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I. Stocked fish may disperse initially in search of adequate food resources and suitable habitat. Generally, stocked Colorado River fishes have moved downstream. When they reach sexual maturity, they may move long distances seeking olfactory cues to spawning sites. Therefore, the greatest risk would be for the fish to migrate into the Green River sub- basin via its confluence with the Colorado River where they could spawn with the middle Green River stock and modify the genetic integrity of that population. However, genetic studies have shown that Colorado River razorbacks are essentially a subset of the Green River population and the very limited gene exchange that might occur should have no negative effect on that population. 2. Although it has been documented that razorback sucker have fidelity to certain spawning sites, it is unknown whether the fish was imprinted to the site as an egg or larvae, or if it is a learned behavior. If imprinting to a natal spawning site occurs, it is possible that the stocked razorbacks may not be able to find a suitable spawning site as adults. However, it is likely that even though the stocked fish are not imprinted to a specific spawning site, they will be attracted to sites with certain physical characteristics or odors from other razorbacks when the desire to spawn occurs. Some fish used in future stockings may be imprinted to artificial chemicals (morpholine and phenthyl alcohol) if ongoing chemoreception studies proceed as planned. The proposed studies include field evaluations using razorback suckers stocked into the Gunnison River - morpholine will be added to the Gunnison River and phenthyl alcohol (PEA) to the Uncompahgre River when the fish reach a mature size to determine if imprinting does occur. If imprinting is shown to be an important factor in successful reproduction, it will become a component of future propagation efforts. i D. Methods and Approach for Field Study 1. Time Frame This stocking plan addresses propagation activities for razorback sucker for a five-year period from FY 1996 through FY 2000. The stocking plan will be evaluated and updated at that time. An initial stocking, based on the protocol presented here, has already occurred. Three hundred sixteen PIT-tagged razorback suckers from five family lots were stocked into the Gunnison River in early October. Monitoring for these fish is ongoing. 2. Assumptions used to develop the stocking plan a. Razorback sucker that are a minimum of 4-inches should be able to escape most predation by nonnative fishes and are large enough to feed on organisms larger than zooplankton that would decrease the potential for competition with nonnative fishes.. Four inches is also the smallest fish that can be safely PIT tagged. 5