Science Advice on Reference Points for Scallop Fishing Areas 25, 26, and 27B

Abstract

The stock status indicator for scallop fishing areas (SFAs) 26C and 27B is the most recent three-year geometric mean of the fully-recruited survey biomass index for each area. The stock status indicator for SFAs 25A and 26A is the model estimated fully-recruited biomass for each area. Where available, model-based approaches were recommended over the survey biomass index-based approaches. Model-based approaches are preferred due to their ability to quantify uncertainty and changes in stock dynamics (productivity). Candidate reference points were considered based on modelled maximum sustainable yield (MSY) simulations for SFAs 25A and 26A. These simulations utilized the stock dynamics between 1994 and 2022. Using the model-based MSY simulations, limit reference points (LRP) were adopted for SFAs 25A at 1,160 tonnes and 26A at 2,000 tonnes; these LRPs correspond to BMSY(40) (40% of biomass at maximum sustainable yield). Candidate reference points were evaluated based on fully-recruited survey biomass index based proxies of BMSY and B0 (unfished biomass) for SFAs 26C and 27B. Using the index-based approaches, LRPs were adopted for SFAs 26C at 890 tonnes and 27B at 628 tonnes; these LRPs correspond to BMSY(30) (30% of biomass at maximum sustainable yield). Guidance was provided for the development of upper stock reference points (USRs) and removal references (RRs) in all areas. For each of SFAs 25A and 26A, a scenario was developed using harvest decision rule simulations to demonstrate how this method could quantify the impact of alternative management objectives.