Canadian Science Advisory Secretariat (CSAS) Research Document 2023/089 Maritimes Region December 2023 Assessment of Scotian Shelf Snow Crab in 2019 B.M. Zisserson, B.J. Cameron, A.C. Glass, and J.S. Choi Fisheries and Oceans Canada Population Ecology Division Bedford Institute of Oceanography PO Box 1006, 1 Challenger Drive Dartmouth, Nova Scotia B2Y 4A2 Foreword This series documents the scientific basis for the evaluation of aquatic resources and ecosystems in Canada. As such, it addresses the issues of the day in the time frames required and the documents it contains are not intended as definitive statements on the subjects addressed but rather as progress reports on ongoing investigations. Published by: Fisheries and Oceans Canada Canadian Science Advisory Secretariat 200 Kent Street Ottawa ON K1A 0E6 http://www.dfo-mpo.gc.ca/csas-sccs/ csas-sccs@dfo-mpo.gc.ca © His Majesty the King in Right of Canada, as represented by the Minister of the Department of Fisheries and Oceans, 2023 ISSN 1919-5044 ISBN 978-0-660-68883-1 Cat. No. Fs70-5/2023-089E-PDF Correct citation for this publication: Zisserson, B.M., Cameron, B.J., Glass, A.C., and Choi, J.S. 2023. Assessment of Scotian Shelf Snow Crab in 2019. DFO Can. Sci. Advis. Sec. Res. Doc. 2023/089. v + 135 p. Aussi disponible en français : Zisserson, B.M., Cameron, B.J., Glass, A.C., and Choi, J.S. 2023. Évaluation du crabe des neiges du plateau néo-écossais en 2019. Secr. can. des avis sci. du MPO. Doc. de rech. 2023/089. v + 142 p. http://www.dfo-mpo.gc.ca/csas-sccs/ mailto:csas-sccs@dfo-mpo.gc.ca iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... v MANAGEMENT ............................................................................................................................ 1 HISTORY ...................................................................................................................................... 2 METHODS .................................................................................................................................... 3 FISHERIES DATA .................................................................................................................... 3 RESEARCH SURVEY DATA ................................................................................................... 4 SPACE-TIME MODELING ....................................................................................................... 6 PREDATION ............................................................................................................................ 6 STOCK ASSESSMENT MODEL .............................................................................................. 7 ECOSYSTEM INDICATORS .................................................................................................... 7 LIFE HISTORY ............................................................................................................................. 7 ECOSYSTEM CONTEXT ............................................................................................................. 9 OVERVIEW .............................................................................................................................. 9 CONNECTIVITY ....................................................................................................................... 9 Larval Dispersion ................................................................................................................ 10 Movement ........................................................................................................................... 10 ENVIRONMENTAL CONTROL (HABITAT) ........................................................................... 13 TOP-DOWN CONTROL (PREDATION) ................................................................................ 14 BOTTOM-UP CONTROL (RESOURCE LIMITATION) .......................................................... 16 LATERAL CONTROL (COMPETITION) ................................................................................ 16 DISEASE ................................................................................................................................ 17 HUMAN INFLUENCE ............................................................................................................. 18 Bycatch of Snow Crab in Other Fisheries ........................................................................... 18 Bycatch of Other Species in the Snow Crab Fishery .......................................................... 18 Oil and Gas Exploration and Development ......................................................................... 19 Undersea Cables ................................................................................................................ 19 Socio-Economics ................................................................................................................ 20 Marine Protected Areas ...................................................................................................... 21 FISHERY ................................................................................................................................ 21 Effort .................................................................................................................................... 21 Landings .............................................................................................................................. 22 Catch Rates ........................................................................................................................ 23 At-sea-observer Coverage .................................................................................................. 24 Carapace Conditions of Catch and Soft-Shelled Crab ........................................................ 24 Old Crab (CC5) ................................................................................................................... 25 RESOURCE STATUS ................................................................................................................ 25 SIZE STRUCTURE ................................................................................................................ 25 iv Male .................................................................................................................................... 25 Female ................................................................................................................................ 25 SEX RATIOS .......................................................................................................................... 26 FEMALE NUMERICAL ABUNDANCE ................................................................................... 27 FISHABLE COMPONENT OF POPULATION ....................................................................... 28 RECRUITMENT ..................................................................................................................... 28 STOCK ASSESSMENT MODEL ............................................................................................ 28 FISHABLE BIOMASS ............................................................................................................. 29 FISHING MORTALITY (F) ...................................................................................................... 29 NATURAL MORTALITY ......................................................................................................... 29 THE PRECAUTIONARY APPROACH ........................................................................................ 30 REFERENCE POINTS AND HARVEST CONTROL RULES ................................................. 30 Current Limitations of Reference Points ............................................................................. 31 RECOMMENDATIONS ............................................................................................................... 31 GENERAL REMARKS ........................................................................................................... 31 NORTH-EASTERN NOVA SCOTIA (N-ENS) ........................................................................ 33 SOUTH-EASTERN NOVA SCOTIA (S-ENS) ......................................................................... 33 AREA 4X ................................................................................................................................ 33 ACKNOWLEDGMENTS ............................................................................................................. 34 REFERENCES CITED ................................................................................................................ 34 TABLES ...................................................................................................................................... 40 FIGURES .................................................................................................................................... 48 APPENDICES ........................................................................................................................... 125 APPENDIX 1: CONTEXT OF THE PRECAUTIONARY APPROACH .................................. 125 APPENDIX 2: STOCK ASSESSMENT MODEL .................................................................. 129 v ABSTRACT Landings in 2019 for North-Eastern Nova Scotia (N-ENS) and South-Eastern Nova Scotia (S-ENS) were 629 t and 6,632 t, respectively, representing a decrease of 15% (N-ENS) and an increase of 9% (S-ENS) relative to the previous year . Total Allowable Catches in 2019 were 631 t, 6,632 t, and 0 t in N-ENS, S-ENS, and 4X, respectively. Due to low commercial biomass levels, there was no allowable catch in 4X for the 2018–19 season. Non-standardized catch rates in 2019 were 87 kg/trap haul in N-ENS and 105 kg/trap haul in S-ENS—which relative to the previous year represents an increase of 40% (N-ENS) and a decrease of 9% (S-ENS). The capture of soft-shelled Snow Crab in N-ENS decreased to 5% from approximately 25% in 2018. In S-ENS, the relative occurrence of soft-shell Snow Crab was approximately 2%, consistent with 2018. Soft-shell discard rates in 4X are traditionally very low, due to season timing. Bycatch of non-target species is extremely low (< 0.4%) in all Crab Fishing Areas (CFAs). In both N-ENS and S-ENS, moderate internal recruitment to the fishery is expected for next year (and likely for 2–4 years) based on size-frequency histograms. Based on survey catches, CFA 4X shows limited potential for substantial internal recruitment to the fishery for the next 4–5 years. Movement is potentially an important source of 4X Snow Crab. In all CFAs, there was a substantial recruitment of females into the mature segment of the population from 2016–2018. Mature Snow Crab densities are now declining but small Snow Crab (< 40mm carapace width) resulting from this period of increased egg production are now observed in all areas in both sexes. These population characteristics are tempered by a number of uncertainties, including the influence of predation and rapid temperature swings (especially in CFA 4X and parts of CFA 24). Both can have direct and indirect influences upon Snow Crab, which are cold-water stenotherms. Predation from halibut is a potentially large and increasing source of natural mortality for Snow Crab on the Scotian Shelf. A new peer-reviewed assessment methodology, conditional auto-regressive spatio-temporal model (carstm), has been adopted that incorporates both survey catches and ecosystem covariates to estimate a commercial Snow Crab abundance index. This index is coupled with a population-dynamics fishery model to determine fishable biomass. The modelled post-fishery fishable biomass index of Snow Crab in N-ENS was estimated to be 4,460 t, relative to 3,299 t in 2018. In S-ENS, the post-fishery fishable biomass index was 54,408 t, relative to 44,705 t in 2018. In 4X, the pre-fishery fishable biomass was 418 t, relative to 428 t in 2018. The N-ENS fishing mortality (F) in 2019 has been estimated to have been 0.14 (exploitation rate 0.13), a decrease from 0.22 in 2018. The S-ENS fishing mortality (F) in 2019 has been estimated to have been 0.12 (exploitation rate 0.13), a decrease from .13 in 2018.The F for 4X in 2018–2019 was 0 as there was no commercial fishery. With expected increasing recruitment for both N- and S-ENS, coupled with falling F over recent years, possibilities for harvest strategy is less limited. Additional work is required to determine more applicable (than current survey-based) Harvest Control Rules and associated management measures in 4X. 1 MANAGEMENT The Scotian Shelf Ecosystem (SSE) Snow Crab (Chionoecetes opilio) stock is managed as three main areas: North-Eastern Nova Scotia (N-ENS), South-Eastern Nova Scotia (S-ENS), and 4X (Table 1; Figure 1). S-ENS is subdivided into two fishery management areas: Crab Fishing Area (CFA) 23 and CFA 24.These areas are ad hoc divisions based upon political, social, economic, and historical convenience, with little biological basis. Fishing seasons have also had a complex evolution based upon economic, safety, and conservation considerations: seasonal weather conditions; catch of soft-shell/white Snow Crab; disruption of mating periods; and overlap with other fisheries, especially American Lobster and Northern Shrimp. From 1982 to 1993, the management of the Eastern Nova Scotia (ENS) fisheries was based on effort controls (size, sex, shell-hardness, season, license, trap limits). Additional management measures were introduced from 1994 to 1999: Individual Boat Quotas (IBQs), Total Allowable Catches (TACs), 100% dockside monitoring, mandatory logbooks, and at-sea monitoring by certified observers (currently at levels of 5%, 5%, and 10% in N-ENS, S-ENS, and 4X, respectively). Vessel Monitoring Systems (VMS) have been implemented in S-ENS and 4X, and voluntary management measures requested by fishers were also introduced in some areas, such as a shortened fishing season and reduced numbers of traps. The designation of a “temporary license” holder was dropped in 2005 with a fleet rationalization that created a permanent stake in the fishery for all license holders. In 2006, the soft-shell protocol was modified in S-ENS due to the expectation of an increased incidence of soft-shelled Snow Crab and the potential harm associated with handling mortality. Soft-shelled Snow Crab incidence observed by at-sea-observers was relayed to Fisheries and Oceans Canada (DFO) within 24 hours of landing, plotted on a two-minute grid, and re- broadcast to all members of industry on the ENS Snow Crab web location (as well as via email and fax). Fishers are asked to voluntarily avoid fishing within 1.5 nautical miles of the locations that had greater than 20% soft Snow Crab in the observed catch. This adaptive fishing protocol allows rapid adjustment of fishing effort, shifting gear away from, or altogether avoiding, potentially problematic areas and also helping to save time, fuel, and other costs. This approach was not required in 4X due to the low incidence of soft Snow Crab in the catch and not adopted in N- ENS due to the short fishing season. However, due to high soft-shell incidence in N-ENS in 2007–2008, further direct management measures were implemented to address concerns of soft-shell handling mortality. These measures now include a spring season, in addition to the traditional summer season. This spring season was so instrumental in drastically reducing soft- shell catches that season start times were moved earlier in S-ENS as well. Finally, the voluntary return to the sea of immature, legal-sized Snow Crab (≥ 95 mm Carapace Width [CW]; pencil- clawed crab) was implemented in 2006 for all areas on the SSE, to allow these Snow Crab to complete their molting cycle and molt to maturity, thereby, simultaneously increasing the total yield per Snow Crab captured, as well as the total lifetime reproductive success of these large- sized males. In 1996, DFO (Gulf Fisheries Centre [GFC], Moncton, New Brunswick) and Scotian Shelf Ecosystem (SSE) Snow Crab fishers initiated a Joint Project Agreement to assess SSE Snow Crab using a fisheries-independent trawl survey (Biron et al. 1997). It was officially accepted for use as an assessment tool in 1999. These surveys demonstrated the presence of unexploited Snow Crab in the south-eastern areas of the SSE, which subsequently led to large increases in TACs (Tables 2–4), fishing effort, landings, and catch rates (Figures 2–4), and the addition of new participants. Trawl surveys were formally extended to 4X in 2004. http://www.enssnowcrab.com/ 2 Since 2013, research has been funded through Section 10 of the Fisheries Act (“fish allocation for financing purposes”). This mechanism provides additional quota to any license holder participating in a “Collaborative Agreement” (CA), which directly funds the Snow Crab scientific research program in the Maritimes Region. Since its inception in 2013, all license holders in the region have participated in the CA. A Marine Stewardship Council (MSC) Certification was granted to the ENS fishery in September 2011. Four surveillance audits have been completed since that time. The Scotian Shelf Snow Crab fishery was re-certified under MSC Version 2 in September of 2017, without conditions. The fundamental difference between the prior standard and Version 2 is that the habitat and ecosystem considerations are much broader, taking into account cumulative impact of all certified fishery in the fishing area being assessed. Though no audits were expected to occur until late summer of 2018, an expedited audit was convened in November 2017 due to numerous interactions between Snow Crab fishing and endangered North Atlantic Right Whales (NARW) in the neighboring Snow Crab regions in the southern Gulf of St. Lawrence. Audit results maintained MSC certification for Scotian Shelf Snow Crab. Through a separate process MSC certification was suspended for the Gulf of St. Lawrence Snow Crab fishery due to negative interactions with NARW. A standard surveillance audit of the ENS Snow Crab trap fishery was convened in the fall of 2018. MSC certification (with conditions) remained intact following this surveillance audit. These conditions relate to minimizing potential impacts of the fishery on the endangered NARW. The assessors also recommend improving the fishery’s reporting of interactions with designated Species at Risk. The most recent surveillance audit occurred in March of 2020; results not yet published. HISTORY The Snow Crab fishery is currently the second most valuable commercial fishery (after American Lobster) in both Atlantic Canada and Nova Scotia. It has been active since the mid- 1970s (Figure 2). The earliest records of landings were at levels of less than 1,000 t, mostly in the near-shore areas of ENS. By 1979, landings rose to 1,500 t, subsequent to which the fishery declined substantially in the mid-1980s and was considered a collapsed fishery. Recruitment to the fishery was observed in 1986 and, since that time, landings, effort and catch rates have increased considerably (Figures 2–4). In 1994, directed fishing for Snow Crab began in 4X, the southern-most range of distribution and continues at low harvest levels. Annual TACs (Tables 2–4) increased to a peak in 2002–2003 at 9,113 t in S-ENS and 1,493 t in N-ENS. Approximately 10,000 t of Snow Crab were landed each year from 2000 to 2004. Thus, in S-ENS the post-1998 period was one of rapid expansion of both the economic importance of the Snow Crab fishery and also the spatial extent of the exploitation. In 2004, with persistent low levels of recruitment and a steady decline in fishable biomass estimates, since the early-2000s, precautionary exploitation strategies were adopted throughout the SSE. In N-ENS, due to negligible recruitment, TACs declined sharply from 2004–2008. Increasing recruitment and fishable biomass estimates saw increased TACs until 2014. In 2015 and 2016, TACs were reduced due to low commercial biomass and an almost complete lack of recruitment to the fishery. These TAC declines were exacerbated by the adoption of Harvest Control Rules forcing the exploitation strategy in N-ENS to be more conservative. A new biomass estimation model, LBM (Lattice Boltzmann Method), was adopted in the 2017 assessment (2016 survey). This novel modelling approach saw a substantial increase in the biomass estimates for N-ENS, as modelled biomass estimates were used in determining a target exploitation rate rather than the previously-used survey index. In 2017, the TAC for N-ENS was the highest since 2004, in spite of continued poor recruitment to the fishery. This high TAC was essentially maintained in https://www.msc.org/ https://fisheries.msc.org/en/fisheries/scotian-shelf-snow-crab-trap/@@view http://www.dfo-mpo.gc.ca/stats/commercial/sea-maritimes-eng.htm 3 2018 (5% reduction). In 2017, this LBM approach was further refined to the spatiotemporal models of variability (stmv) approach which was considered to have yielded unrealistically stable biomass estimates with limited ability to inform annual TAC decisions. In 2019, the N-ENS TAC was reduced by 20% in response to low catch rates and the TAC not being caught in 2018, coupled with minimally informative biomass estimates. In S-ENS, TACs rose from 2005 to reach a previously unseen level in 2010, then gradually declined until 2015. The S-ENS TAC has been declining since 2016 due to decreased biomass estimates. The 2019 TAC increased by 10% given indications of increased recruitment and the highest catch rates since the expansion (number of licenses) of the S-ENS fishery. The TACs in 4X varied between 230 t and 346 t from 2005 to 2012. Reduced biomass estimates and poor performance of the 2012–2013 fishery in 4X (< 1/2 TAC landed) resulted in drastic reductions in the 4X TAC for 2013–2014. The 4X TAC has remained low (relative to pre-2013 levels) as have commercial biomass estimates. No commercial TAC was available in 4X for the 2018–19 season due to low commercial biomass levels and catch rates. Commercial TACs were reinstated in 2019 at 55 mt. METHODS The primary driver of the analytical approaches developed for the assessment of Snow Crab on the SSE is the high temporal and spatial variability in spatial distributions of Snow Crab. This is likely due to the area being the southern-most extreme of the species’ distributional range in the northwest Atlantic. All data analyses were implemented in the statistical computing language and environment R (R Development Core Team 2012) to allow migration and documentation of methods into the future. The complete analytical suite, coded in R, is posted to a GitHub repository website. Conversions between cartographic and Cartesian co-ordinate systems for analytical purposes were computed with PROJ (Evenden 1995, Version 4.4.9) via the R-package rgdal (Bivand et al. 2016) onto the Universal Transverse Mercator grid system (UTM Region 20). A number of spatial and/or temporal interpolation methods were used in this assessment. For rapid visualization of data (but not the actual assessment), thin-plate-splines were computed with the R-package fields::fastTps (Nychka et al. 2015), using a Wendland compactly supported covariance function with a range parameter of 25 km radius (theta) from every datum. This is a range comparable with that observed in the empirical variograms of many variables (Choi and Zisserson 2012). For analytical purposes, a novel lattice-based approach (stmv) was used in 2017 and 2018. This approach was found to be so overly time and computationally expensive and not operationally feasible given the time constraints of annual stock assessments. A more operational lattice- based approach using conditional auto-regressive spatio-temporal models (carstm) has been implemented for the current assessment. (See below for details.) This methodology was formally peer-reviewed in February 2020. FISHERIES DATA Fishery catch rates are potentially biased indicators of Snow Crab abundance. The spatial and temporal distribution of both Snow Crab and the fishing effort are not uniform, varying strongly with season, bottom temperatures, food availability, timing of spring plankton blooms, reproductive behavior, substrate/shelter availability, relative occurrence of soft and immature Snow Crab, species composition, fisher experience, bait type, soak time, and ambient currents. Catch rates have not been adjusted for these influences and are presented here only to https://github.com/jae0/bio.snowcrab https://github.com/jae0/bio.snowcrab 4 maintain continuity with historical records. Fishery catch rates are used as a measure of fishery performance and not necessarily stock performance/abundance. Mandatory commercial fishing logbooks (completed onboard fishing vessels by the captain) provide information on location, effort (number of trap hauls), and landings (verified by dockside monitoring). The data are stored in the MARFIS database (DFO Maritimes Region, Policy and Economics Branch, Commercial Data Division). Data were quality checked. At-sea-observed data provides information about the size structure and the Carapace Condition (CC) of the commercially exploited stock (Table 5; Figure 5). The data are stored in the Industry Survey Database (ISDB). At-sea observers are deployed randomly with the coverage being as evenly distributed as possible between vessels through an automated deployment system. The target coverage (as a percent of total landings) is set at 5% in S-ENS and N-ENS and 10% for 4X. At-sea-observer data is used to compute the potential bycatch of non-Snow Crab species by the Snow Crab fishery. Bycatch estimates of each species i, was extrapolated from the biomass of species i, observed in the catch and the relative observer coverage by: Bycatchi [kg] = Observed catchi [kg] × Total Snow Crab landings [kg] / Observed catchSnow Crab [kg] At-sea observers did not follow proper reporting protocol (only as it relates to bycatch) for the 2018 fishery in N- and S-ENS. Reliable species-specific data is not available for 2018. This issue was resolved for the 2019 fishery. Tables 10–12 include species specific bycatch levels for the past three years when proper reporting occurred by at-sea observers. RESEARCH SURVEY DATA Spatial coverage in the survey is (1) extensive, going well beyond all known commercial fishing grounds and (2) intensive, with a minimum of one survey station located pseudo-randomly in every 10 × 10 minute area (Figure 6). This sampling design was initially developed to facilitate geostatistical estimation techniques (Cressie 1993). Additional stations have been added adaptively based upon attempts to reduce local estimates of prediction variance, as well as identifying the spatial bounds of Snow Crab habitat. Between 2004 and present, approximately 400 stations have been sampled annually. The survey vessel F/V The Gentle Lady was used from 2004–2013. Due to the sinking of F/V The Gentle Lady in December 2013 during a commercial fishing trip, the subsequent surveys have been conducted aboard a vessel with similar characteristics; the F/V Ms. Jessie. Due to adverse weather conditions throughout the survey season of 2017, 32 stations did not get sampled as planned. These stations were on southern side of Banquereau Bank, on the south-east corner of the Scotian Shelf continental edge. All intended survey stations were completed in the 2018 survey. An extended survey vessel breakdown in the 2019 survey saw a later-than-normal completion, potentially affecting inter-annual comparability. To avoid a similar situation to 2017, with an entire block of stations going unsampled for the year, 7 stations were removed systematically towards the end of the 2019 survey. These were in areas where higher station density and lower inter-station variability occurred in past surveys. Total station numbers in 4X were strategically reduced from 34 to 20 since 2017 to match constricting viable habitat and reduce survey costs. The lower station count in 4X should have limited effects on modelled biomass estimates but must be considered in the interpretation of unadjusted density estimates as stations removed have had zero catches of Snow Crab for multiple years. The extensiveness of the sampling design allows the spatial bounds of the Snow Crab population to be objectively determined. This information is essential to provide reliable estimates of biomass and population structure (e.g., size, sex, maturity). The spatial distribution of Snow Crab is dynamic and can rapidly shift to areas where they are not “traditionally” found. In addition, the distribution patterns of immature, soft-shelled, very old and females do not 5 always correspond to those of legal size males. The former are considered to be less competitive and more susceptible to predation (Hooper 1986) and usually observed in environments or substrates with greater cover (gravel, rocks; Comeau et al. 1998). Sampling that focused upon areas where large hard-shelled males occur in high frequency would preclude the reliable estimation of the relative abundance of other segments of the Snow Crab population. Due to the gradual evolution of the aerial extent and alterations in the intensity and timing of surveys since the mid-1990s, direct inter-annual comparisons of the data are difficult over the entire time series. Temporal trends are most reliable for the post-2004 period. In all areas, fishing grounds are left fallow for as long as possible between commercial fishing and surveying of an area. This allows Snow Crab populations to redistribute following localized removals (i.e., commercial catches). Late fishing efforts, resulting from possible fishing season extensions, can impact the redistribution of Snow Crab. A custom Bigouden Nephrops trawl, a net originally designed to dig into soft sediments for a lobster species in Europe, was used to sample Snow Crab and other benthic megafauna (headline of 20 m, 27.3 m foot rope mounted with a 3.2 m long, 8 mm chain, with a mesh size of 80 mm in the wings and 60 mm in the belly and 40 mm in the cod-end). Net configuration was recorded with wireless trawl monitoring sensors; depth and temperature were recorded with Seabird SBE 39 temperature and depth recorders; and positional information was recorded with a WAAS (Wide Area Augmentation System)-enabled global positioning system. Actual duration of bottom contact was assessed from trawl monitoring and Seabird data streams. The ship speed was maintained at approximately two knots. The warp length was approximately three times the depth. Swept area of the net was computed from swept distance and monitored net width. Detailed descriptions of sampling protocols can be found in Zisserson (2015). All Snow Crab were enumerated; measured with calipers; shell condition determined (Table 5); and weighed with motion-compensated scales. Captured Snow Crab were also visually examined for the occurrence of Bitter Crab Disease (BCD). Data entry and quality control was provided by Javitech Ltd. and migrated onto the Observer Database System, held at DFO, BIO (Bedford Institute of Oceanography, Dartmouth, Nova Scotia). In cases where individual Snow Crab animals cannot be weighed (missing legs, excessive barnacle growth, etc.), individual weight estimates were approximated from CW measurements by applying an allometric relationship developed for SSE adult hard shelled Snow Crab (Biron et al. 1999; R2=0.98, n=750): mass [g] = 1.543 × 10-4 × CW [mm]3.206 The maturity status of males was determined from a combination of biological staging through CC and morphometric analysis. While physiological maturity is not directly coincident with the onset of morphometric maturity (Sainte-Marie 1993), the latter is more readily determined and is considered a reasonable proxy for physiological (sexual) maturity. In the terminal molt of male Snow Crab, a disproportionate increase of Chela Height (CH) relative to CW is generally observed. Morphometrically mature males (M(male)) can be discriminated from morphometrically immature males via the following equation (E. Wade, personal communication, GFC): M(male) = -25.324 • ln (CW [mm]) + 19.776 • ln (CH [mm]) + 56.650 where an individual is considered mature if M(male) > 0. The maturity status of females is assessed from visual inspection of egg presence. Where maturity status was ambiguous, maturity was determined morphometrically, as the width of 6 abdomen (measured by the width of the fifth abdominal segment, AW) increases rapidly relative to CW at the onset of morphometric maturity, facilitating the brooding of eggs. This onset of morphometric maturity (M(female)) can be delineated via the following equation (E. Wade, personal communication, GFC): M(female) = -16.423 • ln (CW [mm]) + 14.756 • ln (AW [mm]) + 14.900 where an individual is considered mature if M(female) > 0. Sex ratios (proportion female by number) were calculated as: Sex ratio = N(female) / (N(male) + N(female)) The BCD infections of Snow Crab were first detected on the trawl survey in 2008. From 2009–2011, laboratory analysis of haemolymph occurred to monitor actual infection rates within the Scotian Shelf Snow Crab population. This method was suggested to improve the detection rates as visual assessments are only effective in identifying late-stage infections. Upon critical comparison of the visual and laboratory results of BCD detection, visual assessment was determined to be a more robust method of detection. As such, the laboratory testing of Snow Crab haemolymph was discontinued due to high costs and unreliable results. Size-frequency histograms were expressed as number per unit area swept in each size interval (No./km2; therefore, the arithmetic mean numerical density per unit area). Modes and the bounds of each modal group were identified from size-frequency distributions. During development Snow Crab molt through several instar (I) stages. Each I was determined, after an analysis of size-frequency distributions, to have a lower bound of CW (mm) approximated by (see also Figure 7): CW(I, male) [mm] = exp(1.918 + 0.299 • (I – 3)) CW(I, female) [mm] = exp(2.199 + 0.315 • (I – 4)) SPACE-TIME MODELING Estimation of a fishable biomass index was conducted using Conditional Autoregressive models (for further details on development of this approach and model selection see Choi, 2020). The approach models Snow Crab numerical abundance with environmental (depth, substrate, temperature) and biological factors (species composition) as covariates (Figures 8–10) following a smooth process (second-order Random Walk: RW2); and random errors as a spatial autocorrelation in an Intrinsic Conditional Auto-Regressive model using a Besag York Mollié (BYM2) model grouped by year which is modelled as an AR1 (first-order autoregression) process. Analysis was conducted on numerical counts assuming a Poisson error distribution with swept area as offsets. Fishable biomass was computed from modelled results by multiplication of average weight in each areal unit (Figure 11) and then aggregation to the relevant management units. Parameterizations specific to the assessment can be found online. PREDATION Snow Crab predators were determined using data housed in the DFO Maritimes Region Food Habits Database (Cook and Bundy 2010). This database contains the stomach-contents information for more than 170,000 individuals representing 68 ground and pelagic fish species collected from various sources since 1958. There was consistent sampling of diet data in ENS between 1999 and 2016. From this data set, the predators of Snow Crab were determined, as https://github.com/jae0/bio.snowcrab/blob/master/R/snowcrab_parameters.R 7 well as the frequency with which Snow Crab have been observed as part of the predator species diet and the percent of total weight of stomach contents represented by Snow Crab . As the impact of predation relates not only to the frequency of the species consumed, but also the biomass of the predator species, the trends in biomass for the identified predators from the Snow Crab survey were examined. The biomass indices were presented as the geometric mean and bootstrapped confidence intervals of the area and were standardized weight for each tow (expressed as kg/km2). STOCK ASSESSMENT MODEL A modified discrete logistic model of the fishable biomass component is used to determine the relevant biological reference points (i.e., carrying capacity and fishing mortality [F] at Maximum Sustainable Yield, or FMSY) associated with the Harvest Control Rules of the Snow Crab fishery. Bayesian state-space methods are used to estimate the parameters of this model and associated Harvest Control Reference Points. See Appendix 1 for a general background to the Precautionary Approach (PA) and Sustainability as applied to this fishery. ECOSYSTEM INDICATORS A multivariate data simplification method known as multivariate ordination was used to describe systemic patterns in temporal data series (Koeller et al. 2000; Brodziak and Link 2002; Choi et al. 2005a; Koeller et al. 2006) from 2005 until 2014 in Scotian Shelf Snow Crab assessments. The key environmental, social, economic, and fishery-related indicators were identified and summarized annually. Indicators were made directly comparable by expression as anomalies in standard deviation units (i.e., a Z-score transformation) and then colour-coded. Missing values were coded as white. The metrics were then ordered in the sequence of the primary gradient (first eigenvector) obtained from the ordination. This allowed the visualisation of any temporal coherence in the manner in which suites of these indicators changed over time. The sequence of the indicators reflects the degree of similarity in their temporal dynamics. Specifically, a variant of Principal Components Analysis (PCA) was used that involved an eigenanalysis of the correlation matrices of the indicators, following data-normalisation of those that were not normally distributed (log10(x+1) transformations were sufficient). In classical PCA, it is customary to delete all such cases (years) with missing values, but this would have eliminated much of the data series from the analysis. Instead, Pearson correlation coefficients were computed for all possible pair-wise combinations with the implicit assumption that it represents a first-order approximation of the “true” correlational structure. In many cases, the data sources used to populate this overview have now changed (or ceased to exist completely) which has confounded the ability to keep this overview current. This approach will not be continued annually but reference herein remains to help describe the role of Snow Crab in an ever-changing ecosystem. LIFE HISTORY The Snow Crab is a subarctic species resident along the east coast of North America from northern Labrador to the Gulf of Maine. In the SSE, commercially fished Snow Crab are generally observed between depths of 60 m and 280 m and between temperatures of -1°C and 6 °C. Snow Crab are thought to avoid temperatures above 7°C, as metabolic costs are thought to match metabolic gains (Foyle et al. 1989); though in S-ENS Snow Crab have been observed above the “break-point” temperature. Snow Crab are generally observed on soft mud bottoms, although small-bodied and molting Snow Crab are also found on more complex (boulder, cobble) substrates (Sainte-Marie and Hazel 1992; Comeau et al. 1998). 8 Snow Crab eggs are brooded by their mothers for up to 2 years, depending upon ambient temperatures, food availability, and the maturity status of the mother (up to 27 months in primiparous females—first breeding event; and up to 24 months in multiparous females— second or possibly third breeding events; Sainte-Marie 1993). More rapid egg development (from 12 to 18 months) has been observed in other systems (Elner and Beninger 1995; Webb et al. 2007). Over 80% of female Snow Crab on the Scotian Shelf are estimated to follow an annual cycle, rather than the bi-annual cycle observed in most other areas (Kuhn and Choi 2011). A primiparous female of approximately 57.4 mm CW would produce between 35,000 to 46,000 eggs, which are extruded between February and April (in the Baie Sainte-Marguerite region of the northern Gulf of St. Lawrence; Sainte-Marie 1993). The observable range of fecundity is large, especially as multiparous females are thought to be more fecund with more than 100,000 eggs being produced by each female. Eggs are hatched from April to June when the pelagic larvae are released. The pelagic larval stage lasts for three to five months (zoea stages 1 and 2 and then the megalopea stage) during which Snow Crab are feeding upon plankton. The larvae settle to the bottom in autumn to winter (September to October in the Gulf area). In the SSE, pelagic stages seem to have highest abundance in October and so may begin settling as late as January. Very little is known of survival rates at these early life stages. Once settled to the bottom (benthic phase), Snow Crab grow rapidly, molting approximately twice a year (Sainte-Marie et al. 1995; Comeau et al. 1998; Figure 12). The first inter-molt stage (instar 1) is approximately 3 mm CW. After the 5th instar (15 mm CW), the molting frequency declines to annual spring molts until they reach a terminal maturity molt. Growth is allometric, with weight increasing approximately 250% with each molt (Figure 7). Terminal molt has been observed to occur between the 9th and 13th instar in males and the 9th to 10th instar in females. Just prior to the terminal molt, male Snow Crab may skip a molt in one year to molt in the next (Conan et al. 1992; Figure 12). They generally reach legal size (≥ 95 mm CW) by the 12th instar; however, a variable fraction of instar 11 Snow Crab are also within legal size. Male instar 12 Snow Crab represent an age of approximately nine years since settlement to the bottom and 11 years since egg extrusion. Thereafter, the life expectancy of a males is approximately five to six years. Up to ten months are required for the shell to harden (CC1 and early CC2; Table 5), and up to one year for meat yields to be commercially viable. After hardening of the carapace (CC3 to CC4) the male Snow Crab is able to mate. Near the end of the lifespan of a Snow Crab (CC5), the shell decalcifies and softens and may be heavy with epibiont growth. In some warm- water environments (e.g., continental slope areas), epibiont growth occurs at an accelerated rate creating some uncertainty in the classification of CC. Female Snow Crab reproducing for the first time (primiparous females) generally begin their molt to maturity at an average size of 60 mm CW and mate while their carapace is still soft (early spring: prior to the fishing season in ENS and during the fishing season in 4X). A second mating period later in the year (May to June) has also been observed for multiparous females(Hooper 1986). During mating, complex behavioral patterns have also been observed; the male Snow Crab helps the primiparous female molt and protects her from other males and predators (Hooper 1986). Pair formation (a mating embrace where the male holds the female) may occur up to three weeks prior to the mating event (Hooper 1986). Upon larval release, males have been seen to wave the females about to help disperse the larvae (i.e., prior to a multiparous mating). Females are selective in their mate choice, as is often the case in sexually dimorphic species, and they have been seen to die in the process of resisting mating attempts from unsolicited males (Watson 1972; Hooper 1986). Male Snow Crab compete heavily for females and often injure themselves (losing appendages) while contesting over a female. Larger males with larger chela are generally more successful in mating and protecting females from harm. 9 ECOSYSTEM CONTEXT OVERVIEW An overview of relevant social, economic, and ecological factors that have been used in previous Scotian Shelf Snow Crab assessments is summarized below (for more details, see Choi et al. 2005a). See Cook et al. 2015 for the most recent/complete table of sorted ordination of anomalies of key social, economic and ecological patterns on the Scotian Shelf relevant to Snow Crab. The first axis of variation accounted for approximately 22% of the total variation in the data, and it was dominated by the influence of declines in mean body size of organisms in the groundfish surveys; socio-economic indicators of ocean use by humans and associated changes in their relative abundance were: landings and landed values of groundfish (declining), invertebrates (increasing), declines in sharks and large demersals and landings of pelagic fish, and oil and gas exploration and development (increasing). Nova Scotia Gross Domestic Product (GDP) and population size were also influential factors that have been increasing. Further, the physiological condition of many groups of fish has been declining as has been the number of fish harvesters in Nova Scotia. The temporal differences along this axis of variation indicates that coherent systemic changes of socio-economic and ecological indicators occurred in the early-1990s, with some return to historical states evident. Temperature-related changes were generally orthogonal (independent) to the above axis of variation. This second (orthogonal) axis of variation, accounting for 10% of the total variation, was strongly associated with the cold intermediate-layer temperature and volume, bottom temperatures and variability in bottom temperatures, bottom oxygen concentrations, and sea ice coverage. Anecdotal information from fishers and fishery-based catch rates (Figure 4) suggests that the abundance of Snow Crab was low in the near-shore areas of the SSE, prior to 1980. Increases in catch rates were observed throughout the shelf in the mid-1980s and 1990s in N-ENS and S-ENS, respectively. As commercially exploitable Snow Crab require at least 9 years from time of settlement to reach the legal size of 95 mm CW, their increasing numerical dominance as macroinvertebrates on the shelf must have had its origins as early as the late-1970s and 1980s (N-ENS and S-ENS, respectively). For S-ENS, these timelines are confounded by the expansion of the fishing grounds towards increasingly offshore areas and the exploitation of previously unexploited populations. Most of this expansion was observed in the post-2000 period when TACs and the closely associated landings increased up to six-fold relative to the TACs, and landings of the 1990s, and a doubling of fishing effort (Figure 2 and Figure 3). The catch-rate increases observed in the 1980s and 1990s were, therefore, likely reflecting real increases in Snow Crab abundance. The possible causes of this change in abundance can be broken down into the following categories: connectivity (metapopulation dynamics); environment (habitat); top-down (predation); bottom-up (resource limitation); lateral (competition); and human (complex perturbations). CONNECTIVITY In this assessment, connectivity refers to the manner in which various populations are connected to each other via immigration and emigration, also known as metapopulation dynamics. Connectivity between Snow Crab populations exists through larval dispersion in the planktonic stages and directed movement during the benthic stages. 10 Larval Dispersion The potential for hydrodynamic transport of Snow Crab larvae from the southern Gulf of St. Lawrence to the SSE and internal circulation on the SSE has been studied by J. Chassé and D. Brickman (Ocean Sciences Division, BIO, DFO; personal communication). Treating larvae as passive particles, simulations suggested that a large numbers of larvae could potentially be transported onto the SSE (especially near Sable Bank and in the shallows further west). The possibility exists that Snow Crab larvae enter the SSE from the Gulf of St. Lawrence region and the Labrador current, especially given no genetic differences are found between all Atlantic Snow Crab populations (Pubela et al. 2008). Further, planktonic organisms can maintain their position in a single location in very strong advective conditions via control of vertical migrations. Thus, the degree of larval retention on the SSE, while unknown, can be large. The following observations also suggest that the SSE population may be acting as an autonomously reproducing system: • The temporal dynamics of the SSE Snow Crab population is generally out-of-phase with the cycles seen thus far in the southern Gulf of St. Lawrence. If the SSE was dependent upon the larval drift from the Gulf Region, the temporal dynamics of the populations would be in- phase. • The spatial distribution of Brachyuran larvae (Scotian Shelf Ichthyoplankton Sampling Program (SSIP) in the 1980s; see summary in Choi et al. 2005b, page 14) have been observed to be pervasive throughout the SSE with no spatial clines (i.e., no declines in abundance with distance from the Gulf of St. Lawrence area) as might occur if the source of larvae were solely from the Gulf Region. • A pulse of larval abundance was observed from 1997 to 1999 with peak levels in 1998 (Choi et al. 2005b, Page 14). The timing of this pulse is concordant with the growth schedules of the currently expected ‘local’ recruitment. Approximately nine years would be required to grow from the zoea stages to instar 11/12, the stages in which Snow Crab begin to molt to maturity in 2007, the same timeframe between 1998 and 2007. • The period in the late-1990s, when high larval production was observed, was the same period in which the abundance of mature male and female Snow Crab on the SSE were at their peak. This suggests that the Snow Crab resident on the SSE may be able to function as a self- reproducing system, regardless of inputs from other systems. Even if external sources of larvae do exist, the reproductive potential of the Snow Crab resident on the SSE proper cannot be dismissed. A conservative approach to the harvest of large mature males (i.e., moderate exploitation rates) will help ensure that the earlier maturing females in a recruitment pulse are not subjected to sperm limitations. Compromised mating (such as sperm limitation) could result in potential negative population consequences 7–10 years subsequent. Movement Snow Crab (especially large males) have been shown to have large locomotory potential based on tagging studies within the Maritimes Region. The movement of both males and females in Newfoundland has been postulated (Mullowney et al 2018) to be divisible into two types, seasonal and ontogenetic (life cycle related). This study suggests that ontogenetic movements appear associated with a search for warm water while seasonal migrations appear associated with both mating and molting in shallow water. 11 Both seasonal and ontogenetic movements appear to occur on the Scotian Shelf. Commercial fishing efforts (a strong indicator of large male Snow Crab concentrations) show seasonal patterns of trending to deeper water as shallower depths warm over the course of the spring months. Longer-scale (temporally and geographically) movements of male Snow Crab appear to be related to life-history requirements such as the availability of mature females for mating. Traditional Tagging Program Spaghetti tags have been applied opportunistically to monitor Snow Crab movement since the early-1990s. To encourage participation, a reward program and an online alternative for submitting the tag recapture information has been developed to facilitate reporting of tag recaptures. Movement information is primarily limited to recaptures of mature, terminally-molted male Snow Crab. The application of spaghetti tags prevents molting so only mature males are tagged and tag recaptures are from the male-only Snow Crab fishery. Results suggest that although Snow Crab movements are quite variable, the potential connectivity between regions is still high (Figure 13). Short-term seasonal movement patterns remain unidentified and are a source of uncertainty. Long-term movement patterns are more easily observed. Two distinct patterns of movement have been identified for commercial Snow Crab, which is marked by above-average rates of movement for a segment of the population (Figure 14) and more localized movements for the majority of tagged Snow Crab. There are also two distinct periods (2–4 years each) within the time series where appreciable increases in average movement rates were observed. In both cases, the mature Snow Crab population was male dominated with mature females being low in S-ENS and almost non-existent in N-ENS. This suggests that reproduction is a key factor influencing the movement of mature male Snow Crab in the region. Substantial emigration was observed from N-ENS to the Gulf (CFAs 12 and 19) during these periods. Unfortunately, immigration into N-ENS was not observed as no Snow Crab were tagged in the Gulf for an extended period of time. The movement of immature and female Snow Crab is unknown and remains a source of uncertainty. Additional analysis of potential factors influencing patterns of short- and long-term movement patterns is required. An unknown proportion of tag recaptures remain unreported. Anecdotal information suggests that fishers do not always report recaptures. Concern has been expressed that indication of Snow Crab movement between management areas through tag returns could influence current management practices. Such unreported recaptures negatively impact the understanding of movement patterns. Increased/complete reporting is essential to maximize this knowledge. Since 2004, 24,967 tags have been applied and 1,813 distinct tagged-Snow Crab recaptures (7.3%) have been reported (Table 6) in 4X, N-ENS, and S-ENS. Even with potential tagging- related mortality and exploitation rates of 15–30%, a much higher (than 7.3%) proportion of tags are likely recaptured yet not reported. Since 2004, there have been 171 individuals who have reported recaptures and there have been 1958 total recaptures (Table 6) of 1,813 Snow Crab. On average, each person participating has reported ten or more different captures. Other fish harvesters, operating in close proximity to these individuals, have not reported any tag recaptures. Of the 1,813 distinct tags recaptured, 1395 have been returned to the water and 130 of these have been captured again. Tracking tagged Snow Crab over multiple recaptures provides further insight into the movement patterns over their life cycle. When subsequent recaptures are reported, everyone who previously captured that particular Snow Crab are notified to encourage returning tagged Snow Crab to the water. http://www.enssnowcrab.com/tagentry.html http://www.enssnowcrab.com/tagentry.html 12 Snow Crab recaptured within 10 days of initial release are not included in analyses. This short- term movement could be directly influenced by other factors such as water currents drifting them as they settle to the bottom after release. Traditionally, the movement of tagged animals (e.g., Snow Crab) is stated as a straight line distance between release and recapture locations. This distance traveled calculation is now constrained by depth ranges of 60–280 meters. This depth range is considered to be a conservative estimate of Snow Crab habitat use as compared to previous methods ignoring habitat preferences. On average, Snow Crab tagged between 2004 and 2019 were first recaptured in the season following the tagging event (mean time to recapture was 456 days), with the longest time interval between release and initial capture being 2,278 days (approximately 6 years, 3 months; Figure 14). This Snow Crab had moved at least 132 km in that period. Very few [reported] recaptures occur two years past the tagging event. Most tagging is completed on commercial fishing vessels engaged in Snow Crab fishing operations; tags are generally applied where commercial Snow Crab concentrations and resulting harvesting is high. This high localized exploitation may explain why the majority of Snow Crab are recaptured in the same or following season after tagging. As such, higher recaptures and reporting are expected if all recaptures are reported. The locomotory ability of Snow Crab can be very large, as the average distance traveled was 27 km, with a maximum distance traveled of 504 km (Table 6). The average rate of movement was 1.78 km/month. These distances and rates are most likely underestimates as the actual distance traveled by Snow Crab will be greater due to the topographical complexity and the meandering nature of most animal movement. On average, Snow Crab captured in S-ENS have a “shortest path” (habitat constrained) movement rate of 2.07 km/month, slightly higher than N-ENS of 1.79 km/month. In 4X, the displacement rate is slightly lower again at 1.05 km/month (Table 7, Figure 15). From 2004–2019, movement between N-ENS and S-ENS was seldom observed. In total, 10 Snow Crab tagged in S-ENS were recaptured in N-ENS and 5 Snow Crab tagged in N-ENS were recaptured in S-ENS. These numbers may be underestimates of total movement due to non-reporting of recaptures (Figure 13). Returns from Snow Crab tagged between 2010 and 2014 suggested significant movement from N-ENS into the southern Gulf of Saint Lawrence (“the Gulf”, Figure 13). The apparent unidirectional nature of this movement (from N-ENS to the Gulf) is confounded by the fact that there had been a period of no tagging in the Gulf region during this period of time. As such, the true degree of connectivity between the Gulf and N-ENS remains unknown, and may be substantial given the high concentrations of commercial Snow Crab in the adjacent CFA 19. It is hoped that the renewed tagging program in CFA 19 will provide further insight into the dynamics of Snow Crab movement between these regions. The reporting rates of recaptured tags in 4X is believed to be much higher than other areas (Figure 15), due to the small fleet size (5–6 boats) and high engagement of the 4X Snow Crab fleet in the tagging program. Of the 971 tags deployed in 4X since 2008, 100 (10%) have been captured at least once. Of these, 14 (14%) were captured a second time and 5 (5%) were recaptured a third time. No movement of tagged Snow Crab between 4X and S-ENS has been reported. With high tag reporting and low emigration, a higher return rate for initial capture is expected. Higher mortality in 4X due to warming events (Zisserson and Cook 2017) and bycatch in other fisheries may be contributing factors. It is recommended that recaptured tagged Snow Crab be released immediately with the tag still attached after relevant data are recorded (date, location, depth, condition of Snow Crab, as well as information about the vessel and the individual who recaptured the tag). To view the movement data in more detail go to ENS Snow Crab website and click on the tagging tab. http://www.enssnowcrab.com/ 13 Dwindling return rates of spaghetti tags (Table 6) suggest that the substantial resources spent on this program should potentially be directed elsewhere. Acoustic Tagging Program Since 2013, acoustic tags have been applied to Snow Crab within and adjacent to N-ENS and proximal to the CFA 24/4X line. A methodology for the application of acoustic tags on Snow Crab has been developed (Zisserson & Cameron 2016). Acoustic receivers, both stationary and mobile, recognize and record whenever a Snow Crab with an acoustic tag approaches the receiver. To date, the majority of the acoustic tags were attached to terminally molted, mature male Snow Crab though 8 have been applied to mature female Snow Crab in Northeastern CFA 23 and 6 in CFA 19. None of the females have yet been detected. The acoustic tagging program allows for the potential discrimination of movement patterns without the need for recapture of the tag through commercial fishing activities. As such, reporting rates of tag recaptures do not bias movement data. Seasonal movement patterns into N-ENS from adjacent areas have long been hypothesized by the fishing industry in N-ENS. Acoustic receiver arrays between N-ENS and the Gulf and also N-ENS and CFA 23 may help describe these movement patterns. In the summer of 2013, 27 acoustic tags were deployed in N-ENS. In just over a year, 10 of these tags were detected on the Cabot Strait Line (essentially separating N-ENS and the Gulf) and 3 were later detected within the Gulf Region (Figure 16). This tagging was repeated in 2015 at the same locations. To date, none of these Snow Crab have been detected within, or near, the Gulf Region. Of the 27 that were released, 23 were detected within 15 nautical miles of the release locations. This supports the episodic nature of connectivity between the Gulf and N- ENS observed in the spaghetti tag movement data. In 2015, 40 acoustic tags were released in the Glace Bay Hole area of N-ENS; 45 more tags were added over 2018 and 2019. Detections of these animals have all been from within N-ENS. To determine if Snow Crab movement is unidirectional or bidirectional, acoustic tags have been released in the areas adjoining N-ENS. Since 2015, 57 tags were released in the Gulf Region (CFA 19) and 79 tags were released in S-ENS (CFA 23). To date, only one of these tagged Snow Crab has been detected in N-ENS—it was tagged 17 km south of the N-ENS/S-ENS line in April 2016 and was detected by a wave glider in October 2018. This detection occurred approximately 10 km north of this same dividing line, within N-ENS. In 2017, 10 Snow Crab with acoustic tags were released near the CFA 4X and CFA 24 boundary. Four of the five that were released in CFA 4X have since been detected on the Halifax receiver line and the other was captured and re-released during the fishery. One of the five Snow Crab released on the CFA 24 side was detected by a wave glider. If reproduction is, in fact, a main driver of movement patterns, we would expect to see increasing mobility of large male Snow Crab in the next few years as mature female abundance continues declining. Increased mean movement per month was observed in 2019 (Table 6). ENVIRONMENTAL CONTROL (HABITAT) Known environmental (abiotic) influences upon Snow Crab include substrate type, temperature variations, and oxygen concentrations. Altered temperature conditions over extended periods of time have been observed in the SSE. For example, prior to 1986, the Shelf was characterized by relatively warm bottom temperatures, low volume of the cold intermediate layer, and a Gulf Stream frontal position closer to the continental shelf. The post-1986 period transitioned to an environment of cold bottom temperatures, high volume of the cold-intermediate layer, and a Gulf Stream frontal position distant from the shelf. The principal cause of the cold conditions is 14 thought to have been along-shelf advection from both the Gulf of St. Lawrence and southern Newfoundland, and local atmospherically-induced, cooling. In the southwestern areas (Emerald Basin), the offshore warm slope water kept subsurface temperatures relatively warm throughout the 1980s and 1990s, the exception being in 1997–1998, when cold Labrador Slope Water moved into the region along the shelf break and flooded the lower layers of the central and southwestern regions. While this event produced the coldest near-bottom conditions in these shelf regions since the 1960s, its duration was short, lasting about one year. Bottom temperatures in the distributional centers of S-ENS Snow Crab have been generally increasing since the early-1990s (Figure 17). North-Eastern Nova Scotia shows a relatively more stable bottom temperature field though still exhibits a slight rising trend. In 4X, bottom temperatures continue to be generally warmer and more erratic than the other areas. Increasing temperatures can have multiple effects on Snow Crab populations. Bottom temperatures affect most instars of Snow Crab phenology though the very earliest (pelagic larvae) instars are directly affected by temperatures in the upper water column. Within acceptable temperature ranges, warmer temperatures can result in larger mature animals, hypothesized to be caused by decreased intermolt interval with warmer temperatures (Burmeister and Sainte-Marie 2010; Dawe et al. 2012). Larger mature females could also increase individual fecundity (Sainte-Marie et al. 2008). Unfortunately, these positive effects of minor temperature increases are likely mitigated or over-shadowed by more pronounced temperature changes that increase mean bottom temperatures into a range less suitable for Snow Crab. This can (and has) caused a northward shift of the overall stock’s distribution in both the Atlantic (Agnalt et al. 2010; Burmeister 2010) and Pacific (Orensanz et al. 2004). Temperature-driven biomass decreases in local Snow Crab populations have already been observed on the Scotian Shelf. Both abundance estimates and catch rates declined sharply in CFA 4X (the southernmost Snow Crab population in the Western Atlantic) following a warm water event in 2012–2013 (Zisserson and Cook 2017) and have failed to return to levels previously observed. Outside of direct biological effects on Snow Crab and their distribution, temperature changes potentially create new ecosystem regimes that affect Snow Crab’s relative role within the benthic community. These changes can manifest as changes in predation, food availability, lateral competition, invasive species, etc. TOP-DOWN CONTROL (PREDATION) Top-down influences refer to the role of predators in controlling a population (Paine 1966; Worm and Myers 2003). The capacity of predatory groundfish to opportunistically feed upon Snow Crab, in combination with their numerical dominance prior to the 1990s, suggests that they may have been an important regulating factor controlling the recruitment of Snow Crab. For example, Snow Crab in the size range of 5 to 30 mm CW (with a 7 mm CW mode; that is instars 2 to 7, with instar 7 being strongly selected) were targeted by Thorny Skate and Atlantic Cod (Robichaud et al. 1991). Soft-shelled males in the size range of 77 to 110 mm CW during the spring molt were also a preferred food item. The demise of these predatory groundfish in the post-1990 period, and the resultant release from predation upon the immature and soft-shelled Snow Crab, may have been an important determinant of the current rise to dominance of Snow Crab in the SSE. As the occurrence of Snow Crab (relative to other species) changes within the ecosystem, so does their potential role as both a predator and prey species (Boudreau and Worm 2012). The known predators of Snow Crab in the SSE were, in order of importance: Atlantic Wolffish (Anarhichas lupus), Atlantic Halibut (Hippoglossus hippoglossus), skates (Smooth Skate Malacoraja senta, Thorny Skate Raja radiata, and Winter Skate Leucoraja ocellata), Longhorn Sculpin (Myoxocephalus octodecimspinosus), Sea Raven (Hemitripterus americanus), Atlantic 15 Cod (Gadus morhua), White Hake (Urophycis tenuis), American Plaice (Hippoglossoides platessoides), and Haddock (Melanogrammus aeglefinus). From this data, the overall level of predation on Snow Crab appears to be negligible on the SSE as only Atlantic Halibut and Atlantic Wolffish have Snow Crab observed in more than 1% of the stomachs sampled (Table 8). This constitutes less than 1.5% of diet by weight within each species, particularly compared to other regions where the frequency of observing Snow Crab as prey is often greater than 10% (Robichaud et al. 1989, 1991). Atlantic Halibut biomass has increased almost exponentially (DFO 2018a), suggesting that the total number of Snow Crab consumed are likely increasing in relation to this predator (Figure 18 and Figure 19).Only Snow Crab < 65 mm CW are typically observed in fish stomachs because maximum span exceeds the predators’ mouth gape (Chabot et al. 2008). A proliferation of Atlantic Halibut, particularly the largest fish with large mouth gapes, could create predation on larger Snow Crab seldom experienced previously. Anecdotal reports of large Atlantic Halibut with multiple mature female Snow Crab in their stomachs support this assertion. Increased predation of mature females will impact the reproductive potential of Scotian Shelf Snow Crab. Atlantic Halibut are likely the largest source of predation of larger Snow Crab on the Scotian Shelf. Further study of Atlantic Halibut diet focused in areas of high Snow Crab density are planned. Atlantic Wolffish are important as a potential Snow Crab predator; however, their biomass indices suggest that they are currently at relatively low levels across all areas (Figure 20 and Figure 21). If the Snow Crab survey is more reflective of predators in Snow Crab habitat (vs. groundfish surveys), the biomass of Thorny Skate (Figure 22 and Figure 23) and Smooth Skate (Figure 24 and Figure 25) may be greater across all areas than previously thought. In many other areas, Atlantic Cod have been shown to be an important predator of Snow Crab (Bailey 1982; Burgos et al. 2013; Chabot et al. 2008; Lilly 1984; Orensanz et al. 2004; Robichaud et al. 1989, 1991). Boudreau et al. (2011) suggest that the top-down control effect of Atlantic Cod on Atlantic Canadian Snow Crab is most prevalent on older juvenile and sub-adult Snow Crab. Conversely, diet studies on the Scotian Shelf have not demonstrated Atlantic Cod to be a prevalent predator of Snow Crab (Table 8). Moreover, the Atlantic Cod populations on the SSE are currently at reduced biomass index levels in all regions relative to historic levels (Figure 26 and Figure 27). Haddock may represent an additional increasing source of predation in localized areas of S-ENS and particularly 4X (Figure 28 and Figure 29). The only predator species that strongly co-associated with Snow Crab based on their abundance were American Plaice, likely due to the difference in habitat preferences from the other predator species (Figure 30 and Figure 31). Due to the American Plaice’s small mouth gape size and mode of feeding, they are only capable of consuming early instar Snow Crab. Reports of Snow Crab predation by squids and other crabs have been made (Bundy 2004), however, their relative impacts are not known. Predation levels upon small, immature Snow Crab are also likely to be on the rise with the re- establishment of some groundfish populations (based on Snow Crab survey data) and changing temperature fields. High local densities of groundfish are found in areas where small immature Snow Crab are found in high densities. A change in the size structure of predator populations (towards larger body sizes) could shift predation to include larger Snow Crab as well, especially during the period immediately post-molt. Seals are considered by fishers to be a potential predator of Snow Crab, and their continued increase in abundance (Figure 32; DFO 2017a) is a source of concern for many fishers. Diet studies of Grey Seals in the early 1990s (Bowen and Harrison 1994) found that evidence of Snow Crab species were found in < 1% of the seal scat samples examined with a diet focusing 16 predominantly on Sand Lance, Atlantic Cod, and flatfishes. These studies were also at a time with much lower Snow Crab densities on the SSE as compared to today. While grey seals have on occasion been observed with Snow Crab in their stomachs, it should also be emphasized that some of the highest concentrations of Snow Crab are found in the immediate vicinity of Sable Island, an area where the abundance of Grey Seals is extremely high. The evidence indicating that seals have a negative influence upon the Snow Crab population, therefore, seems to be minimal. Seals and other marine mammals may have a positive influence by physically importing food and food waste (Katona and Whitehead 1988) from distant areas to the immediate vicinity of Sable Island, thereby indirectly “feeding” the Snow Crab and also removing their potential predators (in both early pelagic and benthic stages). BOTTOM-UP CONTROL (RESOURCE LIMITATION) Bottom-up influences refer to changes in a population due to resource (food) availability. Diet studies and field observations (Hooper 1986) indicate that the primary food items of larger (mature) Snow Crab are, in order of importance: echinoderms, polychaete worms (Maldane sp., Nereis sp.) and other worm-like invertebrates, detritus, large zooplankton, shrimps, smaller juvenile crabs (Rock Crab, Cancer irroratus; Toad Crab, Hyas coarctatus; Lesser Toad Crab, Hyas araneus), Ocean Quahog (Artica islandica), bivalve molluscs (e.g., Mytilus edulis, Modiolus modiolus), brittle stars (Ophiura sarsi, Ophiopholis aculeata) and sea anemones (Edwardsia sp., Metridium senile). Smaller Snow Crab have been observed to feed upon, in order of importance: echinoderms, polychaete worms, large zooplankton, detritus, and bivalves (e.g., Mytilus edulis, Modiolus modiolus, Hiatella arctica). Squires and Dawe (2003) demonstrated that male Snow Crab appear to be more capable predators than the females and consume more small fish. Studies have also demonstrated that cannibalism occurs within Snow Crab populations. Cannibalism between cohorts is size selective, with instars VIII and IX being a dominant predator on instar I individuals (Emond et al. 2015). It is also highly prevalent in intermediately-sized (morphometrically) mature female Snow Crab (Sainte-Marie and Lafrance 2002; Squires and Dawe 2003). This cannibalistic behavior can create an important source of density-dependent mortality. Based on the proliferation of Snow Crab in the 1990s and onwards, resource competition does not appear to have been a limiting factor. At the very base of the food web, 2018 annual chlorophyll a levels were at or below normal on the Scotian Shelf. The timing of the spring phytoplankton bloom was variable, of a lower magnitude and of normal duration on the Scotian Shelf generally. The Eastern Scotia Shelf experienced a shorter bloom than normal but it was of greater magnitude (DFO 2018b). The zookankton biomass was below normal on the Scotian Shelf in 2018. The shift in species structure of the zooplankton continues on the Scotian Shelf in 2018 with low (relative to historic mean) abundance of the energy rich Calanus finmarchicus. The effects of systemic changes in the plankton community will potentially echo through the higher trophic levels in the future. The distribution of Northern Shrimp (Pandalus borealis) on the Scotian Shelf appears to remain broad (Figure 33); however, Snow Crab survey shrimp densities (Figure 34) and stock-specific stock assessment results (DFO 2019) suggest that the SSE stock is in a depressed but improving state compared to historical levels. LATERAL CONTROL (COMPETITION) Lateral (and internal) influences refer to the competitive interactions with groundfish, other crab species, cannibalism, and reproduction-induced mortality (direct and indirect). The diet of Snow Crab overlap with some groundfish species; thus, the demise of these groups in the late-1980s 17 and early-1990s would have been doubly beneficial to Snow Crab, through the reduction in predation pressure and resource competition. The spatial distribution of Snow Crab overlaps with basket stars, sea cucumbers, Sand Lance, Capelin, and Toad Crab. Some of these species may be competitors of Snow Crab for food and habitat space. There were no strong negative relationships between Snow Crab and other bycatch species (Choi and Zisserson 2012), suggesting little competitive interaction. The potential competitors, Lesser Toad Crab (Figure 35 and Figure 36) and Jonah Crab (Figure 37 and Figure 38), remain in relatively patchy distributions and, therefore, do not currently appear to pose much threat to the overall health of the Snow Crab stock. Steady increases in near-shore Lobster populations in the past 10 years (DFO 2017b) may increase resource competition (and even predation) for juvenile Snow Crab whose habitat preferences overlap those of Lobster. DISEASE Bitter Crab Disease (BCD) is observed globally in crustaceans, though most-commonly in the northern hemisphere (Stentiford and Shields 2005). The name arises from the bitter (aspirin- like) taste, which infected animals exhibit once cooked, rendering them unmarketable. BCD infections in Snow Crab have been observed in Alaska, Newfoundland, Greenland, and on the Scotian Shelf (Morado et al. 2010). In Atlantic Canada, BCD infected Snow Crab were first observed in Bonavista Bay in 1990 (Taylor and Khan 1995), though the range of infection now extends from southern Labrador to the southern Grand Banks. Infected animals are rare on the southern and western coast (Dawe et al. 2010) of Newfoundland in the waters most proximal to the Eastern Scotian Shelf. Salinity levels and water temperature, as well as ocean currents (affecting the distribution of both crab larvae and the water-borne Hematodinium), are potential limiting factors of disease prevalence (Morado et al. 2010). Infected Snow Crab were first observed on the Scotian Shelf in the 2008 Snow Crab trawl survey, with a handful of anecdotal reports of infected Snow Crab having been seen in the commercial catch in the near-shore areas previous to 2008. The fall-survey timing is advantageous to detection as animals infected during the spring molt are expected to show visible signs of infection by the fall. Visible identification of infection can be confounded by examination of infected animals in early stages of (not yet showing visible) infection earlier in a given year. This disease is caused by a parasitic dinoflagellate of the genus Hematodinium. It infects an animal’s haemolymph (blood), gradually dominating the animal’s haemolymph and resulting in reduced numbers of haemocytes in the blood and the ability of the organism to transport oxygen. Infection appears to occur during molting, and almost all infections appear to occur in crabs that have molted within the past year (new shell). There is a higher likelihood of infection in juvenile crabs as they molt frequently. It is not known if animals infected with Hematodinium will always develop the disease. BCD is considered fatal and assumed to kill the host organism within a year. Infected animals appear lethargic or lifeless, and have a more reddish (“cooked”) appearance, dorsal carapace with an opaque or chalky ventral appearance, and a milky haemolymph appearance. Depending on the severity of the infection, it is readily identified visually. Polymerase Chain Reaction (PCR) laboratory assay performed on an alcohol-fixed haemolymph sample was considered by some researchers to be the definitive test of animal infection; however, the use of this laboratory approach on SSE Snow Crab appears to both costly and unreliable. Based on observational experience and seasonality of the survey, visual identification is now considered to be the most reliable method. The number of visibly infected animals has remained constant and at low levels with prevalence rates near 0.05% (Table 9). Snow Crab of both sexes have been observed with BCD in all areas (Figure 39) across a wide range of sizes (20–100 mm CW; Choi and Zisserson 2012), though generally, in immature animals below legal commercial size (Figure 40). To date, mature, older- 18 shelled crab infected with BCD have not been observed in the region. This suggests that infection may be linked to molting and it increases mortality rates substantially. The pulsed nature of ESS Snow Crab populations can cause apparent infection rates to climb when larger segments of the population are found in smaller size classes. HUMAN INFLUENCE The human influence is a relatively complex mixture of the above controlling influences, exerted both directly and indirectly upon Snow Crab. Directed fishing for Snow Crab is discussed in the next section (Fishery). Here, other forms of human influences are discussed. Bycatch of Snow Crab in Other Fisheries The spatial distribution of Northern Shrimp (Pandalus borealis) largely coincides with Snow Crab, so this fishery represents a potential source of additional Snow Crab mortality through incidental bycatch. The use of trawls by the shrimp industry is of particular concern as they can cause co-incident damage of Snow Crab, especially those susceptible to crushing, such as Snow Crab in newly molted soft-shelled stages. This is concerning since areas with high shrimp fishing activity are the same areas with the highest catch rates and landings of Snow Crab. Directed studies of the mortality and/or carapace damage caused by shrimp trawls on Snow Crab in Newfoundland concluded that the shrimp fishery did not impose substantial damage or mortality (Dawe et al. 2007). The inshore American Lobster (Homarus americanus) fishery may also represent a source of juvenile and adult female Snow Crab mortality in some areas, as anecdotal reports suggest Snow Crab are captured in Lobster traps and (illegally) used as bait. This has been stated by fishers to be more prevalent in 4X, as well as some limited areas along the Eastern Shore of Nova Scotia during the early part of the Lobster season in April. The presence of Snow Crab bycatch in Lobster traps generally occurs when cold bottom-water temperatures coincide with Lobster fishing efforts in near-shore areas. Additionally, bycatch of Snow Crab in Danish seines has been anecdotally reported from the limited flatfish fisheries on the Scotian Shelf, though this fishing method is now seldom used. Bycatch of Other Species in the Snow Crab Fishery At-sea-observed estimates of bycatch of other species in the commercial catch of the SSE Snow Crab fishery can be extrapolated to the entire fleet based on landings and the proportion of landings observed (Table 10 and Table 11). In 2018, at-sea observers did not follow proper reporting protocol in the N-ENS and S-ENS fisheries; therefore, reliable, species-specific bycatch estimates cannot be generated for the 2018 N-ENS and S-ENS fisheries. Proper bycatch sampling did occur during the 2017–2018 4X fishery. To best approximate total bycatch levels, the three-year mean bycatch levels for 2016, 2017, and 2019 species-specific data were used. In ENS, a total of 7,261 t of Snow Crab were landed in 2019 with associated estimates of bycatch at 3.4 t (0.05%). Bycatch rates in ENS are traditionally very low. CFA 4X had no bycatch due to a zero TAC for the 2018–2019 season. CFA 4X traditionally shows higher (relative to ENS) bycatch rates due to lower densities of commercial Snow Crab and higher species diversity in some fishing grounds. In 2013 and 2014, 4X bycatch rates were unusually high (relative to past seasons) due to very low catch rates and increased effort to locate commercial Snow Crab. These search activities increase fishing effort in non-traditional fishing grounds with higher densities of species other than Snow Crab. The hyper-constriction of fishing effort to the eastern-most portion of 4X since 2015, likely resulted in lower bycatch levels. 19 The low incidence of bycatch in commercial catch of the SSE Snow Crab fishery can be attributed to: • Trap design (top-entry conical traps) excludes many fish species. • Passive nature of fishing gear as opposed to other gear types, such as trawl nets (also increases survival of bycatch discards). • Large mesh-size of trap netting (at a minimum 5.25” knot-to-knot). The majority of bycatch for all areas is generally composed of other invertebrate species (e.g., Northern Stone Crab [Lithodes maja] and American Lobster) for which higher survival rates after release are expected, as compared to fin-fish discards. In ENS, Northern Wolffish and Spotted Wolffish, both Species at Risk Act (SARA)-listed species with “Threatened” status, have been observed in the bycatch of the fishery in at least one of the three fishing seasons from 2016, 2017, and 2019 (most recent years with proper data collection). Striped Wolffish (SARA-listed species of “Special Concern”) have also been observed in each of these three seasons. The catch of all three species was at extremely low levels. Their prevalence in Snow Crab catches will continue to be monitored. Oil and Gas Exploration and Development Oil and gas exploration and development has occurred, and continues to occur, on the Scotian Shelf near, or upstream from, major Snow Crab fishing grounds and Snow Crab population centers in both N-ENS and S-ENS. Seismic surveys are used by the oil and gas industry to identify areas of petroleum resource potential beneath the seafloor (Breeze and Horsman 2005). The effects of offshore oil and gas seismic exploration on potentially-vulnerable components of the Snow Crab population (e.g., eggs, larvae, and soft-shelled Snow Crab), as well as on the long-term biological development and behaviour of this long-lived species remain unknown (DFO 2004; Boudreau et al. 2009; Courtenay et al. 2009). Anecdotal reports following seismic exploration that occurred in November 2005 over the Glace Bay Hole and the shallows of the Sydney Bight ( i.e., Hunt Oil 2005; Husky Energy 2010), where immature and females are generally abundant, suggested that seismic activity may have negatively impacted the Snow Crab population proximal to the exploration program. The Canada-Nova Scotia Offshore Petroleum Board (CNSOPB), the regulator that oversees the petroleum industry that operates in the offshore of Nova Scotia, has issued a Call for Bids for offshore exploration in N-ENS and S-ENS in 2019–2021 (Figure 41), as part of its current three year plan (CNSOPB 2019). The potential area of exploration for 2019 is a block west of Sable Island. Potential exploration for 2020 is a large block west of The Gully encompassing Sable Island and substantial Snow Crab habitat. Two exploration blocks are open for bids for exploration in 2021. The offshore block is along the southern edge of the continental shelf east of The Gully, whereas the inshore block runs completely within S-ENS. All potential exploration areas overlap with juvenile, female, and commercial Snow Crab habitat. Future seismic exploration in offshore areas occupied by Snow Crab may need to evaluate the impacts on the species. Undersea Cables Undersea cables have been identified by fishers as another source of concern, in particular, the Maritime Link subsea cables in N-ENS. Two subsea High Voltage DC Cables now span approximately 180 km from Cape Ray, Newfoundland, to Point Aconi, Nova Scotia (Emera 2013), to transport electricity from the Lower Churchill Hydro-electric project. These cables were laid in the spring of 2017, directly through productive Snow Crab fishing grounds of N-ENS.The two 4’ diameter cables are spaced at least twice the water depth at a given location. Trenching to a minimum of 1 meter below the seafloor through spatially-specific jet benthic fluidizing 20 (20 cm path for each cable; EMERA 2016) should lower the likelihood of a physical barrier to movement being created, as opposed to more destructive and expansive methods of cable trenching. The cables may create a barrier to normal Snow Crab movement through static magnetic fields (and/or associated) induced electrical fields or increased temperature (generated by the resistance of flow through cables). These cables were energized in January 2018. Emera Newfoundland and Labrador (ENL) conducted a magnetic emissions survey in early May. Results indicate the intensity of the magnetic fields measured in-situ are lower than the emissions predicted by the models (J.-M. Nicholas, personal communication, EMERA Newfoundland and Labrador). At present, there is no information that can be presented to describe their effects upon Snow Crab. Additional tagging effort has been undertaken in this area since 2013 (see above section: Movement) by both DFO and Emera. This tagging will provide additional information about the movements of Snow Crab into and out of this area prior to, and following, the installation of the undersea cable. Socio-Economics A coherent change in many socio-economic indicators occurred in the mid-1990s, in the same time frame as the large-scale changes in the SSE (see Figure 13, Choi and Zisserson 2012). In general, the demographics of Nova Scotia shifted toward an older and more affluent population base with the ageing of the “baby-boomers”. The total population size has also been increasing over the historical record to approximately 953,869 people in 2017, as well as a trend toward a population with higher levels of education. Nova Scotia’s GDP (Gross Domestic Product) has also been increasing along with the GDP associated with oil and gas exploitation and the number of cruise ships visiting Halifax. These demographic changes are associated with a greater biological demand for fishery resources, locally and as exports. Amongst the more fishery-related indicators, there has been an increased importance of invertebrate fisheries with the demise of the groundfish in the early-1990s, both in terms of total landings and landed values of the fisheries. The number of shellfish closures has increased over time. However, the relative importance of fishing to the Nova Scotia GDP and the total number of fish harvesters has both been on the decline. The fished species have changed greatly since the early-1990s in conjunction with the rapid changes in species dominance structure. Since this time, total groundfish landings have declined, falling from 281 kt in 1991 to 44 kt in 2017 for the province of Nova Scotia. Similarly, the pelagic fish landings have decreased from 125 kt in 1990 to 46 kt in 2017. In contrast, invertebrate landings have increased from 111 kt to 168 kt since the 1990s, as has the total landed value for all fisheries combined, increasing from $445 million in 1990 to $1.4 billion in 2017. The links between the socio-economic changes observed and the changes in the SSE are complex. However, an important issue to consider is whether alterations in social and economic structure can assist in the continued evolution of precautionary and ecosystem-based management of a sustainable and viable Snow Crab fishery. Certainly, transparency in management, communication by science, and a unified voice among fishers with a long-term vision for their resource can assist, as has been the experience in S-ENS in the post-2004 period—a success that merits emphasis. Maintaining and fostering these positive determinants of stewardship is essential for the continued social, economic and ecological sustainability of this fishery. 21 Marine Protected Areas St. Anns Bank area was designated as a Marine Protected Area (MPA) in 2017 pursuant to the Oceans Act. The MPA is subdivided into four zones (Figure 42). The majority of the MPA (Zone 1) is a core protection area. The three remaining (smaller) zones are referred to as “adaptive management zones”, which allow limited human activity to occur within their boundaries. The presence of a refuge from fishing activities serves as a fallowing area; however, if the protection is disproportionately beneficial to other organisms (i.e., Snow Crab predators or prey items), the effects upon Snow Crab can be mixed. The long-term effects of an MPA cannot be determined at this point. The Gully MPA (Figure 42) is a 2,364 km2 area east of Sable Island and is the largest marine canyon in the Northwest Atlantic. This area was designated as a protected area in 2004 and is comprised of three distinct management zones, each with specific allowable activities. No Snow Crab fishing is permitted in any of these zones. The Snow Crab survey continues to occur within the St. Anns Bank and The Gully MPAs (through a designated approval process), providing data on the co-occurrence of Snow Crab and other species within these areas. Increased sampling survey catches (fish lengths, weights, and dietary analysis) occur at reference stations within and immediately outside the MPA boundaries. FISHERY Effort In N-ENS, a spring season was introduced in 2008 in an effort to reduce soft and white Snow Crab capture and handling during the summer season, and now represents the majority of the fishing efforts. This season was in addition to the traditional summer season. Individual fishers were able to fish during either or both seasons. Starting in 2019, there were no longer two distinct seasons. The season ran through the spring and summer, though fishing efforts were still constrained to the two historical fishing periods within the year. This temporal gap in effort is caused by Snow Crab fishers shifting focus to Lobster fishing. The Lobster fishery (Lobster Fishing Area 27) is effort controlled; each fisher realizes their landings/profit with a set number of traps for a set time period of time. Fishing Snow Crab (TAC controlled) during an open Lobster season would likely decrease Lobster landings and overall annual profit. After the successful trial of spring fishing in 2008, landings associated with spring fishing efforts peaked at 91% in 2010 and had remained above 65% of landings since that time, with the exception of 2014 and 2015 when sea ice conditions limited spring fishing efforts (Figure 43). Spring landings represented approximately 70% of total annual landings from 2016–2018. In 2019, 89% of the landings occurred before the shift of focus to Lobster fishing. Total effort (expressed as trap hauls) decreased in N-ENS in 2019 (Figure 2). The 2019 fishing effort (Figure 44) was again focused on the trench of deep water located along the north-eastern coast of Cape Breton (“inside”), with almost no effort in the Glace Bay Hole. Some fishing (albeit limited) occurred on the northern-most portion of N-ENS along the CFA 19 boundary line in 2019. The number of vessels active each season in N-ENS continues to slowly decline (Figure 45). In S-ENS, fishing effort has gradually been shifting from being almost exclusively offshore (> 75km) to a mix of offshore and inshore fishing grounds (Figure 44) with higher landings from offshore areas. Much of the fishing effort in CFA 23 still continued to be focused on the holes found between Misaine and Banquereau banks. The inshore area of CFA 23 saw reduced 22 fishing effort in 2019 as compared to 2018. In both seasons, this inshore effort occurs almost exclusively during the spring. Crab Fishing Area 24 saw a return of fishing efforts north of Sable Island, that had been reduced in 2018, with substantial 2019 fishing effort proximal to Canso and Middle banks. Summer fishing efforts in CFA 24 occurred generally within the same areas as spring fishing efforts, though at lower levels. In 2019, almost no fishing effort occurred along the CFA 23 boundary other than south of Canso Bank. This boundary line (particularly inshore) has traditionally represented important commercial fishing grounds in CFA 24. There was limited effort in the western-most portion (along the “Eastern Shore”; west of 61.5⁰ Longitude) of CFA 24 and no effort on the continental shelf edge throughout S-ENS. This lack of effort on the shelf edge is likely driven by decreased biomass (likely driven by warming bottom temperatures) coupled with increased fishing costs to operate further from shore. In both CFAs 23 and 24, fishing patterns were affected by an overlap with spring fishing activities for shrimp as the Snow Crab fleet has limited access to some of the most productive Snow Crab fishing zones throughout the spring months, due to area closures. (These areas are known as shrimp boxes.) When these areas open to the Snow Crab fleet in the early summer, the majority of fishing effort occurs within these shrimp boxes. Prior to 2010, less than 20% of S- ENS landings occurred before July 1st, whereas now over 50% of total landings consistently occur in this spring period. In comparison to CFA 23, CFA 24 consistently shows a higher percentage of spring landings (Figure 43), possibly indicating that CFA 23 is impacted by spring “shrimp box” closures. In S-ENS, the number of active vessels has shown a generally decreasing trend since 2009 (Figure 45). The current number of active vessels is approximately 50% lower than the pre-2010 period. This reduction is due to many licenses partnering and license holders choosing to lease their quota for the year rather than fishing it themselves. This raises concerns when hired captains and crews potentially have no long-term stake in this fishery. Such individuals may not follow proper handling protocols for discarded Snow Crab, or fish in strategic ways to avoid ones that are soft-shelled, and may not choose not to report tagged Snow Crab that are essential to proper movement studies. The vessel chosen to fish a license holder’s quota may be driven by the desire to maximize profit with little concern for experience of the captain and crew and their regard for conservation-minded harvesting. In 2019, a total of 7,200 and 63,200 trap hauls were applied in N-ENS and S-ENS, respectively. (Tables 2–4; Figure 2). Landings Landings in 2019 for N-ENS and S-ENS, were 629 t and 6,632 t, respectively, representing a decrease of 15% (N-ENS) and an increase of 9% (S-ENS) relative to the previous year (Figure 3 and Figure 46; Tables 2–4). Total Allowable Catches in 2018 were 631 t, 6,632 t, and 0 t in N-ENS, S-ENS, and 4X, respectively. Due to low commercial biomass levels, there was no allowable catch in 4X for the 2018–19 season. The majority of N-ENS landings came almost exclusively from the inner trench. S-ENS saw a general offshore migration of spatial-landings patterns from the 2018 season. (Figure 46). There were no landings on the continental slope areas of S-ENS in 2019. 23 Catch Rates1 Non-standardized catch rates in 2019 were 87 kg/trap haul in N-ENS and 105 kg/trap haul in S-ENS—relative to the previous year, represents an increase of 40% (N-ENS) and a decrease of 9% (S-ENS) (Figure 4; Tables 2–4). The effect of TACs on catch ra