Aquatic Conservation in the Lake Victoria Region

In the field of aquatic conservation, I have focused on patterns of biodiversity loss and recovery in the Lake Victoria basin of East Africa and management options that reconcile fisheries sustainability with biodiversity conservation (for a history of basin, see Balirwa et al. 2003 in my publication list).
This has been collaborative work with colleagues from North America, Europe, and Africa and involves a close association with the Fisheries Resources Research Institute (FIRRI) and the Makerere University of Uganda (where I serve as an honourary lecturer in the Department of Zoology).

The explosive speciation of haplochromine cichlid fishes in Lake Victoria is unrivaled among vertebrates; however, over 40% of its endemic fishes disappeared between 1980 and 1986 associated with various anthropogenic perturbations, including the introduction of the predatory Nile perch. Our research has demonstrated the importance of physiological refugia in modulating the impact of introduced predators on indigenous fish communities, and highlighted the importance of wetland conservation for persistence of ecotonal communities (Chapman et al. 1996, Chapman and Chapman 1998, Rosenberger and Chapman 1999, 2000, Schofield and Chapman 1999, 2000, Chapman et al. 2002).

It is a very dynamic and exciting time in the Lake Victoria basin; recent intense fishing of Nile perch has coincided with a resurgence of a subset (albeit small) of the basin fish fauna (Balirwa et al. 2003, Chapman et al. 2003). These recovering populations will encounter an environmental milieu much changed from that of 20 years ago, and it is reasonable to expect that resurging species will differ from pre-Nile perch conspecifics in ecosystem function and other characters. Some species have survived periods of dramatically reduced population abundance, or persisted in refugia with turbid water.

We anticipate that some of these fishes now represent genetically mosaic stock derived from two or more pre-refugial species. Studies using a combination of molecular genetics, morphometrics, and breeding experiments will be required to study gene flow patterns among the resurging haplochromines, and we are beginning work on this very exciting, albeit concerning, issue in collaboration with Dr. Ole Seehausen (University of Bern) and Dr. Les Kaufman (Boston University). Other species have survived generations of intense predation pressure by Nile perch in open waters. For such species, we anticipate differences between pre- and post-Nile perch populations with respect to predator-associated morphology.

In collaboration with Dr. Tom Dewitt (Texas A & M) and Brian Langerhans (North Carolina State University) we are comparing whole-body morphology of a suite of indigenous fishes between lakes with and without Nile perch, and between contemporary species and archived specimens from the pre-Nile perch era. We also anticipate changes in gill morphology in response to selection pressure in deep swamp refugia, and we are addressing this issue by comparing gill morphometrics between contemporary deep swamp and ecotonal refugees and archived conspecifics.

The faunal resurgence in the Lake Victoria region has given new hope for maintenance of fish diversity in the basin and renewed motivation for management options that marry fishery sustainability with biodiversity conservation (Balirwa et al. 2003). Modeling efforts by colleagues working in the lake basin suggest that conservation of indigenous fishes could actually help to maximize Nile perch production rates. Key to determining an optimal fishing pressure is an understanding of a) the pattern of resurgence, b) prey selection by Nile perch, and c) Nile perch growth rate under different prey regimes.

In our long-term study of Lake Nabugabo, we have witnessed a full cycle of interaction between indigenous fishes and Nile perch. In collaboration with FIRRI and Makerere University, we hope to provide a quantitative picture of fish community dynamics in Lake Nabugabo and reconstruct the history of Nile perch diet and growth over the past decade (though aging studies and diet data from a 10-year record). Aging tropical fish is notoriously difficult because of the weak temperature fluctuations. However, over the past 2 years, we have validated aging techniques for the Nile tilapia from Lake Nabugabo using thin-sections of otoliths in collaboration with Gladys Bwanika (Makerere University) and Dr. Debra Murie (University of Florida).

We are now working on application of this technique to Nile perch (Ph.D. research of Winnie Nkalubo). This should provide opportunities for more sophisticated understanding of Nile perch growth and production in response to a resurging prey base.