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EXECUTIVE SUMMARY The purpose of this study is to reestablish wild bonytail populations in the upper Colorado River basin (UCRB) and fulfill a long-term goal of the Bonytail Chub Recovery Plan; "reintroduce hatchery-reared bonytail chub into the wild" (USFWS 1990). This includes developing a propagation and rearing plan that will maximize survival in the wild, maximize genetic diversity, and promote good post-stocking survival. The specific objectives of this study: 1. Reintroduction ofbonytail into the Colorado River, in the Professor Valley and in the Green River, near the town of Green River, Utah. 2. Determine the appropriate number and size ofbonytail to stock to maximize survival. 3. Determine movement and the potential for habitat utilization overlap between bonytail and roundtail. Investigate whether Gila species utilize similar micro- and meso-habitats. 4. Determine if flow training results in enhanced survivorship of different size classes of bonytail. This objective has not been examined in a hatchery setting as of FY 2001. The broodstock being used to reintroduce populations in the UCRB is maintained at Dexter National Fish Hatchery and was established :from a relict population in Lake Mohave. Eggs were fertilized and hatched at Dexter, bonytail fry are then transferred to Wahweap State Fish Hatchery where they are reared to release size in ten ponds. Wahweap also oversees the marking of all bonytail before their release. From 1996 through 1998, all released bonytail were PIT tagged. During this period, all fish were weighed, measured, tagged and returned to the grow-out ponds one to two weeks prior to stocking. In 1999 through 2001, production was stepped up and less expensive coded wire tags (CWT) were implanted in all stocked fish. The drawback of the CWT is that individual coding contained on the tag can not be retrieved without killing the fish, and lethal sampling was not approved during the 1996-2001 monitoring period. For this study, stocking of hatchery-reared bonytail began in the fall of 1996 in the Colorado River and the fall of 1998 in the Green River and was completed in the fall of 200 1 in both rivers. During these time periods, 84,603 bonytail were released in the Colorado River, and 127,714 were released in the Green River. Fish stocked in the Colorado River ranged in size from 65 to 354 mm during the first three years. The majority of these fish (82%) were under 140 mm and only 1.6% were over 200 mm. Only three releases of cohorts averaging more than 150 mm TL occurred in the six years of stocking. Over the course of all sampling in the Colorado River a total of 663 hatchery-reared bonytail were recaptured, representing 0.8% of all fish released. Seventeen of the fish recaptured in the Vll