7116 ‎(2)‎

• UCREFRP Catalog Number: 7116
• Author: Baxter, G. and J. Simon
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1970
• Copyright Material: YES

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DIRECT CURRENT = - - - - -
ALTERNATE CURRENT - -

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Fig. 4, Current line density needed for attraction of different fish species with direct and alternating current (data from Steroio
el al., 1972).

attracting the fish. By choosing the proper output
effect, the zone of attraction can therefore be
larger with constant than with pulsed direct
current. The total fishing zone (including the
immobilization zone) is, however, always larger
with pulsed direct current. The former case might
under certain circumstances be advantageous.
The physiological effect of pulsed direct current
is. positively correlated with both frequency
(Sternin et al., 1972; Hickley, 1985) and pulse
length and is related to the duty cycle (fre-
quency x pulse length) according to a power
function (Fig. 5). With a duty cycle exceeding 0.2
(1.0 = constant current) the effect of pulsed cur-
rent surpasses that of constant current. The field
strength needed for immobilisation is asymptoti-
cally reaching a minimum value at higher fre-
quences (for roach 0.2 vfcm at frequencies> 50
Hz; Hickley, 1985).

When increasing the pulse length the attraction
radius of the anode will asymptotically reach a
value, which is dependent upon frequency, fish
size and water conductivity. This value varies
between 0.1 and 5 mS (Vibert, 1967; Sternin
et aI., 1972). As, however, the effect needed in-
creases linearly with the pulse length, an optimum
pulse length (considering fishing efficiency and
energy consumption) of 0.5-1.0 mS (10-40 Hz)
is achieved.
The effect of varying the shape of the pulse is
largely unknown. Vibert (1967) states, that con-
denser pulses (having a fast voltage increase and
a slow decrease, cf. Fig. 2f) produce the largest
effects. Sterninet al. (1972), however, were unable
,
to find any empirical evidence for this statement.
The size and the material of the electrodes
determine the current line density and the strength
and corrosion resistance of the electrodes.