True seals (Phocidae)

The group of animals that we call true seals are all members of the family Phocidae .

Seals are mammals that live in the ocean, also known as marine mammals. Together with the family of sea lions and the family of walruses they are placed in a special clade of marine mammals. This clade consists of so called pinnepeds (Pinnipedia).

Pinnipeds got their name from the shape of their flippers. These animals have very short flippers, but with very long fingers and toes. This makes it look as if they have fins.

Seals belong to the order of mammals that mostly eat meat: CarnivoraThis order also includes animals such as bears, lions, wolves, sea lions and walruses .

Seals are carnivores, which means that they must eat other living animals to survive. They often eat fish, crustaceans and shellfish. Some species can eat very small animals such as krill. Others hunt for even bigger prey such as birds and other mammals.

You can partially recognize seals by their special physique. They have a long body with a broad chest and a small lower body. This gives them a streamlined, cone-shaped body. Their flippers are very short and wide and they have five digits which are webbed. This makes them perfectly suited for aquatic life.

Sea lions and walruses have similar physiques and adaptations, so what makes seals stand out? First of all, seals’ hind flippers cannot be folded underneath their body to walk on. Sea lions and walruses are able do this, which it easier for them to "walk" on land.

Seals have to hobble on their bellies to move on land. The way in which seals move is also referred to as caterpillar-like motion.

Another difference are their ears. Sea lions have small external ear flaps. Seals don't have such visible ears, they have ear holes on the side of the head.

Seals are strong swimmers. They have to be, as seals spend a lot of time in the water. In general seals can stay underwater for a longer period of time than sea lions and walruses. To hunt for food, some seal species must be able to dive very deep.

A seal has a special way of swimming. To speed up, seals swim with their hind flippers by holding them flat against each other and moving them quickly side to side. You could compare this to how fish swim. Fish also whip their tail to the side to move through the water. The front flippers are a lot smaller than the back flippers. They also don't use it to move forward, but to steer.  

Most seal species live a solitary lifestyle. This means that they prefer to do almost everything on their own. The only exception is during the mating season, because then the animals congregate in large numbers to birth pups and mate. When mating season is over, the seals moult together, after which they each go their separate ways.

You can see seals resting in groups on beaches and sandbars, but that does not mean that they like to be together. Because seals are less agile on land, they cannot run away from large predators. Therefore, when the seals are on land it is safer for them to be with other seals. Additionally, often times there is not enough space to lie far apart so they are “forced” to be closer than they would want to.

Seals can be found in every ocean of the world. They often live along the coasts or on the ice of the North or South Pole. There is even a species of seal that does not live in the sea, but in the freshwater Lake Baikal in Russia! Each species is adapted to live in certain areas and not one seal species can be found all over the world.

The true seal family (Phocidae) is often divided into two subfamilies: northern seals (Phocinae) and southern seals (Monachinae). The group of northern seals consists of ten species. The southern seal group is made up of eight species. Worldwide there are a total of eighteen different seal species.