Abstract

Miguel Jover, CerdaAna and TomásVidal

Changes in fish species composition and abundance in Lake Naivasha were investigated monthly for a period of 12 months. Data were obtained both from experimental 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 carpioaccounting for over 95% of the total fish landings, with the naturalized fish populations performing dismally both in terms of abundance as well as health conditions. The entry of the common carp into Lake Naivasha may have completely transformed the lake’s ecosystem integrity, driving the initially abundanttilapiine species to near local extinction. The study also confirms a restricted distribution of Micropterus salmoidesto rocky-bottomed habitats of Hippo Point and Crescent Lake. Conversely, the long-fin barb, Barbuspaludinosus, initially confined to thenorth swamp and the mouth of River Malewa, currently exhibits alake-wide distribution. The changing climatic conditions as manifested in the lake level recessions may be a real threat to the fish stocks in the lake. Human activities in the catchment areasmay also have contributed to the recent ecological changes witnessed in Lake Naivasha. This study proposes a number of recommendations with a view to ensuring ecosystem integrity and consequent sustainable fisheries of Lake Naivasha.