Seals are fin-footed, marine mammals that live partly in the sea and partly on land. They are found across the world, even in the tropics (see video below). There are 33 species of seals. Walruses are part of the same group as seals, as are sea lions. Their closest land relatives are bears, weasels, raccoons and skunks.
Seals vary in size. The smallest (Baikal seal) is just 1m long, while the largest (Southern Elephant Seal) is 5m long. They have streamlined bodies with four limbs modified into flippers. Seals are fast and very acrobatic in water, something that helps them to avoid being caught by predators like whales, sharks and polar bears, and helps them to catch their food, which is mainly fish.
Seals use their front limbs to move themselves through the water, in contrast to walruses which use their rear limbs. Seals find it difficult to move about on land.
Seals have eyesight and hearing adapted for both air and water; they also use their whiskers. Seals have a layer of fat, or blubber, under the skin to keep warm in the cold water, and are covered in fur.
Most species live in the colder waters of the Northern and Southern Hemispheres
Most seals live in big groups. Groups of seals are called colonies.
Each year seals lose their fur. While moulting they stay on land.
When they are born they have a fluffy fur. They cannot swim when they are small, so they use the fur to keep warm on land. But just a few weeks after being born this fur falls away and they get a shiny fur. Then they can go into the water.
They have special lungs so that they can dive very deep. They can stay underwater for two hours while they hunt for fish. They simply close their noses.
They have a special clear eyelid so that they can see underwater.
They spend months at sea and so they sleep in the water. When they are snoozing, they float belly up.
There are two kinds of seals: true seals and fur seals. Fur seals and sea lions are closely related. Fur seals are so called because they have a dense underfur for which they were hunted. Fur seals and sea lions can stand on all four flippers, and they also have external ears. Sea lions eat huge amounts when they feed - getting on for ten percent of their body weight. In between feeding they are happy to lounge about. It is the sea lions that help to make the San Francisco pier 39 area attractive.
