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Habitat use by channel catfish and northern pike shows similar behavior in the daytime contacts (Figures 64 and 65). Habitat use was almost identical for channel catfish and northern pike in both 1996 and 1997. Northern pike switched from pool to backwater pool instead of being a main channel pool in 1997. Colorado squawfish during daytime hours were found mostly at depths over three feet. Shallower depths were used at night when fish were active (Figure 66). During the night, observations were made on the fish at depths as shallow as 1.2 feet and only a few contacts were deeper than 3.2 feet. The deeper night locations were observed during the 1996 lower flow year. There was also a difference between the velocity characteristics for daytime and nighttime contacts. Daytime contacts show a use of lower velocity habitats. Nighttime contacts show a wider range of velocities extending up to almost two feet per second for bottom velocity (Figure 67). Mean column velocity measured at locations where squawfish were observed show that daytime hours contacts ranged from 0 to as high as 2.1 feet per second. Nighttime hours showed a wider scatter from 0 to over 2.5 feet (Figure 68). The fish seem to be more sedentary during the day and the bottom velocity is probably a better indication of the velocity experienced by the fish. During the active portions of the night when the fish is moving across, up, and downstream, the mean column velocity is probably more indicative of velocities experienced by the fish. Habitat use by Colorado squawfish during 1996 and 1997 again show distinct habitat use pattern over the 24 hour time period. Daytime observations showed a distinct use of pool habitat with a smaller percentage time used of run habitat (Figure 69). Of the percent time monitored, almost 80% and over 90% of the time in 1996, fish were observed in pool habitat. Nighttime observations for 1997 show a distinct use of run habitat over 50% of the time and nearly 20% of the time monitored a use of riffle habitat (Figure 70). The pool habitat was less used in 1997 at night. In 1996 this habitat had been used almost 90% of the time during the nighttime observations. Again, the activity level even though it was within the pool was more active than the daytime resting mode. Habitat Use Criteria Curves for Use in Modeling Habitat Availability Habitat use criteria were derived from daytime and nighttime depth and velocity observation data. Data collected in 1996 and 1997 were combined to construct the habitat use criteria. The criteria were developed using non-parametric tolerance limits as described in Bovee (1986) and Slauson (1988). These habitat use criteria curves are displayed in Tables 3-5 and Figures 72-74. Observation data show that total depths of less than 3 feet were used infrequently in daytime hours. Nighttime observations showed that the most used depths were in the range of 1.6 feet to 4.2 feet. Depths as shallow as 1.2 feet were used at night by Colorado squawfish. Final Report - Colorado squawfish habitat Page 80 Miller Ecological Consultants, Inc. December 17, 1997