INTRODUCTION because they can wreck fishing gear Selachii-Phylum: Vertebrata, Sub­ with their sharp teeth and sharp denticu­ phylum: Pisces, Class: Chondrich­ Of all the creatures in the sea, sharks lar scales and because they devour the thyes, Subclass: Elasmobranchii, Or­ are the most feared by man. Why trapped fish. (To run one's hand across der: Selachii. shouldn't they be? Some of the large the denticular formation of a shark is Sharks are vertebrates with well de­ sharks can snap off a man's leg with like running it across the teeth of a veloped lower jaws and bony teeth. their powerful jaws-jaws that can freshly sharpened saw.) On the other They have two pairs of appendages exert biting pressures as high as 40,000 hand, sharks represent a source offood, supported by the pectoral and pelvic 2 pounds per square inch (2,812 kg/cm ). pharmaceuticals, and other useful ma­ girdles and a cartilaginous skeleton. Accounts of the slaughter, by sharks, of terials for man, as we shall see later. They have no true bones; however, hundreds of people who abandoned Much has been written about sharks, parts of the skeleton may be stiffened sinking ships at sea leave no question as and two notions eventually become by mineral deposits (e.g., calcium to the shark danger to man. However, evident to the reader: I) Ifanything can ftuorophosphate), such as in the spinal one must be reminded constantly that be said for certain about the behavior of column, resulting in a structure that re­ the image denoted by the word "shark" sharks, it is that one cannot be too cer­ sembles bone so closely that the distin­ is always that of the potentially danger­ tain about it-they can be completely guishing characteristics can only be ous species like the white, blue, mako, unpredictable; and 2) if anyone allows identified by microscopic examination. tiger, and others and that the notoriety himself to get too confident about what Scales are denticular (toothlike) in gained by these species is uncon­ to expect from the different species of structure in that they include the 2 sciously attributed to all sharks. Actu­ sharks and tends to get careless in the mesoderm 1 as well as the ectoderm in ally, there are many more shark species presence of certain species in particu­ their composition. Sharks have two that are not dangerous to man, and most lar, he is apt to get an accelerated educa­ nostrils, a sympathetic nervous system, of these are too small to cause serious tion about shark behavior, which unfor­ a multiple-valve heart, a pancreas, and injury to a person. tunately may last him only for a very a spleen, but they lack a swim bladder. Sharks are a nuisance to fishermen short time. Sharks have 5-7 pairs of gills (most have 5 pairs) that are located laterally or Louis J. Ronsivalli is the Director of DESCRIPTION AND PHYSICAL the Gloucester Laboratory, North­ CHARACTERISTICS OF SHARKS east Fisheries Center, National In the scheme of biological clas­ I Mesoderm-the middle layer. In the case of Marine Fisheries Service, NOAA, teeth, it is the dentine. Emerson Avenue, Gloucester, MA sification, the sharks (ofwhich there are 'Ectoderm-the outer layer. In the case of teeth, 01930. about 300 species) belong to the order it is the enamel.

February 1978 nearly laterally, and they have movable eyelids. The dorsal and pectoral fins are rigid, and the anterior edges of the latter are not attached to the head. A few genera are luminescent (e.g., Isistius) SlOE VIEW but the majority are not. OF HEAD

The body fluids of marine teleosts PECTORAL (bony fishes) are less salty than seawa­ FIN ter, and since they lose water to the sea A. TYPICAL SHARK FORM B. HAMMERHEAD FORM through the process of osmosis, it is necessary for them to continually drink seawater and to dispose of the excess salts. On the other hand, the fluids of freshwater teleosts are more salty than ---- the water around them, and they absorb "0 water through osmosis constantly. C. THRESHER FORM Thus, freshwater fish do not need to drink water. S harks contain large amounts of urea which, together with D. RAY FORM trimethylamine oxide, contribute to a Figure I.-Outlines of different forms of sharks. salt concentration in their body fluids which is greater than that in the sea around them. So, as with the freshwater different outlines are illustrated in Fig­ slowly, which suggests that they live a teleost fishes, sharks do not have to ure I, with outline A labeled so as to relatively long life. Not enough infor­ drink water since they too obtain water provide information on some of the ex­ mation has been accumulated to give from their surroundings through os­ ternal gross anatomy of sharks in gen­ more details, but in one experiment mosis. eral. There is no known explanation for only a few to 20 inches (51 cm) of S harks are known to exist in a state of the development of the unusual lateral growth was noted during a period of 7 commensalism with pilotfish. (Com­ distensions of the head of the "ham­ years. mensalism exists between two or­ merhead sharks," many of which are Mobility ganisms when one benefits from the dangerous to man, and some ham­ other while the other neither benefits merheads are large enough and aggres­ The mobility of sharks is quite vari­ nor suffers from the relationship.) sive enough to butt and capsize small able. The mackerel sharks, Lamnidae, Pilotfish about 2 feet (about 0.6 m) in boats from which they have been har­ are fast swimmers, reaching speeds of length, are the beneficiaries in this case pooned or speared. The eyes of ham­ 40 miles (about 64 km) per hour in short as they find a measure of protection by merhead sharks are at the ends of the bursts, whereas the Greenland Shark, the mere fact that they are near the distensions (see Fig. I) and the nostrils Somniosus, is sluggish and relatively shark, and they eat from the same prey are generally at the outer forecorners. slow. The mako shark, a member of the as does their host. Apparently the The thresher form (Fig. Ie) shows the Lamnidae, is not only a fast, powerful pilotfish are skillful enough to avoid the extreme enlargement of the upper lobe swimmer, but it can leap out of the shark's mouth. A symbiotic relation­ of the caudal fin. The pectoral fins are water covering respectable distances at ship exists between sharks and the rem­ also enlarged. Other sharks have inter­ a leap. Other sharks, including the oras, a class of small fish also about 2 mediate enlargements of these parts. thresher shark and even the more slug­ feet (aboutO.6 m) in length. (Symbiosis The shape of the angel shark (Fig. 10) gish basking shark, are capable of leap­ exists between two organisms when illustrates the ray-like form of some ing out of the water, but the mako shark each benefits from the other.) In this sharks. is a more outstanding and a more spec­ case, the remora fastens itself to the tacular leaper, especially when caught Size and Growth shark by means of a suction cup and on a fisherman's hook. The only ma­ feasts on shark prey, and the shark ben­ Shark sizes vary widely. The largest neuver that a shark is unable to do well efits from the fact that the remora eats shark, Rhincodon typus, commonly is to stop quickly. The reason for this is parasites on its body. called the whale shark, is reported to that its pectoral fins are designed more reach lengths of about 50 feet (about IS rigidly than in other fish. The fixed po­ Shapes m). The smallest shark, SqUilliolus can sition of the fins is to provide lift while The shapes of sharks vary from that be smaller than 0.5 foot (about 15 cm). the sharks are in forward motion, much of the streamlined mackerel shark to In general, adult female sharks are 5 as the flaps on the wings of aircraft that of the angel shark which is flat and percent longer and 25 percent heavier provide lift. (In other fish the pectoral broad, resembling a ray. Four markedly than adult male sharks. Sharks grow fins are movable, and they can be

2 Marine Fisheries Review turned to provide a stopping action.) It their gills continually. Some sharks sharks responded only to low frequency has been speculated that the unusual have spiracles (a hole behind each eye) sounds when they were made in bursts. head form of the hammerhead sharks through which water can enter and pass When sound signals were continuous acts as a rudder, permitting greater directly over the gills. These sharks the sharks were not attracted. Prior data maneuverability. must still swim to keep from sinking, showed that struggling and crippled fish but they can stop and rest on shallow emitted low frequency sounds in bursts; Body Temperature bottoms if they wish since their oxygen therefore it was concluded that sharks Nearly all of the members of Lam­ supply is not dependent on their mo­ are attracted to intermittent bursts of nidae maintain body temperatures tion. Sharks without spiracles are be­ low frequency sounds because they be­ above that of their environment. Other lieved to have to swim continuously lieve these to be the signals to the pres­ sharks have body temperatures at or from birth to death. There are a few ence ofeasy prey. 2) Other fish, such as near the temperature of their environ­ reports which indicate that some sharks barracuda, were also attracted to the ment. Pertinent to this situation, it has sleep, but during such periods they are sounds. been shown that the contraction and able to pump water through the gills by It is believed that the lateral line of relaxation of muscle occurs faster as the an apparent automatic mechanism that sharks is instrumental in their ability to temperature of the muscle is increased coincides with sleep. detect a variety of water movements (within limits). Experimental data such as might be created by the nearby Sensitivity show that when a muscle is allowed to activities of other marine life. The act for a given period of time at two Sharks appear to have a low intelli­ range of detection does not exceed sev­ temperatures that are 18 of (l0°C) gence and to be insensitive to pain. eral hundred feet (I foot = ca. 0.3 m). apart, its activity at the higher tempera­ Especially in "frenzied" attacks, they Tiny sensors called pit organs, scat­ ture is about three times as rapid as its continue their assaults even though re­ tered over the entire surface of the activity at the lower temperature for any taliatory action is highly injurious or shark, are said to detect changes in sa­ given unit of energy supplied to the lethal, or even though their attacks linity and these appear to playa role in muscle. However, to maintain warm bring them in contact with sharp or regulating the activities ofsharks in and body temperatures in the cold aquatic otherwise injurious materials. Sharks near brackish waters. They have small environment where heat transfer out of have a keen sense of smell, permitting cup-like nerve sensors (called ampullae the body could be significant, the body them to detect substances as dilute as of Lorenzini) on their noses and along must have an extraordinary ability to one part per billion. Thus, their olfac­ their lateral lines which are reported to retard heat loss. The anatomy of the tory sense, which allows them to detect be able to detect temperature changes in shark includes the rete mirabile, a net­ prey up to several hundred yards away, the water. But more important, it has work of blood vessels that takes advan­ is a major component of their hunting been determined by experiments that tage of the principle of counter-current ability, and at least one genus, Mus­ these organs permit sharks to detect heat exchange which performs this con­ te/us, hunts chiefly by smell. other fish through the electric potentials servation function. In general, sharks Sharks have sharp eyes that they can they emit. The ampullae, whose role is can tolerate a wider range of water focus and adjust according to available not completely understood, exist as temperatures than can many of the bony light. There is no evidence to show that subcutaneous nerve centers connected fishes, and this advantage would appear sharks can distinguish among colors al­ to tiny openings in the surface by to be related to their ability to control though they may be attracted to the canal-like structures containing a gel of their body temperature. lighter ones. At close range, eyesight is low electrical resistance. Supporting the most effective sense. While it is evidence for the electrical receptor Relationship Among generally accepted that their sense of property of the shark was obtained in Body Density, Oxygen smell is the principal sense that leads experiments in which sharks were able Requirement, and Sleep sharks to food, a study supported by to locate prey which was adequately As sharks have no swim bladder, they both the National Science Foundation protected against visual, auditory, and cannot decrease their density (which is and the Office of Naval Research olfactory detection but was not shielded greater than that of water). Therefore, (Anonymous, 1964) resulted in con­ against electrical transmissions. When they must swim constantly to keep from vincing evidence that sharks are invari­ hidden electrodes were used instead of sinking. Their continuous swimming is ably attracted to the prey by low prey to emit a similar electrical poten­ also necessary, for some sharks, be­ frequency sounds-7.5 to 100 Hertz tial, the test sharks attacked the elec­ cause it is the only way that a constant (cycles per second)-at distances over trodes (apparently convinced that they stream of water can be made to pass 200 yards (about 183 m). were attacking a concealed prey). A through their gills. This is vital to their The sounds were made in the absence measure of the sensitivity of these elec­ survival, because they must have the of any possibility that the sharks could troreceptors showed that a shark can oxygen that is dissolved in the water, either see or smell the source of the detect an electrical field of 0.0 I micro­ and to maintain a sufficient supply of sounds. The sound pulses were varied, volt per centimeter (l centimeter = oxygen they must replace the water in allowing two observations: I) That 0.394 inch). The detection of variations

February 1978 3 in electric signals among other fishes is their eggs internally, and, much like shark might be a good repellent, and promoting speculation among scientists mammals, deliver fully formed active further work resulted in the develop­ that electroreceptors in fish may be in­ pups with placentae. Most sharks, ment of "Shark Chaser," which is de­ volved in intentional as well as uninten­ however, are ovoviviparous. In this scribed later. tional communications. case the eggs are also hatched internally Shark teeth are not set rigidly in the and the young are fully formed and ac­ jaws and some are lost from time to Reproduction tive, but there is no placental connec­ time, especially when sharks go into a Reproduction in sharks involves in­ tion between embryos and mother. violent attack pattern in which they tear ternal fertilization. The male shark has Generally the number of offspring at steel cables and other hard, tough a pair of grooved copulatory organs produced by sharks and other car­ objects. However, lost teeth are re­ called "claspers" that develop as tilaginous fishes is relatively small (a placed when a row of new teeth from penis-like appendages of the pelvic fin few dozen at most) when compared the many rows of replacement teeth (see Fig. IA). While the claspers are with the number of eggs produced by with which sharks are endowed takes normally relaxed, they swell and be­ the bony fishes (up to a few million). the place of the old row of teeth. This come erect just prior to mating. The However, sharks have a high survival complete change of teeth occurs quite erect claspers are inserted into the two rate since they are born either fully often-as often as every 2 weeks. sexual orifices in the cloaca of the formed and able to fend for themselves, Thus, sharks are never without teeth female. (Often only one clasper is or as eggs they are protected by a tough throughout their lives. used.) The sperm is guided in by the casing. The survival rate of the off­ The number, size, shape, and set of groove of the clasper(s). spring of the bony fishes, on the other shark's teeth vary among the different Shark copulation is not simple. The hand, is very low, since there is a high species. One peculiarity reported is that male shark is, as stated above, gener­ degree of susceptibility to predation some sharks have protrusible teeth. ally smaller than the female, and he during their early stages of develop­ When a shark having this characteristic might in some cases end up as food for ment when they are of relatively tiny opens its mouth to bite, the teeth tilt the female instead of her suitor. At any size and practically defenseless. Also, outward, thus making possible a bite rate, the male does not have an easy because fertilization of cartilaginous covering a large area and permitting the time of it, even though he is equipped fishes is done internally, the probability shark to bite into nearly flat surfaces. with clasper hooks and an array ofspurs of fertilizing the eggs is much greater As the jaws close to complete the bite, and spines, in addition to his teeth, that than in the bony fishes where fertiliza­ the teeth start to tilt inward, insuring a enable him to grab the female and cling tion occurs externally. Generally pups firm grip on the bite that is being taken. to her and then to work himself into are born in spring to early summer As the predator of any shark is often a position to fertilize her. either annually or biennially (depend­ larger shark, it is not unusual to find a In the larger species, the male has an ing on the species). The young remain hooked shark on a line that has swal­ even more difficult time and might not in a nursery area, usually in shallow lowed a smaller shark that was origi­ succeed without cooperation from the water, which the adult males do not nally hooked to the line or to find a female. Cooperation may be induced enter. The adult females leave the nur­ hooked large shark that, in its hand­ by slashes to the body of the female sery area quite soon. Fortunately, the icapped position, is ravaged by adja­ inflicted by the male. It is during this females are not inclined to feed while cent sharks. In a feeding frenzy involv­ critical part of the courtship that the they are in the nursery area for reason or ing large numbers of sharks, some of female may respond by devouring the reasons thus far unexplained; otherwise the feeding sharks are devoured by male instead of cooperating with him they might devour the young. others. If one species of shark is the and that the hide of the female is dominant predator of the other sharks, Feeding sufficiently damaged as to lower its it appears that the hammerhead species value for the production of shark Most sharks are carnivorous. Their is in a superior position, and although leather. Even though the courtship of teeth are razor sharp and numerous, and the reason is not known, it seems to be sharks is obviously dangerous, the their jaws are powerful. Some have related to the unique head form (see propagation of sharks over the many crushing teeth that enable them to feed Fig. IB). eons of their existence implies that on hard-shelled mollusks and crusta­ The feeding of sharks is observed to sufficient successful courtships occur. ceans. The majority of sharks feed on follow a unique general behavior. It Sharks vary in their form at birth, and whatever they can get such as small generally starts slowly and gathers there are three general categories. fish, including smaller sharks, squid, momentum, especially as the number Oviparous sharks, which include the and pelagic crustacea. Ironically, the of sharks involved increases. Whether hom sharks, the cat sharks, and the largest species, whale sharks, feeds on hunger is the trigger that starts sharks whale sharks, lay eggs having a tough, minute plankton forms and on small feeding is not known since they may leather-like covering and leave them to schooling fishes. Sharks have been begin to feed on a full stomach in some hatch. Viviparous sharks, which in­ found to avoid decaying shark flesh. It cases, and in some cases (males during clude the hammerhead species, hatch was once considered that decaying mating season) will not feed even

4 Marine Fisheries Review though they may exhaust nearly all of their liver-stored fats. Some evidence has been obtained which suggests that sharks can detect uneasiness and fear and maybe an odor that emanates as a specific consequence of fear or panic in their prey which motivate them to at­ tack. Evidently the shark needs to employ most or all of its senses to ascertain the suitability of foods, but sometimes it swallows objects such as bottles, cans, and other debris indicating that it did not wait for proper identification of the food. While indigestible debris often enters the stomach of the shark, it is reportedly easily regurgitated when its accumulation becomes objectionable. There are numerous stories about the odd indigestible items found in the stomachs of sharks, but one of the Whilelipped sharks and pilolfish. (photo by Reginald M. Gooding.) strangest is a centuries-old account of finding a man encased in armor in a genus, Somniosus, is found in polar for any tagged shark between the time it 22-foot shark caught off France. seas. Sharks are known to roam the was tagged and the time it was recap­ high seas, and some will follow ships to tured is 7.5 years. The tagging experi­ OCCURRENCE AND HABITS feed in disposed garbage or other ments have resulted in the following Sharks are mainly marine species oc­ marine creatures that might be attracted conclusions: curring nearly worldwide, but some to the ship's effluents. Most sharks in­ I. Blue sharks can travel to locations species enter brackish waters and even habit relatively shallow water; however at least 1,000 miles (1,609 km) from the fresh waters of large rivers. The at least one species, Centroscymnus any given point within 1 year. intrusion of sharks into rivers is not too coelolepis, has been reported to go to 2. Blue sharks and mako sharks fol­ uncommon; sometimes they swim into depths of 1,500 fathoms (9,000 feet or low common migratory routes that are the upper reaches of the rivers, and at 2,745 m). also followed by white marlin and least one species, Carcharinus leucas, Migrating adults usually, but not al­ perhaps swordfish. otherwise known as the bull shark, is ways, segregate by sex with males fa­ 3. Migratory routes followed by found in Lake Nicaragua, Nicaragua. voring cooler, deeper water than the sharks may depend on their size. This lake, over 100 miles long (about females, but they nearly always segre­ 4. The growth rate of sharks is slow. 160 km) and nearly 50 miles wide gate by size, except in rare cases. Mi­ More data on movements as well as (about 80 km), empties into the Carib­ grations ofsharks seem to be influenced on longevity, growth rates, and other bean Sea about 100 miles away (about by seasonal temperature changes in the important characteristics of sharks are 160 km) via the Rio San Juan. There water, but there is some evidence to certain to be produced as a result of the has been, and still is, much speculation show that female sharks migrate to tagging experiments now underway. and controversy as to whether or not the specific environments to lay eggs or to RELATIONSHIP TO MAN lake shark commutes to the sea. Even give birth to their young. Whether though the river has many rapids, it is sharks migrate to special mating The objectives in scientific research, believed that the sharks which have grounds is not known although this ap­ especially applied research, are usually been seen in the river can easily swim pears to be the case. relatively important and imply a useful from the sea to the lake. Also, evidence The movement of sharks can be de­ potential for man. Sharks, the object of from the gut contents of lake sharks termined by a tagging method. To date, much applied research, have been points to excursions by lake sharks to more than 10,000 sharks have been studied for their potential as food for the sea. Pilotfish and remoras that may tagged by federal scientists and others. man, for their possible nonfood value, accompany a shark to a river must The maximum recorded distance to for their reputation for attacking man, abandon their host or perish as neither have been traveled by a shark between for the heavy damage they impose on of these fish can survive in rivers. the point it was tagged (in New En­ fishing gear, and for their unusual Sharks are found in all of the oceans, gland) and the point it was caught (in physiological and anatomical charac­ but the great majority inhabit the tropi­ South America) is 2,070 miles (about teristics. Some sharks are held in cap­ cal and subtropical belts. Only one 3,330 km). The maximum time elapsed tivity in a number of aquaria throughout

February 1978 5 Table 1.-Unlled SIal.. laclllll•• reportedly the country (Table I) and considerable holding ahar'" In capllvlty. be about 400,000 metric tons per year information has been gained byobserv­ Faciity Location over the last 5 reporting years, 1969­ Cape Haze Marine Lab. Placida. Fla. ing captive sharks. Scientific study of 74. The landings show an increase of Fairmont Park Aquarium Philadelphia. Pa. sharks, however, is carried out in only a more than 25 percent over a period of 9 Gulfarium Fort Wailon. Fla. Hawaii Marine Lab.. few of the facilities listed. Table 2 lists years, with the greatest increases occur­ Univ. Hawaii Honolulu, Hawaii some of the more common sharks and ring in the catches from the east central Municipal Aquarium Key West. Fla. Marine Arena Madeira Beach. Fla. how they relate to man. Atlantic and West Indian Oceans. Mount Desert Island Because of the strength and ferocity Bio. Lab. Salsbury Cove. Maine There is not su fficient information Marinetand of the Pacific Marineland. Calil. of sharks, they are among the marine about the standing stocks of sharks, but Marine Studios Marineland. Fla. Miami Seaquarium Miami. Fla. species sought by anglers. The shark Table 3 suggests that the present catch New England Aquarium Boston. Mass. species recognized as game for sport level can be tolerated without threat of New York Aquarium New York City. N.Y. Ocean Aquarium Hermosa Beach. Calif. fishermen and which are recognized by depletion of the stocks, However, it Shedd Aquarium Chicago, ill. and listed in the records of the Interna­ must be remembered that sharks have a Sleinhart Aquarium San Francisco, Calif. Theater of the Sea Islamorada, Fla. tional Game Fish Association are: Blue slow growth rate, implying that their Vaughn Aquarium. Scripps shark, mako shark, porbeagle, thresher Institute ot Ocean· availability and the economics of ography La Jolla, Calif. shark, tiger shark, and white shark. fishing for them can be altered rela­ Waikiki Aquarium Honolulu, Hawaii Woods Hole Aquarium Woods Hole, Mass. World shark landings are reported to tively easily and that the time for re­ plenishment of the depleted stocks would be so long that it could end the Table 2.-50me IIICIS aboul some common sharks. fishery, Danger Common name(s) Generic name Features' rating 2 Sharks as Food for Man Basking Catorhinus maximus H,O R Blacktip (small) Carcharhinus limba/us G,L o The utilization of sharks for human Blacktip (large) Carcharhinus macuJipinnis o Blue (great) Prionace glauca G M food will probably increase in the fu­ Brown, Sandbar Carcharhinus milberti L,F M ture. The world's need for protein is Bull, (Lake Nicaragua) Whaler (Zambezi) growing at a rate greater than the rate of Ganges Carcharhjnus leucas M protein production, The pressure to ob­ Common thresher, Fox Sea fox, Swingle Tail tain the protein from the sea is increas­ Thrasher, Whip tail AJopias Yulpjnus F,G R Dusky Cafcharhinus obscurus L,F R ing. But many of the popular marine Great hammerhead Sphyrna mokarran O.F E species are overfished and since sharks Great white Carcharodon carcharias F E Greenland Somniosis microcephalus P R continue to feed on the already shrink­ Grey nurse Odontaspis aren8fius ing stocks and continue to cause con­ AlIantic sand Odon/aspis 'aurus L,F M Lemon Negaprion brevirostris o siderable damage to fishing gear (in Mako, Bonito, Atlantic order to get to the fish held by the gear), mako. Blue pointer Sharpnosed mackeret Isurus oxyrinchus G,G E it seems inevitable that fishing effort Nurse Ginglymoscorna citraCum L,F E will have to be directed to sharks in Porbea91e, Mackerel Lamna nasus F,G 0 Soupfi n Ga/eorhinus zyopCerus F, 0 R order to reduce both the destruction of Spiny dogfish SquaJus acanmias F,L R Tiger GaJeocerdo cUYieri F,G,L E fishing gear and the predation on fish Whale Rhjncodon /ypus R held in nets, etc., as much as to increase Common whaler Ga/eo/amna mmacrurus L 0 Whitetip Carcharhinus longimanus M the harvest of marine protein, The yield 'H ~ hibernate, G= game fish, F = flesh used forfood, L = hide good for lealher, 0 = of shark meat varies between 20 and 60 high oil content, P ~ flesh is poisonous. percent, depending on a number offac­ 'E = extreme danger 10 man, M ~ moderate danger, 0 ~ occasional danger, R= rare danger. tors. The yield varies among species, Table 3.-World landings 01 sharks 196~73 (In Ihousand metric Ions).' and generally male sharks yield more Years edible meat than female sharks of the Location 1965 1966 1967 1968 1969 1970 1971 1972 1973 same size, Females carrying unborn NW. Allantic 10.3 11.1 7.2 8.3 12.0 7.5 14.8 15.2 20.2 NE. Allantic 64.2 67.6 78.6 74.8 88.7 78.0 66.3 694 69.5 offspring have an even lower yield with W. C. Allantic 9.2 9.6 10.1 10.6 9.6 68 7.3 7.5 9.6 about 15 percent of their weights at­ E. C. AIIantic 9.4 8.7 73 11.8 12.8 36.7 42.1 482 48.4 Mediterranean tributable to the embryos within them, and Black Seas 10.3 9.4 16.0 11.3 11.1 6.0 9.6 6.8 6.5 SW. Atlantic 14.4 14.8 22.4 23.3 19.8 18.7 19.1 18.2 22.2 Acceptability ofShark Meat SE. Mantic 3.6 8.4 6.4 6.3 6.9 6.2 3.9 6.3 6.6 W. Indian Ocean 57.9 73.6 78.2 75.1 81.4 75.8 78.9 110.0 150.7 The organoleptic qualities of shark E. Indian Ocean 27.4 26.0 20.6 24.4 29.2 34.3 31.7 28.8 19.9 NW. Pacific 58.7 62.3 62.1 83.7 79.6 81.2 78.9 45.9 42.8 meat vary, depending to some extent on NE. Pacific 0.9 0.8 0.6 0.6 0.3 0.3 0.1 0.2 5.3 W. C. Pac~ic 10.7 12.7 10.2 14.6 16.1 17.4 15.5 17.3 7.4 species. Some species have a relatively E. C. Pacific 12.7 10.1 12.7 9.9 10.5 13.4 12.3 11.6 15.5 good acceptability (e.g" spiny dogfish, SW. Pacific 9.5 11.0 8.8 3.4 2.8 3.3 4.5 3.5 3.6 Squalus acanthus), some species taste SE. Pacific 7.0 8.7 13.0 16.4 --10.5 13.1 --9.8 --8.1 --19.6 TOlals 306.2 334.8 354.2 374.5 391.3 398.7 394.8 397.0 447.8 similar to tuna, halibut, etc., and shark

1 From: FAD "Yearbook of fishery statistics-catches and landings, 1973." Vol. 36, 1974, 590 p. steaks have been sold as halibut or

6 Marine Fisheries Review swordfish steaks. But some species are ammonia problem can be mitigated by same techniques used for freezing the not as acceptable, with objections being washing shark meat with water which steaks and fillets of other fish. The attributed to sour and bitter off-flavors apparently removes urea. This suggests shark should be handled as little and as and to the odor of ammonia. The de­ that a very effective washing would quickly as possible to keep quality de­ velopment of off-odors and off-flavors occur in mechanical deboning ofsharks terioration to a minimum. can be prevented by proper handling. where the meat is obtained in a commi­ Preservation Methods Therefore, much of the unacceptability nuted form with a corresponding large recorded is not due to an inherent poor surface to facilitate the washing. As Shark meat may be preserved in a quality of shark meat, but rather to poor much as 60 percent of the urea has been number of ways. It has been canned handling practices. removed from shark meat by soaking it successfully during wartime, even Species of sharks considered to have in solutions of lactic acid ( 1.5 percent), though early attempts at canning were 3 the best eating qualities are mak0 , or salt (I percent), or in urease extract. frustrated. While the formation of am­ thresher, soupfin, mackerel, white, and Lactic acid seemed to be most effec­ monia in shark meat is generally at­ spiny dogfish. The flavor of the blue tive. Heating the meat also lowers the tributable to the breakdown of urea by shark is considered to be undesirable. urea content. A blanching treatment bacterial ureases, it may also be formed The most desirable of the edible meat lowers it by about 10 percent. A heat­ in canned shark meat due to the heat are the fillets and the flesh from the sterilizing treatment lowers it by about which degrades the urea to ammonia. caudal peduncle, which together make 30 percent. Urea has been removed The conversion occurs at temperatures up about 55 percent of the total edible successfully from shark meat that was as low as 176°F (80°C). At 212°F portions. The belly flaps are considered salted by immersing in brine and then (100°C), the conversion is quite rapid. a delicacy by the Germans, and the fins desalting. For any use of shark meat The problem was eventually solved of all sharks have commercial value as which requires soaking, however, it is with the addition of acid which com­ food for humans, except for the fins of necessary to blanch it first. Otherwise bined with and neutralized the liberated the nurse shark which contain no edible the soaked meat is reported to acquire ammonia. The acceptability of canned gelatin. The Norwegians use dogfish an objectionable off-taste. shark meat was enhanced when the eggs as substitutes for hen's eggs in There may be a relationship between meat was packed with olive oil and peas puddings and in other food preparations the human fear of sharks as man-eaters (or beans) in a ratio of meat 50 parts, oil normally requiring eggs. and the human resistance to shark meat 25 parts, and peas 25 parts. The meat There are enough sharks in the as food, but in many areas, this rela­ was cut in small pieces and blanched world's oceans to permit a much greater tionship does not exist. For example, prior to packing. harvest than is presently taken, but the English, Italians, Japanese, French, Shark meat can be cured and there are several reasons why the shark Swedes, Chinese, and others have no smoked, and when processed in this fishery is not expanding. A major deter­ qualms about eating shark. It is re­ manner the adverse contributions are rent is that shark flesh generates large ported that the English use about 17 minimized. Small pieces are soaked in amounts of ammonia when it is stored, million pounds (about 7,700 metric water for about 6 hours then pickled in due to its unusually high content of urea tons) of dogfish per year. They also saturated brine for about 2lf2 days and (amounts as high as 0.12 percent have consume small amounts of several smoked for about Ilf2 days. They are been reported). It has been demon­ other species of sharks. then held in trays at room temperature strated that the conversion of urea to The flavor and quality of shark meat for about 2 weeks by which time the ammonia is due to ureases (urea split­ and its products depend on effective cure is complete. ting enzymes) produced by bacteria: bleeding of the shark carcass and sani­ Shark meat has been used for making

CO(NH 2)2+ H 2 0 urease 2NH 3 + CO 2 , tary handling practices. Bleeding can sausages but, generally, required the The production of ammonia can be be done most effectively when it is done addition of flesh of other species (e.g., minimized by observing maximum immediately after the shark is caught by hake) to produce an acceptable product. sanitation practices in the handling of chopping off the caudal fin. The heart, The Japanese prepare a paste-like pro­ shark flesh and by keeping the holding which will still be pumping, forces the duct from shark meat after it has been temperatures as low as possible. Low­ blood out of the severed major artery. separated from the skin and the cartil­ ering the pH of shark meat by the addi­ Other bleeding techniques, such as age and comminuted. Salt and various tion of acid, such as citric acid, lemon puncturing the heart or severing major other spices are added and the paste is juice, tomato juice, vinegar, etc., has arteries in other parts of the body, are then molded into rolls which are been demonstrated to be effective in the much less effective. Sharks should then steamed over boiling water for 20 min­ elimination of the ammonia problem. It be eviscerated as soon as possible. At utes. The product, white in color, is has been reported that the addition of the processing plant or in a factory, the considred to be quite acceptable by the acid provides an additional unexpected fins are generally removed to be used Japanese. The Japanese also produce a benefit-it improves the texture of the separately. Large sharks (larger than 3 smoked canned shark meat in soy meat. Experiments have shown that the or 4 feet) are generally cut transversely marinade. into steaks. Smaller sharks may be To produce salted dried fillets, 3Mako shark is also called bonito shark. filleted. Shark meat is frozen by the sharks are beheaded, eviscerated, and

February 1978 7 bled. They are then washed and stored product remains intact and has a meaty that squalene was mixed with cheap in ice (belly down) until ready for use. flavor. vegetable oils and used as an inexpen­ Laterthey are filleted, and the fillets are Shark meat can be cut into fiJlets or sively produced, illegal, substitute for cleaned of blood spots, skin, etc., and steaks which can be handled as fresh olive oil. The substitution was an excel­ ragged edges are trimmed. The washed cuts, or they can be frozen. Shark fi llets lent and valuable outlet for an otherwise fillets are then drained for a few minutes can be used to produce frozen fillet low-value by-product, and it was made and layered with salt in boxes contain­ blocks. possible by the fact that the Food and ing drain holes, taking care that fillets The Norwegians, who export sharks, Drug Administration (FDA) test for do not overlap without salt between use an effective preservation process olive oil purity was related to the them. The boxes are held in the shade that is reported to keep sharks in prime squalene content of the oil. When the for about 6 days. At the end of this quality for long periods. They cut away practice was later discovered by the period the fillets are removed and ex­ the viscera, including the belly flaps, FDA it was, of c<.:urse, terminated. cess salt is brushed off. The fillets are and they pack the fish in an alginate Some shark meat is poisonous. For then dried by any of the available jelly and place them in frozen storage at instance, the meat of the Greenland methods (tunnel drying, sun drying, about 5°F (-15°C). shark, Somniosus microcephalus, is etc.). Sun drying, which takes about I Fins are preserved by drying, freez­ quite poisonous to both man and ani­ week, is the least desirable method be­ ing, or salting. To produce lightly salt­ mals. Other species reported to be cause this process subjects the product ed dried fins, they must be trimmed of mildly poisonous are the black-tipped to various types of contamination, and all flesh and skin, washed, and held for sand shark, Carcharhinus melanop­ there is no way to control the precipita­ about 10 hours in a 3 percent salt solu­ terus, the seven-gilled shark, Heptran­ tion, temperature, humidity, etc. Thus, tion (about \4 pound of salt for every chias perlo, and the six-gilled shark, when precipitation occurs or when the gallon of water). The fins are then sun­ Hexanchus grisseus. humidity is high, the fish, which are dried on wire mesh in single layers for Except for the Greenland shark, the generally dried on racks or trays, must about 2 weeks. When the drying is flesh of the sharks cited above are not be removed to a covered drier area. In completed, the fins will be very stiff. very poisonous and one report indicates tunnel drying and cabinet drying, the They are then packed in boxes in which that the causative agent may be product is protected against contamina­ they may be shipped or held until sufficiently washed away by rinsing the tion and there are various conditions shipped. meat several times. Apparently there is that are controllable (temperature, air considerable danger in eating the livers flow, humidity, etc.), depending on the Composition of these sharks where the concentration facilities. When conditions are con­ and Characteristics of the harmful substance not yet iden­ trollable, the recommended tempera­ Shark meat contains very little fat (as tified must be in more concentrated ture is about 113°F (45 0C), and the rec­ low as 0.1 percent in some species). A form. ommended relative humidity is about few species may have a fat content Symptoms of poisoning from eating 35 percent. Under these conditions, the higher than 6 percent. Generally, shark shark develop within 30 minutes. They drying time is much shorter than that meat is darker, coarser fibered, tough­ include nausea, vomiting, diarrhea, required for sun-drying and the quality er, and stronger tasting than the meat of abdominal pain, headache, aching of the tunnel-dried product is corres­ teleosts. The older the sharks, the joints, tingling about the mouth, burn­ pondingly better. Del Valle and Nick­ stronger the taste. Shark meat is re­ ing sensation of tongue, throat, and erson (1968) developed a quick-salting ported to be lower in protein value, esophagus, and, later, lack ofcoordina­ process for shark meat. The process, contains less quantities of some of the tion. If the illness is severe enough, requiring only simple equipment, pro­ essential amino acids, and has less there is paralysis, coma, and finally duces an acceptable salted product, in­ quantities of total free amino acids than death. Although vitamin A in high con­ expensively, and has an excellent po­ the meat of teleosts, and it has unusu­ centrations (such as found in shark liv­ tential for preserving and making avail­ ally high urea (up to 0.12 percent) and ers) is toxic, it is not the agent that able a high value protein for inhabitants trimethylamine oxide (up to I percent) causes the symptoms cited above. of developing countries where refriger­ contents. Shark meat is more acidic Harvesting ofSharks ation is yet scarce. The process in­ than that of teleost fishes. volves grinding shark flesh with the A component of shark liver oil is Fishing for sharks must be closely simultaneous addition of salt, pressing squalene, an unsaturated terpene hy­ managed; otherwise, the stocks may be

to remove water, and drying the pressed drocarbon having the formula C30H 50 . depleted even more easily than those of cakes in air or by other means when It comprises the bulk of the unsapon­ other species. Such a problem has al­ available. The dried product is stable fiable fraction of the liver oil in some ready occurred with the porbeagle, a without refrigeration, even at tropical sharks, and it was a by-product of the shark averaging 5 feet (1.53 m) in temperatures. To prepare for consump­ process that produced vitamin A from length and 250 pounds (114 kg) in tion, the salt is leached out by boiling in shark liver oil prior to the advent of weight and fished largely for the Euro­ fresh water 2 or 3 times. The resultant synthetic vitamin A. It is noteworthy pean market. Thus, controls have been

8 Marine Fisheries Review placed on the fishing effort for this species in some areas. Prominent fac­ tors that contribute to easy depletion of the stocks are the small number of offspring produced by each female and their slow growth rate. The spiny dogfish has been fished from time to time, especially to minimize its nui­ sance effect. However, when a market demand was developed and the fishing effort became intense, the stocks were reduced rather quickly. Dogfish shark. (Photo by William L. High.) The village of Maloy in Norway is called the dogfish capitol of the world. 50-60 meshes deep. The web is hung so moved. However, in the latter case, the From this port about 40 vessels, 70-90 that two meshes occupy the lateral sharp denticles must be made dull; feet (21.5-27.5 m) long, fish for small space of one fully stretched mesh, and otherwise, the consumer would cer­ sharks. The bait is mackerel or herring, the length of the net is about three times tainly be injured by them. It is when the the gear is the long line, the hook is size longer than the set gill net. Because of denticles are left in that the leather is 7. Each vessel carries 80-100 sections the extreme stresses placed on the drift quite skidproof because even though of line containing as many as J ,500 gill net during hauling, especially in their points are dulled, they still provide hooks. The lines are set through stern acti ve or rough seas, the horizontal top a considerable clinging ability. To re­ chutes and retrieved by hydraulic line has to be extra strong. move the skin from a shark is said to tire power, With crews of 8-10 men, these 3) Otter trawls are used for dogfish. the strongest men and to dull the sharp­ vessels stay at sea for 7-14 days. The The otter trawl is a cone-shaped net est knives, and it takes an expert at least fish are iced whole at sea. The gear that dragged with the large end forward, and 15 minutes to skin a shark. The tough­ is used to catch sharks has to be con­ the opening is maintained by "doors" ness and wearability of shark skin structed ofvery tough materials; ideally which are placed in such a way that the leather is such that it outlasts steerhides it should be made of steel cable or steel forward motion tends to make them and pigskins by about 100 percent. The chain. spread apart from each other, thus tensile strength ofshark leather is about There are five generally accepted spreading open the mouth of the net. 150 percent that of steerhide and methods for fishing sharks with varia­ 4) Harpoons may be used to capture pigskin. Because of the high costs of tions to suit different situations: the large sharks. preparing shark skins, only those from I) Set gill nets are used inshore. The 5) The hook and line method in­ the larger sharks (over 5 feet (1.53 m) in nets are of webbing J0- or I 1- inch volves the stringing of long lines (up to length) are used. However, theoreti­ (25.5- or 28-cm) stretched mesh, hung 2,000 feet (610 m) long) carrying cally, the skins of even the smallest 20-30 meshes deep, and 2,000-2,500 baited hooks set about 12 feet (3.65 m) sharks can be used when the economics feet (610-760 m) long. This length is apart. This form of fishing is now less of preparing them are feasible. attained by joining a number of nets. popular than gillnetting. Some longlin­ The production of leather from shark The upper part of the net is held up by ing similar to that used for catching tuna skins is similar to the process used for uniformly spaced cork floats while the may be used to capture medium-sized other marine fishes as well as marine bottom is stretched downwards by lead sharks. mammals and land animals. This de­ weights. The amount of stretch im­ scription will apply to the production of posed is such that three meshes occupy Nonfood Uses of Shark shark leather only, and for a more gen­ the lateral space of two fully stretched Sharks have unique characteristics eral description of the processing of meshes. The net, anchored and marked that have promoted their utilization in a hides and skins into leather, the reader with a buoy, is pulled aboard the boat variety of nonfood uses which include is referred to O'Flaherty et al. (1956­ once each day or less often, depending the production of shark leather, phar­ 1965). For details on the production of on the abundance of fish and the maceuticals, at one time vitamin A, and shark leathers the reader is referred to weather. If the net is hauled in much 4 5 other miscellaneous uses. Rogers and Kohler • sooner, the catch may not be large enough to warrant the effort. If the net Leather is not hauled in soon enough, the catch The skins of many sharks can be pro­ •Rogers, A. Sharkskins preparatory to tanning. may be eaten by fish that are too small cessed to produce high quality leathers. U.S. patent 1,338,531 (1920). Preserving shark­ to trap and these would include small In most cases the denticles are removed skins and the like. U.S. patent 1,395,773 (1921). sharks, hagfishes, etc. because their presence makes it very Treating sharkskins and the like. U.S. patent 1,412,968 (1922). 2) Drift gill nets are used in deep difficult to cut and stitch the leather, but 'Kohler, T. H. 1925. Tanning and dearmoring offshore waters and they may be strung in a few cases the denticles are not re- fish skins. U.S. patent 1,524,039. January 1927.

February 1978 9 and its edges are folded in to make a square. The square is then made into a roll and tied. The individual bundles are packed in bags of burlap or sisal or in barrels. They are held or shipped to the tannery in this form. To produce leather from skins, they are soaked to remove salt and/or to re­ hydrate them (depending on the preser­ vation process used). They are then put in vats containing lime (calcium hy­ droxide), usually in concentrations such that the weight of the lime is about 10 percent of the weight of the hides. The pH of the solution should be about 12.5. The lime soak is used to loosen School of dogfish sharks. (Photo by William L. High.) the denticles. Sodium sulfate in an amount equal to about 2 percent of the Leather production is a series of steps the head. Next the skin is gripped with lime (by weight) is also added to en­ which includes preparation, tanning, one hand and pulled as the knife is used hance the effectiveness of the lime. and finishing. The skins of sharks are with the other hand to cut the skin away Several lime treatments (using fresh difficult to preserve because of the from the meat, the first hand continu­ lime in each case) may be required. structure of their denticular scales ally pulling in a peeling action. An im­ Any flesh that remains on the skins is which protect microbes lodged among portant factor in keeping the peeling trimmed off and the skins are then them. The most desirable method for time down to a minimum and in produc­ bated. Bating involves the use of pro­ preserving shark skins would seem to ing well-cut hides is the sharpness of teolytic enzymes to hydrolyze the fibers be with ionizing radiation since this the knife. It must be very sharp. How­ which enhances swelling of the skin. form of energy could destroy all de­ ever, it is because of this, precisely, Since bating acts best at pH 8.5, acid is teriorative microorganisms no matter that extreme care must be taken if acci­ added to the bating solution in order to how well protected they might be from dental cutting of the skin (which de­ lower the pH of the skins to the desired other preservation treatments. Radia­ tracts from its value and might even level. tion was demonstrated to preserve ani­ ruin it) is to be avoided. Thus, it is Tanning enables the skins to resist mal hides for long periods at room better to cut a little deeper even though degradation from many environmental temperatures but its use has not been this means more meat must be trimmed conditions as well as from microbes. adopted for this purpose, as far as I from the skin than to try to cut a clean Because of the unique characteristics of know. The preserved skins may be skin (with no meat attached to it) and shark skin, it is tanned only by the veg­ stored until they are to be processed. run the risk of cutting the skin. etable tanning process. Vegetable tan­ To remove the skin from a shark, the As soon as the skin is removed from ning employs the extract of either the tail is cut at about the beginning of the the shark, it must be washed to remove bark or of the bark and wood of a vari­ caudal peduncle as the skin over this the blood and slime. It is then immersed ety of trees that include oak and hem­ area is not used. (The fins of sharks are in a vat containing about 3.5 percent lock. This part of the process is carried removed first since they can be readily sodium chloride (table salt). The skin is out in vats and takes 1 or more weeks, sold as food in a number of overseas held in the brine 3-8 hours and then the depending mainly on the types and markets.) The skin is cut, starting at the flesh is removed. After fleshing, the physical characteristics of the skins. holes left by the removal of the dorsal skin may be trimmed, if necessary, and After tanning, the skins are lubri­ fins, along the backbone from end to then given a final wash. The skins are cated with oils and greases to replace end. A cut is then made over the top of then layered with salt in piles about 3 natural fats that were removed in the the snout. This cut is then continued feet (0.92 m) high on platforms that are preparation and tanning processes. This toward the back along the side of the slightly inclined so that all liquid will be step, called "fat-liquoring," improves head in a line just above the gill slits drained away from the bottom layers of the strength, resistance, and flexibility around the pectoral fin and back to­ skins. They should not be placed in the of the skins. The skins may then be wards the front in a line that runs under sun. After 4 or 5 days the skins are dyed using a variety of aniline dyes. the gill slits and parallel to the line cured (they should not remain in the The skins are then shaved to the desired above the gill slits. The cut continues pile for longer than I week). thickness and passed between rolls that along the lower jaw near, and follow­ Following this, each hide is shaken press out excess water and iron out ing, the opening of the mouth where it to remove excess salt. It is then placed wrinkles. They are then dried by past­ meets the cut made on the other side of flesh side up, sprinkled with new salt, ing them on flat surfaces and passing

10 Marine Fisheries Review •

them through drying tunnels. The dyed of vitamin A. The value of fish oils as a multiple vitamin capsules contammg skins are then given a surface finish source of vitamin A has been reduced other vitamins. When the vitamin A of either by hand or by machines which sharply since the advent of the process an oil is relatively low, it can be concen­ mayor may not include a glaze. for producing synthetic vitamin A in the trated by the saponification process Brody (1965) quotes an official of the late 1940's. However, there is a con­ which carries the vitarrun A in the unsa­ 6 Ocean Leather Corporation , a man­ cern among some that the synthetic ponifiable fraction from which it can be ufacturer of shark leather, as reporting substitute may be inferior to the fish recovered in a concentrated form by that when the toe part of children's liver oils because it lacks minerals, solvent extraction and further purifica­ (especially boys') shoes are made of amino acids, and possibly other uniden­ tion. shark skin such shoes do not abrade or tified nutrients. Prior to the changeover In some work conducted when shark scuff as do shoes made of conventional to synthetic vitamin A, shark livers sold liver oil was used as a source of vitamin leathers. Since the toe part of the shoes for as high as $1.50 per pound, depend­ A, it was observed that the shark liver of children receives the most wear, the ing on the vitamin content. The vitamin oil promoted the growth of white blood shark skin shoes last significantly A content ofshark livers covers a broad cells. Although there is no evidence to longer than shoes made with conven­ range, and the richer oils have been support the theory that shark liver oil tional leather only. reported to contain up to 340,000 contains an anticancer agent, sharks The skins of the male sharks are pre­ U.S.P. units per gram of oil. apparently do not develop tumors of ferred to those of female sharks. The In order to preserve the quality of the any kind, and this fact continues to gen­ reason for this is that the hides of the liver oil, it must be recovered soon after erate hopeful interest in finding the females usually contain mating scars the sharks are slaughtered. When livers reason why sharks are not vulnerable to which at best result in visible imperfec­ cannot be processed, their quality will one of man's most dreaded diseases. In tions in the leather and at worst result in diminish unless they are effectively some work conducted by John Heller, holes in the leather (see section on Re­ preserved. Held in frozen storage, the Executive Director of the New England production) . livers will retain their good quality for Institute for Medical Research in months. Livers may be preserved also Ridgefield, Conn., shark liver extract Pharmaceuticals by salting (finished concentration to be was reportedly used successfully to Sharks have been studied for their about 10 percent by weight), by the treat cancer in rruce, rats, and chickens. pharmaceutical value, and heparin-like addition of Formalin (about 0.25 per­ It is suggested by some researchers that compounds have been found in nearly cent by weight), and by other rruscel­ sharks are immune to other diseases as all parts of dogfish (a small shark) that laneous methods, but the freezing pre­ well as to cancer and that they do not have potencies far in excess of that of servation is the most effective process show old age weaknesses. In one study commercial heparin, while at the same for protecting the quality of the livers. the addition of antibodies from shark time the shark compounds cause less Prior to processing the livers, they blood to a growth medium inhibited the undesirable side effects than does hepa­ must be cleaned of all other material. growth of a variety of microorganisms rin. Commercial heparin, a derivative The livers are then comminuted and this that cause diseases in man. of body tissues, especially the liver, is can be accomplished by a variety of produced from animals. It is prescribed machines such as hammermills, disin­ Miscellaneous Uses for individuals who have a tendency to tegraters, choppers, etc. The commi­ form blood clots. nuted livers are then heated in pots, Sharks have other miscellaneous In the late 1930's the discovery that jacketed kettles, or by direct steam in­ uses. The teeth of sharks have been dogfish liver oil contained about 10 jection which renders out the oil which used for producing novelty items, times the amount of vitamin A con­ can then be decanted or centrifuged. knives, shark tooth gauntlets, as well as tained in cod liver oil, followed by the The oil may also be rendered by hy­ other weapons of defense. Because the discovery that the liver oil of the soup­ draulic pressure or under heat and pres­ scales on shark skins are hard, sharp, fin shark contained about 100 times the sure. It may also be recovered through and close together, shark skins have amount of vitamin A contained in cod an alkali digestion method or by an been used in the past by wood-workers liver oil, started a shark-fishing activity enzyme/alkali digestion method (alkali for abrading wood. However, this use ofsuch intensity that it was likened to a digestion methods are the most popular is neither economical nor practical in gold rush. By 1942 the price of sharks ones). In most cases a centrifuge is used light of the modern effective sandpa­ had risen to $1 ,500 per ton from a price to separate the oil from the aqueous pers available today. Shark skins have of about $10 per ton in 1938. The oil layer. Once the oil is recovered it must been used to polish marble. Because of obtained from the liver of sharks has be preserved to retain its quality until it the nonskid property of shark leather, it been used in tanning as well as a source is used. It is best stored in drums with was used for making sword hilts to in­ no head space and in a cool area. sure retention of possession of the sword for its owner. This property has 6Reference to trade names or commercial firms The oil must meet stringent physical does not imply endorsement by the National and chemical specifications. The oil is been used to produce pickpocket-proof Marine Fisheries Service, NOAA. processed into liver oil capsules or in wallets. The use of urea in shark meat

February 1978 11 has been considered as a feed compo­ There seems to be no doubt that the nate fear signals, although some inci­ nent for farm animals. Ruminants such presence of blood incites sharks to dents might suggest this. On the other as cattle and sheep can utilize the urea ferocious attacks on any object near the hand, it has been observed that when a in sharks in limited amounts (less than blood, at any time, day or night. shark closes in on a group of bathers, it 0.025 percent). Even chicks have been The damage inflicted by sharks is not generally selects one and continues to reported to utilize urea; however a pro­ limited to their numerous sharp teeth, attack his selected victim in spite of the tein deficiency might result without an powerful jaws, and, in some cases, presence and even the actions of the added protein supplement. spikes. The sharp denticles on their skin others. This may only seem so, since can also inflict considerable damage on Danger to Man blood, usually drawn at the first attack bare skin. The great shark scare during even if made randomly, would then at­ The danger of sharks to man is real the first 12 days of July in 1916 off the tract the shark to the bleeding person. although it may not be as prodigious as New Jersey coast was not just a scare. It There is evidence to suggest that sharks their notoriety would imply. Most cost the coastal cities about $1 million attack light-skinned people more read­ sharks are too small, too sluggish, or in cancelled reservations as well as the ily than they attack dark-skinned are just not that dangerous. However, lives of several citizens that were killed people. When all factors, clues, facts, some species (e.g., white shark and by sharks on New Jersey beaches. In at etc., are analyzed and evaluated, we tiger shark) are large enough, fast least one of these cases, both the tibia can only conclude that shark behavior enough, powerful enough, and aggres­ and fibula (leg bones) were actually and motivation are unpredictable, and sive enough to be extremely dangerous snapped off below the knee, giving sharks just cannot be ignored if there is to man. About 35 species of sharks are proof the awesome crushing power of any chance that they may be near considered to be potentially dangerous the jaws of the shark. It was concluded bathers. The term "rogue shark" has to man so it is not unreasonable to find that white sharks were involved since been used in the literature. A rogue that there are about 50 cases of shark one of them, which was later caught in shark is a lone hunter who usually has attacks on people reported annually of the general area of the attacks, con­ attacked at least one human being and which less than 50 percent are fatal. tained parts of human anatomy in its has the inclination to attack others. One can only guess at the number of stomach. In 1959, California suffered a The military, especially, has been in­ shark attacks that are not reported. similar shark scare in which again sev­ terested in sharks because of the hazard Shark attacks occur more frequently in eral people were killed. Again white to downed flyers and to naval personnel warm waters than in cold waters and sharks were involved. that either accidentally or by necessity seem to occur more often at night than The most devastating shark attacks must spend time in the water without during daylight. The reason for the on man have occurred when large ves­ the protection of any type of vessel. former is that the dangerous species are sels have been sunk in shark-infested Until World War II, the danger of natural inhabitants ofwarm waters. The waters. In some of these cases, the sharks to man was not fully appreci­ reason for the latter may be due to number of people killed by sharks have ated, but following unexpected losses higher nocturnal activities of sharks or numbered in the hundreds. In the sink­ of Navy personnel to sharks, the U.S. the inability of many to sight sharks at ing of the U.S. cruiser Indianapolis, Navy became concerned and launched night, or both. It is relevant to note, during World War II, nearly a thousand research to find shark repellents. however, that in a study of shark be­ men were lost at sea. Although the toll In 1944, the Navy disclosed "Shark havior, it was observed the sharks in taken by sharks is not known exactly, Chaser," a water-soluble cake consist­ one area migrated to offshore during the nearly 100 shark-mutilated bodies were ing of black dye (about 80 percent) and day and came close to shore during the later recovered. In the sinking of troop­ copper acetate (about 20 percent). The night where they remained until day­ ship Nova Scotia, in the same war, purpose of the dye was to obscure man break. This pattern was observed over a about 1,000 men were lost, and in this from sharks and the copper acetate was number of days and nights. The pattern tragedy many bodies were recovered, found to repel sharks in initial experi­ indicated that the sharks had set up a still in their life jackets, but without ments. In subsequent uses of shark territory that ranged from inshore to legs. Sharks apparently attack the limbs chaser, it was found to work some­ offshore. It is suggested by some that because they appear easier to sever than times, but not always. It is not consid­ the reason for at least some shark at­ the torso. Yet, there are a large number ered effective against the white shark, tacks on man are due to the territorial of reports that sharks were discouraged nor is it effective when shark activity is jealousy of sharks that makes them in­ by different actions taken by potential aroused. Some experiments showed terpret man's presence as a threat to victims. The accounts do not enable that human sweat repelled sharks, but their waters. This concept is believed to one to arrive at any pattern that could be not reliably. Of the many shark repel­ be supported by the fact that when used to defend against sharks, but nude lents and shark barriers tested, none bathing beaches are protected by en­ persons are more readily attacked than have been proven I00 percent effec­ trapment nets, the number of sharks clothed persons. tive. Injections of numerous poisons, trapped is reduced with time, until There seems to be no conclusive evi­ enough to kill large animals, did not kill eventually there are no sharks caught. dence that sharks attack those that ema- sharks. Only strychnine was effective,

12 Marine Fisheries Review but since the sharks took up to 30 sec­ paralysis of the jaw in the open position (editors). 1956-65. The chemistry and technology of leather. Vols. 1-4. Reinhold Publ. Corp., N.Y. onds to respond, the question is how because the observer reported that the much damage can a shark do in 30 sec­ attacking shark did not close its mouth REFERENCES onds? even after it had retreated from its prey. Anglo-American Caribbean Commission. 1945. Guide The most effective barrier at beaches Repeated experiments produced the to commercial shark fishing in the Caribbean area. is believed to be wire mesh. For protec­ same results-in no case was the little U.S. Fish WildJ. Serv., Fish. Leafl. 135, 149 p. Anonymous. 1957. The shark fishing industry. Ocean tion of humans in the ocean, an opaque fish in any danger. This apparent shark Leather Corp., Newark. N.J.. 15 p. inflatable bag is believed to be effec­ repellent is so powerful that even in Bigelow, H. B., and W. C. Schroeder. 1948. Fishes of the western North Allantic, Part One, 576 p. Sears tive. The device keeps the person at the very dilute amounts it kills small ma­ Foundation for Marine Research, Yale Univ., New surface while at the same time he can­ rine animals. Laboratory studies of its Haven, Conn. Budker, P. 1971. The life of sharks. Columbia Univ. not be seen or smelled by sharks. How­ action indicated that the toxin appears Press, N.Y.• 222 p. ever, bags have been bitten by sharks to attack the nerves and, in addition, it BuUock, T. H. 1973. Seeing the world through a new sense: Electroreception in fish. Am. Sci. 61 :316-325. and the effectiveness of the bags as pro­ destroys red blood cells. Butler. C. 1955. The fish liver oil industry. U.S. Fish tection against sharks is yet to be de­ Of the weapons used to kill sharks, Wildl. Serv., Fish. Leafl. 233. 104 p. Casey, J. G. 1964. Angler's guide to sharks of the termined. "Kevlor", a synthetic bul­ the most desirable one seems to be the northeastern United States, Maine to Chesapeake let-proof fabric manufactured by the carbon dioxide dart gun. By this means, Bay. U.S. Fish Wildl. Serv., Circ. 179,32 p. Cousteau, J., and P. Cousteau. 1970. The shark. DuPont Company, has been demon­ the shark is killed and inflated with car­ Doubleday & Co., Inc.. Garden City, N.Y., 277 p. strated to be effective against tearing by bon dioxide gas which floats the shark Gilbert, P. W. (editor). 1963. Sharks and survival. D. C. Heath Co., Boston, 578 p. sharks. This is still under study. to the surface where it can be seen and ____ , R. F. Mathewson, and D. P. Rail The only truly effective protection taken out of the water if it is advanta­ (editors). 1967. Sharks, skates, and rays. John Hop­ for humans is the cage. Made of steel geous to do so. An additional feature to kins Press, Baltimore, 624 p. ____ , L. P. Schultz. and S. Springer. 1960. bars, it is used to enclose those engaged this weapon is that it does not shed Shark attacks during 1959. Science (Wash., D.C.) in underwater photography, etc. A new blood. This is important when there are 132:323-326. Gordievskaya, V. S. 1971. Shark flesh in the food indus­ and promising repelling device called other sharks in the vicinity since the try. Pacific Scientific Research Institute of Marine "the Hicks repeller" produces pulsed presence of blood in the water incites Fisheries and Oceanograph mNRO), Vladivostok, Russia, 26 p. (Transl. from Russ. by Isr. Prog. Sci. electromagnetic fields that are said to them to violent attacks, Other effective Transl., Jerusalem, 1973.) cause sharks such unbearable annoy­ weapons are "death needles" loaded Halstead, B. W. 1959. Dangerous marine animals. Cor­ nell Maritime Press. Cambridge. Md., 146 p. ance that they move quickly away from with strychnine and the "powerhead", Holmsen, A. A. 1968. Harvesting and processing the repeller. Although the device emits a device to be used like a hammer which dogfish. Univ. Rhode Island, Dep. Food Resour. Econ., Occas. pap. 68-275, 19 p. explosive sounds, its effectiveness is fires a I2-gauge shotgun shell, usually Jensen, A. C. 1965. Life history of the spiny dogfish. believed to be due to the electrical ef­ to the shark's brain. U.S. Fish WildJ. Serv., Fish. Bull. 65:527-554. Lineweaver, T. H., 1II, and R. H. Backus. 1970. The fect on the ampullae which is de­ The American Institute of Biological natural history of sharks. J. B. Lippincott Co., scribed, literally, as a nervous break­ Sciences maintains a Shark Research Philadelphia, 256 p. down. Panel that records information relative McCormick, H. W., T. Allen, and W. E. Young. 1963. Shadows in the sea. Chilton Book Co., Philadelphia. A most promising repellent reported to shark attacks on man and defenses 415 p. in the literature to date is a naturally against shark attacks and promotes re­ Myrberg, A. A., Jr. 1970. The behavior and sensory physiology of sharks. Univ. Miami, Rosenstiel occurring one. It is a highly lethal milky search to broaden the information base School of Marine and Atmospheric Sciences, Miami, toxin secreted from surface glands on sharks, Fla., 19 p' Osterhaug, K. L. 1961. A literature review on possible along the dorsal and anal fins of a small uses for dogfish. U.S. Fish Wildl. Serv.• Tech. Leafl. flatfish, Pardachirus marmoratus, that 16,43 p. LITERATURE CITED Pope, P. 1973. A dictionary of sharks. Great Outdoors inhabits the Red Sea. It is called the Publ. Co., SI. Petersburg, Fla.• 88 p. "Moses sole" by the Israelis who find Anonymous. 1964. Sharks. Comm. Fish. Rev. 26 Roedel, P.• and W. E. Ripley. 1950. California sharks (12):59-60. and rays. Calif. Div. Fish Game, Fish. Bull. 75, 88 p. it to be good eating. Since the fish is Brody, J. 1965. Fishery by-products technology. Avi Thomson, J. R., and S. Springer. 1965. Sharks, skates, cooked prior to consumption, its toxin Publ. Co., Westport, Conn., 232 p. ray, and chimaeras. U.S. Fish WildJ. Serv., Circ. Clark E. 1974. The Red Sea's sharkproof fish. Nat!. 228, 18 p. is presumably destroyed by heat. In ex­ Geogr. Mag. 146:718-727. Tressler, D. K., and 1. M. W. Lemon. 1951. Marine periments conducted by Clark (1974), Del Valle, F. R., and J. T. R. Nickerson. 1968. A products of commerce, 2d ed. Reinhold Publ. Corp., quick-salting process for fish. I. Evolution of the N.Y., 782 p. sharks that attempt to devour this process. Food Technol. 22(8): 104-106. Wagner, M. H. 1966. Shark fishing gear: A historical flatfish seem to undergo an immediate O'Flaherty, F., W. T. Roddy, and R. M. Lollar review. U.S. Fish Wildl. Serv., Circ. 238, 14 p.

MFR Paper 1281. From Marine Fisheries Review, Vol. 40, No.2, February 1978. Copies of this paper, in limited numbers, are available from 0822, User Services Branch, Environmental Science Information Center, NOAA, Rockville, MD 20852. Copies of Marine Fisheries Review are available from the Superin­ tendent of Documents, U.S. Government Printing Office, Washington, DC 20402 for $1. 10 each.

February 1978 13