Density of fish and salamanders in relation to riparian canopy and physical habitat in streams of the Northwestern United States

Relationships between density of fish and salamanders, riparian canopy, and physicalhabitat were investigated by studying 10 pairs of streams. Among vertebrate taxa, salmonidsand sculpins were more abundant in streams without riparian shading than in shaded streams.Abundance of salamanders was not affected by canopy type. Densities of both salamandersand sculpins were correlated with substrate composition, whereas salmonid abundance wasnot or only weakly so. Salamanders were found only at high-gradient sites with coarsesubstrates, and sculpins were most abundant at lower-gradient sites with finer-sized sedi-ments. An interaction was observed between the influence of canopy and that of physicalsetting on density of both invertebrate prey and total vertebrates. Among shaded sites,densities decreased as percent fine sediment increased, but a similar relationship did not existamong open sites. Removal of the riparian vegetation surrounding a stream may thereforemask detrimental effects of fine sediment. These data provide one reason why it has beendifficult in the past to generalize about the effects of fine sediment on stream biota.