Research Document - 2014/052
Assessment of Scotian Shelf Snow Crab in 2013
By A.M. Cook, B.M. Zisserson, B.J. Cameron, and J.S. Choi
Abstract
Landings in 2013 for North-Eastern Nova Scotia (N-ENS) and South-Eastern Nova Scotia(S-ENS) were 783 and 11,309 t, respectively, and they were 118 t in Crab Fishing Area (CFA) 4X for the 2012/2013 season, representing an increase of 17% (N-ENS) and decreases of 3% (S-ENS) and 66% (4X) relative to the previous year. Total allowable catches (TACs) in 2013 were 783 t, 11,311 t and 263 t in N-ENS, S-ENS and 4X. Non-standardized catch rates in 2013 were 106 kg/trap haul in N-ENS, 104 kg/trap haul in S-ENS, and 13 kg/trap haul in 4X in 2012/2013 – which relative to the previous year, represents a decrease of 10%, an increase of 6% and a decrease of 57%, respectively. The capture of soft-shelled crab in N-ENS decreased to 3% of landings from 9% in 2012. This decrease is likely associated with a return to less summer fishing activities (more spring fishing) in 2013. In S-ENS, the relative occurrence of soft-shell crab was 2%, down from 6% in 2012 and at record low levels. This decline is also attributable to earlier fishing activities. Soft-shell discard rates in 4X remain very low, due to it being a fall and winter fishery. Soft-shell incidence and associated potential handling mortality continues to be an issue requiring diligent and adaptive management action. Bycatch of non-target species is extremely low (0.01%) in N- and S-ENS. CFA 4X bycatch levels increased to 2%, likely associated with decreased catch rates and landings of snow crab. Although very limited local recruitment into the fishery is expected for the short to medium term in N-ENS, a pulse of unexpected recruits to the area, likely through immigration, was observed during the 2013 snow crab survey. There remains a gap in the length frequency of male crab in N-ENS between 55 and 85 mm carapace width. Male crab were observed in all size classes in S-ENS, suggesting more stable recruitment into the future. CFA 4X shows little potential for substantial internal recruitment to the fishery for the next four to five years. Movement will likely be an important source of 4X crab for the next several years. The low abundance of both the mature and immature crab in the adjoining portion of CFA 24 and erratic temperature fields in 4X create future uncertainties. Female snow crab in all areas appear to be completely recruited as of the 2012 survey, although there does appear to be some signs of immature female snow crab in both N- and S-ENS. Current egg and larval production is expected to be low in both S-ENS and 4X and nearly non-existent in N-ENS. The post-fishery fishable biomass index of snow crab in N-ENS was estimated to be 3,190 t (3,840 t in 2012). In S-ENS, the post-fishery fishable biomass index was estimated to be 41.92 × 103 t (42.4 × 103 t in 2012). In 4X, the pre-fishery fishable biomass was 510 t (1160 t in 2012/2013). These population characteristics are tempered by a number of uncertainties, including the influence of predation, especially upon immature and soft-shelled snow crab by groundfish, as well as large and rapid temperature swings (especially in 4X and parts of Area 24), as they can have both direct and indirect influences upon snow crab, which are cold-water stenotherms. Signs of a potential return of ecological, social, and economic indicators in the direction of a system less dominated by invertebrates adds further uncertainty to the medium- to long-term sustainability of the population. Fishing mortality in N-ENS was estimated to be 0.19, and has increased slightly since 2009. Fishable biomass has been decreasing for the past several years, mainly through a lack of recruitment. The unexpected increase in recruitment may help to bolster the stock, providing these crab remain in the area. In N-ENS, medium to long-term prospects are uncertain and potentially poor due to an absence of pre-recruits. The fishable biomass is in the “healthy” zone. In N-ENS, a status quo to marginal decrease in TAC is recommended. Fishing mortality in S-ENS was estimated to be 0.17, relatively unchanged since 2009. Good recruitment suggests a positive outlook; however, the capture of soft-shell crab and illegal landings remain important issues for this fleet. The fishable biomass is in the “healthy” zone. In S-ENS a status quo to a marginal increase in harvest strategy is recommended. Fishing mortality in 4X for 2012/2013 was estimated to be 0.14, largely due to only 45% of TAC being landed. In 4X, the modeled fishable biomass is in the “cautious” zone and as recruitment into the 2013/2014 season is uncertain and biomass trends are declining, a very conservative harvest strategy (rate) is recommended.
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