Fish species richness and stream order in Washington State streams |
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Authors: | Hal A Beecher Eric R Dott Robert F Fernau |
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Institution: | (1) Washington Department of Wildlife, 600 N. Capitol Way, Olympia, WA, 98504, U.S.A.;(2) The Evergreen State College, Olympia, WA, 98505, U.S.A. |
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Abstract: | Synopsis We sampled fish at pairs of sites of the same stream order on opposite sides of drainage divides in the Cascade Mountains
and in the southwest portion of Washington state. Elevation, gradient, drainage area, and stream order were significantly
correlated with number of fish species collected at a site. Elevation accounted for the greatest portion of the variation
in number of species and stream order for the least, but in low gradient, low elevation streams, stream order was significantly
related to number of species. Species richness was greatest in low elevation, low gradient, high order streams. Species richness
of a site reflected species richness of the drainage: in paired comparisons, sites in a drainage with a richer ichthyofauna
had more fish species than sites in a drainage with fewer species. Addition of species with increasing stream order occurred
in most streams, but replacement was more frequent than in other studies relating fish to stream order. The apparently higher
frequency of replacement in this study appeared to be a result of headwater introductions of brook charr, Salvelinus fontinalis, and a tendency for cutthroat trout, Salmo clarki, to occupy headwaters when in freshwater. |
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Keywords: | Elevation Gradient Drainage area Ichthyofauna Drainage basin Salmo Salvelinus Cottus Columbia River |
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