Life-history traits (size at age, growth rates, size and age at maturity, size of near-term embryos and litter sizes) of bonnetheads, Sphyrna tiburo, were analysed to test for latitudinal differences by comparing data collected from three areas along Florida's Gulf of Mexico coastline between March 1998 and September 2000. A total of 539 sharks were collected during the study: 207 in north-west Florida (latitude ~30�N), 176 in Tampa Bay (~28�N) and 156 in Florida Bay (~25�N). Male and female bonnetheads in north-west Florida had the largest predicted asymptotic sizes (1007�mm and 1398�mm TL, respectively) and attained the largest estimated median size at maturity (830�mm and 944�mm, respectively) and the oldest estimated median age at maturity (3.0+�years and 4.0+�years, respectively). The largest near-term embryos (297�mm TL) were also collected at the highest latitude, but no latitudinal difference in litter size was found. These differences in life-history traits provide supporting evidence that a pattern of latitudinal variation exists. Male and female bonnetheads in north-west Florida also had the fastest growth rate compared with the other locations, supporting the hypothesis that growth rate is inversely related to the length of the growing season (i.e. a pattern of countergradient variation exists).

The swimming performance of hatcheryreared, juvenile shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus was studied in a laboratory swim tunnel at 20ЊC and 10ЊC. The mean 30-min critical swimming speed was not significantly different between species at either temperature (36.9 cm/ s for shovelnose sturgeon and 35.9 cm/s for pallid sturgeon at 20ЊC, 19.4 cm/s for shovelnose sturgeon and 15.0 cm/s for pallid sturgeon at 10ЊC). Free swimming (swimming without contact with the substrate) was observed less than 18% of the time at speeds greater than 15 cm/s. As speed increased, pallid sturgeon swam significantly less in the water column at 20ЊC; however, speed had no effect on percent free swimming among shovelnose sturgeon at 20ЊC. The results of this study indicate that, over the temperature and size range tested, shovelnose sturgeon and pallid sturgeon probably do not segregate in rivers due to different swimming or stationholding abilities * Corresponding

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In this report, seasonal changes in testicular structure and spermatogenesis in several shark species are reviewed, and new information concerning the bonnethead shark, Sphyrna tiburo, is presented. Shark species are separated into four categories based on the relationship between testicular GSI and mating season: 1) species that have a defined seasonal cycle in GSI and a defined mating season, 2) species that have a defined seasonal cycle in GSI and that mate year-round, 3) species that show no seasonal change in GSI but that have a defined mating season, and 4) species that show no seasonal change in GSI but that mate year-round. The testis of S. tiburo differs from the few species that have been examined in that 1) not all spermatogenic stages are present at all times of the year, 2) a n annual zone of degeneration that progresses through the testis is not present, and 3) there appears to be complete testicular regression and recrudescence.

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