7154

• UCREFRP Catalog Number: 7154
• Author: Holden, P. B.
• Title: Habitat Requirements of Juvenile Colorado River Squawfish.
• USFW Year: 1977.
• USFW - Doc Type: FWS/OBS-77/65,
• Copyright Material: NO

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Preferred Habitat of Rare Fishes

Physical Components

River temperature varied considerably on a diel basis during this

study (Figure 2). Early morning temperatures were generally 3 to 5 C

cooler than late afternoon levels. Backwaters were the warmest areas,

often warming 3-8 degrees above that of the river proper in late after-

noon. Morning temperatures in the Jensen area in August were usually

15-17 C (River Mile 178). Morning temperatures in August in downstream

areas varied considerably with local weather conditions, but were gener-

ally warmer (19-21 C) than those at Jensen. September temperatures in

Desolation Canyon (River Mile 30) were much colder (a low of 10.5 C)

due to the cool ambient air.

The level of the Green River in the study area fluctuates daily due

to releases from Flaming Gorge Dam. The greatest fluctuation occurred

at Jensen where a l6-inch daily rise and fall was noted. Diel fluctua-

tions in Desolation Canyon were only 3 to 4 inches. The large fluctua-

tion noted at Jensen caused a considerable daily change in available

habitat. Low flows provided a variety of habitat types, especially back-

waters. High flows reduced the number of backwaters and generally cre-

ated a full channel situation (i.e., wetted area unbroken by sand bars,

etc.). In this area, juvenile squawfish were primarily caught either

during low river levels when backwaters were available, or in backwaters

which were not affected by the fluctuations.