Most, or all, of the maximum 

 recorded sizes contained in the table 

 refer to female sharks, and, indeed, 

 the females of all shark species studied 

 for this attribute average somewhat 

 longer with the average weight ap- 

 preciably greater than that of males. 

 On the Atlantic coast of the United 

 States, for example, adult male sand- 

 bar sharks vary from 5 feet 10 inches 

 in length to 7 feet 4 inches, whereas 

 female adults vary from 6 feet to 7 

 feet 8 inches. This represents an 

 average 5 percent longer length for the 

 females, and this longer length is ac- 

 companied by an average 25 percent 

 greater weight. 



Food and Feeding Habits 



All sharks are primarily predators 

 in the sense that they all feed on animal 

 life. The variety of animal life con- 

 sumed, however, is almost limitless, 

 and nearly all sharks excepting perhaps 

 such forms as the specialized basking 

 sharks, are secondarily scavengers. 

 Some sharks appear to be indiscrimi- 

 nant in their feeding habits. Curiously, 

 the largest kno^vn species feed on the 

 smallest prey, and some of the smallest 

 sharks consume relatively large crea- 

 tures. 



exploratory research vessel Oregon 

 have confirmed this behavior. Whale 

 sharks have also been observed to 

 drive tuna fishermen out of their fishing 

 racks. But on the basis of accumulated 

 evidence, the whale shark is probably 

 not ordinarily aggressive toward large 

 creatures including man. It probably 

 swallows large objects only if they are 

 taken incidental to its regular feeding 

 activities. This, however, is sufficient 

 reason for treating these huge and 

 powerful sharks with caution. 



A few sharks, including the white 

 shark and the tiger shark, nornaally 

 attack large and active prey. Other 

 sharks, including the snnaller hammer- 

 heads, and small blacktip sharks seem 

 to prefer crustaceans and small fishes. 

 The tiger shark, which would normally 

 be expected to obtain its food by active 

 pursuit and capture of other fishes, 

 sometimes haunts steamer lanes to 

 gather in garbage. A large tiger shark, 

 captured by the crew of the Oregon, 

 contained not only food that had been 

 thrown overboard several hours ear- 

 lier, but also tin cans and milk cartons. 

 Coastal fishermen frequently complain 

 about sharks of several species which 

 follow their vessels and tear up the nets 

 to obtain the fish contained within. 



The huge whale sharks and basking 

 sharks are primarily filter feeders. 

 These sharks s^vim with their mouths 

 open and strain or filter out small 

 planktonic organisms as the ■water, 

 coming in through the mouth, passes 

 over sievelike gill rakers and out 

 through the gill slits. Examination of 

 stomach contents reveals that these 

 large sharks filter great quantities of 

 small Crustacea and minute fishes in 

 this manner, and such small prey con- 

 stitutes the primary source of food for 

 them. On the other hand, there is little 

 doubt that the whale sharks also, oc- 

 casionally, consume larger prey. 

 Fishermen have reported that whale 

 sharks, feeding at the surface on great 

 schools of small fishes, occasionally 

 trap tunas which are also feeding on 

 the small fishes and which, in their 

 quest for food, follow the small fishes 

 straight into the whale shark's mouth. 

 Observations from the Bureau's 



Large sharks such as the ^vhite 

 shark, the dusty shark, and the white- 

 tip eat porpoises' when they can cap- 

 ture them. Porpoises are much faster 

 than sharks and can outrun them or 

 drive them away. If, however, a por- 

 poise is weakened through fatigue or 

 severe injury and is isolated, it may 

 meet a sudden end in an attack by 

 sharks. Observations, made from the 

 Bureau's research vessel Oregon, have 

 substantiated tales of porpoises ac- 

 tively driving sharks a'way from their 

 young and of schools of porpoises, the 

 members of which would take turns 

 driving off attacking sharks and rest- 

 ing. At other times, however, porpoises 

 and sharks may even feed together on 

 trash fish throw^n from a boat, and the 

 porpoises apparently have sufficient 



'porpoises are marine mammals. The term "dolphin" 

 is sometimes used for these animals, but "porpoise" is 

 probably preferable because "dolphin" is used also tode- 

 note a bony fish commonly taken by sport fishermen. 



