Preliminary estimates of age of the bronze whaler Carcharhinus brachyurus (Chondrichthyes: Carcharhinidae) from southern Africa, with a review of some life history parameters

Abstract

Counts of growth bands in sectioned vertebral centra were used to estimate the ages of 61 bronze whalers Carcharhinus brachyurus collected between March 1984 and June 1988 from southern Africa. Estimates of Von Bertalanffy parameters for the observed data were: L _∞ = 384,8, K = 0,0385, t ₀ = −3,477. The t₀ value overestimates the gestation, which is thought to be between 8 and 24 months. Growth in bronze whalers appears to be slower than in any Carcharhinus spp. previously studied. Maximum size recorded during this study was 294 cm total length (TL) for a male and 288 cm TL for a female, and the maximum ages recorded were 30 and 25 years respectively. Age at sexual maturity has been calculated at 13–19 years for males and 19–20 years for females. Differential mortality rates appear to operate on juveniles (Lee's phenomenon). Arguments are presented that indicate two separate populations: one distributed from the Western Cape eastwards and the other from just south of Walvis Bay northwards. The slow growth rate, low fecundity and high age at sexual maturity make the bronze whaler extremely vulnerable to overfishing.