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]72 VALDEZ AND MUTH drift of young occurs in streams and may be fol- lowed by a second drift period in response to popu- lation density (Sigler and Miller 1963). Mottled sculpin and Paiute sculpin are bottom dwellers and feed mostly at night on snails, amphipods, oligocha- etes, insect larvae, and planktonic crustaceans, in- cidentally consuming detritus, and filamentous green algae (Sigler and Sigler 1996). Mountain Whitefish Mountain whitefish are typically 150-450 mm TL and 500-1,300 g (Sigler and Sigler 1996). Thespe- cies is trout-like in appearance, but has a much smaller head, larger adipose fin, large scales, and no teeth. The snout is pointed and extends past the mouth. Mountain whitefish is a game fish with bag and pos- session limits in most upper basin states. It is found in cold mountain streams and is common to abundant above 2, 1 00 m devation. Mountain whitefISh inhabits swift streams and cold, deep lakes. Newly hatched fry use shallow water along shorelines, at stream edges, or in protected backwaters, but they move into deeper water as they grow. Mountain whitefish prefers tem- peratures of 14-160C, but tolerates temperatures far above and below this range, which gives it greater survival abilities than trout or salmon. It is also able to thrive in water with lower DO than most trout spe- cies. Mountain whitefish usually mature in 3-4 years and live up to 17-18 years. Spawning occurs at night between October and December over gravd or rocks in streams or in shallow lake shores at water tempera- tures of 5-60C. Fecundity is about 1,500-7,000 eggs per female. Eggs are broadcast over cobble substrate and hatch in early spring after about 5 months of incubation. Mountain whitefish usually eat aquatic insect larvae, small molluscs, eggs, and sometimes fish. Colorado River Cutthroat Trout Colorado River cutthroat trout are currently a conservation species in Utah, Colorado, and Wyo- ming. A conservation agreement and strategy was developed to provide a collaborative strategy for conservation and to allow more flexibility in man- agement (CRCT Task Force 2001). The Colorado River cutthroat trout is classified as a sensitive spe- cies by Regions 2 and 4 of the U.S. Forest Service (USFS) and by the Bureau of Land Management (BLM). Colorado River cutthroat trout historically oc- cupied portions of the Colorado River system in Wyoming, Colorado, Utah, Arizona, and New Mexico (Behnke 1992), including portions oflarger streams, such as the Green, Yampa, White, Colo- rado, and San Juan rivers, but it was probably ab- sent from the lower reaches of many large rivers because of high summer temperatures (Simon 1935; Behnke 1979). Distribution and abundance of Colorado River cutthroat trout have declined, and the species is limited to small populations in less than 1 % of its historic range (Binns 1977; Behnke 1979; Martinez 1988; Young 1995). Like other inland forms, this subspecies evolved in the absence of other trouts. It is highly susceptible to hybridiza- tion with rainbow trout and competitive replace- ment by brown trout Salmo trutta and brook trout Salvelinus fimtinalis. Pure Colorado River cutthroat trout remain as small populations in Colorado, Utah, and Wyoming (Behnke 1992). Many adfluvial stocks have been lost (Young 1995), and some populations have been reestablished. The largest pure popula- tion of Colorado River cutthroat trout in Trapper's Lake, Colorado, was recently hybridized by rainbow trout (Behnke 2002). Fortunatdy, a 1931 shipment of pure Trapper's Lake fish was traced to Williamson Lakes, California, and 300 fish were procured for transport to Bench Lake, Colorado, for devdopment of pure populations (Martinez 1988; Pister 1990). Remaining populations of Colorado River cutthroat trout occur mostly in headwater streams and lakes. Most lotic populations are in isolated headwater streams with average daily flow less than 0.85 m3 / s, stream gradients that usually exceed 4%, and eleva- tions above 2,290 m (Young 1995). Colorado River cutthroat trout hybridizes with other subspecies of cutthroat trout or with rain- bow trout in many areas of its historic range, com- promising genetic integrity. The Colorado River cutthroat trout conservation team has developed a database that is updated annually to track genetic information for each population. Seven categories have been identified for determining the genetic status of each population and a determination of appropriate management actions. Populations with