A Comparison of Harvest Policies for Mixed Stock Fisheries

Abstract

Existing theory on optimal harvesting policies for exploited populations deals almost exclusively with single stocks of known productivity managed for maximization of discounted average catch. This paper examines alternative harvest policies for mixed stock fisheries in which the manager cannot distinguish between abundances of separate stocks and can deal with total abundance only. Numerical methods are used to show that if the stocks have uncorrelated natural variation, the best harvest policy will be very much like a constant harvest rate rather than a constant escapement. When natural variation is correlated between stocks, even if productivities of stocks are different, a fixed escapement policy appears to maximize average catch. When the objective is not maximization of average catch, but rather the sum of logarithms of the catch, the best policy appears to be quite similar to constant harvest rate.