Modeling submergence success of discarded yelloweye rockfish (Sebastes ruberrimus) and quillback rockfish (Sebastes maliger): Towards improved estimation of total fishery removals

Abstract

Identification of variables that can be used to predict discard mortality is an important step towards improving estimates of total fishery removals. I explored the utility of capture depth, six external signs of barotrauma, two behavioral responses, and an impairment index that summed the physical and behavioral impairment associated with rapid decompression at predicting the submergence success of hook-and-line captured yelloweye (n=95) and quillback (n=65) rockfish that were released at the water's surface. Random forests classification models were used to identify the relative importance of predictor variables (n=11) for each species and to explore the ability of these variables to accurately predict individual submergence success. Capture depth was identified as the most important variable in predicting yelloweye rockfish submergence but provided little improvement to the quillback rockfish model. The impairment index and the barotrauma sign associated with maximal gas retention were identified as important predictor variables for both yelloweye and quillback rockfish. These findings suggest that the impairment index, unlike capture depth, was able to account for individual variability in submergence success or failure of quillback rockfish.