Applicability and Interpretation of Fish Indices of Biotic Integrity (IBI) for Bioassessment in the Upper Midwest

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© 2015, © American Fisheries Society. Abstract: Multiple fish-based indices of biotic integrity (IBIs) and biological condition gradient models have been developed and validated to assess ecological integrity in the Laurentian Great Lakes region. We evaluated the applicability and effectiveness of using fish community indices for assessing site integrity in central Great Lakes streams, which have diverse temperature regimes and can be classified as warmwater, coolwater, or coldwater. Sites with different thermal regimes require different assessment tools to ensure comparability. Streams in the Big Manistee River watershed, Michigan, are near thermal thresholds for classification as coolwater or coldwater. We evaluated two coolwater and three coldwater indices developed for Upper Midwest streams. Output from coolwater indices were not correlated with coldwater index outputs and did not discriminate among the stream systems we evaluated. In monitoring temporal patterns over time (2002–2010), we found that coldwater indices showed similar patterns and agreed in relative scoring of sites from high to low. The three coldwater indices also similarly discriminated among stream systems; however, when the coldwater indices were used for specific site assessments, they produced differential results. Depending on which index was applied, a single site could be classified into three different levels of quality. This highlights the importance of index selection for management actions. An understanding of the factors that drive the indices and an understanding of reference conditions are imperative for effective use of fish-based IBIs in the Upper Midwest. Received July 15, 2014; accepted December 12, 2014

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North American Journal of Fisheries Management