Research Document - 2004/064
The 2003 assessment of snow crab, Chionoecetes opilio, in the southern Gulf of St. Lawrence (Areas 12, E and F).
By Hébert, M., Wade, E., Surette, T., Moriyasu, M.
Abstract
The 2003 assessment of the southern Gulf of St. Lawrence snow crab, Chionoecetes opilio, stock (Areas 12, 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 2003 landings in Area 12 were 16,898 t (quota of 17,148 t) with an average catch per unit of effort (CPUE) of 50.0 kg/trap haul and a total fishing effort of 337,960 trap hauls. Many indicators (e.g., CPUE, mean size, incidence of soft-shelled crabs and high residual biomass of hard-shelled crabs) suggest that exploitation in Area 12 was very conservative in 2003. The 2003 landings for Areas E and F were 345 t and 817 t, respectively. The CPUE was 63.1 kg/trap haul in Area E and 78.1 kg/trap haul in Area F. Fishing effort was estimated at 5,471 trap hauls in Area E and 10,460 trap hauls in Area F. The fishing performance in Areas E and F was good in 2003.
The 2003 trawl survey indicated an increase in the commercial biomass index in Area 12 to 53,250 t ± 13 %. The index of the recruitment to the fishery (35,720 t ± 13 %) represents 67 % of the commercial biomass index. The high level of prerecruits (R-2) abundance indices observed in the 2003 trawl survey could increase the level of recruitment to the fishery until 2005. The abundance, fecundity and mean size of mature females has been decreasing, therefore, it would be prudent to leave enough commercial-sized adult males to maximize the reproductive potential of the stock. Using the same conservative approach as in 2003 (i.e. an exploitation rate of 40 % of the commercial biomass index observed at the time of the survey), the 2004 quota would be 21,300 t. The history of the fishery indicates that an exploitation rate of 60 % would be too high. Considering the positive signs observed in the 2003 fishery, it is likely that the population could sustain an exploitation rate of 50 % (26,600 t) in 2004. 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). This may explain the decline in multiparous fecundity in sector 2 in 2003. The low abundance of commercial-sized hard-shelled adult males available to mate with mature females during the multiparous mating may indicate local overexploitation in these sectors. A change in the present management approach is necessary to protect the reproductive output of the stock.
In Area E, the 2003 survey commercial biomass index of 450 t represents a decrease of 38 % compared to the 2002 estimate. Considering the decrease in commercial biomass index and the uncertainties concerning the future recruitment to the fishery, a high exploitation strategy would accelerate the decline in commercial biomass index in the near future.
In Area F, the survey commercial biomass index was estimated at 1,970 t, a decrease of 27 % compared to 2002. The absence of prerecruits to support this area may contribute to an accelerated decline in the commercial biomass index for the next 2-4 years. A high exploitation strategy will 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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