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Control of large bodied non-native fishes in the San Juan River, New Mexico - Colorado _ Utah is considered integral to recovery efforts for the federally protected Colorado pikeminnow Ptychocheillls lucius and razorback sucker :(vrallchen texanlls. Mechanical removal of channel catfish lctalllrlls pZlnctatlls and common carp ('Yprinlls carpio by electrofishing in the San Juan River began in 1995 but was not tonnally instituted as a long-term management tool until 1998. Riverwide. annual numbers of channel cattish removed have increased with each successive year of sampling since 1998, 1\1ean total 12 I I I I I I I I I I I I I I I I I I I larvae have reduced survivorship at temperatures greater than 34 oC, however, shiner eggs and larvae were able to withstand conductivities up to 19,750 IlS/cm (12.8 ppt salinity). Data also indicate that simulated flood events in the laboratory result in greater displacement of red shiners as compared to spikedace. We develop recommendations for timing and type of environmental manipulations that would suppress shiner populations or their reproductive success, thereby reducing the negative effects of this introduced species on native species. Our goal is to demonstrate the efficacy of this approach to the recovery of threatened native species. Predation on early life stages of razorback sucker in laboratory trials Carpenter, Jeanette, and Gordon Mueller us. Geological Survey. Fort Collins Science Center Few biologists question the impact of introduced predators on endangered fishes of the Colorado River. Substantial effort is being expended to remove large fish predators. However, abundance of smaller non-natives may be increasing as large predators decline, In laboratory experiments we examined predation oflarval razorback suckers by small non-natives now common in the Colorado River: young bluegill, rainbow trout, largemouth bass, yellow bullhead, and channel catfish, as well as red shiners and bullfrog tadpoles. We also tested predation by young bonytail, and bullfrog tadpole predation on razorback eggs. All species tested preyed on razorbacks. Tadpoles consumed 100% of available razorback eggs. Larval predation was >85% in tanks with trout, red shiner, bullhead, and bonytail. In mixed-prey trials, we used larval razorbacks with similar-sized fathead minnows. Channel catfish, largemouth bass, and bluegill showed no preference for prey size or prey species. Our results show a clear negative impact by small non- natives on razorback young. Furthermore, small predators are more numerous and less vulnerable to mechanical removal than their larger cohorts. Small non-natives may pose a more significant predatory threat to young razorbacks than larger predators. Evaluation of mechanical removal of large bodied non-native fishes in the San Juan River, New Mexico - Colorado - Utah, 1998-2003. Davis, lE., United States Fish and Wildlife Service. Nev.' Mexico FislzelY Resources Office. Albuquerque. NM