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Sharks

Conservation

Historically, sharks have been fished for their meat and for liver oil, which was the best source of vitamin A until the 1940s. Shark fin soup is a traditional Asian delicacy and shark meat has recently gained popularity; these are greatly increasing the killing of sharks in marine fisheries. In addition to their food value, many sharks are caught and killed for sport by individuals and in specific shark-catching competitions. Often, sharks are unintentionally caught in nets and lines set for other species. Modern methods used by many commercial fishing fleets involve either baited long-lines stretching for miles, or long drift-nets that entangle and kill anything in their path. Sharks caught by these methods are often either dumped, or are finned (the fins are removed for shark fin soup) and thrown back to die. In the 1980s, 50% of sharks caught recreationally and 90% of sharks caught commercially were discarded back to the ocean dead.

Since the mid-1960s, scientists studying sharks have warned that indiscriminate and wholesale slaughter of these animals was driving their populations to a dangerously low level. Many people, with visions of sharks as monsters, had little interest in saving them. Some sharks do attack humans. However, the risks are very small: a person's chance of being killed by lightning is 30 times greater than that of dying in a shark attack. Each year, humans kill more than one million sharks for every human bitten by a shark.

It is now quite clear that the fishing mortality described above is having a severely negative effect on shark populations. Sharks have relatively low reproductive and growth rates, and they are being fished much faster than they can replace themselves. Scientists have determined the maximum number of sharks that can be caught each year to maintain the population. In the 1980s, the actual amount of sharks killed in areas of the North Atlantic Ocean exceeded that number by 35-70%. Without rapid changes in this wasteful overfishing, many shark species will become endangered.

There are numerous reasons to conserve shark populations, in addition to the fact that they are beautiful animals about which there remains much to learn. Perhaps most importantly, sharks are important predators in marine habitats. Removing them will affect the populations of their prey, which would have impacts on all other species living in the ecosystem. On a different note, scientists have recently discovered a chemical in shark blood called squalamine, which functions as an antibiotic. Further tests on this chemical and others from sharks may produce chemicals toxic to cancer cells. If sharks become endangered, it will not be possible to harvest these medically useful chemicals.

The United States Department of Commerce has established guidelines for and restrictions on shark fishing based on the acceptable maximum catch estimated by researchers. The guidelines limit the recreational and commercial catch of sharks, prohibit finning, and reduce the numbers of shark fishing tournaments. In Australia, species such as the great white shark have been declared endangered, and are now protected from indiscriminate killing. With wider enforcement, guidelines such as these may mean that sharks live to enjoy another 350 million years roaming the world's oceans.


Resources

Books

Allen, Thomas B. The Shark Almanac. New York: The Lyons Press, 1999.

Gruber, Samuel H., ed. Discovering Sharks: A Volume Honoring the Work of Stewart Springer. Highlands, NJ: American Littoral Society, 1991.

Parker, Steve, and Jane Parker. The Encyclopedia of Sharks. Westport, CT: Firefly Books, 2002.

Stevens, John D., ed. Sharks. London: Merehurst Press, 1987.


Periodicals

Manire, Charles A., and Samuel H. Gruber. "Many Sharks May Be Headed Toward Extinction." Conservation Biology 4 (1990): 10-11.


Amy Kenyon-Campbell

KEY TERMS

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Cartilage

—A translucent, flexible connective tissue that composes the skeleton in sharks and their relative.

Continental shelf

—A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.

Fusiform

—Having a shape that tapers towards each end.

Pectoral fins

—The most forward pair of fins on the underside of fish.

Pelvic fins

—The rear-most pair of fins on the underside of fish.

Placenta

—A connection between a mother and a developing embryo, through which the latter receives nutrients.

Temperate

—Having a moderate climate, or temperatures between polar and tropical.

Additional topics

Science EncyclopediaScience & Philosophy: Semiotics to SmeltingSharks - Evolution And Classification, Overview Of Shark Groups, Structural And Functional Adaptations, Locomotion And Buoyancy