AGE AND GROWTH DETERMINATION OF THE BLACKTIP SHARK, CARCHARHINUS-LIMBATUS, FROM THE EAST-COAST OF SOUTH-AFRICA

Age and growth of the blacktip shark, Carcharhinus limbatus, from the east coast of South Africa were investigated by counting growth rings in vertebral centra. The vertebrae of 41 females (41-181 cm precaudal length [PCL]) and 51 males (42-182 cm PCL) were examined. Three method s successfully enhanced the visibility of growth rings: crystal violet staining of the centrum face, microscopic examination of the whole ve rtebra, with transmitted light and dark field, and ''bow tie'' section ing of the vertebra. The results of the three methods were compared by using the average percentage error index and statistical means. Age a nd growth estimates were obtained from microscopic examination of the whole vertebra, the method which provided the most accurate ring count s and gave the second highest reproducibility. The data for males and females were combined and the von Bertalanffy parameters obtained were L(infinity) = 193.6 cm PCL, K = 0.21 yr(-1) and t(o) = -1.2 yr. Age a t maturity was 7 years (156 cm PCL) for females and 6 years (150 cm PC L) for males. The oldest aged female was 11 years (179 cm PCL), the ol dest aged male was 10 years (179 cm PCL) old. Mean calculated growth r ates were 24 cm/yr for the first three years, 11-13 cm/yr through adol escence, and 5-6 cm/yr after maturity. Back-calculated lengths were lo wer than observed lengths and Lee's phenomenon was apparent. In 83% of the vertebrae the band immediately after the change in angle was tran slucent. Opaque band deposition is assumed to occur in summer.