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Final Report 4-2 September 2000 Important seasonal flow-habitat relationships elucidated from life-history requirements are presented last in each species account. The flow and temperature needs of the species and expected benefits of flow and temperature modifications are elaborated for three reaches of the Green River (Figure 2.1) in a summary table. 4.1 OVERVIEW 4.1.1 Native Fishes A total of 12 native fish species in four families has been reported from reaches of the main- stem Green River between Flaming Gorge Dam and the Colorado River confluence (Figure 2.1) and from lower portions of tributaries (Table 4.1). This assemblage of fishes can be partitioned into three categories by grouping species with similar environmental preferences or requirements. The three categories are: (1) warm-water species preferring or requiring large-river habitats, (2) species preferring cool- or cold-water streams or smaller river channels, and (3) species with more generalized habitat requirements. Species in the first category are the so-called "big-river" fishes endemic to the Colorado River basin and include humpback chub, bonytail, Colorado pikeminnow, flannelmouth sucker, and razorback sucker. The distribution and abundance of these fishes have been reduced considerably as a result of human alterations of native riverine habitats (e.g., the construction and operation of main-stream dams and the introduction of nonnative fish species) throughout significant portions of their respective ranges (Carlson and Muth 1989). The flannelmouth sucker is the only member of this group that is not federally listed as endangered and that is still common to abundant in many locations. In contrast, the once widespread and abundant bonytail now exists in the wild as a few scattered individuals and is considered functionally extinct. In the Green River system, the big-river fishes are generally restricted to warm-water reaches of the main-stem or middle-lower portions of larger tributaries. The second category includes mountain sucker, Colorado River cutthroat trout, mountain whitefish, and mottled sculpin. These fishes prefer cool or cold water and are distributed primarily in upper or headwater sections of streams and rivers. In the main-stem Green River near or upstream of the Yampa River confluence, mountain suckers and mountain whitefish are incidental to rare, mottled sculpins are rare to common, and cutthroat trout are common in the tail waters of Flaming Gorge Dam (where they are stocked). Species in the third category are among the most widely distributed and abundant fishes in the Green River system and include roundtail chub, speckled dace, and b1uehead sucker. Roundtail chubs occupy small to large river channels with warmer water. Although widespread in the Green River, roundtail chubs are rare in many main-stem Green River reaches (i.e., Reach 1, alluvial sections of Reach 2, and lower Reach 3). Habitats of speckled dace and b1uehead sucker range from cool, clear streams to warm, turbid rivers, and these fishes are generally common to abundant in the Green River from Browns Park downstream.