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Conclusions The major trend identifiers with YOY Colorado squawfish monitoring has been the continued low reproductive success (including production and survival of age-0 fish through their first growing season) in the Colorado River and higher, but variable reproductive success in the Green River. Basic data on distribution, growth and relative abundance of YOY Colorado squawfish collected with ISMP were consistent with that reported by previous investigators: (1) YOY Colorado squawfish were more abundant in the Green River than they. were in the Colorado River; (2) they were usually more abundant in the lower Green than in the upper Green, but they were always more abundant in the lower Colorado than in the upper Colorado River; (3) YOY Colorado squawfish averaged between 35 and 45 mm long at the end of their first growing season, their size was related to water temperature, and fish from the upper Colorado River were typically smaller than fish from the other three reaches. Observations on habitat use of YOY Colorado squawfish was inconclusive, but suggested avoidance of small and shallow or cool backwaters. Introduced species composed 75 to 9990 of all fishes collected during ISMP (usually > 959'0) and three of those introduced species-fathead minnow, red shiner, and sand shiner-collectively composed about 999 of that total. These three species have increased in the Colorado River since ISMP began, but their abundance in the Green River has been variable. Other introduced fishes that were collected included white sucker, common carp, mosquitofish, plains killifish, black bullhead, channel catfish, bluegils, green sunfish, and largemouth bass. Colorado squawfish were usually the most common native fish collected. Other native species included bluehead sucker, flannelmouth sucker, Gila spp., and speckled dace; most of these specimens were YOY or juveniles of these species. The basic sampling design and sampling reaches for YOY Colorado squawfish monitoring should remain unchanged, but several options to improve the program should be explored further. These options include: (1) further restricting the physical characteristics of backwaters sampled based on conclusions of the Nursery Habitat study, (2) increasing the number of seine hauls taken in large backwaters, (3) incorporating aspects of mark-recapture population estimates into the program, and (4) expanding the investigation to collect more data on species not specifically targeted by ISMP. 25