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1、There are at least 350 species of shark ranging from the smallest, the pygmy ribbontail catshark (8 to 10 inches long) to the largest, the whale shark (upto 45 feet long) Sharks are equipped with a special set of sensors, arranged in clusters over their heads, that can pick up electromagnetic currents emitted from other animals. Sharks have bad eyesight, but these sensors help detect prey from 1 to 3 yards away. Sharks can also detect the electromagnetic fields of the Earth and may use this ability to guide them during migration. Sharks are often thought of as cold-blooded killers that prey on humans. However, only 32 species have been known to attack humans, and most attacks are accidents. Often, sharks inhabit the same shallow, warm-water areas as humans. The shark may mistake a person standing or floating in water for natural prey. The shark goes in for the kill but, after one taste, usually gives up the attack. Many shark attacks involve people trying to free sharks from fishing nets. Sharks also are territorial animals and may attack if they feel threatened. The chances of being attacked by a shark are very small, and the chances of dying from a shark attack have greatly decreased over the years. In fact, in the United States, a person is 30 times more likely to be killed by lightning than by a shark. Dog bites are 1,000 times more common than shark bites. Sharks are fished for their fins and cartilage. Shark-fin soup is a popular food in some areas. After the fin is cut off, the rest of the shark is discarded. Shark cartilage is a subject of much scientific study because medicine made from it may stop the growth of tumors. Shark cartilage is sold in pill form as an alternative medicine. Shark finning and fishing for cartilage have caused a decline in populations in some areas of the world. Sharks mature and reproduce slowly, so it is difficult for them to rebound from a decline.Great white shark: Best known from the movie Jaws, the great white is a large, heavy-bodied shark, about 20 feet long, with large bladelike teeth. Widely the most-feared of sharks, great white attacks are rare, and most scientists agree that its reputation is undeserved. Many scientists believe it is endangered due to sport fishing and shrinking food supplies.Whale shark: Reaching lengths of up to 50 feet, the whale shark is the largest fish on earth. This gentle giant has small teeth like whale baleen, through which it strains small fish and crustaceans.Tiger shark: The tiger shark is considered one of the most dangerous sharks. It is about 18 feet long and inhabits shallower water, often where people swim. The diet of tiger sharks varies widely and includes all types of sea life and even garbage. Blue shark : The graceful blue shark is well known to scuba divers and commercial fishers - they have been seen circling divers and have followed fishing boats for days, eating stray fish.Mako shark : Short-fin and long-fin makos are close cousins with the great white shark. They are very fast swimmers and can reach speeds of up to 60 miles per hour. Mako sharks can even leap out of the water.Hammerhead shark : Hammerheads are best known for their distinctive mallet-shaped heads and widely spaced eyes, which they swing back and forth while swimming to detect prey. They are the only species of shark known to travel in schools.Bull shark : The bull shark gets its name from its snout, which is wider than it is long. It is possibly more dangerous to humans than the great white shark because it lives in shallow, murky water in areas where people swim. The real shark attacks on which the movie and book Jaws were based were done by a bull shark.。

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