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19. Green River Fish Community Response to Flaming Gorge Dam Flow and Temperature Regimes, 2002 to 2004 Authors: KEVIN R. BESTGEN, KOREEN A. ZELASKO, and ROBERT I. COMPTON and TOM CHART " Abstract: We conducted sampling from 2002 to 2004 to evaluate fish community response to flow and temperature regimes present in the Green River, Colorado and Utah, downstream of Flaming Gorge Dam. We used raft-based electrofishing, and seine, drift, and trammel net sampling to assess fish community composition in the Green River from upstream Browns Park downstream to Isl~d-Rainbow Park from 2002 to 2004 and compared those data to results ofa similar 1994 to 1996 study. Summer flows were low, and water temperatures (up to 250C) were likely as warm as those present in the pre- impoundment era. Ten native fishes were collected in the Green River. When all sampling gears were combined, native fishes comprised only 10.3% of total catch and non-natives were 89.3%; the remaining 0.4% were hybrids. Fish species richness was lowest in upstream reaches where cold- or cool-water tolerant species (salmonids, white sucker, fathead minnow) were more abundant; species richness was higher downstream where warm-water tolerant taxa (sand and red shiners, channel catfish, and smallmouth bass) were more abundant. Flannelmouth sucker, bluehead sucker, and common carp were ubiquitous. Abundance of nearly an native fishes in the study area, including large- bodied adults captured by electrofishing and small-bodied fish in seine samples, declined between the 1994 to 1996 and 2002 to 2004 periods. Trammel net sampling detected a small population of humpback chub in Whirlpool Canyon and a relatively large population of roundtail chub. Hatchery-stocked bonytail were also captured. Drift net sampling failed to detect reproduction by Colorado pikeminnow in Lodore Canyon. Abundance of non-native fishes in Browns Park and Lodore Canyon in 2002 to 2004 increased since 1994 to 1996 sampling, particularly in the upper portions of Lodore Canyon, where small-bodied cyprinids, channel catfish, and smallmouth bass increased greatly in abundance. Smallmouth bass reproduction, which was not observed in Lodore Canyon prior to this study, was widespread. Salmonids were temporarily reduced in 2002, but increased in 2003 and 2004, and remained similar in abundance to that observed in 1994 to 1996. Abundance of hybrid suckers and predaceous fishes in the Green River study area has increased. The net effect of flow and temperature regimes on the native fish community, based on 2002 to 2004 sampling, was mixed mostly because of large increases in non-native fish abundance. Reliable information on the response of the fish community to flow and temperature regimes was obtained but only at the lower end of the flow spectrum and the high end of the temperature spectrum. Additional years of sampling when moderate or higher flow conditions are available are needed to fully assess the effects of pending flow and temperature recommendations for Flaming Gorge Dam on the fish community of the Green River. 18