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Preface The decline of the native Colorado River fish fauna is a biological indicator of dramatic environmental change and the potential loss of a unique natural resource. This decline is associated with human population expansion and associated water development in the West, limited interest in nongame fish biology, and a lack of a conservation ethic for fishes of western deserts. For these and other reasons, management and recovery options have been difficult to develop for rare fishes in the Colorado River basin. Only recently have substantive life cycle and habitat use information of these fishes become available and their requirement for large and diverse habitats been recognized. Flow and nonflow management measures for the rare Colorado River fishes are currently being developed based on provisions inherent in Section 7 of the Endangered Species Act. Since passage of that Act in 1973, the proliferation ofliterature and symposia concerning recovery ofthe Colorado River fishes reflects the keen interest in their management and recovery. Major conflicts between various water development groups, the U.S. Fish and Wildlife Service, and others regarding the cumulative effects of water development projects on recovery of the rare fishes led to the formation of the multiagency Upper Colorado River Basin Coordinating Committee in 1984. Active participants include the U.S. Fish and Wildlife Service; U.S. Bureau of Reclamation: States of Colorado, Utah, and Wyoming; private water development interests; and environmental groups. Cooperation of these diverse interests demonstrates the complexity involved in recovery of the rare Colorado River fishes. In 1987 the Upper Colorado River Basin Coordinating Committee produced a Recovery Implementation Program for recovering the rare fishes of the upper Colorado River basin. The ultimate goal of this program was to recover and delist the Colorado squawfish (Ptychocheillls IIICiIlS), humpback chub (Gila cypha). and bonytail chub (G. elegallS). In addition, management options would be developed for the razorback sucker (Xyrallchell texalllls) so that protection under the Endangered Species Act would not be needed. One element of the Recovery Implementation Program is the protection of streamflow needs of the listed fishes. In meeting this goal, the Yampa River has been assigned highest-priority for water rights acquisition. As the only large river in the upper Colorado River basin in which flow patterns have not been substantially altered by water development projects, the Yampa River is considered important for the maintenance and recovery of existing populations of rare Colorado River fishes. In 1988, the Upper Colorado River Basin Coordinating Committee requested that streamflow requirements of the rare fishes in the Yampa River be quantified to aid water acquisition in line with the goals of the Recovery Implementation Program. A two-step process was subsequently outlined: (1) evaluation of habitat use, potential limiting factors, and general flow needs (i.e., relation between life cycle and annual flow events) of the four fish species; and (2) quantification of the identified needs with respect to quantity, duration, and timing of flows. The present report fulfills step 1: it is an evaluation of habitat use and streamflow requirements of the Colorado squawfish, humpback chub, bonytail chub, and razorback sucker in the Yampa River. Questions regarding technical material in this report may be addressed to the authors. Additional information regarding the Recovery Implementation Program may be obtained from Colorado River Coordinator (FWE), U.S. Fish and Wildlife Service, P.O. Box 25486, Denver Federal Center, Denver, Colorado 80225. iv