Habitat heterogeneity facilitates coexistence of native fishes with an introduced predator: the resilience of a fish community 5 decades after the introduction of Nile perch

The introduction of the large piscivorous Nile perch Lates niloticus (L.) into Lake Nabugabo, Uganda, coincided with a collapse of the native fish community and the development of a fishing industry dominated by Nile perch. Some native fish have persisted in the face of Nile perch predation through use of hypoxic wetlands that may serve as both structural and physiological refugia because Nile perch is sensitive to hypoxic stress. In this study, we analyzed one year of monthly sampling using experimental gill nets to describe the Lake Nabugabo fish community 50 years after the introduction of the Nile perch. Using a multivariate approach, we found that water depth and dissolved oxygen concentration were the main descriptors shaping the fish community distribution in the lake, and that Nile perch and its major prey, haplochromine cichlids, have contrasting ecological requirements. Comparison with previous studies over a 15-year period revealed an overall decline in the catch per unit effort of Nile perch and a resurgence of haplochromine cichlids in certain habitats. We suggest that differences in the abiotic requirements of Nile perch and haplochromines combined with heavy fishing on Nile perch have contributed to the resurgence of the native fauna. This highlights the importance of environmental heterogeneity in mitigating the impact of introduced species on recipient communities; and, in the case of the Lake Victoria basin, underscores the critical need to conserve ecotonal wetlands for their essential role as ecological refugia.