AGE-DETERMINATION AND GROWTH OF THE BONNETHEAD SHARK SPHYRNA-TIBURO -A COMPARISON OF 2 POPULATIONS

From July 1982 to December 1986, a study of the age and growth of the bonnethead shark sphyrna tiburo was conducted in Tampa and Florida Bay s, Florida, USA. Tetracycline-injected sharks held in captivity and, t o a lesser extent, tagged, released and recaptured, were utilized for validating the annual nature of the rings (herein defined as the narro w, translucent regions) appearing on vertebral centra. The technique w as validated for all age groups (0 to 6 + yr) included in the study. M arginal increment analysis likewise suggested annual ring formation. T he rings formed during the winter, when water temperatures were lowest . Using the vertebral ring aging-technique, von Bertalanffy growth cur ves for males and females from both Tampa and Florida Bays were constr ucted. Growth of sharks born and held in captivity demonstrated that t he male and female growth curves diverge after approximately 1 yr and that mean sizes at age are statistically distinct after approximately 2 yr. In both populations, females grew to larger sizes than males and apparently are longer-lived. Reproductively mature females from Tampa Bay were significantly larger than those from Florida Bay.