Accounting for Scientific Uncertainty in Stock Assessments Using Management Strategy Evaluation

Quantifying scientific uncertainty is a key part of providing scientific advice in fisheries management. Increasingly, management systems require that catch limits account for scientific uncertainty by specifying a buffer such that the catch limit is lower than that determined based on an assumption of perfect information. A “P* approach” is a method whereby a catch limit is specified such that the probability that a future fishing mortality (F) exceeds the F corresponding to MSY (F_MSY) remains at or below a pre-specified value (P*). Some sources of scientific uncertainty are often ignored when calculating catch limits using a P* approach, such as uncertainty about the configuration of the assessment model. For instance, natural mortality (M) is often assumed to be fixed and constant since data on variability over age and time are rarely available. This likely leads to underestimates of uncertainty about quantities such as spawning stock biomass (SSB) and productivity. A management strategy evaluation was developed to examine the performance of a “P* approach” that included accounting for model configuration uncertainty, with application to Alaska groundfish. The probability that true F exceeded true F_MSY and the probability that true SSB fell below half of SSB corresponding to MSY were calculated.