Rapid biological assessment of the fishery potential of Xonxa Dam, near Queenstown, South Africa

Abstract

Rapid biological assessments have been proposed as the most cost-effective approach to identify suitable target species and to set initial catch and fishing effort levels for new fisheries. Xonxa Dam, a turbid irrigation dam situated in the White Kei catchment, rural Eastern Cape, is shown to provide fisheries potential for two alien species — smallmouth yellowfish Labeobarbus aeneus and sharptooth catfish Clarias gariepinus — that had been previously introduced into the catchment. Rapid appraisal of the biology, relative abundance, and population dynamics of the fish was effected during three sampling events in 2007. Using a combination of empirical yield and dynamic pool models, it was shown that two discrete fisheries can be developed. For L. aeneus a 60 mm stretched mesh gill net fishery could harvest 23 t y^–1 and for C. gariepinus a longline fishery could yield 4 t y^–1. The combined fisheries could be valued at c. R135 000 (USD 18 000) per annum. Periodic monitoring would be necessary; firstly, to ensure that spawner biomass per recruit is not reduced below 40% of current levels and, secondly, to refine the potential harvest available from the resource once harvesting is initiated.