Kinds of Sharks

The largest of all sharks—and of all fish—is the whale shark, which reaches an average of 40 feet (12 m) in iength. It is found throughout tropical waters of the world. It is one of the few sharks with its mouth at the tip of the snout rather than on the underside. Second in size is the basking shark, which averages a length of about 25 feet (7.6 m). It is found in temperate waters. Both feed on plankton and are relatively harmless.

Not really—they just look as if they do. Like whale sharks, basking sharks swim near the ocean’s surface in order to eat tiny plankton. They may look as if they are basking, or warming themselves, in the sun. But basking sharks are actually swimming slowly and filtering water through their gills. An adult basking shark can filter out about 2,400 gallons (9,000 liters) of water in an hour!

A basking shark may measure over 30 feet (9.1 meters) in length. This makes it the second largest shark. Like a whale shark, it poses no danger to humans.

The shark that is most dangerous to humans is the great white shark (also called the man-eater and tommy). It is a warm-blooded species, this shark averages about 18 feet (5.5 m) in length. It is most abundant in tropical waters. Other extremely dangerous sharks are the bull, tiger, and oceanic white-tip sharks.

Yes! The great white shark has probably been responsible for more attacks on people than any other shark, including the hammerhead. Attacks have occurred most frequently along the coasts of California, southern Australia, New Zealand, and South Africa.

Oddly enough, most of these attacks were probably mistakes on the shark’s part. The great white’s favorite prey include sea lions and seals. When swimming, a person looks very much like a seal, and this may explain the attacks.

Even when bitten by a great white, a swimmer often has a good chance of survival. The great white usually takes a bite of its victim and then retreats. Some scientists believe the shark may be waiting for its victim to bleed to death. Others think the shark may find that a human is an unsuitable meal. In any case, during this time, the injured swimmer can often be rescued or swim to safety.

The great white shark has great size. It can grow to a length of 21 feet (6.4 meters). Also, it has great teeth. But, most of all, the great white shark has great speed and tremendous strength.

Most fish have temperatures that are the same as the water in which they are swimming. But a few sharks, including the great white, can keep their bodies warmer than the water. Warm blood flows in and around the muscles. This helps the shark swim faster. It also helps with those sudden bursts of speed that are useful in chasing prey.

While the great white is indeed great, it is not completely white. Young great white sharks have brown coloring on their backs. Old ones are partly gray or blue.

The mako, another warm-blooded species, is a popular game fish. It occurs in tropical and temperate waters of the Atlantic Ocean, and is primarily a deep-sea fish. The mako averages about 12 feet (3.7 m) in length. The leopard shark is a generally timid shark often found along the coast of California. Several species of small sharks commonly found close to shore are called dogfish.

It’s the mako. This shark’s streamlined body is perfect for speed. Mako sharks can swim really fast—about 22 miles (35 kilometers) per hour. In short bursts, they may even be able to reach speeds of 35 miles (56 kilometers) per hour.

In addition to being speedy, makos are quite acrobatic. They are one of only a few types of sharks that leap out of the water—sometimes quite high. Makos can stop, turn, and speed up quite suddenly. About the only thing they cannot do is swim backward. But no sharks can do that.

Because of their speed and agility, makos are a favorite of people who fish for sport. When caught, a mako may struggle for hours, jumping and fighting to get free. The people fishing seem to enjoy the challenge of capturing this great predator after a long struggle.

Among the most unusual sharks in shape are the hammerheads. The head is extended laterally to form flattened lobes. At the end of each lobe are an eye and a nostril. The largest species of hammerhead is the great hammerhead, averaging about 15 feet (4.6 m) in length. It is found in tropical and subtropical waters in both the Atlantic and the Pacific.

A hammerhead has a flattened head with two ends that stick out like the head of a hammer. On each end is an eye and a nostril.

Hammerheads may look strange, but their oddly shaped heads are actually very useful. Their widely spaced eyes give hammerheads a very broad range of vision. This helps them see their prey. Also, widely spaced nostrils help these sharks figure out where the scent of prey is coming from. Their flat heads allow hammerheads to swim faster and better.

There are nine different species of hammerhead sharks. Different species have heads with slightly different shapes and bodies of different sizes. The bonnethead is the smallest at 5 feet (1.5 meters) in length. The great hammerhead is the largest. It can grow to a length of about 20 feet (6.1 meters).

Hammerheads do not lay eggs as most fish and some other sharks do. Instead they give birth to live young. This is somewhat like the way mammals—such as cats and dogs—have babies.

Each fertilized egg develops inside a separate sac. The sac is inside the mother and attached to her by a cord. Inside the egg is a material called yolk. Yolk provides nutrients that sharks need to grow. The young hatch inside the mother and keep growing. When they are ready for birth, the young leave the mother’s body.

Hammerheads give birth to about 40 young at a time. The young are called pups. And they are tiny versions of adult hammerheads. Shark pups are born ready to swim and feed themselves. They are not, however, ready to protect themselves. And shark pups get no protection from their parents. Alone, many shark pups fall prey to larger sharks and other dangers of the deep.

If the hammerhead shark were not constantly moving, it would not be able to breathe. It would also have trouble staying afloat in the water.

Hammerheads do not have lungs. But they still need oxygen to breathe, just as you do. They get the oxygen from the water. Hammerheads breathe by taking water in through their mouths and forcing it out through their gills. Swimming keeps the water—and the oxygen—flowing through the hammerhead. Many kinds of sharks beside hammerheads need to keep moving to breathe.

Most fish have swim bladders. These are internal body sacs that fill with air. The air-filled sac helps keep the fish afloat in the water. Hammerheads and other sharks do not have these sacs. Instead, they have large livers filled with oil. Oil is lighter than water, so this helps when it comes to staying afloat. But it is not enough. The motion of swimming prevents sharks from sinking.

Sharks have the same five senses that you have. They can see, hear, smell, taste, and feel. But hammerheads—and all other sharks—have a sixth sense. It is called electroreception (ih lehk troh rih SEHP shuhn).

Few fish have this special sense. Pores on the skin of a shark’s head lead to sensory tubes. The tubes can detect the small amounts of electricity coming from the bodies of smaller fish and other creatures. The shark can pinpoint the exact location of prey and quickly close in for the kill.

Electroreception can also act like a compass. This helps sharks make their way through the water. It also helps them migrate, or move long distances.

In addition to their special electroreception, sharks have very good vision. They can even see in the dim light of deep waters. Their hearing is excellent, too. It helps them locate prey.

They seem to. One of the most awesome sights in the ocean is a school of hammerheads swimming together.

For some reason, hammerheads come together only at certain times of the year. And they gather only in certain places, such as the Gulf of California in Mexico and the Galapagos (guh LAH puh gohs) Islands in South America.

For years, people off Myrtle Beach, South Carolina, watched schools of hammerheads as they migrated south. Hurricane Hugo disturbed those waters in 1989, causing the hammerheads to change their migration path.

No one knows for sure why hammerheads come together in groups. Shark experts think that they may do so to migrate, to mate, or to hunt together in shallow waters.

They can be. Hammerheads eat fish and shellfish. They do not attack people for food, but they will defend themselves from people when they need to.

Attacks on humans by hammerheads and other sharks are actually very rare. Only about 50 kinds of sharks are dangerous to people. Worldwide, fewer than 50 shark attacks were reported each year between 1990 and 1996. Only about 6 of those attacks resulted in the victim’s death.

Still, people do need to be careful when swimming in waters where sharks are numerous. The most important thing to remember is to stay calm. Don’t start splashing and kicking. Swim away with slow, strong strokes.