7245 - Laserfiche WebLink

Home Browse Search

I. INTRODUCTION An important goal of Region 6, U. S. Fish and Wildlife Service (FWS), is to recover the endangered fishes in the Upper Colorado River Basin (UCRB). Three species, the Colorado squawfish (Ptvchocheilus lucius), humpback chub (Gila ~), and bony tail chub (Gila eleaans), have been listed as endangered under the Endangered Species Act of 1973. A fourth species, the Razorback sucker (Xvrauchen texanus), is extremely rare and is a candidate for Federal listing under the Act. The ultimate goal of the Recovery Implementation program in the UCRB is to recover and delist the three endangered species and manage the razorback so it will not need the protection of the Endangered Species Act (FWS 1987). Two tasks necessary for recovery of the endangered fish involves: 1) quantifying the amount of stream flow needed to support self-sustaining populations and 2) legally protecting such flows. A necessary ingredient for the Green River (part of the UCRB) is to refine the operation of Flaming Gorge dam such that the continued survival and recovery of the endangered fishes is insured. At present, an interim agreement between FWS and the Bureau of Reclamation, initiated by larvae produced in the Yampa River entering the Green River, constrains the summer releases from the dam not to exceed 2600 cubic feet/second (cfs) near Jensen (RM 302) in an effort to increase backwater areas for larvae and young-of-year squawfish (memorandum to: Regional Planning Officer, Salt Lake City, UT from: Randall Peterson, 20 OCT 1987). Such contraints remain in effect until the end of October. During the 1987 field season, the Upper Colorado River Basin Instream Flow Team established two instream flow study sites within Segment 3 of the Green River (Figure 1) in an attempt to determine flow needs for adult and spawning life stages of Colorado squawfish, and adult Razorback suckers. This report documents the results of the 1987 study efforts as well as the 1985/86 work at a site within Ouray National Wildlife Refuge. II. PHYSICAL HABITAT SIMULATION METHODOLOGY (PHABSIM) MethodoloQV The PHABSIM model output displays effects of streamflow alterations on existing riverine fishery habitat (Milhous et al. 1984). The effects are expressed through changes of an index value called weighted-useable-area (WUA)--total surface area of the study area expressed as an equivalent surface area of optimal fish habitat. The model is based on the assumption that changes in physical habitat (WUA) conditions can be predicted and are connected to a corresponding response of a species with respect to such measureable streamflow dependant variables as water depth, mean column velocity, and substrate. Thus it is intended for use in situations where the flow regime and channel structure are the major factors controlling the abundance and distribution of the fishery resource and where field conditions are compatible with the assumptions of the methodology. These assumptions state that steady flow conditions exist within a rigid 1