Stream Habitat Conditions In Western Oregon PDF Download

The objectives of this study were to (1) describe physical environmental conditions and species composition at several sites along an Upstream/downstream gradient in a number of tributaries of the Willamette River in western Oregon; and (2) identify possible relationships between species distributional patterns and physical habitat parameters using detrended correspondence analysis (DCA), graphical techniques, and contingency table analysis. Study sites that contained both pools and riffles were selected at various locations on seven streams. At each site 13 physical environmental parameters were measured, and fish species composition and abundance were determined by snorkeling and electroshocking techniques. Associations between environmental conditions and species composition and abundances were hypothesized using the results of DCA. The DCA analysis revealed three habitat gradients, each of which represents a composite of several physical habitat variables. Axis one was interpreted as a habitat gradient from pools to riffles based upon observations of temperature, depth, and percent gravel and bedrock. Axis two appeared to be a gradient of habitat cover types; instream cover (undercut banks, root wads and boles, woody debris, and rooted vegetation) typified one end of the axis and other cover types (riparian vegetation, large substrate composition, and swift water velocities) were indicative of the opposite end of the axis. Axis three seemed to be gradient of stream discharge. Species scores differed along each axis due to the variation in specific responses to these different physical habitat gradients. A three-dimensional graph of species scores for all three axes was used to predict fish community responses to potential human perturbations of the Willamette River drainage given known effects of these perturbations on the physical parameters underlying the three gradients.