Differential recovery and spatial distribution pattern of haplochromine cichlids in the Mwanza Gulf of Lake Victoria

Lake Victoria had a fish fauna dominated by 500 + species of haplochromines. In the 1980s, the haplochromines from sub-littoral areas of the Mwanza Gulf vanished almost completely. In the 1990s, a recovery of some haplochromine species was observed. To establish the status of the recovery, we studied their relative abundance and distribution pattern in the northern part of Mwanza Gulf in the years 2006 (monthly trawl hauls at 6 stations) and 2008 (bi-monthly trawl hauls at the same stations); the period after environmental changes. The data were compared with those of 1979/80 collected at the same stations before the period of environmental changes. The number of trophic guilds decreased from 12 in 1979/80 to nine in 2006 and 2008 with detritivores, zooplanktivores and oral mollusk shellers being the most abundant guilds. Detritivores were the dominant guild in 1979/80 (average 602 fish/haul) and 2008 (422 f/h) and the second most abundant guild in 2006 (175 f/h). Zooplanktivores were the dominant guild in 2006 (594 f/h) and the second most abundant guild in 1979/80 (159 f/h) and 2008 (270 f/h). Both in 2006 and 2008, oral mollusk shellers were the third dominant guild (27 f/h and 49 f/h respectively). Moreover, the study revealed that the resurgent trophic guilds were more widely distributed in the 2000s than in the 1970s. Possible causes for the recovery of the haplochromines including a decline in the Nile perch population, eco-morphological adaptations of the haplochromines and habitat extension are discussed.