The paucity of data on discard mortality in the commercial blue crab fishery contributes significant uncertainty to stock assessments. The reflex action mortality predictor (RAMP) method is used to predict mortality of commercially fished species by establishing a relationship between reflex impairment and the likelihood of mortality (RAMP curve). The present study adapted the RAMP method to commercially fished blue crabs in two unique habitats in Florida, the Tampa Bay estuary and the St. Johns River. The euryhaline nature of blue crabs permits the fishery to operate in myriad habitats, which adds complexity to cumulative effects that influence discard mortality. A total of 697 crabs were assessed, and a RAMP curve was generated. Logistic regression analyses determined that reflex impairment score, injury score, and salinity are strong predictors of discard mortality, with 91% of predictions correct. For every 1-unit increase in reflex impairment and injury score, mortality was 2.71 and 1.65 times more likely, respectively. Additionally, for every 1-SD (11.35 ppt) increase in salinity, mortality was 2.17 times more likely. Crab size, sex, water temperature, and emersion time minimally influenced mortality. The present study is the first crustacean RAMP research that included water quality and demonstrated that its inclusion increases the predictability of discard mortality. The RAMP curve can be used as a tool to estimate discard mortality aboard commercial vessels and discard mortality in future stock assessments.