Quebec and Newfoundland Canadian Science Advisory Secretariat and Labrador regions Science Advisory Report 2020/019 REDFISH (SEBASTES MENTELLA AND S. FASCIATUS) STOCKS ASSESSMENT IN UNITS 1 AND 2 IN 2019 Image: Redfish (Sebastes spp.) Credit: Fisheries and Oceans Canada Figure 1. Units 1 and 2 Redfish stock management areas. The Unit 1+2 area, where Northwest Atlantic Fisheries Organization (NAFO) Subdivisions 3Pn and 4Vn are located, indicates the seasonal common area (January to May, Unit 1 and June to December, Unit 2). Context The Redfish index and experimental fisheries in Unit 1, and commercial fishery in Unit 2 harvest two Redfish species, Deepwater Redfish (Sebastes mentella) and Acadian Redfish (S. fasciatus), each considered a single stock in Units 1 and 2. Combined annual landings of both species and both Units dropped from over 100,000 t in the 1970s to less than 12,000 t as of 1995. Management measures have been applied to promote stock recovery for both species. Since 1995, the Redfish fishery has been under a moratorium in Unit 1 and a 2,000 t/year index fishery has been authorized since 1999. An experimental fishery in Unit 1 was established with an additional TAC of 2,500 t for 2018-2019 and 3,950 t for 2019-2020, which can be harvested all year round. There has been no moratorium on the commercial fishery in Unit 2 and the TAC has been 8,500 t/year since 2006. In 2011, 2012 and 2013, three strong cohorts recruited to the stock. Genetic analyses have indicated that they were dominated by S. mentella associated with the Gulf of St. Lawrence ecotype. Since then, S. mentella biomass has increased in research surveys in each of Units 1 and 2. This Science Advisory Report is from the January 20-22, 2020 meeting on the Assessment of Redfish Stocks (Sebastes mentella and S. fasciatus) in Units 1 and 2. Problems associated with important fishery and scientific source data for Unit 2 identified at the meeting prevented the provision of advice for Unit 2. Nonetheless, reference points for the two species covering both Units 1 and 2 were identified at the meeting. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada Science Advisory Schedule as they become available. March 2020 Quebec and Newfoundland and Labrador Assessment of Redfish stocks in Units 1 Regions and 2 in 2019 SUMMARY During the ongoing 2019-2020 fishery management year (preliminary data as of December 2019), Redfish landings reached 592 t in Unit 1 under the combined TAC for the index fishery (2,000 t) and the experimental fishery (3,950 t). From 2017 to 2019, the Unit 1 index fishery catch-per-unit-effort (CPUE) increased by a factor of 6.7, reaching the highest value since 1980. Bycatch represented 9% of total landings in the Redfish index and experimental fisheries in Unit 1 from 2000 to 2019. The main bycatch species were Greenland Halibut, White Hake, Atlantic Cod, and Atlantic Halibut. Forecasted increase in Redfish fishing effort could increase the incidental catch of several species, including some depleted species. Based on historical knowledge and preliminary analysis, bycatch and undersized Redfish catches could be mitigated by modifying fishing gear, fishing deeper than 300 m, and avoiding fishing during winter in the Laurentian Channel. However, reducing bycatch of multiple species could be challenging. Total minimum research survey trawlable biomass of S. mentella in 2019 was estimated at 4,365,000 t, the highest value observed in the time series (since 1984). Of that amount, 3,044,000 t were for fish larger than 22 cm (minimum regulatory size) and 497,000 t for fish larger than 25 cm. Total minimum research survey trawlable biomass of S. fasciatus was estimated to be 78,000 t in 2019, suggesting a decrease from 2017. Of that amount 57,000 t were for fish larger than 22 cm and 18,000 t for fish larger than 25 cm. In the summer 2019, the modal size for the 2011 to 2013 Redfish cohorts was 23 cm. If the anticipated growth of these cohorts continues, 51% of the individuals of the 2011 cohort should be larger than 25 cm by 2020. In the research survey in 2019, Redfish accounted for 90% of the total captured biomass as compared to 15% between 1995 and 2012. This relative biomass of Redfish is unprecedented and could have important ecological impacts on other species. A limit reference point (LRP), and proposed upper stock reference point (USR) were estimated for the two species for both management Units 1 and 2, based on surveys in Unit 1. For S. mentella, LRP and USR were estimated at 43 kt and 265 kt, respectively. For S. fasciatus, LRP and USR were estimated at 25 kt and 168 kt, respectively. In 2019, based on the empirical reference points, S. mentella was well above its proposed USR and therefore would be considered in the Healthy Zone. Estimates of adult abundance for 2019 were at or above levels that preceded declines since the mid-1980s that led the COSEWIC to designate the Gulf of St. Lawrence and Laurentian Channel Designable Unit (equivalent to Units 1 and 2) as endangered in 2010. In 2019, based on the empirical reference points, S. fasciatus was between the LRP and proposed USR and therefore would be considered in the Cautious Zone. Advice for Redfish in Unit 2 could not be provided due to data limitations and meeting time constraints. 2 Quebec and Newfoundland and Labrador Assessment of Redfish stocks in Units 1 Regions and 2 in 2019 BACKGROUND Species biology Redfish inhabit cold waters along the slopes of banks and deep channels at depths ranging from 100 to 700 m. Sebastes mentella is typically found in deeper waters than S. fasciatus. In the Gulf of St. Lawrence (GSL) and Laurentian Channel, S. mentella is found primarily in the main channels at depths ranging from 200 to 400 m. In contrast, S. fasciatus is present mainly at depths of less than 300 m, along the slopes of channels and on the banks, except in the Laurentian Fan, where it inhabits deeper waters. Redfish reside near the bottom during the day, leaving the sea floor at night to follow their prey as they migrate. Redfish are slow growing and long lived species. S. fasciatus grows more slowly than S. mentella, although this difference in growth rates only becomes obvious after 10 years of age. In both species, females grow faster than males after about 10 years of age. On average, it takes Redfish seven to eight years to reach the 22 cm minimum legal size. Based on the information currently available, males reach sexual maturity one to two years earlier than females. Male S. mentella mature at 9 years (length at 50% maturity, L50: 22.8 cm) and females at 10 years (L50: 25.4 cm), whereas males S. fasciatus mature at 7 years (L50: 19.6 cm) and females at 9 years (L50: 24.1 cm). Unlike many cold-water marine fish species, Redfish are ovoviviparous. Copulation occurs in the fall, most likely between September and December, and the females carry developing embryos until they are extruded in spring at the larval stage when they are able to swim. Larval extrusion occurs from April to July, depending on the area and species. Copulation and larval extrusion do not necessarily occur in the same locations. In the GSL, S. mentella releases its larvae approximately three to four weeks earlier than S. fasciatus. The larvae develop in surface waters and juveniles gradually migrate to greater depths as they grow. Stock structure based on genomics New genomic analyses from samples collected from 2001 to 2015 confirmed a pronounced genetic distinction between S. mentella and S. fasciatus, despite strong morphological similarity between these species. Three distinct ecotypes of S. mentella were characterised in the Northwest Atlantic: deep, shallow, and Gulf (GSL) (Figure 2). Surprisingly, 33 individuals of S. mentella GSL ecotype were sampled outside of Units 1 and 2, in sites associated with the S. mentella shallow ecotype, indicating mixed ecotype composition in the NAFO Divisions from 2G to 3K. At least five populations of S. fasciatus were identified, three occurring within the GSL. S. fasciatus samples near Strait of Belle Isle were also grouped with samples from Northeast Newfoundland, indicating gene flow and therefore migration between the GSL and the southern Labrador Sea via the Strait of Belle Isle. This result indicates a mismatch between stock structure and management units. Sample sizes in the Laurentian Fan area for the new genomic analyses were not sufficient to confirm or refute previous conclusions about a distinct population of S. fasciatus in that area. It is very difficult to distinguish S. mentella and S. fasciatus morphologically and too costly to distinguish them genetically in large scale fishery and scientific monitoring. However, species composition of samples can be inferred using anal fin ray (AFR) counts. This technique may be sensitive to sample size which may underestimate or overestimate the contribution of a given species. 3 Quebec and Newfoundland and Labrador Assessment of Redfish stocks in Units 1 Regions and 2 in 2019 Figure 2. Map of the 28 locations (black points) sampled from 2001 to 2015 in the Northwest Atlantic. The colored points next to each sampling point indicate the presence of genetic clusters. A genetic cluster was indicated as present if one individual showed at least 50% associated ancestry in the sampling area. Three ecotypes were described for S. mentella: GSL (cyan), shallow (blue), and deep (dark blue). Five populations were described for S.