There are about 350 species of sharks that live in all of the oceans of planet Earth. Sharks vary in size from the massive Whale Shark, that grows to a length of 13 metres or more and weighs up to 15 tonnes, to the small Dwarf Shark that only reaches 25 cm in length. Only a few sharks are dangerous enough to be a threat to humans. These include the Great White Shark, the Tiger Shark and the Hammerhead Sharks of tropical seas.
Most sharks are smaller and eat small fish and crabs.
The huge Whale Sharks and Basking Sharks eat massive quantities of very small animals called copepods. They swim slowly along a gulp up huge quantities of seawater that contains these small animals. Some small sharks called Dogfish and Spurdog and are caught for food which is called Huss in the fish and chip shops of Britain. The skeleton of sharks consists mainly of cartilage and not true bone which is found in humans and most fishes. Sharks have an electrical sense system for detecting prey.