Southern Gulf of St. Lawrence scallop population model and limit reference point review

Abstract

In accordance with the Precautionary Approach Framework, harvested fish stocks require a harvest strategy be incorporated into their fishery management plans to prevent harm to stocks. This involves establishing a Limit Reference Point (LRP), which is often set to 40% of the biomass at the stock’s maximum sustainable yield (BMSY). The goal of this report is to determine an LRP for sea scallops (Placopecten magellanicus) in the Southern Gulf of St. Lawrence (sGSL, Northwest Atlantic Fisheries Organization Division 4T), a stock for which available data is insufficient to perform a standard size- or age-based stock assessment. Despite over a century of scallop fishing in the sGSL and the development of a commercial fishery in the 1950s and 60s, fisheries independent data on the population is limited, and catch at-age/size data is absent for the commercial fishery. This document compiles a historical time series of catch data spanning from 1923 to 2021 and effort (or its proxy), represented as annual counts of active fishing boats, spanning 1976 to 2021. Nine well-known data-limited methods are then applied to these data series to derive estimates of stock status and biological reference points, facilitating the calculation of an LRP. Among the models tested, the Bayesian State Space model, JABBA, is identified as the most suitable choice based on its characteristics, assumptions, estimates, and ease of use. Estimates from this model indicate a BMSY for sea scallops in the core area of the sGSL of 1377 tonnes (t) (meat weight), corresponding to an LRP of 551 t.