Calibrating and validating the Aerobic Mortality Risk Index (IRMA): an index for predicting mass mortality of fish due to anoxia

To develop an early warning tool for mass fish mortality due to eutrophication in tropical estuaries, we calibrated and validated the Aerobic Mortality Risk Index (IRMA). To calculate IRMA, we used a conceptual model that relates the concentrations of PO4 (µmol.L-1), chlorophyll (CLA, µg.L-1) and dissolved oxygen (DO, mg.L-1), incorporating 30 years of monitoring data from the estuarine lagoon Ciénaga Grande de Santa Marta (CGSM) - Colombian Caribbean. We calibrated the model using the fish kill events recorded in CGSM and evaluated its performance through a confusion matrix. Several metrics were used to assess the effectiveness of IRMA, resulting in an optimized threshold value of 60%.