Development of a fish index of biotic integrity (IBI) for satellite lakes within Yala swamp, Lake Victoria Basin, Kenya

Abstract

This study evaluated and tested ten fish community attributes for use in developing a fish-based Index of Biotic Integrity (IBI) for assessing the biotic integrity of Lakes Kanyaboli and Sare in Yala Swamp within Lake Victoria basin, Kenya. Fish assemblages were sampled for a period of three months using beach seining at sampling stations selected from the 1\"10 sites. Physico-chemical water quality parameters were detennined for the two lakes and correlated with fish attributes. Nine out of the ten fish couununity attributes evaluated showed significant correlations' (p<O.05) with the physico-chemical parameters and therefore qualified as metrics for development of the fish IBI for each site. These metrics were mean number of individuals per seine haul percentage of individuals as Oreoclirontis esculentus, percentage proportion as planktivores, percentage proportion as generalists, percentage proportion as introduced individuals, percentage proportion as carnivores, percentage proportion as natives, total number of species and Shannon- Wiener diversity index. Historical fish data from previous studies was used to develop reference baseline conditions for the two lakes while metrics not in the historical data were scored following trisection technique. Lake Kanyaboli was categorized as being of fair biotic integrity (overall IBI score = 33) and Lake Safe was classified as being of poor biotic integrity with a score of 23 out of the maximum expected score of 45. It is concluded that the Index of Biotic Integrity (IBI) method can be used to assess the ecological health and biotic integrity of the two satellite lakes and other aquatic habitats within the Lake Victoria basin. However the IBI developed in this study based on fish assemblages will need further validation and refinement in order to eliminate the confounding effects of anthropogenic influences such as overfishing .