Preliminary estimates of population size and capture rates of mature Acanthopagrus berda in the Kosi lakes system, South Africa, using mark-recapture methods

Abstract

Population size estimates and capture rates by various fishing techniques of mature estuarine bream, Acanthopagrus berda, were determined in the Kosi lakes system using mark-recapture methods. The total population size of mature A. berda was estimated to be 45257 (95% confidence interval: 31 589-74429) based on fish recaptured in fish traps and 56 112 (95% confidence interval: 25505-374080) using recaptures from recreational anglers. Fish traps were estimated to catch about 5% of the mature population of A. berda annually, while recreational rod and line angling and traditional spearfishing accounted for about 1 % and 0.2% of the mature population respectively. Limited mark-recapture data for other species of fishes in the lakes yielded annual capture rates by fish traps ranging from 2.4% to 5.8%. These levels of fishing appear low enough to be sustainable, but evidence from a long-term monitoring programme indicates an increase in overall fishing effort in the Kosi lakes between 1984 and 1996 and a three-fold increase in the proportion of the A. berda population caught annually. However, there is no evidence from available catch per unit effort (CPUE) data that current levels of harvesting of A. berda are unsustainable. This needs to be confirmed through modelling of the A. berda stocks and continued monitoring of CPUE in all components of the Kosi lakes fishery. In the meantime, an increase in fishing effort directed at this species is not recommended .

S. Afr. J. Zool. 1997,32(4)