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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to show the relative size and placement of the habitat sampled. All

sampling sites were marked on U.S.G.S. quadrangle maps.
Dissolved chemicals and turbidity were measured daily in the main

channel. Dissolved oxygen was measured with a YSI model 54 ARC portable
02 meter, and conductivity-salinity with a YSI model 33 portable S-C-T

meter. Alkalinity, ammonia, nitrate, nitrite, sulphate, and turbidity

were measured using a Bausch & Lomb Mini Spec 20, and pH was measured

using an Analytical Pocket pH Meter, model 107.

Fish sampling included seining, electrofishing, and use of a fry
shovel (Vanicek, 1967), although seines were used most of the time be-

cause emphasis was on small fish. Fry traps were available for measuring

movement of Colorado squawfish fry. An attempt was made to sample indi-

vidual habitats where physical components were essentially the same.

For example, a seine haul would not be made through part of a run and

into an eddy since it would have been impossible to determine in which

habitat type the fish were actually caught. Fishes were enumerated and

total length measurements taken of sufficient numbers to produce

length/frequency relationships and provide an estimate of size (age)

classes. Most fishes were returned unharmed to the location of capture.

A reference collection of most of the species caught was field preserved

in 10% formaldehyde and later transferred to 40% isopropyl alcohol.

The fishery-habitat measurements were analyzed to show preferred

habitats of the rare fishes and were expressed as electivity curves.

These curves are part of an instream flow methodology recently developed
by the Cooperative Instream Flow Service Group (U. S, Fish and Wildlife