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19 bonytail chub in the lower Yampa River in 1979, and Service biologists captured one suspected juvenile in 1987. Preliminary results of a radio- tracking study of adult bonytail chub introduced into the upper Green River in 1988 and 1989 indicate that the fish exhibit crepuscular movements and are somewhat quiescent during the day and night (S. Cranney, Utah Division of Wildlife Resources, pers. comm.). Soawnina Bonytail chub spawning locations are unknown. Yanicek and Kramer (1969) believed spawning occurred in the Green River between mid-June and early July when water temperatures were near 18 °C. Similar to humpback chub, the optimum temperature for hatching success was reported at 20-21 °C (Hamman 1982c and 1985) Hatching success decreased considerably when temperatures varied ±10°C. When temperatures are near optimum (20-21 °C) hatching occurs in 4-7 days (Hamman 1982c). Larval and Juvenile Little data exist on larval and juvenile bonytail chub in the wild because of their extreme rarity. Vanicek and Kramer (1969) reported mean total lengths of 55, 100, and 158 mm for age-1 through age-3 bonytail chub from the Green River. Still, like most larval fish, it is presumed that their survival and growth are dependent on-low velocity habitats. Bonytail chub drastically declined in the Echo Park area, presumably due to flow and temperature changes resulting from closure of Flaming Gorge Dam. A similar pattern was noted in the Colorado River downstream from Glen Canyon Dam (Utah State Department of Fish and Game 1964 and 1969). Although the preimpoundment poisoning of riverine habitat in the upper Green River in 1962 contributed to the decline of the bonytail chub in that system, fish collections in Dinosaur before and after the poisoning (Binns et al. 1963; Vanicek and Kramer 1969; Vanicek et al. 1970) suggested that the downstream extent of the poison was not the only factor in the dramatic decline of the species from the Echo Park area. Decreased temperatures and changing flow patterns caused by the construction and operation of Flaming Gorge Dam permanently altered the physical environment, and bonytail chub habitats may have been lost. Thus, Flaming Gorge Dam operations also could affect the future of bonytail chub reintroductions and recovery efforts in the Green River system. RAZORBACK SUCKER General Status Historically, razorback suckers were abundant throughout the Colorado River Basin, primarily in the main stem and the major tributaries from Wyoming to Mexico. At present, the largest concentrations occur in the Green River in the upper basin and Lake Mohave in the lower basin. Fish in reproductive condition also were captured in the Yampa, Colorado, and San Juan Rivers, which suggests the importance of these river systems. Although reproduction in the wild was documented, larvae were seldom captured and may not survive