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ECOLOGY AND CONSERVATION OF NATIVE FISHES IN THE UPPER COLORADO RiVER BASIN 181 possession limits. Scientific evidence demonstrates that northern pike, smallmouth bass, and channel catfish are nonnative fish species that pose significant threats to survival of endangered fish because they prey upon them and compete for food and space. In 2004, the UCRRP revised its nonnative fISh management pro- gram using what was learned in 2002 and 2003. Bi- ologists from the states of Colorado and Utah, USFWS, and Colorado State University conducted work in 772 km of the Colorado, Green, and Yampa rivers in Colorado and Utah to reduce the abundance of northern pike and smallmouth bass. Efforts to manage channel catfish continued in Yampa Can- yon, where effective removal has been demonstrated, but were postponed in other river reaches until meth- ods to improve sampling efficiency are developed. Management of northern pike in the Yampa and Green rivers showed signs of success during 1999- 2002. Biologists reported a 60-68% within-year de- crease in abundance of northern pike in the targeted river sections, and have implemented studies to de- termine if these reductions will persist, or if northern pike populations will rebound as fish are replaced through natural production or movement into the targeted river sections from upstream areas. Where feasible, nonnative fish are relocated to area ponds to provide sportfIShing opportunities. Efforts to manage smallmouth bass have had mixed results. Depending on the section of river and methods being employed, within-year reductions in numbers of smallmouth bass in 2004 ranged from 8% to 69%. Biologists use different sampling meth- ods to increase capture efficiency and improve overall catch rates. These changes include the use of new sampling gear to collect fish more effectively in shal- low-water habitats and during times of low river flows, extending the sampling period into the fall when smallmouth bass are more vulnerable to cap- ture, and expanding management efforts to include smaller smallmouth bass. The UCRRP funded placementofa barrier net at Highline Lake State Park in western Colorado in 1999. The net was designed to control escapement of nonnative fish into critical habitat in the upper Colorado River and to ensure that sportfishing op- portunities continue at this popular reservoir. A non- native fish control structure was also installed at Bottle Hollow Reservoir near Roosevelt, Utah, to prevent escapement of fish into the middle Green River and allow the Ute Indian Tribe to place sportfish in its Elders Pond. Fish screens will be installed on outlets of the enlarged Elkhead Reservoir to prevent escape- ment to the Yampa River. Chemical reclamation has been used to reduce sources of nonnative fish to riv- erine habitats. Altogether, 104 ponds were surveyed and 19 were chemically treated to remove nonnative fish along the upper Colorado and Gunnison rivers in 1998-1999. Current stocking of nonnative fish species (mostly sportfish) in the upper basin is generally con- fined to areas where there is little potential conflict with endangered fish. In 1996, federal and state wild- life agencies in Colorado, Utah, and Wyoming final- ized an agreement on stocking nonnative sportfish (U.S. Fish and Wildlife Service 1996). This agree- ment prohibits stocking of nonnative fish within the 1 OO-year floodplain in designated critical habitat, but does not affect trout stocked in dam tailwaters where native fish are uncommon. Another aspect of nonna- tive fish management is removal of bag and posses- sion limits for nonnative fish in designated critical habitat. The state of Colorado has removed bag and possession limits on all nonnative, warmwater sponflsh in critical habitat. Colorado also has closed river reaches to angling where, and when, angling mortal- ity to native fish is determined to be significant. Endangered fish propagation and stocking.- The endangered fish propagation program in the upper basin has evolved over the past decade based on initial needs for research and later needs fOr popu- lation augmentation. Initially, hatcheries were de- signed to maintain razorback sucker in refuges and begin development of broodstocks for the upper Colorado River and Green River subbasins. In the mid 1990s, hatcheries produced various sizes of ra- zorback sucker and bonytail for experimental stock- ing to evaluate size at stocking, cohort survival, and time of stocking. In the late 1990s, the program increased production oflarge numbers of small ra- zorback sucker, bonytail, and Colorado pikeminnow for individual state stocking plans. These plans were revised and hatcheries were asked to produce larger fish for greater survival in the wild. Smaller fish were marked with coded wire tags and larger fish (greater