7980

• UCREFRP Catalog Number: 7980
• Author: Archer, D. L., H. M. Tyus and R. Valdez.
• Title: Field Methodologies of the Fish and Wildlife Service's Colorado River Fisheries Project.
• USFW Year: 1980.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

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and rapids, with extensive reaches inaccessible except by air or by
floating down the river considerable distances.

Since this study area encompasses some 570 miles of the Colorado
and Green Rivers, it was impossible to study the entire length with
the allocated manpower; therefore, it was deemed necessary to rely on
a statistically sound unbiased sampling scheme from which to infer
habitat/fishery life history relations.

The river system consists of several 30 to 70 mile sections of
relatively homogeneous fishery habitats, e.g., high-gradient canyons,
low-gradient braided winding sections and transition zones between
these two main types. Our sampling scheme identified these homogeneous
sections and handled them as discrete strata of a random sampling
scheme to provide a good distribution of samples and to reduce within-
strata included both geophysical (river channel configuration, substrate
types, gradient and depth) and biological parameters (productive
bottom lands, sterile sand runs, productive backwaters, swift canyons
and point sources of allochthonous materials).

Because we could work sequentially downstream with less investment
of time, we did not use a completely random design to select the
sequence of strata to be sampled; but instead used a systematic sampling
design with a random start. Utilizing a table of random digits, one
stratum was selected as the starting point with the sampling series
progressing sequentially downstream to the last strata, shifting back
to the uppermost stratum to complete the series.

Within each stratum a sample site was selected according to a
completely random sampling design. Each stratum was divided into
river-mile stations. A table of random digits was consulted and the
first numbers encountered in the table that appeared in the section
were chosen as the sample station. To permit replication and to
extend the boundaries of each sample, each station consisted of two
0.5 mile reaches; one extending downstream from the selected river
mile starting point, the other five-miles downstream (Figure 1).
Intensive sampling began in the uppermost 0.5 mile section continuing
for 24 hours. The second day, the intervening 4.5 mile section was
surveyed by electrofishing starting at the lower boundary of the
previous sample site and continuing downstream to the upstream point
of the second 0.5 intensive section. From this point, the second 0.5
mile section was intensively sampled for 24 hours. Generally, sampling
was discontinued after the second intensively sampled reach was comp1ete(
and the field crew usually returned to home station.

In some instances, it was advantageous to sample two reaches by
proceeding immediately from one to another. There were also times
that equipment failure dictated minor schedule changes. No change was
allowed unless compatihle with the philosophy of the sampling design.

The intent of the sampling procedure as outlined was to provide
a basis for the collection of both positive and negative correlations
hetween habitat and endangered fish species by sampling all river