Seals (members of the Family Phocidae) reproduce the same way as most terrestrial mammals, that is, they mate, give birth, and suckle their young on land (or in some cases ice). In these respects that are less specialized for an aquatic life than other marine mammals such as whales (cetaceans) and sea cows (sirenians)--which never leave the water. All of these animals (seals--plus their cousins the sea lions & walrus; cetaceans, and sirenians) had different terrestrial mammal ancestors.

Seals are mammals.This means that their reproduction works like most mammals. It means that the sperm has to fertilize the egg inside the female.

There are some interesting aspects to their reproduction because they are marine mammals. There are many species of seals, but the general pattern is similar.

Seals mate on land about 6 weeks after seal pups are born. The fertilized egg starts to divide, then stops for a few weeks, then continues to develop. This makes the pregnancy last longer so that pups are born when plenty of food is available. Females give birth on land, ice, or shallow water so that the pups can breathe. All mammals feed their babies milk. Seals nurse on land. In some seal species, females live off their fat (blubber) and do not eat while nursing their babies. In other species, females leave their young in order to go to the water and eat fish.

Seal pups can swim, but it is safer for them to stay on shore, away from most predators, until they are old enough to catch their own food. At about this time, adults mate. Usually males compete with each other to see which ones can mate with the females. This means that some males do not get to mate at all. The battles use a lot of energy and can cause injuries, so males usually live much shorter lives than females.

Some marine mammals (such as whales and dolphins) never go on land. How different do you think their reproduction is?