A review of harvest policies: Understanding relative performance of control rules

Harvest policies use control rules and associated policy parameters to dictate how fishing mortality or catch and yield levels are determined, and are necessary for rational management. Common control rules include constant catch, constant fishing mortality rate, constant escapement, or a few variations of these. The “best” among these control rules for meeting common fishery objectives (e.g., maximizing yield) is a source of controversy in the literature, and results are seemingly contradictory. To compare the ability of control rules to meet widely used fishery objectives and identify potential causes for these apparently contradictory results, we did a detailed review of relevant literature. The relative performance of control rules at meeting common fishery objectives is affected by: whether uncertainty in estimated stock sizes is included in analyses, whether the maximum recruitment level (e.g., the asymptote of a Beverton–Holt stock–recruit function) is varied in an autocorrelated fashion over time, fishery objectives, and the amount of compensation in the stock–recruit relationship. Few studies have compared control rules using optimal parameters (e.g., those that maximize some objective function) that were found while including assessment error. More commonly, parameters that are optimal without assessment error are used in a comparison of control rules that includes assessment error. This approach can produce misleading results. Ideally, selection of a control rule and policy parameters is done within the framework of a stochastic simulation that considers key uncertainties. If this is not feasible, an alternative option is to “borrow” control rules from a similar fishery and set policy parameters based on biological reference points developed for a species with similar taxonomy and life-history traits. More research is needed to compare control rules when accounting for uncertainty in key population parameters, when stock–recruitment or other population dynamic parameters vary over time, and for fisheries with non-yield-based or competing objectives.