Shark, a fish found in almost all oceans of the world but chiefly in warm water. Sharks inhabit both deep and shallow water. Open-water species must move constantly to breathe and stay afloat. Some migratory species swim up river to spawn. Sharks range in size from less than 2 feet (60 cm) to 60 feet (18 m) or more. Large sharks may weigh more than 13 tons (11,800 kg).

Contrary to popular belief, most sharks are not aggressive toward humans. Unprovoked attacks are rare; sharks tend to retreat when confronted unless they are threatened. Of the more than 350 species, only about 20 are known to attack humans. These species are usually attracted by blood or by any unusual movement in the water. Many types of shark protection have been developed. Examples include the shark billy, a stick used to push sharks away; the shark dart, which is fired from a gun and explodes upon contact with the shark; the shark screen, a polyvinyl bag, supported by an inflatable collar, that surrounds a person in the water, making him undetectable to sharks; and protective suits made of steel mesh.

Shark meat is used as food in many parts of the world, and commercial fishing of sharks is common in the Far East. The fins serve as the main ingredient in shark-fin soup. Shark skeletons are dried and processed for use in fertilizer and animal feed. Squalene, an oil extracted from the liver, is used to treat burns and as a base for cosmetics.

SharksSharks range in size from less than two feet to sixty feet or more.
What Is a Shark?

A shark is a very special kind of fish. A hammerhead is just 1 of about 370 known species of sharks. Others are makos, great whites, sand tigers, and dogfish.

What makes sharks so special? For one thing, they do not have bony skeletons like the fish you are probably familiar with. Instead, sharks have skeletons made of cartilage (KAHR tuh lihj). Cartilage is light and flexible, like a plastic drinking straw.

Most sharks have bodies shaped like torpedoes. Their smooth shape and powerful fins make them excellent swimmers. A shark has stiff side fins. These fins act like underwater wings as a shark’s tail pushes its body forward. Large fins on a shark’s back keep it from rolling over.

All sharks are carnivores (KAHR nuh vawrz), or meat-eaters. Most have razor-sharp teeth made for tearing the flesh of prey. Sharks mainly eat other fish. Some even eat other sharks.

Where in the World’s Oceans Do Sharks Live?

You can find sharks in all the oceans of the world. The big difference in where sharks live is how close to the shore they get and how deep into the ocean they swim.

Some sharks live in deep ocean waters far from land. Other sharks swim into shallow, coastal waters to hunt for prey. Swimmers need to watch out for sharks that come close to shore.

A number of sharks live and hunt for food on the ocean floor. Others stay near the surface of the water, finding food there.