A retrospective assessment of the stock status of Otolithes ruber (Pisces: Sciaenidae) as bycatch on prawn trawlers from KwaZulu-Natal, South Africa

Abstract

The sciaenid fish Otolithes ruber commonly occurs as bycatch in prawn trawl catches along the East African coast. Most of the trawl catches of this species are discarded because of their low commercial value. In order to evaluate the stock status of this species off the KwaZulu-Natal coast of South Africa, a spawner-biomass-per-recruit (SBPR) assessment was conducted, based on trawl bycatch information collected between 1989 and 1992. Natural mortality (0.68 y⁻¹) was estimated to be higher than fishing mortality (0.53 y⁻¹), and the age at first capture (1y) was lower than the age-at-50% maturity (1.7y). The assessment indicated that O. ruber was overfished during the period 1989–1992, with a likely SBPR level at 33% of the unfished level. However, subsequent changes to the fishery, including seasonal closures, an increase in mesh size and a substantial decline in fishing effort, could have improved the status of the South African stock of O. ruber in South African waters.