Research Document 2024/070
Scientific Requirements for the Rebuilding Plan of Southern Gulf of St. Lawrence (NAFO Division 4TVn) Spring Spawning Atlantic Herring (Clupea harengus)
By Turcotte, F. and McDermid, J.L.
Abstract
The spring spawning component of Atlantic Herring (Clupea harengus) in the southern Gulf of St. Lawrence (NAFO Division 4TVn) is below its limit reference point (LRP) and in the Critical Zone of Fisheries and Oceans Canada (DFO) Precautionary Approach framework. The new Fish Stocks Provisions and the amended Fisheries Act legally require DFO to develop a rebuilding plan for this stock. Rebuilding plans involve several key requirements, many of which are defined and/or supported by advice from DFO Science Sector. A rebuilding plan comprises several elements that require DFO Science sector advice including: (i) stock status, (ii) causes of stock decline, (iii) rebuilding target and timeline, (iv) additional measurable objectives, (v) likelihood of management measures meeting rebuilding objectives, (vi) how to track rebuilding progress, and (vii) frequency of the periodic review of the rebuilding plan.
Southern Gulf of St. Lawrence (sGSL) Atlantic Herring spring spawners sources of serious harm include environmentally-driven recruitment failure associated with a regime shift from cold water/high recruitment to warmer water/low recruitment in the early 1990s, a sustained period of low production low biomass since 2004, reduced growth, high natural mortality, and reduced fecundity.
A review of the biomass reference points generated a new LRP using the statistical catch at age model; 40%BMSYproxy. Its value is estimated at 55,000 tonnes (t) of spawning stock biomass (SSB). With this LRP, the stock has been below the LRP and in the Critical Zone of the DFO Precautionary Approach framework since 2001 (previously 2002).
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 2 consecutive years, and population projections must show the stock is likely to continue its positive trajectory under harvest for 2 years after the rebuilt state has been achieved.
Projections showed that the stock is unlikely to rebuild to the rebuilding target under prevailing conditions, even in the absence of fishing mortality. The environmental conditions that would allow to reverse the decline in sGSL Atlantic Herring spring spawners are the occurrence of intermediate and high recruitment events. Since 1992 recruitment has been limited due to environmental conditions which are unlikely to improve as climate change continues.
Projections showed that at 150 t of annual bycatch, the population SSB in 10 years would be reduced by 1.0%.
Additional measurable objectives for the rebuilding plan should include increasing the proportion of older and larger fish.
Rebuilding progress will be tracked using the stock assessment models. The periodic review of the rebuilding plan should be set to every 4 years, which corresponds to every other stock assessment. Objectives should be revised and models should be updated if stock productivity or external factors influencing stock dynamics change.
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