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EXECUTIVE SUMMARY The Interagency Standazdized Monitoring Program (ISMP) was developed to monitor population trends of two endangered fishes from the Colorado River Basin-Colorado squawfish' and humpback chub. The program tazgeted Young-of-Yeaz (YOY) Colorado squawfish in the Green and Colorado rivers, subadult and adult Colorado squawfish in the Green, Colorado, White, and Yampa rivers, and adult humpback chub in Black Rocks and Westwater Canyon on the Colorado River. ISMP tazgeted areas where these species were most common and specified sampling procedures that could be used to monitor trends in the status of these fishes. This document describes the data collected from ISMP's inception in 1986 through 1992. YOY Colorado squawfish The major trend identified 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 was 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, and they were always more abundant in the lower Colorado than in the upper Colorado; and (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 preferences of YOY Colorado squawfish were inconclusive, but suggested avoidance of small and shallow or cool backwaters. Introduced species composed 75 to 99% of all fishes collected during ISMP (usually > 95%) and three of those introduced species-fathead minnow, red shiner, and sand shiner-collectively composed about 99 % 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, bluegill, green sunfish, and largemouth bass. Colorado squawfish was usually the most common native species collected. Other native fishes included bluehead sucker, flannelmouth sucker, Gila spp., and speckled dace; most of these specimens were YOY or juveniles. The basic sampling design and sampling reaches for YOY Colorado squawfish monitoring are appropriate, but several options to improve the program should be explored further. These options include: (1) further restricting the physical chazacteristics of backwaters sampled based on conclusions of the nursery habitat study currently being conducted by UDWR, (2) incorporating aspects of mazk- recapture population estimates into the program, and (3) expanding the investigation to collect more data on species not specifically targeted by ISMP. 'Scientific names of all fishes mentioned in this report are given in Table A-1 (Table or Figure numbers beginning with A through D appear in the Appendix of the same letter). vii