Enviro Facts - Sharks



48) SHARKS An ancient and diverse group of animals, the first sharks appear in the fossil record in deposits that date back to over 400 million years ago. At least 370 different species of sharks live in the oceans, with a few like the Zambezi shark, that can live in fresh water as well. DID YOU KNOW? * Most species of sharks DO NOT attack people. * No sharks include human beings as regular, important prey items. * Most shark "attacks" involve single bites as if the sharks are not particularly interested in human beings as prey. * Shark attacks are rare: fewer than 100 occur worldwide each year, of which about 20 are fatal. In 1986, 166 people died from lightning strikes in South Africa, whereas there was only one fatal shark attack. * There is an average of about three shark attacks each year in South Africa. THREATS TO SHARKS * Gill nets, used mainly to catch tuna, also catch sharks. The Taiwanese Gillnet Fishery gives the following statistics: in 1986-1987 the by-catch of sharks was 295.7 tonnes, in 1987-1988 it was 20.7! This tremendous drop in the space of under 2 years shows that sharks cannot stand intense fishing pressure, because of their low reproductive rate and slow growth. * The fin trade - dried shark fin sells for up to US$ 118/kg. There have been reports of fisherman cutting fins off live sharks and throwing the poor creatures back into the sea. * Indiscriminate fishing - some fishing competitions are judged simply on the basis of the weight of fish caught resulting in many sharks being killed, weighed and discarded. * Shark nets, in place along the KwaZulu/Natal coast, trap sharks and prevent them from moving. As a result they are starved of fresh, oxygen-rich water for their gills, and die. * Environmental deterioration - the oceans have long been regarded as the planet's refuse bin and many sorts of waste have been released into them, both accidentally and deliberately. The resulting pollution, e.g. oil, pesticides and plastics, affects all life in the oceans, including sharks. HABITAT AND DIET Most sharks live in tropical and temperate inshore waters. Relatively few live in Arctic and sub-Antarctic waters, the open sea and water deeper than 2km. All sharks are predators. The diet of different species ranges from tiny crustaceans to large fishes, other sharks, rays, dolphins, seals, sea birds and marine reptiles. Sharks may also scavenge, but most eat live animals. LIFE HISTORY All sharks reproduce by internal fertilization. Most sharks are long-lived (maximum age 75 years) and bear live young, although some lay eggs. Rates of reproduction are low, with most species producing fewer than 20 young per litter, compared to fish which may produce thousands of young each season. The gestation period may be as long as two years. These low rates of reproduction, long gestation periods and the increasing threats to sharks mean that their survival is increasingly threatened. CONSERVATION ACTION * South Africa is the first country in the world to protect the great white shark by law. Hopefully this will lead to general conservation of cartilaginous fishes. As yet in South Africa, there are no quotas on cartilaginous fishes, while there are very strict quotas on bony fishes, e.g. pilchards. * The Natal Sharks Board is investigating alternatives to shark nets, e.g. keeping bathers and sharks separate at popular swimming sites using electrical shark barriers; equipping surfers and divers with a device that creates a protective electrical field around them. * A national shark management policy should be developed to identify where sharks are killed, particularly as a by-catch, to establish if this need be avoided, and if so, how. In particular selective fishing methods rather than unselective methods (long lines, gill nets and trawl nets) should be investigated. * Sports anglers should tag and release unwanted sharks, rather than killing them. Non-lethal means of determining their size for record keeping should be researched and introduced. * Wanton cruelty and shark abuse must be discouraged. WHAT YOU CAN DO * Support the organisations listed below, including the National Tagging Program run by the Oceanographic Research Institute. * Do not support the unnecessary killing of sharks for trophy products such as teeth and jaws. * Send letters of concern to the Minister of the Environment, the Natal Sharks Board, foreign embassies and sport fishing associations. * Send letters of concern to newspaper and magazine editors, and directors of television networks that feature shark exploitation, exaggeration and misinformation. FURTHER READING GUIDE TO THE SHARKS AND RAYS OF SOUTHERN AFRICA. L.J.V. Compagno, D.A.Ebert, & M.J.Smale. Struik, Cape Town, 1989. SHARKS. J.D. Stevens. Struik, Cape Town, 1987 SHARKS AND STINGRAYS. Rudy van der Elst and Roy Vermeulen. STRUIK POCKET GUIDES FOR SOUTHERN AFRICA. 1986. All books available from Russel Friedman Books, PO Box 73, Halfway House, 1685. Tel. 011-7022300/1. USEFUL ADDRESSES Shark Research Centre. South African Museum, P.O.Box 61, Cape Town, 8000. Tel. 021-243330. Dolphin Action and Protection Group. P.O.Box 22227, Fish Hoek, 7975. Tel. 021-7825845. Sea Fisheries Research Institute. Private Bag X2, Roggebaai, 8012. Tel. 021-4023911. Oceanographic Research Institute. P.O.Box 736, Durban, Marine Parade, 4056. Tel. 031-373536. Natal Sharks Board. Private Bag 2, Umhlanga Rocks, 4320. Tel. 031-5611017. South African Anglers Union. 33 Crake Street, Florida Lake, 1710. Tel. 011-841820.
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