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 American sides of the Atlantic ocean from southern New Jersey and the Mediterranean north to the edge of the ice fields, and in the Asian and American coastal waters of the Pacific Ocean north to Kamchatka. With such a wide variety of environments and climates, different species have developed with special characteristics which enable them to live in such diverse conditions (3).
Seals living in the colder environs must be able to withstand bitter cold win...