Species Distinction and the Biodiversity Crisis in Lake Victoria

Abstract

Until the 1970s, the fish fauna of Lake Victoria in East Africa was dominated by about 500 endemic haplochromine cichlid species, which comprised about 80% of the demersal fish mass. The cichlids were extremely diverse ecologically; however, the small diversity in gross morphology and the presence of intraspecific variation made it difficult to distinguish among species. In the first half of the 1980s, the Nile perch Lates niloticus, an introduced predator, suddenly boomed and cichlids declined dramatically. During the same period eutrophication increased strongly. With the decline of Nile perch catches in the 1990s, the cichlids showed some recovery. These events have triggered many studies and debates. Disagreements about the severity and causes of the decline often stemmed from considering the cichlid flock as a single unit owing to the lack of proper taxonomic and ecological knowledge. By studying cichlid communities, trophic groups, and individual species, researchers uncovered differential impacts that helped them to unravel the causes of the changes. It seems that lakewide Nile perch predation and eutrophication had the strongest impact and that the fishery only had a local effect. Knowledge of the differential decline and recovery of the haplochromine cichlids and the underlying causes is important for the proper management of biodiversity and the fishery in Lake Victoria. Consequently, knowledge of the systematics of cichlids is a key issue in managing the lake.