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Ichthyologists of the late 19th century documented the widespread distribution of the fish in mainstream rivers of the Colorado River Basia, where it was reported as common and abundant (Evermann and Rutter 1895, Girard 1856, Jordan and Evermann 1923, Miller 1961). Although abundant in the lower Colorado River in Arizona until about 1930, records of the fish were rare after the 1940's, and efforts to collect the fish there in the mid 1960's met failure (Miller 1961, Hinckley, 1973). By the early 1970's, the fish was considered essentially extinct in Arizona (Minckleq 1973). Reduced to about 25X of its former range, the fish has fared better in the upper Colorado River Basin in Colorado and Utah, where it exists in largest numbers in the Green River Basin (Archer et al 1986, Tyus et al 1987, this paper). The fish was listed as an endangered species by the U. S. Fish and Wildlife Service in 1967 (Federal Register 32(43): 4001), and received protection of the Endangered Species Act of 1973 (U. S. C. 1531 et seq) in early 1974 (Federal Register 39(3):1175). Historical information about the Colorado squawfish is largely taxonomic and distributional, and little was known about its life history until the 1960's (Miller 1964). Interest in extant populations of Colorado squawfish increased in the Green River Basin in the 1960's, when studies associated with the pre- and postimpoundment of Flaming Gorge Dam begain under Section 8 of the Colorado River Storage Project Act (Binns 1963). These studies, largely conducted by various government agencies (Azevedo 1963, Binns,-1963, Bosely 1960), and graduate studients at Utah State University (Holden 1968,1973, Seethaler 1978, Vanicek 1967), and Colorado State University (Banks 1964), contributed much towards an understanding of the biology of Colorado squawf ish and other endemic Colorado River fishes. However, management and recovery 2