Smith-Root ELECTROFISHING BOATS, User Manual, Page: 46 / 53

44
2007
ELECTROfISHING
BOATS
For many years it has been known that fish react to
electric current passed through water. Electricity was
first used for fishing in 1863 when a British patent
was granted. Major efforts to apply electricity as a
tool in fisheries management did not occur until after
1950. Since then detailed studies have been made
on the physiological effects of electricity on aquatic
organisms.
RESPONSE Of fISH TO ELECTRICITY
To collect fish by electrical means we must create an
electrified zone of sufficient amplitude to stun fish. In
the basic electrofishing circuit, shown in Figure 10, a
current is passed between submerged electrodes. A fish
between these electrodes forms part of a closed circuit
and some current flows through its body.
The effectiveness of the electrofisher is affected by nine
factors: voltage, electrode shape, water conductivity,
water temperature, conductivity of the stream bed, fish’s
distance, size, species, and time in the field.
If these environmental factors are too far out of line, poor
electrofishing will result. To some extent, the effects of
changes in water conductivity may be compensated for
by changing the output voltage.
WATER CONDUCTIVITY
The conductivity of the water and that of the fish’s flesh
are the factors that affect electrofishing most.
The conductivity of water depends on the quantity
of dissolved salts and minerals in the water. The
conductivity of potable waters in the United States ranges
from 20 to 2,000 microSiemens/centimeter. Sufficient
current at realistic power levels will flow through water
in this range to electrofish successfully.
Figure 11 illustrates the field patterns caused by the
presence of a fish in water. In (a) no distortion is caused
by the presence of the fish. In low conductivity water,
(b), the distortion of the electric field is such that the
voltage near the fish is less than it was before the fish
was present. The reverse is true in (c) where the water
conductivity is more than that of the fish. In this case
the distortion is caused by the current concentrating in
the water surrounding the fish. In both (b) and (c) not as
much power is transferred into the fish’s body as in (a).
ELECTROfISHING PRINCIPLES
Electrode
Water
Electrical Field
Voltage Source
Electrode
Figure 10. The basic electrofishing circuit.
0 1 2 3 4 5 6 7 8 9 10
Volts
2V
0 1 2 3 4 5 6 7 8 9 10
Volts
8V
b. Fish more conductive c. Water more conductive
100mm
0 1 2 3 4 5 6 7 8 9 10
Volts
5.3V
a. Equal conductivities
53mm
Figure 11. Electric field patterns caused by fish.