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The word pinniped means 'fin foot', as the four legs of seals, sea-lions and walrus have developed into flippers to better suit their life in the sea.
Adapted to water
Pinnipeds' bodies are specially adapted to help them swim and dive. They are streamlined. The nostrils close underwater. The pupils of the eyes expand widely so they can see well in the darkness deep underwater.
Seals are able to hold their breath for long periods of time. The deepest diving seals can stay underwater for up to 2 hours. Underwater, their heart rate slows down and arteries squeeze shut so that only the sense organs and nervous system get the normal blood flow. Their muscles store oxygen. Once they come up after a deep dive, seals need to recover, and rapid blood circulation through large veins helps their body chemistry return to normal.
They are not fish! Even though a great part of their life is spent in the sea, pinnipeds are warm blooded air-breathing mammals.
Sizes
The largest pinnipeds are the male southern elephant seal (right), at more than 3600 kg, and the male walrus, at more than 3.5m and 1700 kg. The smallest is the ringed seal, at about about 1m in length and 60 kg in weight.
Groups
There are three families of pinnipeds:
earless seals (also called true seals)
eared seals (also called fur seals) and sea
lions
walrus.
Habitat
Most earless seals are found in the cold waters of the Arctic and Antarctic. Some live under ice most of the time, finding cracks and holes in the ice through which to breath. They use claws, teeth or head to break ice as it forms over openings.
While most seals live in the ocean, there are some that are found in lakes. Lake Baikal in southern Russia is believed to be the deepest lake in the world, and is the home of baikal seals. The caspian seal is found in the Caspian Sea in southwest Asia, a huge landlocked sea. Ringed and harbor seals are found in lakes and rivers near the coasts of Russia, Canada, and Alaska.
A few kinds of earless seals are found in warmer waters, such as Harbor seals, northern elephant seals, and monk seals.
Most eared seals are found in warmer waters. The southern fur seal is an exception to this, and is found in southern waters right up to Antarctica.
Some eared seals
migrate great distances, usually after the summer breeding season.
Walrus are found only in the northern hemisphere, in Arctic waters. Large herds travel along the edge of the pack ice with the seasons, although some older males do not migrate. They can cover distances as great as 3000 km.
