Seals

Seals are warm-blooded, carnivorous aquatic mammals whose front and hind feet are modified as flippers (2,3). They are members of the pinniped group, which includes seals, sea lions and walruses (8). For many decades, experts have agreed that true seals, those without ears, evolved from the weasel or otter-like forms, whereas sea lions and walruses, which have ears, developed from bear-like forms. More recently, some experts are turning to the theory that all pinnipeds evolved from one land-based mammal that entered the sea. This is because of studies showing that all pinnipeds share quite similar hand and foot structures, and these structures do not resemble those of other land or aquatic mammals (8). This paper will look at the structural, biochemical, physiological, behavioral, and ecological adaptations of seals that enable them to survive the physical, chemical, and biological challenges of their environment.

Seals are classified into two major groups: Otariidea - the sea lions or eared seals, including the fur seals - and Phocidea - true seals, or hair seals. There are approximately 31 species and about 16 named geographical varieties or subspecies of seals. Walruses belong to a separate family - the Odobenidae (3).

Various species of seals span the globe, from the frozen arctic, down the American west coast and the coast of south America, as far south as Australia, New Zealand, and Antarctica. They are found in the coastal waters of both the European and A

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te fur, which is replaced in the first few weeks of life with the fur characteristic of its species. Unfortunately for the seals, baby harp seals are hunted for this white fur in the first three weeks of their life, making man a major predator of this species. Young northern fur seals have glossy, blackish-brown hair and in the early 1800s, more than 3,000,000 were slaughtered for their fur. The southern fur seal has a coat of thick, soft underfur and a mantle of long, coarse hair on the shoulders in the bulls. It's fur is not of as high a quality as the northern fur seal. Weddell seals are able to winter under the ice as far south as the Ross sea within 10o os the South Pole, in waters whose temperatures would be fatal to man, because they can conserve their body heat in a form of vacuum. This is achieved partly by means of insulating blubber and partly by their ability to reduce the flow of blood to surface tissues, where body heat is most rapidly lost, by shutting off most of the small blood vessels in the skin from the main circulation (6:32-33). Weddell and ringed seals are also able to keep open breathing holes in the thick ice by continually gnawing and sawing at it with their teeth. They swing their heads from

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