Science Advisory Report 2008/020
Assessment of Nova Scotia (4VWX) Snow Crab
Summary
- Landings in 2007 for N-ENS and S-ENS were 233 t and 4942 t, respectively, and 317 t in CFA 4X for the 2006/2007 season, all within their respective TACs of 244, 4950, and 337.6 t. These changes in landings represent a decline of 52% in N-ENS and increases of 10% and 4% in S-ENS and 4X, respectively, relative to 2006.
- Average, non-standardized catch rates in 2007 were 23.6 kg/trap and 100.1 kg/trap in N- and S-ENS, and 27.7 kg/trap in 4X in 2006/2007 – representing a decrease of 34%, an increase of 10% and a decrease of 3%, respectively.
- The soft-shelled crab discard represents up to 271 t (116% of landings) and 353 t (7% of landings) being subjected to potential handling mortality in N- and S-ENS, respectively. 4X discard rates of soft crab are very low.
- The post-fishery fishable biomass of snow crab was estimated to be 970 t in N-ENS (with a 95% confidence range of: 730 to 1,230 t) and 41,590 t in S-ENS (with a 95% confidence range of: 37,260 to 46,320 t) and 1,030 t in CFA 4X (with a 95% confidence range of: 470 to 1,710 t) – representing a 29% increase, a 47% increase and no change, respectively. Fishable biomass estimates were 570, 28,200, and 1,030 t for N-ENS, S-ENS and 4X, respectively, in 2006.
- The main pulse of male recruitment of the Scotian Shelf population continues to grow and is currently centered over a 68 mm CW modal group (instars 11/12). The leading edge of recruitment entered in 2007 and full entry is expected by 2011. Recruitment after 2014 is uncertain.
- The reproductive potential of the Scotian Shelf population has increased with a substantial increase in berried female abundance in all areas. Larval production should continue for another 4 years.
- The numerical abundance estimates of old males (CC5) are currently below the detection limit on the Scotian Shelf surveys and low as well (approximately 1% or less) in the at-sea observed data (<10% of landings observed in all areas).
- A general trend of increasing temperatures since the early 1990s along the Scotian Shelf represents an additional source of uncertainty as this may limit the potential habitat available to snow crab. In 2007, bottom temperatures in all areas were at or below the 38-year mean. CFA 4X has in particular demonstrated stronger inter-annual variability since the late 1990s.
- Potential predators of immature and soft-shelled snow crab continue to be found in areas with high densities of immature snow crab. This adds uncertainty to the potential strength of future recruitment to the fishable biomass.
- By-catch levels are very low in this fishery between 0.015 to 0.325% of mean annual landings, mostly of other crustacean species.
- Relative exploitation rate (by biomass) in N-ENS was 24% in 2007. A range between 10 to 20%, depending upon the strength of recruitment, may help ensure the long-term sustainability of this fishery. A decrease in TAC is recommended until the fishable biomass has increased sufficiently to reduce soft-shell catches and associated potential mortality, unless other management measures can be implemented to lower the handling of soft-shell crab.
- Relative exploitation rate (by biomass) in S-ENS was 10% in 2007. A range between 10 to 30%, depending upon the strength of recruitment, may help ensure the long-term sustainability of this fishery. The snow crab in S-ENS can be considered to be in a healthy state. An increase in TAC is recommended.
- Relative exploitation rate in CFA 4X in 2006/07 was 23%, though due to the very specific spatial extent of the fishery, realized exploitation rates are likely higher. No additional incremental increase to the 2007/08 TAC is recommended. A maintenance or reduction of this TAC is recommended for the 2008/09 season.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: