Response to exploitation and life history characteristics of two Acanthurus fish species with divergent mating behaviour along the Kenyan coastline

Abstract

In reef ecosystems, vulnerability to exploitation is species-specific and may vary with natural abundance, life history characteristics, or ease of capture. Therefore, understanding the growth parameters and exploitation rate of individual species is important, because application of a uniform management strategy in species with different responses or vulnerability to exploitation can be inappropriate. In this study, growth parameters (length at first maturity, length at optimum yield, asymptotic length, growth constant, and growth performance index) and mortality from two Acanthurus fish species were compared, to deduce whether differences in species-specific traits (spawning mating behaviour) could lead to differences in exploitation rate. Despite comparable estimates of the von Bertalanffy asymptotic length (L) in the two species [A. triostegus (27.9–29.6) and A. leucosternon (26.1–27.4)], the growth coefficient constant (K) estimates for A. triostegus (0.85–1.23) were almost three to fivefold higher than those of A. leucosternon (0.29–0.38), suggesting that A. triostegus attains its maximum length faster than A. leucosternon. Length at first maturity (Lm), length at optimum yield (Lopt), and exploitation rate (E) were also different between the two species, specifically indicating exploitation beyond the sustainable yield in A. triostegus but not in A. leucosternon. The finding of a higher exploitation rate in A. triostegus as compared to A. leucosternon could suggest that regardless of similar body sizes, the former is more susceptible to exploitation.