AFSC/RACE/SAP/Urban:Tanner Crab Handling Mortality

Fish and invertebrates that are unintentionally captured during commercial fishing operations and then released back into the ocean suffer mortality 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 Tanner crab, Chionoecetes bairdi, 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 RAMP method. The estimated discard mortality rate was 4.5% (SD = 0.812), significantly below the rate used in stock assessment models. Predicted discard mortality rates from the 2010-2012 study were strongly correlated with the air temperature at the St. Paul Island airport in the Pribilof Islands. Using this relationship the discard mortality rate from 1991-2011was estimated at 4.2% (SD = 1.08).