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xi I I I I I I I I I I I I I I I I I I I 5. Preliminary analyses suggested availability of backwaters per se was not limiting the relative abundance of age-O Colorado squawfish in the upper Colorado River. However, further analyses of backwater use by Colorado squawfish are necessary. 6. Investigations of hatchery-reared Colorado squawfish in ponds along the Colorado River provided evidence that largemouth bass and green sunfish can be important predators on young Colorado squawfish. Whether predation by these species is an important cause of mortality in young wild squawfish in the river needs further investigation. 7. Humpback chub moved relatively little from the turbulent, deepwater habitat of the Black Rocks area, whereas roundtail chub movement was more widespread and in some instances) 30 mi. This observation suggested that the habitat requirements of adult humpback chub, including those necessary for spawning, are met within the Black Rocks river reach. Moreover, this observation suggests the humpback chub population might be limited by the scarcity of turbulent, deepwater habitats. 8. Spawning of humpback chub and roundtail chub were found to temporally overlap. Therefore, concerns that alteration of the river environment might cause interbreeding of these species because of disruption of temporal isolation mechanisms can be dismissed. 9. Some hatchery-reared Colorado squawfish released in the river have been recaptured. Although the rate of survival of these fish is unknown, data indicate finglerling-size hatchery-reared fish grow in the river and sometimes travel long distances from the stocking site. Moreover, adult hatchery-reared squawfish stocked near Potash, Utah, in 1980 have been recaptured in apparent aggregations with wild adult fish. These observations suggest hatchery-reared Colorado squawfish might be useful in augmenting the wild population. 10. Recent laboratory studies demonstrated how some water-development projects have negatively affected endangered Colorado River fishes in the upper basin, namely downstream from mainstream dams where seasonal-high water temperatures are sharply reduced and no longer adequate for reproduction. However, other river reaches are not so affected but the populations of their endangered fishes are nevertheless greatly reduced. This suggests that factors other than modification of temperature regimes are important to the decline of endangered fishes here. The effect of flow modification on endangered fishes is not well understood but assumed to affect the quality and quantity of important habitats (e.g. spawning areas, backwaters). Although habitats that are limiting have not been clearly identified, yet-to-be-determined quantities of each important habitat are necessary to maintain the populations. The quality of these habitats with respect to growth and survival of the endangered fishes should be a consideration with importance on par with the more-traditional quantity concerns.