The Development and Application of Multimetric Indices for the Assessment of Impacts to Fish Assemblages in Large Rivers: A Review of Current Science and Applications

The biological assessment of lotic resources in much of the U.S. and Canada initially focused on wadeable rivers and streams. However, increased emphasis is being placed on larger, non-wadeable rivers. Many of these efforts include the development of multimetric indices represented by the Index of Biotic Integrity (IBI) following the original developmental work in the U.S. They include the pioneering work in the Wabash River of the Midwestern U.S., the inland rivers of Ohio and Wisconsin, the Ohio River mainstem, large western rivers and Quebec rivers, all of which focused on the fish assemblage. Monitoring fish assemblages in large rivers includes logistical and technical considerations that affect obtaining reliable estimates of relative abundance for all species that are amenable to efficient capture. A single gear approach is preferred for practical reasons and electrofishing is the sampling method of choice. Sampling effort is expressed in terms of distance sampled at a site and includes formulas based on fixed distances or multiples of river channel width. Relative abundance data are analyzed via multimetric indices (e.g., Index of Biotic Integrity), which are contingent on the development of a reference condition that supports a derivation and calibration process. Defining reference for large rivers represents a different challenge than with smaller, wadeable streams. For the latter, sufficient and suitable reference analogs usually exist, thus reference condition can be empirically derived. However, such analogs are either rare or do not adequately reflect the restorable potential for large rivers. Thus in developing the expectations that are necessary for metric calibration and IBI development, adequate historical knowledge of the assemblage is critical. Once developed, the metrics and indices provide meaningful measures of assemblage quality and response to chemical, physical, and biological influences and perturbations. This has been demonstrated for a wide variety of human impacts including water pollution, habitat and flow alterations, and land use changes. Successfully applying this protocol to large rivers involves taking the correct sequence of steps in the initial development of sampling and assessment methodologies. The IBI serves not only as an important benchmark of aquatic resource quality and condition, but also as a test of the significance of human impact on the aquatic environment. Developing and implementing a multimetric approach for large, coldwater rivers is feasible and would serve as a useful assessment and planning tool for determining the magnitude and severity of impacts from riverine flow and habitat modifications.

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