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t I the appendix (Table 3). Placing the site of a fish location into a par- ticular category was unambiguous in some cases but not in others. The limits of precision in locating radio-tagged fish created some problem t when habitat types were closely juxtaposed such as at shear zones between runs and eddies. Also, the lack of a clear demarcation between some habitat types, such as runs and pools, is a problem inherent in any such categorization. The categorization of a particular site was, therefore, somewhat subjective and relied on the best judgment of the field crew leader. Microhabitat use was characterized by measuring depth, velocity, substrate and temperature at fish locations. Velocity was measured at a depth 60% of the water column (measured from the bottom) at sites < 3.0 ft deep; at sites > 3.0 ft deep, velocity was averaged from two measurements taken at 20 and 80% of the water column. In addition to temperature measurements made at the fish location, temperature was also measured at a nearby location in the main channel. In 1987 and 1988, water clarity at a loca- tion (RM 174.4-175.2) in the 15-mile reach was routinely monitored using a standard Secchi disk. Possible spawning sites were identified by the aggregation of ripe adults during the spawning season and, for squawfish, by the subsequent collec- tion of larvae. Post-hatching ages of collected squawfish larvae were calculated using total lengths of individual larvae in age-length equa- tions developed by Haynes and Muth (1985). Spawning date was then esti- mated by subtracting four days from the estimated hatching date. Four days was considered the mean embryo incubation time, based on the 3.8-5.0- 7 Ll