Fish species and trophic diversity of haplochromine cichlids in the Kyoga satellite lakes (Uganda)

Abstract

Prior to the 1980s, lakes Kyoga and Victoria previously supported an exceptionally diverse haplochromine ¢sh fauna comprising at least 11 trophic groups. The species and trophic diversity in these lakes decreased when the introduced Nile perch depleted haplochromine stocks. From December1996 to October1998, we studied species and trophic diversity of haplochromine ¢shes in six satellite lakes without Nile perch in the Kyoga basin and compared them with the Kyoga main lake against historical data from Lake Victoria where Nile perch were introduced. Forty-one species were found in the study area, of which, the Kyoga satellite lakes contributed 37 species in comparison to only 14 from the Kyoga main lake. Analysis of trophic diversity based on 24 species that contained food material revealed seven haplochromine trophic groups (insectivores, peadophages, piscivores, algal eaters, higher plant eaters, molluscivores and detritivores) in the Kyoga satellite lakes in comparison to two trophic groups (insectivores and molluscivores) in the Kyoga main lake. Many of the species and trophic groups of haplochromines depleted by the introduced Nile perch in lakes Kyoga andVictoria still survive in the Kyoga satellite lakes. This is attributed to the absence of Nile perch in those lakes. Nile perch has been prevented from spreading into the satellite lakes by swamp vegetation that separate them from the main lakes. If these swamps prevent Nile perch from spreading into the lakes, it is possible to conserve ¢sh species, especially haplochromines, which are threatened by introduction of Nile perch in the main lakes.

Salmonid or nonsalmonid lakes: predicting the fate of northern boreal fish communities with hierarchical filters relating to a keystone piscivore

“…Our current study thus provides strong evidence from a large-scale study to support Jackson et al's (2001) generalization from both our landscape patterns and long-term results from our manipulations (i.e., introductions, rotenone eliminations, and observations of the fish community that reestablishes). Protection from piscivores in ''safe havens'' formed by natural landscape fragmentation from impassable barriers in drainage networks has been recognized as necessary for the persistence of diversity in other fish communities worldwide (e.g., smallbodied fish species diversity (Robinson and Tonn 1989); galaxiid diversity (Townsend 2003); cichlid diversity (Mbabazi et al 2004)). Thus, we suggest that low-connectivity river networks may fulfil a crucial role in maintaining biodiversity by allowing sensitive species safe havens by filtering off detrimental biotic interactions.…”

Differential decline and recovery of haplochromine trophic groups in the Mwanza Gulf of Lake Victoria

“…The hypothesis that Nile perch had a large impact on haplochromine biomass is supported by the observations of a partial recovery of haplochromines in Lake Victoria, Lake Nabugabo and Lake Kyoga, following declines in Nile perch due to heavy fishing pressure (Ogutu-Ohwayo, 1995;Witte et al, 2000;Chapman et al, 2003;Getabu et al, 2003;Mbabazi et al, 2004). On the other hand, the incomplete recovery of mainly one trophic group in Lake Victoria suggests that Nile perch may not be the only factor (see below).…”

“…In contrast, in several small satellite lakes of Lake Victoria and Lake Kyoga, where Nile perch was absent, haplochromines remained abundant (Ogutu-Ohwayo, 1993;Namulemo and Mbabazi, 2000;Aloo, 2003, Mbabazi et al, 2004. However, it has to be mentioned as a confounding factor, that in some of these lakes the water was also clear (Kaufman et al, 1997;G.…”

“…However, it was still present in the adjacent lakes Kayanja, Kayugi and Manywa where Nile perch had not been introduced (OgutuOhwayo, 1993). On the other hand, according to Mbabazi et al (2004), several piscivores, including H. (P.) argenteus (maximum size 20.2 cm SL; Greenwood, 1967), survived the Nile perch introduction in Lake Kyoga. During a more recent sampling programme (2000)(2001)(2002)(2003)(2004), however, no piscivorous haplochromines were encountered in this lake (G. Namulemo, pers.…”

Interspecific Hybridization of Tilapiines in Lake Victoria, Kenya

“…Lake Victoria has a number of satellites: Kanyaboli, Namboyo and Sare, on the Kenyan side and Nabugabo on the Ugandan side. Satellite lakes have been recognized as important functional refugia for fish fauna, since they are connected to main lakes by extensive papyrus swamps that are anoxic to invasive predators like L. niloticus [29,31,[35][36][37]. Anoxic conditions prevent the natural entry of L. niloticus to these habitats, which are inhabited by indigenous fish fauna tolerant to low dissolved oxygen conditions, and this helps to conserve indigenous fish stocks (a valuable food resource for the local communities) from predation pressure, unless the invasive predator is introduced there by man.…”