Science Advisory Report  2013/060

Assessment of Nova Scotia (4VWX) Snow Crab

Summary

• Landings in 2012 for N-ENS (North-Eastern Nova Scotia) and S-ENS (South-Eastern Nova Scotia) were 603 and 11,707 t, respectively, and they were 345 t in 4X for the 2011/12 season, representing an increase of 13%, a decrease of 4% and no change relative to the previous year. Total allowable catches in 2012 were 603, 11,733 and 346 t in N-ENS, S-ENS and 4X, respectively.
• Non-standardised catch rates in 2012 increased by 6% in N-ENS, decreased by 8% in S-ENS and decreased by 24% in 4X, relative to the previous year. In S-ENS, decreased catch rates were attributed to a 14% decrease in Crab fishing area (CFA) 24.
• In N-ENS, the estimated soft shell crab discard (% of total landings) increased to 8.9% in 2012, vs 1.7% in 2011, possibly due to increased summer fishing activities. In S-ENS, 2012 estimated soft shell discards remained near 6.3% of the TAC (Total allowable catch). Soft shell discards in 4X are negligible.
• The post-fishery fishable biomass decreased by 8.7% in N-ENS and by 3.6% in S-ENS relative to 2011. In 4X, the preliminary pre-fishery fishable biomass decreased by 29.2% relative to 2010/2011, but further analysis of the 4X survey data is required to account for extreme temperature conditions in 2012.
• The recruitment index has decreased in all areas. Recruitment is currently at intermediate levels in S-ENS and low levels in N-ENS and 4X. In S-ENS, recruitment will likely continue for the next 4-5 years. However, for N-ENS and 4X little to no recruitment is expected for the next 4-5 years.
• Female snow crab abundance and associated egg production in all areas continue to decline after reaching highs in 2007/2008. Egg production is now below the long-term mean and is expected to remain so for at least 2 - 4 years due to a lack of maturing female crab.
• In ENS, estimates of bycatch were 0.01% of snow crab landings. CFA 4X shows higher (relative to ENS) bycatch rates at 0.02 % of snow crab landings. Bycatch levels are 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 and affect movement patterns of snow crab.
• The surface area of potential snow crab habitat in the SSE was above the long-term mean in all areas and is close to the maximum for reference period of 1998-present.
• A reference points-based Precautionary approach (PA) has been implemented in this fishery. The Limit reference point (LRP) is 25% of carrying capacity and the Upper stock reference (USR) 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. Various secondary (population and ecosystem) indicators are taken into consideration for management decisions.
• In N-ENS, fishable biomass has been stable and in the “healthy” zone (FB > USR) over the past three years. This positive outlook is, however, for the short-term. In the medium to long-term, there is a need to be mindful of the gap in recruitment which may limit the scope for flexibility in this area without immigration from other areas. A status quo TAC (603 t ) is recommended.
• In S-ENS, the population is considered to be in the “healthy” zone (FB > USR). As the fishable biomass continues to be near historically high levels with recruitment expected for at least the next three to four years, there is considerable scope for flexibility. A status-quo (11,707 t) to a marginal decrease in TAC would maintain current exploitation rates.
• In 4X, fishable biomass is in the “healthy” zone (FB > USR). However, as recruitment and potential immigration into the 2012/2013 season is uncertain, a more conservative harvest strategy is recommended pending further analysis before the 2013/2014 season.
• There have been an increasing number of anecdotal reports of unreported illegal landings, particularly in S-ENS. Such activities negatively impact the assessment and the application of a precautionary approach and must be addressed.

This Science Advisory Report is from the 27 February 2013 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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