Impact of environmental change, species introductions and ecological interactions on the fish stocks of Lake Victoria

Abstract

Evidence is presented and discussed for the causes of the changes in the Lake Victoria fish community that have occurred since the beginning of the 20th century. The traditional fishery concentrated on Oreochromis esculentus, Bagrus docmac and Labeo victorianus, which were caught with primitive equipment causing low fishing mortality. Increases in demand, together with gear improvements, increased the fishing mortality and brought new species into the fishery. By the middle of the century catch rates were well down on those of 50 years earlier. Serious depletion of important stocks of food fishes could have been caused by the introduction of four exotic tilapiine species in the late 1950s, drastic changes in water levels brought about by heavy rains in the early 1960s, combined with increased use of beach seines and fine-mesh nets. At about the same time the Nile perch, Lates niloticus was introduced but made little contribution to the fishery for a decade or more after its introduction. At present the fishery is dominated by the Nile perch, with significant contributions from Oreochromis niloticus and Rastrineobola argentea, an endemic species. There is increasing evidence that the lake is becoming eutrophic.