Looking for robust harvest control rules: learning from MSE applications to specific fisheries

PARMA, ANA M

Woods Hole

Conferencia; IMBER-IMBIZO - Linking ecosystems, future states and resource management; 2017

IMBER

Increasing recognition of the wide uncertainty that surrounds fisheries assessments has prompted a change in the science used to formulate management advice. While initially the focus of policy analysis was on optimality, the emphasis has shifted first to risk avoidance, and more recently to achieving robustness in the face of uncertainty. Experience has shown time and again that the use of a ?best-assessment? approach, i.e. a best estimate of the absolute exploitable biomass coupled with a function that specifies the target fishing mortality, can fail to achieve the desired robustness and lead to unnecessary disruptions in the conduct of fisheries. The most important selling point for MSE is that it allows quantification of the performance of management procedures in advance of implementation, so that their robustness in the face of alternative future scenarios can be evaluated. In addition, unresolvable arguments about which model is best to represent past and future system dynamics can give way to more productive discussions about the scenarios to include as operating models for MSE. These important benefits are well illustrated by the process of designing and implementing a strategy for rebuilding the stock of southern bluefin tuna (SBT). Not only did the MSE approach allow progress away from stagnation in the scientific process, but it delivered a strategy that in practice proved to be robust to appreciable changes in the best assessments of absolute stock size. Relatively simple management procedures, like the one adopted for SBT, that work by adjusting allowable catches up or down in response to trends in stock size indicators may, in general,  afford higher robustness to changes in the scale of abundance estimates than the standard best-assessment approach.