Removing the liver from a large silky shark. 



prior to 1950, most of the commercial 

 shark fishing operations in this coun- 

 try were suspended. 



Sharks interfere with commercial 

 fishing operations in many instances. 

 In the Gulf of Mexico, sharks occa- 

 sionally cause severe economic losses 

 through their habit of biting and tearing 

 the trawl nets to get at the catch. An 

 estimated 20 percent loss in salable 

 fish due to shark damage has been 

 cited for the tuna longline fisheries of 

 the world. Also, in many localities, 

 the seasonal abundance and the local 

 concentration of some species of sharks 

 force cessation of gill-net operations 

 and otherwise influence the choice of 

 gear and the location of fishing 

 grounds. 



In 1958 the American Institute of 

 Biological Sciences (AIBS) inaugurated 

 a Shark Research Panel for the pur- 

 pose of studying all aspects of the 

 biology of elasmobranch fishes. One 

 of the functions is to compile a shark- 

 attack file. Records accumulated 

 through this effort show that, in 1959, 

 there were 39 shark attacks on man 

 involving at least 18 fatalities. 



SKATES AND RAYS 



Numbers and General Distribution 



Included in the same group with the 

 skates and rays are the sawfishes, 

 guitarfishes, electric rays, stingrays, 

 eagle rays, and mantas. All told, prob- 

 ably about 400 species of the group are 

 known. 



The group as a whole is widely 

 distributed. Like the sharks, more 

 species, and probably more individuals, 

 are found in tropic and subtropic seas 

 than in colder ^^aters; but there are 

 several species that do frequent the 

 cold-water regions of the world, in- 

 cluding some skates that live in water 

 as cold as 29° F. Skates, rays, and 

 their close relatives may be found from 

 the shoreline to a depth of about 1,500 

 fathoms. At least one species occa- 

 sionally splashes along the very edge 

 of the sea, on the tide line of the 

 beaches, in search of the small crus- 



taceans that characterize the tidal 

 zone. Below 1,500 fathoms, our knowl- 

 edge of the bottom fauna is scanty, but, 

 if skates and rays are present, they 

 undoubtedly are very scarce. 



The eagle rays, mantas, and a few 

 others are capable of tremendous leaps 

 from the water, and authentic reports 

 are available of these large fishes 

 towing moderate-size vessels for rela- 

 tively great distances at high speeds. 

 Other skates and rays probably rely on 

 short bursts of speed followed by 

 periods of drifting or lying quietly on 

 the bottom rather than on sustained 

 high speed or s\vimming po^ver. Even 

 the mantas, usually seen only on the 

 surface of the water, probably spend 

 some of their time resting quietly on 

 the bottom. Stingrays (Dasyatis) are 

 bottom dwellers and are sometimes 

 found partly buried in the sand with 

 only the eyes and the area surrounding 



10 



