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<br />33 <br /> <br />the Upper Colorado basin. He also examined collections of juvenile <br />chubs made by Vanicek (1967) and found only three possible juvenile <br />bony tails from 1964-66 collections. More recent studies have also <br />failed to find many bony tails (Seethaler, McAda and Wydoski 1976; <br />Holden 1977; Holden and Crist 1978). Therefore. it appears that bony- <br />tails started disappearing in the early 19601s. corresponding to the <br />closure of Flaming Gorge Dam. and indications are that loss of repro- <br />duction may have been a major reason. The apparent decline in bony tails <br />throughout the Green River system suggests that the effect of Flaming <br />Gorge Dam was more than just a lowering of river temperatures for about <br />one hundred miles below the dam, and that loss of flow may have been a <br />significant factor. Loss of natural flows from tributaries to the Green, <br />especially the Yampa River, may cause the other already rare fishes to <br />come closer to extinction. much as the bony tail already has come. <br /> <br />FACTORS AFFECTING COLORADO SQUAWFISH REPRODUCTIVE SUCCESS <br /> <br />The data presented in this report indicates that abnormal spring <br />flows are correlated with poor Colorado squawfish reproductive success in <br />about 150 miles of the Green River in 1977. the only year studied with <br />non-natural flows. Abnormally cold temperatures created by cold releases <br />from Flaming Gorge Dam caused poor squawfish success from 1967-1977 in <br />the Green River from Echo Park to Jensen. Squawfish reproductive success <br />in Dinosaur National Monument was low in 1965, even though it was very <br />much better than that seen after 1967 in the same area, or in 1977 from <br />Jensen to Gray Canyon. Abnormally cold spring temperatures appear to be <br />the most likely reason for the low success in 1965. <br /> <br />~ <br />