Species composition , yield and predator/prey relationship of Lake Liambezi

Abstract

6 Abstract The purpose of this study was to document the transformation in species composition brought about by the drying of the lake since 1985. The annual yield harvested by the local fishermen and the effect of fishing activities by the fishermen on the predator-prey relationship of Lake Liambezi were also noted. The field surveys took place once every season in collaboration with the MFMR surveys, over a 12 month period. 1195 fish were sampled from the lake. Total of 955 fish were caught with the monofilament gill nets, while 240 fish were caught with the multifilament gill nets. Eight fish families were recorded. Thirty five fish species were identified from Lake Liambezi experimental gear catches (Peel, 2011) (Appendix 1). The Cichlidae family was represented by most species (ten), with the Cyprinidae in second place with seven species and Mormyridae in third place with four species. Oreochromis andersonii, Serranochromis macrocephalus and Oreochromis macrochir accounted for 64.9%, 21.3% and 6.3%, of all catches according to the index of relative importance, respectively. Seven species (Barbus barnardi, Barbus bifrenatus, Barbus paludinosus, Barbus unitaeniatus, Ctenopoma multispine, Labeo cylindricus, Labeo Lunatus, Marcusenius altisambesi, Micralestes acutidens, Pollimyrus castelnaui, Tilapia ruweti, Pseudocrenilabrus philander and Rhabdalestes maunensis) were recorded from the lake after 2001 but were not recorded before 1986, while 4 species (Hydrocynus vittatus, Serranochromis robustus, Serranochromis longimanus and Sargochromis giardi) that were recorded from the lake prior to its drying up were not recorded during this study. Species richness was high in the experimental gear (29 species) than in the gill net catches (14 species). Multifilament gill nets had higher species richness (14 species) than the monofilament gill nets (13 species). The variety and relative abundance of species are high for the fishery independent data (experimental gears), comparing to fishery dependent data (fishermen gill nets). Species diversity and richness results on fishermen gill nets show that fishermen are fishing selectively and not across the entire range of fish. The annual yield (2 581.8 tons) has doubled compared to previous values (600 to 800 tons) recorded before the dry period by Van der Waal (1990). Monofilament gill nets had relatively higher catch rates than multifilament.