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AQUATIC VERTEBRATE ASSEMBLAGES AT LEAST- AND MOST-IMPACTED STREAM AND RIVER SITES IN THE WESTERN FORESTED MOUNTAINS AGGREGATE ECOREGIONS
Citation:
Whittier, T R. AQUATIC VERTEBRATE ASSEMBLAGES AT LEAST- AND MOST-IMPACTED STREAM AND RIVER SITES IN THE WESTERN FORESTED MOUNTAINS AGGREGATE ECOREGIONS. Presented at Northwest Bioassessment Workgroup meeting, Long Beach, WA, November 6-8, 2002.
Description:
In the West, development of indicators of aquatic vertebrate assemblages condition in streams and rivers is challenged by low species richness (often < 3 species), by strong natural gradients (e.g., elevation), by human impact gradients that often co-vary with natural gradients, and by a lack of un-impacted reference sites in mid- to low-elevation streams, and medium to large rivers. The indicator development and evaluation process should benefit by an evaluation of assemblage data collected at sites representing the least-impacted and the most-impacted conditions along the range of natural gradients. The least-impacted and most-impacted sites were chosen by plotting each of ten water chemistry, watershed-scale, and site-scale indicators of anthropogenic stress against elevation, slope and stream size and selecting sites with multiple low-impact or high-impact scores. I compare and contrast vertebrate assemblages from 18 least-impacted and 16 most-impacted sites sampled by EMAP-Western Pilot in 2000, in the Forested Mountains aggregate ecoregion. These sites include the range of elevations, slopes and stream sizes in that region. In small, mid- to high-elevation streams more often than not, no vertebrates were collected regardless of stream condition. A species population assessment may be possible for sites with vertebrates. Least-impacted medium-sized streams had relatively numerous native trout along with one or two moderately intolerant native benthic fish species, and in some areas, an amphibian species. Fewer individuals and species occurred at higher elevations. Brook trout indicates good physical/chemical conditions but are a biological stressor. Most-impacted medium-sized streams had fewer native trout (or none) and often had tolerant native sucker species, or non-native and/or land-based amphibians. Least-impacted large rivers sites had one or more native trout or salmon and few non-native species, in low numbers. They had five or so other species including some intolerant or moderately intolerant benthic species. Most-impacted large river sites had more non-natives, more tolerant species, and tended not to have native trout or salmon.