Reflex impairment as a predictor of mortality in Panulirus argus: Implications for the live export market

Abstract

Spiny lobster (Panulirus argus) fishers in Florida garner the highest price for lobsters that are sold to the live export market. Lobsters are “graded” using a visual qualitative assessment before export to remove any lobsters unlikely to survive shipping. The current qualitative grading process, while effective in reducing mortality, is conservative and results in a significant number of healthy lobsters being sold at lower prices for the frozen market. This study sought to develop lobster grading methods that more accurately predict lobster mortality to increase the proportion of lobsters suitable for the high-value live export market; thus, we compared two alternative grading/mortality predictor methods to the current exporter grading method. For this, we examined nine candidate lobster reflexes (i.e., appendix turgor and movement in response to a probe) and eight other lobster physiologic and morphometric parameters (i.e., number of injuries, molt stage, nutritional condition via blood serum protein, presence of shell disease, presence of tail fan necrosis, sex, and size) to develop two reflex action mortality predictors. The first mortality predictor was developed using reflex impairment alone, and the second mortality predictor was a quantitative mortality model developed with as many parameters as necessary to increase the model’s performance in predicting mortality. The classification accuracy of these mortality assessments (reflex impairment and quantitative mortality model) was then compared with the current qualitative grading process that occurs prior to shipping. The current grading process was a moderate predictor of mortality (area under the receiver operating characteristic curve, AUC 0.807), which correctly predicted the outcome (survival or mortality) 74.5 % of the time. Both mortality models performed better than the current grading process. A logistic regression indicated reflex impairment alone was a significant predictor of mortality (AUC 0.897), which was able to correctly predict mortality 88 % of the time. The quantitative mortality model included three predictors – blood serum protein, reflex impairment, and collection month – and was also a significant predictor of mortality (AUC 0.938) and had the highest accuracy (90 %) of the three assessments we examined. Results from this study show that mortality assessments using reflex impairment and health indicators can successfully predict mortality in P. argus. These mortality assessments could be applied at fish houses to increase the value of the fishery (3–9 %, $1.71 million USD/season) by increasing the number of lobsters sold for live export.