NATURAL HISTORY OF THE SANDBAR SHARK 



35 



tlie smaller size and less robust body form. The 

 sandbar shark swimming in the open sea or in 

 an exhibition tank may be distinguished readily 

 from the bull sliark because of its comparatively 

 more erect and higher first dorsal fin placed 

 slijihtly further forward, its somewhat larger eye. 

 its somewliat longer snout, and its generally less 

 robust body form. 



Altiiough the sandbar shark inhabits both the 

 eastern and westeiii ])arts of the Atlantic, this 

 report concerns only one population of the spe- 

 cies centered along the southeastern coast of the 

 United States. 



Species of the genus Eulamia usually are sharks 

 of the continental shelves, oceanic banks, and 

 island terraces throughout their life cycles in 

 contrast to most species of Carcharhinus, which 

 are typically shallow-water forms having their 

 nursery grounds in brackish or fresh-water estu- 

 aries, river mouths, or along continental beaches, 

 or in island lagoons. Euhimia milberti occupies 

 the shoalest habitat range of the 5 or 6 species of 

 Eulamia of the Atlantic coa.st of North America 

 and enters estuaries to some extent to give birth 

 to its young. Its habitat preference may thus 

 be said to be intermediate between that typical 

 of Eulainia and that typical of Carcharhiniis. 



The sandbar shark is clearh' separable from all 

 other species within its geographical range and 

 exhibits little variation in form and in tooth 

 count. 



The sandbar shark. Eulmnia miJherti. is found 

 in waters of suitable depth, southward from Cape 

 Cod along the Atlantic coast. It occurs in the 

 Gulf of Mexico and along the Caribbean coast 

 of Central America to Costa Rica. It occurs 

 casually off the northern coast of Cuba and along 

 the western edges of the Bahama Bank, but jirin- 

 cipal elements of the population are confined to 

 tlie western side of the Gulf Stream. Sandbar 

 siiarks occur as bottom dwellers out to depths of 

 100 fathoms (extreme record 135 fathoms) and 

 nuiy occasionally move out in midwater to oceanic- 

 situations. The principal part of the range of 

 adults, away from the nursery grounds, has been 

 shown by commercial catches to be in depths of 

 10 to .30 fathoms. 



The sandbar shark populations of the northern 

 and westein jiarts of the (hilf of Mexico and the 

 Caribbean coast of Centi'al America are small 



and are probably not self-sustaining without re- 

 cruitment from the main population by migra- 

 tory wandering or failure of such orientation 

 mechanisms as the species may po.ssess. 



The primary nursery range lies in shallow 

 coastal waters of less than 20 fathoms from 

 Cape Cod. Mass., to Cape Canaveral, Fla.; and 

 a secondary nursery range lies in the Gulf of 

 Mexico west of Mobile Bay and north of the 

 28th parallel. Newborn sandbar sharks are not 

 known outside the general geographical limits of 

 the nursery ranges, but the young sharks uiove 

 offshore to deeper (and warmer) water during 

 the winter. 



The species is migratoiy with annual move- 

 ments of some segments of the population ex- 

 tending at least 600 miles. Sandbar sharks in 

 migratory passage around the southern tip of 

 Florida hold to depths of 50 fathoms or more 

 in apparent avoidance of coral reef areas. Their 

 vertical distribution in the southern part of the 

 species* geographical range, however, is some- 

 what deeper than in the northern part, suggest- 

 ing thermal influence in the selection of habitat. 



There is reason to believe that female sandbar 

 sharks are inhibited from feeding at the time of 

 birth of the young and for a short time there- 

 after. Nursery grounds are away from the nor- 

 mal range of the males thus giving additional 

 protection to newborn young. Feeding appears to 

 be inhibited in male sandbar sharks during peri- 

 ods of active courtship. 



Young of nearly uniform size, numbering from 

 1 to 1-i in each litter, are born in early summer 

 (probably also in late spring) off northern Flori- 

 da. The average number in a litter is 9 and 

 the modal number 10. The gestation period is 

 from 8 to 12 months' duration, with 9 months 

 estimated in the latitude of northern Florida. 

 Both oviducts ai'e functional, a single embryo de- 

 velops in each shell membrane, aiul a pseudopla- 

 centa with a simple stalk (yolk-sac attachment) 

 forms. 



Length at birth is apjn'oximately 24 to 25 

 inches in the latitude of northern Florida but 

 may be less in higher latitudes. Young born 

 in the vicinity of Long Island. N. Y.. have been 

 i-ejioi-ted to be 22 to 23 inches long at birth, and 

 even smaller young have been reported from 

 Chesajieake Bay. 



