ASSESSMENT OF THE ECOLOGICAL DRIVERS OF FISH SPECIES DISTRIBUTION, DIVERSITY AND ABUNDANCE WITHIN THE LITTORAL ZONE OF LAKE VICTORIA, KENYA

Abstract

In the face of global environmental change, understanding and predicting the effect of abiotic parameters and biotic interactions on fish communities is key to conservation and species recovery. A fish’s habitat includes all the required physical factors and chemical factors in their environment. Massive fish kills affecting both wild fish and farmed fish in Lake Victoria has necessitated the need for robust data on fish responses to changes in abiotic and biotic parameters to inform fisheries management intervention. The overall objective of this study was to assess the interaction of fish species with abiotic and biotic factors including food habits; and determine which of these factors govern their distribution and abundance within the littoral zones in Lake Victoria. Sampling was done at 10 sites covering the entire Kenyan shoreline of Lake Victoria. Habitat differences were graded based on assessment of bottom substrate type and determination of key physico-chemical parameters while water samples were collected for analysis of nutrient fractions, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Oxidation Reduction Potential (ORP) and chlorophyll-a. The fish communities were described on the basis of diversity, abundance and food habits. A Generalized Linear Model (GLM) was used to evaluate the impacts of abiotic factors on fish abundance and distribution. Additionally, multivariate analysis was conducted to establish the relationship between environmental attributes and fish species and plotted on Principle Component Analysis (PCA). To assess the food habits, the food Prominence Value (PV) was calculated and a food web developed using the “food web R package” to show the trophic levels and interactions of the different functional groups. 15 fish species were recorded with haplochromine cichlids being the most abundant fish group. Abiotic drivers of fish species distribution and abundance were observed to be species specific. The most important predictors of variation in both richness and abundance were turbidity, DO, conductivity, chlorophyll-a and ORP while primary productivity across river mouths is a major contributor of fish diversity. Dietary flexibility has promoted opportunistic feeding among littoral fish communities thereby promoting co-existence which in-turn has maintained the high diversity along the littoral zone. Fish species specific responses to abiotic and biotic parameters established form the study are critical towards assessment of fish kills in Lake Victoria. The thresholds generated can be applied in monitoring changes in the water quality towards development of an early warning system for improved fisheries management in the East African region. Exploitation of muddy habitats for bait fish is recommended targeting Synodontis victoriae while the rocky shores are most preferred for harvesting of haplochromines to support the bait industry in the Nile perch fishery of Lake Victoria.