Not Just For Kids

SHARKS

Did you know there are more than 350 different species of sharks, which are divided into 8 orders and 30 families? Scientists think that there may be even more sharks waiting to be discovered, since the oceans of the world have not yet been fully explored.

Sharks are very primitive creatures. They look and live much as their ancient ancestors did. Sharks and rays are related. They comprise one of the two groups of true fishes. The other is the bony fishes. Sharks and rays have no bones; their skeletons are made of cartilage. (The flexible part of your nose is cartilage.)

Most sharks have wedge-shaped noses and long, torpedo-shaped bodies with two wing-like front pectoral fins, two rear pelvic fins, two dorsal fins on their backs (one of which may be seen extending prominently above the surface of the water), and a tail fin. A shark's outer skin is rough like coarse sandpaper, with many tiny tooth-like scales called denticles. Sharks are powerful and swift. They can swim as fast as 43 miles per hour for short distances.

Sharks are carnivores, or meat eaters. They feed on fish and other sea creatures, both large and small, including sea turtles, crabs, squid, seals, dolphins, and even other sharks. Sharks have rows of sharp, pointed teeth that can saw through flesh and bone and kill prey with a single bite. Sharks have excellent hearing and a keen sense of smell. Some sharks can smell one part of blood in 100 million parts of water. They see well, even in dim light, although they cannot see colors.

Like many fish, sharks learn about their surroundings through what is called a lateral line. This is a series of small holes on the sides of their bodies, which sense pressure waves and vibrations in the water. A swimming fish makes tiny waves that are picked up by the shark's lateral line. The shark knows the fish is there by its movement, even if it cannot see, hear, or smell it. Some sharks are able to pick up electrical impulses through hundreds of tiny holes in their faces.

All sharks are marine animals, and most can only live in salt water, although a few can survive in fresh water. Sharks are found in both warm and cold waters, but the largest number live in tropical seas. Many sharks prefer to live in the shallow waters of coral reefs. Some sharks live far out in the open sea. Others, like the sand sharks, usually live close to land.

Some sharks are hatched out of eggs, but most sharks give birth to live, fully formed young called pups. As soon as they are born, the pups can swim and fend for themselves. The parents do not care for their young and may even eat them.

Only about 25 kinds of sharks are dangerous to people. Despite their fearsome reputation as relentless predators, shark attacks on humans are exceedingly rare. Many underwater divers have worked in the midst of sharks without being attacked. But some people have been wounded or killed by sharks, and even small sand sharks have attacked swimmers near beaches. Consequently, many people are afraid of sharks.

Types of Sharks

It is amazing how many varieties of sharks there are. They may be short, fat, skinny, or flat. There are gray sharks, blue sharks, brown sharks, and spotted sharks. Some have strange heads, some have strange tails, and some have strange habits. A few don't even look like sharks. Here are some of the different types of sharks:

Tiger Shark - this stripe-backed "man-eater" grows to 16 feet or more in length.

Great White Shark - this aggressive shark, which may grow to be 35 feet long, is the world's largest predatory shark, weighing between 6,000-7,000 pounds.

Whale Shark - the largest fish in the world, growing to be as long as 60 feet, but it eats only small fish and animal plankton.

Dwarf Pacific Shark - the smallest shark known to science, only 4 inches long!

Hammerhead Shark - has a T-shaped head with an eye on each end.

Basking Shark - floats, or basks, on the surface of the sea to warm itself in the sun.

Greenland Shark - is found in glacier-cold waters of the north.

Spiny Dogfish - this shark, a common pest of fishermen, grows to 4 feet.

Nurse Shark - this lazy scavenger usually has 20-30 pups at a time, each about one foot long.

Thresher Shark - has an unusually long tail, up to 10 feet, for herding and hitting prey.

Bull Shark - often found swimming up rivers, far from the sea.

Carpet Shark- this patterned shark lies on the ocean floor and even has fringe on its head.

Shark Facts