Science Advisory Report 2022/028

Stock assessment of Witch Flounder (Glyptocephalus cynoglossus) in the Gulf of St. Lawrence (NAFO Divisions 4RST) to 2021

Summary

• During the 2017-2018 to 2021-2022 fishing seasons the total allowable catch (TAC) of Witch Flounder in the Northwest Atlantic Fisheries Organization (NAFO) Divisions 4RST was set at 500 t. Landings for that period were between 349 t to 183 t. Preliminary landings for 2021-2022 were 212 t.
• The fishery for Witch Flounder is primarily a directed fishery, with most of the catch taken by Danish seines in southwest Newfoundland (NAFO Div. 4R) and northwestern Cape Breton Island (NAFO Div. 4T).
• There has been a contraction in the size composition of Witch Flounder in the landings. Fish 40 cm or longer made up 70% to 80% of the landings in the late 1970s but less than 20% of the landings in 2003 to 2012. The proportion of these large fish has increased in recent years, accounting for 20% to 30% since 2013.
• Based on research vessel surveys, the abundance of Witch Flounder measuring 30 cm and longer (the proxy for spawning stock biomass; SSB) has increased throughout the historical Gulf of St. Lawrence range since 2013, including the Estuary, western Newfoundland and around Anticosti Island.
• Reference points for the SSB of Witch Flounder were derived from a surplus production model. The Limit Reference Point (LRP), defined as 40% of the biomass for maximum sustainable yield (B_msy), is estimated at 10,700 t. The Upper Stock Reference (USR) of 80% B_msy is estimated at 21,400 t.
• The 2021 median spawning stock biomass estimate of Witch Flounder is 17,770 t, which is in the cautious zone of the DFO precautionary approach at 166% of the LRP and 83% of the USR. There is a 23% chance that the estimated SSB is at or below the LRP. The median estimate of the fishing removal rate in the last 5 years was between 0.011 to 0.023, which is below the maximum removal rate (F_msy) estimated at 0.071.
• Post-removal stock biomass projections for 2022 to 2026 indicate that the biomass is expected to increase up to a total annual catch of 1,000 t. The probability of the biomass being below the LRP in 2026 is 13% in a no catch scenario, 16% under a catch of 500 t and 22% under a catch of 1,000 t. The probability that the stock biomass will be in the healthy zone in 2026 is 60% under a no catch scenario, 52% under a catch of 500 t and 44% under a catch of 1,000 t.
• The stock is showing some positive signs of growth under current catch levels and is estimated to be in the Cautious zone. According to the Precautionary Approach, fisheries management actions for a stock in the Cautious zone should balance socioeconomic considerations while still promoting stock growth towards the Healthy zone.
• An interim year indicator update could be provided mid-way in the five-year assessment cycle to determine if the indicator signals that a re-assessment is warranted. This indicator is based on the combined research vessel surveys in NAFO Divisions 4RST.

This Science Advisory Report is from the Regional Advisory Meeting of March 1-2, 2022 on Stock status and fishery advice for May 2022 to May 2027 for Witch Flounder (Glyptocephalus cynoglossus) from NAFO Division 4RST, Gulf of St. Lawrence. 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 2022/028 (PDF, 1,858 KB)

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