Canadian Science Advisory Secretariat Gulf Region Science Advisory Report 2024/020 April 2024 SOUTHERN GULF OF ST. LAWRENCE (CFAS 12, 12E, 12F, 19) SNOW CRAB (CHIONOECETES OPILIO) STOCK ASSESSMENT IN 2023 CONTEXT The Fisheries and Harbour Management Branch of Fisheries and Oceans Canada (DFO) has requested an assessment of the southern Gulf of St. Lawrence snow crab (Chionoecetes opilio) stock for Crab Fishing Areas (CFA) 12, 12E, 12F and 19. This Science Advisory Report is from the regional peer review of January 23-24th, 2024 on the Southern Gulf of St. Lawrence (CFAs 12, 12E, 12F, 19) Snow Crab Stock Assessment in 2023. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available. SCIENCE ADVICE Status • The 2023 southern Gulf of St. Lawrence snow crab commercial biomass index, estimated at 67,703 tonnes (t), is above the Upper Stock Reference (USR) with very high likelihood, placing the stock in the Healthy Zone of the Precautionary Approach (PA) Framework. Trends • Following a period of high levels from 2018 to 2022, the commercial biomass index decreased by 21% in 2023. • Pre-recruits to the fishery decreased to below the time series (1997-2023) average in 2023. • Female spawning stock indices have increased since 2006 and have remained at high levels in 2023. • The population recruitment index was at the highest recorded level in 2021, but has decreased in 2023 to the time series average. Ecosystem and Climate Change Considerations There is continued evidence of warming conditions in the southern Gulf of St. Lawrence that can impact snow crab population dynamics and distribution; and the mechanisms require further investigation. Stock Advice • Based on the harvest decision rule, the 2023 commercial biomass index corresponds to a target exploitation rate of 38.59% and a catch option of 26,126 t for the 2024 southern Gulf of St. Lawrence fishery. http://www.isdm-gdsi.gc.ca/csas-sccs/applications/events-evenements/index-eng.asp http://www.isdm-gdsi.gc.ca/csas-sccs/applications/events-evenements/index-eng.asp Gulf Region Stock Assessment 2023 Snow Crab 2 • A risk analysis indicates that this catch option would result in a very high likelihood that the commercial stock would remain in the Healthy Zone of the PA after the 2024 fishery. BASIS FOR ASSESSMENT Year Assessment Approach was Approved: November 21-25, 2011 (DFO 2012a) Assessment Type: Full Assessment Most Recent Assessment Date: January 25-26, 2023 (DFO 2023) Assessment Details 1. Broad category: index-based (trends in empirical indices only). 2. Specific category: Index-based (fishery-independent). Stock Structure Assumption • Snow crab in the southern Gulf of St. Lawrence is considered as a single biological stock unit. The snow crab trawl survey covers the majority of crab habitat (Surette and Chassé 2023). Reference Points • Limit Reference Point (LRP): 10,000 t of residual commercial crab biomass (DFO 2012b). • Upper Stock Reference (USR): 41,400 t of total commercial crab biomass (DFO 2012b). Harvest Decision Rule Figure 1. Harvest decision rule used for the southern Gulf of St. Lawrence snow crab fishery (DFO 2014), which maps the commercial biomass index to a target exploitation rate (solid blue line). The red line shows the limit reference point (LRP) for residual commercial biomass and the green line shows the upper stock reference (USR) point for commercial biomass. Fmax represents the maximum allowed exploitation rate. The blue dashed line shows the projected commercial biomass for 2024 and its corresponding target exploitation rate. Dotted blue lines indicate inflection points in the harvest decision rule. Gulf Region Stock Assessment 2023 Snow Crab 3 Data • Commercial landings/sales slips: 1967-2023. • Fishery logbooks: 1987-2023. • Snow crab trawl survey: 1997-2023. • Oceanographic data from September research vessel (RV) survey: 1971-2023. Data changes: • Survey design changes in 2006 and 2012, including expansion of the survey area and survey station redistribution. • The survey vessel was changed in 1999, 2003, 2013 and 2019 with likely changes in survey catchability. ASSESSMENT Figure 2. (Top left) Annual landings (in tonnes) of snow crab in the southern Gulf of St. Lawrence by fishing area, (Top right) Annual commercial recruitment and residual biomass in relation to the Upper Stock Reference (USR) (dashed line) and Limit Reference Points (LRP) (solid line), (Bottom left) Natural mortality and exploitation rate for commercial snow crab, (Bottom right) Observed (open circles and 95% confidence interval error bars) and predicted (black squares and shaded 95% confidence intervals) commercial crab recruitment by survey year. Gulf Region Stock Assessment 2023 Snow Crab 4 Figure 3. (Top left) Surface area within the polygon used for the biomass estimation and with bottom temperatures between -1 °C to 3 °C, an index of snow crab habitat, along with the mean temperature within the area .(Top right) Annual abundance (in millions; means with 95% confidence intervals) of primiparous and multiparous female snow crab and (Bottom left) small male crabs (instar VIII, 34 to 44 mm of carapace width), based on the trawl survey data. The red dashed line shows the average for the series. (Bottom right) Density (number per km2 ) contours of commercial crab in the southern Gulf of St. Lawrence in 2023. Historical and Recent Stock Trajectory and Trends Biomass: Following a period of high levels since 2018, the commercial biomass index decreased by 21% in 2023 compared to 2022. The 2023 southern Gulf of St. Lawrence snow crab commercial stock biomass, estimated at 67,703 t, is still well above the USR, placing the stock in the Healthy Zone of the PA. The residual component of the biomass is 24,393 t which is also well above the LRP (Figure 2, Top right). The density of commercial snow crab in the southern Gulf of St. Lawrence in 2023 is presented in Figure 3 (Bottom right). Abundance: After a period of high abundance in the early 2000’s, the female spawning stock declined to low levels in 2006 and has gradually increased to high levels and presently stands at 607 million in 2023 (Figure 3, Top right). Natural Mortality: Over the time series, natural mortality varied from 19% to 50%, with an average of 33%. In recent years, natural mortality stood at about 40% from 2020 to 2022 but has decreased to 30% in 2023 (Figure 2, Bottom left). Gulf Region Stock Assessment 2023 Snow Crab 5 Recruitment: Population recruitment indices, which were at record levels in 2021, have decreased to average levels in 2023 (Figure 3, Bottom left). After a period of high fishery recruitment, there was a 35% decrease in 2023. A fishery recruitment model is projecting a further 17% decrease in 2024 (Figure 2, Bottom right). History of Fishery Management Snow crab has been commercially exploited in the southern Gulf of St. Lawrence since the mid- 1960s. There are currently four Crab Fishing Areas (CFAs) in the southern Gulf of St. Lawrence: 12, 12E, 12F and 19, with CFA 12 being the largest by area, number of participants, and landings (Table 1). Management of these fisheries is based on quota and effort controls (trap allocations, trap dimensions and seasons). Only hard-shelled males larger than 95 mm carapace width are commercially exploited and landing of female crab is prohibited. Local area closures during the fishing season occur when 1) the proportion of soft-shelled crab exceeds 20% in monitored catches, or 2) North Atlantic Right Whales (NARW) are detected in a given area. Local area closures can result in significant displacement of fishing effort. Historical and Recent Landings, Effort and Catch Per Unit Effort (CPUE) Snow crab landings from the southern Gulf of St. Lawrence were low in the early 1970s but increased more than threefold from 1975 to 1982. There were four periods of high landings (exceeding 20,000 t): 1981 to 1986, 1994 and 1995, 2002 to 2009, and the current period, from 2012 to 2023, the longest in the series (Table 1, Figure 2, Top left). In recent years, CPUE values in CFA 12 ranged from 44.1 kilograms per trap haul (kg/th) in 2020 to 72.2 kg/th in 2023, among the highest in the series. Similarly, CPUE values 12E and 12F increased to their highest values in 2023, at 79.1 kg/th and 96.9 kg/th, respectively. The CPUE value for CFA 19 was 140.6 kg/th in 2023, the third highest in recent years. CPUE values for CFA 19 are typically much higher than those of other CFAs. Table 1. Landings, fishing effort and catch per unit effort from logbooks in the southern Gulf of St. Lawrence snow crab, Chionoecetes opilio, fisheries (Crab Fishing Areas 12, 12E, 12F and 19) from 2017- 2023 (note: landings for 2023 are preliminary). Year Landings (t) Effort (number of trap hauls) Catch per unit effort (kg/trap haul) 12 12E 12F 19 Total 12 12E 12F 19 12 12E 12F 19 2017 39,825 203 684 2,944 43,656 553,125 3,333 9,421 20,616 72.0 60.9 72.6 142.8 2018 20,769 260 1,183 2,048 24,260 469,887 5,579 17,120 13,120 44.2 46.6 69.1 156.1 2019 27,554 224 1,166 2,763 31,707 496,468 3,415 18,083 24,518 55.5 65.7 64.5 112.7 2020 24,554 234 1,084 2,284 28,156 556,780 5,098 22,168 22,458 44.1 45.9 45.2 101.7 2021 21,423* 223 592 2,241 24,479 363,136 5,314 18,612 18,384 57.4 55.7 59.1 121.0 2022 27,620* 197 1,173 2,671 31,661 537,820 2,509 15,240 23,690 51.4 78.5 76.5 112.6 2023 32,084* 291 1,329 1,700 35,404 444,480 3,678 13,718 12,088 72.2 79.1 96.9 140.6 *Total landings in CFA 12 include landings allocated to CFAs 12E (2021, 2022, 2023) and 12F (2021) that were fished in CFA 12. Gulf Region Stock Assessment 2023 Snow Crab 6 Projections for 2024 southern Gulf of St. Lawrence snow crab fishery Table 2. Risk analysis for different catch options for the 2024 southern Gulf of St. Lawrence snow crab fishery showing the probability that the residual commercial biomass (Bres) would be below limit reference point (LPR), the probability that the total commercial biomass (B) would be below the upper stock reference (USR), and the expected biomass for the 2024 survey. In bold is the catch option corresponding to an exploitation rate of 38.59%, the rate as per the harvest decision rule. Catch option (t) Probability Bres < LRP B < USR Predicted survey biomass for 2024 (t) 23,000 0.0% 0.8% 56,333 (43,811 – 71,558) 24,000 0.1% 1.3% 55,333 (42,811 – 70,558) 25,000 0.3% 2.1% 54,333 (41,811 – 69,558) 26,000 0.9% 3.2% 53,333 (40,811 – 68,558) 26,126 1.1% 3.4% 53,207 (40,685 – 68,432) 27,000 2.6% 4.7% 52,333 (39,811 – 67,558) 28,000 6.1% 6.7% 51,333 (38,811 – 66,558) 29,000 12.2% 9.2% 50,333 (37,811 – 65,558) 30,000 21.5% 12.4% 49,333 (36,811 – 64,558) Ecosystem and Climate Change Considerations Water temperature can affect moulting, reproduction, and movement of snow crab. Bottom temperatures over most of the southern Gulf of St. Lawrence are typically between -1 and 3 °C. Overall, bottom temperatures for the southern Gulf of St. Lawrence during 2023 were still much warmer than normal (1991-2020). In CFA 12, temperatures were 0.5 to 1 °C (or more) above normal. Very few areas had below normal temperatures in 2023. The surface area with bottom temperatures between -1 and 3 °C in September, and within the polygon used for the estimation of the commercial biomass, rose slightly in 2023 but remained low (Figure 3, Top left). The average temperature within that area (1.3 °C) is still well above the long-term average (1991-2020) but decreased by 0.1 °C from 2022. The 2023 average temperature is the sixth highest of the 1971-2022 time series. SOURCES OF UNCERTAINTY The southern Gulf of St. Lawrence snow crab survey was developed to provide quality abundance and biomass indices: it uses a bottom trawl with high catchability for commercial crab, contains a fairly large number stations which are sampled annually, and a sampling area that covers most of the crabs’ habitat. Changes in sampling design and fishing protocols have led to improvements in the survey over the years. However these changes, particularly the expansion of the survey area, the relocation of survey stations and variations in the survey's timing, may have led to variations in survey catchability. In addition, trawl catchability is known to vary with bottom type, sea conditions, current, vessel type, trawling speed and trawl symmetry. Fishery pre-recruits (R-4, R-3, R-2) have decreased substantially from 2020 to 2022. R-3s and R-2s continued their downward trend in 2023 and are now below average levels. Despite the decrease in R-2s from 2020 to 2023, R-1s remained relatively stable, with the first significant decrease only appearing in 2023. Thus, a disconnect exists between R-1s and R-2s in recent years. Furthermore, skip-moulting proportions among R-2s are high in 2023. This adds to the Gulf Region Stock Assessment 2023 Snow Crab 7 prediction uncertainty in the fishery recruitment model, which neither accounts for annual variations in mortality, nor accounts for variations in skip-moulting rates. There is continued evidence of warming conditions in the southern Gulf of St. Lawrence that can impact snow crab population dynamics and distribution, in the short to long-term. Although some of these aspects are regularly monitored as part of annual assessments, the mechanisms require further investigation. The collapse of the Eastern Bering Sea snow crab stock in 2021 provides a cautionary tale on how quickly stock status can change. Before the collapse, assessment biologists reported record levels of recruits in 2018, which decreased substantially in 2019 and were at minimal levels in 2021. These decreases coincided with a marine heat wave resulting in a substantial decrease of the cold pool from 2018 to 2021. LIST OF MEETING PARTICIPANTS Name Affiliation Aaron Mike Sock MAWIW Council Inc. (Elsipogtog, Esgenoôpetitj and Neqotkuk) Alan Dwyer MPO GPP - GLF Alden Gaudet Prince Edward Island (PEI) Snow crab Fisherman Association Alexandre Duguay Maritimes Fishermen’s Union (MFU) Amélie Rondeau DFO Science - GLF Andrea Danielle Goff-Beaton DFO GPP - GLF Andrew Bourgeois Gulf Nova Scotia Fleet Planning Board Andrew Harbicht DFO Science - GLF Annie Paulin Government of New Brunswick Basil MacLean Area 19 Snow Crab Fishermen’s Association Ben Zisserson DFO Science - MAR Billy Brophy Area 18 Crab Fishermen's Association Carter Hutt PEI Snow Crab Fisherman Association Chantal Roussel DFO Communication - GLF Christina Burnsed Directrice des pêches Gesgapegiag Craig Knickle Mi'kmaq Confederacy of PEI Daniel Desbois Association des Crabiers Gaspésiens Dominic Boula DFO FHM - QC Emmanuel Saindt-Duguay Mi’gmaq Wolastoqey Indigenous Fisheries Management Association (AGHAMM) and Gespe’gewa’gi Mi’gmaq Resource Council (GMRC) Erin Fedewa National Oceanic and Atmospheric Administration (NOAA)- Fisheries Ethan Augustine North Shore Mi'kmaq Tribal Council - Anqotum Resource Management Fabiola Akaishi DFO Science - GLF Gulf Region Stock Assessment 2023 Snow Crab 8 Name Affiliation Jean Lanteigne Fédération Régionale Acacienne des Pêcheurs Professionnels (FRAPP) Jean-Francois Landry DFO Science - GLF Jenni McDermid DFO Science - GLF Joël Chassé DFO Science - GLF Joël Gionet Association des Crabiers Acadiens Johanne Basque Micmac GESPEG Jolene Sutton DFO Science - GLF Josiane Massiera DFO FHM - GLF Julie Marentette DFO Science - NHQ Kris Vascotto Atlantic Halibut Council / Groundfish Enterprise Allocation Council (GEAC) / Vascotto Resource Services Inc./Area 19 Crab Fishermen's Association Krista Baker DFO Science- NL Lewis Clancey Province of Nova Scotia- Department of Fisheries and Aquaculture Lindsay Carroll The Confederacy of Mainland Mi’kmaq Louis Ferguson Maritime Fishermen's Union (MFU) Marcel Hébert Association des Crabiers Acadiens (ACA) Martin Noël Association des Pêcheurs Professionnels Crabiers Acadiens Inc. (APPCA) Mathieu Hébert MFU Melanie Giffin PEI Fishermen’s Association (PEIFA) Mélanie Roy DFO Science - GLF Melissa Olmstead DFO Science - NHQ Merrielle Ouellette Groupe des Pêcheurs de la Zone F Mikio Moriyasu DFO Science - GLF Nicolas Rolland DFO Science - GLF Paul Boudreau Regroupement des Pêcheurs Professionnels des Iles-de-la- Madeleine Paul Robichaud FRAPP Philippe Girard zone 12E Renée Allain DFO Science - GLF Robert Haché ACA Robert MacMillan PEI Provincial Government Samantha Bois Roy Coopérative des Capitaines Propriétaires de la Gaspésie (ACPG) Gulf Region Stock Assessment 2023 Snow Crab 9 Name Affiliation Sean Triska MAWIW Council Inc. (Elsipogtog, Esgenoôpetitj and Neqotkuk) Stephanie Boudreau DFO Science - GLF Steve Lapierre Groupe des pêcheurs zone F Tanya Arseneault DFO Science - GLF Tobie Surette DFO Science - GLF William Stockhausen NOAA Fisheries (Alaska Fishery Science Center) SOURCES OF INFORMATION DFO. 2012a. Proceedings of the Gulf Region Science Peer Review Framework Meeting of Assessment Methods for the Snow Crab Stock of the southern Gulf of St. Lawrence; November 21 to 25, 2011. DFO Can. Sci. Advis. Sec. Proceed. Ser. 2012/023. DFO. 2012b. Revised reference points for snow crab to account for the change in estimation area of the southern Gulf of St. Lawrence biological unit. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2012/002. DFO. 2014. Assessment of candidate harvest decision rules for compliance to the Precautionary Approach framework for the snow crab fishery in the southern Gulf of St. Lawrence. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2014/007. DFO. 2023. Assessment of snow crab (Chionoecetes opilio) in the southern Gulf of St. Lawrence (Areas 12, 12E, 12F and 19) in 2022 and advice for the 2023 fishery. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2023/017. Surette, T., and Chassé J. 2023. The 2022 assessment of the snow crab (Chionoecetes opilio) stock in the southern Gulf of St. Lawrence (Areas 12,12E, 12F and 19). DFO Can. Sci. Advis. Sec. Res. Doc. 2023/059. v + 44 p. https://www.dfo-mpo.gc.ca/csas-sccs/Publications/Pro-Cr/2012/2012_023-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/Pro-Cr/2012/2012_023-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/Pro-Cr/2012/2012_023-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2012/2012_002-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2012/2012_002-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2014/2014_007-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2014/2014_007-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2014/2014_007-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2023/2023_017-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/SAR-AS/2023/2023_017-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/ResDocs-DocRech/2023/2023_059-eng.html https://www.dfo-mpo.gc.ca/csas-sccs/Publications/ResDocs-DocRech/2023/2023_059-eng.html Gulf Region Stock Assessment 2023 Snow Crab 10 THIS REPORT IS AVAILABLE FROM THE: Center for Science Advice (CSA) Gulf Region Fisheries and Oceans Canada P.O. Box 5030 Moncton, NB E1C 9B6 E-Mail: DFO.GLFCSA-CASGLF.MPO@dfo-mpo.gc.ca Internet address: www.dfo-mpo.gc.ca/csas-sccs/ ISSN 1919-5087 ISBN 978-0-660-70789-1 Cat. No. Fs70-6/2024-020E-PDF © His Majesty the King in Right of Canada, as represented by the Minister of the Department of Fisheries and Oceans, 2024 Correct Citation for this Publication: DFO. 2024. Southern Gulf of St. Lawrence (CFAs 12, 12E, 12F, 19) Snow Crab (Chionoecetes opilio) Stock Assessment in 2023. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2024/020. Aussi disponible en français : MPO. 2024. Évaluation du stock de crabe des neiges (Chionoecetes opilio) en 2023 dans le sud du golfe du Saint-Laurent (ZPC 12, 12E, 12F, 19). Secr. can. des avis sci. du MPO. Avis sci. 2024/020. mailto:DFO.GLFCSA-CASGLF.MPO@dfo-mpo.gc.ca http://www.dfo-mpo.gc.ca/csas-sccs/ http://www.dfo-mpo.gc.ca/csas-sccs/ SOUTHERN GULF OF ST. LAWRENCE (CFAs 12, 12E, 12F, 19) SNOW CRAB (CHIONOECETES OPILIO) STOCK ASSESSMENT IN 2023 CONTEXT SCIENCE ADVICE Status Trends Ecosystem and Climate Change Considerations Stock Advice BASIS FOR ASSESSMENT Assessment Details Stock Structure Assumption Reference Points Harvest Decision Rule Data ASSESSMENT Historical and Recent Stock Trajectory and Trends History of Fishery Management Historical and Recent Landings, Effort and Catch Per Unit Effort (CPUE) Projections for 2024 southern Gulf of St. Lawrence snow crab fishery Ecosystem and Climate Change Considerations SOURCES OF UNCERTAINTY LIST OF MEETING PARTICIPANTS SOURCES OF INFORMATION THIS REPORT IS AVAILABLE FROM THE: