Validated age and growth of the dusky shark, Carcharhinus obscurus, from Western Australian waters

Abstract

Age and growth of Carcharhinus obscurus was studied by vertebral ageing techniques. The annual formation of growth bands in the vertebrae was validated with oxytetracycline-injected individuals at liberty up to 1481 days. Growth-band counts of vertebral samples from 305 individuals ranging in size from 63 to 282 cm fork length were used to construct growth curves. Assuming a mean size at birth of 75.3 cm, estimates of von Bertalanffy growth parameters for males were: L_∞ = 336.5 cm and K = 0.045 year^–1. Growth parameters for females were: L_∞= 354.4 cm and K = 0.043 year^–1. The age at maturity was estimated to be 17–22 years for females (220–250 cm), and 20 – 23 years for males (230–243 cm). The oldest animal aged was a 32-year-old female 274 cm in length. Growth-rate estimates based on vertebral ageing for animals up to 5 years of age are similar to those from tag–recapture studies on the same population. The results of the present study were similar to those for C. obscurus from the south-western Indian Ocean and the western North Atlantic Ocean, indicating that age and growth are similar among these populations.