Development and application of an ecological classification tool for fish in lakes in Ireland

A classification tool suitable for establishing the ecological status of lakes based on fish population parameters has been developed for the Republic of Ireland and Northern Ireland (EU Water Framework Directive Ecoregion 17). A lake typology relevant to fish populations in lakes from Ecoregion 17 was produced as part of the ecological classification tool development. Four lake types were determined based on fish metrics and abiotic variables from 43 “reference” lakes. The specific lake fish typology categorised lakes into low (≤67 CaCO3 mg L−1) or high (>67 CaCO3 mg L−1) alkalinity, and shallow (≤17 m) or deep (>17 m) maximum depth. The fish in lakes classification tool (FIL2) follows a novel multimetric predictive approach, assigning ecological status to a lake using two independent methods. FIL2 qualitatively defines a lakeʹs ecological status based on fish metrics using discriminant classification rules and, using a generalised linear model, quantitatively derives an Ecological Quality Ratio (EQR, 0 < EQR < 1), along with associated confidence intervals. It is recommended that both methods are used to validate output and cross-check and highlight potential misclassification.