Overfishing has left many shark species vulnerable.
Sharks are found worldwide from the equator to the polar oceans, from the deep ocean depths to shallow nearshore waters, and even some distance from the ocean in a few of the world's rivers. Sharks vary greatly in their size and form depending upon the habitats in which they live. Most species of sharks are active swimmers and are sleek, streamlined animals. But some lead a more sedentary lifestyle (like nurse sharks, Australia's wobegong and others) and do not need to swim actively to pass water over their gills as do most other sharks. With a few specialized exceptions, sharks are opportunistic feeders and predators on fish, invertebrates (squid, octopus, crabs and others), and sometimes on marine mammals (like seals and sea lions). Whale sharks and basking sharks, which can grow to lengths of over 40 feet and weigh over a ton, feed only on microscopic plankton!
Because most species of sharks are predators and occur where people fish, sharks are often caught incidentally by recreational and commercial fishermen. A number of species are known to form aggregations or schools based on age, sex or reproductive status, which almost certainly contributes to their vulnerability to exploitation by fishing. Sharks are particularly susceptible to overfishing because they grow and mature slowly, are relatively long-lived, and produce small broods. Although many of the larger inshore and pelagic sharks may live for more than 20 years, they may not attain reproductive maturity until their teens or later. Depending on the species, broods typically contain fewer than ten pups and a number of species produce no more than two young in any given brood. Moreover, mature sharks may not reproduce each year. This combination of low reproductive potential, behavioral characteristics which have served sharks well for their survival over millions of years, and the potential for exploitation and overfishing, has caused major concerns for conservation biologists and fishery managers. In past years there have been fisheries directly targeting some sharks, either for food (for example, sharkfin soup), as sources of vitamin A (before it was synthesized chemically), or for industrial purposes. These directed fisheries in past years were largely unregulated, and some sharks were overfished to the point that fisheries on them became uneconomical after shark populations declined. The collapse of former fisheries for shark clearly demonstrated the need for management of this resource. Currently, shark fishing-commercial and recreational-in the United States is highly regulated to help conserve shark populations and maintain the health of our marine ecosystems.
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Camhi, M., Fowler, S.L., Musick, J.A., Bräutigam, A., and S.V. Fordham (1998). Sharks and their relatives-Ecology and Conservation. IUCN/SSC Shark Specialist Group. IUCN, Gland, Switzerland and Cambridge, U.K.
Hart, T.J., and P.J. Hart (1983). Fisheries Ecology. AVI Publishing Company. Westport. CT.
Hoese, H.D., and R.H. Moore (1998). Fishes of the Gulf of Mexico, Texas, Louisiana, and adjacent waters. Texas A&M Press, College Station, TX.
Weber, M.L., and S.V. Fordham (1997). Managing shark fisheries: Opportunities for international conservation. TRAFFIC International and Center for Marine Conservation. Washington, DC.
Florida Museum of Natural History Web site with links to major shark related sites
National Marine Fisheries Service Marine Recreational Fisheries Statistics Survey