Abstract:

An ecological study of wetlands was undertaken in northern Lake Victoria (East Africa) between 1993 and 1996 with a major aim of characterising shallow vegetation dominated interface habitats, and evaluating their importance for fish, in particular, for the stocked and socio-economically important Oreochromis niloticus LINNÉ (the Nile tilapia). From field and laboratory experiments, five major habitat types could be defined by the type of the dominant emergent macrophyte at the shore from the more than 40 identified plant species along a 110 km shoreline. These were: Cyperus papyrus L. (papyrus), Phragmites mauritianus Kunth (reeds), Typha domingensis Pers. (bulrush), Vossia cuspidate (Roxb.) (hippo grass), and the alien floating Eichhornia crassipes (Martius) Solms-Laubach (water hyacinth). From digital data, considerable long term changes in the shoreline wetland landscape of the lake were discerned and appeared to be primarily associated with increasing human activity (e.g., agriculture, biomass harvests) which had resulted into a 5 % reduction of wetland cover. Inspite of the absence of a well developed euhydrophyte community (e.g., Potamogeton and Ceratophyllum), and increasing infestations with E. crassipes mats, the width of then littoral zone was established by secchi transparency as being about 50 - 70 m away from the shallow (less than 1 m deep) vegetation fringe sloping to between 2 and 4m in depth at its outer fringe. Hyd