Research Document - 2008/003

An assessment of the snow crab resident on the Scotian Shelf in 2006, focusing upon CFA 4X

By Choi, J.S. and B.M. Zisserson

Abstract

Landings in 2006 were 319 (TAC of 337.6 t) – an increase of 6% from 308 t in 2005. Most landings were obtained from the inshore area near Sambro. Average, non-standardized catch rates were 27.7 kg/trap, representing a marginal decrease from 28.6 kg/trap. Soft-shelled crab incidence in the commercial catch of legal sized crab is low, estimated to be 0.05% as also were by-catch of non-target species which represented approximately 0.324% of annual snow crab landings.

In the near-term, recruitment is expected to increase. Pre-recruits near a 54 mm CW modal group (instars 9/10) have been found in large numbers. The leading edge of this modal group should begin to recruit in 2007 and full entry observed in 2010 to 2011. In the long-term, the reproductive potential of the Scotian Shelf population has increased with the substantial increase in berried female abundance in all areas. Larval production should continue for another 5 years. However, potential predators of (immature and soft shelled) snow crab have been found concentrated in areas with high densities of immature snow crab. This adds uncertainty to the potential strength of future recruitment to the fishable biomass. Increasing bottom temperatures on the Scotian Shelf and shrinking of potential habitat is also an uncertainty that may have particularly negative consequences upon the CFA 4X snow crab.

The post-fishery fishable biomass of snow crab was estimated to be 850 t, a 13.5% decline from 990 t in 2005. Exploitation rates (by biomass) were 27% in 2006, relative to 20% in 2005. Projections suggest that an exploitation rate between 10 and 20% may be suitable for long-term sustainability in CFA 4X. Current exploitation rates are closer to those found in the nearly collapsed N-ENS fishery. Numerical abundance estimates of old males (CC5) are also below the detection limit in both trawl surveys and the observed commercial catch. This may be indicative of high exploitation rates. Caution is warranted for 2007 due to low fishable biomass and low recruitment and indications of high exploitation. A reduction in TAC is recommended.

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