Document: DAN-3-5-6

Conservation, harvest and human behavior in Lake Victoria fisheries.

SCHINDLER, D.E.* ¹, R.OGUTU-OHWAYO ² and J.F.KITCHELL ³

University of Washington, Seattle, WA 98195 USA ¹
Fisheries Research Institute, Jinja, Uganda ²
University of Wisconsin, Madison, WI USA ³

Abstract:
Despite the impressive progress that has been made towards developing a predictive understanding of the dynamics of interacting species, very little effort has been devoted towards embracing the roles of exotic species, and especially humans, in ecosystem dynamics. The food webs of Lake Victoria (East Africa) have been altered greatly by the interactive effects of exotic species and exploitation by fisheries. An exotic predator (Nile perch) has contributed to the extinction of more than 200 endemic fish species and presently threatens at least that many more. However, fisheries for the exotic species is a major economic activity in this region and their sustainability is a critical management concern. We used individual-based models calibrated to field data and fisheries catch data to investigate the ecological impacts of commercial fisheries on the structure and dynamics of the food web of Lake Victoria, and estimate the consequences of these impacts for the conservation of endemic fishes and sustainability of fisheries. Our analyses show that the size-selective mortality imposed by fishing strongly mediates the effects of exotic predators on the native food webs. We estimate that fishing presently reduces predation by the exotic predator on native species by >10 fold. Analyses that incorporate adaptive behaviors by fishers in response to changes in the exploited populations further reinforce the importance of humans as strong interactors in this system. Nile perch populations are especially vulnerable to overexploitation when fisher behavior is flexible and can track changes in population size-structure. Thus, in this ecosystem, adaptive human behaviors may actually benefit the short-term goals of conservation by reducing predation by an exotic species, but at the possible expense of the sustainability of an economically valuable resource.

Keywords: exotic species, fisheries, Lake Victoria

This abstract is being presented at: 1:15 PM in session:
Oral Session #62: Freshwater Fish Ecology.