Age and growth of the queen mackerel Scomberomorus plurilineatus from KwaZulu-Natal, South Africa

The age of the western Indian Ocean pelagic scombrid Scomberomorus plurilin eatus was determined by counting rings in whole otoliths. Validation using marginal increment analysis was inconclusive and it was assumed that a sing le opaque band was laid down annually in the otolith of this species. The m aximum observed age was six years. S. plurilineatus is fully recruited to t he fishery at the age of one year and 50%-maturity is attained at the age o f two years. For the age-length data, the von Bertalanffy model was found t o be the best fitting growth model. Growth was also estimated using a lengt h-based method, Shepherd's Length Composition Analysis, but this proved to be inappropriate because of the seasonality of the catches of S. plurilinea tus in KwaZulu-Natal. Based on a catch curve analysis, fishing mortality wa s estimated to be 0.28 yr(-1). Preliminary per-recruit analyses revealed th at spawner biomass of S. plurilineatus is currently reduced to 50% of its u nfished level and it appears that the species Is optimally exploited. (C) 1 999 Elsevier Science B.V. All rights reserved.