FISH ABUNDANCE AND DIVERSITY DURING THE PRE- AND POST-IMPOUNDMENT PERIODS OF THE BLACK VOLTA AT BUI, GHANA

Abstract

The fisheries of the Black Volta near the Bui dam in Ghana were studied during the pre- and post-impoundment periods between February 2011 and December 2012. The primary objective was to assess the ecological impact of the dam on the fisheries. During the survey, a sampling unit was considered as a fishers’ catch per canoe per day. A three-level stratified random sampling approach was adopted. The first stratum which was defined by four designated hydrological seasons in the study area was as follows: dry season (January to March); pre-wet season (April to June); wet season (July to September); and post-wet season (October to December). The second stratum was defined by the three impoundment periods: pre-impoundment (March to May 2011); immediate post-impoundment (June to December 2011); and late post-impoundment (January to December 2012). The third stratum, on the other hand which was defined to improve sampling for accuracy was: above the dam site or reservoir area with sampling station at Bui (old town currently submerged); and below the dam site area with sampling station at Bamboi. Sixty-three fish species belonging to thirty-eight genera and twenty families were recorded in commercial gill net catches while thirteen species in nine genera and six fish families were recorded in experimental gill nets during the study. The change from riverine to lacustrine conditions during the formation of the reservoir, led to the immediate reduction in the numbers of a variety of fish families, including Latidae, Clarotidae and Distichodontidae which were very sensitive to oxygen depletion. The trend found in this study was towards the development of a community of herbivore fish species such as Sarotherodon galilaeus, Labeo coubie and Labeo senegalensis. The study revealed that the impoundment altered the fisheries characteristics of the downstream station. Hence, river management strategies should be implemented by fisheries managers and officials of the Bui Power Authority to lessen the impact of the dam on the downstream ecology.