Age and growth of two commercially imported sharks (Carcharhinus tilstoni and C. sorrah) from Northern Australia

Abstract

The age and growth of Carcharhinus tilstoni and C. sorrah, the two most abundant shark species in commercial gill-net catches off northern Australia, were investigated by the examination of vertebral rings. Corroborating evidence for age and growth estimates was obtained from length-frequency distributions and tag-recapture data. To aid validation of these estimates, tetracycline was injected into sharks at the time of tagging. Growth is relatively rapid in the first year of life: vertebral ageing indicated 17 cm growth in total length (TL) for C. tilstoni and about 20 cm for C. sorrah during the first year after birth. By the time the sharks are 5 years old, growth has declined to 8-10 cm per year in C. tilsoni and 5 cm per year or less in C. sorrah. The von Bertalanffy growth parameters for C. tilstoni are L_∞ = 194.2, K = 0.14, t₀ = -2.8 for females, and L_∞ = 165.4, K = 0.19, t₀ = -2.6 for males; for C. sorrah the parameters are L_∞ = 123.9, K = 0.34, t₀ = -1.9 for females, and L_∞ = 98.4, K = 1.17, t₀ = -0.6 for males. The greatest recorded ages for C. tilstoni were 12 years for females and 8 years for males, and for C. sorrah, 7 years for females and 5 years for males. Sexual maturity is reached early: at 3 to 4 years in C. tilstoni and 2 to 3 years in female C. sorrah.