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Discussion The three habitats represented to be usable by squawfish are consistent with the habitat use information collected by radio telemetry in this study (Miller and Rees, 1997), and are also consistent with the literature that reports adult Colorado squawfish habitat requirements (Tyus and Karp 1989, Osmundson et al. 1995, Nesler 1996, and Wick and Hawkins 1986). The main concern in the river above Cross Mountain for squawfish habitat availability is for the adult life stage, because juvenile squawfish have not been commonly collected in this reach of river. Below Cross Mountain Canyon all life stages of humpback chub as well as adult Colorado squawfish reside in the river. Following habitat use data collection in 1997, specific habitats will be identified that are necessary for these fish. There may be qualitative differences among the three usable habitat types used in this study. Wick and Hawkins (1986) habitat suitability index is based on squawfish catch rate data from the Yampa River near Lily Park. They reported that catch rates were 2.5 times higher in Class I pools than Class II pools. However, Wick and Hawkins (1986) did not measure numbers and area of these habitats, which are needed to determine habitat preference. Therefore the higher catch rate they reported for squawfish from Class I pools (2.5 times that of Class II pools) were not corrected for the relative amount of those two habitats. If these two habitat types were in equal abundance, then the higher catch rate would indicate strongly selection for deeper habitats (Class I pools). Results of the 1996 habitat survey show that Class I pools are very rare at all flows under 400 cfs in the upper study reach. Class II pools are the most common usable habitats in the river at flows less than 100 cfs, and deep run is the most common usable at flows over 100 cfs. Therefore, in this flow range, there appears to be few habitat types for adult squawfish to select between. Of the 35 squawfish telemetry contacts in 1996, the median length of the occupied habitat was 450 ft. Only two contacts were made with fish in habitats that were less than 250 ft. Incorporating habitat size may increase our ability to determine relative importance of habitat types. Larger runs and pools may be more likely to maintain a higher survivorship of adult fish at very low flows. In other words a deep run that is 450 ft in length may be selected for over a run that is only 200 ft in length. Selection might occur because as flows drop there is increased probably of fish becoming stranded in isolated pools, and a large pool would probably be a less stressful habitat during an isolation event than a small pool. If squawfish appear to select habitats based on a minimum length, then those less than that, e.g. 200 ft, should not be included as usable habitat. In Strata 6, two of the four sequences sampled had long deep runs and two did not. In Strata 8, a long deep run was measured upstream of lower sequence in cluster 115.5 and included in that cluster. These data indicate that physical habitat is available for adult squawfish at low flows, in three of the six clusters sampled so far. Inflection points in the width/flow relationship and the usable-habitat/f10w relationship are useful to indicate thresholds between rapid changes versus uniform changes in habitat due to flow. Inf1ection points for these relationships were found at about 60 to 80 cfs, which might suggest a critical flow threshold that influences habitat availability among the stations sampled in 1996. 40