The conservation of the fishes of Lake Victoria,Africa: an ecological perspective

Synopsis The African Great Lakes are considered to be dynamically fragile ecosystems that are relatively resistant to minor changes with which they have co-evolved but vulnerable to major perturbations such as overfishing, the introduction of alien species and pollution. These lakes are inhabited by large species flocks of cichlid fishes which are characterised by a complex structure of interaction both between and within species, as is typical of mature ecosystems. Major perturbations, such as the disruption of trophic interactions through the introduction of alien fishes, may reverse the domination of relatively precocial, specialised forms and result in the creation of conditions that are conducive to the survival of more altricial, generalised forms with strong colonising abilities. The introduction of Nile perch and Nile tilapia, as well as other alien fishes, into Lake Victoria, combined with overfishing for the indigenous cichlid species, has resulted in marked changes to the fish communities and the fisheries that depend on them. The most important impacts of the Nile perch appear to be predation and aggressive effects whereas those of the tilapias include hybridization, overcrowding, competition for food and possibly the introduction of parasites and diseases. While the three proposed methods of conserving the indigenous flocks of cichlid fishes (captive propagation, reducing Nile perch stocks and closure of the haplochromine trawl fishery) all have merit, the changes that are occurring in Lake Victoria are basically irreversible. The highest priority should be to assist the governments of the riparian countries (Tanzania, Uganda and Kenya) with monitoring and research programmes and to support their policies of non-introduction of further alien fishes into any of the African Great Lakes so as prevent the same cycle of events from occurring, for example, in Lakes Tanganyika and Malawi. The diverse animal and plant communities of the African Great Lakes are a heritage of all mankind and it is the duty of every country to play a role in their conservation. It is therefore proposed that an internationally funded research programme should be mounted on the African Great Lakes on the scale of the tropical forest biome project of the IUCN. Editorial