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I I I I I I I I I I I I I I I I I I I INTRODUCTION The razorback sucker, Xvrauchen texanus (Abbot) is an endemic species of the Upper Colorado River Basin, including the Green River (Sigler and Miller 1963). Historic records indicate this species was once widespread and common within the Colorado River Basin. However, current distribution and abundance of the razorback sucker is greatly reduced due to changes in flows, water temperature, loss of riverine and off-channel habitats and predation (Bestgen 1990). Remaining concentrations of razorbacks are relic populations comprised primarily of large, old individuals. There is little evidence that successful recruitment of young into the population is occurring (Tyus 1987). The continued loss of existing adults through various types of mortality and the lack of young age classes present a real concern for the continued existence of razorback suckers. The population status of this species prompted the U.s. Fish and Wildlife Service to list the razorback sucker as endangered in 1992. The Recovery Implementation Program (RIP) for Endangered Fish Species in the Upper Colorado River Basin was developed to promote the protection and recovery of threatened and endangered fish species with a goal of achieving self-sustaining population levels. The objectives of this program include the development and restoration of flooded bottomland habitats to provide important nursery habitat, as well as short-term augmentation programs to increase population numbers to levels which would allow for more effective study of the species and offset losses due to predation and other sources of mortality. The Escalante Ranch area, located along the Green River in northeastern Utah, has been identified as an area with bottomlands which could potentially be developed to benefit razorback suckers. The purpose of this conceptual Plan is to describe the Escalante Ranch site and present alternatives for development which could accomplish objectives outlined in the RIP regarding habitat enhancement and population augmentation. The Escalante Ranch site is characterized by a number of conditions which are important with regard to developments for the recovery of razorback suckers. These conditions include, but are not limited to: the fact that the Green River supports the largest numbers of razorback suckers in a native riverine environment (Tyus and Karp 1991); a natural source of larval razorbacks from a known spawning area located approximately four miles above the site; a large wetland area which is occasionally flooded by the Green River; bottomland sites which could be connected to the river system to provide flooded bottomland habitat or grow-out ponds. 1