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 methods successfully enhanced the visibility of growth rings: crystal violet staining of the centrum face, microscopic examination of the whole vertebra, with transmitted light and dark field, and ''bow tie'' sectioning of the vertebra. The results of the three methods were compared by using the average percentage error index and statistical means. Age and growth estimates were obtained from microscopic examination of the whole vertebra, the method which provided the most accurate ring counts 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 at maturity was 7 years (156 cm PCL) for females and 6 years (150 cm PCL) for males. The oldest aged female was 11 years (179 cm PCL), the oldest aged male was 10 years (179 cm PCL) old. Mean calculated growth rates were 24 cm/yr for the first three years, 11-13 cm/yr through adolescence, and 5-6 cm/yr after maturity. Back-calculated lengths were lower than observed lengths and Lee's phenomenon was apparent. In 83% of the vertebrae the band immediately after the change in angle was translucent. Opaque band deposition is assumed to occur in summer.