Research Document - 2007/028
The 2006 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 and M. Moriyasu
Abstract
The 2006 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’s measurements and quota monitoring reports) and trawl surveys. The 2006 landings in Area 12 were 25,889 t (quota of 25,869 t) with a partially standardized average catch per unit of effort (CPUE) of 64.4 kg/trap haul (kg/th) and a total fishing effort of 402,702 trap hauls. Some indicators (e.g., CPUE, mean size of commercial-sized adult males and incidence of soft-shelled crabs) indicate that the fishery performance was good in 2006. In Area 19, landings were 1,989 t (quota of 2,000 t). The partially standardized CPUE increased from 68.8 kg/th in 2005 to 84.4 kg/th in 2006. In Area E, landings were 411 t representing 74.7% of their quota of 550 t. The partially standardized CPUE decreased from 80.6 kg/th in 2005 to 40.8 kg/th in 2006. The 2006 landings in Area F were 787 t representing 96.7% of their quota of 815 t. The partially standardized CPUE decreased from 93.7 kg/th in 2005 to 55.9 kg/th in 2006.
The 2006 survey biomass index of commercial-sized crabs in Area 12 was 61,886 t (56,880 t – 67,246 t), which is comparable to the 2005 estimate of 62,939 t (58,840 t – 67,246 t). Seventy one percent (71%) of the 2006 survey biomass index is composed of new recruitment estimated at 44,087 t (39,970 t – 48,508 t). The recruitment to the fishery is expected to decline in 2008 by approximately 50%. The recruitment to the fishery will probably continue to be low until about 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 2006 trawl survey. The abundances of males smaller than 56 mm CW have been low since the 2002 trawl surveys. The survey abundance of mature females has been decreasing since 1999 (the earliest year of the survey that can currently be used) while the mean size of mature females in the survey has been decreasing since 1988. The decrease in abundance is expected to continue. The estimated total egg production showed a decline since 2001 and reached the lowest observed in 2006. This fishery has become largely dependent on the annual recruitment to the fishery. If recruitment decreases as expected from 2008 to about 2011, the continued high exploitation rates combined with the expected low recruitment would result in a rapid decrease in commercial biomass.
In Area 19, the September 2006 survey biomass index of commercial-sized crabs was 4,285 t (2,910 t – 6,090 t), which represents an increase of 13% compared to the 2005 fall estimate of 3,802 t (2,890 t – 4,912 t). Fifty nine percent (59%) of this survey biomass index is composed of new recruitment estimated at 2,519 t (1,443 t – 4,096 t). The prerecruits larger than 56 mm CW (R-4, R-3 and R-2) observed in the 2006 trawl survey increased compared to 2005, 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 and adjacent fishing areas (Areas 12 and F). The June survey, immediately prior to the July fishery provides a more reliable biomass estimate.
In Area E, the 2006 survey commercial biomass index was estimated to be 368 t (45 t – 1,394 t), a 56% decrease compared to the 2005 estimate of 845 t (417 t – 1,534 t). In Area F, the 2006 survey commercial biomass index was estimated at 562 t (74 t – 2,074 t), a 71% decrease compared to the 2005 estimate of 1,923 t (1,024 t – 3,303 t). The Areas E and F are overflows (heavily influenced by) from Areas 12 and 19. The low survey biomass estimates and the rapidly decreasing CPUE, suggest that the biomass in those areas is expected to be low. 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 severely in the next few years.
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