Their name being derived from the Latin words 'pinna' ('fin', 'flap' or 'wing') and 'pedis' ('foot'), there are 33 living species of the 'fin-footed' pinnipeds, distributed mainly in polar, sub-polar and temperate waters.
Unlike whales and dolphins, pinnipeds share their time between the water and the land (or ice), generally hauling out on land in order to mate, rest, give birth and moult. Descended from either bear-like or otter -like creatures who entered the seas millions of years ago, these mammals have adapted to their marine existence in many ways.
Photo: Baikal Environmental Wave
To protect themselves from the cold, pinnipeds have developed large layers of blubber under their skin. This blubber also helps in the streamlining of their shape, allowing these torpedo-shaped animals to chase their prey underwater with amazing effectiveness. Pinnipeds also have a larger relative volume of blood than other mammals allowing them to store large amounts of oxygen in their blood on very deep and prolonged dives with dives of up to 1600 metres and 2 hours having been recorded.
The 33 living species of pinniped are divided into 3 families: the Phocidae ('true seals'), the Otariidae ('eared seals'), which include the fur seals and sea lions, and the Odobenidae (the walrus). The Otariidae differ from the Phocidae in several ways but perhaps the most noticeable ones are that otariid seals have external ear flaps, generally walk on both their hind and fore flippers, and propel themselves through the water by their fore flippers with a sculling motion. Phocid seals on the other hand do not have visible ear flaps, drag themselves along land by their fore flippers or bodies and use their hind flippers to propel themselves through the water, their fore flippers being used for steering. The walrus possesses a curious mixture of both phocid and otariid characteristics.
Pinnipeds around the world eat a wide variety of food, ranging from krill in the Southern Ocean through crustaceans and molluscs to fish and squid. Some leopard seals even specialise in eating penguins. Pinnipeds have few natural predators, the main ones being killer whales, some sharks, polar bears and man.
Subantarctic Fur Seal
Photo: Miguel Iguez,
Seals, sea-lions and walruses have suffered from heavy commercial exploitation ever since the early traders realised that they could make money from selling seal skins, blubber and meat. Many species of pinniped were brought to the point of extinction while earlier this century one species, the Caribbean monk seal, disappeared altogether.Commercial exploitation has become less of a threat to some species but still carries on in several countries. New threats such as pollution, over-fishing, entangleme