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shiner, sand shiner, and smallmouth bass), and four hybrid suckers. Early collections documented the presence of Utah chub and mountain sucker, which were not collected in the two more recent periods. Overall, relative abundance of native species in the upper Lodore Canyon site declined from 92 to 65 to 13% of the fish community over the three study periods. Only a single native taxon, mountain whitefish, increased in relative abundance, but only by 0.1 %. Bluehead sucker and speckled dace declined dramatically, while flannelmouth sucker were severely reduced over the last two periods. Colorado pikeminnow, roundtail chub, and mottled sculpin remained but were rare. Nearly all non-native taxa increased in relative abundance in 2002 to 2004 compared to prior periods. Largest increases in non-native fishes between the first two periods were by cool-water tolerant fishes such as brown trout, redside shiner, and white sucker. Largest increases in non-native fishes between the 1994 to 1996 period and 2002 to 2004 was by redside shiner and fathead minnow, and warm-water tolerant red and sand shiner and channel catfish. Abundance of hybrid suckers increased between the two early periods, but declined in the 2002 to 2004 period. At the lower Lodore Canyon site at Alcove Brook, collections in 1978 to 1980 documented the presence of eight native fishes, 13 introduced ones, and one hybrid sucker. Sampling in 1994 to 1996 captured seven native fishes, 13 introduced ones, and five hybrid sucker. Sampling in 2002 to 2004 captured seven native fishes, 14 introduced ones (added black bullhead and creek chub, lost cutthroat trout Oncorhynchus clarki, the non-native Snake River subspecies), four hybrid suckers and one hybrid centrarchid . Six native taxa (speckled dace, Colorado pikeminnow, roundtail chub, flannelmouth sucker, bluehead sucker, and mottled sculpin) were common to all three periods. Razorback sucker and mountain sucker were captured at this site in 1978 to 1980 but not later, and mountain whitefish was detected in the two later periods but not earlier. Collections made in 1994-1996 documented presence of introduced northern pike, green sunfish, and smallmouth bass, all of which may have only recently colonized from the Yampa River; their presence was verified in the 2002 to 2004 period. Overall, relative abundance of native species in lower Lodore Canyon declined from 32 to 21 to 6% of the fish community over the three sampling periods. Native taxa declined in - 64 i