Shark

thumb|The whale shark, which is the longest and heaviest of all sharks.

Sharks are fish that live in every ocean of the world. Some also live in lakes. Sharks are predators: most of them eat fish and other animals in the ocean. When Sharks are swimming on the surface of the water you can see their triangular fin. Sharks have existed for the last 400 million years, which is why they are one of the oldest still existing animals on the planet.

The dwarf shark is the smallest shark as it is just 25 centimeters long. The whale shark is the biggest shark, measuring up to 14 meters. The whale shark is also the heaviest shark: it can weigh up to 12 tons. That’s as much as 5 big cars. There are about 500 types of shark.

Sharks have a special jaw: behind their first row of teeth they have another one, so when they fight and one row gets hit out they still have one more. Because of that they use up to 30,000 teeth in their life. The skin of a shark is not normal fish skin. Their skin is made out of the same material as their jaw. This material is called “Skin Teeth”. From the head to the back fin the skin feels very smooth. The other way it feels very rough.

How do sharks live?

Sharks aren't researched very well yet, so people don’t know much about them. However, one thing is known about them is: Sharks must always be moving so that they don't sink to the bottom of the ocean. This is because unlike other animals, sharks do not have an air bubble which is filled with air.

Most shark types feed on fish and other larger sea animals. But especially some larger shark types feed on Plankton as well. Planktons are little animals or plants that let themselves be pushed by the currents. About five humans are killed by shark attacks per year.

Sharks also have enemies: smaller sharks are eaten by larger sharks and stingrays while the large sharks and small sharks are usually eaten by birds and seals when they are close to the coast. The biggest enemies of sharks remain humans. Mostly in Asia people eat shark meat as it is a delicacy.

How do sharks breed?

The reproduction of sharks takes a long time as they must become 30 years old to mate for the first time. Some shark types lay their eggs on the ocean floor and then keep on swimming. Some other shark types carry their babies in their stomachs for up to two years. They have about five babies in their stomach and usually, they eat each other. Only the strongest one will be born. Most babies are eaten as eggs or babies. When baby sharks are born, they are up to half a meter long. Most shark types are threatened with extinction. This isn't only because of humans and other natural causes it is also because they need to be older to mate.