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11/ 14/01 draft report, Schmi dt and Box than in the other years, because the number of larval fish drifting in the river in 1990 was approximately twice that of other years. Field data indicate that late summer larval populations in backwaters were greater in 1991, although juvenile fish sampling nest year, descri bed above, is consistent with model predictions and inconsistent with larval sampling data. If the model predictions and CPE data for 1990 are not considered, then R2 of the relationship improves to 0.29 (Fig. 11). Such differences suggest that (1) the model may poorly describe the process of larval drift and transport into backwaters, (2) biotic factors, such as predatory behavior by non-native species, may playa large role in controlling late summer backwater populations (Trammell and Christopherson 1999, Trammel and Chart 1999), or (3) the field data collection program may not adequately describe the longitudinal distribution and abundance of age-O fish in late summer. The last possibility is plausible because there is large error in CPE estimates. It is also possible that Colorado pikeminnow use backwaters that are never sampled. Although Colorado pikeminnow have been caught inbackwaters as small as 19 m2 and as shallow as 0.04 m (Day et al. 1999), the established sampling protocol calls for sampling backwaters with a minimum surface area of30 m2 and 3 minimum depth of 0.3 m (D. S. Fish and Wildlife Service 1987). We predict pikeminnow populations in all backwaters, and not simply the larger ones that are sampled. Aspects of the longitudinal distribution of larval fish were successfully predicted (Fig, 12). Model predictions and field measurements agree that total larval fish populations were very small in 1994and 1995. The field data and model predictions demonstrate that reach 265250 was an important area of larval fish concentration in 1991, 1992, 1993, and 1995. Field data and model predictions indicate that reaches with wide alluvial valleys and restricted meanders typically have dense concentrations of larval fish. Reach 265250 has been identified by Green River fishery scientists as the most important reach for nursery habitat for pikeminnow larvae, and this reach is the focus of many river management activities. Field data and model predictions demonstrate that the reaches with the largest populations of larval pikeminnow change from year to year, and that reach 265250 is not always the location where larval pikeminnow ar~_most abundant. Model predictions also indicate that there may be significant concentrations of larval pikeminnow upstream from the reaches where sampling presently takes place. Comparison of Predictions of Larval Fish Distribution in a Geomorphically Homogeneous and Heterogeneous River Various studies have shown that the middle Green River has narrowed since the late 1920' s in response to climate change and the construction of Raming GOTge Dam (Allred and Schmidt 1999; Grams and Schmidt in press). Van Steeter and Pitlick (1998) and Allred and Schmidt (1999): showed that channel narrowing involves channel simplification in restricted meandering reaches with mid-channel islands. Grams and Schmidt (in press) showed that narrowing of part of the 14