Science Advisory Report 2020/042

Assessment of Scotian Shelf Snow Crab

Summary

• 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. The Total Allowable Catch (TAC) was 631 t and 6,632 t in N-ENS and S-ENS, respectively. 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. Relative to the previous year, this represents an increase of 40% (N-ENS) and a decrease of 9% (S-ENS).
• Commercial catches of soft-shelled (newly moulted) Snow Crab were 5% in N-ENS and 2% in S-ENS for the 2019 season. This is a decrease from 25% in N-ENS and is consistent in S-ENS from the previous season. Higher soft-shell catches for N-ENS were almost exclusively from the summer fishery.
• Estimation of a fishable biomass index was conducted using newly developed conditional, auto-regressive, spatiotemporal models. This “carstm” approach models Snow Crab numerical abundance with environmental (depth, substrate, temperature) and biological factors (species composition) as covariates.
• The modelled, post-fishery, fishable biomass 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 fishable biomass was 418 t, relative to 428 t in 2018.
• Substantial recruitment of female Snow Crab into the mature (egg-bearing) segment of the population occurred from 2016–2018, and egg/larval production is expected to be high, though decreasing, as the numeric densities of mature female Snow Crab are now declining.
• Bycatch of non-target species is extremely low (<0.4%) in all Snow Crab fishing areas.
• Based on stomach sampling, Atlantic Halibut, Atlantic Wolffish, Thorny Skate, and other skate species appear to be the predominant predators of Snow Crab on the Scotian Shelf. Increased Halibut biomass lowers both the abundance and reproductive potential of Snow Crab on the Scotian Shelf.
• A reference points-based Precautionary Approach has been implemented in this fishery. The Limit Reference Point is 25% of carrying capacity, and the Upper Stock Reference is 50% of carrying capacity. The Target Removal Reference is 20% of the fishable biomass in each area, and the Removal Reference is not to exceed fishing mortality at Maximum Sustainable Yield. Various secondary (population and ecosystem) indicators are taken into consideration for management decisions.
• In N-ENS, minor TAC decreases for the past two seasons and increased recruitment to the fishery have helped catch rates and fishable biomass estimates to rebound. N-ENS has moved from the cautious zone in 2018 to the healthy zone in 2019. Given stock status and incoming recruitment, catch levels similar to those in 2017 and 2018 would help to maintain recent exploitation levels.
• In S-ENS, substantial TAC reductions from 2016–2018 helped maintain stable fishery performance (catch rates) in spite of reduced recruitment, increased predation, and falling fishable biomass estimates throughout that time. Increased recruitment to the fishery is likely for the upcoming season. Exploitation rates derived from the fishery model have been declining in recent years. An increase in catch levels would help to maintain recent exploitation levels.
• 4X is the southern-most extent of Snow Crab distribution in the North Atlantic. Snow Crab behavior and distribution in 4X is affected by increased volatility of ecosystem pressures such as water temperature, predation, and bycatch in other fisheries. Due to a lack of coherence in inter-annual size-frequency distributions, the current Harvest Control Rules and associated management practices (ultimately based on survey results) for 4X should be revisited. Alternate harvest strategies will be explored before the upcoming fall season.

This Science Advisory Report is from the February 27, 2020, Stock Assessment of Scotian Shelf Snow Crab. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2020/042 (PDF, 2,365 KB)

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