Evaluation of fish and benthic invertebrate bioassessments and the effects of placer mining on Yukon River Basin streams

This study focussed on the development and evaluation of bioassessment methods for wadeable streams of the Yukon River basin within Yukon Territory. There were three components to this study. The first was the detailed development, evaluation and comparison of Reference Condition Approach (RCA) bioassessments using fish and benthic macroinvertebrates (BMI) from the same stream sites. Second, methods were developed for examining the relationships between stream biota and a gradient of placer gold mining. Finally, the statistical power of bioassessments developed for the Yukon River basin was evaluated by applying the bioassessments to stream site data subjected to simulated impacts.;This study generated a number of useful stream bioassessment tools as well a considerable amount of data that have been made widely available to researchers, resource managers and others. As a result of this study, the data and many of the bioassessment techniques developed are currently being regularly used by federal, territorial and first nation government agencies in the Yukon and other parts of Canada.;Keywords. bioassessment, Reference Condition Approach, benthic macroinvertebrates, fish, Yukon River basin, placer mining, power analysis;Comparison of RCA bioassessments of streams in the Yukon River Basin based on fish and BMI showed the same assessment determination for only about half of the test sites assessed (34 of 69). Eighteen sites found to be undisturbed by the fish bioassessment were determined to be at least possibly disturbed by the BMI bioassessment and 13 sites judged to be undisturbed by the BMI bioassessment were considered at least possibly disturbed by the fish bioassessment. Analysis of these differences indicated that fish and BMI respond to different stressor characteristics, suggesting that both be used for effective bioassessment programs. An effective means of characterizing a highly variable activity like Yukon placer mining was developed and a significant correlation between the level of placer mining activity and diversity of the BMI communities was found. Lastly, RCA bioassessments based on a Biotic Index consistently had higher power than those based on either taxon richness or Simpson's Diversity. The power of all models examined was generally modest, even at high Type I error probabilities.