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most YOY Colorado squawfish in the upper Green River are believed to originate) during those same years. Jones and Tyus (1985) concluded that the discrepancy between the larvae produced and those retained in the Green River was related to the high runoff events of that year, and especially, to high releases from Flaming Gorge Reservoir throughout the summer. Those high flows inundated most backwaters along the Green River and Colorado squawfish larvae could not find suitable habitat. A similar discrepancy between numbers of larval Colorado squawfish leaving the Yampa River and their relative abundance as YOY in the upper Green River occurred during this study. During a 3-year period when larval Colorado squawfish were collected using drift nets as they left the Yampa River, they were most abundant in 1990, less so in 1992, and least abundant in 1991 (K. Bestgen, Larval Fish Laboratory, personal communication). In contrast, relative abundance of YOY Colorado squawfish in the upper Green during those years was greatest in 1991 and about equal in 1990 and 1992. The factors that may be responsible for the discrepancy between relative numbers of larvae produced and relative numbers of YOY that survive their first growing season need to be further addressed. An event that confounds understanding the relation between relative abundance of YOY Colorado squawfish and various physical factors that may affect them is an oil spill that occurred on the upper Yampa River in 1989 during the estimated spawning period. Gmean CPE in the upper Green River was the lowest in 1989 of any years sampled during ISMP. Researchers have speculated that the oil may have hurt reproductive success by either affecting the olfactory senses of the migrating adults or by destroying the eggs after they were laid or larvae after they hatched. Unfortunately, no sampling for adults was done near the spawning area in 1989 so it is not known whether fewer fish spawned than in other years. No larval Colorado squawfish were collected in drift samples that year (CDOW, unpublished data); however, drift sampling was conducted for a relatively short period compared to other years. Runoff in 1989 was the lowest of any observed during ISMP, which also may have been a factor. McAda and Kaeding (1989a) reported some of the early monitoring data collected from the Colorado River (1986-1988) as well as similar data collected from 1982 through 1985. They reported low CPE in Reach 1 during 1982-1984 and high CPE in 1985-higher than observed during any year of ISMP, but just greater than observed in 1986. In Reach 2, they observed low catch rates in 1982 and 1985. Mean CPE in 1983 and 1984 in Reach 2 was comparable to the first year of ISMP. Clearly, the trend in reproductive success and survival of young Colorado squawfish in the Colorado River is downward. YOY Colorado squawfish abundance is down in both reaches when compared with early monitoring program data, as well as data collected before 1986 (Archer et al. 1982; McAda and Kaeding 1989a). McAda and Kaeding (1989a) reported a significant positive correlation between gmean CPE of YOY Colorado squawfish in the lower Colorado River and flow events the previous spring. The ISMP data reported here follow that trend, although the correlation is not as high when the analysis is done for ISMP data alone. Mean CPE was positively correlated with a number of parameters representing flow events throughout the year including spring runoff. When ISMP data collected since 1988 are added to the analysis done by McAda and Kaeding (1989a), the correlation values improve slightly, primarily because of increased sample size. They hypothesized that reproductive success is improved for Colorado squawfish when spring runoff is moderately high. All of the data reviewed here have come from years of low to moderately low snow pack and reproductive success has remained low. A test of the hypothesis will come during years when spring runoff is increased. Mean CPE in the upper river has been so low in recent years that assessment of any relations with 20