An assessment of the purse-seine (winch-net) fishery in Lake Volta, Ghana

Abstract

An assessment has been made of the stock conditions of five major component fishery species (Chrysichthys nigrodigitatus, Chrysichthys auratus, Hemisynodontis membranaceus, Oreochromis niloticus and Schilbe intermedius) exploited with illegal purse-seine (winch-net) gear in the Yeji sector of Lake Volta, Ghana. Chrysichthys nigrodigitatus was clearly found to be overexploited, but the others were being exploited near to, or under, optimum harvest levels. All five species were harvested at an inappropriate age-at-first-capture of ≈ 6 months, suggesting overfishing of young fishes. Consequently, the computed Lm:L∞ ratios were > 0.64. For most fish species, such a ratio implies their exploitation when at early maturity and at very small sizes. The estimated range of mesh sizes in the cod-ends was far lower (5-8 mm) than the legal mesh size of 25 mm, calling for urgent enforcement of rules and regulations. Single-species yield-per-recruit analyses indicated that yields could be improved by the reduction in the current fishing effort. As the fishery of the lake is not segmented to allow fish to be taken by the illegal small-mesh purse seines, studies on the interactions between the different fishery sectors need to be undertaken, alongside the proposed ban of the gear as enshrined in the Fisheries Law of Ghana. © 2005 Blackwell Publishing Asia Pty Ltd.