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Colorado Squawtish--This species is the only living representative of the genus Ptychocheilus in the Basin, where it is endemic. Its origins there predate recorded history, but by the mid-Pliocene epoch (about 6 million years ago) fossils indicate that early Ptychocheilus had riverine adaptations that were similar to modem forms. Native populations of the Colorado squawfish are restricted to the Upper basin in Wyoming, Colorado, Utah, and New Mexico. Colorado squawfish populations have been extirpated from the Lower Basin. During winter, adult Colorado squawfish use backwaters, runs, pools, and eddies, but are most common in shallow, ice-covered shoreline areas (Osmundson and Kaeding 1989; Wick and Hawkins 1989); In spring and early summer, adult squawfish utilized shorelines and lowlands inundated during typical spring flooding. This natural lowland inundation is viewed as important for their general health and reproductive conditioning (Osmundson and Kaeding 1989; Tyus 1990). Use of these habitats mitigate some of the effects of winter stress and aid in providing energy reserves required for migration and spawning. Migration is an important component in the reproductive cycle of Colorado squawfish. Tyus (1990) hypothesized that migration cues, such as high spring flows, increasing river temperatures, and possible chemical inputs from flooded lands and springs, are important to successful reproduction. Colorado squawfish spawning has been documented in canyons in the Yampa and Green Rivers. This reproduction is associated with declining flows in June, July, or August, and average water temperatures ranging from 72 to 770F depending on annual hydrology. After spawning, adult Colorado squawfish utilize a variety of riverine habitats, including eddies, backwaters, shorelines: and others (Tyus 1990). River mile 130 on the Colorado River, near the Colorado-Utah state line, also has been identified as a spawning site and radio tagged adults have moved to a specific 0.1 mile area in four different years (Osmundson and Kaeding 1989; USFWS unpublished data 1992-1993). In the mainstream Colorado River, McAda and Kaeding (1991) determined that spawning occurs at many locales. They also suggested that Colorado squawfish spawning may have been adversely impacted by construction of mainstream dams and a 48 percent reduction in peak discharge. On the San Juan River a spawning reach has been identified between river mile 133.4 and 129.8, near the confluence of the Mancos River (Ryden and Pfeifer 1993). In the Green River Basin, larval Colorado squawfish emerge from spawning substrates and enter the stream drift as young fry (Haynes et al. 1989). The larval fish are actively or passively transported downstream for about 6 days, traveling an average distance of 100 miles to reach nursery areas (Tyus and Haines 1991). These areas are nutrient rich habitats that consist of ephemeral alongshore embayments that develop as spring flows decline. These nursery habitats are associated with lower gradient reaches. Humpback Chub--Humpback chub remains in archaeological sites have been dated to about 4000 B,C., but the fish was not described as a species until recent times (Miller 1946). This disparity has been attributed to its restricted distribution in remote, white water canyons (USFWS 1990b). The abundance and distribution of the species until recently was not well 15