THE NILE PERCH IN LAKE VICTORIA - INTERACTIONS BETWEEN PREDATION AND FISHERIES

Introduction of the exotic Nile perch (Lates niloticus) into Africa's Lake Victoria accelerated decline of the diverse, endemic ichthyofauna , altered food web structure, and created valuable fisheries. As the N ile perch population expanded and predation rates increased, many of t he endemic fish species disappeared, total fishery yield increased nea rly fourfold, and fishery-related employment approximately doubled. Ec ological changes in this system now occur rapidly, are due largely to human actions, and have profound socioeconomic effects. We used a bioe nergetics model of Nile perch predation rates to evaluate the conseque nces of previous, current, and future fishery exploitation patterns an d their ecological implications. The analysis produced three main conc lusions: (1) Development of fisheries based on large-mesh gill nets re duced total predation by Nile perch to approximate to 40% nf that esti mated during the late 1970s, when Nile perch densities were greatest. (2) Expansion of recent intensive beach seine and small-mesh gill net fisheries for juvenile Nile perch could reduce total predation to appr oximate to 25%. (3) The combination of fishing methods could reduce to tal predation to approximate to 10% of previous levels. Reduction in e stimated predatory impact corresponds with recent reports of recovery by haplochromine populations and increased fish species diversity in r egions (e.g., Napolean Gulf, Mwanza Gulf, and Winam Gulf) where fisher ies are locally intense.