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

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Table 4

Herring Caught by Gill Net When Exposed to Physical
Fields Moving at Different Speeds

Fields used

Elec:tric field
Pulsed acoustic field
Both fields

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Pulse length (-r), ms

Herring caught at
various speeds,
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9,15 I 0.25 0,5

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Total DO.
. of fish

18
13
29

155
44
323

Fig. 1

'-----~Fig. 1, Threshold sensitivity as a function
etition frequencies 20 (1) and 100 (3) Hz; 2
added.

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00,02 0,05 D,f.. Il,fll 0, 18
Electric field iII1:eliSi.:y
(E), V/cm
Hokuug m;;-e (t). S
1 2 J 1/ 5 6
01 J I I I J I
6 12 16 21/ JO J6
Fish cODCeDtratioD per uD.lt
volume (n!V)

Fig,2

of pulse length E='l'('t) for pulse rep-
and 4, same but with acoustic stimulus

Fig. 2, Number offish retained in catch area as a function of stimulus.

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1) Electric field intensity; 2) electric field intensity with additional acoustic
field; 3) time of holding of fish in electric field; 4) time of holding of fish in
combined electric and acoustic fields; 5) concentration of fish per unit volume
(specimens per cubic meter).

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Herding fish into tpape. The combined results of experiments studying the ef-
fect of the fields used on Baltic herring are presented in Table 4, As we can see
from the table, in all experiments using the combined electric and acoustic fields
tbe number of fish caught was greater than when a single stimulus was used, Using
the average data for all three field movement speeds, the combination of electric
and acoustic fields yielded a catch approximately twice as great as the electric

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field alone. The best and most stable result in all experiments was obtained by
the combined application of both fields (in the pool) with the beam moving at 0.15
mls by a factor of approximately 2.6, increasing the speed to 0,5 mls decreased the
catch by a factor of 7.3, We can assume however that in the open sea this speed
could be significantly higher, since it would be in addition to the speed of the
fish schools themselves,

The use of the combined pulsed electric and acoustic fields decreases the power
consumption required by 8.4% in comparison to the pulsed electric field alone.

Holding of fish in the oatoh zone. Holding of fish was studied by means of an
electric field and a combination of electric and acoustic fields as a function of
the electric field intensity (E), holding time (t) and concentration of fish per
unit volume (n/V, where n is the number of fish, V is the volume of space limited
by the field). The results are shown in Fig. 2. As we can see from these graphs
(curves 1 and 2) as the field intensity increases the holding power of the electric
and combined electric and acoustic fields first increases, then as the area of
anodic reaction is reached within the space limited by the fiel~, it decreases.
The holding point is shifted upon combined application of electric and acoustic
fields by approximately 0.03 V/cm in the direction of lower intensity, confirming
the hypothesis that tbe combined action of bot~ fields increases sensitivity. The
number of fish held was 16% for the two fields, 72% for the electric field.

The influence of holding time on departure of fish from the space surrounded
by the electric field decreases with increasing time (Fig. 2, curve 3). This can
be explained by the fact that after they have spent some time in the vicinity of
the field, the fish begin to avoid-tontactwith the surrounding field, (Curve 4,
Fig. 2) shows that the combination of two fields has little influence on the hold-
ing ability, and all fish gradually leave the space surrounded by the field.

The study showed that the holding power of an electric field on Baltic herring
depends on the size of the surrounded space, i.e., there is a certain limit of
concerntration (in..this case 25 to 30 fish per cubic meter) and catching of the
fish should be started before the limit is reached.

CONCLUSIONS

1. Application of two stimuli to a school of Baltic herring - electric and
acoustic -- increases the sensitivity of the fish in comparison to the action of
the electric stimulus alone.

2. Comparative studies of the properties of the electric and acoustic fields
for herding of Baltic herring into fish traps showed good effectiveness of the
combined fields, with a decrease in the total power consumption required by at
least 8.4%,

3. A study of the effectiveness of electric and combined electric and acoustic
fields for holding of fish in a catch (trap) zone showed that the electric field
alone was quite effective.

Submitted March 19, 1981

REFERENCES

Gyul'badamov, S.B, 1958, Primeneniye elektricheskogo toka v rybolovstvye. (Use
of electric current in fishing). Moscow: Znaniye Press, 79 pp.
Mironov, A.T. 1948, Electric current at sea and its effect on fish. Tr, Morsk.
gidrofizich, in-ta, Vol. 1, pp. 134-152. .
Nikonorov, I.V. 1968, Nepreryvniy sposov lova ryby. (A continuous method of
catching fish), Moscow: Pishchevaya promyshlen Press, 103 pp,
Priss, V.N, 1976. Second National Conference on Mariculture. Rybn. kb-vo, No,
6, pp. 89-91,

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