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INTRODUCTION The fish community of the Colorado River was historically dominated by endemic species -- species found nowhere else (Miller 1959). Because of limited distribution, survival of these species is more tenuous than it is for species with wider distributions. Alteration of the Colorado River ecosystem has greatly reduced the populations of some of these endemic species, and continued alterations of the river could reduce a few species to extinction. The recent decline in abundance of three endemic fishes; Colorado squawfish Pt chocheilus lucius , humpback chub Gila c ha , and bonytail chub JL. ele ans ; has been significant enough to justify classifying them as endangered by the United States Fish and Wildlife Service. Under the provisions of the Endangered Species Act of 1973, endan- gered species designation dictates that Federal agencies involved in development must assure that their actions do not further reduce populations of endangered species. Proposed developments that would further reduce populations of endangered species might be modified or canceled. Thus, the presence of an endangered species can greatly influence the development of natural resources and this has been a particularly controversial issue affecting proposed Colorado River water projects. Information on the distribution, abundance, and habitat associations of endangered Colorado River fishes was required in order to determine the effects that proposed water development projects might have on these endangered species. In 1979 the Fish and Wildlife Service (FWS) and the Bureau of Reclamation (BR) cooperated in the development of the Colorado River Fishery Project (CRFP) in order to collect and interpret information on endangered Colorado River fishes. Among the many findings of CRFP was that the endangered Colorado squawfish and humpback chub apparently experience an unusually high rate of mortality during the first few years of life (Miller et al. 1982). If these causes of early mortality could be determined, it might be possible to lessen or eliminate their influence on the survival of Colorado squawfish and humpback chub. The intent of the present Windy-Gap work program includes determining the factors that affect the survival of Colorado squawfish and humpback chub during their first year of life. Knowledge of these limiting factors would then be used in an attempt to increase the population size of these species, perhaps to the extent that the endangered species designations can be removed. The specific objectives of the Windy-Gap work plan are: 1) to locate and describe reproductive habitats for Colorado squawfish and humpback chub in the Grand Junction area, 2) to locate and quantify rearing areas for young Colorado squawfish and humpback chub, 3) to identify the major factors that affect the survival of Colorado squawfish and humpback chub during the first year of life,