Research Document - 2008/040
The 2007 assessment of snow crab, Chionoecetes opilio, stocks in the southern Gulf of St. Lawrence (Areas 12, 19, E and F)
By M. Hébert, E. Wade, P. DeGrâce, P. Bélanger, and M. Moriyasu
Abstract
The 2007 assessment of the southern Gulf of St. Lawrence snow crab, Chionoecetes opilio, stock (Areas 12, 19, E and F) was based on data from the commercial fishery (fishermen’s logbooks, at-sea observer measurements and quota monitoring reports) and trawl surveys. The 2007 landings in Area 12 were 23,243 t (quota of 23,207 t) with an average catch per unit of effort (CPUE) of 65.7 kg/trap haul (kg/th) and a total fishing effort of 353,775 trap hauls. The CPUE remained high from 2005 to 2007 and has been increasing since 2002. Some indicators (e.g., CPUE, mean size of commercial-sized adult males and incidence of soft-shelled crabs) show that the fishery performance was good in 2007. The exploitation rate in 2007 was 49% while they were between 45% and 70% since 2000. In Area 19, 2007 landings were 3,034 t (quota of 3,074 t). The CPUE was 71.3 kg/th and was within the range observed in the previous decade. The exploitation rate was 67%, the highest of the time series for this fishery. In Area E, 2007 landings were 220 t (quota of 221 t). The CPUE decreased from 80.6 kg/th in 2005 to 37.2 kg/th in 2007. The 2007 landings in Area F were 370 t, representing 90.7% of their quota of 408 t. The CPUE decreased from 93.7 kg/th in 2005 to 30.2 kg/th in 2007.
The 2007 survey biomass index of commercial-sized crabs in Area 12 was 50,600 t (46,400 t – 55,100 t), a decrease of 18% compared to the 2006 estimate of 61,900 t (56,900 t – 67,200 t). Fifty three percent (53%) of the 2007 survey biomass index is composed of new recruitment, estimated at 27,000 t (24,000 t – 30,300 t). The recruitment to the fishery decreased by 39% compared to the 2006 estimate, but the residual biomass (23,700 t) increased by 25%. The recruitment to the fishery is expected to decline and remain low until 2011 because of the decrease in abundance of prerecruits larger than 56 mm of carapace width (CW), (R-4, R-3 and R-2) observed in the 2007 trawl survey. The abundances of males smaller than 56 mm CW have been low since 2002. The survey abundance of mature females has declined since 1990 and reached the lowest observed in 2006-2007. This fishery has become largely dependent on the annual recruitment to the fishery. A risk analysis of consequences to biomass indicators relative to catch options for the 2008 fishery is available. In the absence of any exploitation in 2008, there is a 19% chance that the commercial biomass in Area 12 will decrease in 2008 relative to 2007.
In Area 19, the September 2007 survey biomass index of commercial-sized crabs was 5,500 t (4,300 t – 7,000 t), which represents an increase of 29% compared to the September 2006 estimate of 4,300 t (2,900 t – 6,100 t). The recruitment to the fishery was estimated at 4,000 t (3,100 t – 5,000 t) and accounted for 72% of the 2007 commercial biomass index. The residual biomass in 2007 was 1,500 t (1,000 t – 2,200 t), has been decreasing since 2003, and represents the lowest value since 1998. The prerecruits larger than 56 mm CW (R-4, R-3 and R-2) observed in the 2007 trawl survey decreased compared to 2006. The fishery has become largely dependent on new annual recruitment to the fishery. The commercial biomass index estimates based on the fall trawl survey may not reflect the fishable stock at the time of the fishery 8-10 months later, mainly because of a dynamic movement of commercial-sized adult males that occurs in Area 19 and adjacent fishing areas (Areas 12 and F). The June survey prior to the July fishery provides a more reliable biomass estimate.
In Area E, the 2007 survey commercial biomass index was estimated at 600 t (200 t – 1,300 t), and was within the range of uncertainty of the 2006 estimate of 360 t (45 t – 1,400 t). In Area F, the 2007 survey commercial biomass index was estimated at 1,300 t (600 t – 2,500 t), within the range of uncertainty of the 2006 estimate of 560 t (74 t – 2,100 t). The Areas E and F are overflows (heavily influenced by) from Areas 12 and 19. With the expected decline in commercial biomass and the overall retraction of the densities into the central part of the Area 12 after 2008, the commercial biomass is expected to decrease in the next few years.
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