Leslie Galloway, age 11, of Gaffney, S.C., for his question:
IS IT TRUE THAT SHARKS DON'T HAVE BONE SKELETONS?
All sharks are meat eaters. They eat live fish, including other sharks. A shark's only natural enemy, strangely enough, is a larger shark. He will eat his prey either whole or in large chunks. He also feeds on dead or dying animals. You'll find the shark in just about every ocean of the world, although he is most commonly found in the warm seas.
Sharks come in all sizes and shapes. There are more than 250 different species, and they range from 15 ton sharks that are 60 feet long down to those who weigh less than one ounce and are only four inches long.
A shark is unlike other fish in a number of ways. First of all, the shark has no bones. His skeleton is made of a tough, elastic material called cartilage.
Also, sharks have fewer young at a time than do most fish. Some give birth to 60 or more pups in a litter but most have far fewer. Parents don't take care of their young, either. In fact, quite often they'll eat the young if the little ones aren't fast enough to get away.
Most fish have swim bladders, gas filled organs that help them to stay at certain depths without sinking. Sharks don't have this organ. They do have large livers, however, that are filled with oil. The oil is lighter than water, so it does help keep the shark from sinking. But even with this boost, a shark must swim constantly from the very moment he is born. If he doesn't, he will sink to the sea's bottom.
Some people believe that a shark must roll over on his back to bite, but this isn't true. In all species except the whale shark, the shark's mouth is on the underside of his head. He has several rows of sharp teeth. When an old tooth wears out or is knocked out, a new one will grow in to replace it. Some types of sharks have razorlike teeth, while others have molarlike grinding teeth.
Most sharks have graceful, torpedolike bodies. This streamlined shape helps them to flash quickly through the water with very little swimming effort.
Sharks have toothlike scales covering their bodies. Called placoid scales, the skin is extremely rough. At one time sharkskin was called shagreen and it was used as sandpaper.
About 25 species have been known to attack human beings. Although the shark has a reputation of being a man eater, fewer than 100 attacks are reported throughout the world each year with very few deaths resulting.
Swimmers should take special care in waters that are known to have sharks. You should never swim or dive alone ¬always have a friend along. Also, never swim or dive if you have an open wound. Sharks are attracted by blood. And be sure to leave the water immediately if a shark is sighted. Swim as smoothly as you possibly can as you leave the water since any thrashing movement will often lure a shark.