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<br />the native fishes indicates that habitat conditions are suitable for certain <br />life stages of Colorado squawfish, humpback chub, and razorback sucker, <br />despite the proliferation of many non-native species. Population augmentation <br />and study of razorback sucker and bony tail chub in the upper Green River <br />should aid in their recovery. <br /> <br />Flow needs of the rare fishes in the mainstream Green River are <br />influenced by many factors including time of year, life history stage, and <br />associated species. As indicated in Figure 9, reproductive activities of the <br />Colorado squawfish, razorback sucker, and humpback chub are associated with <br />spring and early summer hydrologic events. Additional alteration of these <br />hydrologic events may affect migration of Colorado squawfish and razorback <br />sucker, and spawning of Colorado squawfish, razorback sucker, humpback chub <br />and other native fishes. <br /> <br />Gradually declining summer flows and maintenance of low, stable flows in <br />late summer and autumn are presumably necessary for growth and survival of <br />young Colorado squawfish and young of the other rare native fishes. Abrupt <br />fluctuations in surface water elevation in late summer to spring could strand <br />Colorado squawfish (young and adults) and presumably other backwater <br />inhabitants. Unnatural, high Flaming Gorge releases during the summer and <br />early autumn are correlated with recruitment failure of Colorado squawfish. <br />Stable winter flows through ice breakup provide suitable shoreline habitats <br />and reduce shoreline scouring during some years, especially in the upper Green <br />River near Jensen, Utah. Such flows may be important to overwinter survival of <br />young and adults of native species in some locations. Very high winter flows <br />flood off-channel, shoreline habitats and may provide an undesirable winter <br />refugium for some introduced fishes including channel catfish. Alteration of <br />historic flow regimens may have directly impacted razorback sucker recruitment <br />in the Green River basin, and its survival is imperiled. Humpback chub is rare <br />in Whirlpool Canyon of the upper Green River, and its status and habitat needs <br />in Desolation and Gray Canyons are not well understood. <br /> <br />Changes in Green River flows due to the operation of Flaming Gorge Dam <br />have resulted in alteration of river morphology. A reduction in the magnitude <br />and duration of flooding, and sediment removal by the dam, are presumably <br />responsible for stream channel changes that may continue for some time in the <br />future (Andrews 1986). Although future changes in instream habitats of the <br />Green River are difficult to predict, there is an indication that the <br />continuing invasion of riparian and upland vegetation into riverine flood <br />zones can stabilize banks and also produce a narrowed, deeper channel (Graf <br />1978; Fisher et al. 1983). In addition, dense growths of saltcedar become <br />established when dependable moisture is provided to river banks via daily <br />flooding as occurs in regulated systems (Turner and Karpiscak 1980). All of <br />the above changes may impact the endangered fishes by reducing or eliminating <br />ephemeral backwater and eddy habitats. <br /> <br />Studies of factors limiting the distribution and abundance of rare fishes <br />in the Green River are complicated by the variability of the environment <br />(e.g., seasonal fluctuations in discharge, temperature, food base, and species <br />abundance) and logistical problems associated with studying fishes in large, <br />turbid rivers. The determination of limiting factors for rare fishes is <br /> <br />27 <br />