Extending the Northern Cod (Gadus morhua) assessment model - part III : revisiting the Limit Reference Point

Abstract

Under the Canadian Precautionary Approach (PA) to fisheries management, a Limit Reference Point (LRP) is defined as the stock status below which serious harm is occurring. Since 2010, the LRP for Northern cod has been defined as the average spawning stock biomass (SSB) from the 1980s as this was the last time medium levels of recruitment were observed. This definition has been formally revisited using the Beverton-Holt stock-recruitment relationship by calculating the level of SSB that produces 50% of maximum predicted recruitment. Potential maximum sustainable yield (MSY) based alternatives are also considered and the limitations of both recruitment-based and MSY-based reference points are discussed in this perspective piece. In short, the suitability of an MSY-based LRP is called into question for Northern cod as estimates are sensitive to changes in vital rates and fisheries selectivity, both of which have exhibited substantive changes through time since 1954. I suggest that estimates of MSY may be more suitable for the provision of tactical, ecosystem-informed advice. Ultimately, continued use of the recruitment-based LRP is recommended since it should be above the point at which recruitment rates are impaired and depensation or extirpation is a concern.