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1 ' Larval drift may be an important part of the Colorado squawfish life cycle (Tyus and Haines 1991) and laboratory studies indicate that "drift" may be active rather than a passive response to water current (Paulin et al. 1991). ' Larval squawfish drift downstream after hatching in the Green and Yampa Rivers and rear in reaches of the river that are different from those in which spawning occurred (Haynes et al. 1984; Tyus and Haines 1991). f th f e-year - or young-o The most important rearing area in the Colorado River Colorado squawfish is between Moab, Utah, and the confluence with the Green River (RK 0-96 [RM 0-60]) (Archer et al. 1985). Other nursery areas in the Colorado River have been found: (1) in the upper Professor Valley (RK 112-129 [RM 70-81]); (2) between the confluence with the Dolores River and Westwater ' Canyon (RK 144-175 [RM 90-109]); (3) between Black Rocks and Loma (RK 225-241 [RM 140-150]); and (4) downstream from the confluence with the Gunnison River (RK 257-273 [RM 160-170]). ' No larval Colorado squawfish ,have been found in the White River. Some adults that were tagged in the White River have been recaptured or radio-tracked to the Yampa and Gray Canyon spawning sites (Tyus 1990). Osmundson and Kaeding (1989) reported the capture of a single larval Colorado squawfish in the lower 3 km (1.9 miles) of the Gunnison River. In 1987, a total of 18 young-of-the-year Colorado squawfish were captured in the San Juan River at various locations. These fish were collected from backwaters of the river: 2 were taken from the area downstream of Shiprock, New Mexico, at RK 222 (RM 139) and RK 228 (RM 143); 6 near Bluff, Utah, at RK 150-161 (RM 94-101); and 10 were taken in the lowermost 38 river kilometers ' immediately upstream from Lake Powell. An additional young-of-the-year also was taken from this lowermost river area in 1988, collected from backwaters at RK 18 (RM 11) (Platania et al. 1991). In 1990, a young-of-the-year Colorado squawfish was collected from backwaters near Bluff, Utah (Bill Bates, Utah Division of Wildlife, pers. comm. 1990). 1 1 Colorado squawfish were first successfully propagated at Willow Beach National Fish Hatchery in 1974. Progeny since have been obtained by both artificial and natural spawning (Hamman 1981; Toney 1974). Wild Colorado squawfish obtained from the Green and Colorado Rivers in autumn 1979 spawned over filter gravel in raceways. Wild-caught and hatchery-produced broodstock at Dexter National Fish Hatchery, New Mexico, spawned in May and June after an injection of pituitary extract; production was primarily limited by the physical constraints of the facility for holding and growing young (Hamman 1986). Growth As with most fishes, Colorado squawfish growth rates are variable and dependent upon water temperature, food, water quality, age, and numerous other parameters. Tyus (1988) reported that the growth rate of 59 tagged and recaptured adult fish in the Green River averaged 10.2 mm/year (.4 in./year). Vanicek and Kramer (1969) back-calculated mean TL's at annulus formation for 182 Colorado squawfish from the upper Green River, Utah. The fish ranged in 11