Evaluating the Impact of Buffers to Account for Scientific Uncertainty when Setting TACs: Application to King Crab in Bristol Bay, Alaska
ESSR Program economists Brian Garber-Yonts and Mike Dalton collaborated with AFSC stock assessment scientists and researchers at the University of Washington, the North Pacific Fishery Management Council (NPFMC), and the ADF&G in the development of new methods for evaluating the economic and biological trade-offs associated with the implementation of annual catch limits (ACLs) under an acceptable biological catch (ABC) control rule.
Results of this work were presented recently at the NMFS National ACL Workshop in February 2011. The approach was well received by scientists and resource managers as a novel method for incorporating biological and economic uncertainty in management decision making. In addition, the new methods are being documented in a manuscript (Punt et al. 2011) for publication in a peer-reviewed journal.
Under the Magnuson-Stevens Fishery Conservation and Management Act (MSA), the overfishing level (OFL) for a stock is defined as the level of harvest which exceeded would constitute overfishing. In reauthorizing the MSA in 2006, Congress specified the ABC as the level of harvest that accounts for scientific uncertainty in the estimate of the OFL and is hence equal to, or lower, than the OFL. The requirement to adjust OFLs to account for scientific uncertainty has proved challenging for the regional fishery management councils, and each has followed a different course. A new paper by Punt et al. outlines the approach developed for crab fisheries in Bering Sea and Aleutian Islands for the NPFMC.
An approach based on simulation is outlined which can be used to evaluate the trade-offs among performance metrics for fisheries management for different "buffers" (i.e., the differences between the target catch level given perfect information and the set catch limit, when only a fraction of the uncertainty related to estimating the target catch level is quantified through stock assessments). Specifically, the performance of different buffers is evaluated in terms of their impact on short- and long-term catches, expected values of economic earnings, the probability of overfishing (i.e., the catch exceeding the true, but unknown, target catch), and the stock becoming overfished (i.e., in the case of crab mature male biomass, MMB, dropping below half of the MMB corresponding to maximum sustainable yield).
The paper presents the approach as applied to the fishery for red king crab, Paralithodes camtschaticus, in Bristol Bay, Alaska. The application, which formed the basis for NPFMC decision making for this stock, accounts for the complexities induced by joint state-federal management of the fishery and also for catches in fisheries other than the directed male-only pot fishery. The approach is also unique in the application of forecasting methods to account for uncertainty in future market values for crab products as well as in stock condition.
