The Influence of Flooding on Fish Species Diversity and Fisheries Patterns in the Floodplain Lakes of Lower Tana River, Kenya

Abstract

Floodplain fisheries resources are under frequent disturbances due to seasonal variation in flood peaks and intensity. This study investigated the influence of flooding on fish biodiversity and fisheries patterns in the floodplain lakes of lower Tana river, Kenya. Fish diversity and abundance in the floodplain lakes were assessed in relation to changes in space and flooding period. Influence of patterns of hydrological connectivity and water quality on fish assemblages were determined. The impacts of seasonal flooding on annual fishing pattern and governance in the Tana River delta lakes was also investigated. Fish was sampled by using monofilament gillnets, and six water quality parameters (pH, temperature, dissolved oxygen, electrical conductivity, salinity and water clarity (turbidity)) recorded using multi-metre probe (YSI Model 85/50) and turbidity tube at three sampling points in each lake in pre-flood, during flood and post-flood period. Thirty-two fisher-folk were interviewed across the entire study area using semi-structured questions. A total of 2982 fish comprising 15 species in 9 families, were captured. The predominant species in the floodplain lakes were Zanzibar barb (Enteromius zanzibaricus, 41%), Gregori’s labeo (Labeo gregorii, 11%), Red-fin robber (Brycinus affinis, 8%) and Sabaki tilapia (Oreochromis spirulus, 7%).Lake Gumba and Kongolola had the highest Margalef’s richness index (2.06 and 2.07) respectively. Shannon Weiner diversity index was highest at Lake Dalu (2.16) while fish found at Lake Shakababo was least diverse (1.67). Two-way ANOVA on transformed data showed a statistically significant effect of sampling period on fish species abundance (p<0.01). Non-metric multidimensional scaling (nMDS) plots showed a high similarity of fish assemblages during floods in the floodplain lakes. Pearson’s correlation matrix showed fish abundance was positively correlated with increasing dissolved oxygen (p<0.01), and water depth (p<0.05). The length-weight regression lines suggested normal fish growth patterns and the calculated relative condition factors indicated fish in the floodplain lakes were generally in good body condition. Although hydrological connectivity showed inconsistent association with fish species composition and abundance, findings of this study suggested that preservation of river-floodplain connectivity was important in maintaining fish species diversity in the floodplain lakes. Fisheries patterns indicated that communities did not entirely depend on fishing. Fisheries governance structures existed; however, they essentially were non-functional due to seasonality of floodplain lakes.