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2. Assess abundance of predators in treatment and reference reaches to determine • <br />removal effects. - <br />3. Implement removal of smallmouth bass and northern pike in treatment reaches in <br />spring (mostly conducted in a different study). - <br />r <br />4. Estimate response of native fishes in autumn after spring-summer predator • <br />removal. <br />STUDY AREA - <br />The Yampa River drains mountainous and high desert portions of south-central Wyoming <br />and northwestern Colorado and is the largest tributary of the Green River. The mainstem Yampa <br />River begins in Colorado and flows west from near Steamboat Springs, CO, downstream to the <br />Green River confluence in Dinosaur National Monument. The main study area was in the <br />vicinity of Little Yampa Canyon, just downstream of Craig, Colorado. The length of the study <br />area expanded over the study period from 19.4 RK in 2003 to 38.6 RK in 2006 (RK's 16]- <br />199.6). The original 19.4 RK study area reach had a 9.7 RK upstream treatment and a 9.7 RK <br />downstream control reach. Non-native fish predators were removed from the treatment reach in <br />spring and summer (J. A. Hawkins, RIP annual reports). The length of each of the treatment and <br />control reaches was doubled in 2004 and reach positions were swapped, with the treatment reach <br />extended downstream and the control reach extended upstream by 9.7 RK each. Thus, each <br />reach was then 19.4 RK (12 river miles) long. This was done because movement of tagged <br />smallmouth bass among the smaller treatment and control reaches was substantial. <br />Each of the treatment and control reaches was geomorphically similar because portions <br />of each were within Little Yampa Canyon, and portions were in less constrained valley reaches. <br />In the late summer and autumn low-flow sampling season, habitat consists mostly of low- <br />velocity pools separated by shallow, higher-velocity riffles. Substrate is typically a mix of <br />boulder, cobble, gravel, and sand in low velocity areas, and cobble and gravel in riffles. <br />Backwaters and isolated pools are created mostly by cutoff high-flow side channels and are <br />shallow to deep, with cobble, gravel, and fine-grained substrate. <br />2 <br />