Science advice on a performance threshold for the management strategy evaluation for Southwest NovaScotia/Bay Of Fundy Atlantic herring (Clupea harengus)

Abstract

Potential performance thresholds for the Southwest Nova Scotia/Bay of Fundy Atlantic Herring stock were evaluated to ensure that the selection of a management procedure in the Management Strategy Evaluation (MSE) process be consistent with the objectives of DFO’s Fishery Decision-Making Framework Incorporating the Precautionary Approach (PA Policy). The performance threshold is to be used in the Management Strategy Evaluation (MSE) to identify candidate management procedures that result in a high probability of spawning stock biomass (SSB) remaining above the threshold during the projection period. Several empirical and theoretical approaches were identified as potential thresholds. Empirical approaches were based on a historical biomass from which the stock has recovered or remained stable, as well as a biomass below which recruitment dynamics are unknown. Theoretical approaches were evaluated for defining an equilibrium biomass at a fishing mortality rate based on the concepts of maximum sustainable yield, yield-per-recruit or spawning stock biomass-per-recruit, and replacement fishing mortality rate, as well as methods based on unfished biomass. The suite of operating models (OMs) implemented in the MSE represent a broad range of simulated stock recruitment dynamics. It was agreed that a theoretical approach for defining the threshold is more consistent with the simulated population dynamics in each OM and thus a more comparable performance metric across OMs. A threshold was defined as 70% of the SSB at maximum sustainable yield, 0.7 SSBMSY. The recommended probability and time period to apply the performance threshold in the MSE was P(SSB > 0.7 SSBMSY) > 75% in each year beginning in year 10 of the 25-year projection period. A dynamic SSBMSY is to be used for evaluating the performance of management procedures in the MSE. The dynamic SSBMSY was estimated separately for each simulation using annual time-varying growth, maturity, and selectivity, as well as the annual simulation specific recruitment deviations. It was recommended that the dynamic SSBMSY be used only in the evaluation of management procedures in the closed-loop simulations and not used for evaluating stock status.