Research Document - 2006/029
The 2005 assessment of snow crab, Chionoecetes opilio, stocks in the southern Gulf of St. Lawrence (Areas 12, 19, E and F)
By Hébert, M., E. Wade, T. Surette, P. DeGrâce, R. Ruest and M. Moriyasu
Abstract
The 2005 assessment of the southern Gulf of St. Lawrence snow crab, Chionoecetes opilio, stock (Areas 12, 19, E and F) was done based on data from the commercial fishery (fishermen’s logbooks, at-sea observer’s measurements, purchase slips from processing plants and quota monitoring reports) and trawl surveys. The 2005 landings in Area 12 were 32,363 t (quota of 32,336 t) with an average catch per unit of effort (CPUE) of 63.7 kg/trap haul and a total fishing effort of 508,053 trap hauls. Many indicators (e.g., CPUE, mean size and incidence of soft-shelled crabs) indicate that the fishery performance was good in 2005. In Area 19, landings were 2,827 t (quota of 2,878 t). The CPUE remained the same in 2005 as in 2004 at 69 kg/th. The 2005 landings for Areas E and F were 449 t and 479 t, respectively. The CPUE was 80.6 kg/th in Area E and 93.7 kg/th in Area F. Fishing effort was estimated at 5,571 trap hauls in Area E and 5,112 trap hauls in Area F. The fishing performance in Areas E and F was good in 2005.
The 2005 survey biomass index of commercial-sized crabs in Area 12 was 59,606 t (53,920 t – 65,723 t), which represents a decrease of 17% compared to the 2004 estimate of 71,859 t (65,697 t – 78,438 t). Sixty-nine percent (69%) of the 2005 survey biomass index is composed of new recruitment estimated to be 41,384 t (37,312 t – 45,775 t). A decline in the recruitment to the fishery is expected until 2010 because of the decrease in abundance of prerecruits (R-4, R-3 and R-2) observed in the 2005 trawl survey. The retention rate of the stock has been decreasing since 1999 (less than 40%) indicating a high fishing pressure on the recruitment to the fishery compared to the 1991-1998 period (over 40%). Continued high fishing pressure on the recruitment to the fishery would accelerate the decline of the commercial biomass index after 2006 and would require even greater conservative management measures in the coming years to address the situation.
In Area 19, the September 2005 survey biomass index of commercial-sized crabs was 3,421 t (2,220 t – 5,045 t), which represents a decrease of 17% compared to 2004 fall estimate of 4,113 t (3,042 t – 5,440 t). Forty three percent (43%) of this survey biomass index is composed of new recruitment estimated to be 1,484 t (720 t – 2,724 t). The prerecruits (R-4, R-3 and R-2) observed in the 2005 trawl survey slightly increased compared to 2004, which may indicate an increase in the commercial biomass index in the near future if these crabs stay within the zone after reaching the legal size. 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 (a relatively small fishing area) and adjacent fishing areas (Areas 12 and F).
In Area E, the 2005 survey commercial biomass index was estimated to be 817 t (285 t – 1,863 t), a 50% increase compared to the 2004 estimate. A high exploitation rate could accelerate the decline in commercial biomass index in the near future. In addition, the commercial biomass index seems to be significantly influenced by recruitment from Area 12.
In Area F, the 2005 survey commercial biomass index was estimated to be 1,629 t (1,000 t – 2,512 t), a 53% increase compared to 2004. The absence of prerecruits in this area may contribute to an accelerated decline in the commercial biomass index in the near future. A high exploitation rate could accelerate the decline in commercial biomass index in the near future.
It is essential to continue an annual trawl survey and a soft-shelled crab protocol to optimize the exploitation of the southern Gulf snow crab stock.
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