RESEARCH ON THE LURING OF FISH SCHOOLS BY UTILIZING UNDERWATER ACOUSTICAL EQUIPMENT

YOSHINOBU MANIWA, YOSHIMI HATAKEYAMA and HISAJU MOTEGI

Fishing Boat Laboratory Fishery Agency Tokyo, Japan

ABSTRACT UNDERWATER ACOUSTICAL EQUIPMENT

The device for gathering fish schools by using underwater acoustical equipment was conceived on the idea that if fish schools could be lured to a location and driven into a fish net by emitting the effective sound, fishing efficiency could be increased. The underwater sound pro- jector of a flat frequency response from 150Hz up to 4,500Hz was produced, corre- sponding to acoustic features of fish. Yellowtail responded to their swimming and bait eating sound of 5-17dB re 1 ubar. The catch of squid was definitely more for the periods of emitting effective sound than for the periods of not emitting sound. Mackerel and jack mackerel responded to its swimming and bait eating sound of higher than 22dB and ascended. In the stationary net fishing, fish was lured by sound into the net and the big catch never got before was obtained.

INTRODUCTION

The underwater acoustical equipment consisted of an amplifier, a tape recorder, an oscillator and an underwater sound projector.

The first transducer was made of barium titanate. The general frequency response, which was compensated by the power amplifier, was flat in the range of 500-7,000Hz. Generally, the lowest threshold of auditory capacities of fish is in the frequency range below 1,000Hz and besides the main component of sound produced by fish is in the similar range. Taking these acoustic features of fish into consideration, a dynamic sound projector was produced. It has a flat frequency response with deviation of 42dB from 150Hz up to 4,500Hz as shown in Fig.1. The impedance of projector is 16 ohms at 1,000Hz. The projector source level is 60 dB re 1 ubar at 1 meter at 1,000Hz. The beam pattern is omnidirectional at the frequency range less than.3,OOOHz. The depth capability is 70 meters.

The response of fish schools to sound is very much interesting. The device for luring fish schools by using underwater acoustical equipment is being researched in order to increase catch of fish.

A special underwater sound projector was produced. It has a flat frequency response from 150Hz up to 4,500Hz.

Experiments have been performed on many species of fish, such as carp, yellowtail, mackerel, jack mackerel, squid, sea bream, salmon, trout, etc. by 0.1 0.2 0.5 2 2 emitting effective sound from the pro-

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jector. It has been confirmed that the device is useful for the increase of catch in squid fishing. And :xperiments Fig.1 Frequency response characteristic are being performed for practical use in of the underwater dynamic sound stationary net fishery and purse seining projector. OdB re 1 ubar/V at and so on. It is important to find 1 meter. effective sound and the effective pressure level of sound.

Frequemy Kls’z

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EXPERIMENTS ON THE LURING OF FISH SCHOOLS

Experiments on the lur ing of f ish schools have been carrked on by u t i l i z i n g the underwater acous t ica l equipment. It is very impor tan t to f ind ou t the e f f e c t i v e sound. The effect ive underwater sound was de tec t ed by a hydrophone and tape recorded, and the recorded sound was a r r a n g e d t o b e u s e f u l t o c o n t r o l f i s h schools . This tape was played back on a tape recorder and emi t ted in to the sea water through the sound p ro jec to r .

(1) Yellowtai l

Yel lowta i l responded to the i r s w i m - ming and b a i t e a t i n g sound of the level of 5-17dB re 1 ubar. These schools were lu red up t o 1 0 meters depth from 50-80 meters

is u s e f u l t o i n c r e a s e t h e e f f i c i e n c y o f the angl ing . The frequency spectrum of sound i s shown i n F i g . 2 .

epth a t the f ishing ground. The device

0.2 0.5. 1 2 4 Frequency KHz

Fig.2 Frequency spectrum of swimming and b a i t e a t i n g sound of young ye l lowta i l .

(2 ) Squid

A number of experiments on squid f i s h i n g h ve been carr ied on since 1969 . They swam upward r e spond ing t o i n t e r - mi t ten t pure tone of about 600Hz, and more squid were caught by angling on t h e research boat than on the others . Based on t h e f a c t t h a t t h e c a t c h i n c r e a s e d when t h e f i sh ing boa t goes as tern, such underwater sound produced by the boa t are conceived t o be ava i l ab le a lso.

The experiments were performed on the research boa t on the deck of which squid f ishing machines were equipped, a t Yamato- t a i f ishing ground in Japan Sea i n 1971. Effect ive sound was emi t t ed fo r t en minutes and then not emitted for next ten minutes. These periods were repeated and numbers of squid.caught by angl ing were counted for each period. The numbers of caught squid were d e f i n i t e l y more f o r t h e per iods of emit t ing sound t h a n f o r t h e

per iods of not emit t ing sound. One of examples i s shown i n F i g . 3 . The inc rease percentage is 6 0 % . I n some case it i s 1 0 0 %.

These experiments were performed a t n i g h t by adding e f fec t o f sound t o f i s h lamps, s i n c e the angl ing i s operated usua l ly a t n ight . Addi t iona l ly , the similar experiments were s u c c e s s f u l i n t h e daytime.

0 200 0 3w a m T5.m

Fig.3 Numbers of squid caught in the case of emi t t i ng sound and those i n t h e case o f no t emitt ing sound. White p a r t : i n t h e case of no t

emitting sound, t o t a l i s 482. Obl ique l ines par t : kn t h e case of

emit t ing sound, t o t a l i s 774. Increase percentage i s 60%.

(3) Mackerel and jack mackerel

It is d i f f i c u l t t o c a t c h f i s h s c h o o l s c l o s e l y on the sea bottom by a purse seiner , because the net i s damaged by rocks. So it i s n e c e s s a r y t o r a i s e f i s h schools away from the bottom by some device. And i f f i s h s c h o o l s are gathered, t he pu r se s e in ing and t he ang l ing become easy. The acous t i ca l dev ice is expected f o r t h e s e o b j e c t s .

Experiments on mackerel and jack mackerel have been carried on s i n c e 1 9 6 6 .

Mackerel responded t o t h e i r swimming and b a i t e a t i n g sound of the level of about 22dB. Schools of mackerel were lured by t h i s sound a t the f ishing ground. The frequency spectrum of the sound is shown i n Fig.4.

Experiments on the pu r se s e in ing were c a r r i e d on f i r s t i n December 1971. Mackerel schools which appeared a t t h e depth of 80 meters were lu red nea r t he p ro jec to r hung a t t h e d e p t h o f 30 meters, r e spond ing t o t he i r swimming and b a i t eat ing sound, as shown in F ig .5 . As t he p ro jec to r w a s ra ised towards the sea

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scrface and hung at ,the depth of 10 meters, fish schools ascended following the projector.

G,1 0.2 0.5 1 2 5 .8 Frequency KHz

Fig.4 Frequency spectrum of swimming and bait eating sound of mackerel.

Fig.5 Echo traces of fish finder during sound emission. Mackerel schools were lured near the underwater sound projector hung at the depth of 30 meters. As the projector was raised towards the depth of 10 meters, fish schools ascended, following the projector.

Fig.6 shows that fish schools which appeared near the bottom ascended by 30 meters away from it. These fish schools might be easily caught by the appropriate net.

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Fiq.6 Echo traces of fish finder during sound emission. Mackerel schools ascended away by 30 meters from the bottom.

( 4 ) Stationary net fishery

Stationary nets on which experiments were performed are shown in Fig.7. Fish schools enter into the bag net, following arrows. In order to convert this to an active fishery, application of the under- water sound projector system has been tried. The system consists of plural sound projectors. Examples of arrangement of projectors are shown in Fig.7. Effective sound is emitted from the projectors in order of A, B and C.

Experiments were performed on this system at the stationary net as shown in Fig.7(a), in September 1971. By emitting swimming and bait eating sound of vellow- tail, catch of young yellowtail, round herring, etc. increased.

Experiments were performed at the salmon stationary net as shown in Fig.7 (b), in October 1971. Swimming and bait eating sound of pink salmon, the frequency spectrum of which is shown in Fig.8. Amount of fish entering into the right bag net was generally very small. But by application of the system, much bigger amount of fish entered into that bag net, compared with ordinary catch.

Experiments on jack mackerel were carried on in November 1972. Usually, those fish schools ascended only by 10 meters above the sea bottom. But they ascended by 20-40 meters, responding to swimming and bait eating sound of mackerel.

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CONCLUSION trap ne t sec0r.d

play ground bag n ~ t bag net I

I

(a) Ordinary Stationary net.

(b) Salmon stationary net.

Fig.7 Stationary nets on which experiments were performed.

The special underwater sound projector applicable to fishery was produced. By utilizing the underwater acoustical equipment, the luring of yellowtail, mackerel, jack mackerel, squid, salmon, etc. was proven to be successful.

As it was confirmed that the device was effective to increase catch in squid angling, it is practically used. Possibility of practical uses in purse seining of mackerel and jack mackerel and stationary net fishery was found out also.

Additionary, application to the cultural fishery is planned.

ACKNOWLEDGEMENT

The authors wish to thank Prof. T. Hashimoto, the Shibaura Institute of Technology, who directed the authors, and Assist. Prof. H. Suzuki, the Tokyo University of Fisheries, who cooperated.

REFERENCES

HASHIMOTO T. and MANIWA Y. Research on the Luring of Fish Schools by Utilizing Underwater Acoustical Equipment. Marine Bio-Acoustics, V01.2, 93p (1967). Modern Fishing Gear of the World 3, FAO, 501p (1971).

Fig.8 Frequency spectrum of swimming and bait eating sound of pink salmon.

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