Avis scientifique à l'appui du plan de rétablissement de la composante de reproducteurs de printemps du hareng de l'Atlantique (Clupea harengus) dans le sud du golfe du Saint-Laurent (divisions 4T-4Vn de l'OPANO)

Abstract

The main source of serious harm to the southern Gulf of St. Lawrence (NAFO Division 4T 4Vn) Atlantic Herring spring spawning stock productivity and the probable cause of stock decline was environmentally-driven recruitment failure since 1992 associated with a regime shift from cold water/high recruitment to warmer water/low recruitment. Other sources of serious harm include reduced growth, increased predation-driven natural mortality, high fishing mortality during and after the stock decline in the late 1990s and early 2000s, reduced fecundity, and a state of low production and low biomass. A review of candidate spawning stock biomass (SSB) reference points identified the Limit Reference Point (LRP) of 0.4BMSYproxy. A proposed Upper Stock Reference was 0.8BMSYproxy, a target reference point of BMSYproxy, and a removal reference of FMSYproxy. The stock has been below the LRP and in the Critical Zone of Fisheries and Oceans Canada (DFO) Precautionary Approach framework since 2001 (previously 2002). The current definition of the rebuilding target from the rebuilding plan is that the stock must have a 75% probability of being at or above the LRP. It should be amended to include that: (1) the stock must be at or above this level for 2 consecutive years (rebuilt state), and (2) population projections must also show that the stock is likely to continue its positive trajectory under a directed fishery for 2 years after this rebuilt state has been achieved. Even in the absence of fishing mortality, the SSB is unlikely to increase to the rebuilding target under prevailing stock productivity and ecosystem conditions or under various scenarios of natural mortality. In order for the stock to rebuild, recruitment must increase to the intermediate to high levels observed prior to the mid-1990s. With annual fishery removals (directed, bycatch, bait, science) of 150 to 500 tonnes (t), it is expected that SSB will decrease by a small amount (1 to 4%) over a decade compared to no fishery removals. These differences may be negligible because of the associated uncertainty. The main source of spring spawning Atlantic Herring bycatch is the fall season Atlantic Herring fisheries. Historically, the fall mobile gear fishery has landed more spring spawning Herring, however in half of the years from 2017 to 2022, the fixed gear fishery landed the majority. Bycatch in the fall fixed gear fishery is greatest in the South and North regions with minimal contribution from the Middle region. The removals from the spring season bait fishery are highly uncertain, but recent analysis indicates that they were higher than previously assumed and reported. In the event that this bait fishery reopens, removals should be monitored and reported to accurately estimate the associated fishing mortality. An additional measurable objective of the rebuilding plan is increasing the proportion of older fish to levels observed historically (1978-2004). Rebuilding progress will be tracked using the stock assessment model. The periodic review of the rebuilding plan should be set to every 4 years (every other stock assessment cycle) unless the stock productivity or external factors influencing stock dynamics change.