Évaluation du stock jusqu'en 2022 et exigences scientifiques pour le plan de rétablissement de la Merluche blanche (Urophycis tenuis) du sud du golfe du Saint-Laurent, division 4T de l'OPANO

Abstract

The White Hake (Urophycis tenuis) stock in the southern Gulf of St. Lawrence (sGSL) is below its limit reference point (LRP) and in the Critical Zone of the Precautionary Approach (PA). The new Fish Stocks Provisions and the amended Fisheries Act legally require Fisheries and Oceans Canada (DFO) to develop a rebuilding plan for this stock. The sGSL stock assessment was updated using data up to 2022. The spawning stock biomass (SSB) in 2022 was 6.1 kilotonnes and the stock was in the Critical Zone of the PA. Fishing mortality of sGSL Hake ages 6+ has been below 0.02 since 2018. A review of the biomass reference points generated a new LRP based on a proxy for BMSY using the statistical catch-at-age model. With this new LRP, the stock is now estimated to have declined into the Critical Zone in 1992. Upper Stock and Target Reference points based on the proxy for BMSY were also calculated. In addition to the stock having a 75% probability of being at or above the LRP, the rebuilding target should include that the stock must be at or above this level for 5 consecutive years, and population projections must show the stock is likely to continue its positive trajectory under harvest for 5 years after the rebuilt state has been achieved. Population projections showed that the stock is unlikely to rebuild to the rebuilding target under prevailing conditions, even in the absence of fishing mortality. For the stock to rebuild, simulations showed that important reductions in natural mortality where necessary. Simulations also showed that the stock is highly vulnerable to declines in recruitment rates. Projections showed that at 100 tonnes (t) and 1,000 t of bycatch, SSB in 10 years would be reduced by 3.3% and 17.6% compared to no fishing, respectively. Preliminary analyses suggests the stock structure should be further investigated as Hake life history parameters in the St. Lawrence Estuary are more similar to Hake outside the sGSL. Additional measurable objectives for the rebuilding plan should include to increase the proportion of larger Hake and Hake aged 5+ to averages observed historically, to observe a return of Hake to their inshore spawning grounds, as well as an overall return of Hake to the inshore waters of the sGSL during the summer where they were historically distributed, to maintain the high recruitment observed in recent years and making enhanced efforts to understand the causes of the current high recruitment rates and how to promote it until the age structure has recovered, and finally to monitor discards and bycatch in fisheries intercepting White Hake more closely. Rebuilding progress will be tracked using the interim indicator derived from an annual survey and from stock assessment models. The periodic review of the rebuilding plan should be set to the 5-year stock assessment cycle with an interim update at the halfway point.