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(PH214) A comparison of the sensitivity of fish multimetric indices with multivariate statistics to detect effects along large rivers in Oregon.
Thomas, J.1, Ragsdale, R.1, Hall, T.1, 1 National Council for Air and Stream Improvement, Anacortes, WA, USA
ABSTRACT- Multimetric indices, such as the Index of Biotic Integrity (IBI), have been available for over 20 years, but their use as regulatory assessment tools is a growing phenomenon. IBIs are straightforward to use and result in easily communicated results, but have been criticized for oversimplifying complex systems. This study compared the sensitivity and repeatability of two published fish IBIs, one a river specific IBI and the other a regionally developed method, and their individual metrics with a multivariate statistical method. Their ability to distinguish spatial differences (between rivers and sites within a river), methodology differences (fish capture methods), and temporal differences (seasonal or annual differences) was assessed for two large Pacific Northwest rivers. Results demonstrated that the IBIs had little ability to identify differences without analysis of the individual metrics. The results also suggested that caution should be taken when using IBI results since misinterpretation may result with the use of non-site specific IBIs or with too few sample numbers. Multivariate statistical analysis of the same datasets allowed for more consistent identification of differences and a greater ability to identify and quantify subtle to moderate spatial differences. Disadvantages to the multivariate method include that it does not provide a classification system nor result in one easy to communicate number. In addition, although multivariate procedures are able to discern subtle effects there remains the question of whether or not they are ecologically relevant. An alternative approach is suggested, pairing multivariate analysis with individual metrics to provide a way of labeling the subtle to moderate differences found in the multivariate analysis with some specific community differences.
Key words: index of biotic integrity, multimetrics, multivariate analysis, fish community
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