Status of the estuarine-dependent riverbream Acanthopagrus berda (Sparidae) harvested by the multi-sectoral fishery in Kosi Bay, South Africa

Abstract

A stock assessment was undertaken for the tropical sparid Acanthopagrus berda harvested in the Kosi Bay estuarine system, northern KwaZulu-Natal, South Africa, by a multi-sectoral fishery using traditional traps and gillnets, and recreational angling using rod-and-line. Input parameters used in a catch curve analysis included age and growth parameters, and an estimate of natural mortality derived from life-history parameters. The values of spawner biomass-per-recruit estimated from this model, using different selectivity curves for the gear types used in the different fishing sectors, indicate that A. berda is likely to be reduced to around 24% of its unfished level of spawner biomassper-recruit by current levels of fishing mortality. These results indicate that A. berda in Kosi Bay is heavily overexploited. The longevity of the species, coupled with its late maturation, sex change and estuarine dependency, and the increasing catches of A. berda give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal.

Keywords: fishing mortality; natural mortality; selectivity; spawner biomass-per-recruit; yield-per-recruit

African Journal of Marine Science 2008, 30(1): 45–53