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I I I I I I I I I I I I I I I I I I I may have resulted in the electro-fishing raft traveling a greater distance in the same amount of time, Also, there was a constant supply of stunned fish on the Gunnison River. There were very few fishless habitats like large unproductive backwaters (Colorado River), long very-shallow runs (Yampa River), or deep pools that added electro-fishing time without fish. Nonetheless, the most likely explanation for the much higher fish catch per unit effort in the Gunnison River was better habitat quality. Anderson and Stewart (2003) identified increasing habitat diversity and invertebrate productivity with increasing base flows up to a threshold, The Gunnison River appeared to be an example where habitat and productivity was vel;' good for native fish. DISCUSSION YAMPA RIVER Each of the Yampa River sites had distinctive characteristics for fish composition, In the baseline years (1998 and 1999) flannelmouth sucker composition was about 5% at Duffy, 50% at Sevens and 70% at Lily Park. Bluehead sucker composition was about 4% at Duffy. 20% at Sevens and 8% at Lily Park, After three years oflow base flows there were sharp decreases in native fishes and strong increases in nonnative fish species at all sites, Fish biomass estimates were also greatly different between sites on the Yampa River, Duffy had relatively low biomass and Lily Park had relatively high biomass. Total biomass was reduced in the dry years compared to the baseline years at all sites, Native fish biomass was lowest at each site in 2003, Smallmouth bass were likely first introduced in the Yampa River basin in the late 1970s and were uncommon during Yampa River fish surveys prior to 1992, the year Elkhead Reservoir was drained (P, Martinez, Colorado Division of Willdlife personal communication). By 1998 and 1999 Age-O smallmouth bass were commonly collected from shoreline habitat at Duffy. The smallmouth bass population rapidly increased during the low-tlow period 2000-2002, Shallow pool habitat with warmer water temperatures increase with reduced flows (Bain et al 1988). If these conditions promoted earlier spawning or a longer growing season then small mouth bass recruitment could have been improved in drought years, because Age-O small mouth bass larger than 75 cm could have had higher over-winter survival rates than smaller YOY (P. Martinez, Colorado Division of Wi lid life personal communication). Cooler water temperatures during the summer, a possible side effect of releases from an enlarged Elkhead Reservoir, might interfere with over winter survival Age-O smallmouth bass, The impact of small mouth bass on the fish community of the Yampa River can not be underestimated, Speckled dace (Rhinichrhys oscu/us) and mottled sculpin (COllUS hairdi), two native species, were effectively eliminated from the Yarnpa River by 2001 (Anderson 2002). Speckled dace occupied swiftly flowing riffle habitats and both the fish and their habitat were common in the baseline years. During the low flow years velocities in riffles became slower and riffles provided productive nursery habitats for Age-O small mouth bass, 35