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in the Yampa and White Rivers of the Green Basin produced additional catches of 0.7 and 0.2 Colorado squawfish per hour. These collections support the premise that the Green River supports colorado squawfish populations of about one. order of magnitude greater than the Upger Colorado River. It is generally agreed that the Green River Basin supports viable populations of the Colorado squawfish and is the stronghold of the species (Archer et al 1986, Benhke and p r ~ c,. c~,.~--- Bensen 1983, Tyus et al 1986, USFWS 1988b).'^ ~2s--~~~5 i°` ~ ~~`' ~~~~-,mss g~ -~I~- M2- S''~1'~Z Y~~~ 2 ` \ G~ ~j ~ L ~t ~`- ~2 cr I ° ~ 5~0'' 6 d' ~ ~- The relative abundance of Colorado squawfish populations in the upper Colorado River Basin is evident from the preceding, but the size of these populations remains unknown. The rarity of the species and lack of knowledge about movements, recruitment, and mortality has precluded the use of standard population estimation techniques. However, many years of study in the mainstream Green River allows some meaningful interpretations regarding standing stocks of adults. Crude approximations were developed from: 1. A comparison between catch rates of razorback sucker and Colorado squawfish, and a razorback sucker population estimate, 2. Use of electrofishing catch rates converted to number of fish per mile, corrected for an assumed catch rate efficiency, 3. use of electrofishing catch rates corrected by using an estimated catch rate efficiency of razorback sucker, 4. An opinion survey of experienced fishery workers to determine the relative numbers of razorback suckers and Colorado squawfish observed per mile electroshocked, 5. A similiar survey using the number of Colorado squawfish estimated per km, based on electrofishing catches, 6. A crude capture/recapture estimate, disregarding 15