7784

• UCREFRP Catalog Number: 7784
• Author: Snyder, D. E.
• Title: Impacts of Electrofishing on Fish.
• USFW Year: 1992.
• USFW - Doc Type: \
• Copyright Material: NO

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Impacts of Electrofishing on Fish

simplifies conditions for the experiment and
facilitates determination of cause and effect. But
results may be difficult to extrapolate to normal
electrofishing operations.

Bounding Substrates and Interspersed Objects

Bounding surfaces or substrates of a basin define
the body of water in which an electric field is
generated. Depending on their electrical properties
or conductivity, they also have an effect on the field
in and beyond the water. The conductivity of bottom
substrates can vary considerably with location, even
in the same body of water. Haskell (1954) and
Zalewski and Cowx (1990) reported that substrates of
fine particles and organic debris are more conductive
than those of coarse gravel and rubble. Because of
substrate and interstitial water conductivity, electric
fields can extend well into the bottom substrate and
even onshore. Riddle (1984) suggested that a person
standing barefoot on a bank could be shocked. Some
of the first electrofishing systems in the United States
used AC with one electrode or electrode array
implanted in the ground along shore (Haske)) 1940,
1950, 1954). Smith (1991) described an
experimental electric shark barrier that also
incorporated electrodes implanted onshore rather than
directly in the water.
Bounding surfaces and interspersed objects that
are more conductive than the water tend to
concentrate the current and thereby reduce field
strength near that surface or object. Conversely, the
field is intensified along or around less conductive
media including the air at the surface (Zalewski and
Cowx 1990). As noted by Haskell (1954) and many
other authors since, fish themselves distort the field
in their immediate vicinity if they are more or less
conductive than the water (Figure 8).
Riddle (1984) recommended that metal boats not
be used for electrofishing because they can have a
large effect on the field. He suggested that if a
conductive vessel is positioned between the
electrodes, it would interfere with the field
(concentrate the current) and might adversely affect
electrofishing efficiency, presumably by altering the
size and shape of the effective field. This idea
seems to have been overlooked in much of the
literature on boat electrofishing, although some,
especially earlier, authors strongly discouraged use of

Review I Electric Fields in Water 15

metal boats for safety reasons (Goodchild 1990,
1991). Interestingly, with appropriate equipment and
wiring, some of today's electrofishing systems use
aluminum boats themselves as cathodes; others use
fiberglass vessels with metal plates mounted on the
bottom as cathodes (Vibert I 967b).

Size, Shape, and Position of the Electrodes

According to Novotny (1990), the electrodes are
the most crucial part of an electrofishing system.
Their size, shape, surface area, and spacing, along
with water conductivity, determine the electrical
resistance of the system and, for a specified power
output, the distribution of the current (field intensity)
and size of the effective field. Electrode systems
that are inappropriate for the power supply and
waters to be sampled can lead to poor electrofishing
results or unnecessary harm the fish. Novotny and
Priegel (1974) listed the following characteristics as
desirable for an effective electrode system:

. Establishment of the largest region of
effective electric current distribution in the
water to be sampled.
. Avoidance of local regions of unnecessarily
large current densities which waste power
and are potentially harmful to fish.
. Adjustability to meet changes in water
conductivity .
. Ability to negotiate weeds and obstructions.
. Ease of assembly and disassembly.
. A voidance of unnecessary disturbance to
water to permit easy visual observation of
fish.

For electrodes spaced sufficiently far apart (more
than several radii in the case of spherical
electrodes-Novotny 1990; 10 to 20 radii for
rings-Smith 1989), the distance between electrodes
no longer has a significant effect on electrode or
system resistance and the fields around each
electrode are effectively independent. The water
outside well-separated anodic and cathodic fields is
considered to be at "ambient potential" because its
electrical potential does not vary significantly and its
voltage gradient is nil (Cuinat 1967). Fish that
remain in water of ambient potential, even between
the electrodes, are theoretically unaffected by the