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ice (up to 807 mi., or 1300 km. from shore); it will attack prey in the water and relies almost entirely on marine species for prey; it has adaptations for a marine environment; and is able to swim long distances. Most significantly, the polar bear is dependent upon the marine environment ecologically.

Other marine mammals include two species of otter (Order Carnivora; family Mustelidae): the marine otter (Lontra felina) and sea otter (Enhydra lutris). Myotis vivesi, the marine-dependent fishing bat (Order Chiroptera), might also be considered to be a marine mammal. Less debatable marine mammals are the manatees and dugongs (Order Sirenia), whales, dolphins, and porpoises (Order Cetacea) and the various species of seal (Order Pinnipedia). The pinnipeds include true seals (family Phocidae), walruses (family Odobenidae), and eared seals (family Otariidae), the last of which, in turn, contains sea lions (sub-family Otariinae) and fur seals (sub-family Arctocephalinae).

There has been much concern about the impacts of climate change on marine mammals, particularly polar bears, cetaceans, and pinnipeds. Likely effects include shifts or depletion of important prey species, changes in distribution, exposure to new diseases and predators, and habitat loss. Several arctic-dwelling seal species haul out onto ice to give birth, and may be vulnerable to reductions in area, or thinning, of sea ice. Loss of ice as a haul-out substrate and fierce storms have led to several seasons of high harp seal pup (Pagophilus groenlandicus) mortality in the Gulf of St. Lawrence, Canada. As humans cull juveniles of this population, this adds an additional stressor to the population. Pinnipeds are also very well-adapted to cold temperatures and global warming may lead to heat stress.

sEE ALsO: Polar Bears; Sea Ice.

BIBLIOGRAPHY. W.F. Perrin, et al., eds., Encyclopedia of Marine Mammals (Academic Press, 2002); D.W. Rice, Marine Mammals of the World: Systematics and Distribution (Society for Marine Mammalogy, 1998); M.P. Sim-monds and S.J. Isaac, "The Impacts of Climate Change on Marine Mammals: Early Signs of Significant Problems," Oryx (v.41, 2007).

Edward Christien Michael Parsons George Mason University

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