Recent changes in fish communities of the equatorial Lake Naivasha, Kenya

Abstract

Changes in fish species composition and abundance i n Lake Naivasha were investigated monthly for a period of 12 months. Data were obtained both from e xperimental surveys as well as commercial fish landings. The structure metrics considered included species abundance and composition, length- frequency and physico-chemical attributes. Results of the study showed that the fishery is currently dominated by the recently introduced common carp, Cyprinus carpio accounting for over 95% of the total fish landings, with the naturalized fish popul ations performing dismally both in terms of abundance as well as health conditions. The entry o f the common carp into Lake Naivasha may have completely transformed the lake’s ecosystem integri ty, driving the initially abundant tilapiine specie s to near local extinction. The study also confirms a re stricted distribution of Micropterus salmoides to rocky-bottomed habitats of Hippo Point and Crescent Lake. Conversely, the long-fin barb, Barbus paludinosus, initially confined to the north swamp and the mout h of River Malewa, currently exhibits a lake-wide distribution. The changing climatic condi tions as manifested in the lake level recessions ma y be a real threat to the fish stocks in the lake. Hu man activities in the catchment areas may also have contributed to the recent ecological changes witnes sed in Lake Naivasha. This study proposes a number of recommendations with a view to ensuring e cosystem integrity and consequent sustainable fisheries of Lake Naivasha.