Mary Allen
Sharks are fish that are at home in all oceans. A few species also live in rivers. They belong to the group of predatory fish: most of them eat fish and other marine animals.
When sharks swim to the surface of the water, they can be identified by their triangular dorsal fin sticking out of the water. Sharks swam the seas 400 million years ago, making them one of the oldest animal species in the world.
The pygmy shark is the smallest at 25 centimeters in length, while the whale shark is the longest at 14 meters. The whale shark is also the heaviest shark: At up to twelve tons, it weighs as much as ten small cars. In total there are about 500 species of sharks.
Sharks have a special set of teeth: further rows grow behind the first row of teeth. If teeth fall out in a fight with other animals, the next teeth move up. In this way, a shark “consumes” up to 30,000 teeth in its lifetime.
Sharks’ skin is not made of normal scales, but of the same material as their teeth. These scales are called “skin teeth”. This skin is smooth to the touch from the head to the caudal fin, and rough the other way around.
How do sharks live?
Sharks are still poorly researched, so little is known about them. However, one special feature is known: sharks have to keep moving so that they don’t sink to the sea floor. That’s because, unlike other fish, they don’t have a swim bladder that’s filled with air.
Most shark species feed on fish and other larger sea creatures. But some of the largest shark species feed on plankton, which are small animals or plants that float in the water. Around the world, about five people are killed by sharks every year.
Sharks have enemies: smaller sharks are eaten by rays and larger sharks. Sharks are also on the menu of seabirds and seals near the coast. Killer whales also hunt larger sharks. However, the biggest enemy of sharks is humans with their fishing nets. Shark meat is considered a delicacy, especially in Asia.
How do sharks have their young?
Shark reproduction takes a long time: some sharks have to be 30 years old before they can mate for the first time. Some species lay eggs on the seabed. The mother does not take care of them or of the cubs. Many are eaten as eggs or as juveniles.
Other sharks carry a few live young in their stomachs every two years. There they develop from half a year to almost two years. During this time, they sometimes eat each other up. Only the strongest are born. They are then about half a meter long.
Many shark species are threatened with extinction. This is not only due to humans and natural enemies. It’s also because sharks have to get very old before they can even reproduce.