Aquatic assessment in the Lake Tumba landscape, RDCongo : fish diversity and conservation

Abstract: The 80,000 km² Lake Tumba Landscape (LTL) is the only one of the 12 UN Priority Conservation Areas in Africa with a focus on freshwater ecosystems. Surprisingly little though is known about fish in this area. The objective of this thesis is to increase knowledge of fish occurrence in the LTL. The first paper uses catch statistics to quantify the fish populations in three LTL streams against the background of their physical and chemical environments (Paper I). All the species caught represented 23% of the known Congo Basin fish species. The Lebomo stream had higher catches during the dry than wet season, but this was not the case for the Bambou and Bongo streams. Significant differences in fish species composition between the streams were found, but this probably related more to pH and nutrient status than land use. These streams yield too little fish to be a regular part of the local diet, but the streams may be important reservoirs of biodiversity in the landscape, and also serve as ”sentinels” of change for larger downstream aquatic ecosystems. The aim of the second paper was to characterize the breeding sites of Tilapia congica in order to guide the zoning process for fishery management in Lake Tumba. For this purpose, the nest depths, distances from the shoreline, exposure to sunlight and habitat types were measured. Four extensive groups of breeding sites were located near where tributary rivers entered the lake. All nest sites were exposed to the sun and 90% of sites were within 51-250m of the shoreline. The breeding substrates for T. congica are sandy and under hippo grass (Vossia cuspidata) (48%) or water lilies (Nymphaea stellata) (39%). Tilapia congica shared 42% of its nesting sites with other fish species, so protecting the breeding habitat of T. congica would likely help other species. The major overall findings of this thesis are that there is much diversity in the running waters of the LTL, and that knowledge of the location as well as the seasonality of fish breeding patterns can inform better fish management. At this point, it is not clear what effect land use/land cover has on the fishery, but better monitoring can establish a baseline against which eventual changes can be defined in relation to changes in land use and even climate.

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