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D <br />delimits the lower and upper basins. To date, reintroduction of razorback <br />sucker has been limited almost exclusively to the lower basin in Arizona and <br />California. However, approximately 1,900 (40 to 271 mm total length) and <br />4,500 (mean of 104 mm) juvenile fish, progeny of wild razorback sucker, were <br />released in the upper Green River near Jensen, Utah in 1988 and 1990, <br />respectively (Steve Severson, pers. comm.). One razorback sucker stocked in <br />the fall of 1990 in the Green River was recovered the following spring in a <br />backwater near the release site (Bruce Haines, pers. comm.). Razorback sucker <br />have not been stocked in the upper Colorado River. <br />0 Justification For Stocking Razorback Sucker <br />Few riverine adult razorback sucker in the upper Colorado River <br />population are available to spawn. Further, although fish may attempt to <br />spawn, survival of resulting young has not been verified; at best recruitment <br />is very low. In the upper Colorado River, too few razorback sucker remain in <br />the river with which to conduct studies or to sustain stable populations. <br />Research with hatchery- and pond-reared fish would provide information useful <br />to understanding the ecology of wild razorback sucker in the river environment <br />and evaluating the utility of stocking on a larger scale. Initially, stocking <br />hatchery- and pond-reared fish in the wild for research purposes would answer <br />specific questions essential for recovery, but would not be intended to <br />augment existing wild populations or establish new ones. Research with <br />hatchery- and pond-reared fish may also provide a method to determine their <br />habitat needs and biological interactions and thus eventually provide a <br />mechanism to enhance their recovery. Field experiments using these fish could <br />provide information on the factors that impact wild razorback sucker <br />populations. Experimental stocking of razorback sucker may discern whether <br />11 <br />9