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Mr. Calvin Joyner 7 t:) apparently never found in colder headwater areas, Seethaler (1978) indicated C) that the species was abundant in suitable habitats throughout the entire ~ Colorado River Basin prior to the 1850's, Platania and Young (1989) ,\') summarized historic fish collections in the San Juan River drainage which ~ indicate that Colorado squawfish once inhabited reaches above what is now the r~ Navajo Dam and Reservoir near Rosa, New Mexico. Since closure of the dam in 1962 and the accompanying fish eradication program, physical changes (flow and temperature) associated with operation of the Navajo Project have eliminated Colorado squawfish in the upper San Juan River, both from the reservoir basin as well as from several miles of river downstream of the dam. The San Juan River currently flows approximately 222 river miles from the Navajo Dam downstream to lake Powell. The reach of currently known occupied Colorado squawfish habitat extends from lake Powell upstream to river mile 144.9 and could be significantly impacted due to upstream water withdrawals. Of the 222 miles, about 159 of those are potentially available to the Colorado squawfish. Two concrete diversion structures near Fruitland, New Mexico (the Hogback at river mile 158.6 and the weir at river mile 166.2), span the entire river channel and are believed to be effective blocks to upstream fish migrations (Platania 1990). Critical Habitat Critical habitat has been designated within the 100-year floodplain of the Colorado squawfish's historical range in the following section of the San Juan River Basin (59 F.R. 13374). New Mexico. San Juan County: and Utah. San Juan County. The San Juan River from the State Route 371 Bridge in T. 29 N., R. 13 W., section 17 to Neskahai Canyon up to the full pool elevation in the San Juan arm of lake Powell in T. 415., R. 11 E., section 26. BioloQY Colorado squawfish were captured between 1987 and 1989 within the San J~an River in all seasons during which ichthyofaunal surveys were performed (spring, summer, and fall) and are presumed to remain there during winter (Platania 1990), Information on radiotagged Colorado squawfish during the fall suggests that fish seek out deepwater areas in the Colorado River (Miller et aI, 1982). Within the Upper Basin, winter habitat for adult Colorado squawfish is generally characterized as areas of slow water velocity that are relatively deep. Pools, backwaters, runs, shorelines, and eddies are all commonly used habitats during winter (Osmundson and Kaeding 1989; Tyus and Karp 1989; Valdez and Masslich 1989). Wick and Hawkins (1989) reported that during low flow years on the Yampa River, pools and runs were used most frequently, suggesting that habitat availability influenced habitat selection by adult Colorado squawfish. The fish are largely sedentary during winter and exhibit only localized movement suggesting feeding activity. The life-history phases that appear to be most critical for the Colorado squawfish include spawning, egg fertilization, and development of larvae through the first year of life. These phases of Colorado squawfish