Science Advisory Report 2010/040
Assessment of Nova Scotia (4VWX) Snow Crab
Summary
- Landings in 2009 for N-ENS and S-ENS were 579 and 10,760 t, respectively, and they were 229 t in CFA 4X for the 2008/9 season, representing increases of 143%, 30% and 0%, respectively from the previous year.
- TACs in 2009 were 576, 10,800 and 230 t in N-ENS, S-ENS and CFA 4X. In 2008, they were 238, 8253, and 230 t.
- Non-standardized catch rates in 2009 were 75.7 kg/trap haul and 89.6 kg/trap haul in N-ENS and S-ENS, and 28.4 kg/trap haul in CFA 4X in 2008/2009 – representing an increase of 125%, a decrease of 7% and an increase of 61%, respectively, relative to the previous year.
- In N-ENS, the soft-shelled crab discard declined from 49% in 2008 to 6.6% in 2009. In S-ENS, soft-shell handling increased from 13% in 2008 to 16% of the TAC in 2009. Soft-shell discard rates in CFA 4X are very low.
- The post-fishery fishable biomass of snow crab was estimated to be 1,342 t in N-ENS (with a 95% confidence range of: 946 t to 2,059 t) relative to 4,836 t in 2008. In S-ENS, the post-fishery fishable biomass was 66.2 × 103 t (with a 95% confidence range of: 55.7 to 77.2 × 103 t), relative to 45.8 × 103 t in 2008. In CFA 4X, the pre-fishery fishable biomass was 1,730 t (with a 95% confidence range of 580 to 5,070 t), relative to 1,180 t in 2008.
- The leading edge of recruitment to the fishery entered in 2007 and full entry is expected in 2010/2011. Recruitment to fishable size should continue in all areas up to 2014.
- The egg production of the Scotian Shelf population is declining and should continue to decline for the next 2 years, potentially affecting long-term recruitment.
- High 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 potential strength of future recruitment to the fishable biomass.
- Average bottom temperatures in 2009 were generally lower than the long-term means, especially in CFA 4X. The surface area of potential snow crab habitat was near or above historical maxima in S-ENS and CFA 4X, respectively, while it was near the long-term mean for N-ENS.
- The abundance estimates of old male crab (CC5) has been stable in the historical record and below the detection limit on the Scotian Shelf surveys and as well as in the at-sea observed data.
- By-catch levels, mostly of other crustacean species, are less than 0.013% of annual landings in ENS and approximately 1.9% in CFA 4X. By-catch has been consistently low in the historical record.
- Relative exploitation rate (by biomass) in N-ENS was 29% in 2009, relative to approximately 5% in 2008. The N-ENS fishable biomass has begun to recover. However, there was an unexpected decline in fishable biomass due to very low recruitment to fishable sizes in 2009. The exact cause is at present not known. The 2009 TAC of 576 t would lead to an target exploitation rate of 45% in 2010. The 2009 exploitation rate of 29% would represent a TAC of 389 t in 2010. A 20% target exploitation rate would represent 268 t in 2010. Given the high numbers of adolescent snow crab (40-95 mm CW), representing long-term recruitment, there exists some flexibility between these strategies.
- Relative exploitation rate (by biomass) in S-ENS was 14% in 2009, relative to approximately 15% in 2008. The snow crab in S-ENS can be considered to be in a healthy state. An increase in TAC is recommended recognizing the importance of soft and immature snow crab. Shifting the season earlier in the year may help further reduce the handling of soft-shelled snow crab.
- Relative exploitation rate (by biomass) in CFA 4X for 2009/2010 if the all the TAC is landed will be 12%. In 2008/2009 relative exploitation rate was 16%. An increase in TAC is recommended.
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