Discard mortality rates in the Bering Sea snow crab, Chionoecetes opilio, fishery

Fish and invertebrates that are unintentionally captured during commercial fishing operations and then released back into the ocean suffer mor-tality at unknown rates, introducing uncertainty into the fishery management process. Attempts have been made to quantify discard mortality rates using reflex action mortality predictors or RAMP which use the presence or absence of a suite of reflexes to predict discard mortality. This method was applied to snow crab, Chionoecetes opilio, during the 2010–2012 fisheries in the Bering Sea. Discard mortality in the fishery is currently assumed to be 50 % in stock assessment models, but that rate is not based on empirical data and is widely recognized to be in need of refinement. Over 19 000 crab were evaluated using the RAMPmethod. The estimated discard mortality rate was 4.5 % (s.d. 0.812), significantly below the rate used in stock assessmentmodels. Predicted discardmortality rates from the 2010 to 2012 studywere strongly correlatedwith the air temperature at the St Paul Island airport in the Pribilof Islands.Using this relationship, the discardmortality rate from1991 to 2011was estimated at 4.8 % (s.d. 1.08)