Decision analysis of alternative harvest policies for the Gulf of Alaska Pacific ocean perch fishery

Abstract

By the mid-1970s the estimated biomass of Pacific ocean perch (POP), Sebastes alutus, in the Gulf of Alaska (GOA) had been reduced to about 10% of the estimated level present during the early 1960s. Although fishing mortality was greatly reduced, the stock has shown only modest increases in biomass; the current estimate of spawner biomass is between 15% and 20% of the estimated peak levels. This decline has raised concern that past management measures may have been inadequate to allow growth of the POP stock in the GOA. Consequently, we performed an analysis to: (a) identify optimal fishing rates for rockfish species such as Pacific ocean perch, (b) identify the biomass level that would produce an optimum yield, and (c) evaluate alternative fishing policies designed to improve the condition of the POP resource. The selection of an optimal fishing rate for POP in the GOA was based on a maximin criterion. Recruitment variability was shown to play an important role in determining the effects of different harvest policies. Based on estimates of optimal biomass and fishing mortality rates, four alternative harvest policies were developed and evaluated using a stochastic simulation model. These policies ranged from harvests based on rates under the status quo policy to increasingly restrictive measures. Policy outcomes were measured in terms of yield in weight and dollar-value, female spawner biomass, and risks. We presented the results in the form of Bayesian decision tables. The ability to predict future stock levels with a high degree of certainty is poor. In no case is there a guarantee that rebuilding will occur.