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---) .~) f... C) c.:J co Colonel John N Reese DRAFT 5 As the southernmost tributary of the Upper Colorado River Basin (Upper Basin), the San Juan River peaks earlier in the year and attains warmer water temperatures than other Upper Basin streams and is conducive to longer and better growth. potential for young Colorado sQuawfish and razorback suckers. Any additional lar<Je loss of water or further degradation of remaining habitats of the San Juan River will exacerbate problems the Colorado sQuawfish and razorback sucker are currently experiencing in the San Juan and other subbasins throughout the Upper Basin. Colorado Souawfish Hi storical and Current Oi stribution The Colorado sQuawfish evolved as the main predator in the Colorado River and San Juan River systems. The diet of Colorado sQuawfish longer than 3 or 4 inches consists almost entirely of other fishes (Vanicek and Kramer 1969). The Colorado sQuawfish is the largest cyprinid fish (minnow family) native to North America and, during predevelopment times, may have grown as large as 6 feet in length and weighed nearly 100 pounds (Behnke and Benson 1983). These large fish may have been 25-50 years of age. The Colorado sQuawfish currently occupies about 1,030 river miles in the Colorado River system (25 percent of its original range) and is presently found only in the San Juan and other subbasins above Glen Canyon Dam (Tyus 1990). ., Based on early fish collection records, archaeological finds, and other observations, the Colorado squawfish was once found throughout warmwater reaches of the entire Colorado River Basin, including reaches of the upper San Juan River and possibly its major tributaries. Colorado sQuawfish were apparently never found in colder headwater areas. Seethaler (1978) indicated 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 Navajo Dam and Reservoir near Rosa, New Mexico. Since closure of the dam ~n 1962 and the accompanying fish eradication program, physical changes (flow and temperature) associated with operation of the Navajo Project has eliminated Colorado sQuawfishin 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). Extreme fluctuations occurring within the framework of a natural annual hydr09raph may enhance spawning success of native species and inhibit exotic species. Haynes et. al. (1984) reported that fish species, such as Colorado .'.!