Fish species composition, size structure and distribution in non-Trawlable areas of Lake Victoria (Tanzania) with emphasis on Mwanza gulf and Mori bay

Abstract

Fish diversity studies in littoral non-trawlable areas of Lake Victoria (Tanzania) were undertaken during six systematic surveys (November 2000 to December 2002). Information on fish species composition, size structure as well as spatial and temporal distribution was generated from gill-netting, beach-seining and electric fishing. Lates niloticus, indicated a declining trend in composition from 78.9% in March 2001 to 5.1% in July 2002. The species, however, increased to 40.6 % in catch composition as of December 2002, exhibiting somewhat inverse trends in distribution with Oreochromis niloticus and haplochromines in the lake fisheries. The surveys identified over 50 species for which 42 and 38 species were respectively encountered in Mwanza Gulf and Mori Bay. The two areas registered consistently high Shannon Wiener diversity indices. Subsequent annual monitoring of species richness and rarity in randomly fixed sites (21 in Mwanza Gulf and 13 in Mori Bay) promoted the selection of fish diversity hotspots. Comparatively, many rare and threatened species were encountered in Mori Bay than Mwanza Gulf and resource conservation measures by establishment of an aquatic reserve in Mori Bay as opposed to an aquatic park in Mwanza Gulf are discussed.