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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variety of habitats, but preferred no current, a firm silt substrate, and

a depth of two feet (Figure 8). Adult humpback chubs were taken primarily

in eddies and runs with sand bottoms and a variety of velocities and
depths (Figure 9). Temperature did not appear to be selected by any size
of humpback chub (Figure 10).

Turbidity varied considerably during the study, and was highest after
rainstorms (Figure 11). There is considerable natural variation in the

turbidity levels of the Green River because the watershed is highly erod-
able. The native fishes seldom have the opportunity to select a preferred

turbidity as the entire river may change dramatically overnight. They
,.. - ~"".,

are well adapted to sudden and extensive changes in turbidity, which are

usually associated with increases in flow.

River cross-sectional measurements of depth, velocity, and substrate

were taken around a backwater where young-of-the-year squawfish were abun-

dant. Figures 12 and 13 show the depth and velocity isolines of the area

measured. The area was quite deep, with steep, sloping banks and a well-

defined main current with slower areas near the shore.

Chemical Components
Graphs of water chemistry values recorded during the study can be

found in Appendix II. Green River water chemistry changed little during

the course of the study. Fluctuations of the various parameters are with-

in the normal expected range. Fishes seldom are able to select preferred

chemical ranges in the river as all habitats are very similar in chemical

analysis.