Age and growth of the common blacktip shark Carcharhinus limbatus from Indonesia, incorporating an improved approach to comparing regional population growth rates

Abstract

Age and growth estimates from length-at-age data were produced for the common blacktip shark Carcharhinus limbatus from Indonesia. Back-calculation techniques were used due to a low sample size (n = 30), which was dominated by large, mature sharks. A multi-model approach incorporating Akaike’s information criterion with a bias correction (AIC_c) was used to estimate growth rates, with the von Bertalanffy growth function (VBGF) providing the best fit for the separate sexes using the back-calculation data. These age and growth estimates were then compared to those of other populations of C. limbatus from the USA and South Africa using a combination of VBGF parameters and instantaneous (empirical) growth rates at birth (dL/dt₀) and maturity (dL/dt_mat). In comparison with populations from the USA, C. limbatus from Indonesia grow substantially larger and are more similar to South African populations. Differences in empirical growth rates were also determined between the populations, although this was not detected by the VBGF parameter k. This occurred because the parameter k is a measure of the rate at which a population reaches asymptotic length (L_∞) and is not a measure of growth. This study demonstrated that the use of dL/dt₀ and dL/dt_mat to measure and compare empirical growth rates can be a useful addition to life-history studies.

Keywords: Akaike’s information criterion (AIC), back-calculation, Carcharhinidae, elasmobranch, life history