Seals and sea-lions, together with the walrus, are in the group of animals called pinnipeds.

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 water. 

They are not fish!  Even though a great part of their life is spent in the sea, pinnipeds are warm blooded air-breathing mammals known as marine mammals.

Groups

There are three families of pinnipeds:

• earless seals (also called true seals)

• eared seals (also called fur seals)  and sea lions

• walrus

What's the difference between seals and sea lions?

Seals have furry front flippers, with a claw on each small toe. Sea lions have larger front flippers, longer and mostly covered in skin.

Seals don't have ears on the outside of their heads, which are sleek and smooth, with small ear holes. Sea lions have small ear flaps.

Seals are quiet, making soft grunts,  and are more solitary, spending more time in the water. Sea-lions are social and noisy. They gather on land in large groups of over a thousand.  A group 0f sea-lions is called a herd or raft.

Seals are better adapted for living in the water than on land. Their hind flippers angle backwards and don't rotate so movement on land is more like crawling on their bellies than walking.

Sea lions can rotate their hind flippers forward under their bodies, so they move better on land. 

Sizes

The largest pinnipeds are the male southern elephant seal 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. 

How are they adapted to water?

Pinnipeds' bodies are specially adapted to help them swim and dive. They are streamlined so that they are the best shape for moving through the water smoothly, with their bodies making no resistance to movement. Sea lions are the faster swimmers, and can swim at 40 km per hour. Their 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.

Habitat

Earless seals

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. A few kinds of earless seals are found in warmer waters, such as harbour seals, northern elephant seals, and monk seals.

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 harbour seals are found in lakes and rivers near the coasts of Russia, Canada, and Alaska.

Eared 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.

Communication

Seals and sea lions can communicate underwater. Their sounds are varied, from whoops, barks and moans to mating calls.

Some seals, including bearded seals and Weddell seals, sing songs that may last more than a minute.

Diet

Most seals eat fish or squid. However, the leopard seal in Antarctica hunts penguins and other birds, other seals, fish, squid, krill (small shrimplike creatures), and other invertebrates, as well as feeding on carcasses of dead whales. They will attack humans too, on the ice and divers in the water.  

Another unusual seal feeder is the crabeater seal of the Antarctic because they eat krill, sieving water through their teeth to trap the tiny krill inside their mouth.

Sea-lions generally eat fish.

Life Cycle

All pinnipeds must come ashore to breed, give birth and suckle their young. Some species, such as elephant seals and sea lions, form large groups in the breeding season. These are called rookeries. The strongest males gather a harem, or group of females with which to mate. They allow less strong males to join the group. In these species, males are much bigger than females.  Other species, particularly those that breed on the ice, don't form harems, but do gather in colonies that spread out over large areas. These seals, including ribbon seals, harp seals, and Weddell seals, generally form pairs, and males and females are about the same size.

About 12 months after mating, female seals give birth to a single pup. The size of the young depends on the species: a newborn ringed seal weighs 12 kg, and a newborn walrus 63 kg. The young grow very fast, and quickly build up a layer of blubber because pinniped milk is extremely rich in fat and protein. The blubber is important because it keeps seals warm under the water. How long the young suckle milk from their mothers depends on the species: hooded seals suckle for three to five days and the pups grow from 22 to 43 kg in that time. Sea lions, fur seals and walruses suckle their young for one to two years. Although newborn seals don't have blubber when they are born, they do have fur that traps air next to the skin to give them insulation. Newborn harp seals on the Arctic ice, have white fur that may trap more solar heat next to the skin. Most seals lose infant fur as they develop blubber.

Conservation status and threats

Commercial hunting of seals in the 18th and 19th century and in the early years the 20th century played a large role in the decline of seal numbers. Elephant seals were killed for their blubber, which was boiled down to make oil. Their oil was prized as second only to that of sperm whales.  Fur seals were killed for their skins, and many populations were wiped out.

Dangers for seals today include drowning after getting entangled in rubbish in the sea and in fishing nets and lines.

They are affected by pollution and oil spills as well as being hit by ships. They are still hunted for fur and meat.

  It is always a good idea to use more than one source of information, so here are some others for you to investigate

Read the kidcyber page:

  Antarctic seals

Read more about seals:

http://www.seals-world.com/

Read about the dangers marine mammals face from humans:

http://www.onegreenplanet.org/animalsandnature/biggest-threats-marine-mammals-face-today/