7124

• UCREFRP Catalog Number: 7124
• Author: McAda, C. W. and R. S. Wydoski.
• Title: Technical Papers
• USFW Year: 1980.
• USFW - Doc Type: \
• Copyright Material: YES

,

Table 1
Boundary Values of Electric Field Parameters

Pulse Minimum I Puhe Minimum
Frequeucy length CeDeraror reaction F requeDcy leDgtb reaction
(1), Hz outputyol lDtensity (I), Hz (T), "m. iDteDSlty
(T),Im, (lJI,V EI. Vfcm (El. Vfcm
20 0,12 250 0,161:0,010 , 100 I 0,12 250 10'106:0'009
0,60 j50 0,094:0,08 0,60 125 0,046:0,005
1,50 100 0,061:0,004 1,50 162 0,051:0,004
2,00 100 0,06:0,002 2,00 160 0,05:0,002

simultaneously) turned on, ~fter a certain time had passed the number
in !:he net bag was counted, 'The current was varied from experiment to

RESULTS

::

Effect of physical fields on fish. The electric field caused great excitation
in schools of Baltic herring, increasing their motor activity and causing them to
swim rapidly to the area with the lowest field intensity. An "excitation wave"
floved through the school (Radakov, 1972): individual fish reacting before the
others formed two or three small groups in which "the "wave of movement" had a
steeper trajectory'than ,for. the main ~chool, These groups consisted of 6 to 10
fish located 3 m from the electrodes/which turned 'from the radial path and attached
themselves to one flank of the main school, Once they had reached the safe area,
the herring reassembled in the school and swam in a circle, not approaching the
electrodes more closely than 3 meters. The nature of the reaction did not change
with repeated application of the field. Table 1 shows the minimum values of elec-
tric field parameters which.caused the school to swim to the area with 'lowest field
intensity (center of holding net),

~

When the acoustic field was turned on, the school dispersed. The overall
tion of the school did not change, but individual fish changed their direction.
The intensity of ~he~eaction increased with decreasing frequency. The mean time
of adaptation of the herring to an acoustic field at 50 Hz was about 4,3 s, at 300
Hz - 2,6 s. By the third time the field was switched on,/the school no longer re-
acted to it, It was found that a frequency F of 800 Hz caused the school to move
-"lDOre slowly, seeming to hand in space while spreading apart, Some of the fish
separated into a smaller school which swam slowly in a circle, gradually approach-
jng the sound source, These fish then rejoined the main school, which also swam
;in a circle around the sound source,' After the sound was turned off, the school
became more compact and began to move more rapidly, The results of school
observation in an acoustic field are presented in Table 2,

The use of both fields caused significant spreading of the school, reorienta-
tion from .the source of sound and an increase in motor activity, Some individual
fish oriented themselves along equipotential electric field lines, The school of
Baltic herring moved rapidly away from the radiating surfaces at lower radiated
power, As would be expected, addition of the acoustic stimulus increased the
sensitivity of the school (Protasov, 1976). The results of these experiments are
shown in Table 3, Figure 1 shows curves of electric field intensity as a function
of pulse length -E='t('I), for pulse repetition frequencies f = 100 Hz and f = 20
Hz, We can see irom,Figure 1 that with the pulse length .=1,5 ms which is used in
fishing the electric field intensity causing a reaction among herring differs very
little for f=100 Hz and f=20 Hz. Consequently, to decrease the power consumption
while producing a clear .response reaction it would be desirable to use electric
pulses with a repetition frequency of f=20 Hz and a length 'of 1.5 ms, electric
field intensity 0.06 V/cm, Figure 1 gives a clear idea of how the pulse length
repetition frequency influence the sensitivity of the school, At a repetition

136

Frequency, F,
Hz

1000

"Pilot whale"
radiator

75

100

125

150

175

Table 2
Behavior of Baltic Herring School in Acoustic Field

Behavior of herring in school in acoustic field

1) When sound was turned on, school rapidly swam away
from the radiator
2) Some individuals turned against the general move-
ment of the school
3) Repeated sound caused no reaction
1) Slight spreading of school when soun~ was turned
on
2) Reorientation of direction of school movement
3) No repeated reaction observed
1) Slight alarm reaction
2) No reorientation of fish
3) No repeat reaction
1) When sound started, school changed direction of
movement.
2) Restarting of sound caused no reaction
1) Slight spreading of school when sound was turned
on
2) School did not change direction of motion
3) No repeat reaction
1) No spreading of school observed
2) No reorientation of fish
3) No reaction to repeated sound
1) When sound was turned on, school spread out, form-
ing smaller schools, reorientation of direction
pf motion

Table 3

Minimum Electric Field Parameters When Used with Acoustic
Stimulus

FrequeDCY lPulse I C......ter I }~te:;\:r_ FrequeDcy I Pulse I c.....tor /'form;.?:
Hz ength output volt- ft'Jum re- length output voh- mum re"
(I), (T),msag.(UI.V lEi.~'f';'" (I),Hz (T).mSag.(U),V ;~~n

2C g;~ ~g I g:6~~;g;~~ ., 100 I g:M I ~ g,::g,~
1,50 ,87 0,048:0,003 1,50 87 0;044:0:014
2,00 0,052:0,002 2,00 0,052: 0,002

Mean
adaptation
time, B

3.9

3.2

3.0

2.8

3,1

84.3

f~equency of f=20 Hz the difference (due to the application of the additional
a~oustic field) varies from 7 to 18%m at repetition frequency f=100 Hz -- from 3
to 6%.

Determination of this dependence for commercially significant fish allows not
only a decrease in power consumption, but also an increase in the fishing effective-
ness of the use of combined electric and acoustic fields,

'The desirability of using a single physical stimulus or a combination of stim-
uli was determined in the second stage of the research separately for the effec-
tiveness of herding fish into traps and the effectiveness of holding them in the
catch area,

137