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The role of sound in the British Columbia troll salmon fishery 1982

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THE ROLE OF SOUND IN THE BRITISH COLUMBIA TROLL SALMON FISHERY by DAVID ROSS BOYES .Sc., The University of B r i t i s h Columbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPT. OF AGRICULTURAL MECHANICS We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1982 ® David Ross Boyes 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. David R. Boyes Department of A g r i c u l t u r a l Mechanics The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date January 24 1983 ACKNOWLEDGEMENTS T h a n k s a r e due K e r v B l a c k o f t h e D e f e n s e R e s e a r c h E s t a b l i s h m e n t P a c i f i c f o r c a l i b r a t i n g and e s t a b l i s h i n g t h e f r e q u e n c y r e s p o n s e o f t h e r e c o r d i n g and p l a y b a c k e q u i p m e n t used i n t h i s s t u d y . E r r o l Cramer and Dave H a b l e o f Cramer E n g i n e e r i n g p r o v i d e d t e c h n i c a l a d v i c e and a s s i s t a n c e i n t h e d e s i g n and a s s e m b l y o f t h e e q u i p m e n t . J o h n F o r d o f UBC made a v a i l a b l e t h e s p e c t r u m a n a l y z e r and g a v e o f h i s e x p e r t i s e i n m a r i n e b i o - a c o u s t i c s . J u d y M c L a r e n a s s i s t e d i n t h e s e a t r i a l s . D r . R o b e r t B l a k e and my s u p e r v i s o r D r . J o h n Z a h r a d n i k gave s u p p o r t and g u i d a n c e f o r t h e p r o j e c t . F i n a l l y , I am g r a t e f u l t o t h e M i n i s t r y o f E d u c a t i o n , V i c t o r i a , f o r p a r t i a l f u n d i n g u n d e r t h e G.R.E.A.T. p r o g r a m . ABSTRACT Sparked by anecdotal accounts of boat noise i n f l u e n c i n g the c a t c h r a t e s of commercial salmon t r o l l e r s on the B.C. c o a s t , a c o u s t i c a l s t u d i e s of both boats and f i s h were undertaken. The study was in four p a r t s : 1. A c o u s t i c a l output of salmon t r o l l e r s : Recordings were made of t r o l l v e s s e l s and examined on a spectrum a n a l y z e r . Sonic output was predominantly of low frequency, under 300Hz. Output l e v e l s at t r o l l i n g speed (l-2m/s) were about 20dB r e l y b a r at lmeter from the h u l l . Higher frequency spikes (1-2.5kHz) were observed with o p e r a t i o n of h y d r a u l i c pumps f o r a u x i l i a r y equipment. Broadband, t r a n s i e n t output (approximately l-6kHz), was thought to be c o r r e l a t e d with c a v i t a t i o n from p r o p e l l o r s . 2. F i s h sounds: Recordings were made of h e r r i n g , salmon and rainbow t r o u t swimming r a p i d l y and feeding on p e l l e t s i n net pen e n c l o s u r e s . These were examined on a spectrum a n a l y z e r . Two types of sounds were e v i d e n t , "knocks" and " s c r a t c h e s " . Knocks were c o r r e l a t e d with r a p i d swimming and maneuvering and are l i k e l y of hydrodynamic o r i g i n . Scratches were thought to be produced by branch i a t e and s k e l e t a l movements and were r e l a t i v e l y f a i n t . Knocks were l-2kHz, s c r a t c h e s 3.5-5.5kHz. The dominant sounds in a c t i v e l y f e e d i n g , subsurface salmonids, were knocks. Recordings of feeding schools sounded remarkably l i k e t r i c k l i n g water to the human ear. i v 3 . A t t r a c t i n g salmon in net pens: Attempts were made to l u r e coho (Oncorhynchus k i s u t c h ) and chinook (Oncorhynchus tschawy tscha) as w e l l as rainbov/ t r o u t (Salmo g a i r d n e r i ) to a speaker p r o j e c t i n g recorded feeding sounds of the t a r g e t f i s h . No responses of any kind were observed to output l e v e l s as high as 55dB re l u b a r at lmeter. 4 . A t t r a c t i n g salmon at sea: Recorded and simulated f e e d i n g and swimming sounds of salmonids were p r o j e c t e d w i t h i n the gear a r r a y of a commercial salmon t r o l l e r f i s h i n g on the west coast of Vancouver I s l a n d , B.C. Catch r a t e s were monitored with the t e s t sounds on and o f f . Output l e v e l was 55dB re ILI bar at l meter. No s i g n i f i c a n t change in catch rate was observed in response to the t e s t sounds. TABLE OF CONTENTS Page ACKNOWLEDGMENTS i i ABSTRACT i i i TABLE OF CONTENTS v LIST OF FIGURES v i LIST OF TABLES v i i i 1.0 INTRODUCTION 1 1.1 JUSTIFICATION 1 1.2 LITERATURE REVIEW 6 1.3 MORPHOLOGY & ACUITY OF HEARING IN FISH 12 1.4 SOUND IN THE SEA 18 1.5 OBJECTIVES OF THE STUDY 25 2.0 THEORY FORMATION AND EXPERIMENTAL DESIGN 28 2.1 THEORY FORMATION 28 2.2 EXPERIMENTAL DESIGN 28 3.0 METHODS AND MATERIALS 31 3.1 RECORDING, PLAYBACK AND ANALYTICAL EQUIPMENT ... 31 3.2 RECORDINGS OF TROLLERS 34 3.3 RECORDINGS OF FISH 37 3.4 PLAYBACK IN PENS AND AT SEA 37 4.0 RESULTS AND DISCUSSION 43 4.1 RECORDINGS OF TROLLERS 43 4.2 RECORDINGS OF FISH 50 4.3 PLAYBACK IN PENS 53 4.4 PLAYBACK AT SEA 55 4.5 GENERAL DISCUSSION 63 5.0 CONCLUSIONS 68 6.0 SUGGESTIONS FOR FUTURE WORK 70 7.0 LITERATURE CITED 72 v i LIST OF FIGURES Page 1-1 The standard gear array of a B.C. salmon t r o l l e r . 2 1-2 Some t e r m i n a l l u r e s used i n the B.C. t r o l l f i s h e r y . 3 1-3 A u d i t o r y t h r e s h o l d s of three o s t a r i o p h y s i n e s p e c i e s . 14 1-4 A u d i t o r y t h r e s h o l d s of three n o n - o s t a r i o p h y s i n e species.14 1-5 A u d i t o r y t h r e s h o l d s of three n o n - o s t a r i o p h y s i n e species.15 1-6 A p l o t of p a r t i c l e displacement vs. d i s t a n c e from a monopole sound source. 24 1-7 A composite i l l u s t r a t i o n of oceanic ambient n o i s e . 27 3-1 Measured s e n s i t i v i t y of a Sparton 60 LX 123 hydrophone and p r e a m p l i f i e r . 32 3-2 The noise r e d u c t i o n c i r c u i t of the hydrophone power supply. 33 3-3 Measured output of the Aquavox VW 60 loudspeaker. 35 36 3-4 Low pass f i l t e r used with complex sound generator to produce T e s t Tape I I . 3-5 The p o s i t i o n of the sound p r o j e c t o r w i t h i n the gear a r r a y d u r i n g t r i a l s . 38 3-6 Sonogram of T e s t Tape I; a r e c o r d i n g of t r i c k l i n g water.40 3-7 Sonogram of Test Tape I I ; i r r e g u l a r l y pulsed output of a n o i s e generator c y c l i n g at 28 Hz. 41 3- 8 Sonogram of Test Tape I I I ; feeding sounds of rainbow t r o u t (2.5-3kg). 42 4- 1 Sonogram of a 10m wooden t r o l l e r at a slow t r o l l i n g speed (1.5 m/s). 44 4-2 Sonogram of a 10m wooden t r o l l e r at a f a s t t r o l l i n g speed (2 m/s) . 45 4-3 Sonogram of a 10m wooden t r o l l e r at tuna speed (4-5 m/s). 46 4-4 Sonogram of a 14.5m wooden t r o l l e r at a slow t r o l l with h y d r a u l i c l y d r i v e n r e f r i g e r a t i o n compressor o p e r a t i n g . 47 4-5 Sonogram of the authors v e s s e l (13.1m), used in the sea t r i a l s , at a slow t r o l l . 49 v i i Page L i s t of F i g u r e s (Continued) 4-6 Sonogram of h e r r i n g " s c r a t c h e s " . 51 4-7 Sonoyram of h e r r i n g "knocks". 52 4-8 Sonogram of j u v e n i l e coho salmon a c t i v e l y f e e d i n g . 54 4-9 Sonogram of k i l l e r whale t a i l beats dur i n g r a p i d a c c e l e r a t i o n . 66 v i i i LIST OF TABLES Page 1-1 Conversion table for reference sound l e v e l s . 19 4-1 Salmon catch during cycled playback of Test Tape I. 57 4-2 Salmon catch during cycled playback of Test Tape II. 59 4-3 Salmon catch during cycled playback of Test Tape I I I . 61 1 1.0 INTRODUCTION 1.1 JUSTIFICATION There are about 2200 v e s s e l s that f i s h f o r P a c i f i c salmons (Oncorhynchus spp.) on the B r i t i s h Columbia coast by means of t r o l l gear. In the past coho (0. k i s u t c h ) and chinook ( 0 . tschawytscha) were the p r i n c i p a l t a r g e t s p e c i e s of t h i s f l e e t but d e c l i n i n g stocks of these f i s h have r e d i r e c t e d e f f o r t to p ink ( 0 . gorbuscha) and to a l e s s e r extent sockeye (0. nerka) and chum (0. keta) salmon. T r o l l e r s f i s h p r i m a r i l y in outside waters from the Washington border to Dixon entrance as the f i s h must be a c t i v e l y f e e d i n g f o r capture by t h i s gear and salmon g e n e r a l l y forego food as they approach t h e i r parent stream. T r o l l v e s s e l s use a r t i f i c i a l l u r e s and b a i t s rigged to r o l l , f l u t t e r or dodge as they are p u l l e d through the water a t 1-2 m/s. A high degree of s k i l l i s r e q u i r e d in the p r e p a r a t i o n and p r e s e n t a t i o n of l u r e s , p a r t i c u l a r l y to l a r g e r , o l d e r coho and s p r i n g salmon to tempt them to b i t e . The b a s i c f i s h i n g r i g of a t r o l l e r i s shown i n F i g . 1 - 1 , while some l u r e s are shown i n F i g . 1 - 2 . Anecdotal evidence suggests that sound has an i n f l u e n c e on the catch r a t e of t r o l l e r s . Experienced fishermen b e l i e v e that components of the boats d r i v e t r a i n and s t e e r i n g gear can a f f e c t f i s h i n g s u c c e s s . Care i s taken to ensure that engine and s h a f t alignment i s true and that intermediate and s t e r n bearings are t i g h t and w e l l l u b r i c a t e d . P r o p e l l e r s are examined r e g u l a r l y to ensure they are undamaged and balanced. Many t r o l l e r s p r e f e r a four bladed p r o p e l l e r to a three bladed 2 FIGURE 1-1. The standard gear array of a B.C. salmon tr o l l e r . The vessel fishes two of each line shown, a set from each pole. 3 FIGURE 1-2. Some terminal lures used in the British Columbia t r o l l salmon fishery. A. Flasher and hootchie. B. Plugs. C. Spoons. one, f e e l i n g they are q u i e t e r and thus " f i s h i e r " . T i g h t rudder stock bearings are a l s o thought necessary for best r e s u l t s . Some t r o l l e r s f e e l that gas engines f i s h b e t t e r than d i e s e l s because of smoother, q u i e t e r performance. O f t e n , fishermen monitor the c a t c h r a t e of the l u r e s c l o s e s t to the boat as an index of t h e i r v e s s e l s s o n i c performance. There i s no agreement whether these p r e c a u t i o n s guard a g a i n s t p r o d u c t i o n of r e p u l s i v e sounds or ensure output of a t t r a c t i v e ones. The range of a l t e r n a t i v e e x p l a n a t i o n s f o r a boat with the " r i g h t " sounds o u t f i s h i n g one with the "wrong" sounds i n c l u d e : 1/ An i n c r e a s e i n the p r o p e n s i t y of f i s h , otherwise aware of the gear, to a t t a c k i t through a s s o c i a t i o n of the boat sounds with a fe e d i n g o p p o r t u n i t y . This might be due to s i m i l a r i t i e s between boat sounds and b a i t f i s h or feeding sounds. 2 / An increase in the area of i n f l u e n c e of the gear; that i s , f i s h t h a t would not otherwise have sensed the gear's presence becoming aware of i t by homing on the sound source. 3 / both of the above. 4 / Absence of f r e q u e n c i e s or p a t t e r n s in the boat's s o n i c output that cause i n h i b i t i o n of feeding a c t i v i t y amongst f i s h in the path of the gear. Such sounds might resemble those of salmon p r e d a t o r s . 5 / Absence of f r e q u e n c i e s or p a t t e r n s causing a c t i v e r e p u l s i o n of f i s h from the v i c i n i t y of the gear before they can otherwise sense i t ' s presence. 6 / Both 4 and 5 . The feeding behavior of salmon at sea suggest that sound may be important in prey l o c a t i o n and c a p t u r e . Spring salmon i n p a r t i c u l a r , but a l s o coho, are o f t e n taken at c o n s i d e r a b l e depths (100fathoms). These salmon feed p r i m a r i l y on small s c h o o l i n g s p e c i e s such as h e r r i n g (Clupea harengus), and sand lance (Amnodytes hexapterus). In the t u r b i d c o a s t a l waters of B.C. l i g h t p e n e t r a t i o n i s r e s t r i c t e d by dense phyto and zooplankton blooms in the "mixed l a y e r " as w e l l as suspended m a t e r i a l from r u n o f f . T h i s i s p a r t i c u l a r l y so i n the s p r i n g and summer. Salmon o f t e n feed most a c t i v e l y at dawn and dusk when the l i g h t f i e l d i s f u r t h e r attenuated. V i s i o n can be u s e f u l o n l y at s h o r t range under these c o n d i t i o n s . Considerable turbulence i s a l s o a f e a t u r e of c o a s t a l waters, as a r e s u l t of t i d a l (5-8m range) and wind generated c u r r r e n t s d r i v i n g water masses across rugged underwater topography (Thompson 1981). Thus the f i s h e s o l f a c t o r y sense i s l i k e l y u n r e l i a b l e d i r e c t i o n a l l y f o r l a c k of a smooth c o n c e n t r a t i o n g r a d i e n t . Another common o b s e r v a t i o n of t r o l l fishermen i s that catch r a t e s o f t e n suddenly i n c r e a s e (and subsequently decrease) over a l a r g e area (20 n a u t i c a l miles or more) almost i n s t a n t a n e o u s l y ; the f i s h "come on the b i t e " i n the j a r g o n . The occurrence of t h i s phenomenon i s e s t a b l i s h e d through r a d i o communication between boats. P e r i o d s of high catch r a t e are o f t e n a s s o c i a t e d with high and low s l a c k water in inshore waters, however t i d a l c u r r e n t s over o f f s h o r e banks do not stop, then reverse d i r e c t i o n i n a simple manner (Thompson 1981). F u r t h e r , such p e r i o d s often occur at the same time each day f o r s e v e r a l weeks in c e r t a i n areas (Boyes p e r s . obs.) while t i d a l c y c l e s advance an hour or 6 so each day. A c o u s t i c a l s t i m u l i nay be r e s p o n s i b l e f o r the t r a n s m i s s i o n of t h i s "feeding f r e n z y e f f e c t " over these d i s t a n c e s i n such a s h o r t time. Although concrete evidence f o r P a c i f i c salmon responding to sound i s l a c k i n g , there are many accounts of other f i s h , p a r t i c u l a r l y predatory s p e c i e s , doing so. Examples are found in the f o l l o w i n g s e c t i o n . 1.2 LITERATURE REVIEW Man has long used sound f o r a t t r a c t i n g , and f r i g h t e n i n g f i s h i n o r d e r to c a t c h them. Accounts on f i s h responding to sound can be found in the works of A r i s t o t l e and P l i n y ( c i t e d i n Moulton 1963). Parker (1918), von F r i s c h (1936), Kleerekoper and Chagron (1954), Moulton (1963, 1964), Protasov (1965), Tavolga (1971), Popper and Fay (1972), and Hawkins (1973) have reviewed the modern l i t e r a t u r e . Sounds that a t t r a c t (or r e p e l ) f i s h must have s i g n i f i c a n c e , e i t h e r learned or i n n a t e , to the animal. U s u a l l y there i s an a s s o c i a t i o n with f e e d i n g or r e p r o d u c t i v e behavior. Hook and l i n e f i s h e r i e s r e q u i r e sounds that represent feeding o p p o r t u n i t i e s to t a r g e t f i s h . These are most o f t e n in the form of prey sounds or the c h a r a c t e r i s t i c n oises of a t t a c k and feeding behavior by p r e d a t o r s . Following are a number of examples from the l i t e r a t u r e of a c o u s t i c a t t r a c t i o n or r e a c t i o n in a v a r i e t y of f i s h both c a p t i v e and w i l d . Moulton (1960) played recorded sounds of the e n g r a u l i d ( A n c h o v i e l l a choerstoma) to young, c a p t i v e j a c k s (Caranax l a t u s ) , a n a t u r a l predator of the anchovy. The jacks 7 showed "quickened swimming movements of a n o n - d i r e c t i o n a l type". Playback to C. l a t u s of i t s own pharyngeal tooth rasps "appeared to i n i t i a t e f e e d i n g r e a c t i o n s " and r e s u l t e d i n the j a c k s a c t u a l l y n i b b l i n g at the t r a n s d u c e r . H a b i t u a t i o n to the s t i m u l u s was apparent a f t e r a few minutes. Sharks have been known to appear as i f from nowhere durin g f i s h i n g o p e r a t i o n s where there are wounded, s t r u g g l i n g f i s h on l i n e s or i n n e t s . I t appears that an a b i l i t y to p e r c e i v e and home on sounds from t h i s a c t i v i t y allows them to do t h i s . S t u d i e s by Hobson (1963), Nelson and Gruber (1963), Nelson (1967), Banner (1968, 1972), Nelson et a l (1969), Myreberg _et_ _al (1969 , 1975 , 1970 ), Myreberg (1972), and Nelson and Johnson (1972, 1975) have shown that a v a r i e t y of sharks i n both the A t l a n t i c and P a c i f i c are a t t r a c t e d to sources of pulsed low-frequency sound. These may be the recorded sounds o f s t r u g g l i n g or r a p i d l y swimming f i s h or s i m u l a t i o n s e l e c t r o n i c - a l l y generated. Nelson and Johnson (1975) observed t h a t r e s i d e n t sharks i n Rangiroa a t o l l , near T a h i t i responded q u i c k l y and d i r e c t i o n a l l y to the sounds of speared, s t r u g g l i n g r e e f f i s h from s e v e r a l hundred meters away. The sharks e v e n t u a l l y came to a s s o c i a t e the noise of a d i s c h a r g i n g speargun with a p o s s i b l e meal whether or not a f i s h was h i t . Hashimoto and Maniwa (1966, 1971), and Maniwa (1975), have had success i n a t t r a c t i n g carp, y e l l o w t a i l , mackerel, sea bream, squid and even crab (no s p e c i e s names given) with playbacks of sounds these animals make durin g f e e d i n g . Carp could a l s o be a t t r a c t e d simply by "tapping the si d e of a boat with a p i e c e of s t i c k " . 8 S t e i n b e r g et^ al_ (1965), using an underwater v i d e o camera monitoring a speaker noted that y e l l o w t a i l snappers (Ocyurus chrysurus) were c o n s i s t e n t l y a t t r a c t e d to a source of p u l s e d 20Hz s i g n a l s . Iverson (1966, 1967), c o n d i t i o n e d c a p t i v e y e l l o w f i n tuna (Thunnus a l b a c a r e s ) and f a l s e a lbacore (Euthynnus a f f i n i s ) , to a food reward upon p l a y i n g a pure tone s t i m u l u s . A sudden noise or a r a p i d i n c r e a s e i n volume of a s i g n a l e l i c i t e d speedy withdrawal from the source and i t i s suggested that sound n i g h t thus be used to hold tuna in a seine while the net i s c l o s e d and pursed. Richard (1968), using remote video monitoring of an underwater speaker near B i m i n i , Bahamas, was able to a t t r a c t and i d e n t i f y e i g h t s p e c i e s of t e l e o s t s and three s p e c i e s of shark. Pulsed, pure-tone s i g n a l s , 25-50Hz were the s t i m u l u s . Notably, o n l y demersal predatory f i s h were a t t r a c t e d although herbivorous r e e f f i s h were common around the t e s t s i t e . York (1972) has demonstrated a t t r a c t i o n of s k i p j a c k (Katsuwonus pelamis) and a l b a c o r e (Thunnus alalunga) to sounds of s u r f a c e s c h o o l i n g anchovies ( E n g r a u l i s a u s t r a l i s ) . I t was found that the s p l a s h i n g sounds of the anchovies and the d i v i n g b i r d s (gannets, Sula bassana s e r r a t o r and shearwaters, P u f f i n u s g a v i a g a v i a ) , p r e y i n g on them were the predominant component of the a t t r a c t i v e r e c o r d i n g s . 9 Chapman (1975), showed that three s p e c i e s of p i s c i v o r o u s t e l e o s t s , the cod (Gadus morhua ( L . ) ) , the s a i t h e ( P o l l a c h i u s v i r e n s (L.)) and the l y t h e ( P o l l a c h i u s p o l l a c h i u s ( L . ) ) , r e s i d e n t i n Loch T o r r i d o n , S c o t l a n d , could be a t t r a c t e d by low frequency pure-tone s t i m u l i . The f i s h a l s o developed a strong p o s i t i v e response to the sounds of d i v e r s o p e n - c i r c u i t scuba gear. T h i s was thought to be a s s o c i a t e d with the s t i r r i n g up of feed by the d i v e r s a c t i v i t i e s on the bottom. E r i c k s o n (1979), found a r e l a t i o n s h i p between the a c o u s t i c spectrum of a l b a c o r e t r o l l e r s and t h e i r catch r a t e . A n a l y s i s of v e s s e l r e c o r d i n g s with r e s p e c t to w i t h i n f i s h i n g group r e l a t i v e catch r a t e s brought out a negative c o r r e l a t i o n between f i s h i n g success and sound output above 1500Hz. Spectrum peaks above t h i s frequency were a t t r i b u t e d to worn or dry p r o p e l l e r s h a f t b e a r i n g s , damaged p r o p e l l e r s and i n one case a supercharger. I t i s i n t e r e s t i n g to note that a l b a c o r e fishermen, l i k e salmon t r o l l e r s , have long held that boat and gear sounds i n f l u e n c e d catch r a t e s (the boats e l e c t r i c a l output was thought to be important a l s o - see Nomura 1980), but that t h i s study i s the f i r s t to s u b s t a n t i a t e i t . There are few accounts in the l i t e r a t u r e of salmonid response to sound. As f a r as I am aware onl y three r e l a t e to P a c i f i c salmons. D i s l e r (1960) observed that f i n g e r l i n g chum salmon "perceived the d i r e c t i o n of a source of v i b r a t i o n s caused by thumping on the ground at a d i s t a n c e of 1.5-2meters". VanDerwalker (1966), reviewed some attempts to guide down m i g r a t i n g rainbow (Salmo g a i r d n e r i ) and brown (S. t r u t t a ) t r o u t , 10 and chinook salmon past t u r b i n e intakes with sound f i e l d s . S t a r t l e r e a c t i o n s to low f r e q u e n c i e s (up to 280Hz) could g e n e r a l l y be obtained but r a p i d h a b i t u a t i o n was apparent, even at very high sound i n t e n s i t i e s (82dB re l u b a r ) . Stober (1969), i n v e s t i g a t e d sounds made by c u t t h r o a t t r o u t (Salmo c l a r k i ) and t h e i r response to playback of these sounds. The predominant sound made was a "thump", a s s o c i a t e d with a sudden t a i l beat. The p r i n c i p l e frequency of a thump was at 150Hz. C u t t h r o a t were shown to hear up t o 650Hz, with a t h r e s h o l d o f -35dB re lubar at 150Kz. R e l a t i v e l y high ambient and equipment noise makes the t h r e s h o l d l e v e l and maximum frequency u n c e r t a i n . Abbott (1972), c o n d i t i o n e d pond reared rainbow t r o u t to feed at the source of a 150Hz pure tone. About 90% of the f i s h were c o n d i t i o n e d a f t e r 45 t r i a l s . The f i s h responded to a 300Hz tone but not to a 600Hz tone. K o l ' t s o v a ^t_ _al_ (1977) using both c o n d i t i o n a l r e a c t i o n s and e l e c t r o p h y s i o l o g i c a l monitoring of inner ear p o t e n t i a l s , produced a f r e q u e n c y - t h r e s h o l d curve f o r the pink salmon. They found that the f i s h responded to f r e q u e n c i e s from 30-2600HZ. Hawkins and Johnstone (1978), s t u d i e d the hearing of the A t l a n t i c salmon (Salmo s a l a r ) by means of a c a r d i a c c o n d i t i o n i n g technique and obtained a t h r e s h o l d curve showing s e n s i t i v i t y between 30-400Hz. I f salmon use sound i n prey l o c a t i o n and ca p t u r e , the no i s e s of prey s p e c i e s and of the salmon themselves are of i n t e r e s t . The sounds that f i s h make have been grouped i n t o three c a t e g o r i e s by Tavolga (1964). These a r e : s t r i d u l a t o r y - produced by hard p a r t s such as d e n t i c l e s , t e e t h , f i n rays and 11 bones being rubbed or scraped a g a i n s t one another; hydrodynamic - swimming sounds r e s u l t i n g from undulatory p r o p u l s i v e and t u r n i n g movements, flow turbulence and a s s o c i a t e d i n t e r n a l sounds; swim bladder - sounds a s s o c i a t e d with gas t r a n s f e r to and from the gut or with muscular c o n t r a c t i o n s e f f e c t i n g rhythmic compression of the b l a d d e r . A p r i n c i p a l prey s p e c i e s of coho and chinook salmon i s the h e r r i n g which occurs i n l a r g e schools on the B.C. c o a s t . The sounds produced by h e r r i n g i n c l u d e ; e a t i n g n o i s e , a s t r i d u l a t o r y sound from jaw and operculum movement (Shwartz pers.comm.); hydrodynamic sounds, knocks or thumps from r a p i d a c c e l e r a t i o n or v e e r i n g ( F i s h 1980, Boyes p e r s . o b s . ) ; and c r o a k s , l i k e l y r e s u l t i n g from swim bladder to gut gas t r a n s f e r (Boyes p e r s . obs., Shwartz pers. comm.). Probably the l o u d e s t sounds from a school of h e r r i n g under the a t t a c k by predators are the hydrodynamic or swimming noises a s s o c i a t e d with "streaming" ( c o o r d i n a t e d movement of the school) and "veering" ( r a p i d simultaneous change of d i r e c t i o n of the s c h o o l ) . Koulton (1960), found t h i s to be the case with l a r g e schools of anchovies, of s i m i l a r s i z e to a h e r r i n g , under a t t a c k by p r e d a t o r s . Here, v e e r i n g sounds were the most intense and were centered i n the frequency band 500-1500Hz. There has been l i t t l e work done on the sounds of P a c i f i c salmon and only one paper on hearing t h r e s h o l d s appears i n the l i t e r a t u r e . Neproshin (1971, 1974), and Neproshin and K u l i k o v a (1975), have s t u d i e d the a c o u s t i c behavior of sockeye, pin k , coho and chinook on the spawning grounds. They found that 12 salmon make at l e a s t nine d i s t i n c t sounds, f i t t i n g i n t o a l l three of Tavolga's (1964), c a t e g o r i e s . The loudest were drumming sounds, measured at about 40dB re l p b a r (see Table 1-1 f o r sound u n i t c o n v e r s i o n s ) and thought to be produced by muscular c o n t r a c t i o n s of the swim bladder. Hydrodynamic sounds were a s s o c i a t e d only with f i s h breaking the s u r f a c e and could not be d e t e c t e d from the movements of submerged f i s h . Ambient noise l e v e l s are not g i v e n but are l i k e l y q u i t e high as salmon spawn i n running water, thus masking may account fo r the absence of swimming sounds. The s o l e r e f e r e n c e to the hearing a b i l i t y of P a c i f i c salmon i s the K o l ' t s o v a _ejt a_l (1977) paper on the pink salmon. The very wide range of frequency d i s c r i m i n a t i o n r e p o r t e d (30-2600Hz), c o n t r a s t s with those determined fo r f i s h of a s i m i l a r form and a u d i t o r y morphology such as the A t l a n t i c salmon (30-400Hz). E x t r a p o l a t i o n of these r e s u l t s to other P a c i f i c salmon, p a r t i c u l a r l y the coho and s p r i n g salmon targeted by t r o l l e r s must t h e r e f o r e be c a u t i o u s . 1.3 THE MORPHOLOGY AND ACUITY OF HEARING IN FISH Although there has been l i t t l e work done on the a u d i t i o n of P a c i f i c salmons, much i n f o r m a t i o n e x i s t s on the h e a r i n g of other f i s h . The inner ear of t e l e o s t f i s h i s g e n e r a l l y homologous to that of mammals, having three s e m i - c i r c u l a r c a n a l s and three or more o t o l i t h s . There i s c o n s i d e r a b l e s t r u c t u r a l v a r i a t i o n between s p e c i e s : reviews of f i s h l a b y r i n t h morphology i n c l u d e Grasse (1958), Moulton (1963), and Lowenstein (1971). 13 The superorder O s t a r i o p h y s i ( f a m i l i e s C y p r i n i d a e , C h a r a c i n i d a e , and S i l u r i d a e ) , have a s m a l l e r and more complex s a c c u l a r o t o l i t h r e l a t i v e to the lagenar o t o l i t h and an endolymphatic connection between the two (the t r a n s v e r s e c a n a l ) , not seen i n other s p e c i e s (Moulton 1963). The O s t a r i o p h y s i f u r t h e r have a d i r e c t connection between the swim bladder and inner ear v i a the Weberian o s s i c l e s . This l i n k i s thought to account f o r the acute hearing of these f i s h , the swim bladder a c t i n g as a r e s o n a t o r and t r a n s m i t t i n g v i b r a t i o n s to the inner- ear (Poggendorf 1952, Kleerekoper and Roggenkamp 1959). Audiograms of three o s t a r i o p h y s a n f i s h appear in Fig.1-3 i l l u s t r a t i n g the wide range of s e n s i t i v i t y and low t h r e s h o l d s g e n e r a l l y found i n t h i s group. A number of other f i s h seem to have swim b l a d d e r - i n n e r ear connections of one kind or another (see the review of Hawkins 1973), and experimental evidence suggests that many of these have r e l a t i v e l y good hearing. Non-ostariophysan f i s h l a c k i n g an a l t e r n a t i v e method of swim b l a d d e r - i n n e r ear l i n k a g e , or l a c k i n g a swim bladder e n t i r e l y such as the Elasmobranchii g e n e r a l l y have poor he a r i n g , with r e s t r i c t e d frequency range and high t h r e s h o l d s . Fig.1-4 shows audiograms f o r the lemon shark (Negaprion b r e v i r o s t r i s ) , the pink salmon ana the A t l a n t i c salmon. As noted in s e c t i o n 1.2, the high frequency d i s c r i m i n a t i o n (above 1000Hz or so) r e p o r t e d f o r the pink salmon by K o l ' tsova _et a l (1977 ) i s a s u r p r i s i n g r e s u l t and may be a r t i f i c i a l l y high as a r e s u l t of the experiments being done in a small tank ( P a r v u l e s c u 1964, Hawkins and Maclennan 1975). Audiograms f o r the y e l l o w f i n and 14 • 5 0 • 4 0 r • 3 0 f- 2 *20 m 2 +10 4) > ^ 0 (A 10 -10 0 •o -20 3 O CO -30 - 4 0 -50 ' ' • _1_ JL 2 0 4 0 6 0 1 0 0 2 0 0 4 0 0 1 0 0 0 4 0 0 0 F r equency (Hz) FIGURE 1-3. Auditory thresholds of three ostariophysine species. A/ Mexican cave fish (Astyanax mexicanus), Popper 1970. B/ Catfish (Ictarulus nebulosus), Poggendorf 1952. C/ Carp, (Cyprinus carpio) Popper 1973. 10 -1 L 1 I I I I I I I I I i I I I I 20 40 60 100 200 400 1000 4000 F r equency (Hz) 1-4. Auditory thresholds of three non-ostariophysine species. A/ Lemon shark, (Negaprion brevirostris), Banner 1967. B/ Pink salmon, (Oncorhynchus gorbuscha), Kol'tsova et al 1977. C/ Atlantic salmon, (Salmo salar), Hawkins and Johnstone 1978. 16 f a l s e a l b a c o r e tunas and f o r the cod appear in F i g . 1-5. Again, the range i s narrow and t h r e s h o l d high f o r these n c n - o s t a r i o p h y s a n s . I t i s i n t e r e s t i n g to note that r e l a t i v e l y l a r g e , p i s c i v o r o u s f i s h tend to hear l e s s w e l l than s m a l l e r h e r b i v o r o u s s p e c i e s , p a r t i c u l a r l y r e e f d w e l l e r s . Because sound i s r e l a t i v e l y w e l l t r a n s m i t t e d i n the sea, background noise (see s e c t i o n 1.4) i s a constant feature of the ocean environment. A f i s h ' s a b i l i t y to p e r c e i v e an important sound over or through t h i s background i s t h e r e f o r e v i t a l to i t s a b i l i t y to u t i l i z e s o n i c i n f o r m a t i o n i n capture of prey, avoidance of p r e d a t o r s e t c . A review of the work on a u d i t o r y masking and the c r i t i c a l band concept i n f i s h i s found i n Tavolga (1974). F i s h with good h e a r i n g , the o s t a r i o p h y s i and o t h e r s with the swim b l a d d e r - i n n e r ear l i n k a g e have good frequency d i s c r i m i n a t i o n and thus a narrow c r i t i c a l band. Non-o s t a r i o p h y s i a n f i s h g e n e r a l l y d i s p l a y poor frequency d i s c r i m i n a t i o n but attempts to measure a c r i t i c a l band have been u n s u c c e s s f u l (Tavolga 1974). S u r p r i s i n g l y , f o r the few s p e c i e s t e s t e d , s i g n a l to noise r a t i o s appear to be i n the same range f o r both o s t a r i o p h y s i a n and n o n - o s t a r i o p h y s i a n s , 20-22dB with broadband noise (Buerkle 1969, Chapman and Hawkins 1973, Tavolga 1974). D i r e c t i o n a l hearing i n f i s h i s c u r r e n t l y an area of a c t i v e experimentation and much t h e o r e t i c a l debate. A review of the o l d e r l i t e r a t u r e i s found i n Moulton and Dixon (1967). VJhile many e a r l y experiments, u s u a l l y i n tanks or ponds, f a i l e d to demonstrate d i r e c t i o n a l d i s c r i m i n a t i o n i n c o n d i t i o n e d f i s h , 17 • 50 •40 •30 2 +20 CD 3 +10 > 01 -10 •o -20 c 3 O CO -30 -40 -50 -I • ' i ' _1_ J I 10 20 40 60 100 200 4 0 0 1000 4 0 0 0 F r equency (Hz) FIGURE 1-5. Auditory thresholds of three non-ostariophysine species. A/ Yellowfin tuna, (Thunnus albacores), Iverson 1966. B/ False albacore, (Euthynrun a f f i n i s ) , Iverson 1967. C/ Cod, (Gadus morhua), Buerkle 1967. 18 more recent work under c o n d i t i o n s nearer to an a c o u s t i c f r e e f i e l d have shown that some sp e c i e s at l e a s t have t h i s a b i l i t y ( s e c t i o n 1.2). Newer reviews of the s u b j e c t appear i n Hawkins (1973) and S c h u i j f (1975), the l a t t e r i n c l u d i n g t h e o r e t i c a l c o n s i d e r a t i o n of phase d i f f e r e n c e and timing a n a l y s i s models of the d i s c r i m i n a t i o n mechanism in the inner ear. 1.4 SOUND IN THE SEA Sound may be d e f i n e d as a p e r i o d i c motion of the molecules i n an e l a s t i c medium. Adjacent molecules t r a n s m i t k i n e t i c energy from an i n i t i a l d i s t u r b a n c e p a r a l l e l to the d i r e c t i o n of propagation of the "sound wave". V a r i a t i o n i n p r e s s u r e , p a r t i c l e v e l o c i t y , and p a r t i c l e displacement are a l l m a n i f e s t a t i o n s of the passage of sound through a m a t e r i a l . The i n t e n s i t y of a sound i s u s u a l l y expressed in pressure u n i t s f o r p r a c t i c a l reasons of measurement. In underwater a c o u s t i c s , sound l e v e l s are commonly given i n terms of d e c i b e l s with r e s p e c t to a r e f e r e n c e l e v e l of ldyne/cm = l u b a r , at a standard d i s t a n c e from source of lm. Use of the a i r standard of 0.0002bar was d i s c o n t i n u e d because of the negative values of sound pressure expressed i n d e c i b e l s that r e s u l t from underwater measurements. Table 1-1 allows comparison of sound pressure v a l u e s using some of the r e f e r e n c e standards that appear in the l i t e r a t u r e . The s i m p l e s t model r e l a t i n g p r e s s u r e , p a r t i c l e v e l o c i t y and displacement i n a sound wave assumes great d i s t a n c e from the source and small amplitude waves and i s known as the 19 TABLE 1-1 CONVERSION TABLE FOR REFERENCE SOUND LEVELS dB re dB re dB re db re Plane dyn/cm 0 . 0 0 0 2 lyPa l p b a r Wave dyn/cm RMS Pressure dyn/cm 4 0 1 1 4 1 4 0 4 0 1 0 2 2 0 94 1 2 0 20 1 0 0 74 1 0 0 0 1 - 2 0 54 80 - 2 0 1 0 " 1 - 4 0 34 6 0 - 4 0 I O - 2 - 6 0 14 4 0 - 6 0 I O - 3 - 8 0 - 6 20 - 8 0 I O " 4 1 0 0 - 2 6 0 - 1 0 0 I O " 5 20 plane wave equation ( d e r i v e d in f u l l in most a c o u s t i c s textbooks e.g. Camp 1970). For a plane wave of sound the pressure (p) (rms), i s r e l a t e d to the p a r t i c l e v e l o c i t y (u) by: p = pcu where: P = d e n s i t y of medium c = propagation v e l o c i t y of wave. The term Pc i s c a l l e d the " s p e c i f i c a c o u s t i c r e s i s t a n c e " or " a c o u s t i c impedance" of the medium. For seawater, pc i s about 1.5x10 gm/cm sec as compared to 42gm/cm sec f o r a i r . T h i s i s because the speed of sound in the sea i s about 4.5 t i n e s and the d e n s i t y some 850 times that i n a i r . As- a r e s u l t , an underwater speaker must produce about 60 times the f o r c e and 1/60 the diaphragm displacement of a speaker r a d i a t i n g the same energy in a i r . The i n t e n s i t y ( I ) of a sound expresses the rate of energy flow through a given area and i s the product of the sound pressure and p a r t i c l e v e l o c i t y : 2 2 I = PU=£ = U PC P c The d e c i b e l as a u n i t of i n t e n s i t y i s then d e f i n e d by: L = 10 log I r e f where: L = l e v e l i n d e c i b e l s I r e £ = the r e f e r e n c e l e v e l of i n t e n s i t y h e r e i n 2 ldyne/cm or l y b a r . S u b s t i t u t i o n leads to the working equation f o r sound p r e s s u r e l e v e l (SPL): SPL = 20log P r m s db re l y b a r where: Py-T,c i s the measured root-mean-square p r e s s u r e . A l l sound l e v e l s in the t e x t correspond to t h i s d e f i n i t i o n . Propagation and T r a n s m i s s i o n Loss: Sound emanating from a p o i n t source diminishes from the e f f e c t s of spreading, a b s o r p t i o n and s c a t t e r i n g . "Spreading l o s s " d e s c r i b e s the weakening i f the s i g n a l due to geometrical e f f e c t s . N e g l e c t i n g a b s o r p t i o n and s c a t t e r i n g , propagation from an o m n i d i r e c t i o n a l source can be viewed as a s e r i e s of c o n c e n t r i c , s p h e r i c a l pressure waves, of equal net energy, r a d i a t i n g outward. Thus, in the absence of r e f l e c t i n g or r e f r a c t i n g boundaries, sound pressure d i m i n i s h e s according to the i n v e r s e square law: P = 4 ir i r 2 where: P = t o t a l a c o u s t i c a l power flowing through a sphere of r a d i u s r . For spheres of d i f f e r e n t r a d i i : P = 4 n r 2 I i = 4 IT r 2 12 I f ri_ i s the r e f e r e n c e d i s t a n c e of In, then the l o s s due to spreading (SL) i s : SL = 1 0 1 o g / l _ T l = l O l o g r 2. = 201og r 2 121 22 Thus, f o r each doubling of the d i s t a n c e from source, a 6dB l o s s i n sound pressure i s observed due to s p r e a d i n g . A b s o r p t i o n i s d e f i n e d as the t r a n s f o r m a t i o n of a c o u s t i c a l energy to heat i n the medium. T h i s r e s u l t s from the e f f e c t s of shear v i s c o s i t y , volume v i s c o s i t y , and the " i o n i c a b s o r p t i o n " e f f e c t of magnesium sulphate and the boron-borate complex (Yeager et a_l 1973 , U r i c k 1975). Changes in p r e s s u r e , temperature and s a l i n i t y a f f e c t the a b s o r p t i o n c o e f f i c i e n t v a r i o u s l y , ( U r i c k 1975 , S c h u l k i n et _al_ 1962), but f o r f r e q u e n c i e s below 50kHz t r a n s m i s s i o n l o s s to t h i s e f f e c t can be n e g l e c t e d . S i m i l a r l y , the a t t e n u a t i o n i n sound pressure due to s c a t t e r i n g from t h e r m o c l i n e s , h a l o c l i n e s and suspended p a r t i c u l a t e m a t e r i a l i s s m a l l . A f i g u r e of about 0.003dB/km, independent of frequency, has been estimated f o r the s c a t t e r i n g e f f e c t i n the sea by K e l l e n et a_l (1974). For p r a c t i c a l purposes, i t i s u s u a l l y assumed in underwater sound c a l c u l a t i o n s that i n t e n s i t y d i m i n i s h e s s o l e l y due to spreading. The assumption of a monopole sound source i s of course an o v e r - s i m p l i f i c a t i o n f o r b i o l o g i c a l sources as well as underwater sound p r o j e c t o r s . These w i l l emit sound waves of a much more complex nature. The plane wave equation a p p l i e s only to sound waves at a d i s t a n c e (as noted above), or those gener- ated by sources l a r g e r e l a t i v e to the wavelength of the frequency produced. Sound c l o s e to a small source i s propagated i n d i v e r g i n g s p h e r i c a l waves. Here, the p a r t i c l e v e l o c i t y i s not i n phase with the sound pressure but f a l l s behind by a phase angle that approaches 90° at the source. In t h i s region the p a r t i c l e v e l o c i t y i s not r e l a t e d to the sound pressure by the simple r e l a t i o n f o r plane waves, but i n c r e a s e s d i s p r o p o r - t i o n a t e l y towards the source. The r e g i o n of high p a r t i c l e displacement has been termed the "near f i e l d " and the region beyond i t the " f a r f i e l d " ( H a r r i s and van B e r g e i j k 1962, H a r r i s 1964, and van B e r g e i j k 1964). VJhile there i s no abrupt t r a n s i t i o n between these zones, f a l l o f f of p a r t i c l e displacement i s r a p i d and c u r r e n t p r a c t i c e sets the d i v i s i o n at about r = A / 2T T . F i g . 1-6 i l l u s t r a t e s the near f i e l d - f a r f i e l d e f f e c t . R e f l e c t i o n and R e f r a c t i o n at Boundaries: Sound propogating through a medium r e f l e c t s from boundaries with contiguous mediums to an extent dependent upon the d i f f e r e n c e i n a c o u s t i c a l impedances and the wavelength of the sound ( U r i c k 1967). A calm sea surface i s an almost p e r f e c t r e f l e c t o r to normally i n c i d e n t sound and while h i g h e r f r e q u e n c i e s pass to a small extent through a choppy s u r f a c e , low frequency sound, having a longer wavelength r e l a t i v e to the wavelength of s u r f a c e waves i s n e g l i g i b l y t r a n s m i t t e d . The sea bottom r e f l e c t s l e s s w e l l , having a higher a c o u s t i c a l impedance than water. Here l o s s e s through the i n t e r f a c e vary with s u b s t r a t e , ranging from about 14dB i n sandy s i l t to 5dB in rock f o r normally i n c i d e n t 5kHz sound (Mackenzie 1960). R e f l e c t i v e or r e f r a c t i v e i n t e r f a c e s i n the water column such as therraoclines and h a l o c l i n e s , combined with r e f l e c t i o n from the s u r f a c e and bottom, can r e s u l t in extremely 24 FIGURE 1-6. A plot of particle displacement vs. distance from a monopole sound source illustrates the near-field, fa r - f i e l d effect for several frequencies projected at 1 y bar re 1 meter (after Hawkins 1973). 25 complex sound pathways, p a r t i c u l a r l y in shallow water. Simple s p h e r i c a l spreading c a l c u l a t i o n s of t r a n s m i s s i o n l o s s may pr o v i d e imprecise estimates of sound i n t e n s i t y at a g i v e n d i s t a n c e from the sound source. In a d d i t i o n the s i g n a l , i f complex may become jumbled as sound waves a r r i v i n g at a p o i n t by d i f f e r e n t paths get out of phase. Ambient Noise i n the Sea: Review papers on the sonic environment in the ocean i n c l u d e Loye and Proudfoot (1946), Knudsen et a l (1944, 1948), Wenz (1962, 1964) and P i g g o t t (1964). Predominant are sounds from p h y s i c a l sources such as wind and r a i n , t i d e s and s e i s m i c a c t i v i t y . Sounds of b i o l o g i c a l o r i g i n may t r a n s i e n t l y be ascendant (Dobrin 1947; F i s h 1964; York 1972), p a r t i c u l a r l y i n shallow water. Probably the most widespread and p e r s i s t e n t b i o l o g i c a l sound i s a " c r a c k l i n g " or " f r y i n g " that has o f t e n been traced to snapping shrimp (Alpheidae) and a l s o to barnacles ( C i r r i p e d i a ) , mussels ( M y t i l i d a e ) , sea u r c h i n s (Echinidae) and other i n v e r t e b r a t e s . Reviews of sound p r o d u c t i o n in f i s h i n c l u d e Tavolga (1960, 1964, 1971), Moulton (1963), F i s h (1964), Winn (1964), and F i s h and Mowbray (1970). A composite i l l u s t r a t i o n of ambient noise s p e c t r a from Wenz (1962), appears i n F i g . 1-7. 1.5 OBJECTIVES OF THE STUDY The study was i n i t i a t e d to s a t i s f y the c u r i o s i t y that the author, himself a t r o l l e r , had developed regarding the r o l e of sound i n the B.C. t r o l l f i s h e r y . Numerous -dockside s t o r i e s 26 120 - 2 0 - 1 1 I | I I 111 1 1 I | I l " | 1 1 I | I I I l | I N T E R M I T T E N T AND L O C A L E F F E C T S CARTHOUAKES . a i o L o a c s • TTTTTj- • (SUftFACC AGITATION) UURFAGE WAVES-SECOHO-ORDER PRESSURE EFFECTS ! J — (KISMIC •ACKSROUNO)- • ' l I I ml A. _L LAJ. -UAAAL O-ua 10 10* 10 s F R E Q U E N C Y - C P S I 0 4 10° FIGURE 1-7. A composite illustration of oceanic ambient noise showing sound spectra from various sources (after Wenz 1962). Sound pressure units may be converted to dB re 1 u bar by adding 74 dB. 2 7 of dramatic catch i n c r e a s e s a t t r i b u t e d to changes in a v e s s e l s d r i v e t r a i n or s t e e r i n g gear lead to t h i s attempt at systematic i n v e s t i g a t i o n of the phenomena. The main p o i n t at issue i s whether v e s s e l s with good sound p r o f i l e s a c t i v e l y a t t r a c t f i s h or j u s t do not r e p e l f i s h by non-emission of r e p u l s i v e sounds. 28 2.0 THEORY FORMATION AND EXPERIMENTAL DESIGN 2.1 THEORY FORMATION PROPOSITIONS Catch r a t e s vary widely between v e s s e l s in the B r i t i s h Columbia t r o l l salmon f i s h e r y . Fishermen a t t r i b u t e at l e a s t p a r t of the v a r i a n c e to the sound output of the v e s s e l (Boyes pe r s . o b s . ) . ASSUMPTIONS P a c i f i c salmon u t i l i z e sound in a d d i t i o n to t h e i r other senses i n the l o c a t i o n of prey and avoidance of p r e d a t o r s . INFERENCES P r o j e c t i o n of c h a r a c t e r i s t i c prey or predator sounds at a high l e v e l from w i t h i n the gear array of a salmon t r o l l e r w i l l e i t h e r a t t r a c t salmon and s t i m u l a t e f e e d i n g , or r e p e l the f i s h and suppress feeding a c t i v i t y . The catch r a t e of the v e s s e l , compared to a c o n t r o l c o n d i t i o n , w i l l improve or decrease as a r e s u l t of the sound p r o j e c t i o n . 2.2 EXPERIMENTAL DESIGN An obvious s t a r t i n g p o i n t f o r the study was the sounds of the boats and the f i s h themselves. A n a l y s i s and comparison of these sound s p e c t r a might show s i m i l a r i t i e s r e s p o n s i b l e f o r a t t r a c t i o n or s t i m u l a t i o n of feeding in salmon. S i m i l a r l y , comparison of boat spectrums with those of salmon p r e d a t o r s could r e v e a l the source of a negative e f f e c t on catch r a t e . The study was d i r e c t e d towards the a t t r a c t i o n a l t e r n a t i v e 29 based on the success recorded with a number of f i s h s p e c i e s i n the l i t e r a t u r e (reviewed i n s e c t i o n 1 . 2 ) . That the author makes h i s l i v i n g c a t c h i n g salmon r a t h e r than chasing them away was not an i n c o n s i d e r a b l e p a r t of t h i s d e c i s i o n . The second stage of the i n v e s t i g a t i o n c o n s i s t e d of r e c o r d i n g the sounus made by v a r i o u s salmonids a c t i v e l y taking p e l l e t e d feed, then p r o j e c t i n g these sounds back to the f i s h . Success in e l i c i t i n g feeding or searching behavior i n a number of s p e c i e s has been repo r t e d (see s e c t i o n 1.2) with t h i s procedure, although negative r e s u l t s have been common a l s o . A p o s i t i v e r e s u l t of some kind would e s t a b l i s h that the sound equipment was performing adequately in l e v e l of output and f i d e l i t y of r e p r o d u c t i o n . At sea playback of salmonid feeding sounds and simulated feeding sounds i n an e f f o r t to i n c r e a s e the catch r a t e of a commercial t r o l l e r comprised the t h i r d stage of the study. The catch r a t e of t r o l l e r s c h a r a c t e r i s t i c a l l y e x h i b i t s wide v a r i a t i o n through the day with maxima o f t e n a s s o c i a t e d with p e r i o d s of s l a c k t i d e and/or low l i g h t at daybreak and dusk. Thus, f o r much of the day gear i s being presented to the f i s h with no response. They are, i n the v e r n a c u l a r , " o f f the b i t e " . The experiment was s t r u c t u r e d and performed to minimize the e f f e c t s of t h i s n a t u r a l v a r i a t i o n on the r e s u l t s . T r i a l s were o n l y conducted dur i n g slow p e r i o d s of the day so that t e s t sounds were presented to m i n i m a l l y e x c i t e d f i s h . I t was expected that i f these sounds had a s t i m u l a t i v e or a t t r a c t i v e c h a r a c t e r to the f i s h , the e f f e c t s on catch r a t e would be l a r g e r 30 than with f i s h a l r e a d y b i t i n g w e l l and thus more v i s i b l e . With fewer f i s h per l i n e the time r e q u i r e d to p u l l the gear and r e s e t i t i s a l s o reduced, g i v i n g a lower p u l l i n g time/soaking time r a t i o and d e l i n e a t i n g more c l e a r l y the t e s t and c o n t r o l p e r i o d s . In a d d i t i o n , low catch r a t e s mean fewer hooks are occupied during a t r i a l l e a v i n g more a v a i l a b l e to new f i s h . S a t u r a t i o n of the gear (commonly 7-10 hooks/side) i s thus avoided. 31 3.0 METHODS AND MATERIALS 3.1 RECORDING, PLAYBACK AND ANALYTICAL EQUIPMENT Underwater r e c o r d i n g s were Made with a Sparton 60CX123 hydrophone onto a JVC K13-1636 MKII c a s s e t t e tape r e c o r d e r . Playback was from the same r e c o r d e r , through an Aquavox UW 60 underwater loudspeaker with a b u i l t - i n lOOvolt l i n e t r a n s f o r m e r , d r i v e n by a Sonic B a r r i e r p u b l i c address a m p l i f i e r (lOOvolt o u t p u t ) . Sonograms were made on a Kay 7029A spectrum a n a l y z e r . S p e c i f i c a t i o n s and c a l i b r a t i o n data f o r r e c o r d i n g and playback equipment f o l l o w . HYDROPHONE: MODEL: Sparton 60CX123 COMPOSITION: Lead-Zinconate, Piezo E l e c t r i c with i n t e g r a l p r e a m p l i f i e r RECEIVING RESPONSE (dB/volt/ybar) : 49+ 3dB F l a t 0.04-5.0 kHz (see F i g . 3-1) POWER REQUIREMENTS: 8.7v ± 5% @ 500 A Low noise power supply shown i n F i g . 3-2. TAPE RECORDER: MODEL: FREQUENCY RESPONSE: . . . . SIGNAL/NOISE: WOW & FLUTTER: CROSSTALK: INPUT SENSITIVITY/IMPEDANCE: OUTPUT LEVEL/IMPEDANCE: . . POWER CONSUMPTION: . . . . MODEL JVC K13-1636 MKII 25-17,000Hz (30-15,000± 3dB 57dB 0.08% (WRMS) 65dB (1kHz) 0.14mV, 20-10k OHMS 50mV, 2.5k OHMS 9watts 0 ~-20 m 73 --40 > 0) S-60 0) C o (/) -80 -100 10 J L_L J L J L 100 1K 10K Frequency (Hz ) FIGURE 3-1. A/ Measured sensitivity of a Sparton 60 CX 123 hydrophone and preamplifier at a depth of 30m. B/ Manufacturers curve of frequency response for the Sparton 60 CX 123 hydrophone and preamplifier. 33 2.7KJI -Wv-r 2 2 0 K J I Output H y d r o p h o n e and p r e a m p l i f i e r FIGURE 3 - 2 . The noise reduction circuit of the hydrophone power supply. SOUND PROJECTOR: MODEL: Aquavox UW60 MAXIMUM POWER INPUT: . . . . 50watts RMS FREQUENCY RESPONSE: 100Hz - 50kHz (See F i g . 3-3) MAGNETIC SYSTEM: Permanent Magnet MAXIMUM OPERATING DEPTH: . . 50m AMPLIFIER: MODEL: POWER INPUT: INPUT IMPEDANCE: INPUT LEVEL (MIC): OUTPUT IMPEDANCE (lOOv l i n e ) : SOUND GENERATOR: MODEL: POWER SUPPLY: Sonic B a r r i e r 12V D.C. 200 OHMS - 50k OHMS 3mV 16 OHMS Custom, using T . I . SN76477N Complex sound g e n e r a t o r I.C. 9V D.C. LOW PASS FILTER: R o l l o f f at 800Hz C i r c u i t shown in F i g . 3-4 3.2 RECORDINGS OF TROLLERS Fi s h b o a t s were recorded from the end of a dock with the hydrophone suspended two meters below the s u r f a c e . Boats ran by about 4meters from the hydrophone and were recorded at three speeds; a "slow t r o l l " (a slow salmon t r o l l i n g speed, about 1.5m/s), " f a s t t r o l l " (2m/s), and "tuna speed" (approx. t r o l l i n g speed f o r tuna, 4-5m/s). Skippers were i n s t r u c t e d to s e l e c t these speeds using t h e i r own judgement and experience with t h e i r boats. 35 F requency (Hz) FIGURE 3-3. A/ Measured output of Aquavox UX60 loudspeaker used i n playback driven at 1 amp., RMS at a depth of 40m i n an aco u s t i c a l free f i e l d . B/ Measured output of an Aquavox UW60 driven at a constant current of 1 amp. i n the AMTE acoustic tank, England (manufacturers data). C/ Measured impendance of the UW60 at 1 amp i n the AMTE acoustic tank (manufacturers data). 36 3.3KJ1 wv FIGURE 3-4. Low pass f i l t e r used with complex sound generator to produce Test Tape II. 37 3.3 RECORDINGS OF FISH H e r r i n g were recorded i n "wi l d " schools and c a p t i v e i n net pens. Wild s c h o o l s were l o c a t e d by echo sounder while i n shallow water duri n g spawning season on the west coast of Vancouver I s l a n d or i n the Gulf o f Georgia (March 1980). The hydrophone was lowered to the depth of the school and r e c o r d i n g s made. Captive h e r r i n g were recorded at the P a c i f i c B i o l o g i c a l S t a t i o n i n Nanaimo. Here the hydrophone was placed w i t h i n the net pen. Coho and chinook salmon (1-2.5kg), as we l l as l a r g e r rainbow t r o u t (2-3kg) were recorded i n net pens at the P a c i f i c B i o l o g i c a l S t a t i o n . The hydrophone was placed w i t h i n the e n c l o s u r e . P e l l e t e d feed was thrown i n t o the pens to i n i t i a t e f e eding motions such as a c c e l e r a t i o n s , f a s t swimming and r a p i d t u r n s . 3.4 PLAYBACK IN PENS The sound p r o j e c t o r was placed i n s i d e or j u s t o u t s i d e the net en c l o s u r e and t e s t sounds played to h e r r i n g , coho, chinook, and rainbow t r o u t . Reactions of the f i s h to t e s t sounds were observed from the catwalk around the pens. 3.5 PLAYBACK AT SEA For the sea t r i a l s , the p r o j e c t o r was towed behind the t r o l l v e s s e l w i t h i n the gear a r r a y , F i g . 3-5 at a depth of 7-8meters. The two main l i n e s were p u l l e d every l/2hour, the 38 FIGURE 3 - 5 . The position of the sound projector within the gear array during test and control periods. 39 numbers and s p e c i e s of f i s h captured recorded, and the l i n e s r e s e t . T h i s g e n e r a l l y took about 4-5mins. The t e s t sounds were c y c l e d on and o f f every l/2hour with the switch o c c u r r i n g j u s t a f t e r the l i n e s had been r e s e t . Three separate sounds were used i n the t r i a l s , denoted t e s t tapes I, II and III, shown i n the sonograms of F i g u r e s 3-6, 3-7 and 3-8. The l u r e s f i s h e d i n c l u d e d f l a s h e r s and h o o t c h i e s , spoons, plugs and b u t t e r f l i e s , arranged i n a p a t t e r n a p p r o p r i a t e to the species s e l e c t i v i t y of the i n d i v i d u a l types of l u r e s and to the v e r t i c a l s p e c i e s d i s t r i b u t i o n of the salmon in the area. No changes to gear were made durin g the t r i a l p e r i o d s save r e p l a c i n g worn or l o s t p i e c e s . T Y P E B / S 3 S O N A G R A M • K A Y E l E M E T R I C S C O . P I N E B R O O K . N . J . FIGURE 3-6. Sonogram of Test Tape I; a recording of trickling water. Fil t e r bandwidth 22.5 Hz. " ' 4* O T Y P E B / B 3 S O N A G R A M • K A Y E L E M E T R I C S C O . P I N E B R O O K . N . J . FIGURE 3-7. Sonogram of Test Tape II; irregular pulsed output of a noise generator cycling at 28 Hz. F i l t e r bandwith 22.5 Hz. T Y P E 8 / 8 3 S O N A G R A M • K A Y E L E M E T R I C S C O . P I N E B R O O K . M . J . 4.0 RESULTS AND DISCUSSION 4.1 RECORDINGS OF TROLLERS Recordings were made of ten t r o l l e r s from 9.7-14.5m in l e n g t h . E i g h t were of t r a d i t i o n a l c a r v e l plank c o n s t r u c t i o n and two were s i n g l e s k i n f i b e r g l a s s . Wide v a r i a t i o n in a c o u s t i c output was apparent between boats and at d i f f e r e n t speeds. F i g u r e s 4-1, 4-2 and 4-3 are sonograms of a 10m wooden t r o l l e r at a slow t r o l l , f a s t t r o l l and at tuna speed. Frequency i s on the y a x i s , time on the x, with i n t e n s i t y a f u n c t i o n of the darkness of the t r a c e . The two jagged t r a c e s at the top of each sonogram are instantaneous s e c t i o n s of the r e c o r d i n g . For these the frequency s c a l e i s reversed and i n t e n s i t y i s p r o p o r t i o n a l to the height of the t r a c e . F i g u r e 4-2 shows the c h a r a c t e r i s t i c broadband (here l-6KHz) t r a c e s a s s o c i a t e d with c a v i t a t i o n of the p r o p e l l e r (Ross 1976). T h i s may be due to one or more bent blades, an unbalanced wheel, or a bent t a i l s h a f t ( E r i c k s o n 1979). T r o l l e r s guard a g a i n s t c a v i t a t i o n noise which may be heard in the s t e r n of the v e s s e l by p u t t i n g one's ear to the h u l l , as i t i s b e l i e v e d to a f f e c t c a t c h r a t e . A c o n s i d e r a b l e i n c r e a s e in both i n t e n s i t y and the upper frequency l i m i t of the sonogram i s e v i d e n t at tuna speed, Figure 4-3. Here the v e s s e l i s encountering wave-making r e s i s t a n c e so that i n a d d i t i o n to the engine, r e d u c t i o n gear, s h a f t and p r o p e l l e r t u r n i n g c o n s i d e r a b l y f a s t e r s u r f a c e water noises are appearing a l s o . The o p e r a t i o n of a u x i l i a r y equipment, h y d r a u l i c s , pumps, motors, e t c . was o f t e n n o t i c e a b l e when c y c l e d on and o f f . F i g u r e 4-4 shov/s a FIGURE 4-1. Sonogram of 10m wooden troller at a slow trolling speed (1.5m/s). F i l t e r bandwidth 45 Hz. T Y P E B / S B S O N A O R A M 8 K A Y K L E M E T R I C S C O . PINK B R O O K . N. J . FIGURE 4-2. Sonogram of a 10m wooden troller at a fast trolling speed (2m/s). A/ Indicates traces associated with cavitation of the propeller. F i l t e r bandwidth 45 Hz. T Y P K B / S S S O N A O R A M * K A Y • U M E T R I C * C O . P I N K B R O O K . M . J . T Y N I B / 6 8 S O N A G R A M * K A Y E L X M E T R I C S C O . P I N K B R O O K . N . J . 8KHZ 4KHz 80Hz FIGURE 4-4. Sonogram of a 14.5m wooden troller at a slow t r o l l with hydraulically driven refrigeration compressor operating ( A ) . F i l t e r bandwith 45 Hz. 4^ 48 t r a c e at about 2.2KHZ caused by a v a r i a b l e speed h y d r a u l i c pump d r i v i n g a r e f r i g e r a t i o n compressor. A s l o w - t r o l l sonogram of the author's v e s s e l , used in the sea t r i a l s i s shown i n F i g u r e 4-5. P r o p e l l e r noises are reduced i n t h i s r e c o r d i n g as the hydrophone was c l o s e to the boat (1.5m) and abeam the v e s s e l . Engine noises are predominant, showing narrow bandwidth t r a c e s a s s o c i a t e d with p a r t i c u l a r engine components at about 600RPM. The output l e v e l of the t e s t v e s s e l with main and a u x i l i a r y engines running was 20dB re l y b a r at lm while s t a t i o n a r y . T h i s i s a p p r e c i a b l y h i g h e r than the l e v e l measured by E r i c k s o n (1979) with albacore j i g boats (about lOdB r e u l b a r ) . Gear, s h a f t and p r o p e l l e r sounds would l i k e l y not add to t h i s a p p r e c i a b l y at t r o l l i n g speed as engine n o i s e s tend to predominate. The t h r e s h o l d s r e p o r t e d f o r pink and A t l a n t i c salmon, and some other n o n - o s t a r i o p h y s i n e s p e c i e s ( F i g u r e s 1-4, 1-5) i n d i c a t e that salmon can a c o u s t i c a l l y d e t e c t t r o l l v e s s e l s i n the frequency range 20-400hz. In the most s e n s i t i v e r e g i o n the range of d e t e c t i o n w i l l approach 30m. I t i s noteworthy that i f E r i c k s o n ' s (1979) output l e v e l s are v a l i d , the maximum d e t e c t i o n d i s t a n c e i s only lm. TYPE B/68 S O N A O R A M • K A Y E L E M E T R I C B C O . P I N E B R O O K . N . J . 2KHz 1KHz i 20Hz 9.6 sec FIGURE 4-5. Sonogram of the author's vessel (13.1m), used in the sea t r i a l s , at a slow trolling speed (1.0-1.5m/s). F i l t e r bandwidth 11.25 Hz. 50 4.2 RECORDINGS OF FISH O b t a i n i n g q u a l i t y r e c o r d i n g s of h e r r i n g while schooled i n shallow, calm water proved d i f f i c u l t due to the u b i q u i t o u s h e r r i n g f l e e t and the c o n s i d e r a b l e background noise r e s u l t i n g . F i s h were l o c a t e d by echo sounding and the boat e i t h e r anchored on the school or allowed to d r i f t with machinery shut down. These pre-spawning f i s h proved to be f a i r l y q u i e t with the only sound apparent being high p i t c h e d " c r a c k l i n g " or " f r y i n g " sounds centered on 4KHz. These may be produced by b r a n c h i a t e or s k e l e t a l movements of the h e r r i n g , although t h i s type of sound i s a l s o made by c e r t a i n b a r n a c l e s ( C i r r i p e d i a ) , mussels ( M y t i l i d a e ) , and u r c h i n s ( E c h i n i d a e ) ( F i s h 1964). Recordings of c a p t i v e h e r r i n g ( s e v e r a l thousand) i n the net pens at FBS were of b e t t e r q u a l i t y with lower background nois e l e v e l s . D i r e c t o b s e r v a t i o n of the f i s h d u r i n g r e c o r d i n g a l s o allowed s o u n d - a c t i v i t y c o r r e l a t i o n s . The f i s h tended to c i r c l e w i t h i n the net, sometimes p i l i n g up i n one corner which occasioned s u r f a c e t h r a s h i n g and r a p i d swimming u n t i l the school reversed i t s d i r e c t i o n . The above mentioned f r y i n g sounds found i n r e c o r d i n g s of w i l d f i s h were presented at a l l times near the s c h o o l . A sonogram showing the p a t t e r n s and bandwidth of these sounds i s shown i n Fig.4-6. They range 3.5-5KHz. During crowding and accompanying r a p i d swimming, sounds dubbed "knocks" were very e v i d e n t . These are shown in Fig.4-7. The f r y i n g sounds of Fig.4-6 appear p e r i o d i c a l l y i n t h i s sonogram as w e l l . Some of the low frequency (<500Hz) p u l s e s are due to f i s h h i t t i n g the hydrophone and cord and causing feedback. T Y P E B / 6 S S O N A O R A M • K A V E L E M E T R I C S C O . PINK BROOK. N . J. 8KHZ 4KHz » 80Hz FIGURE 4-6. Sonogram of herring "scratches". The recording was of captive herring in a net pen at the Pacific Biological Station. F i l t e r bandwidth 45 Hz. TYPK B/6S S O N A G R A M • K A Y KLEMETRIC8 C O . PINK BROOK. N . J . FIGURE 4-7. Sonogram of herring "knocks", produced by active fish in a net pen at the Pacific Biological Station. F i l t e r bandwidth 45 Hz. 53 A sonogram of j u v e n i l e coho (500gm) feeding a c t i v e l y on p e l l e t s i s shown in F i g .4 - 8 . These f i s h v/ere swimming q u i c k l y with r a p i d turns and a c c e l e r a t i o n s as they competed f o r the food. The f i s h d i d not break the surface during t h i s r e c o r d i n g , thus these knocking sounds were p l a i n l y generated underwater. S i m i l a r sounds occurred in r e c o r d i n g s of j u v e n i l e chinook (500gm), a d u l t coho (1.5-2.5kg) and a d u l t rainbow t r o u t (2.5-3kg). F r y i n g sounds v/ere absent from r e c o r d i n g s of c a p t i v e salmonids but c o n s i d e r a b l e s h i p p i n g noise i s e v i d e n t in the background of F i g .4 - 8 . 4.3 PLAYBACK IN PENS As d e t a i l e d i n s e c t i o n 1.2, p o s i t i v e responses to playback of feeding sounds have been obtained with a number of s p e c i e s (Moulton 1960, Hashimoto and Maniwa 1966, Kaniwa 1975). Attempts to e l i c i t s i m i l a r responses with coho and chinook salmon and rainbow t r o u t f a i l e d . The s u b j e c t f i s h were enclosed i n net pens a t PBS and l i v e d on a p e l l e t e d d i e t . Playback of the sounds of p e l l e t s being thrown i n t o the pens and of the f i s h f e e d i n g on them was made to u n s a t i a t e d f i s h at output l e v e l s as high as 55dB re l u b a r at lm. Figs.3-8 and 4-8 are sonograms of such sounds. The sound p r o j e c t o r was suspended w i t h i n the pen, not more than 2m from the f i s h . No response of any kind was observed. Attempts to produce a s t a r t l e e f f e c t with pure tone and o s c i l l a t i n g tones a l s o f a i l e d . I t may be that these f i s h , hand fed and held in an area with a very high background noise l e v e l , have become c o n d i t i o n e d to v i s u a l cues o n l y . P e l l e t s thrown i n t o the pens T T P K B / O T a O t M O H A M * RAY • L K M B T M C B CO. PDOt BROOK. N. J . FIGURE 4-8. Sonogram of juvenile coho salmon actively feeding on pellets. The intense broadband traces are the fish noises (indicated) considerable shipping noise is evident in background. Fi l t e r bandwidth 45 Hz. make a s i g n i f i c a n t d i s t u r b a n c e on the s u r f a c e . The f i s h are a l s o s h e l t e r e d from p r e d a t i o n w i t h i n t h e i r nets and thus l a c k another powerful stimulus to use of t h e i r a u d i t o r y sense. These c o n s i d e r a t i o n s may e x p l a i n the observed l a c k of r e a c t i o n to sounds. 4.4 PLAYBACK AT SEA Attempts to a t t r a c t salmon at sea to a sound source were c a r r i e d out d u r i n g August and September of 1981 and 1982 o f f the southern west coast of Vancouver I s l a n d . The number of t r i a l s was c o n s t r a i n e d by the f i s h i n g p a t t e r n s of the v e s s e l and by weather. T e s t s were p r a c t i c a l o n l y when the number of f i s h caught per day was l e s s than about 50 due to the time r e q u i r e d to p u l l the gear, remove f i s h , and r e s e t as w e l l as p r o c e s s i n g time (the f i s h must be stunned, b l e d , dressed, washed, f r o z e n , g l a z e d and stowed). Two people were r e q u i r e d to conduct t r i a l s so t hat gear could be checked and r e s e t i n accordance with the s chedule. Often only a few c y c l e s were p o s s i b l e before the crew was c a l l e d to other d u t i e s . Moderate weather with good v i s i b i l i t y was r e q u i r e d to tow the sound p r o j e c t o r without r i s k i n the l a r g e f l e e t s of boats that p r e v a i l e d i n the area. Strong t i d a l a c t i o n caused a number of tangles between the speaker and t r o l l i n g l i n e s r e q u i r i n g a b o r t i o n of the t r i a l in p r o g r e s s . The three types of sounds used in the t r i a l s ( F i g s . 3 - 6 , 3-7, 3-8), were chosen based on sounds reported to be s u c c e s s f u l in the l i t e r a t u r e , and f o r resemblance to recorded sounds of h e r r i n g and salmonids. 56 Test Tape I was a recording of t r i c k l i n g water (Fig.3-6). The broadband pulses evident in a l l the recordings of active f i s h were well mimicked by this method, and a very low noise tape could be made. The e r r a t i c pulsed timing of the sound, roughly 20Hz, accorded well with successful sounds in the l i t e r a t u r e (Steinberg _et a_l 1965, Richard 1968). Test Tape II is the recorded output of a custom made sound generator u t i l i z i n g a Texas Instrument SN76477N complex sound generator integrated c i r c u i t (Fig.3-7). The noise function of the chip was modified with a low-pass f i l t e r (Fig.3-4) to r o l l o f f at about 800Hz, then cycled at about 28Hz. This sound v/as then pulsed i r r e g u l a r l y . Again, this sound was designed to resemble observed f i s h sounds and those in the l i t e r a t u r e . It d i f f e r e d from Tape I in i t ' s greater emphasis on low frequency. Test Tape III (Fig.3-8) consisted of repeated rainbow trout feeding sounds. This tape was used at the end of the sea t r i a l s after i t became apparent that the synthesized sounds were i n e f f e c t i v e . The results of the playback at sea are shown in Tables 4-1, 4-2 and 4-3. VJith Tape I, 31 f i s h v/ere caught with the sound on, and 31 with i t o f f . Tape II gave a result of 17 and 24 respectively, VJhile Tape III yielded 7 and 8. A s l i g h t negative co r r e l a t i o n is evident with Tape II but a paired t-test on the data indicated that the result was not s i g n i f i c a n t at a= .05 . 57 TABLE 4-1: Salmon Catch During Cycled Playback of Tes t Tape I; Water Noises ON OFF ON OFF DATE : LOCATION: DEPTH: SPEAKER DEPTH! OUTPUT LEVEL: P e r i o d 10:00-10:30 10:30-11:00 11:00-11:30 11:30-12:00 J u l y 14/81 S w i f t s u r e bank llOmeters l l m e t e r s 55dB re ljuBar at lm Coho 2 0 1 3 Pink 1 0 0 1 Chinook C 1 0 0 ON OFF ON OFF DATE: LOCATION: DEPTH: SPEAKER DEPTH! P e r i o d 17:30-18:00 18:00-18:30 18:30-19:00 19 :00-19:30 August 30/81 North end of La Perouse bank 55-75meters 13meters Coho 2 2 1 1 Pink 2 1 1 0 Chinook 1 2 2 0 ON OFF ON OFF ON OFF ON OFF DATE: LOCATION: DEPTH: Pe r i o d 10:00-10:30 10 :3 0 - l l : 0 0 11:00-11:30 11:30-12:00 12:00-12:30 12:30-13:00 13:00-13:30 13:30-14:00 Sept. 2/81 West side of La Perouse bank 82-92meters Coho 2 0 0 0 2 1 0 0 Pink 0 0 0 0 0 0 0 0 Chinook 0 0 0 0 0 0 1 0 58 DATE: LOCATION: DEPTH: P e r i o d ON 14:30-15:00 OFF 15:00-15:30 ON 15:30-16:00 OFF 16:00-16:30 ON 16:30-17:00 OFF 17:00-17:30 ON 17:30-18:00 OFF 18:00-18:30 ON 18:30-19:00 OFF 19:00-19:30 DATE: LOCATION: DEPTH: P e r i o d ON 12:30-13:00 OFF 13:00-13:30 ON 13:30-14:00 OFF 14:00-14:30 Sept. 3/81 South-east end of La Perouse bank 59meters Coho Pink Chinook 2 1 0 3 0 0 0 0 0 1 3 1 3 1 0 0 0 0 0 0 1 1 1 0 0 2 2 2 3 2 Sept. 6/81 S w i f t s u r e bank 55-75meters Coho Pink Chinook 0 0 0 3 0 0 0 0 1 0 0 0 59 TABLE 4-2: Salmon Catch During Cycled Playback of Tes t Tape I I ; Pulsed Low Frequency Noise ON OFF DATE: LOCATION: DEPTH: SPEAKER DEPTH: OUTPUT LEVEL: P e r i o d 08:00-08:30 08:30-09:00 Aug. 25/82 P o r t l a n d P o i n t 80meters 14meters 55dB re luBar at lmeter Coho 0 0 Chinook 0 0 ON OFF ON OFF ON OFF DATE: LOCATION: P e r i o d 08:30-09:00 10:00-10:30 10:30-11:00 11:00-11:30 11:30-12:00 12:00-12:30 Aug. 26/82 As Above Coho 0 1 0 0 0 3 Chinook 0 0 0 0 0 0 ON OFF ON OFF ON OFF DATE: P e r i o d 16:30-17:00 17:00-17:30 17:30-18:00 18:00-18:30 18:30-19:00 19:00-19:30 Aug. 28/82 Coho 0 0 0 0 0 0 Chinook 0 0 0 0 0 0 ON OFF ON OFF ON OFF DATE: LOCATION: DEPTH: P e r i o d 09:30-10:00 10 :00-10:30 10:30-11:00 11:00-11:30 11:30-12:00 12:00-12:30 Sept. 6/82 North si d e of Juan de Fuca Canyon 130-200meters Coho 2 4 1 4 2 3 Chinook 0 0 1 1 0 1 60 DATE: Sept. 7/82 P e r i o d Coho Chinook ON 1 5 : 0 0 - 1 5 : 3 0 1 0 OFF 1 5 : 3 0 - 1 6 : 0 0 1 0 ON 1 6 : 0 0 - 1 6 : 3 0 0 1 OFF 1 6 : 3 0 - 1 7 : 0 0 0 0 ON 1 7 : 0 0 - 1 7 : 3 0 1 0 OFF 1 7 : 3 0 - 1 8 : 0 0 0 0 DATE: Sept. 15/82 LOCATION: La Perouse bank DEPTH: 80meters P e r i o d Coho Chinook OFF 16:30-17:00 2 0 ON 17:00-17:30 4 0 OFF 17:30-18:00 3 1 ON 18:00-18:30 4 0 61 TABLE 4-3: Salmon Catch During Cycled Playback of Test Tape I I I ; Feeding Sounds of Large Rainbow Trout ON OFF ON OFF DATE: Sept. 9/82 LOCATION: S w i f t s u r e bank DEPTH: lOOmeters OUTPUT LEVEL: 55dB re LuBar at lm P e r i o d Coho Chinook 14:30-15:00 0 0 15:00-15:30 1 0 15:30-16:00 2 0 16:00-16:30 2 0 DATE: Sept. 16/82 LOCATION: La Perouse bank DEPTH: SOmeters Pe r i o d Coho Chinook ON 16:00-16:30 3 0 OFF 16:30-17:00 0 1 ON 17:00-17:30 1 0 OFF 17:30-18:00 2 0 ON 18:00-18:30 0 1 OFF 18:30-19:00 2 0 62 As a footnote to the playback t r i a l s , John Ford of UBC conducted p r e l i m i n a r y playback experiments of recorded k i l l e r whale sounds to the s u b j e c t pods i n Johnstone S t r a i t s d u r i n g the summer of 1982 (John Ford p e r s . comm.). He used the same sound p r o j e c t o r (the Aquavox UW 60) employed i n these experiments. Strong r e a c t i o n to the sounds was e v i d e n t , with some i n d i v i d u a l s becoming extremely a g i t a t e d , approaching the sound at high speed, and a c t u a l l y bunting h i s v e s s e l . T h i s i s at l e a s t an i n d i c a t i o n that the equipment i s capable of producing sounds of a b i o l o g i c a l l y meaningful l e v e l and c h a r a c t e r i n f i e l d c o n d i t i o n s . 63 4.5 GENERAL DISCUSSION The predominant sounds in the f i s h r e c o r d i n g s were the p e r i o d i c broadbank pulses e v i d e n t i n the sonograms ( F i g s . 3 - 8 , 4-7, 4 - 8 ) . These ranged approximately 0.1-8kHz f o r h e r r i n g , 1.5-7kHz f o r coho (1-2.5kg) and 0.15-3.5kHg f o r rainbow t r o u t . The source of these sounds is u n c e r t a i n but some s p e c u l a t i o n s f o l l o w . The h e r r i n g were r e l a t i v e l y s i l e n t u n t i l the school p i l e d i n t o a corner of the net pen. The "knocking" sounds then o c c u r r e d as the f i s h became a c t i v e , t h r a s h i n g and o c c a s i o n a l l y s p l a s h i n g as they attempted to reverse d i r e c t i o n . Franz (1959) measured the underwater noise a s s o c i a t e d with the impact of water d r o p l e t s on the s u r f a c e . He found that two mechanisms were r e s p o n s i b l e ; a sharp pulse r e s u l t s from the i n i t i a l impact, followed by sounds emitted by p u l s a t i o n and c o l l a p s e of e n t r a i n e d a i r bubbles. The a c o u s t i c spectrum he measured was wide, 0.5-10kHz with maximum sound pressure l e v e l s at the lower end. Fig.3-6, the sonogram of Test Tape I shows the c h a r a c t e r of these sounds. Observation during a c o u s t i c monitoring of the swimming h e r r i n g r e v e a l e d that surface s p l a s h i n g , while undoubtably a c o n t r i b u t o r to the h e r r i n g sounds recorded, d i d not always c o r r e l a t e with the occurrence of the "knocks". Another e x p l a n a t i o n i s r e q u i r e d , p a r t i c u l a r l y as the same type of sounds, although lower in p i t c h were evident in the coho, chinook and rainbow t r o u t r e c o r d i n g s where surface s p l a s h i n g was not observed during sound p r o d u c t i o n . C a v i t a t i o n noise i s a common source of broadband n o i s e i n the sea, u s u a l l y a s s o c i a t e d with s h i p ' s p r o p e l l o r s . Ross (1976) estimates t h a t 80-85% of the a c o u s t i c energy p r o j e c t e d from a v e s s e l at speed r e s u l t s from c a v i t a t i o n . T h i s occurs when the l o c a l pressure near a body in motion r e l a t i v e to the medium i s lowered to or near the value of the s t a t i c p r e s s u r e . Rupture o c c u r s , r e s u l t i n g in a m i c r o s c o p i c bubble c o n t a i n i n g water vapor and d i s s o l v e d gases. Most l i q u i d s , and p a r t i c u l a r l y sea water in the mixed l a y e r , c o n t a i n many m i c r o s c o p i c and sub-microscopic v o i d s which act as c a v i t a t i o n n u c l e i . These e f f e c t i v e l y reduce the t e n s i l e s t r e n g t h of the l i q u i d , a l l o w i n g c a v i t a t i o n to occur at negative pressures above the a c t u a l s t a t i c p r e s s u r e . The c o l l a p s e of c a v i t a t i o n bubbles as they r e e n t e r regions of higher pressure r e s u l t s in r a d i a t i o n of broadband n o i s e . T h i s can reach 30dB re lubar in the r e g i o n l-10kHz (Barker 1973). I f c a v i t a t i o n caused the observed broadband p u l s e s , a c t i v e l y swimming or feeding f i s h must be capable of t r a n s i e n t l y lowering the pressure to near ambient l e v e l s . Examination of f i l m e d f u s i f o r m f i s h movements d u r i n g t u r n i n g and r a p i d s t a r t manoeuvres (Vveihs 1972, Webb 1976), p o i n t s to movement of the caudal f i n as a p o s s i b l e source. T i p speeds of 6m/s were recorded during f a s t s t a r t s of small rainbow t r o u t (<500gm) by Webb (1976). A r e l a t i o n used i n marine design (and elsewhere) i n c a l c u l a t i o n of c a v i t a t i o n i n c e p t i o n c o n d i t i o n s i s the c a v i t a t i o n equation; where, a = c a v i t a t i o n number o" = Po-Pv Po =ambient pr e s s u r e 1 p u Pv =vapor pressure of sea 2 water at r e l e v a n t temperature p =density of seawater u =speed A v e l o c i t y of about lOm/s near the s u r f a c e a t 30°C g i v e s a sigrna of 2, about the upper l i m i t f o r onset of c a v i t a t i o n of a h y d r o f o i l at a high angle of a t t a c k (Morgan 1969). The r i s e i n P D with i n c r e a s i n g depth r e q u i r e s an increase in u to achieve a constant sigma, p r e c l u d i n g c a v i t a t i o n at depth i f an animal cannot produce the r e q u i s i t e speed at the s u r f a c e . There i s no i n f o r m a t i o n i n the l i t e r a t u r e on the q u i c k - s t a r t and manoeuvring a b i l i t i e s of P a c i f i c salmon, hov/ever given that s m a l l rainbow t r o u t ( s i m i l a r l y shaped f i s h ) could a t t a i n caudal f i n t i p speeds approaching the r e q u i r e d lOm/s, salmon may be s i m i l a r l y a b l e . C e r t a i n cetaceans are capable of speeds (llm/s) i n the r e g i o n of c a v i t a t i o n onset (Lang 1975). T a i l speeds w i l l be somewhat higher. Fig.4-9 i s a sonogram of k i l l e r whales (Qrcinus orca) a c t i v e l y feeding on salmon (provided by John F o r d ) . These are sounds a s s o c i a t e d with r a p i d a c c e l e r a t i o n s i n p u r s u i t of the e l u s i v e prey (John Ford p e r s . comm.). The broadband c h a r a c t e r of the sounds i n d i c a t e that c a v i t a t i o n may be the source. I t should be noted that the whales d i d not break the s u r f a c e during the r e c o r d i n g . Another p o s s i b l e source of c a v i t a t i o n noise in salmon (and other f i s h arid cetaceans) i s s u c t i o n f e e d i n g . Because of the r e l a t i v e s i z e d i f f e r e n c e between predator and prey, water T Y P E B / 6 3 0 O N A O R A M • K A Y E L E M E T R I C S C O . P I N E B R O O K . N . J . FIGURE 4-9. Sonogram of k i l l e r whale (Orcinus orca), t a i l beats during rapid acceleration. The whales were actively feeding on salmon in the Straight of Juan de Fuca, near Sheringham Point(recording courtesy of John Ford). F i l t e r bandwidth 45 Hz. 67 movement from the p r e a a t o r ' s approach a f f e c t s the p o s i t i o n of the prey. S u c t i o n c r e a t e d by r a p i d e x t e n s i o n of the mouth c a v i t y i s used by most t e l e o s t f i s h to overcome t h i s e f f e c t and draw the prey i n t o the jaws (Lauder 1980). Buccal c a v i t y p r e s s u r e s of -650cm H^O have been measured in s u n f i s h e s (Lauder 1980). T h i s r e p r e s e n t s about 64% of the negative pressure t h e o r e t i c a l l y r e q u i r e d (-1020 cm R^O) to cause c a v i t a t i o n at the s u r f a c e . Salmon u t i l i z e a combination of s u c t i o n and forward body movement in prey capture and although they probably cannot develop negative p r e s s u r e s from mouth expansion approaching the slower s u n f i s h e s , the a d d i t i v e e f f e c t of body v e l o c i t y and s u c t i o n may be s u f f i c i e n t to induce c a v i t a t i o n . Whatever the source of the broadband pulses evident i n the r e c o r d i n g s of v a r i o u s f i s h , these v/ere c e r t a i n l y the l o u d e s t and l i k e l y the most s i g n i f i c a n t sounds observed. They may be analogous to the " v e e r i n g " sounds of Moulton(1960) with anchovies and the "thumps" Stober (1969) observed i n c u t t h r o a t t r o u t . Sonograms of these sounds showed the same broadband c h a r a c t e r . The s i m i l a r i t y between t h i s c l a s s of sounds made by salmon and the c a v i t a t i o n n oises made by damaged or unbalanced p r o p e l l o r s ( F i g . 4 - 2 ) , and k i l l e r whale t a i l beats (Fig.4-9) may be the source of the v a r y i n g f i s h i n g performances i n salmon t r o l l e r s that has been a s s o c i a t e d with s o n i c output. 68 5.0 CONCLUSIONS Towards understanding the r o l e of sound i n the B.C. t r o l l salmon f i s h e r y , t h i s study showed t h a t : 1/ The sound spectrum produced by t r o l l v e s s e l s c o i n c i d e s witli the probable hearing range of P a c i f i c salmon w i t h i n the approximate l i m i t s of 20-500Hz. 2/ The sound output l e v e l of t r o l l v e s s e l s i s about 20dB re l y b a r at lm in the absence of d r i v e t r a i n n o i s e s . C a v i t a t i o n noise from a f a u l t y p r o p e l l o r or v e n t i l a t i o n during rough weather would i n c r e a s e t h i s l e v e l . 3/ The maximum d e t e c t i o n d i s t a n c e of a t r o l l v e s s e l by a P a c i f i c salmon i s at l e a s t 30m. 4/ The predominant sounds made by a c t i v e l y feeding salmonids are broadband pulse dubbed "knocks". These may r e s u l t from c a v i t a t i o n induced by t a i l b e a t s or by s u c t i o n f e e d i n g . 5/ Playback of v a r i o u s pulsed low-frequency and recorded salmonid feeding sounds at a high l e v e l to c a p t i v e salmonids i n net pens and to w i l d f i s h from w i t h i n the gear a r r a y of a commercial salmon t r o l l e r had no observable e f f e c t on the c a p t i v e f i s h nor d i d i t s i g n i f i c a n t l y a f f e c t the catch r a t e of the t r o l l v e s s e l . Although the study f a i l e d to e s t a b l i s h the cause o f , or s u b s t a n t i a t e the p a r t sound p l a y s i n the t r o l l salmon f i s h e r y , some i n s i g h t i n t o the problem was gained. I t now seems more l i k e l y t h a t the e f f e c t of boat noise i s r e p u l s i v e or i n h i b i t o r y to the salmon due to s i m i l a r i t i e s with predator sounds. Some recommendations f o r f u t u r e s t u d i e s i n t h i s area are o f f e r e d i n the f o l l o w i n g s e c t i o n based on p o i n t s that arose i n these i n v e s t i g a t i o n s . 70 6.0 SUGGESTIONS FOR FUTURE WORK A number of p o i n t s have emerged from t h i s study t h a t are d e s e r v i n g of f u r t h e r work. 1/ Playback at sea with an underwater video camera mounted on the sound p r o j e c t o r . The camera would allow d i r e c t o b s e r v a t i o n of f i s h a t t r a c t e d to the sound source. A l u r e might be towed from the apparatus w i t h i n the camera's f i e l d to provide a v i s u a l focus f o r incoming f i s h . 2/ Playback t r i a l s at sea as performed in t h i s study but using recorded or simulated predator sounds (marine mammals, s h a r k s ) . I f r e p u l s i o n or i n h i b i t i o n were o c c u r r i n g catch rates d u r i n g t e s t p e r i o d s would be lower than d u r i n g c o n t r o l s . 3/ An a c o u s t i c p r o f i l e - r e l a t i v e catch l e v e l c o r r e l a t i o n a l study with the t r o l l salmon f l e e t such as E r i c k s o n (1979) d i d with the US a l b a c o r e j i g f l e e t . 4/ An attempt to c o r r e l a t e d a i l y "on the b i t e " p e r i o d s with environmental c o n d i t i o n s such as s t a t e of the t i d e , l i g h t c o n d i t i o n s and water c h a r a c t e r i s t i c s (temperature, s a l i n i t y ) . Log book r e p o r t s or d a i l y r a d i o contact with the f l e e t c ould be used to d e l i n e a t e these p e r i o d s . 5/ A more thorough examination of sound pr o d u c t i o n i n salmon. E v a l u a t i o n of f a s t s t a r t c a p a b i l i t i e s , peak swimming speeds and s u c t i o n feeding i n salmon are needed to explore the o r i g i n s of the "knocks". Recording of feeding salmon at depth should c o n f i r m i f c a v i t a t i o n i s i n v o l v e d . 6/ Determination of f r e q u e n c y - t h r e s h o l d curves f o r a l l s p e c i e s of P a c i f i c salmon (to confirm and extend the f i n d i n g s 71 o f K o l ' t s o v a et ^1_ 1977) i s needed to a c c u r a t e l y determine d e t e c t i o n d i s t a n c e s from sound sources. These data might be u s e f u l i n p r e d i c t i n g e f f e c t s from i n d u s t r i a l noise such as o f f s h o r e o i l e x p l o r a t i o n . 72 LITERATURE CITED Abbott, R.R. 1972. 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