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EXECUTIVE SUMMARY INTRODUCTION This report presents the results of a process to develop flow recommendations for the native fish community, including the endangered Colorado squawfish (Prychocheilus lucius) and razorback sucker (Xyrauchen texanus), in the. San Juan River of New Mexico, Colorado, and Utah. Flow recommendations are a major milestone of the San Juan River Basin Recovery Implementation Program (SJRlP), which Was initiated in 1992 with the following two goals: 1. To conserve populations of Colorado squawfish and razorback sucker in the basin, consistent with the recovery goals established under the Endangered Species Act, 16 U.S.C. 1531 et seq. 2. To proceed with water development in the basin in compliance with federal lII1d state laws, interstate compacts, Supreme Court decrees, and federal trust responsibilities to the Southern Utes, Ute Mountain Utes, Jicarillas, and the Navajos. Mimicry of the lIatural hydrograph is the foundation of the flow recommendation process for the San Juan River. The linkages between hydrology, geomoq,hology, habitat, arid biology were used to define mimicry in terms of flow magnitude, duration, and frequency for the rtInoff and base-flow periods. The flow characteristics of these linkages were compared with the statistics of the pre- Navajo Dam !Iydrology to assist in fine-tIlning the flow recommendations. The flow recommendatiolls require mimicry of statistical parameters of flow, based on the linkages developed and the statistical. variability of the pre-dam hydrology rather than mimicry of each annual hydrograph. A 65-year-long period of record (1929 [0 1993) was used to assess the relationship between water development scenarios and the ability to meet the flow recommendations. Data were gathered and analyzed during a7-year research period (1991 to 1991) to determine fish population and habitat responses to reregulation of Navajo Dam to mimic a natural hydrograph. The research involved quantification of several relationships, including flow/geomorphology, geomorphology/fish habitat, and flowlhabitat availability relationships. The SJRIP will use an adaptive management process, along with monitoring and continued research, to adjust the flow recommendations in the future. The ability to adaptively manage the system is important because flow recommendations can be refined in response to the emerging understanding of the mechanisms involved in recovery of the endangered species in the San Juan River. SJRJP Biology Committee 16 September 1998 S -1 Executive Summary Draft Aow Report .~ !:..... .' .