Fishes

IMPORTANCE

Economic uses of elasmobranchs.

Sharks as food.

The meat of sharks is marketed for food in all maritime countries. It may be prepared in various ways--fresh, salted, smoked, or pickled--offered in such forms as steaks, fillets, or flakes and under such names as shark, whitefish, grayfish, swordfish, sea bass, and halibut. The flesh is often rather strong tasting; this quality, however, is one that can be removed by cleaning and washing and soaking the flesh in brine.

Since ancient times, Chinese people have used the dorsal fins of certain sharks and rays as the basis of an epicurean soup. To meet the demand for this product, they have imported fins from far-distant countries. The fins are prepared for market by removing the skin and flesh, leaving only the gelatin-rich cartilaginous rays, which are dried before shipment. Shark liver oil is used in various regions for tanning leather; for preserving wood; as a lubricant; as a folk medicine against rheumatism, burns, and coughs; as a general tonic; as a laxative; and as an ingredient of cosmetics. The liver of a basking shark yields 80 to 600 gallons of oil, which was used in lamps until petroleum products replaced animal oils for illumination. The discovery around 1940 that the liver of the soupfin shark of California is peculiarly rich in vitamin A led to an explosive development of a special fishery in California for this species and a search in other parts of the world for sharks having livers of comparable potency. Within a few years, however, the economic bubble burst, with the invention of a method for manufacturing synthetic vitamin A. The Australian school shark, which was used originally for vitamin A, is now caught for fish fillets.

Other shark products.

The hard scales provide an abrasive surface to the skin of sharks and some rays, giving it a special value, as a leather called shagreen, for polishing hard wood. When heated and polished, shagreen is used for decorating ornaments and, in Japan, for covering sword hilts.

Shark leather is made in several countries, including the United States, from the skin of certain shark species after removal of the scales by a chemical process. A luxury product, much more durable than cowhide, shark leather is used for footwear, belts, wallets, and other accessories. The most suitable skins for leather are from tiger, dusky, brown, sand, blacktip, and nurse sharks.

In Greenland some Eskimos make rope from strips of the skin of the sleeper shark. Polynesians once added to the effectiveness of their war clubs with sharks' teeth. Sharks' teeth have some commerical value as curios. The Maori of New Zealand formerly paid high prices for mako sharks' teeth, which they wore as earrings.

Economic value of rays.

About 126,000 tons (roughly 110,000,000 kilograms) of rays are marketed for food in various countries about the world, principally in Europe and Asia. By-products in local demand are skins of scaleless species for drumheads; those of scaly species are used for shagreen. Livers are used for oil, fins for gelatin. People of many tropical regions--Polynesia, Oceania, Malaysia, Central America, and Africa--have used the spines of stingrays for such items as needles and awls, spear tips and daggers, and for the poison they contain. The entire tails of stingrays, complete with spines, have been used as whips in various tropical areas.

The electric rays, or numbfish, have little commercial value. The ancient Greeks and Romans used the electric shock of Torpedo to relieve diseases of the spleen, chronic headaches, and gout. From the Greek word for electric ray, narke, comes the word narcotic. Today these fishes are of interest chiefly as a source of irritation (if not danger) to bathers who step on them and to fishermen who may be shocked when hauling in their wet nets. (L.A.Wa.)

Danger to human life.

Among the known shark species, 27 have been authoritatively implicated in attacks on persons or boats. Hospital and other records attest to many attacks on bathers, divers, and people awash in the sea following sea or air disasters. There are also many documented cases of sharks attacking small boats. A number of surviving victims have been able to identify the attacking animal as a shark; a few even reported the type of shark, such as a hammerhead. In many instances, witnesses have seen the assailant clearly enough to determine the species. Fragments of teeth left in wounds of victims or in the planking of boats have often been large enough to provide ichthyologists with the means for precise identification.

In 1958 the American Institute of Biological Sciences established a Shark Research Panel at the Smithsonian Institution and Cornell University to gather historical and current records of shark attacks throughout the world. For the 35 years from 1928 to 1962, inclusive, the panel listed 670 attacks on persons and 102 on boats. Attacks occur most frequently throughout the year in the tropical zone between 21 {degree} north and south of the Equator; from midspring to midfall they extend as far north and south as the 42 parallels. For this reason, it was formerly believed that the most dangerous sharks lived in waters warmer than 21 C (70 F) and that the risk of attack was greatest in the tropics and in the summer months. It is now thought that this circumstance simply results from the fact that more people swim in warm water. It is known, for example, that the most dangerous shark, the white shark, or man-eater (Carcharodon carcharias), ranges into the cooler waters of both hemispheres. (L.A.Wa. /Ed.)

In Australia, New Zealand, South Africa, and along other coasts heavily infested with sharks, public beaches have lookout towers, bells or sirens, and nets to protect bathers. Since 1937 Australia has used meshing offshore to catch the sharks. Gill nets suspended between buoys and anchors running parallel to the beach and beyond the breaker line have decreased the danger of attack. The nets enmesh sharks from any direction, and although they touch neither the surface nor the bottom, and are spaced well apart, they provide effective control. South Africa has used a similar protection system and has also conducted experiments with electrical barriers.

The 27 species implicated by the Shark Research Panel in attacks on persons or boats are mostly large sharks with large, cutting teeth. Size, however, is not a dependable criterion, for man-eaters become dangerous when they are about one metre (three or four feet) long; and the largest ones, the basking shark and the whale shark, which grow to 12 and 18 metres (40 and 60 feet), respectively, subsist on minute planktonic organisms and on small schooling fishes. Although either might attack a boat if provoked, only two records of such occurrences have been reported, both in Scotland and both identified with the basking shark. More than 85 percent of all the shark species are too small, too unsuitably toothed, or too sluggish or live at depths too great to be potentially dangerous. The most dangerous sharks include in addition to the white shark, the hammerheads (Sphyrna), tiger (Galeocerdo), blue (Prionace), and sand sharks (Odontaspis).

Most stingrays live in shallow coastal waters. Some move with the tides to and from beaches, mud flats, or sand flats. Anyone wading in shallow water where these fishes occur runs some risk of stepping on one and provoking an instant response--the ray lashes back its tail, inflicting an agonizingly painful wound that occasionally leads to fatal complications. Rays can be serious pests to shellfisheries, for they are extremely destructive to oyster and clam beds.