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I I I I I I I I I I I I I I I I I I I The major reason for the dec1 ine of Colorado squawfish in the past is the loss of habitat due to construction and operation of dams prior to 1965. Colorado squawfish do not survive in reservoirs, and also avoid cold, clear tai1waters (Holden and Wick 1982). These factors e1 i- minated squawfish from the lower Colorado Basin totally. In the upper basin, Colorado River Storage Project dams e1 iminated habitat in the main Colorado River in Glen Canyon and in the upper Green River due to F1 aming Gorge Dam. Habitat was a1 so lost on the San Juan River due to Navajo Dam, and perhaps on the Gunnison River due to the Aspina1 Unit dams. Reasons for decline of squawfish in free flowing portions that were not affected by temperature or direct habitat alteration, such as the Colorado River above Glen Canyon (Lake Powell), are less clear. In the Colorado River squawfish were apparently more corrrnon prior to the early 1960's than at present (Holden 1979; Kidd 1977), which was before the major dams were completed on the Gunnison River. Holden (1979) suggested that altered flows from these dams were the major factor affecting squawfi sh by causi ng poorer reproducti ve success, and simil ar concl usions have been drawn for the Green River below F1 aming Gorge Dam (Holden 1980). The actual mechanism involved with altered flows in lowering repro- ductive success is not known. A number of potential factors have been suggested including competition or predation with non-native fishes, disease and parasites, loss of spawning habitat, loss of young rearing habitat and changes in water quality (Seetha1er 1978). It is highly possibl e that all or several of these mechanisms have reduced Colorado squawfish reproductive success since flows are variable and; therefore, different factors may operate different years. Little pre-1960 data are - 23 -