Comparison of Constant Effort Harvest Policies for Fish Stocks with Variable Recruitment

Abstract

Environmental variability may have a substantial influence on marine fish stocks, primarily by affecting survival to the time of recruitment. Simulation studies at low, intermediate, and high levels of variability in recruitment were used to compare alternative constant effort policies for anchovy (Engraulis capensis), Atlantic menhaden (Brevoortia tyrannus), and Pacific ocean perch (Sebastes alutus) fisheries. These policies were either to maintain effort at the level producing maximum sustainable yield (fMSY), or to permit levels of effort 25–100% greater than fMSY. An increase in effort of 25% above fMSY typically did not reduce annual yield significantly; however, a significant reduction in yield was apparent in all cases when effort increased by 75–100%. When recruitment is highly variable, comparable yields may be obtained at several levels of fishing effort. In such cases, environmental variability provides the fishery manager with considerable flexibility to enhance social or economic benefits without decreasing yields significantly.