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Though nonnative channel catfish (Ictalurns punctatus) have been recognized as the principal predator and competitor affecting humpback chub populations in the lower Yampa River, a highly prolitic and migratory population of smallmouth bass may raise the bar of demise in Yampa Canyon. Anderson (2002) and Fuller (2003) reported that smallmouth bass in the Yampa and Green Rivers have been increasing since 2001. It is 24 I I I I I I I I I I I I I I I I I I I Catch rates were correlated to both floodplain size and quantity of submergent vegetation. Posters Channel Catfish Control in the Lower Yampa River Fuller, Mark H. u.s. Fish and Wildlife Service, Vernal, UT Since 1998 mechanical removal strategies to reduce sub adult and adult channel catfish abundance in the lower Yampa River have been successful. In 1998 methodologies were tested and in 1999 electrofishing and volunteer assisted angling resulted in significant population reductions in several test reaches (57.4 -81.5%). In 2000, the Vernal Field Office made recommendations to expand the control effort and emphasize reduction of channel catfish abundance in the entire Yampa Canyon for 2001 -2003. Study recommendations from the 1998-99 study included removal strategies based on catfish behavior and flow regimes to increase capture effectiveness. Electrofishing on flows between 3000 and 1000 cfs provided the highest catch rates and effectively sampled shallow higher velocity environments (runs and riffles), and volunteer assisted angling provided the most fish per trip when flows were too low to navigate electrofishing rafts in the canyon. Angling effectively sampled the deeper slower velocity habitat (pools) in late summer during lower water levels and when catfish movement between habitats was minimal. The majority of catfish collected in the canyon have been between 200 and 400 mm total length and data show a steady decrease in average length over the years. Juvenile catfish (<150 nun) are absent from the canyon. Fyke netting, shoreline electro fishing and seining during other studies have failed to detect yoy channel catfish in the canyon. Thus, recruitment (catfish between three and four years of age) of catfish into the canyon consists of catfish mostly> l50mm TL. Channel catfish growth is slow in the lower Yampa River. Growth data (Tyus and Nikirk 1990) indicates that the most common sized catfish collected from the study area (200 - 400 mm) ranged between five to fourteen years of age. Channel catfish mature between 250 mm and 400 mm (Carlander 1969). Because growth rates are slow, and densities of larger catfish are fairly low (Modde and Fuller 2000), it appears that we are removing much of the mature catfish population in the canyon.