shark
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Any member of various orders of cartilaginous fishes (class Chondrichthyes), found throughout the oceans of the world. There are about 400 known species of shark. They have tough, usually grey skin covered in denticles (small toothlike scales). A shark's streamlined body has side pectoral fins, a high dorsal fin, and a forked tail with a large upper lobe. Five open gill slits are visible on each side of the generally pointed head. They shed and replace their teeth continually, even before birth. Teeth may be replaced as frequently as every week. Most sharks are fish-eaters, and a few will attack humans. They range from several feet in length to the great white shark Carcharodon carcharias, 9 m/30 ft long, and the harmless plankton-feeding whale shark Rhincodon typus, over 15 m/50 ft in length.
Relatively few attacks on humans lead to fatalities, and research suggests that the attacking sharks are not searching for food, but attempting to repel perceived rivals from their territory.
Endangered species
An estimated 100 million sharks are killed each year for their meat, skin, and oil (basking shark). Some species, such as the great white shark, the tiger shark, and the hammerhead, are now endangered and their killing has been banned in US waters since July 1991. Other species will be protected by catch quotas. The Convention on International Trade in Endangered Species (CITES) agreed in 1994 to investigate the extent of the shark trade.The fins of 90% of sharks caught are traded, almost all destined for Asia, to be made into soup. Many sharks are ‘finned’: the fins are sliced from live sharks, which are then thrown back to die. Finning was banned in US Atlantic waters in 1993, and by Canada in 1994. As most sharks tend to be long-lived, not reaching sexual maturity till the age of almost 30, and produce small numbers of young with a high juvenile mortality rate, they are ill-equipped to withstand high levels of fishing.
| The prehistoric shark megalodon was the largest fish that ever lived, reaching 17 m/56 ft in length and weighing up to 65 tonnes. It died out 1–3 million years ago. |
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