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INTRODUCTION The introduction of exotic species is routinely listed as a contribut- ing factor in the decline of the native Colorado squawfish. To date, re- search substantiating this claim has been scanty at best, and citations in the literature alluding to its importance continue to be based soley on con- jecture. The Utah Cooperative Fishery Research Unit, having a long history of Colorado River fishes investigations, was asked in 1983 by the Colorado River Fishery Project (CRFP) to conduct a study looking into the effects of predation on young squawfish by the non-native largemouth bass. River backwaters are thought to attract young squawfish because of their value as nursery habitat and thus are important in the early life history of the fish (Holden 1977, Taba et al. 1965, Holden and Stalnaker 1975, Kidd 1975). It is here that young squawfish would be likely-to come in contact with the introduced largemouth bass that are now found in the lentic backwaters (Miller et al. 1983, Valdez and Wick 1982). Because of the present rarity of Colorado squawfish, stomach sampling of backwater-dwelling largemouth bass was felt to be a hit-or-miss proposi- tion and results would tend to be nonconclusive. The release of thousands of hatchery-reared squawfish would overcome this problem, but difficulties in monitoring the survival of these still existed due to the "open" nature of river backwaters. Although not completely analogous to open backwater habitat, the use of a closed system was necessitated by the logistics of the study. Flooded gravel pits along the river have added to existing backwater habitat and are often used by squawfish. They provide either seasonal habitat when temporarily connected to the river, or year-round habitat if permanately connected through breached dikes. Ones that are seasonally isolated from the river would therefore meet the requirements of the study as a closed backwater system. The use of gravel pit ponds as study sites opened up other research possibilities. Recovery plans for the Colorado squawfish call for stock- ing hatchery-reared squawfish for.reintroduction into former range and to bolster existing stocks. Semi-controlled river-side ponds could conceiv- ably be used as low maintenance grow-out areas for hatchery-reared squaw- fish before their release into the river. Investigating the value of these ponds for that purpose proved to dovetail well with the bass predation study. OBJECTIVES The major goals of the study are to determine the impact that largemouth bass predation may have on the survival of young squawfish, to increase our understanding of the ecology of river backwaters, and to investigate means of increasing survival of released hatchery-reared squawfish. Six specific objectives are: 1) Estimate overall mortality and mortality attributable to preda- tion of first-year squawfish stocked in several different types of ponds. 1