Science Advisory Report 2024/033

Science Advice to Support the Rebuilding Plan for Atlantic Cod (Gadus morhua) in the Southern Gulf of St. Lawrence, NAFO Division 4T-4Vn (November-April)

Summary

• Southern Gulf of St. Lawrence Atlantic Cod biomass was stable and relatively high from 1917 to the late 1940s. Biomass declined in the 1950s as catches increased and fishing mortality was high. The 2018 biomass was 2.4% of the 1917 biomass, which is consistent with the scale of depletion found for adjacent Cod stocks.
• The main source of serious harm to stock productivity and cause of decline was overfishing starting in 1955. High natural mortality associated with predation by Grey seal has prevented the stock from recovering since the fishery moratorium.
• Other sources of serious harm include a lasting state of low production and low biomass, recruitment overfishing, high natural mortality, a predation-driven Allee effect, low growth and body condition, and a decrease in age at maturity.
• A review of the spawning stock biomass (SSB) reference points identified a new Limit Reference Point (LRP) of initial 0.25B₀. A proposed Upper Stock Reference was 0.8BMSYproxy and a target reference point of BMSY_proxy.
• The stock crossed the LRP into the Critical Zone of Fisheries and Oceans Canada (DFO) Precautionary Approach framework in 1990.
• The definition of the rebuilding target, where the stock has a 75% probability of being at or above the LRP, should be amended to include that the stock must be at or above this level for 4 consecutive years and population projections must show the stock is likely to continue its positive trajectory under harvest for 4 years after the rebuilt state has been achieved.
• Even in the absence of fishing mortality, the SSB is unlikely to increase to the rebuilding target under prevailing conditions or under various stock projections using natural mortality and recruitment rates consistent with historical levels.
• At annual removals of 200 tonnes (t) or less, the stock trajectory is indistinguishable from projections under zero fishing. At 300 t, SSB is reduced 10% in 10 years compared to zero fishing; at 500 t, SSB is reduced 16%.
• The main sources of Cod bycatch are the Atlantic Halibut, Witch Flounder, and Greenland Halibut commercial fisheries, as well as the experimental and index fisheries that target Redfish.
• Implementing dynamic closures (seasonal and/or annual) of specific areas and fishing depth restrictions reduced species distribution model-predicted bycatch.
• Bycatch was reduced 18% in the Atlantic Halibut fishery in NAFO 4T, and 14% in the Cod overwintering area in 4Vn,
• 98% in the NAFO 4T Witch Flounder fishery, and
• 81% to 84% in the NAFO 4T Greenland Halibut fishery^{Footnote 1}.
• As the commercial Redfish fishery reopens, bycatch of Atlantic Cod is expected to increase. Implementing an area closure and a minimum fishing depth restriction of 300 m and limiting fishing to June through August reduced predicted bycatch of Cod by at least 56% compared to historical fishing and at least 46% compared to current fishing in NAFO 4T. In NAFO 4Vn, an area closure combined with a minimum latitude limit in winter reduced predicted Cod bycatch by at least 22% compared to historical fishing and at least 14% compared to current fishing.
• Although a winter (November to April) Redfish fishery had greater potential bycatch compared to a summer (June to August) fishery, the proposed area closures for NAFO 4T and NAFO 4Vn combined with a 300 m minimum fishing depth in NAFO 4T reduced predicted bycatch by at least 96% compared to without these restrictions.
• Additional measurable objectives of the rebuilding plan include; increase the proportion of larger fish, increase size and condition at length, recover the spatial distribution in shallow waters, and promote recruitment by protecting spawning grounds.
• Rebuilding progress will be tracked using the stock assessment model. The periodic review of the rebuilding plan should be set to the 4-year stock assessment cycle with an interim update at the halfway point. Objectives should be revised and models should be updated if stock productivity or external factors influencing stock dynamics change.

This Science Advisory Report is from the regional peer review of February 22-23, 2024 on Science Advice to Support the Rebuilding Plan for Atlantic Cod (Gadus morhua) in the Southern Gulf of St. Lawrence, NAFO Division 4T-4Vn (November-April). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2024/033 (PDF, 1,041 KB)

Data sets:

• NAFO Division 4T groundfish research vessel trawl survey (September Survey) dataset
• Evaluation of groundfish and shrimp annual multidisciplinary survey in the Estuary and northern Gulf of St. Lawrence (CCGS Teleost 2004 - 2022)
• Otolith Collection of Atlantic Cod in the southern Gulf of St. Lawrence

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