7824

• UCREFRP Catalog Number: 7824
• Author: Miller, W. H., et al.
• Title: Colorado River Fishery Project, Part III, Final Report, Contracted Studies.
• USFW Year: 1982.
• USFW - Doc Type: \
• Copyright Material: NO

of stations on each transect line and their spacing was selected to
accurately represent the area and at least'10 sets of observations were
made along each transect.
Current velocities were measured with a Marsh-McBirney Model 201
electromagnetic flow meter at points 5 cm above the substrate and
3 cm below the surface. Measurements were also made at one or more
points to estimate mean velocity. In depths less than l meter, mean
velocity was measured at. 0.6 of the depth; in depth greater than 1 meter,
velocities were measured at 0.2 and 0.8 of the depth.
Snorkelers visually estimated substrate composition by 'assigning
approximate proportions to each of four particle size-classes. Particles
less than 0.1 cm in diameter were classed as sand, those between 0.1 and
10 cm as gravel, those between 10 and 30 cm as cobble, and particles
larger than 30 cm were boulder or bedrock. Estimates of substrate com-
position at actual spawning sites were compared with photos taken with
an underwater camera to insure accuracy.
During the spawning season and for several weeks before and after,
gill and trammel nets were set each evening and checked the following
morning. Nets included a sinking trammel net (6 feet' deep by 100 feet
long with 1 square-inch nylon mesh and 10 inch panels), a sinking experi
mental gill net (6 feet deep by 125 feet' long with 3/4, 11, and 1 1/4'
square-inch nylon mesh), and a floating' experimental gill net (6 feet
deep by 50 feet long with 1 1/4 and 2 square-inch monofilament mesh).
Because net effectiveness was highly dependent on both net type a'nd set
location, the same nets were always set in the same manner-"at the" same'
five sites. Three sites- were in the'fastwater area at river miles
38-1/2, 36-1/2, and 35-1/2, and the other two sites were in the 'slack
water at river miles 30-3/4 and 29-1/2. Sets were made parallel to
shore and were anchored to the bottom in low velocity areas. The
floating monofilament gill net was always set at river mile 38-1/2, while
the other pair of nets was set alternately in the fastwater and the
slackwater.
Fish removed alive and ih'good condition from nets were Floy-tagged
beneath the dorsal fin and released. Tag color and location (left
or right side) were specific to date and area of`capture . Thus, a fish'
with a yellow tag on the left side was tagged in the slackwater between
June 2`and 10. This was done to enable snorkelers to 'identify time
and location of capture of fish sighted `on spawning sites without having
to recapture the fish. Fish were also tagged on one spawning site.
Fish to be tagged were captured by angling or by drifting a 30-foot
section of monofilament gill net through the site (swimmers held the ends
of the net apart). Fish were marked-over a 2-day period soon after
spawning began. After this effort, snorkelers counted numbers of tagged
fish while swimming standardized transects.
All fish that were not tagged and released after capture were
sacrificed, weighed to the nearest gram, and measured (`fork length) to
the nearest 5 cm increment. Sex and general development were determined, •
and gonads were removed and weighed to the nearest 0.1 gm. Scales were
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