36 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Although approximately equal numbers of 

 males and females are born, catches indicate a 

 much larger proportion of adult females than 

 adult males except off the coast of Nicaragua. 



Females produce young no oftener than every 

 other year, but since only about 18 percent of 

 the adult females taken in the fishery were found 

 to be gravid, this apparent low productivity may 

 be the result of the low proportion of males in 

 the adult population. 



In samples from Florida, adult males are from 

 71 to 89 inches in total length and adult females 

 from 72 to 92 inches. Average weights of adults 

 in samples from southern Florida are for males, 

 114 pounds, and for nongravid females, 145 

 pounds. 



The mean length and length-frequency distri- 

 bution (size range) by sex in catches believed to 

 have been made from single large schools closely 

 approximated the mean length and size range by 

 sex of all adults of the species from southern 

 Florida. No appreciable difference was noted in 

 mean lengths and size ranges of adults in sam- 

 ples taken at various seasons on the east coast of 

 Florida, the west coast of Florida, and the Carib- 

 bean coast of Nicaragua and Costa Rica except 

 the constant difference of about 4.2 inches be- 

 tween average lengths of adult males and adult 

 females. Differences in the average lengths of 

 gravid and nongravid females were small. 



The rate of growth is not known. Indirect 

 evidence indicates that it may be very rapid until 

 sexual maturity is reached, after which little 

 growth occurs. 



The sandbar shark feeds chiefly on small bot- 

 tom-dwelling fishes, moUusks, and crustaceans. 

 It rarely swallows indigestible materials. Uni- 

 formly plump livers suggest that mUberti has little 

 difficulty in meeting its requirements for food. 



From commercial catches it is estimated that 

 the population is small in species mass as com- 

 pared with many teleosts. 



The only important predators on sharks are 

 other sharks and not necessarily sharks of other 

 species. Full-grown sandbar sharks, unless in- 

 jured or caught on a shark line, appear rarely 

 to be eaten by other sharks. Young sandbar 

 sharks are e.specially vulnerable to attack by 



large sharks, particularly by bull sharks, but 

 also to a lesser extent by tiger sharks, dusky 

 sharks, and full-grown sharks of tlieir own 

 species. 



LITERATURE CITED 



Backus, Richard H, 



1957. Notes on western North Atlantic sharks. 

 Copeia, No. 3, pp. 246-248. 

 Backus, Richard H., Stewart Springer, and Edgar L. 

 Arnold, Jr. 



1956. A contribution to the natural history of the 

 white-tip shark, Pterolamioips longimanus (Poey). 

 Deep-Sea Research, vol. 3, pp. 178-188. 



Beebe, William, and John TeeVan. 



1928. The fishes of Port au Prince Bay, Haiti. 

 Zoologica, vol. 10, No. 1, pp. 1-279. 

 BiGELow, Henry B., and William C. Schroeder. 



1948. Sharks. In Fishes of the western North At- 

 lantic. Memoir No. 1, Sears Foundation Marine 

 Research, pt. 1, pp. 59-576. 

 1953. Fishes of the Gulf of Maine. U.S. Fish and 

 Wildlife Service, Fishery Bulletin 74, vol. 53, pp. 

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 Brocklesby, H. N. 



1941. The chemistry and technology of marine 

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 Canada. Fisheries Research Board of Canada, 

 Bull. 59, pp. 1-442. 

 BuDKER, Paul. 



1938. Les cryptes sensorielles et les denticules cutan^s 

 ' des Plagiostomes. Annales de I'lnstitut Ocdano- 

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 BuLLis, Harvey R., Jr. 



1955. Preliminary report on exploratory longline 

 fishing for tuna in the Gulf of Mexico and the 

 Caribbean Sea. Commercial Fisheries Review, 

 vol. 17, No. 10, pp. 1-15. 

 Cadenat, John. 



1950. Rapport sur les S^laciens des cotes du S6n6gal 

 et plus sp^cialement sur les Requins. Bulletin de 

 I'lnstitut francais d'Afrique noire, vol. 12, pp. 

 944-975. 



1957. Notes d'ichtyologie ouest-africaine. XVII 

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 franpais d'Afrique noire, vol. 19, .ser. A, No, 1, 

 pp. 274-294. 



Captiva, Francis J. 



1955. Longline gear used in yellowfin tuna explora- 

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 pp. 16-20. 

 CowLEs, Raymond B. 



1945. Temperature induced sterility and evolution. 

 Science, vol. 101, No. 2618, pp. 221-222. 

 Evermann, Barton W., and Millard C. Marsh. 



1902. The fishes of Puerto Rico. Bulletin of the 

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