GEOGRAPHIC-VARIATION IN REPRODUCTION BETWEEN 2 POPULATIONS OF THE BONNETHEAD SHARK, SPHYRNA-TIBURO

A study of two populations of the bonnethead shark, Sphyrna tiburo was conducted in Florida Bay and Tampa Bay, Florida from September 1982 t o December 1986. The maintenance of sharks in captivity at the Marine Science and Conservation Center in the Florida Keys, and the collectio n of sharks from widely separated geographical areas allowed the exami nation of latitudinal variation in reproduction. Several reproductive parameters were found to differ: (1) size at maturation, (2) age at ma turation, (3) time of fertilization, (4) rate of embryonic development , (5) size at birth, (6) the energetic investment in producing offspri ng, (7) gestation period, and (8) the incidence of infertility. Averag e litter size and maximum age of females was not different between the two populations. These contrasting life history parameters are not ea sily explained. Food limitation and seasonal differences between the t wo areas are considered as factors controlling reproduction in these p opulations. It is noteworthy that the average size of adult females in Tampa Bay is significantly greater than that of Florida Keys sharks. This size difference may be important in explaining the observed diffe rences in reproduction.