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<br />' Habitat availability and ice formation in backwaters are currently being studied in a separate BIO/WEST - <br />UDWR investigation entitled Effects of flow regulation and ice on ovenvinter nursery habitat of aye-0 <br />Colorado squawfish in the Green River below Flaming Gore Dam. The results of that study will hopefully <br />bring a greater understanding of the factors influencing age-0 Colorado squawfish survival during the winter. <br />4.2 SUMMARY <br />Survival of age-0 Colorado squawfish in the upper basin may be low. High mortality of age-0 squawfish may <br />account for low recruitment to the population and continued endangerment of this species. Overwinter <br />decreases of age-0 squawfish CPE, observed in this study, averaged approximately 60% for six year classes. <br />We feel a large portion of this decrease is due to mortality during the winter months. Downstream transport <br />and use of habitats other than backwaters were recognized as important considerations, but did not account <br />for substantial decreases. <br />Another factor to consider in decreased density of age-0 Colorado squawfish is the role of spring runoff in <br />transporting fish downstream. It is possible that a large number of fish are transported downstream, into <br />' Cataract Canyon and Lake Powell by high spring flows. The large number of fish predators in Lake Powell <br />would greatly reduce the survivability of young Colorado Squawfish. Spring runoff is typically in late April <br />and May, after spring sampling. Therefore runoff did not influence decreases observed in this study, but is <br />' probably another significant source of mortality for age-0 Colorado squawfish. <br /> <br /> <br /> <br /> <br /> <br />ii <br /> <br /> <br /> <br /> <br />21 <br /> <br />