Changes in fish species composition and their abundance in Lake Naivasha, Kenya

Abstract

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, lengthfrequency 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 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 abundant tilapiine species to near local extinction. The
study also confirms a restricted 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 mouth of River Malewa, currently exhibits a lake-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 areas may 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.