10,000 Lakes -> 4 Indices: The Minnesota Fish IBI Tool

Minnesota DNR developed four fish-based Index of Biotic Integrity (FIBI) Tools for Minnesota lakes with surface area 100-10,000 acres.  One thousand surveys were completed on 700 lakes with gillnets, trapnets, backpack electrofishers, and beach seines.  The number of sampling stations was based on effort required to achieve 90% species accumulation of various categories of fish within lake size categories.  Metric selection was based on relations to measures of human-induced watershed and in-lake stressors evaluated with a variety of statistical analyses including Spearman rank correlations, Principle Components Analysis, and linear regression.  FIBI Tools have 8–15 metrics, with metric scoring individualized for each tool using a mixed model.  Composite FIBIs have a score range of 0-100 and are correlated with aquatic plant floristic quality, trophic state, and in some cases dock density.  Repeatability of FIBI composite scores within and between seasons varied between FIBIs, 90% CI was typically 9 points. Biological Condition Gradient Models were developed in collaboration with TetraTech Inc. and were used to help determine impairment and exceptional thresholds.  The FIBIs are being used in the Minnesota watershed assessment process to guide Clean Water planning, restoration, and protection efforts and complement pollutant-based water quality sampling efforts on lakes.