The Effects of Life History Strategy and Uncertainty On a Probability-Based Approach to Managing the Risk of Overfishing

Implementation guidelines for U.S. federal fisheries policy involve a series of catch level reductions that explicitly account for uncertainty. A transparent approach to compliance proposes that managers define an allowable risk of overfishing, P*, which specifies the probability that scientists’ catch recommendation exceeds the true value of the overfishing limit (OFL). But stock life history strategy and level of uncertainty in the assessment influence the actual risks resulting from P*-based management.  I selected three fish stocks with a range of life history strategies and simulated fishing for five years, under three P* levels and three levels of uncertainty. Probabilities of overfishing occurring represented the observed risks of overfishing.

Trends identified among example species were consistent with predictions based on life history. The two periodic strategists, with highly variable recruitment, experienced probabilities of overfishing which exceeded P* and which increased in time. The equilibrium strategist, with more predictable recruitment, showed more predictable risks of overfishing. Differences in size of OFL distribution—representing differences in uncertainty—led to mixed results depending on whether the distribution was biased or whether uncertainty was fully characterized. In the absence of in-depth risk evaluations for individual stocks, these general patterns provide crucial insights to management decisions.