Jennifer Engle, age 12, of Pittsfield, Mass., for her question:
WHAT ARE THE MOST COMMON SHARKS?
Scientists tell us there are about 250 species of sharks. Sharks are meat eating fish and about 10 percent, or about 25, are considered dangerous to human beings.
Among the common sharks is the whale shark. In spite of its enormous size, it only eats plankton and small fish. It lives in tropical waters and is harmless to man.
The white shark, also known as man eater, ranks as the most dangerous shark. It measures agout 20 feet long and lives in tropical and warm waters. It swims powerfully and preys on such large animals as sea lions, tuna and other sharks. They have attacked human beings and even small fishing boats.
Thresher sharks are long tailed subtropical fish that swim along the surface. They grow to about 20 feet, half of which is tail. The long tails are used to gather into "herds" the fish they feed on and to stun fish before eating them. No thresher shark has been known to attack a human being.
Nurse sharks are slow growing fish that grow to be 14 feet long. They live among reefs in shallow tropical and subtropical waters. Unlike,most species of sharks, the nurse shark can pump water over its gills. Therefore, it does not have to swim constantly and often lies motionless on the sea bottom.
Nurse sharks eat bottom dwelling fish as well as crabs, lobsters and shrimp. They only attack people if grabbed by the tail.
Mako sharks are swift, powerful creatures. They are considered one of the best species of game fish among all the sharks. They may reach a length of 12 feet. They have attacked small fishing boats and may have attacked swimmers as well.
Basking sharks measure up to 40 feet long and live in cool temperate waters. They eat only small animals and plant life called plankton. They often float on the surface in the sun.
Bull sharks can live in fresh water. They often enter rivers that empty into the sea and they have attacked swimmers.
Hammerhead sharks, which include a number of similar species, rank among the strangest looking sharks. They have flattened heads, which in most of the species resembles the head of a hammer. Their eyes and nostrils are at the end of the "hammer." The largest hammerhead, called the great hammerhead, is about 15 feet long.
Sharks differ from most other kinds of fish in that they have no bones. Their skeletons are made of a tough, elastic substance called cartilage. Most species of sharks have a rounded body, shaped somewhat like a torpedo. This streamlined shape aids in swimming.
The body of a newborn shark resembles that of an adult in almost every way except size. Sharks have fewer young at a time than most fish do. Some species give birth to 60 or more pups in a litter, but most have far fewer. The parents do not take care of the young ¬and may even eat them.