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1-1 1.0 EXECUTIVE SUMMARY The U.S. Fish and Wildlife Service plans to focus certain work elements of its Colorado River Fishes Monitoring Project in 1985 on a IS-mile reach of the Colorado River from Pal isade downstream to Grand Junction. The work elements include radiotelemetry to assess movement and locate possible spawning sites of Colorado squawfish; seine for newly-hatched larval squawfish and razorback sucker; and measure physical habitat of one or more suspected squawfish spawning sites. Colorado squawfish and razorback sucker have been found almost annually within the IS-mile reach since 1974. The fish continue to be found in the reach when sampled from May to October, and the presence of ripe fish suggests spawning attempts by both species. Only one humpback chub was found in the reach in 1977, and no bony tail chub have ever been reported therein. The reach may ha ve si gnificance to the Colorado squawfi sh and razorbac k sucker, but does not appear to affect the status of the humpback chub or bony tail chub. Spawning by any of the rare fishes has not been documented within this reach. Capture of larval squawfish during two sample periods in August 1982, indicates that the species spawned successfully somewhere in or near the reach during that year; newly-hatched squawfish often drift downstream and their capture location may not reflect the spawning site. No evidence of successful reproduction by razorback sucker has been found within the 15- mile reach. Major irrigation diversions between May and October of each year deplete flows in the subject rea,ch annually. During dry years, this diversion of water nearly dries the river immediately below the Grand Valley Canal, which is the upstream boundary of the subject reach. Most of the diverted water returns to the Colorado River well below the reach. Accretion and irrigation returns provide some flow in the river for the 15 miles until supplemental flow is provided by the Gunnison River. It appears that the significance of the IS-mile reach lies in the possible use of the area by spawning Colorado squawfish and razorback sucker. This cannot be fully assessed until spawning sites are documented within the reach, and reproductive success is verified with larval seining. The true signi ficance of the reach should be determined from its total contribution of young Colorado squawfish and razorback sucker to the population of the Colorado River. From these considerations, it appears that some effort by FWS to locate spawning sites and survey larval production within the IS-mile reach is warranted. Establ ishment of a new physical habitat cross-section in this reach could add to the database necessary to address habitat needs, but such a cross-section should not automatically result in a designation of "essential reach" or "sensitive area".