Fisheries Assessment and Trophic Modelling of Tono, Bontanga and Golinga Reservoirs, Ghana

Summary: Due to the dispersed nature of inland fisheries, most individual systems are rarely adequately assessed or monitored, therefore reliable data on the target stocks are largely unavailable to implement management strategies. This thesis focuses on Tono, Bontanga and Golinga reservoirs in northern Ghana which contribute significantly to food and nutrition security and community livelihoods. The thesis presents studies that demonstrate how differences in reservoir use patterns, reservoir morphometry and physicochemical characteristics influence ecosystem structures and fisheries resource productivity. To improve the estimation of current harvest potential of West African reservoirs, the relationship between total annual fish catch and reservoir surface area was modelled, which compared to a previous model, indicated that catches from reservoirs in the region have more than doubled over the last two decades. The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii were found to be heavily exploited in all three reservoirs. The giraffe catfish, Auchenoglanis occidentalis was found only in Tono and Bontanga reservoirs. In Bontanga, the catfish stock is fully exploited. While in Tono, the giraffe catfish is underexploited, the current fishing mortality could be doubled to increase yield.  While fisheries productivity (per unit area), is inversely related to lake size, we conclude that the use of small reservoirs in populated semi-arid environments for both irrigated farming and fisheries production is unsustainable due to problems associated with seasonal water loss, siltation and aquatic habitat degradation. The findings of this thesis suggest that the use of man-made lakes and respective catchment areas should be assessed and managed carefully to prevent the loss of nutrition and livelihoods contributions.