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.. ~~ Other than isolated reports of captured fish, however, the distribution and abundance of the Colorado squawfish was poorly understood until systematic surveys of the mainstream rivers of the upper Colorado River were made in the late 1960's and early 1970's (Holden and Stalnaker 1975ab). More quantitative studies in areas of highest apparent densities on the upper Colorado River Basin (reviewed by USFWS 1988, Miller et al 1982, this paper), have further contributed to our knowledge of the distribution and abundance of this species. The upper Colorado River Basin (Figure '~'1 was divided into three hydrologic sub units, the Green (largest), Upper Main Stem Colorado, and San Juan- Colorado sub-basins, by Iornes (1965). Colorado squawfish are found in small numbers throughout the mainstream rivers of the upper Colorado River Basin (reviewed by USFWS 1988), but presumably only the larger populations approach viable, self sustaining status. I consider only the Green River Basin, and Colorado possibly the Main-stem Colorado River populations, in this category. .~ sub- squawfish are still collected in small numbers in the San Juan basin, but the status of these populations are unknown, and ostensibly remnant. lthough the exact size of the Green River populations are unknown, they are presently larger than others, based on catch data and size of occupied range. Table I summarizes collections of the Colorado River Fisheries Pro3ect for the years 1979-1981. Using standardized methodology (Archer et al 1979), this pro3ect sampled the highest density of occupied range of the Colorado 12