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River both years and indicates that spawning may be restricted to the lower 20 mi (32 km) as suggested by radiotelemetry and the collections of ripe fish in that area. Prewitt (Appendix A) carried out extensive surveys of this area for hydraulic simulation modeling. His work was demonstrated the unique nature of this reach. A general physical survey was made of the river section at RM 16.5 (km 26.4) on 5 July.by fisheries field crews. Sonar depth profiles are presented in Figure 15 which were taken at locations illustrated in Figure 14. Table 22 summarizes major physical paramet5rs. The noon temperature was 22°C and conductivity was 340 umhos/cm . The largest number of spawning squawfish was captured in a floating trammel net which was set at transect 3 and was hauled out at transect 1 (Figure 14). The depth profiles and velocity components are best represented by la, 2a,b, and 3a for this collection. The depth ranged from 3 to 7 ft (0.9 to 2.1 m) and the velocity ranged from 0 to 2.8 £t/s (0.0 to 0.8 m/s), averaging 1.2 ft/s. Primary substrate was cobble/ rubble with a mean diameter of about 7.5 cm. When these data are com- pared to observations for the northern squawfish (Beamesderfer and Bjornn, 1981) it is apparent that major differences in habitat selection were observed between the two species: the northern squawfish was found spawning at about 10°C in water depths of 4.8 ft and a velocity of 1.9 ft/s. Age, Growth And Mortality - Scales collected from Colorado squawfish captured in the Yampa River were analyzed by Musker (1981). Apparently, the lack of scales from smaller fish (less than 471 mm TL) did not allow for accurate detection of early annuli. Musker's calculations indicated the average length of Yampa fish was 194.9 mm at annulus I. However, CRFP collections in the Green River from 1979-1981, including many small fish (less than 150 mm), indicated Colorado squawfish did not attain this length until after annulus II was formed. Seethaler (1978) found the average length for Colorado squawfish at annulus III was 173 mm. Thus, the 194.9 mm TL average reported by Musker for annulus I was most likely for annulus III. If this is correct, then Yampa River Colorado squawfish averaged slightly smaller at each annulus than sizes reported by Seethaler (1978) and Vanicek and Kramer (1969). Mean fish length reported from annulus length by Musker indicated an average annual growth rate of 56.5 mm for Yampa River fish. Slowest growth increment (36 mm) was found between annulus VIII and IX. Humpback Chub And Bonytail Chub The bonytail chub (Gila elegans) was reported abundant in the Green River at Echo Park in 1964-66 Vanicek et al. 1970) but Holden and Stalnaker (1975) found the species to be rare. No bonytail chub were found during 1981 and the species appears to be absent from the study 66