4. Pre-Impoundment Fish Stock Assessment of the Black Volta: A Contribution to Fisheries Management of Bui Reservoir in Ghana

Abstract

A length-based fish stock assessment of the Black Volta River in Ghana was undertaken prior to its damming at Bui in 2011. The approach involved estimation of the population parameters and exploitation rates of dominant fish stocks using TropFish R. The targeted species were: Alestes baremoze, Hydrocynus forskalii, Hemisynodontis membranaceus and Labeo coubie. The estimated asymptotic length (L_∞) ranged from 30.8 – 48.2 cm standard length (SL) with derived longevity of 11 – 27 years for the assessed species. The estimated growth coefficient (K) value ranged from 0.10 – 0.25 yr^-1 which suggested slow growth rates. The estimated length at first capture (Lc₅₀) was lower than the length at first maturity (Lm₅₀) for all the assessed fish species which suggests the presence of recruitment overfishing within the fish stocks. The total mortality rate (Z) was relatively high ranging between 0.51 and 1.34 yr^-1 suggesting that the stocks were over-exploited during the pre-impoundment period. The exploitation rate (E) for the assessed fish species were lower than the maximum exploitation rate (E_max) which indicates that the species are far from collapse. These estimates are baseline scientific information for designing a Fisheries Management Plan for the Bui reservoir. Meanwhile, alternative livelihood and employment opportunities such as cage fish culture are to be explored to reduce the fishing pressure on the reservoir.