DANGEROUS SEA LIFE 



Adult sharks range in size from 18 inches to more than 50 feet 

 in length. The giant whale shark and many other species feed ex- 

 clusively on small marine organisms and do not ordinarily pose a 

 great threat to a man in the water. A great many sharks eat large and 

 small fish, including other sharks, seals, and a variety of organisms 

 or material, depending upon feeding circumstances. Many sharks 

 are too small or are equipped with inadequate teeth to be of any real 

 danger to a man in the water. Considering the feeding habits of all 

 sharks more than 4 feet in length and adequately equipped with 

 teeth, the situation may be considered dangerous for swimmers or 

 divers if blood or other attraction may be present. 



Detection by sharks of blood, food, or injured animals in the 

 water has always posed a subject of considerable interest. Although 

 possessed of poor visual acuity and a low order of intelligence, a 

 shark's ability to detect food is phenomenal. Detection is probably 

 accomplished by a highly developed sense of smell and an extremely 

 sensitive system for reception and detection of low frequency vibra- 

 tions in the water. Their ability to detect a disabled or wounded 

 animal at long range has been considered most uncanny. 



In addition to these abilities and habits concerned with casual 

 eating, either alone or in small numbers, sharks have also demon- 

 strated unpredictably wild conduct, under circumstances involving 

 many sharks or much food. This may occur subsequent to an explo- 

 sion in the water, the sinking of a vessel, or crash of a plane. When 

 resorting to these mob tactics, sharks may be observed in a frenzy, 

 attacking vertically from the depths, dramatically breaking the 

 water, and snapping savagely at everything in sight. During this 

 most dangerous situation, nearly all repellant devices are ignored. 

 Sharks may be seen ripping and devouring each other, with one 

 unfortunate fish the target of attack by several larger ones. It is 

 under circumstances like these that sharks may attack one swimmer 

 out of many in the water and concentrate on this one to the total 

 exclusion of those attempting a rescue. This, however, cannot be 

 depended upon, and eicperienced divers explain that shark conduct 

 even under mob frenzy conditions is unpredictable. 



The danger of attack by sharks is greatest in tropical and sub- 

 tropical areas between Latitudes 30°N., and 30°S. Temperate waters 

 are generally considered to be free of shark attacks. However, this 

 is not always true, as the records prove. Certain shark species mi- 

 grate periodically into cooler waters in search of food. Areas which 

 have been found particularly dangerous are Australia, South Africa, 

 and the Pacific coast of Panama. Most recorded attacks have taken 

 place in water temperatures greater than 70°F., but fatalities have 

 taken place in temperatures of 60 °F. or less. The season with the 

 greatest number of recorded attacks is during the summer, especially 

 from 3:00 p.m. to 4:00 p.m. daily. This is also the time when most 

 recreational bathers are attracted to the beach. Sharks are round- 

 the-clock eaters, however, and frequently feed during the hours of 

 darkness when the risk of attack may be even greater. 



In considering those sharks most dangerous to man, members of 

 4 families are believed to be of greatest concern to divers or swimmers: 



(a) The Mackerel or Man-eater Shark family (ISVRIDAE) 



(b) The Requiem Shark family (CARCHARHINIDAE) 



(c) The Sand Shark family (CARCHARIIDAE) 



(d) The Hammerhead Shark family (SPHYRNIDAE) 

 Four species are described and illustrated as being representative 



of these families, but are not to be considered the only dangerous 

 members : 



(1) White Shark, Carcharodon carcharias (Figure 1), is one 

 of the most dangerous of its kind. It is savage, aggressive, fast- 

 swimming; it has been known to attack boats. Numerous 

 human attacks are accorded to this species. Distinctive charac- 

 teristics are the lunate or moon-shaped tail fin and coarse serrate 

 teeth. Color is slate-brown, slate-blue, gray, or almost black 

 above, shading to dirty white below. The tips of the pectoral 

 fin are also black, usually with some adjacent spots black. They 

 may attain a length of 30 feet or more. Distribution is oceanic 

 — widespread in tropical, subtropical, and warm temperate belts 

 of all oceans. 



(2) Tiger Shark, Galeocerdo cuvier (Figure 2), is sluggish in 

 character except in pursuit of food. The tiger shark when stim- 

 ulated becomes a vigorous and powerful swimmer. Attacks on 

 humans are credited to this shark, although it tends normally to 

 being a scavenger. Distinctive features are the very short snout 

 and sharply-pointed tail. It is colored gray or grayish brown, 



and darker above than on the sides or belly. The oblique trans- 

 verse bars usually appear only in the smaller specimens. It 

 attains a length of 30 feet, but the largest recorded specimens 

 measured 18 feet. The tiger shark is widespread in the tropical 

 and subtropical belts of all oceans, botb inshore and offshore 

 and is reported to be the commonest large shark of the tropics. 



(3) Sand Shark, Carcharias iaurus (Figure 3), is a shore 

 species which lives on or close to the bottom and is compara- 

 tively sluggish but has a voracious appetite. This shark, in 

 East Indian waters, enjoys a bad reputation, however, this is 

 not true of the North American species. Gill openings in front 

 of the pectoral fin, a second dorsal fin about as large as the first, 

 with the first dorsal entirely in front of the pelvic are distinctive 

 features. It is colored a bright gray-brown above, darkest along 

 the back with the snout and upper sides of the pectorals shading 

 to gray white on the belly. The body rearward from the pec- 

 torals is marked with round to oval yellow brown spots. The 

 sand shark may reach a length of 10 feet. It inhabits the west- 

 ern Atlantic from the Gulf of Maine to Florida and southern 

 Brazil, as well as the Mediterranean Sea, tropical West Africa, 

 Canaries, and Cape Verde Islands in the Eastern Atlantic. In 

 Argentine waters and the Indo-Pacific it is represented by simi- 

 lar species. 



(4) Hammerhead Shark, Sphyrna dipUma (Figure 4) . This 

 powerful swimmer may frequently be seen at the surface, in- 

 shore, or far at sea and is definitely known to attack humans. 

 It is colored ashen-gray above, fading to white below. The 

 hammerhead is readily distinguished by the widely expanded 

 head with eyes at the outer edge. It may attain 15 feet in length 

 or more, and closely related species are distributed throughout 

 tropical warm temperate zones of all oceans, including the Medi- 

 terranean Sea. 



The bites of sharks are almost always severe, and death is 

 usually due to loss of blood and to shock. Fifty to eighty percent of 

 those bitten may die. Severe skin abrasions are suffered by brushing 

 against the very rough, sharp skin of sharks. First aid requires 

 prompt and vigorous action to control the bleeding and shock. The 

 patient must be kept warm. Use of large gauze pressure bandages 

 held with elastic bandages may be best to control the bleeding. 

 Tourniquets have been described as dangerous and impractical for 

 use by the inexperienced person. Hospital or surgical treatment is 

 required . Intravenous fluids should be administered as soon as pos- 

 sible, while whole blood may be required later. 



The prevention of shark bite depends mostly upon avoidance of 

 the contact. When sharks are present, persons should not dangle 

 arms or legs in the water. Injured swimmers should be removed 

 from the water quickly. If obliged to be in the water, the use of 

 dark clothing and equipment is preferred. All movements should be 

 slow and purposeful to avoid attracting sharks. Should sharks ap- 

 pear and individuals unavoidably remain in the water, they should 

 remain perfectly still. In a number of instances, curious sharks have 

 left the scene under these circumstances. In other cases, they have 

 been successfully thrust away by use of a large stick. In close con- 

 tact, some sharks have departed when struck on the snout, eyes or 

 gills. However, attempts to wound the shark may be useless and 

 may only aggravate the situation. 



BARRACUDA 



Barracudas are an extremely pugnacious and dangerous fish 

 which may attain a length of 6 to 8 feet. They have a large mouth 

 equipped with knife-like canine teeth, and, being swift swimmers, 

 strike rapidly and ferociously. They are feared more than sharks in 

 some areas of the West Indies. 



Great Barracuda, Sphyraena barracuda (Figure 5), which is 

 found off Brazil, in the West Indies, and northward up to Florida, 

 appears to be the most feared fish. It is also known in the Indo- 

 Pacific area from the Red Sea to the Hawaiian Islands. Other 

 species are widely distributed throughout the tropical and subtropical 

 waters of the world. Among these species are some which differ 

 greatly in nature and size and are never known to attack man, how- 

 ever, none of them seems to exhibit any undue fear of man . 



Barracudas are attracted by almost any bright or colored object 

 in the water and may attack indiscriminately. This is especially true 

 in murky water where it appears they are handicapped by poor vision, 

 but because of their predatory nature they attack anyway. 



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