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• 101. [Article] The Influence of Riparian Habitat and Microhabitat Selection on Fish Assemblaqe Structure in the Upper John Day Basin, Oreqon

  Fish assemblage structure was determined along a longitudinal gradient for three drainages in the upper John Day basin: Middle Fork, South Fork, and upper Mainstem proper. One or two tributaries in each ...

  Citation × Citation Citation Abstract Copy Title: The Influence of Riparian Habitat and Microhabitat Selection on Fish Assemblaqe Structure in the Upper John Day Basin, Oreqon Author: Leitzinger, Eric J. Fish assemblage structure was determined along a longitudinal gradient for three drainages in the upper John Day basin: Middle Fork, South Fork, and upper Mainstem proper. One or two tributaries in each drainage were included. Where possible, sites were paired: those with good versus those with poor riparian habitat. Detrended correspondence analysis was used to determine how the assemblages were structured and to determine which environmental variables influenced that structure. Two assemblages resulted: a warmwater assemblage dominated by speckled dace (Rhinichthys osculus), redside shiners (Richardsonius balteatus), northern squawfish (Ptychocheilus oreqonensis), and suckers (Catostomus spp.); and a coldwater assemblage dominated by juvenile steelhead (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus tshawytscha), but also containing mountain whitefish (Prosopium williamsoni), piute sculpins (Cottus beldingi), and other salmonids. This coldwater assemblage had two distinct components: the chinook component and the steelhead component. The chinook component was concentrated in the mid-elevation reaches of the Mainstem and the Middle Fork, between the steelhead component and the warmwater assemblage. The primary physical gradient on which all assemblages aligned was an elevation/stream size gradient. A secondary gradient consisted of various riparian habitat and bank condition variables. Generally, riparian habitat improved moving toward the headwaters. Microhabitat use was compared for salmonids within a habitat type (i.e. pools, riffles, and runs) for mainstem and tributary streams. It was also compared for the same age classes and species between stream types (mainstem versus tributary). Finally, microhabitat selection (versus availability) was examined for significant differences between microhabitat available and that selected. Different age classes of steelhead and juvenile chinook salmon used different microhabitats in the same habitat type. These did not change significantly between habitats or stream type. All groups selected microhabitats that varied significantly from that available. The most important variables in all cases were focal point depth and focal point velocity, total depth and mean velocity. Title: The Influence of Riparian Habitat and Microhabitat Selection on Fish Assemblaqe Structure in the Upper John Day Basin, Oreqon Author: Leitzinger, Eric J. Fish assemblage structure was determined along a longitudinal gradient for three drainages in the upper John Day basin: Middle Fork, South Fork, and upper Mainstem proper. One or two tributaries in each drainage were included. Where possible, sites were paired: those with good versus those with poor riparian habitat. Detrended correspondence analysis was used to determine how the assemblages were structured and to determine which environmental variables influenced that structure. Two assemblages resulted: a warmwater assemblage dominated by speckled dace (Rhinichthys osculus), redside shiners (Richardsonius balteatus), northern squawfish (Ptychocheilus oreqonensis), and suckers (Catostomus spp.); and a coldwater assemblage dominated by juvenile steelhead (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus tshawytscha), but also containing mountain whitefish (Prosopium williamsoni), piute sculpins (Cottus beldingi), and other salmonids. This coldwater assemblage had two distinct components: the chinook component and the steelhead component. The chinook component was concentrated in the mid-elevation reaches of the Mainstem and the Middle Fork, between the steelhead component and the warmwater assemblage. The primary physical gradient on which all assemblages aligned was an elevation/stream size gradient. A secondary gradient consisted of various riparian habitat and bank condition variables. Generally, riparian habitat improved moving toward the headwaters. Microhabitat use was compared for salmonids within a habitat type (i.e. pools, riffles, and runs) for mainstem and tributary streams. It was also compared for the same age classes and species between stream types (mainstem versus tributary). Finally, microhabitat selection (versus availability) was examined for significant differences between microhabitat available and that selected. Different age classes of steelhead and juvenile chinook salmon used different microhabitats in the same habitat type. These did not change significantly between habitats or stream type. All groups selected microhabitats that varied significantly from that available. The most important variables in all cases were focal point depth and focal point velocity, total depth and mean velocity. Close