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, Wahle and Johnson (1984) made a third attempt to develop flow recommendations for endangered fishes by modifying the 1983 field data and SI curves. Bovee (1986) states that it is illegitimate to change species criteria (SI curves) to alter the results of PHABSIM. Such practice constitutes deliberate manipulation of the model to justify a preconceived notion. Again, predictive model outputs (habitat vs. flow relationships) were not biologically defensible and were rejected by species experts, and the professional community at large. This paper presents the calibration of four Yampa River instream flow study sites (see study area map) and the simulated weighted-useable-area (WUA; i.e. available habitat as characterized by depth, velocity and substrate) versus stream flow relationships. The Physical Habitat Simulation System for IBM Compatible Micro Computers, developed by BIO/WEST Incorporated, (BIO/WEST 1987) and habitat suitability index (SI) curves (Valdez et ale 1987), completed under Contract #14-16-006-86-055, have been used for these analyses. The suitability index (SI) curves used in this paper were developed by analyses of data and professional judgement of species experts through workshops organized and conducted by BIO/WEST Incorporated. Each curve set consists of a one-page documentation, followed by two pages of depth, velocity, and substrate coordinate pairs and the resultant curves (Attachment 1). The documentation identifies where and when the data were collected, as well as where and when the experts feel these curves are to be applied. The same SI curve sets for adult and spawning Colorado squawfish, and adult humpback chub, were used at each study site where appropriate. All constraints outlined by the species experts (Attachment 1) were strictly adhered to. For more detailed information on SI curves used in this analysis see Valdez et ale (1987). Flow and habitat time series were not performed since preliminary optimal flow versus WUA predictions did not agree with empirical field data and therefore were judged erroneous by field species experts. Further calibration refinement and additional computer runs did not appear warranted. STUDY SITES The spawning and adult habitat used by Colorado squawfish is represented by two historic study sites established by Rose (1984): the Spawning Bar study site at RM 16.5 and the Replicate study site at RM 18.5. These sites represent segments of the Yampa River which are characterized by large, deep pools intermingled with riffles and runs. Shallow water habitats are dominated by an imbricated cobble substrate (O'Brien 1987). Adult habitat used by Colorado squawfish was also represented by the study sites at Maybell and Government Bridge. The Maybell study site is located at RM 72 and is characterized by an open meandering channel, with deep canyon habitat in the vicinity. The Government Bridge study site is located at RM 91 and is dominated by ephemeral side channels. Habitat types include riffles, pools, runs and some backwaters. Islands are present but not ubiquitous. The adult humpback chub habitat was represented by the Replicate study site, located at RM 18.5. The segment represented by this site is characterized by a slow, braided stream channel interlaced with cobble and sand bars. 2