Estimating Dungeness Crab Bycatch Mortality Rates in Oregon Fisheries

Oregon’s Dungeness crab (Cancer magister) fisheries are managed using a “size, sex, and season” management strategy, which dictates that no female or undersized male crab be retained. Oregon’s trawl fisheries are not permitted to retain any bycaught Dungeness crab. To evaluate the sustainability of these fishing practices and to understand how different fisheries affect Oregon’s Dungeness crab population, it is important to determine mortality rates for discarded crab. To accomplish this we utilized the reflex action mortality predictor (RAMP) approach, which relates reflex impairment to probability of survival. Discard mortality rates were also determined using a mark-recapture approach. With these two methods we could evaluate both immediate and long-term mortality rates, in laboratory and natural settings. In addition to determining these rates, data were gathered to evaluate how different fishing, biological, and environmental variables (e.g., time a crab spends out of water or in a crab pot or trawl, catch size, carapace width, shell hardness, air temperature) can influence discard mortality. By identifying variables that influence survival we identify ways that fishing practices can be modified to reduce mortality of discarded crab and to promote sustainability in fisheries.