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S ~, . was made using U$FWS data collected using the same equipment, personnel, and methods. As indicated by Tyus (1987), razorback sucker comprised 21X of the Colorado squawfish catch rate (0.20 razorback sucker per hour, 0.97 Colorado squawfish per hour). Assuming the population size for the razorback sucker (948 individuals) estimated by Lanigan and Tyus (1988) is correct, the Colorado squawfish abundance in this area would be 20X of 948 = 4,107 fish. (Because this figure includes both larger juvenile (300-400 mm TL) and adult 0400 mm TL) fish, the adult component would be about 79X of the total, based on the adult/juvenile ratio for the Green River provided by Tyus et al (1987), or 79X of 4,107 3,225 adults, or about 19 adults per km.) The catch rate in the upper Green River was extended to the entire Green River Mainstem (552 km), by substituting an average catch rate of 0.68 fish/h for the entire river, in place of the average catch rate of 0.97 fish/hr given above for the upper Green River (Tyus 1987), or, a catch rate of about 13 fish/km, or (13 fish/km)(552 km) 7,176 adult Colorado squawfish in the mainstream Green River. Method 2. If the average electrofishing catch rate far the Green River is 0.56 adult Colorado squawfish/hr (Tyus et al 1987), and assumed that one boat could shock one shoreline at the rate of 4 km/hr, this would average 0.56 adult fish/4 km 0.14 fish /km for one shoreline. The number of fish for both shorelines would be double that number, or (0.14)(2) = 0.28 fish per km. The number of Colorado squawfish in the mainstream Greece River would then be approximated by (0.28)(552 km) = 154.6 fish, if electrofishing efficiency = 100X. However, electrofishing efficiency is affected by many factors (Reynolds 1983), and has been documented from 4-54X (Jacobs and Swink 19 , 40