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Larval_ and Young-of-the-Year Colorado squawfish Green River Collections of larval Colorado squawfish were made from the Yampa and Gray Canyon spawning areas in order to evaluate the spawning success. Weekly samples were taken from three reference stations in the lower Yampa Canyon by seining backwater habitats (Table S). A total of 104 - larval Colorado squawfish were collected from 17 samples, comprising 10% of all fish specimens taken from the Yampa River. These samples indicated that spawning occurred in the Yampa River by August 10~, c larvae were most abundant in the lower Yampa River between August 19-30. Fewer samples were taken in the Green River (only 7) and larval Colorado squawfish were not collected until September 15 (Table 6). Larval sampling was almost impossible in the lower Green River in August and the very high water levels in the mainstem Green River resulted in an almost complete lack of shallow backwaters immediately below the Gray Canyon spawning site. It is not known whether the larval Colorado squawfish collected were hatched in the Gray Canyon site or drifted from further upstream. A fall YOY survey was conducted in the Green River in 1982 using the same sampling design as in previous years. Results from the 1979-82 seasons (Figure 10) indicated that the Green River below Jensen is good nursery habitat for Age-0 Colorado squawfish, with two peaks of abundance occurring yearly, in the Ouray and Labyrinth Canyon areas (Figure b). YOY surveys and other sampling in 1.983 indicated poor survivorship of YOY Colorado squawfish (Figure 11) . The cause of this year class failure in the Green River is unknown; however, it is probably related to the increased discharge of co1.d water from Flaming Gorge Dam. Temperatu re records taken at the confluence of the Yampa and Green Rivers during the period of abundance for Colorado squawfish larvae, indicated about a 10°C difference in temperatu re between the Yampa River (21°C) and the Green River (]_2°C) in Echo Park. In addition, warm backwater nursery habitat was virtually nonexistant in the downstream Green River, due to the 1983 high flow. We will try to learn more about this apparent heavy mortality of young Colorado squawfish by conducting more intensive monitoring, by the retrieval and analysis of past data and by laboratory experimentation. Colorado River e The relative abundance of age-0 Colorado squawfish collected in the Colorado River during September and October 1983 su rveys (Figure 12; Table 7) was generally greater than in 1982. However, b-mm-mesh seines were used in 1982 whereas 3-mm-mesh seines-were used in 1.983 and the resulting data are therefore not entirely comparable between years. ` Age-0 Colorado squawfish were collected from the upstream river reach in 1983 where they were not found in 1982. This could be a result of using the finer mesh seines in 1983 which would capture a smaller sized age-0 squawfish. 21