Research Document - 2004/063

Area 19 snow crab, Chionoecetes opilio, stock assessment in the southeastern Gulf of St. Lawrence in 2003

By Hébert, M., Wade, E., Giard, D., Moriyasu, M.

Abstract

The 2003 assessment of the southeastern Gulf of St. Lawrence snow crab, Chionoecetes opilio, stock (Area 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 19, the 2003 landings decreased by 5.7% (3,103 t) compared to 2002 (3,279 t). The fishing effort decreased by 46 % in 2003 (29,952 trap hauls) compared to 2002 (46,828 trap hauls). The fishing effort was widely spread all over the area in 2003. The average CPUE increased from 72.3 kg/th in 2002 to 103.6 kg/th in 2003. The annual percentage of soft-shelled crabs was 3.7%, the same level as the previous year. The mean size of commercial-sized crabs in sea samples increased from 110.0 mm CW in 2002 to 114.0 mm CW in 2003.

The 2003 survey biomass index of commercial-sized crabs (8,080 t ± 18 %) has increased by 64 % compared to 2002 (4,930 t ± 30 %) to reach the highest level recorded since we began conducting the trawl survey in 1990. This survey biomass index is composed of new recruitment to the fishery (50 %) and is estimated at 4,070 t ± 24 %. The abundance of prerecruits R-3 and R-2 has been decreasing which may indicate a reduction in commercial biomass index in the near future if no immigration of adult males ≥ 95 mm CW occurs. The female-male ratio is at a level that seems more favorable to reproduction compared to the southwestern Gulf of St. Lawrence. Using the historical exploitation level of 63 % seems to be beneficial in terms of female-male ratio and reproductive output and would also promote an accumulation of residual biomass for the subsequent fishing seasons. Any increase in exploitation compared to the current level may not improve the population's reproductive potential in the future. To protect the future recruitment to the fishery and the reproductive potential of the stock, management measures, such as a soft-shelled crab protocol, are necessary. Also, the continuation of the trawl survey is essential to provide annual abundance and commercial biomass indices, detect any anomalies in reproductive potential of the stock and estimate the loss or gain of commercial sized crabs between the time of the survey and the next fishing season due to natural mortality, emigration or immigration. The trawl survey is considered the major tool in assessing the snow crab stock in the southern Gulf of St. Lawrence. )

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