Fish community dynamics in an inland floodplain system of the Okavango Delta, Botswana

Tropical floodplain fish populations fluctuate at temporal scales and understanding the variability in these systems will contribute to comprehensive management of these resources. Therefore, the aim of this study was to assess the dynamics of a floodplain fish assemblage. Data were collected using standard methods between 1999 and 2009 from the delta's panhandle. Various analytical tools (e.g. CCA, SIMPER, ANOVA, etc.) were used to assess fish assemblage dynamics at seasonal and annual scales. ANOVA and cluster analyses showed that the fish assemblage underwent significant changes along the seasonal hydrograph, while index of relative aboundance (%IRI) revealed that the fish assemblage was dominated by Clarias gariepinus, Schilbe intermedius and Hydrocynus vittatus respectively. These species, including Clarias ngamensis and Marcusenius altisambesi, contributed more than 50% to variations in fish assemblage structure along the seasonal hydrograph (based on SIMPER analysis). Furthermore, canonical correspondence analysis (CCA) revealed a significant (p = 0.004) association between environmental factors and fish assemblage structure. CCA analysis also showed that spawning for different species is associated with various environmental factors. Annually, results showed that C. gariepinus dominated the fish assemblage during low flood years, while S. intermedius dominated during high flood years. Detrended correspondence analysis (DCA) showed that the hydrological gradient had a significant effect on fish assemblage structure at an annual scale, while SIMPER analysis established significant variations in fish assemblage structure among years characterized by different hydrological features. One major conclusion we made was that fish assemblages are stochastically different at an annual scale. This study contributes knowledge to floodplain fish ecology and thus enhances fisheries management.