An application of optimal control to the marine artisanal fishery in Ghana

Abstract

This study focuses on the determination of an optimal fishing effort for the marine artisanal fishery in Ghana. That is, the rate of harvest maximizing the net economic benefits while also maximizing the stock size. Employing the Gordon-Schaefer bioeconomic model and using empirical data on the round sardinella (Sardinella aurita), the static reference points of the model comprising the maximum sustainable yield (MSY), maximum economic yield (MEY) and open access yield (OAY) are determined and discussed. Further, the dynamic reference point of the model, the optimum sustainable yield (OSY), is also explored. Bifurcation analysis of the model shows that it undergoes transcritical bifurcation, and it is structurally stable for rate of effort not exceeding the bifurcation point. The characterization of the optimal control indicates that the resource should only be harvested by exerting up to the maximum available effort if the net revenue per unit harvest exceeds (or equals) the shadow price. Numerical simulations carried out on the dynamic model indicate that the optimal fishing effort should be set at 351,328 trips per year, provided the initial stock size is at least 554,654 tonnes. However, given the current high rate of fishing effort, due to the open access nature of the fishery, the recommended optimal effort strategy is bang-bang, which translates into implementation of closed fishing seasons