Protection of post-molt male snow crab (Chionoecetes opilio) in the southwestern Gulf of St Lawrence: Strategy to avoid discarding mortality offuture recruitment to the fishery

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Snow crab, Chionoecetes opilio, is one of the commercially important species in eastern Canada with total landings exceeding 100,000 mt with corresponding value at 600 million Canadian dollars in 2004. The fishery only fish terminally molted hard-shelled males larger than 95 mm in carapace width (CW). Newly molted males bear soft carapace (soft-shelled crab) during the spring fishing season with significantly lesser weight and meat yield and have no commercial value. As these newly molted crabs constitute the major part of future recruitment to the fishery as well as potential genitor, the protection of these crabs from fishing induced mortality is paramount for the protection of the population reproductive potential and future commercial stock. A mandatory closure protocol by grids or sectors when the incidence of soft-shelled male (SSM) snow crabs exceeds a threshold of 20% was implemented in the southwestern Gulf of St. Lawrence snow crab fishery in 2000. It also allows fishermen for fishing by shifting their effort from areas of high SSM incidence to non-or less-problem areas. Data from fishermen’s logbooks, at-sea observer biological information and experimental trawl surveys were analyzed for a 13-year period (1990-2002) to determine the variations in the SSM incidence in commercial catches. There was a negative exponential relationship between the percentage of SSM larger than 83 mm CW in the catch and the catch rate of hard-shelled males larger than 95 mm CW. There was a positive exponential relationship for a period between 1990 and 2000 between the percentage of SSM in catches and the ratio of projected abundance of SSM to the estimated remaining abundance of hard shelled males larger than 95 mm CW after the fishery. There was also a linear relationship between the observed and predicted values in the percentage of SSM from 1990 to 2000, while the predicted values in the percentage of SSM were much higher than the observed values in 2001 and 2002. These outliers occurred after the implementation of SSM protocol, thus suggest that the implementation of the new protocol introduced in 2000 substantially reduced the incidence of SSM in commercial catches.