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Evidence of stenotopy and anthropogenic influence on carbon source for two major riverine fishes of the Lake Victoria watershed

Authors

  • W. Oweke Ojwang,

    Corresponding author
    1. * Kenya Marine & Fisheries Research Institute, Kisumu Research Center, P. O. Box 1881, Kisumu, Kenya and Department of Biology, Boston University, Boston, MA 02215, U.S.A.
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  • L. Kaufman,

    1. * Kenya Marine & Fisheries Research Institute, Kisumu Research Center, P. O. Box 1881, Kisumu, Kenya and Department of Biology, Boston University, Boston, MA 02215, U.S.A.
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  • E. Soule,

    1. * Kenya Marine & Fisheries Research Institute, Kisumu Research Center, P. O. Box 1881, Kisumu, Kenya and Department of Biology, Boston University, Boston, MA 02215, U.S.A.
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  • A. A. Asila

    1. * Kenya Marine & Fisheries Research Institute, Kisumu Research Center, P. O. Box 1881, Kisumu, Kenya and Department of Biology, Boston University, Boston, MA 02215, U.S.A.
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‡Tel.: +1 671 353 6969; fax: +1 617 353 6340; email: ojwang@bu.edu

Abstract

Stable isotope analysis was used to investigate the migratory status and to determine the relative contribution of allochthonous and autochthonous sources of carbon for the major riverine fish species (Barbus altianalis and Labeo victorianus) in rivers draining the Kenyan side of Lake Victoria. The two fish species derived carbon from both C4 and C3 plant sources, although L. victorianus exhibited less enriched isotopic carbon values. Fish samples from stations under direct influence of effluents from sugar factories exhibited enriched δ13C signals. Assuming that this reflects carbon sourcing from riparian C4 plants, it suggests that carbon from terrestrial sources can be a major energy source in some rivers. This heavy carbon enrichment associated with sugar factories was spatially restricted and occurred in all seasons, implying that sub-populations of the two fish species are non-migratory. The large migratory populations of these two species, for which Lake Victoria was once famous, may be no more.

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