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• 1 69 suggestions that multiple spawning may occur to a certain extent, on the same sites (Jones and Sumner 1954; Linda Ulmer, pres. comm.). The same spawning areas were used for 2 consecutive years at SWR. Relative fecundity, based on a small sample size, was estimated at 27,000-144,00 eggs per female with a poor correla- tion between the number of eggs and the units of female body length (McAda and Wydoski, 1980; Minckley, 1981 in press). There are suggestions that viability decreases in older females, but a good sequence of gonads from aged individuals or a reliable aging technique has not been available. Eggs are mildlyadhesive to the substrate (Moyle, 1976; Minckley, 1973) and range in size from 1.8 to 3.2 mm in diameter (Gustafson, 1975; Calif. Fish and Game, unpublished data). Time to hatching is variable, but appears to decrease as temperatures increase. Culture experiments at Willow Beach National Fish Hatchery indicated poor survival occurs when incubation temperatures are near 12°C (Toney, 1974). At Dexter National Fish Hatchery 14-16°C incubation temperatures resulted in 10-20% survival, but many other factors besides water temperature may explain the low survival (Inslee, 1981). We removed 100 eggs from spawning areas at Senator Wash Reservoir (SWR) and incu- bated them in aquaria at 20-23.50C and had 46% survival (Loudermilk et al., 1981, unUU- blished manuscript).. Experiments at Utah State University using sub-adult fish (1974 fereni d: C OIL-Lort frviaa i„ t' _ ch" H stock' 'w thL' n-ai -refci. °ia:.e -.ia, -ci di?ccu tee „rrE'- s i. 1i0?+ if'' a .,o?.++ j om. rcaTaa?l.S` indicated of 25.4°C were chosen (Bulkey, et al. 1981). Within four years after the closure of Flaming Gorge Dam, native fish of all ages, including razorbacks, were displaced for 7 miles downstream, their abundance was reduced for many miles further downstream, and cold hypolimnetic releases were suggested as the major cause (Vanicek, 1967; Vanicek et al. 1970; Holden, 1973). Very little is known about the larval stage of this species other than identi- fication characters of the post larvae (Winn and Miller, 1954). For 2-3 days after swim-up, post larvae in aquaria used the upper 1/3 of the water column and displayed little tendency to seek shelter. If in a mild current, they would have been carried downstream. After this period they began moving to the bottom and gradually began feeding on or near the substrate and began using the vegetation and rock provided as cover when disturbed. They rarely entered the upper half of the water column beyond 15 days after hatching (Loudermilk et al., 1981, unpublished manuscript). At larvae were collected from both the surface and by disturbing the substrate. Dead or mortibund larvae were observed in relatively high numbers (Linda Ulmer, pers. comm.) there. It has been suggested (Hubbs and Miller, 1953) that young razorbacks followed adults back out of streams to the main river. The young have been reported to travel in large schools along stream or reservoir margins. The terminal mouth migrates O the sub-terminal position within m_ the of hatching and the nuchal keel --=' rs when the young are n total length. Adults reach 5 to 6 kg in weight and feed on algae, dipteran larvae and zooplankton. They have long digestive tracts, poorly differentiated stomachs, no pyloric caecae and well-developed hearing. Based on very limited information, egg survival may be best between 16-250C and spawning occurs between 12-18°C. Tributary water temperatures in that range histor- ically would have occurred March - July, depending on the water year, but generally during the later part of the runoff period. Before dams, gravel bars or wash fans W' likely available for spawning and water temperatures were rising with ambient temper- ature increases as runoff subsided. In the river below Parker, Arizona most of the substrate was and is sand, mud or silt. The only likely spawning gravels, with a few exceptions, were alluvial fans created by flood events down tributary washes or up the Gila River drainage into southwest Arizona.