ICCS2004 Application Submission/Review

Abstract for
"Trophic structure of the fish communities in the Kyoga Basin lakes (East Africa) based on stable Nitogen and Carbon isotopes."


Trophic structure of the fish communities in the Kyoga Basin lakes (East Africa) based on stable δ15N and δ13C isotopes . Mbabazi D1., R. Ogutu-Ohwayo2, J.S. Balirwa1., R.E. Hecky3, F. Orach-Meza4, B. Makanga5, S.B. Wandera1 and G. Namulemo1 Fisheries Resources Research Institute,P.O. Box 343, Jinja, Uganda1 Lake Victoria Fisheries Organisation, P.O.Box 1625, Jinja, Uganda2 Biology Department, University of Waterloo, 200 University Avenue, Waterloo, ON, N2L-3G1; Canada3 Lake Victoria Environmental Management Project, P.O.Box 5, Entebbe, Uganda4 Zoology Department, Makerere University, P.O.Box 7062, Kampala, Uganda5 Abstract Until 20 years ago, Lake Kyoga had a similar fish fauna to that of Lake Victoria. Lake Victoria alone contained at least 500 fish species comprising at least 12 trophic groups out of at least 350 species, dominated by a monophyletic species flock of haplochromine cichlids, about 99% of them endemic exploiting virtually all food sources in the lake. Introductions of exotic species prompted by overfishing, and habitat degradation fuelled by an expanding human population resulted into reduction of the native species, number of trophic groups and led to the simplification of the lakes’ food web and therefore reduced ecological efficiency of the lake. Between 1998 and 2001 this study examined the trophic structure of the fishes present in Lake Kyoga, and the less impacted satellite lakes in its basin, using stable carbon (δ13C) and nitrogen (δ15N ) isotopes. Results indicated that, isotope composition of the fishes in the main lake Kyoga ranged from –25.4 to –13.8 ‰ for δ13C and 5.3 to 9.9‰ for δ15N. Among the satellite lakes, Bisina recorded the largest range both for δ13C (–25.9 to –11.3 ‰) and δ15N (3.2 to 10.4 ‰). Lakes Nawampasa and Nakuwa recorded the least ranges for δ13C (-24.4 to -21.7 ‰) and δ15N (4.1 to 6.3 ‰) respectively. Noteworthy, Lake Nakuwa with the least ranges in δ15N like Lake Kyoga contain the predatory Nile perch. The broad ranges in (δ15N) indicate a more diverse trophic status in the Nile perch free satellite lakes. The broad ranges in (δ13C) indicate a wide range of food sources. Lakes with less disturbance had a narrower range of food sources compared with the more disturbed ones. The Kyoga satellite lakes are important refugia for functional and species diversity lost in lakes Kyoga and Victoria and deserve targeted conservation measures to protect them.