Spatial-temporal dynamics of water hyacinth, Eichhornia crassipes (Mart.) and other macrophytes and their impact on fisheries in Lake Victoria, Kenya

Invasive aquatic macrophytes in Lake Victoria including water hyacinth (Eichhornia crassipes) exhibit periodic cyclical patterns of decline and proliferation with attendant ecological and economic impacts. This study aimed to monitor the extent of macrophytes and other invasive weeds on Lake Victoria to establish their impact on fisheries. The study employed a combination of remote sensing and geographical information system (GIS) techniques to estimate the coverage of water hyacinth and other invasive macrophytes. Data on fish landings and their respective market values were acquired from the Electronic Fish Market Information Service (EFMIS) database, which is hosted by the Kenya Marine and Fisheries Research Institute (KMFRI). Analysis of consistent temporal satellite data showed that the weeds frequently cover sheltered bays and river mouths. These areas of Winam Gulf had higher coverage (average 5000 ha) of macrophytes than the open waters (<200 ha). The proliferation of the invasive weeds showed fluctuations over the study period reaching the highest peak between September and November 2016. Other aquatic plants that have invaded the littoral areas of Lake Victoria include Egeria densa, Ceratophyllum demersum and Potamogeton spp. Increased coverage of macrophytes was found to be correlated inversely with the commercially important tilapia Oreochromis niloticus, but not with other species. The study concludes that there is a need for sustained monitoring of the invasive macrophytes alongside ecosystem modelling studies using the available time series data to clearly identify the ecological factors that drive water hyacinth dynamics and predict more precisely its impact on the fishery.