Sensitivity of Optimum Harvest Strategy Estimates to Alternative Definitions of Risk

Abstract

A stochastic age-structured bioeconomic simulation model was developed as a tool for evaluating economic returns to a fishery from alternative harvest policies. The model, which was applied to the Gulf of Alaska walleye pollock (Theragra chalcogramma) fishery, combines the dual goals of protection of the base stock and efficient use of the public resource into an explicit objective function. This paper presents the results 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 productivity, threshold biomass, economic factors, and hybrid formulations. The bioeconomic extension of the population dynamics model is used to quantify differences in the estimates of optimum fishing mortality obtained from the different risk definitions. Model results demonstrate that estimates of optimal fishing mortality and economic return to the fishery are sensitive to the specific definition of risk used to manage the fishery. The recruitment assumption turned out to be more important to optimum harvest strategy estimates than did risk definitions.