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1 <br /> <br /> <br /> <br /> <br />1 <br />t <br />t <br />t <br /> <br /> <br /> <br />t <br />1 <br /> <br /> <br />1 <br /> <br />INTRODUCTION <br />Artificial propagation of fish is a potentially important component of <br />recovery programs for the endangered fishes of the upper Colorado River <br />basin (USFWS 1987). The decline of Colorado squawfish (Ptychocheilus <br />lucius) and razorback sucker (X)rrauchen texanus) in their remaining upper <br />basin habitats may largely be the result of increased rates of mortality <br />acting on the early life stages (Minckley 1983, Kaeding and Osmundson <br />1988, Lannigan and Tyus 1989, Marsh and Minckley 1989). If low survival <br />of young is an important factor limiting these species and such early-life <br />mortality cannot be reduced, stocking may be necessary to augment wild <br />subpopulations. Experimental stocking may also be an important means by <br />which we can learn about distribution, population size, survival rates and <br />growth of fish in wild populations. During 1982-84, for example, hatch- <br />ery-reared Colorado squawfish (35-95 mm long) were experimentally stocked <br />into the upper Colorado and lower Gunnison rivers near Grand Junction, <br />Colorado; growth rates of young squawfish in the natural environment were <br />revealed by the subsequent recapture of known-age stocked fish. In addi- <br />tion, the observation that hatchery-reared fish made up a seemingly large <br />proportion of all 100-200-mm-long Colorado squawfish captured in subse- <br />quent years suggested the natural production or early-life survival of <br />wild squawfish is limited in the Colorado River (USFWS, unpublished data). <br />Concurrent with those preliminary efforts in the upper basin, hatchery- <br />reared Colorado squawfish and razorback sucker were experimentally stocked <br />into unoccupied reaches of former habitat in the lower Colorado River <br />basin. Marsh and Brooks (1989) found that juvenile razorback sucker (45- <br />