SENSITIVITY OF OPTIMUM HARVEST STRATEGY ESTIMATES TO ALTERNATIVE DEFINITIONS OF RISK

A stochastic age-structured bioeconomic simulation model was developed as a tool for evaluating economic returns to a fishery from alternati ve harvest policies. The model, which was applied to the Gulf of Alask a walleye pollock (Theragra chalcogramma) fishery, combines the dual g oals of protection of the base stock and efficient use of the public r esource into an explicit objective function. This paper presents the r esults of several experiments in which the simulation model is used to examine the sensitivity of the optimum harvest strategy estimates to alternative definitions of risk and assumptions regarding recruitment. Alternative definitions of risk consider assumptions about stock prod uctivity, threshold biomass, economic factors, and hybrid formulations . The bioeconomic extension of the population dynamics model is used t o quantify differences in the estimates of optimum fishing mortality o btained from the different risk definitions. Model results demonstrate that estimates of optimal fishing mortality and economic return to th e fishery are sensitive to the specific definition of risk used to man age the fishery. The recruitment assumption turned out to be more impo rtant to optimum harvest strategy estimates than did risk definitions.