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I I I I I I I I I I I I I I I I I I I available to compare with the post-1960 information. Available data suggest the major factors for decl ine in the Colorado River are loss, or changes, in habitat availabil ity for young fish and the increased pre- sence of non-native fish predators (Holden 1979). Backwaters, preferred young squawfi sh habitat, are very rare except below Moab, Utah on the Colorado River, and spawning habitat may also be limiting. Non-native fishes have become abundant in flooded gravel pits near Grand Junction, which provide constant pond type habitat not found in the natural river systems. These ponds are more constant now that flows have become less variable and high flows have become reduced and; therefore, they are more suitable for the non-native species. This increase in non-native fish at the same time that preferred squawfish habitat decl ined is pro- bably the major mechanism affecting squawfish in the Colorado River today. Other authors have suggested that competition or predation by introduced fish was the major factor in the decl ine of squawfish (Behnke and Nugent 1983), but it appears that these interactions with introduced species are primarily important in marginal habitat caused by depleted flows (Holden 1979; Holden and Wick 1982). Holden (1980) compared yearly flow hydrographs for the Green and Yampa rivers with success of Colorado squawfish reproduction measured by the number of young of the year (yoy) found. He showed that during a very low flow year (1977) reproductive success was extremely poor. Haynes (1984) has sampled larval squawfish spawning sites for several years. In 1983, a very high flow year, his catch of larval squawfish in the Yampa River increased nearly thirty-fold over 1982. Similar collec- tions in the Colorado River near Grand Junction were al so made but no dramatic increase in larvae were seen. The U.S. Fish and Wildlife - 24 -