Seals and sea lions are mammals that live in the oceans all around the world. The ancestors of seals and sea lions were land mammals that returned to the oceans millions of years ago. It is thought that these ancestors were related to early dogs, cats and other carnivores. Being mammals, they breathe air, are warm-blooded and give birth to live young which they suckle with milk produced by the mother. They are all amphibious, able to live on land or in the water. They are more at home in the water, however, and often only come ashore to give birth to their young and shed their fur and grow a new layer (moult). All the pinnipeds have 4 flippers - 2 at the front (foreflippers) and 2 at the back (hind flippers). These flippers are the same as the four legs of most other mammals, but have become specialised for swimming. There are two main groups - the otarid seals which includes the fur seals and sea lions, and the phocid seals, sometimes known as true seals. The most obvious difference between the two groups is that the fur seals and sea lions can turn their hind flippers forwards and walk on land, whereas the phocid seals have to wriggle along on land like giant slugs.

• To be a mammal and so breathe air, have warm blood, and give birth to live young that are suckled on milk produced by their mothers.
• To have fur and a layer of fat or blubber to keep warm.
• To have 4 flippers, 2 foreflippers and 2 hindflippers. Like the four legs of land mammals, with a similar bone structure.
• To have a streamlined and agile body for fast swimming
• To have the ability to dive deep and hold your breath for a very long time.
• To be able to leave the sea to give birth and moult.

Elephant seals, leopard seals, Australian sea lions, Australian fur seals.

Pinnipeds come in a great variety of sizes, but all have a similar basic appearance. They all have streamlined bodies for fast and agile swimming. They all have fur, short on some, very thick on others, and long whiskers on their muzzles. In most species the male is bigger than the female. All pinnipeds have 4 flippers - 2 at the front (foreflippers) and 2 at the back (hindflippers). Some can turn their hind flippers forwards and walk on land, whereas others have to wriggle along on land like giant slugs, dragging their hindflippers behind them. The males of elephant seals have noses with enormous sacs which flap when they move. Most seals are a brown or grey colour but lighter on the belly. Some have spotted coats. Young seals (pups) often have very different fur to their parents. They have to stay on land until this fur is replaced by proper fur that will keep them warm in the water. Many seals and sea lions form large breeding colonies on beaches but can also be found in smaller numbers on land. At sea they are usually solitary.

Seals and seal lions are found in most seas of the world. Some are found only in inland seas. Others live on and under the ice of the polar oceans. Still others live in the sub-tropics. Each species, however, tends to have their own preferred climate. All species must come ashore at least once a year for the females to give birth and for all to moult their fur. They may ‘haul-out’ on beaches, rocky headlands or even onto floating ice floes. As they are more visible when they are ashore, more is known about this part of their lives than their activities at sea. There they are usually solitary and may wander enormous distances in both deep and shallow waters, but generally return to their original haul-out site, coming ashore to breed and moult. During the breeding season, they can become very territorial, mainly on the land but also sometimes underwater. In some species the males have territories they try to fill with many females, defending it aggressively against any other males that attempt to “steal” their females.

All seals and sea lions are carnivores. They need speed and agility in the water to catch their main food, fish. Squid is the main diet of some species. Most species have large canine teeth for gripping their prey. They have developed a special ability to dive to great depths for up to two hours and have enormous eyes for seeing in the gloomy depths. Others eat shrimp-like zooplankton (krill) which they strain through specially shaped teeth. Still others eat penguins and even other seals! They have large cutting teeth for demolishing prey that is too large to swallow all at once. Some forage among rocky reefs in shallow coastal waters looking for fish. They are important top predators, in some ecosystems, being the only significant predator of some animals. When seals and sea lions are on land to breed and moult, they can go without food for many weeks at a time.

Seals and sea lions are close to the top of the food chain. In the water they are hunted by sharks but are usually too agile and fast to be caught. However, some of the larger seals that are not so agile or are diseased may be hunted by white pointer sharks. Killer whales are probably the main predator of most temperate and polar species and have been observed throwing themselves onto beaches to take seals, then sliding back into the water. Some seals are also eaten by other, larger species of seals. On land the main predators are humans and many seals and fur seals are killed each year by commercial sealing operations for their fur and meat. Some species have disappeared as a result of sealing and several species are currently endangered.

Seals and sea lions usually form large groups on land or on ice floes during the breeding season (once a year for most species). Mating and giving birth (whelping) occur at these times. Some species may mate in the water, but all have to return to land (or ice) for whelping. Most pinnipeds have a gestation period of about one year. Some species can stop the development of the young pup during pregnancy for a few months, resuming development later on so that pups are born about one year after mating. Very few mammals can do this. Only one pup is born at a time. The pups are sometimes born with a thick fur coat that is warm in air but not in water, and so have to stay on land or ice until their first moult. After this they grow an adult coat that will keep them warm in water. All seal and sea lion pups spend at least their first week or two on land where they grow at a great rate on their mother’s very rich and fatty milk. Most seals and sea lions mate again soon after giving birth or weaning their young.

Seals that beach themselves on land often gather in huge colonies consisting of many thousands of animals. Those that gather on ice, however, tend to be found in smaller, less sociable groups. Little is known about the activity of many seals when at sea, but they are usually seen alone or in small groups. Seals and sea lions also have their own species of parasites, both internally (like intestinal worms) and externally (like lice). In some parts of the world, seals and sea lions live very close to humans, and may follow fishing boats looking for scraps thrown overboard.

People have hunted seals and sea lions since ancient times. For many coastal native tribes in the colder parts of the world, seals and sea lions have been important sources of food and skins. Many species were over-hunted last century and at the beginning of this century, and some were wiped out. Others are still endangered today. Commercial hunting of seals continues in many places in the world. Many seals are shot by fishermen who believe the seals are stealing their fish. Others are drowned when they get caught in fishing nets. Some good news, though, is that the numbers of many species of seal and sea lion that were once hunted are now increasing. In many places, seals have become a tourist attraction and people visit them just to see them in the wild and photograph them. Scientists study seals around the world, counting them, seeing what they eat and how deep they can dive. Seals and sea lions are also kept in captivity in many countries where their agility and playful natures are admired by visitors, especially when they perform tricks like balancing balls on their muzzles.