The Nile perch (Lates niloticus) is a large, freshwater fish that provides a classic example of the dangers of invasive species. Introduced to Lake Victoria in the 1950’s, the Nile perch can weigh up to 200kg , and is highly valuable to the fishing industry for both food and sport fishing. Problems arose when the carnivorous fishes diet led to extensive predation of endemic cichlid species.
Covering over 68,000km2, Lake Victoria is the largest tropical lake in the world, which supports a diverse community of several hundred endemic cichlid species. In just 60 years, approximately half of the lakes cichlid have become extinct, from an original 400 estimated species to a current estimate of just 200. Upon introduction, Nile perch first fed on the abundant cichlid supply, but in recent years have moved towards a shrimp and minnow diet as a result of the decline. Overall populations have seen a dramatic decline, cichlids, which used to make up 80% of the fish biomass, now comprise just 1%.
This rapid ecological impact would be alarming in any ecosystem, however it is of particular importance in this case for several reasons. Firstly, the cichlid speciation in Lake Victoria is very young with little genetic diversity, increasing the chances of substantial losses in genetic diversity and the Allee effect. The species found here are endemic, not occurring anywhere else in the world, and thus would be unrecoverable if they become extinct in this single body of water. Finally, this problem has developed in a very short time, with no natural mechanisms to prevent further damage. Further complexities are added by the commercial value of sustaining the Nile perch population, eutrophication due to sewage disposal in the lake depleting food supplies for cichlids, and local fisheries being outcompeted.
In response to the growing problems at Lake Victoria, there have been some attempts to aid the situation. Researchers have begun captive breeding of some of the cichlid species, funded by the IUCN. The Lake Victoria Research Team continue to investigate and monitor the lakes ecology and the threats to its wildlife. Conservation laws, such as fines for dumping sewage, have been established, particularly in Kenya, however conservationists must monitor both the implementation and effectiveness of these laws. OSIENALA, an NGO consisting of local communities that use the lake, was founded in 1992, and has helped local education about the lakes ecology whilst supporting the local community.
There are many challenges facing Lake Victoria, the Nile Perch has already had a major impact on the lakes unique ecology, but the problems are furthered by the key role of the lake in many peoples livelihood. Despite the problems, local and international efforts to target the threats and protect both ecology and the surrounding culture make a suitable starting point in protecting this highly threatened ecosystem.