Science Advisory Report  2011/045

Assessment of Nova Scotia (4VWX) Snow Crab

Summary

• Landings in 2010 for N-ENS and S-ENS were 576 and 13,150 t, respectively, and they were 229 t in CFA 4X for the 2009/10 season, representing increases of 0%, 22% and 0% relative to the previous year.
• Total allowable catches (TACs) in 2010 were 576, 13,200 and 230 t in N-ENS, S-ENS and CFA 4X. In 2009, they were 576, 10,800, and 346 t.
• Non-standardised catch rates in 2010 were 55.0 kg/trap haul and 102.5 kg/trap haul in N- and S-ENS, and 36.0  kg/trap haul in 4X in 2009/2010 – representing a decrease of 27%, an increase of 14% and an increase of 27%, respectively, relative to the previous year.
• The shift towards earlier fishing seasons appears to have improved soft shell crab handling rates in both N- and S-ENS. In N-ENS, the soft-shelled crab discard declined from 6.6% in 2009 to 3.5% in 2010. In S-ENS, soft-shell handling decreased from 16% in 2009 to 7.7% of the Total allowable catch in 2010. Soft-shell discard rates in CFA 4X are very low.
• In N-ENS, the post-fishery fishable biomass of snow crab in 2010 was 2,810 t (95% CI: 2,180 to 3,780 t; relative to 2,790 t (95% CI: 2,220 to 3,840 t) in 2009. In S-ENS, the post-fishery fishable biomass of snow crab was estimated to be 48.5 × 103 t (95% CI of: 32.2 to 77.9 × 103 t) relative to 49.3 × 103 t (95% CI of: 33.2 to 79.3 × 103 t) in 2009. In CFA 4X, the pre-fishery fishable biomass was 930 t (with a 95% CI of 590 to 1,440 t), relative to 1,070 t (95% CI of 640 to 1,730 t) in 2009/2010, representing a decrease of 13%.
• The leading edge of the main recruitment pulse of male crab detected in the mid-2000s first entered fishable sizes in 2007 and full entry to fishable sizes is expected in 2011/2012. Positive signs of adolescent crab suggest continued recruitment to the fishery for the next 2 to 3 years in N- and S-ENS. Recruitment beyond 2-3 years is potential due to the existence of animals in the 40-60mm size classes in S-ENS. These size classes are not observed in N-ENS. 4X currently shows a lack of adolescent crab recruiting to the fishery in next 3-4 years.
• Egg production remains above historic means though less than the peak observed in 2007/2008. Egg production is expected to begin to decline below historic means due to a lack of immature female crab between 30-60 mm, potentially affecting long-term recruitment patterns.
• High relative densities of predators of immature and soft-shelled snow crab were found in areas with high densities of immature snow crab. This adds uncertainty to the possible strength of future recruitment to the fishable biomass.
• Average bottom temperatures in 2010 were generally similar to those in 2009. The surface area of potential snow crab habitat was above the historical mean in all areas.
• By-catch levels, mostly of other crustacean species, are less than 0.014% of annual landings in ENS and approximately 0.17% in CFA 4X. By-catch has been extremely low in the historical record.
• Fishing mortality in N-ENS was estimated to be 0.19 (95% CI: 0.14, 0.24) or a harvest rate of 17.3%, unchanged relative to 2009. Good recruitment and significantly reduced soft-shell handling results in a positive outlook. Until a strong and persistent increase in fishable biomass is observed, long-term harvest rates between 10% and 20% is part of the strategy for sustainability in this fishery. A decreased or status quo harvest strategy is recommended.
• Fishing mortality in S-ENS was estimated to be 0.23 (95% CI: 0.15, 0.33) or a harvest rate of 20.5%, a small increase relative to F=0.20 in 2009. Good recruitment suggests a positive outlook; however, the capture of soft shell crab remains an important issue for this fleet. Long-term harvest rates between 10% and 30% are part of the strategy for sustainability in this fishery. A decreased or status quo harvest strategy is recommended.
• Fishing mortality in CFA 4X for 2009/2010 was estimated to be 0.22 (95% CI: 0.15, 0.33) or a harvest rate of 19.7%, relative to F=0.19 in 2008/2009. Long-term harvest rates between 10% and 30% are part of the strategy for sustainability in this fishery. As recruitment into the 2011/2012 season is uncertain, a decreased or status quo harvest strategy is recommended.

This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of 1-2 March 2011 on Atlantic Nova Scotia Snow Crab Assessment. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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