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This is SCIENCE IN THE NEWS in VOA Special English. I'm Doug Johnson.

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And I'm Faith Lapidus. On our program this week, we tell about sharks. They are among the oldest animals on Earth.

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Not long ago, Kyle Gruen was swimming near the Hawaiian island of Maui when he felt something bite him. Mister Gruen was wearing special eyeglasses for use in water. He could see his attacker. It was a purple and gray shark.

The twenty-nine-year old Canadian was wounded on his left upper leg and hand. But he turned and pushed away the shark with his other foot. He watched the blood flow from his body as he swam away.

Others hurried to help Mister Gruen. Soon the Canadian man was in a hospital operating room, having his injuries repaired.

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Before leaving the hospital, Mister Gruen had a visit from Nicolette Raleigh. A shark had bitten Miz Raleigh earlier near Maui. The shark struck the fifteen-year-old girl as she stood in water only about a half-meter deep. She suffered a serious wound in her right leg.

Like Mister Gruen, she needed an operation. But she has recovered. Shortly after his operation, Kyle Gruen left the hospital to take part in the marriage ceremony of a friend.

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Miz Raleigh and Mister Gruen survived shark bites. But a young member of America's Peace Corps did not. Tessa Marie Horan was swimming near Tonga when a shark attacked and killed her. It was one of four such tragic incidents worldwide last year. That is about the same as in two thousand five.

Taken together, shark attacks are far from the most dangerous incidents that can harm human beings. George Burgess directs the International Shark Attack File at the University of Florida. As the name suggests, his group keeps records of shark attacks. Mister Burgess says people have more to fear from some snakes, insects and lightning than from sharks.

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It is hard to get people to think of sharks as anything but a deadly enemy. But these fish perform a valuable service for earth's waters and for human beings. Yet business and sport fishing are threatening their existence. Some sharks are at risk of disappearing from Earth.

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One reason for the shark's bad image is that people still watch a movie called "Jaws." The nineteen seventy-four film takes place in an American coastal town. The people there sought protection from a great white shark that killed swimmers in the ocean.

The number of shark attacks reported has risen during the past century. But the worldwide attack totals in two thousand five were similar to those of recent years. Shark expert George Burgess says more bites have been reported in this century because more people are in ocean waters.

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Surprisingly, the International Shark Attack File has records of attacks back to the sixteenth century. It says five hundred ninety-nine unprovoked attacks took place between fifteen eighty and March fifteenth of last year. Of that number, one hundred thirty three were deadly. An unprovoked attack means the person is alive when bitten and in the shark's living space or habitat. Also, the person must not have interfered with the shark.

How does the I.S.A.F. know about attacks hundreds of years ago? With some difficulty, says Mister Burgess. His team of scientific researchers works hard to confirm them. They investigate stories in old newspapers, which sometimes noted reports of seagoing ships and swimmers. The researchers investigate stories of attacks in books and historic documents.

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Mister Burgess says the I.S.A.F. has a worldwide team of scientists who offer their time to report attacks. He says the media also provide stories about shark bites. And people who have observed attacks communicate with his team. Mister Burgess says modern technology has made it easier to get the news of shark bites. Every report is investigated for confirmation and placed in computer record systems.

In two thousand five, fifty-eight unprovoked shark attacks took place around the world. That was seven less than the year before. The majority of the attacks took place in American waters. Four were deadly. During the same year, business and sport fishing killed an estimated one million or more sharks.

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Warm weather may influence both fish and shark activity. Many fish swim near coastal areas because of their warm waters. Experts say sharks may follow the fish into the same areas, where people also swim. Mister Burgess says most shark activity during the current season is taking place in the Southern hemisphere. Waters near Australia and South Africa are popular with these fish.

Mister Burgess says most sharks do not purposely bite humans. They are thought to mistake a person for a sea animal, like a seal or sea lion. That is why people should not swim in the ocean when the sun goes down or comes up. Those are the times when sharks are looking for food. Experts also say that bright colors and shiny jewelry may cause sharks to attack.

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There are hundreds of kinds of sharks. Most are about two meters long. The dogfish shark, however, is less than twenty centimeters in length. The biggest whale shark can grow to twenty meters in length. Sharks do not have bones. The skeleton of a shark is made of cartilage. Human noses and ears are also made of cartilage.

A shark has an extremely good sense of smell. It can find small amounts of substances in water, such as blood, body liquids and chemicals produced by animals. Sharks also sense electrical and magnetic energy linked to nerves and muscles of living animals.

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These powerful senses help sharks find their food. Sharks eat fish, other sharks, and plants that live in the ocean. Some sharks will eat just about anything. Many unusual things have been found in the stomachs of tiger sharks. They include shoes, dogs, a cow's foot and metal protective clothing.

Sharks grow slowly. About forty percent of all sharks lay eggs. The others give birth to live young. Some sharks carry their young inside their bodies as humans do. A cord connects the mother to the fetus.

Some sharks are not able to reproduce until they are twenty years old. Most reproduce only every two years. And they give birth to fewer than ten young sharks. For this reason, over-fishing of sharks is of special danger to the future of the animal.

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Medical researchers want to learn more about the shark's body defense system against disease. Researchers know that sharks recover quickly from injuries. They study the shark in hopes of finding a way to fight human disease.

Sharks are important for the world's oceans. They eat injured and diseased fish. Their hunting activities mean that the numbers of other fish in ocean waters do not become too great. This protects the plants and other forms of life that exist in the oceans.

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People hunt sharks for sport, food, medicine and their skin. Experts say the international market for some kinds of sharks has increased because many parts of a shark are valuable.

Collectors pay thousands of dollars for the jaws of a shark. Shark liver oil is a popular source of Vitamin A. The skin of a shark can be used like leather.

In Asia, people enjoy a kind of soup made from shark fins. Experts say a fisherman can earn a lot of money for even one kilogram of shark fins.

Finning, as it is called, means cutting the fins off a live shark. Many times, the fish is then thrown back into the water. The goal is to save space on the boats. Animal activists denounce this as cruel.

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Each year, thousands of sharks die in traps set for other fish. Some scientists say that about the half the sharks caught were not the target of the fishing. But no one really knows that if returned to the water, these sharks go on living. If too many sharks in one area are killed, that group of sharks may never return to normal population levels.

In two thousand four, sixty-three nations approved laws to protect sharks. But, as George Burgess says, some laws are effective near land. Laws can be difficult to enforce on the high seas.

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This program was written by Jerilyn Watson. Our producer was Brianna Blake. I'm Faith Lapidus.

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And I'm Doug Johnson. Our reports are online at WWW.51VOA.COM. Join us again next week for Science in the News in VOA Special English.