PATTERNS OF THE REMNANT CICHLID FAUNA IN SOUTHERN LAKE-VICTORIA

During the years 1984-1987 Lake Victoria in East Africa experienced wh eat is probably the largest mass extinctions of contemporary vertebrat es. Within a decade about 200 endemic species of haplochromine cichlid s disappeared. The extinctions that occurred in the 1980s have been do cumented predominantly on species of offshore and sub-littoral waters in the Mwanza Gulf of southern Lake Victoria. Although the littoral fa una of southern Lake Victoria had not been examined in detail, their d iversity seemed less affected by the changes in the ecosystem. We give results of the first comprehensive inventory of the littoral cichlid fauna in southern Lake Victoria and discuss its conservation status. W e also report on new developments in the sub-littoral fauns after 1990 . more than 50 littoral and 15 sub-littoral stations were sampled betw een the years 1991 to 1995. Of the littoral stations, 34 were sampled for the first time. One hundred sixty three species of haplochromines were collected. Of these, 102 species were previously unknown. About t wo thirds of them live in rocky areas that were sampled for the first time. Littoral rocky habitats harbored the highest diversity. Since 19 90, however, 13 more species disappeared from established sampling sta tions in littoral habitats. Fishing practices, spreading of exotic fis hes, water hyacinth, and eutrophication are considered important threa ts to the littoral fauna. Also in the upper sub-littoral the number of species declined further. On deeper sub-littoral mud bottoms individu al and species numbers increased again, although they are nowhere clos e to those found before the Nile perch (Lates niloticus) upsurge. This fauna differs from the well studied pre-Nile perch fauna. At well-est ablished sampling stations, the sub-littoral zone is dominated by prev iously unknown species, and some known species have performed dramatic habitat shifts.