7792

• UCREFRP Catalog Number: 7792
• Author: Kolz, A. L.
• Title: In-water Electrical Measurements for Evaluating Electrofishing Systems.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

Ix-wATES ELEcTRicAL MEASUREMENTS 11
The voltage gradient probe is usually inserted
into the electric field at a near-vertical angle to the
surface of the water. When positioned in the water,
the probe must be rotated for a maximum reading
because voltage gradient is a vector (directional)
quantity (Rogers 1954). The CRO or DVM will
indicate two maxima and two nulls with each ro-
tation of the probe. By probing a volume of electri-
fied water at known depths, the gradient readings
at each depth may be plotted to create a family of
voltage gradient maps (analogous to a geographic
contour map) for a three-dimensional analysis. It
is often convenient to have predetermined those
thresholds of voltage gradient having biological
importance (electrotaxis, stun, tetany, etc.) and to
just locate these constant gradient loci in the
water. Explicit voltage gradient maps are not al-
ways necessary for comparing electrode arrays.
boom above the water. This electrode configura-
tion became popular following its description by
Novotny and Priegel (1974) and is commonly
known as the Wisconsin array. Seven variations
of this array were tested. Four of the arrays were
constructed by using a 30.5-cm-diameter ring to
support four or six 60-cm-long cylinders with
diameters of 0.64 or 2.54 cm. The cylinders were
spaced equidistantly around the circumference
of the supporting ring. The other three arrays
were constructed similarly except that a 58-cm
ring provided the support for 4 or 6 droppers, and
the cylinder diameters were 0.64 or 2.54 cm.
Vertical plates. Flat aluminum plates measuring
0.32 cm thick by 122 cm wide were immersed
vertically into the water to depths of 15.2, 30.5,
and 45.7 cm.
Test Procedures
The empirical data compiled for this study used
only voltage profiles (method 1); the voltage gradi-
ent probe (method 2) was not applied as a meas-
urement tool. Voltage profiles were recorded for 18
balanced electrode configurations.
Description of the Test Electrodes
Five basic electrode configurations were se-
lected as representative of the geometric shapes
common to electrofishing applications: spheres,
cylinders, circular loops, Wisconsin arrays, and
vertical plates.
Spheres. Two sizes of spheres, 15.2 and 27.7 cm
diameter, were measured at immersion depths of
30 and 40 cm, respectively.
Cylinders. The voltage profiles for four sizes of
cylinders, with diameters of 0.64,1.27, 2.54, and
5.08 cm, were recorded. All cylinders were im-
mersed vertically from the water's surface to a
depth of 60 cm.
Loops. Two horizontal loops were suspended in
the water at a depth of 30 cm. The smaller loop
measured 36 cm in diameter and was con-
structed with 0.64-cm-diameter tubing. The
larger loop was 61 cm in diameter and was con-
structed with 1.27-cm-diameter tubing.
Wisconsin arrays. A common electrofishing ar-
ray consists of vertical cylinders (often called
rods or droppers) suspended into the water from
a supporting circular ring that is attached to a
Measurement Site and Techniques
The electrode measurements were conducted at
the Hydraulics Research Laboratory of the Bu-
reau of Reclamation in Denver, Colorado. This
facility has numerous 3-m-wide indoor canals
constructed with concrete walls and floors. The
minimum water depth was 1.4 in, and the canals
were fully accessible from above through a grid
of metal grates. The water conductivity varied
from 111 to 190 µS/cm. The voltage data were
recorded only during those periods when the
canals were not in major use by other re-
searchers; the surface of the water was usually
almost mirror-perfect. Each pair of test elec-
trodes was powered by a voltage-adjustable
autotransformer operating from a standard 60-
Hz AC main. The applied voltage was consis-
tently set to 100 volts so that each balanced
electrode dissipated 50 volts. For added safety
and the elimination of possible leakage currents,
the autotransformer was connected to the mains
through an isolation transformer. The section of
canal in which the electrodes were measured was
found to be free of any metal structures that might
create a shock hazard or distort the electric field.
For recording the voltage profiles, a wooden
beam was fitted with a centimeter scale for meas-
uring distance and suspended above the center of
the canal between the test electrodes. A bracket
was constructed to slide along this beam and sup-
port the "bared" voltmeter lead that was weighted
vertically into the water. In this manner, the end
of the wire extending into the water could be
adjusted to any desired depth, and the slider was