9491

• UCREFRP Catalog Number: 9491
• Author: Snyder, D. E.
• Title: Electrofishing and Its Harmful Effects on Fish.
• USFW Year: 2003.
• USFW - Doc Type: Denver.
• Copyright Material: NO

20 INFORMATION AND TECHNOLOGY REpORT--2003-0002

the system. When cathodes are larger than anodes, most
of the total potential between electrodes is associated
with the anode, and the voltage differential between an-
ode and ambient potential is proportionately greater than
between ambient potential and cathode. If cathodes are
very much larger than anodes, the very low voltage dif-
ferential between the cathode and soil and water in the
vicinity may reduce the risk of severe shock or electrocu-
tion to people or animals that inadvertently approach or
touch the cathode (Smith, 1989). Because cathodic resis-
tance for well-separated electrodes is halved each time
the surface area of the cathode is doubled, Smith (1989)
suggested that 10m2 may be a practical limit to the size of
the cathode. However, according to Temple (personal
communication), A. Kolz maintains that in shore-based
systems with buried cathodes, the earth itself becomes a
very large cathode. With appropriate equipment and wir-
ing on metal boats, cathode size is often maximized for
DC or PDC electrofishing systems by using the boats
themselves as cathodes (Kolz, 1993; Reynolds, 1996); on
fiberglass vessels, cathode size is sometimes maximized
by mounting large metal plates on their bottoms (Vibert,
1967b ).
Kolz (1993) discussed the importance of and proce-
dures for determining electrode and system resistance as
well as making in-water measurements for mapping field
intensity around and between various types of elec-
trodes. Such data are necessary for comparing electrodes
of various shapes, sizes, and designs, optimizing
electro fishing efficiency, minimizing hazardous field in-
tensities, and standardizing electrofishing fields. Kolz
(1993) emphasized that electrofishing fields generated
through different electrode systems cannot be standard-
ized only by output voltage, current, or power. The distri-
bution of field intensity around and between electrodes
depends in large part on the specific size, shape, and
configuration ofthose electrodes and must also be known
or measured.
To this end, Kolz (1993) determined and compared
the electrical resistance and voltage-gradient and volt-
age-differential profiles for 18 commonly used electrodes,
including spheres, cylinders, horizontal loops, Wiscon-
sin-ring dropper arrays, and vertical plates of various
sizes. Measurements were taken in a concrete canal (wa-
ter 1.4 m deep, 3 m wide) with matching electrodes 4 m
apart (except for cylindrical electrodes which were 2.7 m
apart), water conductivities of III to 190 I-lS/cm, and an
electrical output of 100 V nTIS' Electrical resistance data were
normalized for a water conductivity of 100 I-lS/cm but can
be adjusted by calculation for different water conductivi-
ties (electrode resistance is inversely proportional). Simi-
larly, voltage-gradient and voltage-differential profile data
for each electrode can be calculated for different applied
voltages (directly proportional; for unmatched electrodes

data must also be adjusted by the inverse ratio of their
electrical resistances).
Spherical electrodes are considered electrically su-
perior to other shapes (e.g., cables or narrow cylinders)
and allow more accurate calculation of electrode resis-
tance and voltage gradient maps. Electric fields gener-
ated immediately around well-submerged spheres are
uniform and without the hot spots (localized regions of
higher intensity) produced near the comers and edges of
many other electrode shapes. For example, according to
Sharber et al. (1995), charge is not distributed uniformly
over long thin electrodes but concentrated at their distal
ends. Except near their surfaces where tetanizing voltage
gradients may exist, Novotny and Priegel (1974) and
Novotny (1990) suggested that circular and ringlike elec-
trodes, including dropper arrays, produce electric fields
similar to those of spheres. However, Kolz (1993) docu-
mented that Wisconsin-ring dropper arrays project their
fields somewhat further in a horizontal direction than simi-
lar-size spheres. Spheres, on the other hand, project their
fields more evenly in all directions, including vertically
towards the bottom and, perhaps less advantageously,
upward to the water surface.
In addition to transfer of electrons, the process of
electrolysis at the electrodes results in generation of gases
and, more importantly, loss of metal ions from the anode
to the water and deposition of metal ions from the water
onto the cathode, usually as metallic oxides (Sharber,
personal communication). Periodically, anodes may need
to be replaced and cathodes cleaned (scraped or sanded)
to recover lost surface area and performance (oxide coat-
ings reduce electrode resistance). When electrodes are
of the same size and type, some biologists periodically
alternate their use as anodes or cathodes to reverse the
buildup of metallic oxides (Sharber and Carothers, 1988),
but the effectiveness of this procedure has not been re-
ported.
Riddle (1984) suggested that it was not wise to buy
aluminum punts (boats) second-hand from electro-
fishermen because the gauge of the metal might be
substantially reduced. According to Sharber (personal
communication), this is not a problem when a metal boat
is used as the cathode. But when a metal boat is situated
in an electric field and not used as an electrode, it has an
intermediate electric charge, negative with respect to the
anode and positive with respect to cathode. In this case,
electrolytic reactions result in both formation of
nonconductive metallic compounds on the boat's surface
and loss of structural metal. Over time, the latter reaction
can reduce the structural integrity of the boat. When a
boat is used as a cathode, no metal is lost, but the
nonconductive metallic compounds that form on the
boat's surface can increase its electrical resistance. This
coating can be scraped or sanded away periodically, but