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<br />C..1 <br />C-) <br />t-\ <br />co <br />-.1 <br /><.D <br /> <br />The middle graph of Figure 3.3 shows the habitat use during the spawning period when runs were used <br />most, followed by slackwaters, runs/riffles, and eddies. In 1993, fish movements and visual observations <br />indicated that two spawning sites (RM 131.1 and RM 132.0) were used. The fish used a complex of <br />habitats, including slower-velocity habitats (runs, eddies, slackwaters) and proximal higher-velocity riffle <br />or chute habitats. The fish spent most of their time resting in low-velocity habitats, but they moved to <br />riffle/run and chute habitats to spawn. Spawning habitat, therefore, included chutes and riffle/runs where <br />they spawned and the adjacent eddy and slackwater resting areas. Similar habitat use and spawning <br />behavior was identified in the Green, Yampa, and Colorado rivers (Wick et al. 1983, Osmundson et al. <br />1995). <br /> <br />During the August 1993 post-spawning period, the fish used mainly run and chute habitats (Figure 3.3, <br />bottom graph). Autumn radiotelemetry contacts in 1994 indicated that runs were the primary habitat used, <br />along with pools and eddies. Miller and Ptacek (2000) also conducted a brief radiotelemetry study in <br />February 1994, and the three fish monitored used runs, undercut runs, and eddies. Others showed that <br />Colorado pikeminnow used low-velocity habitats during the winter in the Green (Valdez and Masslich <br />1991) and Yampa (Wick and Hawkins 1991) rivers. <br /> <br />Habitats in the general area of radio-tagged Colorado pikeminnow were mapped by Miller and Ptacek <br />(2000) to determine habitat "richness," which was calculated as the number of habitat types within the area <br />mapped. Typically, a section of river, about 100 yards from the most upstream and downstream areas <br />used by a radio-tagged fish, was mapped during a radiotelemetry encounter. This mapping showed an <br />average habitat richness of eight habitats during the pre-spawning period, nine habitats during spawning and <br />post-spawning periods, and five habitats during the winter (Miller et al. 1999). <br /> <br />Miller et al. (1999) also calculated habitat selection by comparing the availability of various habitats to <br />Colorado pikeminnow use of those habitats. Habitat types used more than they would be by chance were <br />considered "selected." This analysis showed that eddies, slackwaters, and pools were highly selected most <br />of the time, and chutes were selected during the spawning period. As shown in Figure 3.3, the selected <br />habitats were not the most used, but they were rare within the areas used by the fish; hence the habitats <br />were used more than would be expected by chance. This suggests that the fish sought these habitats out, <br />or selected them over more-available habitats, indicating that they are key habitats for the fish. <br /> <br />Tributaries are an important habitat component for Colorado pikeminnow in the Green River system, <br />where tributaries are still available to the fish. Both the Yampa River and White River were heavily <br />used by Colorado pikeminnow subadults and adults, apparently as foraging areas (Tyus 1991). <br />Adults returned to these tributaries after spawning, making tributaries their primary area of <br />residence. Tributaries to the San Juan River no longer provide this type of function for Colorado <br />pikeminnow because they are dewatered or access is restricted. Miller and Rees (2000) summarized <br />San Juan River tribulaiy fish collections from the 1930s to the present, and they did not find any <br />Colorado pikeminnow reported. Colorado pikeminnow utilized the Animas River in the late <br />1800s (Jordan 1891), and this river may still provide suitable habitat; however, the present <br /> <br />September 2000 <br /> <br />3-7 <br /> <br />Program Evaluation Report <br />