Comparison of Fisheries Control Systems That Utilize Catch and Effort Data

Abstract

The relative merits of various methods for estimating the parameters of the Schaefer model from catch and effort data and of controlling the fishery are compared by simulation techniques. Estimation procedures compared are the linear and nonlinear methods for the discretized Schaefer model and Schnute's method for the continuous form of the Schaefer model. The control systems compared are feedback effort limitation, quota control for fixed escapement policies, and application of equilibrium effort. It is found that all estimation systems frequently fail to provide reasonable estimates of the Schaefer model and will produce poor catches, especially when managing long-lived, low productivity species. These estimation problems are most severe when the catch and effort data series begins after the stock has been heavily exploited. The failure of the estimation systems is primarily due to insufficient contrasts in the two independent variables of the multiple regression used for estimation, effort and catch per effort. The need for alternative policies that will explore the effort, catch per effort space is discussed. Application of the equilibrium effort may frequently be preferred to a fixed escapement policy; average catch may not be reduced, and variability in catch is much lower. Quota regulation is dangerous when the stock is heavily exploited and the biological parameters of the stock uncertain; at other times the quota method produces results comparable with effort limitation. Key words: Schaefer model, feedback control, catch and effort, fisheries regulation, adaptive control