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<br />001013 <br /> <br />The middle graph of Figure 3.3 shows the habitat use during the spawning period when runs were <br />used most, followed by slackwaters, runs/riffles, and eddies. In 1993, fish movements and visual <br />observations indicated that two spawning sites (RM 131.1 and RM 132.0) were used. The fish used <br />a complex of habitats, including slower-velocity habitats (runs, eddies, slackwaters) and proximal <br />higher-velocity riffle or chute habitats. The fish spent most of their time resting in low-velocity <br />habitats, but they moved to riffle/run and chute habitats to spawn. Spawning habitat, therefore, <br />included chutes and riffle/runs where they spawned and the adjacent eddy and slackwater resting <br />areas. Similar habitat use and spawning behavior was identified in the Green, Yampa, and <br />Colorado rivers (Wick et al. 1983, Osmundson et al. 1995). <br /> <br />During the August 1993 post-spawning period, the fish used mainly run and chute habitats (Figure <br />3.3, bottom graph). Autumn radiotelemetry contacts in 1994 indicated that runs were the primary <br />habitat used, along with pools and eddies. Miller and Ptacek (2000) also conducted a brief <br />radiotelemetry study in February 1994, and the three fish monitored used runs, undercut runs, and <br />eddies. Others showed that Colorado pikeminnow used low-velocity habitats during the winter in <br />the Green (Valdez and Masslich 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 <br />Ptacek (2000) to determine habitat "richness," which was calculated as the number of habitat types <br />within the area mapped. Typically, a section of river, about 100 yards from the most upstream and <br />downstream areas used by a radio-tagged fish, was mapped during a radiotelemetry encounter. <br />This mapping showed an average habitat richness of eight habitats during the pre-spawning period, <br />nine habitats during spawning and post-spawning periods, and five habitats during the winter <br />(Miller et al. 1999). <br /> <br />Miller et al. (1999) also calculated habitat selection by comparing the availability of various <br />habitats to Colorado pikeminnow use of those habitats. Habitat types used more than they would <br />be by chance were considered "selected." This analysis showed that eddies, slackwaters, and pools <br />were highly selected most of the time, and chutes were selected during the spawning period. As <br />shown in Figure 3.3, the selected habitats were not the most used, but they were rare within the <br />areas used by the fish; hence the habitats were used more than would be expected by chance. This <br />suggests that the fish sought these habitats out, or selected them over more-available habitats, <br />indicating that they are key habitats for the fish. <br /> <br />Tributaries are an important habitat component for Colorado pikeminnow in the Green River <br />system, where tributaries are still available to the fish. Both the Yampa River and White River <br />were heavily used by Colorado pikeminnow subadults and adults, apparently as foraging areas <br />(Tyus 1991). Adults returned to these tributaries after spawning, making tributaries their primary <br />area of residence. Tributaries to the San Juan River no longer provide this type of function for <br />Colorado pikeminnow because they are dewatered or access is restricted. Miller and Rees (2000) <br />summarized San Juan River tributary fish collections from the 1930s to the present, and they did <br />not find any Colorado pikeminnow reported. Colorado pikeminnow utilized the Animas River in <br />the late 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 />