7945

• UCREFRP Catalog Number: 7945
• Author: Bovee, K. D. and T. Cochnauer.
• Title: Development And Evaluation Of Weighted Criteria Probability-Of-Use Curves For Instream Flow Assessments
• USFW Year: 1977.
• USFW - Doc Type: Fisheries, Instream Flow Information Paper No. 3.
• Copyright Material: NO

After completion of the sampling or observation run, the observer
returns to each buoy, where measurements are made of the depth, velocity,
substrate, and cover. The velocity sought is the mean velocity in the
water column, therefore, velocities should be measured at 0.6 of the
depth (from the surface) if the water is less than 3 feet (90 cm) deep.
If greater than 3 feet (90 cm), two measurements, at 0.2 and 0.8 of the
depth should be averaged. Substrate size should be estimated from the
modified Wentworth scale (Table 2). In water deeper-than 4 feet (120 cm),
these measurements may be made from a boat using cable sounding gear and
a current meter.
For univariate frequency analysis, a total of approximately 300
measurements for each life stage of each species are needed to ensure
a representative analysis. For multivariate analysis, 1,000 to~2,000
measurements are required.
OPTION 2 - AREA GRID MEASUREMENTS
This method has its best application with species or life stages
which school or form large congregations. Collection is nearly always
required because the subjects are often small and difficult to identify
by simple observation. Exceptions would include spawning congregations
of adults where there is little doubt concerning the species, life
stage, and activity.
Sampling techniques amenable to this method provided the subjects
can be identified and counted, include electrofishing, spot concussion,
seining, and observational techniques. Markers are used to outline
areas of fish concentrations as determined from sampling or observation.
A measurement grid is established visually over the outlined area
(Figure 6} and the number of individuals of the species counted for
each outlined area. Hydraulic parameters are measured at each grid
intersection. Measurements of each parameter are then averaged, and the
standard deviation calculated. If the standard deviation is greater
than 25% of the mean, the sample should be discarded and option 1 used
instead. Under option 2, the mean of several measurements (tested for
variance) is used to represent a large number of individuals, rather
than one at a time as in option 1.
Under the area grid approach a total of 100 to 200 outlined areas
should be measured for each life stage and species.
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