9647

• UCREFRP Catalog Number: 9647
• Author: Wydoski, R. S.
• Title: Fish Population Manipulation.
• USFW Year: 1990.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Use of Electricity to Control or Guide Fish
McLain and Neilson (1953) summarized the use of electricity in guiding the
movement of fish. Their study revealed several factors which appear to be
obstacles to the practical use of pulsed direct current as an effective means
of leading desirable fish away from control structures. Size selectivity is
without doubt the major limiting factor. Voltage gradients effective for
leading fish vary inversely with the length of the fish. A voltage gradient
sufficient to control small fish would narcotize, injure, or even kill any
large fish in the electrical field. Needless to say, water temperature is a
major factor. Water resistivity changes with temperature and with changes in
amounts of dissolved or suspended materials. More important than water
resistivity per se is the ratio of water resistivity to bottom resistivity.
Where the bottom is more conductive than the water, it is doubtful whether a
usuable voltage gradient between the electrodes spaced more than a few feet
apart could be established without the use of artificial insulating materials
on the stream bottom. Several conclusions on the use of electricity to
control sea lampreys are provided by McLain, Smith, and Moore (1965): (1) it
is possible to block the upstream migration of sea lampreys or fish with
electric barriers of the design and type developed and used; (2) the electric
barriers are subject to mechanical failures or breakdowns. Although the
frequency of interruptions of operation can be reduced greatly, some
escapement is to be anticipated each season at some barrier in a system;
(3) because the method of control requires continuous operation over a number
of years, the opportunity for inefficiency as a result of abnormal conditions
is increased accordingly; (4) electric barriers are now the principal means
for evaluation of chemical control of lampreys.
Electric Fish Barrier
Electrical fish barriers have been somewhat neglected due largely to poor
results in blocking fish migration, the undesirable killing of fish and the
equipment maintenance required to keep a barrier operational during different
seasons of the year. Many times these undesirable effects were due to an
overall lack of electric field theory, knowledge of the physiological effects
of electricity on fish, and the cumbersome mechanical designs required. An
electric fish barrier produces an electric field in water by establishing an
electric current flow between an appropriate array of electrodes. An electric
fish barrier can be imagined as "a water a wall electrified by electric
current." One of the most desirable characteristics of an ideal electric fish
barrier is one where fish are gradually introduced to an electric zone that
they can sense. The electric zone should frighten the fish away from the
barrier, without causing damage to the fish. The barrier should, however, be
able to stop fish from swimming directly through the electrified area. To
produce the most efficient electric field pattern to block the passage of fish
in a free flowing stream, it is desirable to produce a pattern with electric
field lines running in the same direction as the normal migration of the fish.
Because fish normally swim with their heads pointed into the water flow, the
most effective field pattern is one where the field lines exist in an
upstream-downstream direction in relation to the water flow and are parallel
in relation to the top and bottom surfaces. This type of field pattern
produces a maximum head-to-tail voltage across the fish, transferring maximum
power from the water to the fish.