ds, snow and ice on land and freezing waters. They are generally larger species with thick layers of blubber for heat retention and thick fur. Those living in more temperate climes face less daunting environmental challenges. They tend to be smaller, with thinner layers of blubber and thinner coats. Seals are most numerous in the colder regions, particularly around the polar ice caps, but seals and sea lions are found in the shore waters of most seas and oceans of the world (3). Some polar species of seals migrate in winter to avoid the advancing ice, while others winter under the ice (4), surfacing through holes to breathe.
Most true seals (earless species) fall into one of three geographical groups: northern, antarctic, and warm water species (4). The northern seals include the common seal (harbor seal) of the North Atlantic and North Pacific, and the gray seal of the North Atlantic. The harp seal is found in the arctic Atlantic and the ribbon seal in the arctic Pacific. The small ringed seal and the larger bearded seal are circumpolar arctic species. The antarctic seals include the voracious leopard seal, which feeds on penguins and other sea birds, and the Ross, Weddell, and crabeater seals. The warm water seals are the Mediterranean, Caribbean, and Hawaiian species of monk seals. A fourth group includes the Northern and the Southern Hemisphere elephant seals, distinguished by their immense size and trunk-like snout, and the hooded seal, distinguished by an inflatable bladder over the snout, which is found in the arctic Atlantic.
Seals feed on fish, cephalopods (mollusks such as squid and cuttlefish), shellfish, larger forms of plankton, sea birds, other seals, and occasional cetaceans, so they thrive where these food sources are plentiful (4). Many are bottom-feeders, and have to dive to great depths to find food. The chief natural enemies of seals are the sharks, the killer whale, the polar bear, and th...