Proposed harvest control rule for managing the snow crab stock in the southwestern Gulf of St. Lawrence,Canada

We developed limit and target harvest control rules based on an age-, sex- and stage-structured model for managing the southwestern Gulf of St. Lawrence snow crab (Chionoecetes opilio) stock. We determined an F_x% (F resulting in a spawning biomass-per-recruit equivalent to x% of virgin spawning biomass-per-recruit) as a proxy for F_MSY and a minimum spawning stock biomass to open the fishery to incorporate them into the control rules. We evaluated the selected limit and target control rule parameters under stochastic simulations by considering various performance statistics. Because of the complexity in determining an effective female spawning biomass that involves a mating ratio, we choose the total mature male biomass (MMB) regardless of crab size as the spawning index to develop the stock–recruitment relationship for stochastic simulations. The MMB based F_37% appears a reasonable proxy for limit control rule while F_45% appears a reasonable target control rule. The corresponding limit and target harvest rates of legal size crab when the standing stock MMB exceeds the proxy MSY level are approximately 36% and 25%, respectively. The difficulty in establishing an appropriate stock–recruitment relationship for this stock was recognized hence a precautionary F_45% target level was chosen. Scenarios under biomass independent random recruitment were also investigated and performances of F_37% and F_45% control rules under this hypothesis behaved similar to those observed under S–R model based simulations.