Citation:

Blocksom, K. AND D. Peck. Comparison of Traditional and Modeled Fish Multimetric Indices for Rivers and Streams in the Western U.S. Pacific Northwest Chapter of Society for Freshwater Science, Coeur d'Alene, WA, November 03 - 05, 2015.

Impact/Purpose:

This abstract is for a presentation to be given at the Pacific Northwest Chapter of the Society for Freshwater Science in Coeur d'Alene. The attendees of this meeting will largely consist of regional biologists working in biological assessment in the Northwest. This presentation will describe multimetric indices for fish developed specifically for the West and should be of interest to potential users in the region. The presentation includes a comparison of a more complex approach to multimetric index development common in recent years to a more traditional approach and weighs the pros and cons over each approach.

Description:

The development of multimetric indices (MMIs) for use in assessing the ecological condition of rivers and streams has advanced in recent years with the use of various types of modeling approaches to factor out the influence of natural variability and improve performance. New modeling approaches may be constrained by data requirements and difficulty of applying the model construction process to new data. This necessitates a careful evaluation of the degree of improvement provided by alternative modeling approaches. We used data collected for the 2008-09 National Rivers and Streams Assessment (NRSA) to develop three variants of a fish MMI for use in assessing ecological condition within the Western aggregated ecoregions of the conterminous USA. We classified candidate metrics into eight categories: non-natives, taxonomic composition, habitat guild, migratory strategy, reproductive guild, taxa richness, tolerance to disturbance, and trophic guild. We constructed a model-based MMI for the combined Western aggregated ecoregion by adjusting metric responses using regression models constructed with a random forest algorithm. We then constructed two separate traditional MMIs for the Western Mountains and the Xeric aggregated ecoregions by adjusting candidate metrics only for watershed area using linear regression. For both MMI variants, we evaluated candidate metrics for range, responsiveness (comparison of least-disturbed sites to more highly disturbed sites), and repeatability (variability among sites vs. variability within sites). For each MMI variant, we used metrics that had passed these screens and calculated all possible MMIs that included at least one metric from each category. For each variant, we selected a final MMI that had high responsiveness, a reasonable value for repeatability, low mean pairwise correlation among component metrics, and a maximum pairwise correlation among component metrics that was <0.7. We present the performance of each MMI variant and discuss implications of adapting either MMI variant for use in current and future NRSA efforts.This is an abstract for a proposed presentation and does not necessarily reflect EPA policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

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