Hammerhead Shark

The hammerhead shark is a type of shark with a wide, flat head shaped like a hammer. The strange head is called a cephalofoil. Hammerheads live in warm ocean waters around the world, from shallow coasts to the open sea. There are nine known species of hammerhead. The biggest is the great hammerhead, which can grow up to 20 feet long. That is about as long as a small car.

The shape of the head is the shark's most famous feature. Scientists think the wide head gives hammerheads several advantages at once. The eyes sit on the far ends of the head, so the shark can see in a full circle around its body. The head is also covered in tiny jelly-filled pores called ampullae of Lorenzini. These pores pick up faint electric signals given off by other animals. Every living creature makes a small electric field when its muscles move. A hammerhead can sense that field even when the animal is hiding under the sand.

Stingrays are a favorite meal. A hammerhead will swim along the sea floor, sweeping its wide head back and forth like a metal detector. When it finds a stingray buried in the sand, it pins the ray down with its head and takes a bite. Hammerheads seem to be mostly unbothered by the stingray's venomous tail barb.

Most sharks are loners, but some hammerheads are not. Scalloped hammerheads gather in huge schools during the day, sometimes hundreds of sharks swimming together. Scientists still argue about why. Some think the groups help the sharks find mates. Others think the schools may help young females learn migration routes from older ones. At night the schools break up and the sharks hunt alone.

Hammerheads give birth to live pups rather than laying eggs. A single litter can have more than 30 babies. The pups are born with their heads already shaped like hammers, though the head is softer and folded back so it does not hurt the mother.

Several hammerhead species are now in serious trouble. The great hammerhead and the scalloped hammerhead are listed as critically endangered. Their fins are highly valued for shark fin soup, and millions of hammerheads have been killed for the fin trade. Laws in many countries now protect them, but populations are still falling. The hammerhead is one of the oldest shark designs in the ocean, and scientists are racing to keep it from disappearing.