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

Abstract

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 Nile perch population expanded and predation rates increased, many of the endemic fish species disappeared, total fishery yield increased nearly fourfold, and fishery-related employment approximately doubled. Ecological changes in this system now occur rapidly, are due largely to human actions, and have profound socioeconomic effects. We used a bioenergetics model of Nile perch predation rates to evaluate the consequences of previous, current, and future fishery exploitation patterns and their ecological implications. The analysis produced three main conclusions: (1) Development of fisheries based on large-mesh gill nets reduced total predation by Nile perch to ≈40% of that estimated 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 ≈25%. (3) The combination of fishing methods could reduce total predation to ≈10% of previous levels. Reduction in estimated predatory impact corresponds with recent reports of recovery by haplochromine populations and increased fish species diversity in regions (e.g., Napoleon Gulf, Mwanza Gulf, and Winam Gulf) where fisheries are locally intense.