Research Document - 2003/018
Areas 18 and 19 snow crab, Chionoecetes opilio, stock assessment in the southeastern Gulf of St. Lawrence in 2002
By Hébert M., Wade, E., Giard, D., and Moriyasu, M.
Abstract
The 2002 assessment of the southeastern Gulf of St. Lawrence snow crab, Chionoecetes opilio, stock (Areas 18 and 19) 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 survey.
In Area 18, the 2002 quota was increased from 476 t in 2001 to 680 t, but landings only reached 72% of the quota. The fishing effort in 2002 was estimated at 26,414 trap hauls, an increase of 60% compared to 2001 (16,446 trap hauls). As usual, the majority of the fishing effort and landings was located in one or two small areas at the northern bundary of the Area. The average catch rates (CPUE) in 2002 was estimated at 18.6 kg per trap haul (kg/th), an increase of 22% compared to 2001 (15.3 kg/th). The annual percentage of soft-shelled crabs was 5.0%, a decrease compared to 2001 (8.6%). The mean size of commercial-sized crabs in sea samples has been decreasing since 1995 from 118.6 to 106.7 mm of carapace width (CW).
The 2002 trawl survey indicated an increase in the commercial biomass (B) index in Area 18 to 3,438 t ± 36%, which represents a 323% increase compared to the 2001 estimate (1,065 t ± 115%) and the highest record since the beginning of the survey. The index of recruitment to the fishery (3,283 t ± 36%) represents 96% of the biomass index. The high abundance of prerecruits (R-3 and R-2) observed in the 2002 trawl survey could increase the level of recruitment to the fishery for the next two or three years. Although the survey biomass index of commercial-sized crabs was estimated at its highest observed level, the exploitation strategy for next year should be set to allow an accumulation of residual biomass. It is also important to consider the factors of uncertainty (seasonal movement of crabs, possible overestimation of survey biomass index) and some negative signs of the stock condition (low CPUE, decrease in the mean size of commercial-sized crabs and high dependency on the new recruitment). A close in-season monitoring is necessary to protect the future recruitment to the fishery.
In Area 19, the 2002 landings decreased by 16% (3,279 t) compared to 2001 (3,910 t). The fishing effort in 2002 was estimated at 46,828 trap hauls, which is comparable to the 2001 level (46,251 trap hauls). The fishing effort was widely spread all over the Area in 2002. The average CPUE decreased by 22.4% from 88.5 kg/th in 2001 to 72.3 kg/th in 2002. The annual percentage of soft-shelled crabs was 3.5%, the lowest level since 1990. The mean size of commercial-sized crabs in sea samples has been decreasing since 1995 from 120.5 to 110.0 mm CW.
The 2002 survey biomass index of commercial-sized crabs (4,930 t ± 30 %) has decreased by 5 and 20% compared to 2001 and 2000 respectively, but still above the 1993-1998 levels. The index of recruitment to the fishery was estimated at 2,947 t ± 47%, which was comparable to the level of 2001
(2,927 t ± 47%). The 2002 recruitment to the fishery index represents 60% of the total commercial biomass index. The abundance of prerecruits R-2 is at the highest level observed since the beginning of the trawl surveys. In addition, the abundance of prerecruits R-3 has just slightly decreased from 2001. These pulses of prerecruits may maintain recruitment to the fishery for the next 2 or 3 years. Although the survey biomass index of commercial-sized crabs remained relatively high at a level above the 1993-1998 average, the exploitation strategy for next year should be set to allow an accumulation of residual biomass. It is also important to consider the factors of uncertainty (seasonal movement of crabs, possible overestimation of survey biomass index) and some negative signs of the stock condition (decrease in CPUE and the mean size of commercial-sized crabs). A close in-season monitoring is necessary to protect the future recruitment to the fishery.
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