Age and growth of two populations of West Coast steenbras Lithognathus aureti in Namibian waters, based on otolith readings and mark-recapture data

Abstract

Age and growth of West Coast steenbras Lithognathus aureti, sampled from two separate populations (northern and southern) along Namibla's coast, was determined using sectioned otoliths, and the results were validated using mark-recapture data. For both populations, the special three-parameter Von Bertalanffy growth model described growth adequately. Growth of the southern population was described by the equation Lt = 73.556(1-e-0.065(t+3.92)) cm and for the northern population by Lt = 84.601(1-e-0.088(t+2-756) cm. Environmental conditions, such as difference in sea surface temperature, density-dependent competition for food, or biochemical genetic variations between the two populations, are possible reasons for the geographic differences found in the growth rates and length-at-age. Slow growth and longevity are characteristics of West Coast steenbras that make it extremely susceptible to overfishing; careful management of the resource is therefore essential.