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<br />METHODS <br /> <br />Study area- The Yampa River is located in arid, northwestern Colorado and drains <br />portions of the southern Rocky Mountains, Wyoming Basin, and Colorado Plateau to <br />the Green River. It remains one of the last relatively unregulated rivers in the Upper <br />Colorado River Basin and has an average annual discharge of 1.2 million acre feet and <br />a snow-melt discharge that peaks in spring. This study focused on the area <br />downstream of Craig, Colorado, where the Yampa River meanders primarily through <br />low-gradient alluvial floodplain except for four high-gradient canyons of varying length. <br />Canyon-bound reaches include Little Yampa Canyon (RM 129.9-103.4), Juniper <br />Canyon (RM 91.1-89.1), Cross Mountain Canyon (RM 58.9-55.5) and Yampa Canyon <br />(RM 45-0). We selected two study areas based on high concentrations of small mouth <br />bass observed during previous sampling for northern pike (Hawkins et al. 2005). The <br />two areas were Little Yampa Canyon, from Roundbottom to 1-mile upstream of <br />Government Bridge near Lay, Colorado (RM 124-100) and Lily Park between Cross <br />Mountain Canyon and the Little Snake River confluence (RM 55.5-50.5; Figure 1). <br />River reaches downstream of RM 177 and outside of our study sites were sampled by <br />either us or other agencies. These included Craig (RM 177-135), South Beach (RM <br />135-124), Lower Juniper (RM 100-89), Maybell / Sunbeam (RM 89-59), and Yampa <br />Canyon (RM 45-0; Figure 1). <br /> <br />Sampling protocol-- Sampling began in 2003 with a single study site at Little Yampa <br />Canyon and our study design divided the site into equal-sized control and treatment <br />reaches with the intent of determining whether abundance of adult smallmouth bass <br />(~.150 mm total length; TL) declined in the treatment reach after smallmouth bass <br />removal. Beginning in 2004, at the start of each annual sampling season, we estimated <br />abundance of adult smallmouth bass in each study site. On subsequent sampling <br />occasions in the same year we removed smallmouth bass from the treatment reach and <br />marked and returned them to the river in the control reach. In 2003, each reach was 6- <br />miles long with the treatment (RM 111.2-117.2) upstream of the control (RM <br /> <br />4 <br />