134 Commercial Shark Fishing in the Caribbean Area 



Figure 49 



Family Sphrynidae, Hammerhead Sharks. 



Figure 49. Sphyrna zygaena, Common Hammerhead. 



Description: Trunk strongly flattened from side to side; the 

 front contour of head with a deep depression opposite each nostril 

 and a shallow depression midway between each nostril and the 

 mid-line of the head. The mid-line, however, is evenly convex and 

 has no indentation as has Sphyrna diplana and S. tudes; the dis- 

 tance from nostril to eye is only about 1/2 as great as the diameter 

 of the eye (about as great as eye in diplana) ; the corners of the 

 mouth are slightly in front of the rear margin of the head or 

 "hammer"; diameter of eye about 1/3 as long as head in front of 

 mouth ; length of first gill opening a little less than diameter of 

 eye; fifth gill opening over origin of pectoral fin; the teeth are 

 broadly triangular and there are 15 teeth on each side of upper jaw 

 and 13 on each side of lower jaw which also has a small tooth in 

 the center; the 1st upper tooth is nearly symmetrical and erect 

 but the others are strongly oblique; the lower teeth resemble the 

 uppers toward corners of mouth except that they are a little 

 smaller, but the 4 teeth next to center of mouth are narrower and 

 less oblique than the uppers ; free rear margin of second dorsal 

 is about twice the vertical height of the fin and about equal to 

 front margin ; rear margin of anal fin deeply concave. 



Color: Deep olive-leaden or brownish gray above, paler on sides, 

 shading into pure or grayish white below ; tips or margins of fins 

 more or less dusky ; the pectoral fins are black-tipped in some speci- 

 mens but not in others. 



Size: Born at a length of about 20 inches; adults appear to 

 mature at about 8 to 9 feet. They are often caught up to 10 or 

 11 feet and occasionally to 13 feet. 



Habits: A strong swimming shark often seen at surface with 

 tips of first dorsal and caudal fins exposed. Many are found far 

 out at sea as well as close inshore, where small ones are often 

 taken with beach seines. Their diet consists chiefly of fish, com- 

 monly sting rays and small sharks, including their own kind. They 

 also eat shrimps, crabs, barnacles and other Crustacea, as well 

 as squid. 



Range: Tropical and warm temperate belts of the Atlantic. In 

 the western Atlantic it is found from southern New England to 

 Uruguay, straying northward to Nova Scotia and southward to 

 northern Argentina. Many previous records are confused with its 

 close relative, S. diplana, but it is undoubtedly widespread along: 

 the middle Atlantic coast of the United States, the West Indian- 

 Caribbean region, and the coast of northern Brazil. 



