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

The age of the western Indian Ocean pelagic scombrid Scomberomorus plurilineatus was determined by counting rings in whole otoliths. Validation using marginal increment analysis was inconclusive and it was assumed that a single opaque band was laid down annually in the otolith of this species. The maximum observed age was six years. S. plurilineatus is fully recruited to the fishery at the age of one year and 50%-maturity is attained at the age of two years. For the-age-length data, the von Bertalanffy model was found to be the best fitting growth model. Growth was also estimated using a length-based method, Shepherd's Length Composition Analysis, but this proved to be inappropriate because of the seasonality of the catches of S. plurilineatus in KwaZulu-Natal. Based on a catch curve analysis, fishing mortality was estimated to be 0.28 yr^-1. Preliminary per-recruit analyses revealed that spawner biomass of S. plurilineatus is currently reduced to 50% of its unfished level and it appears that the species is optimally exploited.