Estimating discard mortality in Florida's blue crab Callinectes sapidus fishery using reflex impairment, injuries, and salinity

Objective We sought to apply the reflex action mortality predictor method and to predict discard mortality of intermolt blue crabs Callinectes sapidus in two regions of Florida to better inform stock assessments and management decisions. We additionally sought to provide an empirical estimate on market-bound mortality, which has not been incorporated into landings data or stock assessments.Methods Intermolt crab condition (measured as reflex impairment), injury score, and environmental salinity were collected in the northeast (NE) and west-central (WC) regions of Florida during the summer and winter from 2019 to 2021. A subset of market-bound crabs provided an empirical estimate of market-bound crab mortality at the time of live-market sale.Results Predictive modeling estimated that discard mortalities were 5.78% in the NE region and 3.76% in the WC region of Florida during the winter months and 2.35% (NE) and 14.4% (WC) during the summer months. Market-bound crab mortality was relatively low in the winter months (0% [NE]; 3.19% [WC]) and increased to 10.11% (NE) and 12.81% (WC) in the summer months.Conclusions The discard mortality estimates derived in this study showed that the highest mortality occurred at higher salinities during summer. The lowest mortalities were observed at lower salinities during summer and at higher salinities during winter. Market-bound mortality was highest in the summer and did not appear to be influenced by salinity. The results of this study underscore the importance of adding seasonal- and habitat-based estimates of discard mortality due to the complexity and diversity of the habitats fished during all seasons. This study provides crucial information on two important types of mortality that can now be considered explicitly when refining mortality estimates in Florida blue crab stock assessments. Discard mortality and market-bound mortality are unaccounted for, thus contributing to uncertainty in Florida blue crab stock assessments. The reflex action mortality predictor tool was used to predict discard mortality, which was largely influenced by environmental salinity and seasonal temperatures, whereas empirical market-bound mortality was influenced by seasonal temperatures.