Science Advisory Report  2012/050

Assessment of Nova Scotia (4VWX) Snow Crab

Summary

• Landings in 2011 for N-ENS and S-ENS were 536 and 12,135 t, respectively, and they were 345 t in 4X for the 2010/11 season, representing decreases of 7%, 8% and an increase of 51% relative to the previous year.
• Total allowable catches in 2011 were 534, 12,120 and 346 t in N-ENS, S-ENS and 4X.
• Non-standardized catch rates in 2011 were 110.1 kg/trap haul in N-ENS, 106.4 kg/trap haul in  S-ENS, and 38.3  kg/trap haul in 4X in 2010/2011 – representing increases of 100%, 4% and 6%, respectively, relative to the previous year.
• The shift towards earlier fishing seasons continues to improve soft shell crab handling rates in both N- and S-ENS. In N-ENS, the estimated soft shell crab discards declined from 3.5% in 2010 to 1.7% in 2011. In S-ENS, estimated soft shell crab discards decreased from 7.7% in 2010 to 5.5% in 2011. Soft shell discards in 4X are negligible.
• In 2011, the post-fishery fishable biomass in N-ENS was estimated to be 3,010 t relative to 3,170 t in 2010. In S-ENS, it was estimated to be 45,830 t relative to 47,270 t in 2010. In 4X, it was estimated to be 540 t, unchanged from 2010/2011.
• A large recruitment pulse has propagated through the system since the early 2000s. This pulse has now fully entered into fishable sizes. Continued recruitment to the fishery is expected for the next 2-3 years in N- and S-ENS. Recruitment beyond 2-3 years is possible due to the existence of animals in the 40-70 mm size classes in S-ENS. In N-ENS, a potential gap in recruitment is possible as was experienced in 2003-2005. Currently, 4X shows a lack of adolescent crab recruiting to the fishery in the next 2-3 years and may rely heavily on immigration for commercially exploitable crab.
• Egg production continues to decline after reaching highs in 2007/2008. Egg production is now below the long-term mean and is expected to remain so for 2-4 years due to a lack of maturing female crab, potentially affecting long-term recruitment.
• Bycatch levels, mostly of other crustacean species, are less than 0.01% of annual landings in ENS and approximately 0.9% in 4X. By-catch continues to be extremely low in this fishery.
• High relative densities of predators were found in areas with high densities of immature snow crab. This predation may lower future recruitment to the fishable biomass.
• The surface area of potential snow crab habitat was above the 1998-2011 mean in all areas.
• A reference points-based Precautionary Approach is being adopted 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 F_MSY. Secondary indicators are used to inform management decisions under the harvest control rules linking the stock references to harvest strategies.
• In N-ENS, modelled fishing mortality was estimated to be 0.15 from 2009 to 2011. Good recruitment in the short-term and significantly reduced soft-shell discards result in a positive outlook. The fishable biomass was above the Upper Stock Reference (3.26 kt in 2011), i.e. in the “healthy” zone, where harvest rates between 10% and 20% are considered sustainable in this fishery. A status quo to a marginal increase in harvest strategy (rate) is recommended.
• In S-ENS, modelled fishing mortality was estimated to be 0.22 in 2010 and 2011. Good recruitment suggests a positive outlook. Continued reduction of soft shell crab interactions will benefit the long-term outlook of the fishery. The fishable biomass was above the Upper Stock Reference (35.0 kt in 2011), i.e. in the “healthy” zone, where harvest rates between 10% and 30% are considered sustainable in this fishery. A status quo to a marginal increase in harvest strategy (rate) is recommended.
• In 4X, assuming the Total Allowable Catch is reached, fishing mortality in 2011/2012 is expected to be 0.44. The modelled fishable biomass was above the Upper Stock Reference (0.63 kt in 2011), i.e. in the “healthy” zone, where harvest rates between 10% and 30% are considered sustainable in this fishery. As recruitment into the 2012/2013 season is uncertain, a decreased harvest strategy (rate) is recommended.

This Science Advisory Report is from the 28 February 2012 Assessment of Nova Scotia (4VWX) Snow Crab. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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