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State line (hereafter referred to as 'State line') gage (Appendix Table I). As discussed below, recent studies have corroborated these earlier observations. High spring flows also appear to be the only means available to reduce the numbers of some prolific non-native fish species. Several species of introduced minnows predominate in backwater nursery habitats of Colorado squawfish. In addition, predatory centrarchids, though not abundant, are commonly found in backwater habitat in the Grand Valley area (Valdez et al. 1982, Valdez and Wick 1983, Osmundson and Kaeding 1989, Nesler 1990). Many researchers have speculated on the negative effects these introduced species may have on native fishes, particularly competition for food re- sources and predation (Holden 1973, McAda 1977, Seethaler 1978, Valdez et al. 1982, Wick et al. 1982, Valdez and Wick 1983, McAda and Tyus 1984, Osmundson 1987, Osmundson and Kaeding 1989, Tyus and Karp 1989, Valdez 1990, Karp and Tyus 1990). In laboratory studies, Karp and Tyus (1990) found that green sunfish (Lepomis cyanellus), red shiner (Notropis lutren- sis) and fathead minnow (Pimephales promelas) displayed far more interspe- cific aggressive behavior than young Colorado squawfish, and suggested that squawfish young would be competitively inferior in a resource-limited environment. Current studies conducted by the Colorado State Larval Fishes Laboratory (CSLFL) have revealed the high susceptibility of Colorado squawfish and razorback sucker larvae to predation by red shiner, young green sunfish, and young channel catfish (Ictaluras punctatus) under aquaria conditions (Robert Muth, personal communication); predation by other common, non-native species has yet to be tested by CSLFL. Osmundson (1987) documented predation by largemouth bass, green sunfish and black 11