Science Advisory Report 2023/004

*This advice was developed in a peer review meeting in 2021 and should be interpreted within the context of the situation at that time.

Stock Status of Redfish in Northwest Atlantic Fisheries Organization (NAFO) Subarea 0, and Subarea 2 + Division 3K

Summary

This meeting assessed two redfish (Sebastes spp.) stocks, NAFO Subarea (SA) 2 + Division (Div.) 3K and NAFO SA 0. These stocks are assessed and managed as a species complex that has been historically dominated by S. mentella and also includes S. fasciatus and S. norvegicus.

Environmental and Ecosystem Information

• The warmest period of ocean temperatures over the last 70 years in Divs. 2HJ3K was the 1960s and the coldest was the early-1990s. Between the early 1990s and the early 2010s, a sustained warming trend was observed. After a short return to cooler near average conditions in the mid-2010s, temperatures warmed again during 2018–20 at bottom and Cold Intermediate Layer (CIL) depths.
• In Divs. 2HJ3K, higher nitrate inventories since roughly 2015 have resulted in improved primary (chlorophyll biomass) and secondary (zooplankton biomass) production indices over the past 4–5 years. Since the mid-2010s, the zooplankton community has undergone structural changes characterized by a higher proportion of small copepods along with an increase in overall biomass. Changes in zooplankton seasonality (lower spring and higher summer and fall signals) and community size structure (fewer large, energy-rich calanoids and more small copepods) may impact energy transfer to higher trophic levels.
• Ecosystem conditions in the Newfoundland and Labrador (NL) bioregion continue to be indicative of limited productivity of the surveyed fish and shellfish community, with total biomass levels much lower than prior to the fisheries collapse in the early 1990s. Following some improvement between the mid-1990s and mid-2010s, total biomass declined after 2015. While there have been improvements since, current total biomass has not returned to the 2010–15 levels. Increases in medium-large predatory groundfish from 2010–15 were primarily associated with bottom-up processes, including availability of capelin and shrimp.
• An ocean climate index derived for Subarea 1 (considered representative for Div. 0B), including sea surface temperatures from West Greenland shelf, Labrador Sea and Hudson Strait, was at its highest value in 2019 since the record-high of 2010.
• The initiation of the spring phytoplankton bloom in Div. 0B was delayed for a second consecutive year in 2019, compared to the 1998–2015 average and total spring bloom production was below normal in 2019.
• Fish species diversity is greater in Div. 0B than in 0A. S. mentella was common to both divisions and was identified as an indicator species in a fish assemblage occupying the shallow, warm water of the South Baffin shelf. Additionally, S. mentella have been found to comprise 10% (wet weight) of the diet of Greenland halibut caught in 0B.

Subarea 2 and Division 3K Redfish Assessment

• The 2020 Divs. 2J3K recruitment index (abundance of redfish < 15 cm length) was substantially higher than any value observed previously in the time series (1978–2020). Signals indicate that recruitment was also high in Divs. 2H and 2G in 2020. Redfish recruitment is episodic and conditions that produce strong recruitment are not understood, including the potential for recruits to originate from neighbouring areas.
• The Divs. 2J3K abundance index from the fall DFO research survey generally declined from 2011–2017, followed by a sharp increase in 2020, to the third highest value in the time series (1978–2020). Abundance indices from surveys conducted in 2H (1978–2020) and 2G (2005–20) were at time series highs in 2020. Biomass indices across all survey areas were comparable to the observed abundance trends, with the exception of recent increases in abundance that were not reflected in the biomass indices (since these increases have been driven by very small fish that do not yet contribute significantly to biomass).
• While the fishery remains under moratorium (in place since 1997), the impacts of removals (bycatch landings and discards) from other fisheries on the stock are currently unknown. Redfish removals, mainly of small sized fish, averaged 55 t from 2015–19, but increased to more than 200 t in 2020 across the stock area, which occurred predominantly in the 2G shrimp fishery. Even small amounts of removals, by weight, can equate to large numbers when fish are small.
• There is currently no accepted population model for this stock and projections could not be generated. Redfish are very slow-growing and strong recruitment pulses do not always persist. Therefore it is unknown whether the 2020 pulse will make a significant contribution to the stock or any potential fishery.
• While there is no defined PA framework for this stock, current total survey biomass levels remain low; therefore, it is advised that management measures focus on encouraging stock growth.

Subarea 0 Redfish Assessment

• There is no commercial redfish fishery in Subarea 0. Fishing mortality is limited to bycatch, mainly of small fish caught in shrimp fisheries, and to a lesser extent in Greenland halibut fisheries. Annual total bycatch for both the shrimp and Greenland halibut fisheries peaked in 2005 (229 t) and since declined to less than 50 t per year (2014–19). Small amounts of bycatch, by weight, can equate to large numbers of removals when fish are small, but overall impacts of bycatch on the stock are not currently known.
• Abundance and biomass indices from DFO research surveys in Divs. 0A (1999–2019) and 0B (2000–16) peaked in 2012 and have since declined to levels similar to the time series lows of the early 2000s.
• Abundance and biomass indices in the Northern Shrimp Research Foundation (NSRF) survey of Shrimp Fishing Areas (SFAs) 2, 3 and Resolution Island, which are primarily composed of redfish < 20 cm, reached higher levels in the mid-2000s, subsequently declined and then reached a time series high in 2020. The SFA 2 survey is considered most representative as an index for this stock; the survey biomass and abundance indices decreased from 2010–19 with a sudden increase in 2020.
• A recruitment index of < 15 cm redfish is not available for SA 0. The multispecies survey is conducted at depths greater than 400 m and therefore has low catches of redfish < 15 cm which occupy shallower habitats. The NSRF survey occurs at depths at which < 15 cm redfish occur but length frequency data are not collected.
• Length-frequency data from DFO multispecies surveys in Divs. 0A and 0B indicate that in Div. 0A few year classes are present with no evidence of incoming recruitment since 2016, while in Div. 0B there is a broader range of year classes, with more consistent recruitment signals.
• There is currently no accepted population model for this stock and projections could not be generated. Redfish are very slow growing and strong recruitment pulses do not always persist. Therefore, it is unknown whether the 2020 pulse in the SFA 2 survey index will make a significant contribution to the stock or any potential fishery.
• There is no defined PA framework for this stock. Given the declining trend in the SFA 2 biomass time series prior to 2020 and the uncertainty around the persistence of the peak observed in 2020, it is advised that management measures take a cautionary approach to managing this cohort until it achieves exploitable size.

This Science Advisory Report is from the May 4–7, 2021 Zonal Advisory Meeting on the Assessment of Redfish in Northwest Atlantic Fisheries Organization (NAFO) Subarea 0, and Subarea 2 + Division 3K. 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 2023/004 (PDF, 2,839 KB)

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