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itively identified have been collected from the Upper Colorado River Basin. <br />Smith (1959) reported two juvenile razorback suckers from Glen Canyon during a <br />preimpoundment study. Taba et al. (1965) collected eight juvenile razorback <br />suckers from a Colorado River backwater downstream from Moab, Utah. In 1991, two <br />juvenile razorback suckers were collected from the lower Green River (Gutermuth <br />et al. 1994). <br />Background <br />So few adult riverine fish remain in the wild that it is unlikely that a <br />population can be restored through natural reproduction. As a consequence, the <br />Biology Committee has placed a high priority on reestablishing razorback sucker <br />in the Upper Colorado and Gunnison rivers. Augmenting or restoring populations <br />by stocking endangered fishes has been identified as one of the five elements for <br />recovery of endangered fishes in the upper basin. A plan to evaluate stocking <br />to augment or restore razorback sucker in the Upper Colorado River (Burdick 1992) <br />was accepted by Recovery Program participants. That plan addressed the essential <br />elements for an experimental stocking program to obtain fundamental information <br />on the ecology of razorback sucker and to determine the feasibility of stocking <br />as a recovery tool. The plan discussed the rationale and justification for the <br />experimental stocking of adult fish, the genetic risks associated with <br />experimental stocking, justification for selection of stocking areas, and the <br />protocol and criteria to investigate the relation between size at stocking and <br />survival and time of stocking. The plan also outlined research efforts and <br />general procedures to monitor stocked fish and evaluate the stocking program. <br />Because too few ri veri ne razorback sucker exist in the Upper Colorado River <br />with which to conduct scientific studies or to sustain populations, stocking a <br />few adult hatchery- or pond-reared fish would provide information to understand <br />the ecology of wild razorback sucker in the river environment and evaluate the <br />utility of stocking on a larger scale. Research with hatchery- or pond-reared <br />fish may also provide a method to determine their habitat needs and biological <br />interactions and thus eventually provide a mechanism to enhance their recovery. <br />The factors affecting survival of razorback sucker in the riverine system must <br />be determined before large-scale augmentation or re-introduction stocking can be <br />expected to be successful. Experimental stocking of razorback sucker may discern <br />whether factors such as competition, predation, imprinting, homing, survival, <br />etc., are critical to their survival. More could be learned about distribution, <br />movement, reproduction, recruitment, and growth following experimental stocking. <br />This information would guide future stocking activities to augment existing <br />populations or to restore extirpated ones. <br />Purpose and Objectives <br />The purpose of this study was to evaluate the survival and performance of <br />pond-reared, radiotagged adult razorback sucker following stocking in the Upper <br />Colorado and Gunnison rivers. This study was intended to answer specific <br />research questions essential for recovery, and evaluate the utility of stocking <br />sub-adult and adult-size, hatchery-produced fish in achieving recovery goals. <br />Specific objectives were to: <br />2