears measure 2.4- 2.6 m (8-9 ft) from nose to tail and generally weigh up to 600 kg (1,320 lbs), but may reach up to 800 kg (1,760 lbs). Females measure around 2 m (6-7 ft) and are typically about half the weight of males.
Polar bears are specially adapted to the polar marine environment in which they live. Adaptations include: white coloration for camouflage; water repellent guard hairs, dense underfur, and black skin for absorbing warmth; small “suction cups” on the soles of their feet for traction on slippery ice; teeth specialized for a carnivorous rather than omnivorous diet; and the ability to store large amounts of fat when food is available and then use it later when food is unavailable. Polar bears’ primary food source are ringed seals but they also hunt bearded seals, walrus, and beluga whales, and will scavenge on beached carrion such as whale, walrus and seal carcasses found along the coast.
Polar bears generally live alone except when concentrating along the coast during the open water period, or when mating or rearing cubs. Pregnant females will enter maternity dens in October/November; most dens in the circumpolar Arctic are located on land in areas where snow accumulates, such as along coastal bluffs or river banks. In Alaska, dens are excavated on either sea ice or on land. One to three cubs are born in December/January; cubs remain with their mother for about 2 1/4 years.
On May 15, 2008 (Federal Register, vol. 73, p. 28212), the U.S. Fish and Wildlife Service (Service) listed polar bears as threatened under the Endangered Species Act (ESA) because of observed and forecasted evidence that circumpolar warming is melting sea ice, the polar bears’ primary habitat. Critical habitat was designated on December 7, 2010 (Federal Register, vol. 75, p. 76086).
Habitat and Habits
Polar bears’ primary habitat is sea ice, which they depend on as a platform for hunting ice seals (their primary prey), seasonal and long-distance movements, travel to terrestrial maternal denning areas, resting, and mating. Polar bears are not evenly distributed throughout the Arctic, nor do they comprise a single nomadic population, but rather occur in 19 relatively discrete subpopulations throughout the ice-covered marine waters of the northern hemisphere. The U.S. contains portions of two subpopulations: the Chukchi Sea (CS) and the Southern Beaufort Sea (SBS) subpopulation, shared with Russia and Canada, respectively. Although a precise population estimate does not currently exist for polar bears in Alaska, the SBS population is estimated to be approximately 1,526 bears; the size of the CS population is unknown. Globally, the total polar bear population is estimated to be 20,000 to 25,000.
The main threat to polar bears is the loss of their sea ice habitat due to circumpolar warming. Recorded declines in sea ice have been correlated with declines in polar bear body condition, survival rates, and population size in portions of their range. The extent and duration of sea ice is projected to continue to decline into the foreseeable future. Polar bear populations also are susceptible to other human-caused disturbances, such as offshore development, habitat alteration and human-caused mortality.
Management and Protection
In the U.S., polar bears are a federally protected species under the Marine Mammal Protection Act of 1972 (MMPA) and the ESA. The MMPA prohibits hunting of polar bears by non-Natives, although Alaska Natives are allowed to harvest some polar bears for subsistence and handicraft purposes. The Service is the Federal agency responsible for managing polar bears in the U.S.
An international conservation agreement for polar bears signed in 1976 by the U.S., Russia, Norway, Canada, and Denmark (Greenland) calls for cooperative management of polar bears. Another treaty, the Agreement between the Government of the United States of America and the Government of the Russian Federation on the Conservation and Management of the Alaska Chukotka Polar Bear Population (U.S.-Russia Agreement), covers the shared CS population of bears. Notably, the treaty calls for the active involvement of Native people and their organizations in polar bear management programs. It also enhances long-term cooperative efforts such as conservation of Susi Miller / USFWS U.S. Fish & Wildlife Service Threatened Under Endangered Species Act Polar Bear ecosystems and important habitats, sustainable harvest allocations, collection of biological information, and increased consultation and cooperation with State, local, and private interests.
A number of protective measures have been taken to reduce human activities along the coast in polar bear denning areas, as the animals are most sensitive to outside disturbances while denning. For example, oil and gas activities have been modified to avoid these areas. The Service also provides expertise to industries on how to minimize conflicts with bears while conducting their operations.
The Service’s overall conservation goal is to adaptively manage Alaska’s polar bears in the face of projected climate change impacts so they remain a healthy, resilient component of the CS and SBS ecosystems. In 2010, we initiated a collaborative planning process with our conservation partners to develop a Conservation and Management Plan (Plan) for polar bears, as mandated by the ESA and MMPA. The Plan will include prioritized research and monitoring actions to address key uncertainties and build upon existing baseline data. For example, although we predict that polar bear populations will suffer at a global level from loss of sea ice, the specific response of polar bears at the subpopulation level is less clear.
From the U.S. Fish & Wildlife Service