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INTRODUCTION This five year study to determine the effect of Colorado River flows on the humpback chub (Gila cypher) reproduction and recruitment is a component of the Recovery Implementation Program (RlP) Aspinall Studies. The purpose of the Aspinall studies is to provide the United States Fish and Wildlife Service (FWS) with adequate biological and physical data to support flow recommendations which will be included in their Final Biological Opinion on the operation of the Aspinall Unit on the Gunnison River. The biological base for current flow recommendations in the Upper Basin focuses on the relationship between Colorado squawfish population dynamics and observed flows. The goal of this project was to develop relationships between observed flows and humpback chub life history, whde concentrating on the earlier life stages. To meet this goal, the following study objectives were identified: determine spawning and nursery requirements, describe the relationship between geomorphic processes of sediment transport and nursery habitat formation, identify and describe reproductive isolating mechanisms, and to assess recruitment. Simdar research is being conducted on the Green Ritrer in Desolation Canyon as f part of the Flaming Gorge Studies. ` . The humpback chub,. originally described from specimens collected in Grand Canyon of the Colorado River in 1945 (Miller 194, has been found in several .canyon-bound areas of the upper basin: Black Rocks, Westwater Canyon, and Cataract Canyon of the Colorado River and Desolation /Gray Canyon and Yampa Canyon in the Green River sub-basin. The Westwater Canyon population, discovered in 1979 during the FWS `s Colorado River Fishery Project and monitored annually since by the Utah Division of Wildlife Resources (iJDWR), is the largest population of humpbacks in the upper basin. The present study represents the most intensive sampling effort in this canyon. Greater emphasis has been placed on the earlier life stages than has been in the past. Although the early life history work in this study was patterned after concurrent UDWR studies of Colorado squawfish mirsery habitat requirements and habitat /flow relationships, it was soon evident that even at the earlier life stages native chubs habitat use /behavior differed greatly from Colorado squawfish . Native chubs complete life cycles in short sections of the river. {Valdez and Clemmer 1982). The steep walled, deep canyon habitats of Westwater Canyon that were known to harbor juvenile and adult DRAFT 1