Research Document - 2005/029
The 2004 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 2004 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 2004 landings in Area 12 were 26,626 t (quota of 26,600 t) with an average catch per unit of effort (CPUE) of 54.9 kg/trap haul and a total fishing effort of 484,991 trap hauls. Many indicators (e.g., CPUE, mean size and incidence of soft-shelled crabs) indicate that the fishery performance was good in 2004. In Area 19, despite the fact that the 2003 trawl survey projected the highest commercial biomass index ever recorded for the 2004 fishing season, the 2004 fishery was prematurely closed on August 24 with reported landings of 3,894 t representing only 76.5% of the total quota of 5,092 t. The fishery was closed due to high incidence of white crabs and low CPUEs in the last two weeks of the fishing season. The CPUE decreased by 33% from 103.6 kg/th in 2003 to 68.9 kg/th in 2004. The 2004 landings for Areas E and F were 349 t and 806 t, respectively. The CPUE was 55.6 kg/th in Area E and 74.8 kg/th in Area F. Fishing effort was estimated at 6,277 trap hauls in Area E and 10,775 trap hauls in Area F. The fishing performance in Areas E and F was good in 2004.
The 2004 survey biomass index of commercial-sized crabs in Area 12 was 71,859 t ± 9%, 35% higher than the 2003 estimate (53,250 t ± 13%). The recruitment to the fishery (57,809 t ± 9%) represents 80% of the commercial biomass index. The decline in the abundance of prerecruits (R-4, R-3 and R-2) observed in the 2004 trawl survey may be a sign of recruitment decline into the fishery starting in 2006. Using a similar approach as in 2003 (40 % of the commercial biomass index observed at the time of the survey), the 2005 quota would be 28,743 t. By using the same exploitation level as in 2004 (50% of the commercial biomass index), the 2005 quota would be 35,930 t. A conservative approach is suggested to attenuate the rapid decline in the commercial biomass index after 2005. The female-male ratio in sectors 1 (Baie des Chaleurs) and 2 (Shediac Valley) for multiparous mating was skewed toward females in a much higher level than what was observed in sectors 3 (Bradelle bank) and 4 (Magdalen channel and Cape Breton corridor). In 2004, about 90% of the fishing effort and landings occurred during the first 3-4 weeks of the fishery in sectors 1 and 2 compared to 7-8 weeks in sectors 3 and 4. Local depletion of large adult males before the mating season could impact the success of multiparous mating that occurs in late May-early June. The importance of the reproductive potential of the stock from Baie des Chaleurs and Shediac Valley is unknown but given the fact that most of the adult males ≥ 95 mm have been fished in a period of 3-4 weeks since 2000, it would be prudent to leave enough commercial-sized adult males prior to the multiparous mating to permit these males to participate in mating.
In Area 19, the September 2004 survey biomass index of commercial-sized crabs (4,113 t ± 29%) has decreased by 49% compared to 2003 (8,083 t ± 18%). Thirty-six percent of this survey biomass index is composed of new recruitment (1,495 t ± 56%). The prerecruits (R-4, R-3 and R-2) have been decreasing since 2001. A decrease in the commercial biomass index is now expected for the next 3 to 5 years if no immigration occurs in this area. Multiple trawl surveys (regular fall and pre-fishery) would be helpful to estimate the level of commercial-sized adult males in Area 19.
In Area E, the 2004 survey commercial biomass index was estimated at 544 t ± 151%, a slight increase compared to the 2003 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 2004 survey commercial biomass index was estimated at 1,063 t ± 127%, a decrease of 46% compared to 2003. The absence of prerecruits in this area may contribute to an accelerated decline in the commercial biomass index for the next 3-5 years. A high exploitation rate would 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.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: