A biointegrity index for coldwater streams of western Oregon and Washington

Hughes, R.M., S. Howlin, and P.R. Kaufmann. 2004. . Transactions of the American Fisheries Society 133:1497-1515. WED-00-036

Low IBI scores (Index of Biological Integrity) were associated with low bed stability, instream cover, and riparian cover and structural complexity but high percent fine substrate, road density, and human disturbances of riparian areas. Applying this IBI, we assessed fish assemblage condition in the Coast Range, inferring our results to all mapped (1:100,000-scale) wadeable streams in this region. Using 2 SDs from the reference sites mean as a biological criterion, 45% of stream kilometers (10,646 km) were classified as impaired. High IBI scores clustered near national parks and wilderness areas. Our results indicate that minimally disturbed regional reference sites and probability survey designs, which produce statistically representative sites and inferences with known confidence bounds, offer considerable advantages over least disturbed reference sites and hand-picked survey sites for making regional ecological assessments.