Research Document - 2015/068
Assessment of Scotian Shelf Snow Crab in 2014
By A.M. Cook, B.M. Zisserson, B.J. Cameron, and J.S. Choi
Abstract
Snow crab landings in 2014 for North-Eastern Nova Scotia (N-ENS) and South-Eastern Nova Scotia (S-ENS) were 778 t and 11,267 t, respectively, and they were 79 t in Crab Fishing Area (CFA) 4X for the 2013/2014 season, representing a decrease of 1% (N-ENS) and decreases of 1% (S-ENS) and 33% (4X) relative to the previous year. Total allowable catches (TACs) in 2014 were 783 t, 11,311 t and 80 t in N-ENS, S-ENS and 4X. Non-standardized catch rates in 2014 were 104 kg/trap haul in N-ENS, 112 kg/trap haul in S-ENS, and 15 kg/trap haul in 4X in 2013/2014 which, relative to the previous year, represents a decrease of 2%, an increase of 8% and an increase of 25%, respectively. The capture of soft-shelled crab in N-ENS stayed stable at 3% over the past two seasons. In S-ENS, the relative occurrence of soft-shell crab was 2% for each of the last two seasons. 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-ENS 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 CC1 and CC2 crab did appear during the fishery, likely through migration; however, this same pulse of crab was not observed during the autumn survey. There remains a gap in the length frequency of male crab in N-ENS between 60 mm and 95 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 adjacent portion of CFA 24 and erratic temperature fields in 4X create future uncertainties. The mature component of female snow crab in all areas appear to be low and decreasing, however, there does appear to be positive signs of immature female snow crab in both N-ENS and S-ENS. The post-fishery fishable biomass index of snow crab in N-ENS was estimated to be 2,075 t (3,451 t in 2013). In S-ENS, the post-fishery fishable biomass index was estimated to be 40.1×103 t (46.2×103 t in 2013). In 4X, the pre-fishery fishable biomass was 2,059 t (503 t in 2013/2014), however, the biomass estimate in this area is uncertain as only a subset of survey stations were completed. 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 CFA 4X and parts of CFA 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 0.30, 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 proportion of CC1 and CC2 crab during the fishery may have helped to bolster the stock and catch rates during the season. 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 decrease in TAC is recommended. Fishing mortality in S-ENS was estimated to be 0.18, relatively unchanged since 2009. Good recruitment suggests a positive outlook. The fishable biomass is in the “healthy” zone. In S-ENS a status quo to a marginal decrease in harvest strategy is recommended. Fishing mortality in 4X for 2013/2014 was estimated to be 0.08, largely due to the large reduction in TAC. In 4X, the modeled fishable biomass moved from the “cautious” into the “healthy” zone, albeit with considerable uncertainty, and recruitment into next season is uncertain. A continued conservative harvest strategy is recommended pending further analysis prior to the 2015-2016 season.
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