UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A study of the relationship between zooplankton and high-frequency scattering of underwater sound Pieper, Richard Edward 1971

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
831-UBC_1971_A1 P54.pdf [ 6.38MB ]
Metadata
JSON: 831-1.0302442.json
JSON-LD: 831-1.0302442-ld.json
RDF/XML (Pretty): 831-1.0302442-rdf.xml
RDF/JSON: 831-1.0302442-rdf.json
Turtle: 831-1.0302442-turtle.txt
N-Triples: 831-1.0302442-rdf-ntriples.txt
Original Record: 831-1.0302442-source.json
Full Text
831-1.0302442-fulltext.txt
Citation
831-1.0302442.ris

Full Text

A STUDY OF THE RELATIONSHIP BETWEEN ZOOPLANKTON AND HIGH-FREQUENCY SCATTERING OF UNDERWATER SOUND Richard Edward P i e p e r A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of ZOOLOGY and INSTITUTE OF OCEANOGRAPHY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1971 In presenting th i s thes i s in p a r t i a l f u l f i lmen t of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ib ra ry sha l l make i t f r ee l y ava i l ab le for reference and study. I fu r ther agree that permission for extens ive copying of th i s thes i s fo r s cho la r l y purposes may be granted by the Head of my Department or by his representat ives . It is understood that copying or pub l i c a t i on of th i s thes i s fo r f i nanc i a l gain sha l l not.be allowed without my wr i t ten permiss ion. Department of The Un ivers i ty o f B r i t i s h Columbia Vancouver 8, Canada i Chairmen: Dr. B. McK. Bary, Dr. A. G. Lewis ABSTRACT Quantitative volume-scattering measurements were compared to the d i s t r i b u t i o n of euphausiids i n Saanich I n l e t , B r i t i s h Columbia. Scattering was recorded at 42, 107, and 200 kHz from the depths of high euphausiid concentrations, and volume-scattering c o e f f i c i e n t s were determined. No s c a t t e r i n g from euphausiids was recorded by a 11 kHz echo-sounder. D a i l y v a r i a t i o n s i n the volume-scattering c o e f f i c i e n t s , m(Az), generally compared well with v a r i a t i o n s i n the concentration of euphausiids. The d a i l y behaviour of the high-frequency s c a t t e r i n g layer., and therefore m(az) and the concentration of euphausiids, was influenced by moonlight and weather conditions as well as the presence or absence of an oxycline i n the i n l e t . In the absence of an oxycline conditions would have been cl o s e r to conditions i n the open ocean. Under these circumstances euphausiid concentrations and m(iz) were low i n the mornings and gradually increased throughout the day; the high-frequency s c a t t e r i n g l a y e r consolidated. During the evening migration, the l a y e r became more d i f f u s e , and the number of euphausiids per cubic metre decreased. The s c a t t e r i n g cross-section, O (cm 3), of a euphausiid was found to increase with the average dry weight and length, and with increased frequency. For each cruise 0 was approximately one order of magnitude apart at the three frequencies. The values of CT ( i n cm2) ranged from 4.81 x 10"5 to 5 .21 x 10~3 (200 kHz), 5 . 4 9 x 1 0 - 6 to 3 .99 x I O - 4 (107 kHz), and 2.30 x IO"? to 3.67 x 10 - 5 (42 kHz). i i TABLE OF CONTENTS Page I . INTRODUCTION 1 I I . MATERIALS AND METHODS 8 F i e l d Work 8 L a b o r a t o r y A n a l y s e s : B i o l o g i c a l 16 L a b o r a t o r y A n a l y s e s : A c o u s t i c 17 M a t h e m a t i c s and T h e o r y . . . . . . . . . . . . . . 20 I I I . RESULTS 27 D i e l V a r i a t i o n s D u r i n g Each C r u i s e 27 S c a t t e r e r s O t h e r Than E u p h a u s i i d s 4 l C r u i s e A v e r a g e s 43 I V . DISCUSSION 51 V. SUMMARY AND CONCLUSIONS 66 V I . REFERENCES ' . 67 i i i L IST OF TABLES T a b l e S u b j e c t Page 1. C r u i s e numbers, d a t e s and t h e p r e s e n c e o r absence o f an o x y c l i n e a r o u n d 100 m i n t h e w a t e r column 10 2. Times o f moonset, s u n r i s e , s u n s e t , moonrise, moon phase, and t h e p o s s i b l e e f f e c t o f t h e moon on t h e p l a n k t o n 29 3. Weather c o n d i t i o n s d u r i n g p e r i o d s when b i o l o g i c a l o r a c o u s t i c d a t a were c o l l e c t e d 30 4. T o t a l r a d i a t i o n f o r each h o u r i n l a n g l e y s a t D e p a r t u r e Bay, 1969 36 5. P o t e n t i a l s c a t t e r e r s o t h e r t h a n e u p h a u s i i d s caught i n t h e 20 m i n t e r v a l w h i c h d e f i n e d t h e h i g h - f r e q u e n c y s c a t t e r i n g l a y e r . . 42 6. Average v o l u m e - s c a t t e r i n g c o e f f i c i e n t s , m(az), o v e r d i f f e r e n t t i m e i n t e r v a l s 44 7 . S p e c i e s c o m p o s i t i o n , mean d r y w e i g h t , and mean l e n g t h o f e u p h a u s i i d s from t h r e e samples from each c r u i s e . . . . . 50 i v LIST OF FIGURES Figure Subject Page 1. Chart of Saanich I n l e t w i t h l o c a t i o n s of the mooring buoys and the b i o l o g i c a l sampling area . . . . 9 2. A chart-paper record of the a c o u s t i c information recorded on magnetic tape 1^ -3. Block diagram of the ship-board r e c o r d i n g apparatus f o r the a c o u s t i c recordings on magnetic tape . . . . . 15 4. Block diagram of the l a b o r a t o r y equipment f o r the a c o u s t i c analyses 18 5. Diagram of the experimental model 22 6. Temperature and oxygen d i s t r i b u t i o n s at the Saanich buoys on three c r u i s e s 28 7. Cruise 69/3. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations (b) . . . . 33 8. Cruise 69/8. D a i l y v a r i a t i o n s i n m(az)(a) and euphausiid concentrations ( b ) . 33 9. Cruise 69/14. D a i l y v a r i a t i o n s i n mC&z)(a) and euphausiid concentrations ( b ) . . . 34. 10. Cruise 69/22. D a i l y v a r i a t i o n s i n m(iz ) ( a ) and euphausiid concentrations (b) 34 11. Cruise 69/25. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations (b) 38 12. Cruise 69/27. D a i l y v a r i a t i o n s i n n i(iz ) ( a ) and euphausiid concentrations ( b ) , . . . . . . 38 13. Cruise 70/3. D a i l y v a r i a t i o n s i n m(4z)(a) and euphausiid concentrations (b) 40 14. Cruise 70/8. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations ( b ) . 40 15. Average values of the s c a t t e r i n g c r o s s - s e c t i o n , o(cm 3), of a euphausiid f o r each c r u i s e a t 42, 107 and 200 kHz 45 16. Average values of the s c a t t e r i n g c r o s s - s e c t i o n , <j(cm 3), of a euphausiid f o r each c r u i s e at 200 kHz and the average dry weight of a euphausiid f o r each c r u i s e 47 V LIST OF FIGURES (continued) F i g u r e Subject Page 17. The average volume-scattering c o e f f i c i e n t , ra(iz), f o r each c r u i s e a t 200 kHz and the t o t a l weight of euphausiids t h a t correspond t o the volume defined by ra(Az) 48 18. Echograms a t 11, 42, 107, and 200 kHz d u r i n g the day when moored a t the buoys ( c r u i s e 68/35» 5 December 1968) 52 19. Echograms of the high-frequency s c a t t e r i n g l a y e r m i g r a t i n g t o the surface i n the evening as recorded a t 42 and 200 kHz when moored a t the buoys and an 11 kHz record from the same time p e r i o d ( c r u i s e 68/35» 5 December, 1968) . . . 58 20. Echograms a t 200 kHz t o show the behaviour of the high-frequency s c a t t e r i n g l a y e r around morning t w i l i g h t . . . . . . . . . . . . 59 21. Echograms of the morning descent of the s c a t t e r -i n g l a y e r s recorded a t 11, 41 , 107, and 200 kHz when the s h i p i s moving ( c r u i s e 68/35> 5 December, 1968). 61 22. Echogram a t 200 kHz during b i o l o g i c a l sampling operations w i t h a depth t r a c e of the sampler, plus a chart r e c o r d o f the temperature v a r i a t i o n s detected' by a th e r m i s t o r on the sampler and recorded a t the time of sampling . 62 v i ACKNOWLEDGMENTS The author wishes t o thank the many persons who have helped during t h i s study. S p e c i a l thanks must go t o my a d v i s o r s , Dr. B.McK. Bary f o r supporting the p r o j e c t through i t s p r e l i m i n a r y stages and sup p l y i n g the equipment needed f o r the work, and Dr. A.G, Lewis f o r help i n completing the study and c r i t i c i z i n g the manuscript. This work was supported by the Defense Research Board of Canada t o whom I owe s p e c i a l thanks. I am a l s o indebted t o Dr. H.D. F i s h e r , Dr. P.H. LeBlond, Dr. T,R, Parsons and Dr. R.W. Stewart f o r t h e i r h e l p f u l suggestions and c r i t i c i s m s . Many people deserve thanks f o r h e l p i n g w i t h the many aspects of the p r o j e c t . Mr. Wayne Ross and Ross L a b o r a t o r i e s , Inc. f o r the c a l i b r a t i o n s of the echo sounders and t h e i r continued i n t e r e s t i n the p r o j e c t ; Captain CMacaulay and the o f f i c e r s and crew of the C.S.S. Vector f o r t h e i r help and a s s i s t a n c e d u r i n g the c r u i s e s ; Mr. David E n g l i s h and Mrs. V a l e r i e Macdonald f o r t h e i r help on the c r u i s e s , i n the data r e d u c t i o n , and f o r keeping the author a l e r t on many occasions; Dr. R.W. Stewart, Dr. P.H. LeBlond and Mr. Ken Denman f o r advice and help w i t h the theory and mathematics; Mr, Don Hume f o r help w i t h the e l e c t r o n i c s ; Mr. Bob Johns and Miss P h y l l i s Champoux f o r a s s i s t a n c e w i t h the manuscript; and Miss Diane DeBruyn, Mrs. Marion Jones, Mrs. Dorothy James, and Miss Marion Canty f o r help i n s o r t i n g the b i o l o g i c a l samples. A STUDY OF THE RELATIONSHIP BETWEEN ZOOPLANKTON AND HIGH-FREQUENCY SCATTERING OF UNDERWATER SOUND I . INTRODUCTION. Trophodynamic theory on food chains i n the marine environment r e q u i r e s accurate estimates of the standing stock and d i s t r i b u t i o n (patchiness) of plankton. While phytoplankton can be r e l a t i v e l y e a s i l y determined from c h l o r o p h y l l a a n a l y s e s , zooplankton concentrations, both i n terms of absolute numbers and the degree of patchiness i n a water column, are much more d i f f i c u l t t o o b t a i n . The use of high-frequency echo sounders could a s s i s t i n t h i s e s t i m a t i o n f o r those organisms which are p o t e n t i a l sound s c a t t e r e r s . Three groups of zooplankton which are i n the sea i n high numbers f i t i n t o t h i s category; these are copepods, euphausiids, and amphipods. A l l three groups are major food organisms f o r f i s h e s i n the marine environment. Fishermen began using echo sounders t o l o c a t e h e r r i n g i n shallow water as e a r l y as 1930. The existence of a sound s c a t t e r i n g l a y e r a t mid-depths (100 m to 1000 m) i n deeper water was f i r s t s t u d i e d near the end of World War I I . Marine animals were suggested as the sound s c a t t e r e r s when i t was noted t h a t the "Deep S c a t t e r i n g Layer" (D.S.L.) migrated towards the surface around sunset and to deeper depths around s u n r i s e . A review of most s t u d i e s and t h e i r r e s u l t s through 1962 i s given by Hersey and Backus (1962). A more recent summary of papers i n the f i e l d i s found i n Farquhar (1970). The r e l a t i o n s h i p between zooplankton and s o n i c s c a t t e r i n g has not been adequately s t u d i e d i n the past. Besides f i s h e s , s e v e r a l -2-types of organisms have been suggested as p o s s i b l e s c a t t e r e r s of sound a t frequencies centered around 12 kHz. These i n c l u d e euphausiids and other crustaceans (Boden, 1950S Moore, 1950), physonectid siphonophores (Barham, 1963» 1966), and squids (Lyman, 1948). Some i n v e s t i g a t o r s have found hi g h concentrations of zooplankton from the depths where s t r o n g s c a t t e r i n g was recorded. The crustacean Euphausia p a c i f i c a , f o r example, was reported t o be the most s i g n i f i c a n t p l a n k t o n i c component i n c o l l e c t i o n s from the depths of a so n i c s c a t t e r i n g l a y e r recorded a t 12 kHz (Boden and Kampa, 1965). In recent years s t u d i e s of the D.S.L. have branched out i n many d i r e c t i o n s . These s t u d i e s , however, have been made p r i m a r i l y w i t h 12 kHz sounders (2-30 kHz range), and the primary i n t e r e s t has been w i t h f i s h e s . Most authors have concluded t h a t f i s h e s are the most l i k e l y s c a t t e r e r s of sound a t frequencies around 12 kHz (Hersey and Backus, 1962). The g a s - f i l l e d f l o a t s of physonectid siphonophores appear t o be good sound s c a t t e r i n g s t r u c t u r e s (see Barham, 1963» 1966), but the organisms have only been caught s p o r a d i c a l l y from depths where the D.S.L. has been recorded. Hersey and Backus (1962) f i n d i t h i g h l y improbable t h a t euphausiid shrimp would be the s c a t t e r i n g agent a t frequencies around 12 kHz. Bary (1966b) compared the v e r t i c a l d i s t r i b u t i o n of both euphausiids and amphipods w i t h the l o c a t i o n of a 12 kHz s c a t t e r i n g l a y e r i n Saanich I n l e t , B r i t i s h Columbia. Because he found no con s i s t e n t r e l a t i o n s h i p between the recorded s c a t t e r i n g and the biomass or numbers pf specimens, he concluded t h a t zooplankton -3-organisms of lengths up t o 2 cm were not causing b a c k s c a t t e r i n g of s u f f i c i e n t i n t e n s i t y to be recorded a t t h i s depth. A l s o i n Saanich I n l e t , Barraclough and Herlinveaux (1965) found high concentrations of hake (Merluccius productus) a t the depths where the 12 kHz s c a t t e r i n g l a y e r e x i s t e d . There has been some sporadic use of echo-sounders a t frequencies greater than 30 kHz i n s t u d i e s of the r e l a t i o n s h i p between a c o u s t i c s c a t t e r i n g and the d i s t r i b u t i o n s . o f e i t h e r zooplankton or f i s h e s . Barraclough, LeBrasseur, and Kennedy (1969) concluded t h a t shallow s c a t t e r i n g l a y e r s recorded a t 200 kHz i n the P a c i f i c probably r e s u l t e d from zooplankton, p r i m a r i l y l a r g e copepods, i n concentrations up t o 150 per cubic meter. A 200 kHz sounder was used i n a lake by Northcote (1964) t o record the d i s t r i b u t i o n of Chaoborus l a r v a e , but the exi s t e n c e of a gas bubble i n the head of the organism makes i t s a c o u s t i c a l p r o p e r t i e s c o n s i d e r a b l y d i f f e r e n t from most marine crustaceans. McNaught (1969), using various frequencies g r e a t e r than 12 kHz t o study plankton i n a l a k e , found t h a t a c o u s t i c b a c k s c a t t e r i n g strengths were p r o p o r t i o n a l t o the biomass of zooplanktonic t a r g e t s when the proper frequency was used. At 200 kHz s c a t t e r i n g records corresponded to b i o l o g i c a l catches c o n s i s t i n g p r i m a r i l y of Daphnia sp. He suggests t h a t the use of va r i o u s frequencies would make i t p o s s i b l e t o separate zooplankton species without bubbles (as Daphnia) from those w i t h bubbles (such as Chaoborus). In h i s study, back-s c a t t e r i n g strengths were determined s e m i - q u a n t i t a t i v e l y by using a r e f l e c t a n c e spectrophotometer on the g r a p h i c a l r e c o r d s . Hansen and Dunbar (1970) have shown th a t the existence of a 100 kHz s c a t t e r i n g l a y e r i n the A r c t i c corresponded w i t h the accumulation of thecosomatous pteropods. Bary ( p e r s . comm.) and Bary and P i e p e r (1970) have reported that the depth d i s t r i b u t i o n of euphausiids i n Saanich I n l e t , B r i t i s h Columbia, corresponded to the depth of a s c a t t e r i n g l a y e r a t 200 kHz. This high-frequency s c a t t e r i n g l a y e r and the maximum concentration of euphausiids were l o c a t e d a t a depth shallower than the 12 kHz s c a t t e r i n g l a y e r . Fishes and physonectid siphonophores were caught only r a r e l y from t h i s high-frequency s c a t t e r i n g r e g i o n . Numerous measurements have been reported on the t a r g e t strengths (analogous to the s c a t t e r i n g c r o s s - s e c t i o n ) of many f i s h e s (see f o r example Cushing et a l . , 1963? H a s l e t t , 1962 a, b; Love, I969). Few values have been reported f o r plankton. Beamish (1969) lowered an echo-sounder transducer and hydrophone a r r a y i n t o a high-frequency s c a t t e r i n g l a y e r i n Saanich I n l e t , B r i t i s h Columbia. He concluded t h a t , a t 102 kHz, the a c o u s t i c c r o s s - s e c t i o n of a euphausiid was 1.35 x 10*"^  cm 3. Volume-scattering measurements a t low frequencies and t h e i r p o s s i b l e r e l a t i o n t o f i s h e s have been reported by many authors. For example, volume-scattering measurements a t 12 kHz have been reported by B a t z l e r and Vent (196?) and P i c k w e l l et a l . (1970) . Volume-scattering measurements over a wider band of frequencies ( l - 30 kHz), using point charges as sound sources, were shown i n the papers of Chapman and M a r s h a l l (1966), Gold (1965), Hersey, Backus and H e l l w i g (1962), and M a r s h a l l and Chapman (1964). I n t e g r a t i o n techniques f o r averaging the r e f l e c t e d s i g n a l s from t a r g e t s , as w e l l as s i g n a l p r o c e s s i n g , have been developed using these same fr e q u e n c i e s ; the major i n t e r e s t i n these s t u d i e s has been i n f i s h e s (see f o r example Dowd, Bakken and Nakken, 1970, and Lenarz and Green, 1971). A great d e a l of work on underwater s c a t t e r i n g has been c a r r i e d out i n Saanich I n l e t , which i s l o c a t e d on the east coast of Vancouver I s l a n d , B r i t i s h Columbia (see F i g . l ) . Saanich I n l e t i s i d e a l l y s u i t e d f o r these s t u d i e s f o r a number of reasons . The maximum depth of the i n l e t i s 235 ra» i f has a l a r g e population of euphausiids, and appears t o serve as a nursery f o r stocks of d o g f i s h , h e r r i n g , and hake (Barraclough and Herlinveaux, 1 9 6 l ) . As a r e s u l t of a number of f a c t o r s i n c l u d i n g a lack of c i r c u l a t i o n i n the i n l e t , a shallow s i l l depth, and a low freshwater r u n - o f f , an o x y c l i n e around 100 m i s present during most of the year (see Herlinveaux, 1962, f o r a d i s c u s s i o n of the p h y s i c a l oceanography of Saanich I n l e t ) . When present, oxygen concentrations below the oxyc l i n e are l e s s than 0.5 m l / l , and the bottom waters may be completely anoxic. The o x y c l i n e stops the downward m i g r a t i o n of euphausiids but not the f i s h e s ; thus the two populations are often separated v e r t i c a l l y . The 12 kHz s c a t t e r i n g l a y e r i n Saanich I n l e t and i t s r e l a t i o n t o the hydrographic p r o p e r t i e s of the water column, and t o plankton and f i s h d i s t r i b u t i o n s have been discussed by Bary (1966 a, b, 1967)* Bary, Barraclough, and Herlinveaux (1962), and Barraclough and Herlinveaux ( l 9 6 l , 19°5) . I n i t i a l s t u d i e s of the 200 kHz s c a t t e r i n g l a y e r and i t s r e l a t i o n s h i p t o zooplankton and f i s h d i s t r i b u t i o n s have been discussed by Bary and P i e p e r (1970); the s c a t t e r i n g c h a r a c t e r i s t i c s of euphausiids have been reported by Beamish (1969). - 6 -In previous studies i n Saanich I n l e t , scattering was recorded graphically by echo-sounders mounted i n the h u l l s of ships (except f o r Beamish, 1970). While the graphical records were adequate to show scattering layer depths, they did not enable the measurement of back-scattering i n t e n s i t i e s , variations i n scattering i n t e n s i t i e s being recognized only as darker or l i g h t e r marks on the recording paper. Problems associated with attenuation (spreading) and absorption of the sound were also not considered. The r e s u l t was that records were not very useful i n comparing scattering i n t e n s i t i e s . The purpose of the present study was to continue the work i n Saanich Inlet with more exacting techniques using echo-sounders with hull-mounted transducers. The echo-sounder systems were calibrated and ten cruises were completed from September I968 to March 1970. Signals reflected from the scattering layers were recorded on magnetic tape. From these recorded signals the back-scattered acoustic i n t e n s i t y was calculated. The volume-scattering c o e f f i c i e n t and the acoustic cross-section of the scatterers was then determined. The volume-scattering c o e f f i c i e n t s and the acoustic cross-sections were then compared to b i o l o g i c a l collections taken during the same cruises. The study was intended to show quantitatively the r e s u l t s of using various sound frequencies to study marine organisms and to better define the role of zooplankton in scattering. I t was also hoped that the results would show whether or not the echo sounder could be used to ( i ) study the behaviour and population dynamics of zooplankton, and ( i i ) serve as an e c o l o g i c a l t o o l f o r observations on seasonal, d a i l y , and c l i m a t i c changes i n numbers of zooplankton ( i n s i t u ) . - 8 -I I . MATERIALS AND METHODS. F i e l d Work. The study was c a r r i e d out i n Saanich I n l e t on the southeast coast of Vancouver I s l a n d , B r i t i s h Columbia ( F i g . l ) . The area sampled was i n the immediate v i c i n i t y of two mooring buoys l o c a t e d i n the center of the i n l e t . The q u a n t i t a t i v e a c o u s t i c information was c o l l e c t e d w h i l e moored t o the two buoys; the b i o l o g i c a l c o l l e c t i o n s were taken from the area j u s t west of the buoys. The data were c o l l e c t e d from September 1968 through March 1970. Ten, two-week c r u i s e s were completed d u r i n g t h i s p e riod (Table l ) . Because of changes i n the a c o u s t i c - r e c o r d i n g procedures the f i r s t two c r u i s e s (September and December 1968) have not been used f o r the q u a n t i t a t i v e part of t h i s study; they were, however, u s e f u l f o r q u a l i t a t i v e observations and c a l i b r a t i o n d ata. Hydrographic s t a t i o n s were occupied a t f o u r l o c a t i o n s i n the i n l e t ( F i g . l ) at the beginning of each c r u i s e t o determine some oceanographic parameters which might have a f f e c t e d the d i s t r i -butions of the zooplankton and nekton. The measurements taken included temperature, s a l i n i t y and oxygen. B i o l o g i c a l and a c o u s t i c instruments were checked and c a l i b r a t e d on a r r i v a l i n the i n l e t . The order i n which the a c o u s t i c a l and b i o l o g i c a l i n f o r m a t i o n was c o l l e c t e d v a r i e d . This depended on a v a i l a b i l i t y of the r e c o r d i n g equipment and the use of the sampling area by the Royal Canadian Navy. Figure 1. ( f a c i n g ) Chart of Saanich I n l e t w i t h l o c a t i o n s of the mooring buoys, the b i o l o g i c a l sampling area, and the hydrographic s t a t i o n s . -10-TABLE 1 Crui s e numbers, dates, and the presence or absence of an o x y c l i n e around 100 m i n the water column. Cruise Dates Oxycline Present or absent 68/31 23 September - 4 October, 1968 Absent 68/35 25 November - 5 December, I968 Present 69/3 29 January - 9 February, I969 Present 69/8 1 - 1 3 A p r i l , 1969 Present 69/14 7 - 2 0 June, 1969 Present 69/22 25 J u l y - 8 August, 1969 Absent 69/25 1 5 - 2 6 September, I969 Absent 69/27 28 October - 7 November, I969 Present 70/3 20 - 30 January, 1970 Present 70/8 17 - 26 March, 1970 Present -11-The primary b i o l o g i c a l sampler was the instrumented Catcher I I (CAT) (Bary and F r a z e r , 1970), which c o l l e c t s d i s c r e t e samples a t depth. The f i l t e r s (nets) used were e i t h e r 2.5 or 16 mesh/cm (mesh opening 2.16 mm or 0.47 mm). An instrument package on the CAT enabled measurements t o be recorded (throughout a l l tows) on the depth, temperature, number of flow meter r e v o l u t i o n s , and the r a t e of flow through the n e t . The volume of water f i l t e r e d was c a l c u l a t e d from the recorded f l o w meter counts. The s i g n a l from the depth transducer on the instrument package was transformed a t the surface and i n t e r f a c e d t o a Ross* echo-sounder. This produced a t r a c e of the sampler depth on the echogram d u r i n g the sampling oper a t i o n s . The depth t r a c e was adj u s t e d a t the s t a r t of each c r u i s e t o the s c a l e of depth as shown by the Ross echo-sounders (± 0.5 m). B i o l o g i c a l c o l l e c t i o n s were a l s o obtained w i t h a 6-foot Isaacs-Kidd midwater t r a w l (IKMT) (Isaacs and K i d d , 1953). The IKMT could not be closed and, t h e r e f o r e , c o l l e c t i o n s from one depth may have contained specimens from s h a l l o w e r depths. The depth-temperature instrument package was a l s o attached t o t h i s sampler. B i o l o g i c a l samples were taken mainly from the depths of the high-frequency ("zooplanktonic") s c a t t e r i n g l a y e r . C o l l e c t i o n s were a l s o taken from the remainder of the water column. Tows were predominantly during the daytime ( i . e . s u n r i s e t o sunset p e r i o d s ) ; o c c a s i o n a l tows were a l s o made during the n i g h t . The samplers were towed a t speeds of 5 ± 1 k t s (9.3 km/hr) f o r the CAT and 3.5 ± 1 k t s (5.5 km/hr) f o r the IKMT. The sampling d u r a t i o n f o r the CAT tows *Ross L a b o r a t o r i e s , Inc., S e a t t l e , Washington. -12-was from 2-14 minutes, depending on the abundance of zooplankton at the sampling depth. IKMT tows were maintained "at depth" f o r a duration of 16-30 minutes. B i o l o g i c a l c o l l e c t i o n s were preserved on the ship i n 5$ formalin buffered with tetraborate (borax). C o l l e c t i o n s were sub-sampled on board i f the approximate volume of specimens was greater than 8 oz (232 ml). Large decapods, cephalopods, f i s h e s , and f i s h larvae were removed before sub-sampling. Three, Ross " F i n e l i n e " echo-sounders were used to record the s c a t t e r i n g . These operated at frequencies of 42, 107, and 200 kHz. An 11 kHz Simrad transducer, operated with a Simrad EH^R transceiver/recorder or a Gifft(GDR-T) transceiver/recorder, was al s o used. A l l transducers were h u l l mounted f o r the recordings used to examine the s c a t t e r i n g . Comparative echograms from the four sounders were made while moored at the c e n t r a l buoys, during the b i o l o g i c a l c o l l e c t i o n s , and during the hydrographic casts. Comparative soundings were conducted at the buoys f o r 24 hours on every cruise to observe the d i e l change i n the s c a t t e r i n g l a y e r . Quantitative acoustic information was also c o l l e c t e d from a l l four sounders. C a l i b r a t i o n of the echo-sounder systems f o r t h i s purpose was ca r r i e d out by Ross Laboratories, Inc. in November 1968 in Lake Washington. C a l i b r a t i o n checks were thereafter conducted on the systems at the s t a r t of a l l subsequent c r u i s e s . The sounders were a l s o modified to obtain the return s i g n a l before i t had been a l t e r e d to s u i t the requirements of the graphic recorder. The gain controls on the Ross sounders were changed to permit the use of a - 1 3 -c a l i b r a t e d , stepped gain c o n t r o l . This gain c o n t r o l could be va r i e d c o n t i n u a l l y between steps when r e c o r d i n g g r a p h i c a l l y . The s i g n a l r e t u r n s from the f o u r sounders were recorded on magnetic tape f o r l a t e r a n a l y s i s i n the l a b o r a t o r y (F'ig. 2 ) . Such recordings were taken only while moored to reduce s h i p noise ( e l e c t r i c a l ) and t o reduce the p o s s i b i l i t y of i n t e r f e r e n c e due t o water motion and a i r - b u b b l e s produced when the s h i p was underway. A block diagram of the shipboard apparatus i s shown i n F i g . J. While t a p i n g was i n progress, a l l f o u r echo-sounders were t r i g g e r e d simultaneously by the t r i g g e r pulse from the 107 kHz Ross re c o r d e r . The t r i g g e r pulse and the f o u r r e t u r n echoes were monitored by a Tekt r o n i x model 5^9 storage o s c i l l o s c o p e and recorded on f i v e channels of an Ampex model FR-1300 tape r e c o r d e r . These were recorded a t a tape speed of 30 inches/sec, using FM r e c o r d and reproduce modules. While r e c o r d i n g the s i g n a l r e t u r n s from the sounders, the pulse d u r a t i o n of a l l sounders was 0.5 msec. A l l w h i t e - l i n e c o n t r o l s and t i m e - v a r i a b l e - g a i n c o n t r o l s on the Ross sounders were turned o f f . The beam angle (half-power p o i n t ) f o r the Ross sounders was 5° x 10° and f o r the Simrad was 22° x 22°. S i g n a l processing by the Ross system before r e c o r d i n g on the magnetic tape was to a m p l i f y , r e c t i f y , and take the envelope of the a c o u s t i c r e t u r n ( f i l t e r ) . The s i g n a l from the Ross t r a n s c e i v e r had a dynamic range of 0.5 t o 100 v o l t s . Since the r e c o r d i n g range of the tape r e c o r d e r was ± 1 . 0 v o l t s , the returned s i g n a l s were attenuated by a three p o s i t i o n a t t e n u a t o r t o f i t the requirements of the tape r e c o r d e r and to best record s c a t t e r i n g from the area of i n t e r e s t . -14-Figure 2 . ( f a c i n g ) A chart-paper r e c o r d of the a c o u s t i c information recorded on magnetic tape. Due t o the slow response time of the graphic recorder the f i n e d e t a i l present on the tape i s not shown. imi] 60 80 100 200 kHz 107 kHz : " ipitaiiilit CRUISE 69/ 3 Tape 7 pas 0 >' J. 23 20 nrW/ line 0702 hr» 5 Feb 69 50 m e t r e s 30 m e t r e s 0 m e t r e s - 1 5 -Figure 3 . ( f a c i n g ) Block diagram of the ship-board r e c o r d i n g apparatus f o r a c o u s t i c recordings on magnetic tape. Ross 107 kHz graphic recorder trigger pulse trigger Ross 200 k H z transceiver 200 k H , return signal Ross 107 k H z transceiver Ross 42 k H z transceiver 107 k H , return signal 42 k H , return signal Simrad 11 k H z 11 k H z transceiver return signal Atten Atten trigger Atten trigger "return signal Transceiver output pulse 7 return echo Transducer Tektronix 549 storage oscil loscope -**\ Ampex FM FR 1300 FM record tape repro-mode recorder J?^? 30 ips mode -16-Acoustic information was recorded on tape f o r a period of approximately two minutes once every other hour, unless the recording s i t u a t i o n was such that f i s h e s were obscuring the high-frequency s c a t t e r i n g l a y e r . These tape recording periods s t a r t e d at sunrise with the downward movement of the l a y e r , and continued u n t i l the l a y e r had migrated to the surface near sunset. Laboratory Analyses; B i o l o g i c a l Plankton c o l l e c t i o n s obtained i n the f i e l d were counted i n the laboratory and sorted into the following groups: euphausiids, amphipods, decapods, chaetognaths, medusae, siphonophores, cephalopods and f i s h e s . The euphausiids, of major i n t e r e s t i n t h i s study, were sorted into " n a t u r a l " s i z e groups which u s u a l l y r e s u l t e d i n classes of mean length 0,6, 1.2,and 1.8 cm. Amphipods were separated by species where possible, and into l a r g e r taxonomic groups where species i d e n t i f i c a t i o n s were d i f f i c u l t or the number of specimens were low. Decapods were separated into pasiphaeids, sergestids, and miscellaneous decapods. Chaetognaths and medusae were not subdivided, nor were siphonophores with the exception of physonectid siphonophores. Fishes and f i s h larvae were measured f o r t h e i r standard length and the f i s h e s which were numerically abundant were i d e n t i f i e d . A f t e r i n i t i a l s o r t i n g , portions of selected samples of euphausiids (10 from each s i z e group) were i d e n t i f i e d , measured, and the freeze-dried weight determined. The euphausiids were l e f t in the freeze-dryer ( V i r T i s Research, Gardiner, N.Y.) f o r 10 hours before being weighed. The number of organisms per cubic meter of water f i l t e r e d f o r the CAT c o l l e c t i o n s was determined. C o l l e c t i o n s -17-of f i s h e s were p r i m a r i l y from the IKMT. F i s h l a r v a e were c o l l e c t e d both by the CAT and IKMT. Laboratory Analyses t A c o u s t i c In order t o o b t a i n the r e t u r n a c o u s t i c i n t e n s i t i e s from the recorded voltages (the voltage i s p r o p o r t i o n a l t o a c o u s t i c p r e s s u r e ) , i t was necessary t o i n t e g r a t e the s i g n a l of both the voltage and the square of the voltage over the area of i n t e r e s t (high-frequency s c a t t e r i n g l a y e r ) . To s i m p l i f y analyses of the d a t a , a standard i n t e g r a t i o n i n t e r v a l of 20 m was s e l e c t e d as t h i s was the usual th i c k n e s s of the high-frequency s c a t t e r i n g l a y e r i n Saanich I n l e t . To a v o i d the n e c e s s i t y of a n a l o g - t o - d i g i t a l conversion and d i g i t a l i n t e g r a t i o n , an analog computer, developed at the I n s t i t u t e of Oceanography, U n i v e r s i t y of B r i t i s h Columbia, was employed f o r i n t e g r a t i o n of the recorded a c o u s t i c s i g n a l ( F i g . 4 ) , The frequency response of the i n t e g r a t o r s i n the analog computer could not handle the three higher frequencies used i n t h i s experiment which n e c e s s i t a t e d a r e d u c t i o n i n the tape speed f o r the reproduce mode of the tape recorder from 30 inches/sec (30 i p s ) to 3^ i p s ( i . e . tape speed slowed by a f a c t o r of 8 ) . Thus the i n t e g r a t i o n period f o r the 20 m depth i n t e r v a l was c a l c u l a t e d t o be 220 msec. Two, v a r i a b l e - t i m e - d e l a y t r i g g e r s were developed t o s t a r t and to stop i n t e g r a t i o n . The f i r s t t r i g g e r ( t ^ ) , i n i t i a t e d by the tape-recorded t r i g g e r s i g n a l ( t 0 ) , determined the s t a r t of the i n t e g r a t i o n p e r i o d which corresponded t o the top of the high-frequency s c a t t e r i n g l a y e r . The second t r i g g e r (t£) was set f o r a constant -18-Figure 4 . ( f a c i n g ) Block diagram of the l a b o r a t o r y equipment f o r the a c o u s t i c a n a l y s e s . Ampex FR 1300 tape recorder 3 % ips FM reproduce mode o o X o -J X N ro X X N trigger pulse Tektronix 549 storage osc i l l oscope Analog computer x1/p / x or y*x2 y*y or yv Variable 220 t ime m sec delay t ime trigger delay 0 - 2 1 trigger I j /off trigger for analog computer Sanborn two pin chart recorder -19-i n t e r v a l of 2 2 0 msec and turned o f f the i n t e g r a t o r s a t the end of t h i s time p e r i o d . T h i s second t r i g g e r ( t 2 ) was i n i t i a t e d by the f i r s t t r i g g e r ( t ^ ) . In the i n i t i a l t a p i n g , the s i g n a l t h a t went onto the magnetic tape was a m p l i f i e d and/or attenuated with a p p r o p r i a t e combinations so t h a t peak voltages of the high-frequency s c a t t e r i n g were around o r s l i g h t l y below 1 . 0 v o l t s peak. I f a " f i s h " echo was present i n t h i s l a y e r i t produced a l a r g e s p i k e , much l a r g e r than the 1 . 0 v o l t s l e v e l . In order t o minimize the e f f e c t of t h i s s p i k e , present only d u r i n g some c r u i s e s , the reproduced s i g n a l was passed by two diodes i n s e r i e s before a r r i v i n g a t the analog computer. The e f f e c t of the diodes was t o d r a i n any s i g n a l g r e a t e r than 1.2 v o l t s o f f t o ground. The analog computer was used here only as an i n t e g r a t o r of the r e c t i f i e d voltage o r of the square of the v o l t a g e . The system i n t e g r a t e s only two s i g n a l s a t a time (X and Y ) , so th a t s i x runs were needed to obt a i n the values f o r each data block ( i . e . each, two minute t a p i n g p e r i o d ) . The echoes used i n each run were from the same time p e r i o d . A f t e r three echoes had passed from the s t a r t of each run (data b l o c k ) , the f o l l o w i n g 2 0 echoes were recorded f o r the numerical a n a l y s i s . Numerical values of the i n t e g r a t i o n s were read o f f of a d i g i t a l v o l t meter (Hewlett-Packard} 3 4 4 0 A D.V.M., 3443A high-gain auto-range u n i t ) and were a l s o recorded on a two channel Brush chart r e corder (model 2 2 0 , C l e v i t e Corp.). The s i g n a l s were monitored by the storage o s c i l l o s c o p e t o check the reproduced -20-s i g n a l s and t o make c e r t a i n t h a t the i n t e g r a t i o n t r i g g e r s i g n a l corresponded t o the p o r t i o n of the r e t u r n a c o u s t i c s i g n a l t h a t was d e s i r e d . The i n t e g r a t e d voltages were then used t o obtain the a c o u s t i c i n t e n s i t y r e f l e c t e d from t h i s high-frequency ( o r "zooplanktonic") s c a t t e r i n g l a y e r . Since i t was not p o s s i b l e t o record any s c a t t e r i n g from the high-frequency s c a t t e r i n g region on the 11 kHz Simrad echo-sounder, numerical analyses d i d not include t h i s frequency. Mathematics And Theory The s c a t t e r i n g c r o s s - s e c t i o n of a s c a t t e r e r i s an expression of i t s s c a t t e r i n g s t r e n g t h , or i t s a b i l i t y t o s c a t t e r sound from an impinging a c o u s t i c wave. The s c a t t e r i n g c r o s s - s e c t i o n , OT defined by Hersey and Backus (1962), i s is = A- (i) where I g i s the i n t e n s i t y (ergs/sec/cm 3) of the s c a t t e r e d wave a t a distance z (cm) from the s c a t t e r e r , 0 (cm 3) i s the s c a t t e r i n g c r o s s - s e c t i o n , and I i s the i n t e n s i t y of the impinging a c o u s t i c wave. I f there i s more than one s c a t t e r e r i n the a c o u s t i c beam, the volume-scattering c o e f f i c i e n t , m(Az), i s defined by Hersey and Backus (1962) as m(Az,f) = Ncr(f) (2) -21-where N i s the number of s c a t t e r e r s i n the volume defined by A z and the beam angle, and a i s the s c a t t e r i n g c r o s s - s e c t i o n of the s c a t t e r e r which w i l l vary w i t h the frequency ( f ) used. liquation 1 can be modified t o include more than one s c a t t e r e r , where Is now r e f e r s to the t o t a l i n t e n s i t y of the sc a t t e r e d wave from N organisms, and or The a c o u s t i c i n t e n s i t y i s given by A l b e r s (1965) t o be I = E l (4) where p i s the root-mean-squared (rms) a c o u s t i c pressure (dynes/cm 2), jo i s the de n s i t y of the water (gms/cm3) and c i s the sound v e l o c i t y i n the water (cm/sec). The experimental s i t u a t i o n f o r the a c o u s t i c r e c o r d i n g i s shown i n F i g . 5 . The beam angle of the sounders i s de f i n e d by the half-power p o i n t s ; t h i s value i s f o r the f u l l angle and i s shown i n the f i g u r e as 2-©-. The depths of recorded s c a t t e r i n g are from z± to %2 ( i n c m ) measured from the transducer f a c e , and the mean depth of the recorded s c a t t e r i n g i s z. Since the a c o u s t i c s i g n a l i s recorded as a f u n c t i o n of time, the depth can a l s o be w r i t t e n as z = ct or t = £ c -22-Figure 5 . ( f a c i n g ) Diagram of the experimental model. transducer Om z = 1m -23-where c i s the v e l o c i t y of sound i n cm/sec, and t i s the time i n sec. The average s c a t t e r e d a c o u s t i c i n t e n s i t y from the depths z-^  t o Z2 (o r t]_ to t2) can be w r i t t e n as 1 r t 2 t o - t - , J t-, p * dt , . I s = 1 1 L_s; (5) where p s i s the recorded rms pressure over the 20 m i n t e r v a l (the pressure i s determined from the recorded voltages by the c a l i b r a t i o n values a t 1 m below the t r a n s d u c e r ) . S i m i l a r l y the a c o u s t i c i n t e n s i t y (see equation 4) a t 1 metre from the surface - the c a l i b r a t i o n depth) i s 3 I = ^ (6) where p i s the c a l i b r a t e d a c o u s t i c pressure a t 1 m from the transducer. To c a l c u l a t e the value f o r the a c o u s t i c i n t e n s i t y of the in c i d e n t wave reaching the s c a t t e r e r , i t i s necessary t o c o r r e c t f o r d i s p e r s i o n of the wave w i t h i n c r e a s i n g depth. Since c a l i b r a t i o n of the sounders i s at 1 m, the change i n areas i s given by the r a t i o A c/A or T T T c 2 ( z c tan 0 ) 2 TTT 2 " ( z tan 0 ) 2 (7) -24-where z Q i s the depth of c a l i b r a t i o n (lOO cm) and z i s the mean depth of the 20 m i n t e r v a l ( i n cm). Equation (6) then f o r the impinging wave i s as „ 2 2 I = EL • _£_ (8) , 2 The volume s c a t t e r i n g c o e f f i c i e n t , m(az), can be w r i t t e n I . 4TT(Z-100) 3 Z 2  m ( 4 z ) = ^ ( 9 ) c where I = _ 1 J 1 / p 2 d t Frequency-dependent l o s s e s due t o absorption were c a l c u l a t e d by the formula given by Vigoureux and Hersey (1962, from Horton 195?) • Thus, (9) i s modified t o read m(Az) = ll . . 4tr(z-100) 2 . E2<<X'l) (10) 1 z c where a i s the absorption i n db/m and X i s the dis t a n c e i n m. The value m(^z) then i s the sum of the s c a t t e r i n g c r o s s -s e c t i o n s of a l l organisms i n the volume defined by the beam angle and the 20 m depth i n t e r v a l . -25-The volume of th a t s e c t i o n of the cone cut by Zj and Z2> i n cubic metres, i s V = V 2-V 1 = l /3ro:2 2 z2 " l/3iWi 3Z! ( l l ) = l/3-rr tan 0 ( z 2 3 - Z ] 3 ) where z-^  i s the upper depth of the l a y e r ( i n metres) and Z2 i s the lower depth of the 20 m i n t e r v a l . The concentration of euphausiids i s determined from the b i o l o g i c a l c o l l e c t i o n s made by the CAT. The t o t a l number of euphausiids i n the volume corresponding t o m(&z) i s N = V n (12) where n i s the number of euphausiids per m3 and V i s the volume - 2 6 -i n m3. Using formula ( 2 ) , the s c a t t e r i n g c r o s s - s e c t i o n of euphausiid i s N -27-I I I . RESULTS. The main oceanographic f e a t u r e a f f e c t i n g the d i s t r i b u t i o n of euphausiids i n the i n l e t was an o x y c l i n e which, i f present, was found a t a depth of around 100 m. An example of c o n d i t i o n s i n the i n l e t when the o x y c l i n e was present i s shown i n F i g . 6a ( c r u i s e 69/8, A p r i l I969). F l u s h i n g occurred i n the i n l e t (Table l ) between c r u i s e s 69/l4 and 69/22 (June to the end of J u l y ) and F i g . 6b shows the oxygen d i s t r i b u t i o n a t the end of t h i s p e r i o d . During c r u i s e s 69/22, 69/25, and 69/27 ( J u l y through November 1969) the ox y c l i n e was not as strong as before; oxygen concentrations were g r e a t e r than 0.5 m l / l i n the bottom waters of the i n l e t . In January and March 1970 ( c r u i s e s 70/3 and ?0/8) the o x y c l i n e had re-formed. D i e l V a r i a t i o n s During Each Cruise The d a i l y v a r i a t i o n i n the volume-scattering c o e f f i c i e n t , I T I (AZ ) , and the concentration of euphausiids (from the CAT tows using the 10 mpi net unless otherwise stated) are included i n F i g s . 7-14a and 7-14b r e s p e c t i v e l y . Table 2 l i s t s the times of s u n r i s e , sunset, moonrise, and moonset f o r the dates when a c o u s t i c recordings or b i o l o g i c a l c o l l e c t i o n s were taken. Weather c o n d i t i o n s and cloud cover f o r these periods are found i n Table 3. There was a general r e l a t i o n s h i p between m(Az) and the conc e n t r a t i o n of euphausiids (see F i g s . 7-14). The presence or absence of the o x y c l i n e , moonlight, and cloud cover appeared to a f f e c t the d i s t r i b u t i o n of euphausiids. Conditions during the eig h t c r u i s e s were a l l s l i g h t l y d i f f e r e n t and, t h e r e f o r e , each c r u i s e merits separate c o n s i d e r a t i o n . -28-Figure 6 . ( f a c i n g ) Temperature and oxygen d i s t r i b u t i o n s a t the Saanich buoys on three c r u i s e s . The temperature p l o t was drawn from a bathythermograph s l i d e and the p o i n t s shown on t h i s p l o t were from r e v e r s i n g thermometers. (a) Cruise 69/81 a strong o x y c l i n e was present. (b) Cruise 69/22; the i n l e t had been f l u s h e d . This was shown by the r e l a t i v e l y high oxygen concentration near the bottom of the i n l e t . (c) Cruise 69/275 the o x y c l i n e had almost reformed. Temperature (°C) Temperature (°C) Temperature (°C) Oxygen concentration (ml/L) Oxygen concentration (ml/L) Oxygen concentration (ml/L) -29-TABLE 2 Times o f moonset, s u n r i s e , s u n s e t , m o o n r i s e , moon phase, and t h e e f f e c t o f t h e moon on t h e p l a n k t o n . Times (P.S.T.) were c a l c u l a t e d from t h e N a u t i c a l Almanac, a o r b (column 3) r e f e r t o d a t e s when e i t h e r a c o u s t i c (a) o r b i o l o g i c a l ( b ) d a t a were c o l l e c t e d . a o r Moon- Moon- Moon E f f e c t on C r u i s e Date b s e t S u n r i s e S u n s e t r i s e Phase P l a n k t o n 69/3 Feb. 4 a 0830 0726 1702 1918 f u l l p o s s i b l e 5 a/b 0844 0725 1703 203.I f u l l p o s s i b l e 6 b 0857 0723 1705 2146 3/4 p o s s i b l e 7 b 0910 0722 1707 2303 3/4 p o s s i b l e 69/8 A p r i l 7 a 0729 0527 1839 0011 3/4 ? 9 a 0938 0522 1842 0220 1/2 7 12 b 1350 O516 1846 0351 1/4 u n l i k e l y 13 b 1509 0514 1848 0408 1/4 u n l i k e l y 14 b 1626 0512 1850 0424 new u n l i k e l y 69/14 June 17 a 2229 0355 2006 0553 new u n l i k e l y 19 b 2312 0355 2007 0754 1/4 u n l i k e l y 69/22 J u l y 30 b 0555 0429 1942 2045 f u l l p o s s i b l e 31 b 0722 0431 1940 2102 f u l l p o s s i b l e Aug. 1 b 0844 0433 1938 2116 3/4 p o s s i b l e 5 a 1352 0437 1934 2225 1/2 p o s s i b l e 69/25 Sept.2 2 b 0053 0545 1759 1647 3/4 u n l i k e l y 24 a 034? 0549 1754 1725 f u l l 7 69/27 O c t . 29 a II36 0642 1645 1844 3/4 p o s s i b l e 31 a 1306 0644 1642 2047 2/3 p o s s i b l e Nov. 5 a/b 1443 0653 1633 0129 1/2 7 6 b 1455 0655 I632 0240 1/4 7 70/3 J a n . 22 a 0806 0743 1640 1628 f u l l p o s s i b l e 23 a 0828 0742 1642 1740 f u l l p o s s i b l e 27 b 0925 0737 1648 2214 2/3 7 28 b 0938 0736 1650 2325 1/2 7 70/8 Mar. 18 a 0438 0608 18 09 1313 3/4 ? 19 a 0458 . 0606 1811 1426 f u l l 7 20 b 0514 0604 1812 1536 f u l l p o s s i b l e 23 b 0544 0558 1817 1905 f u l l p o s s i b l e 24 b 0608 0555 1819 2017 f u l l p o s s i b l e -30-TABLE 3 Weather c o n d i t i o n s d u r i n g periods when b i o l o g i c a l o r a c o u s t i c data were c o l l e c t e d . A c o u s t i c (a) Cruise 69/3 69/8 69/14 69/22 Date Feb. Apr. or Time Cloud B i o l o g y (b) (P.S.T.) Cover 4 a 1200 10/10 5 a/b 1117 10/10 M i s t 1400 9/10 6 b 1233 1/10 Hazy, b r i g h t 7 b 0714 10/10 1438 10/10 D r i z z l e 7 a 0843 2/10 P a r t i a l l y overcast 9 a 1000 10/10 L i g h t l y overcast 1300 .10/10 Heavy overcast 12 b 1231 10/10 D r i z z l e 1426 10/10 D r i z z l e 13 b 0840 10/10 1206 3/10 1413 4/10 1737 8/10 14 b 0546 6/10 Hazy 0955 2/10 Sunny 15 b 0845 1/10 Sunny 17 a 0300 0 Sunny 0641 0 Sunny 1102 0 S l i g h t l y hazy 19 b 1200 10/10 Thin overcast - c l e a r 30 b 0700 1/10 Sunny - hazy 31 b 0731 0 Sunny - hazy 0850 Sunny - hazy 1522 Sunny - hazy 1 b 0750 C l e a r 1038 5 a 0602 1/10 0702 1/10 1500 10/10 1800 10/10 -31-C r u i s e 69/25 69/27 70/3 70/8 Date Sept. 22 24 O c t . 29 31 Nov. 4 5 6 J a n . 22 23 26 27 28 Mar. 18 19 20 23 24 A c o u s t i c ( a ) o r B i o l o g y (b) b a b a b b a b b a b b Time (P.S.T.) 0845 1308 1?24 0300 0405 0502 0602 1102 0522 1343 1317 0920 1656 0818 1018 0600 1214 0615 1500 0849 0830 0926 1102 1342 0622 1700 2230 06 33 1735 0812 0838 1507 0506 1012 C l o u d C o v e r 10/10 M i s t and f o g 10/10 Hazy - b r i g h t 10/10 Showers P a r t l y c l o u d y P a r t l y c l o u d y 8/10 10/10 10/10 10/10 O v e r c a s t - r a i n 10/10 O v e r c a s t - d r i z z l e 10/10 O v e r c a s t - f o g 10/10 M i s t - r a i n l O / l O O v e r c a s t - Occ. r a i n 8/10 6/10 8/10 C l e a r , d a r k 3/10 T h i n c l o u d s 10/10 l O / l O Heavy o v e r c a s t 5/10 Sunny 10/10 Occ. s p r i n k l e 7/10 Sunny 5/10 Sunny 3/10 Sunny 1/10 0 C l e a r 0 C l e a r 1/10 1/10 10/10 10/10 O v e r c a s t 9/10 showers 0 0 C l e a r C l e a r -32-The a c o u s t i c and b i o l o g i c a l data from c r u i s e s 69/3» 69/8, and 69/14 (Fig,7 - 9 ) a l l showed the e f f e c t of the absence of moonlight and of the presence of an o x y c l i n e . The conc e n t r a t i o n s of euphausiids (as r e f l e c t e d by both m(Az) and the number of euphausiids/m 3) were low i n the morning f o l l o w i n g s u n r i s e . In c r u i s e 69/3 ( F i g . 7) cloud cover was complete and there was no e f f e c t from moonlight, while i n c r u i s e s 69/8 and 69/l4 the moon was at an e a r l y stage. Thus, the absence of moonlight r e s u l t e d i n a midnight descent and few euphausiids were found near the surface a t dawn. As downward m i g r a t i o n occurred, the concentra-t i o n of euphausiids i n the high-frequency s c a t t e r i n g l a y e r i n c r e a s e d . The lower l i m i t of the high-frequency s c a t t e r i n g l a y e r was determined by the depth of the o x y c l i n e . The e f f e c t of f i s h i n the high-frequency s c a t t e r i n g l a y e r was shown on c r u i s e 69/3 ( F i g . 7 ) . F i s h echoes were observed both on the echograms ( i . e . s o l i t a r y echoes t h a t remained under the echo-sounder beam f o r a pe r i o d of time and appeared as h o r i z o n t a l l i n e s on the echogram) and as l a r g e " s p i k e s " on the tape-recorded s i g n a l . This e f f e c t was e s p e c i a l l y , i f not t o t a l l y , confined t o the values a t 42 kHz. Values of m(Az) f o r 42 kHz appear high i n most instances and one value (1200 hours) surpasses the value a t 107 kHz. Unf o r t u n a t e l y , the b i o l o g i c a l c o l l e c t i o n s on c r u i s e 69/3 and 69/l4 were few i n number. T h i s , plus the e f f e c t of the v a r i a b i l i t y of the b i o l o g i c a l d a t a , have made the r e s u l t s d i f f i c u l t t o compare w i t h the a c o u s t i c data. Data c o l l e c t e d during 69/8 ( F i g . 8) a t f i r s t appear t o show an in c o n s i s t e n c y between the a c o u s t i c ( A p r i l 9) and b i o l o g i c a l r e s u l t s ( A p r i l 12, 13, 14). While both show a low concentration e a r l y i n the -33-Figure 7. ( l e f t ) Cruise 69/3. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations ( b ) . Figure 8 . ( r i g h t ) Cruise 69/8. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations ( b ) . Time (P.S.T.) Time (P.S.T.) -34-Figure 9« ( l e f t ) Cruise 69/lk. D a i l y v a r i a t i o n s i n m ( i z ) ( a ) and euphausiid concentrations ( b ) . Figure 10. ( r i g h t ) Cruise 69/22. D a i l y v a r i a t i o n s i n m(Az)(a) and euphausiid concentrations ( b ) . Time (P.S.T.) Time (P.S.T. ) -35-morning, the patterns reverse from 1100 t o 1800 hours. The weather data, however, show t h a t weather c o n d i t i o n s were d i f f e r e n t d u r ing these periods (Table 3 ) . On A p r i l 7» 12, 13> and 14 the sky was only p a r t i a l l y overcast and c o n d i t i o n s (and b i o l o g i c a l r e s u l t s ) were s i m i l a r t o cruises6 9 / 3 and 6 9 / l 4 . The one a c o u s t i c value taken on A p r i l 7 appears t o agree w i t h the b i o l o g i c a l r e s u l t s . On A p r i l 9» however, the sky was overcast and by 1300 hours had become h e a v i l y overcast (see a l s o s o l a r r a d i a t i o n measurements a t Departure Bay, Table 4 ) . The echograms from t h i s p e r i o d show th a t while part of the high-frequency s c a t t e r i n g l a y e r remained a t a constant depth, another part moved up i n the water column during the h e a v i l y overcast c o n d i t i o n . U n f o r t u n a t e l y , tows were not conducted t o determine which part of the l a y e r moved upwards and which part remained s t a t i o n a r y . The a c o u s t i c r e s u l t s from c r u i s e 69/l4 ( F i g . 9) were b r i e f l y mentioned before w i t h respect t o the l a c k of b i o l o g i c a l o b s e r v a t i o n s. The s l i g h t decrease i n m(Az) a f t e r 0700 hours was not t y p i c a l but was probably due to weather c o n d i t i o n s during t h i s p e r i o d which showed an increase i n haze and t h e r e f o r e a p o s s i b l e decrease i n l i g h t i n t e n s i t y . Cruise 69/22 ( F i g . 10) was unique i n a number of ways. F i r s t , a 3/4 or f u l l moon was present u n t i l a f t e r s u n r i s e . This appears t o have helped t o maintain the i n t e g r i t y of the l a y e r a t the surface a t nigh t and during the morning m i g r a t i o n . Thus both high values of U ( A Z ) and high concentrations of euphausiids were observed i n the morning. Second, the o x y c l i n e had disappeared and no longer hindered migration of the euphausiids i n t o deeper waters. As they reached daytime depths, the co n c e n t r a t i o n s , and m(Az), decreased. Then, the l a y e r g r a d u a l l y re-formed throughout the day u n t i l the evening - 3 6 -TABLE 4 T o t a l r a d i a t i o n f o r each h o u r (L.M.T. +) i n l a n g l e y s a t D e p a r t u r e Bay*, I969 ( f r o m t h e M o n t h l y R a d i a t i o n Summary, Canadian Department o f T r a n s p o r t ) . A p r i l O c t o b e r November Hour 7 9 29 31 5 6 1 2 3 4 5 6 1 2 7 3 8 0 0 8 8 12 0 1 1 2 9 28 20 1 4 2 12 10 48 19 2 8 3 18 11 61 27 2 9 6 26 12 66 25 3 19 10 19 13 66 18 5 12 10 9 14 63 19 6 17 4 5 15 53 15 2 13 4 . 4 16 40 10 1 6 2 3 17 27 7 + 1 1 1 18 9 3 0 + 19 1 1 20 21 22 23 24 * D e p a r t u r e Bay i s a p p r o x i m a t e l y 38 m i l e s n o r t h o f S a a n i c h I n l e t . +L.M.T.; l o c a l mean t i m e . -37-m i g r a t i o n again r e s u l t e d i n d i s p e r s i o n . The other unique f e a t u r e of t h i s c r u i s e was the presence of l a r g e numbers of sm a l l euphausiids which was shown by the d i f f e r e n c e i n catches from the 10 mpi (mesh per inch) net and the 40 mpi net. The r e s u l t s a f t e r 0900 hours from c r u i s e 69/25 ( F i g . .11) were almost i d e n t i c a l to 69/22. The o x y c l i n e was s t i l l absent; however, weather c o n d i t i o n s (10/10 overcast, see Table 2) negated the p o s s i b l e e f f e c t of the moon to hol d the high-frequency s c a t t e r i n g l a y e r together d u r i n g the n i g h t . Thus the r e s u l t s from the p e r i o d p r i o r t o 0900 showed low numbers and a low m(Az), s i m i l a r t o r e s u l t s from c r u i s e s 69/3, 69/8, and 69/ l4 . The b i o l o g i c a l data from t h i s c r u i s e were of f u r t h e r i n t e r e s t i n two regards. F i r s t , the conce n t r a t i o n of euphausiids was higher below the f i r s t 20 m of the high-frequency s c a t t e r i n g l a y e r (20 m i n t e r v a l ) than i n i t . The upper p o r t i o n was used i n t h i s instance because of p o s s i b l e l o s s e s of a c o u s t i c i n t e n s i t y due t o absor p t i o n and s c a t t e r i n g of the sound as i t passed through the f i r s t p art of the l a y e r . The second po i n t was the tremendous increase i n the concen-t r a t i o n of euphausiids as they were stopped a t the surface upon m i g r a t i n g upwards around sunset ( i . e . 95/m3 at 1800 hours and 668/m3 a t the surface a f t e r m i g r a t i n g - 1900 hours). The r e s u l t s from c r u i s e 69/27 ( F i g . 12) were more v a r i a b l e than those found during any other c r u i s e . The o x y c l i n e during t h i s p e r i o d s t a r t e d t o reform (see F i g . 6c) but there was s t i l l oxygen a t the bottom of the i n l e t (0 . 5 m l / l ) . Euphausiid concentrations showed d a i l y v a r i a t i o n s s i m i l a r t o c r u i s e s 69/3* 69/8, and 69/l4 where the ox y c l i n e was present. There were maximal concentrations i n the l a y e r around 1100 hours, with lower numbers during m i g r a t i o n p e r i o d s . -38-Figure 11. ( l e f t ) C r u i s e 69/25. D a i l y v a r i a t i o n s i n m(/iz)(a) and euphausiid concentrations ( b ) . Figure 12. ( r i g h t ) C r u i s e 69/27. D a i l y v a r i a t i o n s i n m .Az)(a) and euphausiid concentrations ( b ) . Time (P.S.T.) Time (P.S.T.) -39-There was a p o s s i b l e e f f e c t of moonlight on the plankton the n i g h t before the a c o u s t i c measurements, but t h i s e f f e c t was u n l i k e l y the n i g h t p r i o r to the b i o l o g i c a l c o l l e c t i o n s made on November 6 (moon only i f u l l , o v e r c a s t ) . S i m i l a r l y , as reported i n c r u i s e 69/25, there was an increased concentration a f t e r the euphausiids reached the surface f o l l o w i n g the evening m i g r a t i o n ; the euphausiids then dispersed i n the water column. The a c o u s t i c data f o r c r u i s e 69/2? were a l s o v a r i a b l e . The s i t u a t i o n here appeared to be s i m i l a r t o t h a t discussed f o r c r u i s e 69/8. The r a d i a t i o n data (Table 4) from Departure Bay i n d i -cate t h a t c o n d i t i o n s on October 31 and November 5 (two of the three a c o u s t i c r e c o r d i n g periods) were s i m i l a r t o those on November 5th and 6th when the b i o l o g i c a l sampling occurred. On October 29, however, the r a d i a t i o n values were much lower. This was a s s o c i a t e d w i t h part of the high-frequency s c a t t e r i n g l a y e r r i s i n g i n the water column; the concentration of euphausiids and the values of m(iz) decreased over the 20 m i n t e r v a l . The d a i l y v a r i a t i o n i n the concentration of euphausiids then could be expected t o be s i m i l a r to t h a t of the s c a t t e r i n g c o e f f i c i e n t s recorded on October 31 and November 5» and d i f f e r e n t from those recorded on October 29; t h i s r e l a t i o n s h i p i s seen i n F i g . 12. During c r u i s e s 70/3 and ?0/8 the o x y c l i n e was again a s t a b l e feature i n the i n l e t . During c r u i s e 70/3 ( F i g , 13) only three a c o u s t i c records were taken. This was due to the presence of l a r g e schools of f i s h i n the high-frequency s c a t t e r i n g r e g i o n . U n f o r t u n a t e l y , these three data points do not i n d i c a t e much about the nature of the s c a t t e r i n g during t h i s p e r i o d . However, the -40-Figure 13. ( l e f t ) Cruise 70/3. Daily variations i n m(4z)(a) and euphausiid concentrations (b). Figure 14. (right) Cruise 70/8. Daily variations i n m(&z)(a) and euphausiid concentrations (b). 200 k H z 107 kH, 42 kHz • January 22 ® January 23 - i 1 r • . V I 200 k H z 107 k H z 42 k H z • March 18 ©March 19 • January 27 o January 28 O 40 mpi net layer at surface -• March 20 o March 24 O 40 mpi net 1000 1200 1400 1600 1800 2 0 0 0 0 5 0 0 0 7 0 0 0 9 0 0 1100 1300 1500 1700 1900 Time (P.S.T.) Time (P.S.T.) -41-b i o l o g i c a l c o l l e c t i o n s were s i m i l a r to 69/3 and 69/8 during the morning hours. The euphausiids were i n low concentrations i n d i c a t i n g the absence of moonlight during the night (the moon at t h i s time was only ^ f u l l ) . A f t e r the morning period, the data indicate a l e v e l i n g o f f i n the concentration of euphausiids. The r e s u l t s of cruise 70/8 (March 1970, F i g . 14) showed the best r e l a t i o n s h i p between euphausiid concentrations and the volume-sc a t t e r i n g c o e f f i c i e n t . A l l days during t h i s period were c l e a r except f o r March 23. Moonlight (Table 2) d i d not seem to have af f e c t e d the d i s t r i b u t i o n of euphausiids during the acoustic recording periods, but may have had an e f f e c t when b i o l o g i c a l sampling occurred. The peak value of m(az) at 1200 hours appeared to correspond to the high number of euphausiids c o l l e c t e d at 1100 hours. Unfortunately, however, t h i s was not substantiated very well i n that only one b i o l o g i c a l c o l l e c t i o n showed a high concentration. The low values of m(^z) in the e a r l y morning hours and the s l i g h t increase i n concentration of euphausiids i n the b i o l o g i c a l c o l l e c t i o n s agrees with the suggested e f f e c t of the moonlight as mentioned e a r l i e r . Scatterers Other Than Euphausiids A l i s t of other p o t e n t i a l sound scatterers caught i n the s c a t t e r i n g l a y e r i s given in Table 5-> As shown i n the t a b l e , pasiphaeid shrimp, sergestid shrimp, mysids, cephalopods, amphipods, and physonectid siphonophores do not appear to be i n numbers large enough to add s i g n i f i c a n t l y to the s c a t t e r i n g . Although only one f i s h was caught (69/25) by the samplers used, neither sampler i s thought to be very successful i n catching the l a r g e r f i s h e s . F i s h larvae were not caught on cruises 69/3* 69/8, 70/3» or ?0/8. Larvae TABLE 5 P o t e n t i a l s c a t t e r e r s other than euphausiids caught i n the 20 m i n t e r v a l which defined the high-frequency s c a t t e r i n g l a y e r . Except f o r amphipods, numbers l i s t e d are the number of samples which contained a p a r t i c u l a r organism; the average number per sample i s i n parentheses. No. of F i s h Physonectid S e r g e s t i d s Av. No. Iruise Sampler Samples Fishes Larvae Siphonophore Mysids and Cephalopods Amphipoc Nectophores Pasipaeids per m" c9/3 CAT 11 • 0 0 0 3(4) 2(1) 0 3.2 IKMT - - - - - - - -69/8 CAT 27 0 0 Kl)+ 0 2(1) 3(1) 0.4 IKMT 1 0 0 0 0 0 0 -69/14 CAT 6 0 4(3) 0 0 0 KD 0 . 9 * IKMT - - - - - - - -69/22 CAT 28 0 16(3) 0 0 0 M 2 ) 0.4* IKMT 3 0 3(8) 0 0 0 KD -69/25 . CAT 11 0 2(2) 0. 0 1(1) 2(1) 0.9 IKMT 2 1(1) 2(2) 0 0 1(2) KD 69/27 CAT 24 0 1(2) 1(1) 0 0 0 7.3 IKMT 2 0 0 0 0 0 KD 70/3 CAT 18 0 0 0 0 0 0 2.0 IKMT - - - - - - - -70/8 CAT 26 0 0 0 2(1) 2(1) 0 3.0 IKMT 2 0 0 0 0 0 0 -*Amphipod counts from 10 mpi net c o l l e c t i o n s o n l y . +0ne physonectid pneumatophore was a l s o found i n one sample -43-were few i n numbers during 69/25 and 69/2? and probably d i d not add s i g n i f i c a n t l y t o the s c a t t e r i n g . F i s h l a r v a e caught during c r u i s e 69/14 were mainly f l a t f i s h (without a swimbladder) and the eulachon (Thal e i c h t h y s p a c i f i c u s - with a swimbladder). On c r u i s e 69/22 the f i s h l a r v a e were mainly the eulachon (37%)» hake (Merluccius productus, 3^%), L i p a r i s f u c e n s i s (15%)» and f l a t f i s h (10$). Both the eulachon and the hake c o n t a i n swimbladders and would t h e r e f o r e be good s c a t t e r e r s of sound. Due t o the techniques used t o rec o r d the s c a t t e r i n g (see m a t e r i a l s and methods), i t i s f e l t t h a t these d i d not add s i g n i f i c a n t l y t o the s c a t t e r i n g a t 107 and 200 kHz. Cruise Averages The average volume-scattering c o e f f i c i e n t s f o r each c r u i s e are l i s t e d i n Table 6. Averages are l i s t e d f o r the 0800 - 1600 hour i n t e r v a l , f o r the period from one hour a f t e r s u n r i s e t o one hour before sunset, and f o r a l l values a f t e r the l a y e r l e f t the surface i n the morning t o before i t reached the surface i n the evening. Means are l i s t e d f o r the three f r e q u e n c i e s . T-tests were run comparing the means of the three frequencies (42 vs 107 and 107 vs 200); s i g n i f i c a n t d i f f e r e n c e s are noted a t the 5% or 1% l e v e l s (Table 6 ) . The s c a t t e r i n g c r o s s - s e c t i o n of a euphausiid a t the three frequencies f o r a l l c r u i s e s , and f o r the 0800 - 1600 hour time p e r i o d i s p l o t t e d i n F i g . 15. The range of values (o, i n cm 2), as shown i n the f i g u r e s (0800 - 1600 hour average), i s 2.30 x IO"? to 3.67 x 10-5 (LL2 kHz), 5.49 x 10~6 to 3.39 x IO-'4- (107 kHz), 4.81 x 10" 5 t o 5.21 x 1 0 - 3 (200 kHz). -44-TABLE 6 Average volume-scattering c o e f f i c i e n t s , JI(AZ), over d i f f e r e n t time i n t e r v a l s . Values a t 42 kHz were omitted from the average i f they were > the values a t 107 kHz ( i n d i c a t i n g f i s h were making the value too l a r g e ) . C ruise Time I n t e r v a l Av. H I ( A Z ) A V . m(A.z) Av. m(iz) 42 kHz 107 kHz 200 kHz 69/3 0800-1600 - 1.17 10.2 0713-1747 .0448 .590 5.36 69/8 0800-1600 1.78 * 5.84 74.6 0631-1630 1.73 * 4.99 * 63.0 0631-1930 1.59 * 5.21 *-* 69.8 69/14 0800-1600 .485 *•* 4.48 ** 68.8 0700-1800 .5^ 7 •** ^.95 *•* 71.4 0500-2000 .499 ** 3.99 •** 56.1 69/22 0800-1600 .897 * 3.89 61.7 0700-1700 .861 -** 3.83 *•* 64.8 0600-1900 1.05 3.90 * * 64.1 69/25 0800-1600 4.88 13.3 98.6 0700-1606 3.99 * 11.4 * 79.8 0600-1802 3.71 * 10.6 * 8O.7 69/27 0800-1600 3.61 15.0 * 92.7 0800-1626 3.53 13.8 * 94.0 70/3 0842-1234 1.40 3..01 •* 33.0 70/8 0800-1600 .533 ** 4.99 *- 48.2 0800-1720 .599 4.74 ** 45.4 0642-1820 .532 4.05 *-•* 39.6 *means s i g n i f i c a n t l y d i f f e r e n t a t the 5^ l e v e l . **means s i g n i f i c a n t l y d i f f e r e n t a t the 1% l e v e l . -45-Figure 15. ( f a c i n g ) Average values o f the s c a t t e r i n g c r o s s - s e c t i o n , a (cm 2), of a euphausiid f o r each c r u i s e a t 42, 107, and 200 kHz. -46-For c r u i s e 69/22 the concentration o f euphausiids was c a l c u l a t e d f o r samples taken w i t h the coarse mesh net (10 mpi) and the f i n e mesh net (40 mpi). As would be expected, 0 decreased as the average s i z e of the organisms became s m a l l e r (more s m a l l euphausiids were caught i n the f i n e mesh n e t ) . The mean dry weight of a euphausiid f o r each c r u i s e i s p l o t t e d i n F i g . 16 below the p l o t of G a t 200 kHz. The general shape of the two curves i s s i m i l a r , e s p e c i a l l y f o r the c r u i s e s where th l a r g e r v a r i a t i o n s of euphausiid dry weight were observed. The euphausiids c o l l e c t e d on 6 9/l4, f o r example, had the great e s t average dry weight as w e l l as the l a r g e s t value f o r O. In F i g . 17 the average volume-scattering c o e f f i c i e n t , m(Az), i s p l o t t e d f o r each c r u i s e a t 200 kHz. The t o t a l weight of euphausiids t h e o r e t i c a l l y contained i n the volume de f i n e d by m(az) i s a l s o p l o t t e d . T his value of t o t a l weight was c a l c u l a t e d by m u l t i p l y i n g the mean dry weight times the t o t a l number of euphausiids present i n the volume ( t o t a l number i s the average number per m3 times the volume d e f i n e d by the beam angle and the ' 2 0 m i n t e r v a l ) . This p l o t shows a c l o s e r e l a t i o n s h i p between the t o t a l weight and IH(AZ) but, as before ( F i g . 16), v a r i a t i o n s i n C and average dry weight are apparent. The p o i n t of major i n t e r e s t i n t h i s comparison i s the two values c a l c u l a t e d f o r the t o t a l dry weight from c r u i s e 69/22. One point was c a l c u l a t e d based on the c o l l e c t i o n s from the 10 mpi mesh net (coarse) and one c a l c u l a t e d from c o l l e c t i o n s from the 40 mpi mesh net ( f i n e ) . The trend i n the values f o r m(iz) showed a gradual decrease from c r u i s e s 69/8 t o 69/l4 t o 69/22. -47-Figure 16. (facing) Average values of the s c a t t e r i n g cross-section O (cm 2), of a euphausiid f o r each cruise at 200 kHz, and the average dry weight of a euphausiid f o r each c r u i s e . - 4 8 -Figure 17. ( f a c i n g ) The average volume-scattering c o e f f i c i e n t , m(Az), f o r each c r u i s e a t 200 kHz, and the t o t a l weight of euphausiids that correspond t o the volume defined by M(AZ) (the beam angle and the 20 m depth i n t e r v a l ) . Average m (A z , 200 k H z ) 0800 - 1600 hours Average total weight of euphausi ids / volume defined by m ( A z ) in grams -49-The biomass ( w e i g h t ) of e u p h a u s i i d s b a s e d on t h e 10 mpi n e t c o l l e c t i o n s f o l l o w e d t h i s t r e n d , w h i l e v a l u e s c a l c u l a t e d from t h e 40 mpi c o l l e c t i o n s showed a r e v e r s a l o f t h i s t r e n d . E u p h a u s i a p a c i f i c a was t h e most abundant e u p h a u s i i d on a l l c r u i s e s (76-100% o f a l l e u p h a u s i i d s , T a b l e 7 ) » w h i l e Thysano'essa  r a s c h i i was t h e second most abundant. The a v e r a g e l e n g t h a n d d r y w e i g h t o f t h e e u p h a u s i i d s i s a l s o shown i n T a b l e 7 . -50-TABLE 7 Species composition, mean dry weight and mean length of euphausiids from three samples from each cruise. Cruise % Euphausia p a c i f i c a % Thysanoessa r a s c h i i % Other Mean Dry Weight (mg) Mean Length (mm) 69/3 80.5 19.5 - 3.15 13.2 69/8 87.2 12.5 .3 5.41 15.6 69/14* 99.9 .1 - 11.5^ 19.0 69/22* 90.5 9.5 - 3.55 11.5 69/25 86.4 13.5 .1 4.33 13.9 69/27 82.7 17.1 .2 4.54 13.9 70/3 76.6 23.2 .2 3.33 12.9 70/8 87.0 12.6 .4 3.36 13.2 *10 mpi Samples only. -51-IV. DISCUSSION. Barraclough, LeBrasseur, and Kennedy (1969) have i n d i c a t e d t h a t s c a t t e r i n g a t 200 kHz may have r e s u l t e d from high concentrations of copepods. McNaught (1969) has suggested t h a t Daphnia was an adequate s c a t t e r e r of sound i f the proper frequency was used (200 kHz). S i m i l a r l y , Bary ( p e r s . comm.) and Bary and Pi e p e r (1970) have shown t h a t a s c a t t e r i n g l a y e r recorded a t 200 kHz was found a t depths where l a r g e numbers of euphausiids were c o l l e c t e d i n Saanich I n l e t . Bary (pers. comm.) a l s o suggests t h a t t h i s high-frequency s c a t t e r i n g l a y e r was a l s o recorded a t 107 kHz and sometimes a t 42 kHz w i t h h i g h - r e s o l u t i o n Ross echo-sounders ( s c a t t e r i n g l a y e r s recorded a t the high frequencies and a s s o c i a t e d w i t h zooplankton were not recorded on an 11 kHz, Simrad echo-sounder which was used c o n c u r r e n t l y ) . Results of the present study support the work o f Bary ( p e r s . comm.) and Bary and Pieper (1970), Echograms from the f o u r echo-sounders are shown i n F i g . 18. These echograms show an area of high-frequency s c a t t e r i n g (55-75 m) on the 42, 107, and 200 kHz echo-sounders, but not on the 11 kHz echo-sounder. A f i s h l a y e r centered around 85 m i s shown on a l l echograms. The values f o r the volume-scattering c o e f f i c i e n t s , m(Az), f o r the three frequencies (42, 10?, 200 kHz) were u s u a l l y an order of magnitude a p a r t , the value f o r ITI(AZ) a t 200 kHz always being the l a r g e s t . Only d u r i n g periods when there were l a r g e numbers o f f i s h i n the high-frequency s c a t t e r i n g l a y e r d i d t h i s r e l a t i o n s h i p change; i n a few instances values of U(AZ) were l a r g e r at 42 kHz than a t 107 kHz (see c r u i s e 69/3 a t 1100 hours, F i g . 7a) . On most c r u i s e s the average - 5 2 -Figure 18. ( f a c i n g ) Echograms at 11, 42, 107, and 200 kHz d u r i n g the day when moored at the buoys ( c r u i s e 68/35, 5 December 1968). • -53-m(Az) f o r the three frequencies were s i g n i f i c a n t l y d i f f e r e n t from each other (Table 6 ) . The average m(flz) f o r each c r u i s e showed a s i m i l a r r e l a t i o n s h i p t o the dry weight of euphausiids c a l c u l a t e d to be i n the same volume as t h a t which d e f i n e d m(<az) ( F i g . 17). This r e l a t i o n s h i p i n d i c a t e d t h a t the l a r g e r euphausiids were r e s p o n s i b l e f o r most of the sound s c a t t e r i n g . Values of the dry weight of euphausiids from c r u i s e 69/22 c a l c u l a t e d from 1 0 mpi net (coarse mesh) samples were more c l o s e l y c o r r e l a t e d with m(az) than samples c o l l e c t e d w i t h a kO mpi net ( f i n e mesh). The a c o u s t i c c r o s s - s e c t i o n , o, of a euphausiid increased w i t h an increase i n the dry weight ( F i g . 16) and an increase i n length (Table 7 ) . The values of O a l s o increased w i t h frequency ( F i g . 15). The value of a at 107 kHz f o r J u l y I 9 6 9 was 3 .0 x 1 0 " ^ cm 2. This compares w e l l w i t h 1.35 x 1 0 " ^ cm 2 c a l c u l a t e d by Beamish (1969) using 102 kHz f o r the same time p e r i o d i n I968 ( a l s o i n Saanich I n l e t ) . Other p o t e n t i a l s c a t t e r e r s of sound were r a r e l y caught i n the 20 m high-frequency s c a t t e r i n g zone (Table 5 ) . Cephalopods, mysids and decapods were c o l l e c t e d i n only a few samples and i n these instances the numbers of organisms were low. Physonectid siphonophores were i d e n t i f i e d from only two samples from a l l c r u i s e s ; i n these two samples only one nectophore per sample was found. L a r v a l f i s h e s were caught on about h a l f of the c r u i s e s , but i n high numbers only on two c r u i s e s . Of these f i s h l a r v a e c o l l e c t e d , the hake and the eulachon were the major c o n s t i t u e n t s and both of these c o n t a i n swimbladders and are t h e r e f o r e good - 5 4 -s c a t t e r e r s o f s o u n d . F i s h e s were o n l y f o u n d i n one c o l l e c t i o n a l t h o u g h n e i t h e r s a m p l e r used i n t h i s s t u d y i s t h o u g h t t o be a good c o l l e c t o r o f a d u l t f i s h e s s u c h a s t h e s a l m o n , hake, o r e u l a c h o n . By m a x i m i z i n g t h e r e c o r d e d p l a n k t o n i c s c a t t e r i n g , t h e e f f e c t o f s o l i t a r y , h i g h - a m p l i t u d e echoes from f i s h e s o r f i s h l a r v a e have been m i n i m i z e d ( s e e m a t e r i a l s and m e t h o d s ) . I n s i t u a t i o n s where l a r g e f i s h s c h o o l s were p r e s e n t i n t h e same d e p t h s a s t h e h i g h - f r e q u e n c y s c a t t e r i n g , a c o u s t i c r e c o r d i n g s f o r t h e q u a n t i t a t i v e a n a l y s e s were n o t t a k e n . The v o l u m e - s c a t t e r i n g c o e f f i c i e n t s , m ( ^ z ) , o f t h e h i g h -f r e q u e n c y s c a t t e r i n g l a y e r have been compared t o t h e c o n c e n t r a t i o n of e u p h a u s i i d s (number/m 3) c o l l e c t e d ; t h e d a t a a r e r e p o r t e d i n F i g s c 7-14. The c o n c e n t r a t i o n o f e u p h a u s i i d s , i n g e n e r a l , c o r r e s p o n d e d t o thie v a l u e s o f m(Az). V a r i a t i o n s i n t h e r e s u l t s d u r i n g any one c r u i s e have been a t t r i b u t e d t o v a r i a t i o n s i n w e a t h e r c o n d i t i o n s ( o r s o l a r r a d i a t i o n measurements), t h e t i m e o f moonset, and phase o f t h e moon. V a r i a t i o n s i n t h e g e n e r a l p a t t e r n s f r o m d i f f e r e n t c r u i s e s a p p e a r e d t o r e s u l t from t h e p r e s e n c e o r a b s e n c e of an o x y c l i n e a r o u n d 1 0 0 m. When t h e o x y c l i n e was p r e s e n t ( c r u i s e s 6 9 / 3 , 69/8, 6 9 / 1 4 , 7 0 / 3 , 70/8, and p r o b a b l y 6 9 / 2 7 ) , t h e c o n c e n t r a t i o n o f e u p h a u s i i d s and m(az) i n c r e a s e d a s t h e h i g h - f r e q u e n c y s c a t t e r i n g l a y e r r e a c h e d , and was s t o p p e d by, t h e o x y c l i n e ( F i g s . 7 , 8, 9 , 1 3 , 1 4 ) . D i s c o n t i n u i t y l a y e r s , o r t h e s e p a r a t i o n o f d i f f e r e n t w a t e r t y p e s w h i c h a r e d e n o t e d by d i s c o n t i n u i t y l a y e r s , a r e known t o l i m i t t h e m i g r a t i o n o f e u p h a u s i i d s ( s e e f o r example M a u c h l i n e and F i s h e r , 1 9 6 9 ) 0 . -55-The i n l e t was f l u s h e d between c r u i s e s 69/14 and 69/22 (20 June t o 25 J u l y , 1969) and the bottom waters became oxygenated ( F i g . 6 ) . In the absence o f an o x y c l i n e ( c r u i s e s 69/22, 69/25) t o hinder downward m i g r a t i o n , the high-frequency s c a t t e r i n g l a y e r went deeper i n the water column and was d i s t r i b u t e d over a wider depth i n t e r v a l . As a r e s u l t , the con c e n t r a t i o n of euphausiids and I(AZ) remained low a l l morning. The l a y e r g r a d u a l l y reformed during the day, the volume-scattering c o e f f i c i e n t and the concentration of euphausiids being maximal i n the l a t e afternoon (1500-1600 hours, c r u i s e 69/22} 1400 hours, c r u i s e 69/25). This p a t t e r n probably most c l o s e l y resembles t h a t i n oceanic s i t u a t i o n s , although such work usi n g the high frequency sounders has not been c a r r i e d out i n the open ocean. The presence of st r o n g moonlight d u r i n g the n i g h t appeared to maintain the i n t e g r i t y of the l a y e r near the surface on c e r t a i n c r u i s e s . In such cases p a r t of the population of euphausiids remained near the surface a l l night i n s t e a d of p a s s i v e l y s i n k i n g (midnight s i n k i n g as des c r i b e d by Cushing, 1 9 5 l ) . This e f f e c t was shown on c r u i s e s 69/22 and during the b i o l o g i c a l c o l l e c t i o n s of c r u i s e 70/8 ( F i g s . 10, 14b), In these instances the concentration of euphausiids ( F i g s . 10b, 14b) and ITI(AZ) ( F i g , 10a) was high i n the e a r l y morning p e r i o d when the l a y e r was m i g r a t i n g from the surface down t o i t s daytime depth. In the absence of a moonlight "cue" f o r the euphausiids t o remain near the surface d u r i n g the n i g h t , midnight s i n k i n g occurred. In these cases few euphausiids were i n the near-surface waters before s u n r i s e and thus the concen-t r a t i o n s , and m(az), were low du r i n g the morning, downward m i g r a t i o n s . -56-The weather a l s o a f f e c t e d the d i s t r i b u t i o n of the . euphausiids besides masking the e f f e c t of moonlight. The e f f e c t of submarine i l l u m i n a t i o n on the movement of s c a t t e r i n g l a y e r s has been reported by a number of authors (see f o r example Clarke and Backus, 1956; Kampa and Boden, 1954). Clarke (l9?0) and Lewis (l95^) have a s s o c i a t e d the d i s t r i b u t i o n of euphausiids w i t h a p a r t i c u l a r isolume. The e f f e c t of weather on the high-frequency s c a t t e r i n g l a y e r was seen i n the r e s u l t s from c r u i s e s 69/8 and 69/27 ( F i g s . 8 , 12; Tables 3» 4). On both c r u i s e s the weather was sunny part of the time and h e a v i l y overcast a t another; surface i l l u m i n a t i o n and t h e r e f o r e submarine i l l u m i n a t i o n changed markedly during these p e r i o d s . On c r u i s e 68/9 the c o n c e n t r a t i o n of euphausiids and ITI(AZ) were high i n the morning, the euphausiids being compressed a g a i n s t the o x y c l i n e . On sunny days the values remained high d u r i n g the day. In the presence of a h e a v i l y overcast sky, the surface and submarine i l l u m i n a t i o n decreased, and p a r t of the high-frequency s c a t t e r i n g l a y e r moved upwards i n the water column ( i . e . the l a y e r became more d i f f u s e ) . This r e s u l t e d i n a decreased m(*z) i n the 20 m i n t e r v a l d u r i n g t h i s p e r i o d , A s i m i l a r spreading i n d i s t r i b u t i o n and reduced concentration a t any one depth has a l s o been r e p o r t e d by Mauchline and F i s h e r (1969). The high-frequency s c a t t e r i n g l a y e r migrated from the surface t o depth around morning t w i l i g h t and then back t o the surface a t dusk i n a manner described by Bary (1967) and Cushing ( l 9 5 l ) . The r a t e of ascent during m i g r a t i o n was c a l c u l a t e d t o be 63 m/hr (163O-I65O hours, c r u i s e 68/35, 5 December, 1968, - 5 7 -F i g . 1 9 ) . This value i s l e s s than the average swimming speed of a euphausiid (90 m/hr) determined e x p e r i m e n t a l l y by Hardy and Bainbridge ( 1954) . The "morning r i s e " of the plankton was discussed by Cushing (1951) f o r many spepies of organisms i n c l u d i n g euphausiids ( p a r t i a l l y based on data on euphausiids by E s t e r l y , 1914, and Lewis, 195*0. E s t e r l y found much l a r g e r numbers of Nyctiphanes  simplex near the surface between 4 and 6 a.m. than during any other p e r i o d of the day. Lewis (195*0 presented data which suggested t h a t a morning r i s e occurred w i t h Euphausia tenera but not wi t h S t y l o c h e i r o n carinatum. Mauchline and F i s h e r (1969) were unable t o show the morning r i s e w i t h Meganyctiphanes norvegica or Thysanoessa  r a s c h i i and concluded t h a t t h i s probably r e s u l t e d from i n s u f f i c i e n t data. A s e r i e s of dawn echograms a t 200 kHz i s shown i n F i g . 2 0 . A pre-dawn r i s e i n the high-frequency s c a t t e r i n g l a y e r was observed during c r u i s e 69/25 and t o a l e s s e r extent during c r u i s e 70/8. Both r i s e s , however, occurred before n a u t i c a l t w i l i g h t and appeared to be c l o s e l y r e l a t e d to the time of the moonset [/the moon on 25 September ( c r u i s e 69/25) was a f u l l moon and the sky was only 4 / l 0 overcast; on 18 March ( c r u i s e 70/8) there was a 3/4 f u l l moon and the weather was c l e a r ^ j . The echograms from c r u i s e 69/27 showed no moon e f f e c t ( l / 2 f u l l moon,-8/10 overcast sky, and a moon which rose a t 0129 and s et at 1443). The planktpn descended during the nig h t and d i d not r i s e i n the morning; the only n o t i c e a b l e e f f e c t of su n r i s e appeared t o be a c o n s o l i d a t i o n of the l a y e r . - 5 8 -Flgure 1 9 . (facing) Echograms of the high-frequency s c a t t e r i n g l a y e r migrating to the surface i n the evening as recorded at 42 and 200 kHz when moored at the buoys, and an 1 1 kHz record from the same time period (cruise 68/35* 5 December I 9 6 8 ) . 42 ROSS metres - 5 9 -Figure 20. ( f a c i n g ) Echograms at 200 kHz t o show the behaviour of the high-frequency s c a t t e r i n g l a y e r around morning t w i l i g h t . The gain s e t t i n g s on the sounder were v a r i e d but the t i m e - v a r i a b l e -gain (TVG) was the same on a l l f o u r occasions. The TVG was set f o r these recordings'; a t values which were hoped to produce a l i n e a r response w i t h depth ( i . e . t o c o r r e c t f o r abso r p t i o n and s p h e r i c a l spreading l o s s e s ) . -60-0n c r u i s e 69/22 the moon again rose i n the evening (2225 hours) and set a f t e r s u n r i s e (1352). The moon was 2/3 f u l l and the sky l / l O o v e r c a s t . The moon seemed t o have kept part of the high-frequency s c a t t e r i n g l a y e r near the surface a t night so t h a t , w i t h t w i l i g h t and s u n r i s e , a d i s c r e t e l a y e r appeared t o migrate downwards. No morning r i s e was apparent although t h i s could have been obscured by the l a r g e numbers of f i s h e s a t the surf a c e a t t h i s time. The only evidence of a "morning r i s e " (Cushing, 1951) of the plankton found i n t h i s study appeared t o be most c l o s e l y a s s o c i a t e d w i t h moonset. T h i s would le n d support to the work of Ringelberg (1964), who suggested that i t was the r a t e of change of l i g h t i n t e n s i t y which was the stimulus f o r m i g r a t i o n , r a t h e r than the searching f o r an optimum isolume. The main argument ag a i n s t Ringelberg*s theory i n the past has been i t s f a i l u r e to e x p l a i n the pre-dawn r i s e of the plankton. One of the l a r g e s t problems i n t h i s study has been the v a r i a b i l i t y of the b i o l o g i c a l data. This can be seen i n the values f o r the concentration of euphausiids as shown i n F i g s . ? - l 4 b , and i n the echograms ( F i g s . 21, 22) . In a few instances ( f o r example Ca s s i e , 1959) aggregation of zooplankton has been a s s o c i a t e d w i t h hydrographic f e a t u r e s but, more f r e q u e n t l y , the reason f o r such aggregation has not been shown. Mauchline and F i s h e r (1969) have reported that euphausiid swarms have been observed f o r a number of sp e c i e s , i n c l u d i n g Euphausia p a c i f i c a . Mauchline a l s o has reported (from Marr 1962) t h a t Euphausia superba aggregates i n t o dense swarms or "patches" i n a l l phases of i t s l i f e c y c l e , -61-Figure 21. ( f a c i n g ) Echograms of the morning descent of the s c a t t e r i n g l a y e r s recorded at 11, 42, 107, and 200 kHz when the s h i p was moving ( c r u i s e 68/35> 5 December 1968). -62-Figure 22. ( f a c i n g ) Echogram a t 200 kHz during b i o l o g i c a l sampling operations w i t h a depth t r a c e of the sampler, p l u s a chart r e c o r d of the temperature v a r i a t i o n s detected by a t h e r m i s t o r on the sampler and recorded a t the time of sampling. metres Or- -^L 20 40 60 80 100 *— Sampler (CAT) depth t race L 2 0 0 kHz Ross i /<5*5 10SS CAT opened ® CAT closed ICll F l o w Temperature r v i «5 7 0 / 8 24 March 1970 -63-Patchiness i n Saanich I n l e t , as recorded by the 200 kHz echo-sounder, i s shown i n F i g s . 21 and 22. A t r a c e of the tempera-t u r e v a r i a t i o n a t the depth of the b i o l o g i c a l sampler i s a l s o shown i n F i g . 22. I t i s i n t e r e s t i n g t o note that the temperature decreases from 9.2°C t o 8.?°C as the gear moves from an area where no "patch" occurs t o an area where a "patch" e x i s t s . The s i z e of a "patch" can be determined from the echogram ( F i g . 22) . S u b j e c t i v e l y , one can choose a symmetrical "patch" which i s 15 m deep. The h o r i z o n t a l dimension i s then c a l c u l a t e d t o be around 500 m i n diameter ( c a l c u l a t e d both by the echo-sounder/beam angle/paper speed method and by the r e v o l u t i o n s of the flow meter i n the CAT du r i n g the b i o l o g i c a l sampling p e r i o d ) . Due t o the beam angle of the echo sounder, however,"patches"less than about 15 m i n diameter would not be d i s c e r n i b l e a t these depths unless the "patches" were widely separated. Thus, a symmetrical 15 m aggrega-t i o n or "patch", as described by Wiebe (1970), might not be d i s c e r n -i b l e . Such "patches", however, would be evident i f the echo-sounder transducer were lowered t o depths near that of the "patch". A collecting/echo-sounder system as described i n t h i s t h e s i s provides an e x c e l l e n t experimental system t o look i n t o the patchiness problem. The a d d i t i o n of a s a l i n i t y sensor to the e l e c t r o n i c s package of the CAT would a l l o w simultaneous measure-ments to be recorded on hydrographic parameters, along w i t h a c o u s t i c , b a c k - s c a t t e r i n g strengths and the b i o l o g i c a l c o l l e c t i o n s . In order t o a v o i d d i f f i c u l t i e s i n c o r r e l a t i n g surface i l l u m i n a t i o n w i t h underwater changes i n the s c a t t e r i n g or d i s t r i b u t i o n of organisms, -64-a h i g h - r e s o l u t i o n bathyphotometer should be added t o determine submarine i l l u m i n a t i o n a t depths where the organisms are found. The need f o r concurrent data f o r a l l measurements i s shown. I t i s apparent t h a t d i f f e r e n t days, w i t h d i f f e r e n t m e t e o r o l o g i c a l c o n d i t i o n s , d i f f e r e n t l o c a t i o n s , and d i f f e r e n t hydrographic c o n d i t i o n s a l l can s i g n i f i c a n t l y a f f e c t the r e s u l t s . The a c o u s t i c and b i o l o g i c a l data shown i n F i g s . 7-14 would be much b e t t e r i f they had been c o l l e c t e d s imultaneously. A l a r g e number of parameters should be recorded c o n c u r r e n t l y t o reduce the problems r e s u l t i n g from v a r i a b i l i t y , i n the environment. Thus, multi-parameter observations must n e c e s s a r i l y be undertaken i n f u t u r e s t u d i e s ; such s t u d i e s should be able to adequately handle the v a r i o u s parameters which a f f e c t the physiology and behavior, and t h e r e f o r e the ecology, of the organisms. High-frequency ( g r e a t e r than 50 kHz), h i g h - r e s o l u t i o n , echo-sounders appear t o be a v a l u a b l e t o o l i n studying the ecology of the euphausiids. Although s i m i l a r systems w i l l a l s o be u s e f u l f o r l o o k i n g at the other crustaceans, they w i l l probably be l e s s u s e f u l than f o r studying the euphausiids which tend t o s h o a l or swarm (Mauchline and F i s h e r , 1959) and are t h e r e f o r e more l o c a l i z e d i n the water column. Increased knowledge about the euphausiids, t h e i r numbers and d i s t r i b u t i o n would a l s o be of help i n a s s e s s i n g food stocks i n the ocean. Euphausiids are known to be the main supply f o r such economically important f i s h e s as h e r r i n g , mackerel, and some species of salmon. In f a c t , the euphausiids are thought t o be only second i n importa.nce to the copepod as the b a s i c animal food i n the sea, -65-and i n some areas they exceed the numbers of copepods i n mass and numbers (Boden, Johnson, and B r i n t o n , 1955)• More r e c e n t l y a great d e a l of commercial i n t e r e s t has been shown i n the p o s s i b i l i t i e s of h a r v e s t i n g euphausiids, p a r t i c u -l a r l y the l a r g e a n t a r c t i c s p e c i e s , Euphausia superba (Burukovskiy, 1967). One p a r t i c u l a r d i f f i c u l t y encountered i n f i s h i n g these animals i s to l o c a t e them i n s u f f i c i e n t d e n s i t i e s f o r n e t t i n g . I t i s b e l i e v e d t h a t information of the type given i n t h i s p r e s e n t a t i o n w i l l a s s i s t i n the understanding of such problems. -66-V. SUMMARY AND CONCLUSION. Euphausiids caused sound s c a t t e r i n g a t frequencies of 42, 107, and 200 kHz but not a t 11 kHz. D a i l y v a r i a t i o n s i n the volume-scattering c o e f f i c i e n t , ID(AZ) as determined from the zone of high-frequency s c a t t e r i n g , corresponded to v a r i a t i o n s i n the concentration of euphausiids c o l l e c t e d from the same depths. V a r i a t i o n s i n the patterns of v e r t i c a l m i g r a t i o n between c r u i s e s were p r i m a r i l y due to the presence o r absence of an o x y c l i n e at 100 m i n the i n l e t and s e c o n d a r i l y t o me t e o r o l o g i c a l e f f e c t s . When the o x y c l i n e was present, downward m i g r a t i o n stopped a t or near the top of the o x y c l i n e . In these i n s t a n c e s , the v e r t i c a l range over which the euphausiids were d i s t r i b u t e d was compressed. The concentration of euphausiids was high a l l day, as was m(Az); the concentration of euphausiids, and u ( d z ) , decreased during the evening m i g r a t i o n . In the absence of an o x y c l i n e , m i g r a t i o n occurred to greater depths i n the water column and the d i s t r i b u t i o n of euphausiids occurred over a wider v e r t i c a l range. The concentration a t depth was low i n the morning, and then g r a d u a l l y became higher throughout the day. The a c o u s t i c data showed t h i s p a t t e r n b e t t e r than the b i o l o g i c a l data, the b i o l o g i c a l data showing a grea t e r e f f e c t of patchiness. The p a t t e r n shown i n the absence of an o x y c l i n e probably best describes most oceanic s i t u a t i o n s . The general d a i l y nature of the high-frequency s c a t t e r i n g l a y e r [JII(AZ), and the euphausiid concentration and d i s t r i b u t i o n ] v a r i e d w i t h the presence or absence of moonlight and with the -67-weather c o n d i t i o n s . The presence of s t r o n g moonlight a c t s as a "cue" f o r a t l e a s t part of the population of euphausiids and these remain near the surface d u r i n g the n i g h t . Thus l a r g e r numbers of euphausiids, as shown by the zone of high-frequency s c a t t e r i n g , were observed d u r i n g the morning m i g r a t i o n periods when preceded by a moonlit n i g h t , than when preceded by a night w i t h l i t t l e o r no moonlight. The e f f e c t of v a r i a t i o n s i n i l l u m i n a t i o n as a r e s u l t of weather c o n d i t i o n s was more pronounced when an o x y c l i n e was present. In s i t u a t i o n s without the o x y c l i n e , reduced i l l u m i n a t i o n r e s u l t e d i n the population of euphausiids moving upwards i n the water column; t h e i r r e l a t i v e c oncentration remained unchanged. With reduced i l l u m i n a t i o n and the presence of an o x y c l i n e only p a r t of the population moved upwards r e s u l t i n g i n d i s p e r s i o n of the high-frequency s c a t t e r i n g l a y e r . In t h i s case, both m(az) and the euphausiid c o n c e n t r a t i o n decreased. Values f o r the s c a t t e r i n g c r o s s - s e c t i o n , O (cm 3), of a euphausiid increased w i t h the frequency of sound used; the values at the three frequencies f o r each c r u i s e were about one order of magnitude a p a r t . These values ranged from 4.81 x 10~5 t o 5»21 x 10"3 (200 kHz), 5.49 x IO" 6 t 0 3,99 x 1 0 - 4 ( 1 0 7 kHz), and 2.30 x 10~7 t o 3.67 x 10"5 (42 kHz). For a l l f r e q u e n c i e s , O was lowest f o r c r u i s e s where the average dry weight and length of a euphausiid were s m a l l and increased as the average s i z e and weight of a euphausiid i n c r e a s e d . The concentration of euphausiids c o l l e c t e d w i t h a 10 mpi net (coarse, 2.16 mm opening) showed b e t t e r agreement with the volume-scat ter ing c o e f f i c i e n t s , !H(AK), than catches with a 40 mpi net ( f i n e , 0.47 >™ opening) i n s i t u a t i o n s where l a r g e numbers of -68-s m a l l (<10 mm i n length) euphausiids were present. This would be expected since the l a r g e euphausiids are much b e t t e r s c a t t e r e r s of sound ( l a r g e r o ) . A "dawn r i s e " i n the plankton r e s u l t i n g from s u n r i s e was not observed. In two instances a r i s e i n the plankton towards the surface occurred j u s t p r i o r to downward mi g r a t i o n and appeared to be a s s o c i a t e d w i t h moonset. An echo-sounder system such as the one used i n the present study appears to be extremely w e l l s u i t e d f o r studying the problem of patchiness which has plagued marine e c o l o g i s t s f o r years. Q u a n t i t a t i v e measurements are p o s s i b l e and could provide u s e f u l infor m a t i o n on zooplankton standing s t o c k s ( p r i m a r i l y euphausiids and, s e c o n d a r i l y , other c r u s t a c e a n s ) . Such inform a t i o n would be u s e f u l i n a s s e s s i n g and developing p o l i c i e s r e l a t e d t o the environ-ment and to commercial and sport f i s h e r i e s . -69-V I . REFERENCES ALBERS, V.M. 1965. Underwater A c o u s t i c s Handbook - I I . Pennsylvania S t a t e U n i v e r s i t y P r e s s , U n i v e r s i t y Park, Pennsylvania. 356 pp. BARHAM, E.G. 1963. Siphonophores and the deep s c a t t e r i n g l a y e r . Science, 40(3568): 826-828. , 1966. Deep s c a t t e r i n g l a y e r migration and composition: observations from a d i v i n g saucer. Science, 1 5 l ( 3 ? l 6 ) : 1399-1402. BARRACLOUGH, W.E. and R.H. HERLINVEAUX. 196I. Midwater t r a w l i n g through the echo s c a t t e r i n g l a y e r i n Saanich I n l e t , March 1-2, I 9 6 I . Manuscripts Report S e r i e s ( B i o l o g i c a l ) , No. 712. F i s h . Res. Bd. Canada. 11 pp. , 1965. E x p l o r a t o r y s t u d i e s of the echo s c a t t e r i n g l a y e r s i n Saanich I n l e t and the S t r a i t of Georgia, B r i t i s h Columbia. Manuscript Report S e r i e s , No. 199. F i s h . Res. Bd. Cars.da. 29 pp. & f i g s . BARRACLOUGH, W.E., R.J. LeBRASSEUR and O.D. KENNEDY. I969. Shallow s c a t t e r i n g l a y e r i n the s u b a r c t i c P a c i f i c Ocean: d e t e c t i o n by a high-frequency echo sounder. Science, 166(3905): 611-613. BARY, B.McK. 1966a. Q u a l i t a t i v e observations of s c a t t e r i n g of 12 kc/s sound i n Saanich I n l e t , B r i t i s h Columbia. Deep-Sea Res., 13: 667-677. , 1966b. Back s c a t t e r i n g a t 12 kc/s i n r e l a t i o n to biomass and numbers of zooplanktonic organisms.in Saanich I n l e t , B r i t i s h Columbia. Deep-Sea Res., 13: 655-666. , I967. D i e l v e r t i c a l m i g r a t ions of underwater s c a t t e r i n g , mostly i n Saanich I n l e t , B r i t i s h Columbia. Deep-Sea Res., 44 : 35-50.. BARY, B.McK., W.E. BARRACLOUGH and R.H. HERLINVEAUX. 1962. S c a t t e r i n g of underwater sound i n Saanich I n l e t , B r i t i s h Columbia. Nature, 194(4823): 36-37. BARY, B.McK. and E . J . FRAZER. 1970. A high-speed, opening-closing plankton sampler (catcher I I ) and i t s e l e c t r i c a l a c c e s s o r i e s . Deep-Sea Res., 17(4): 825-835. BARY, B.McK. and. R.E. PIEPER. 1970. S o n i c - s c a t t e r i n g s t u d i e s i n Saanich I n l e t , B r i t i s h Columbia: a p r e l i m i n a r y r e p o r t , p. 601-6 l l . G.B. Farquhar (ed.) i n Proceedings of an I n t e r n a t i o n a l Symposium on B i o l o g i c a l Sound S c a t t e r i n g i n the Ocean. Maury Center f o r Ocean Science, Department of the Navy, Washington, D.C. -70-BATZLER, W.E. and R.J. VENT. 1967. Volume-scattering measurements a t 12 kc/s i n the Western P a c i f i c . J_. Acoust. Soc. Am., 41! 15^-157. BEAMISH, P.C. 1969. Q,uantative measurements of marine a c o u s t i c s c a t t e r i n g from zooplanktonic organisms. U n i v e r s i t y of B r i t i s h Columbia, Ph.D. T h e s i s . 89 pp. BODEN, B.P. 1950. Plankton organisms i n the deep s c a t t e r i n g l a y e r . U.S. Navy E l e c t r o n i c s Lab. Rep. No. 186. 29 pp. BODEN, B.P. and E.M. KAMPA. I965. An aspect of euphausiid ecology revealed by echo-sounding i n a f j o r d . Crustaceana, 9' 1.55-173• BODEN, B.P., M.W. JOHNSON, and E.. BRINTON. 1955. The euphausiacea (Crustacea) of the North P a c i f i c . B u l l . S c r i p p s I n s t . Oceanogr., 6(8): 287-400 BURUKOVSKIY, R.N. (e d . ) . 1967. A n t a r k t i c h e s k i y k r i l ( A n t a r c t i c k r i l l ) . A t l a n t i c Sr. j ent i f ic-Research I n s t i t u t e f o r F i s h e r i e s  and Oceanography, K a l i n i n g r a d . 1-92 p. T r a n s l a t i o n No, 42,053• U.S. Department of Commerce, J o i n t P u b l i c a t i o n s Research S e r v i c e . CASSIE, R.M. 1959* An experimental study of the f a c t o r s inducing aggregation i n marine plankton. New Zealand J , S c i . 2: 339-365. CHAPMAN, R.P. and J.R. MARSHALL. 1966. Reverberation from deep s c a t t e r i n g l a y e r s i n the western North A t l a n t i c . J . Acoust. Soc. Am., 40: 405-411. CLARKE, G.L. and R.H. BACKUS. 1956. Measurements of l i g h t p e n e t r a t i o n i n r e l a t i o n to v e r t i c a l m i g r a t i o n and records of luminescence of deep sea animals. Deep-Sea Res., 4: 1-14. CLARKE, W.D. 1970. Comparison of d i f f e r e n t i n v e s t i g a t i v e techniques f o r s t u d y i n g the deep s c a t t e r i n g l a y e r s . , p. 551-562. G.B. Farquhar ( e d . ) . i n Proceedings of an I n t e r n a t i o n a l Symposium  on B i o l o g i c a l Sound S c a t t e r i n g i n the Ocean. Maury Center f o r Ocean Science, Department of the Navy, Washington, D.C. CUSHING, D.H. 1951. The v e r t i c a l m i g r a t i o n of pl a n k t o n i c c r u s t a c e a . B i o l . Rev., 26: 158-192. CUSHING, D.H., F.R. HARDEN JONES, R.B. MITS0N, G.H. ELLIS, and G. PEARCE. 1963. Meausrements of the t a r g e t s t r e n g t h of f i s h . J . B r i t . I n s t . Radio Engr. 1963. p. 299-303. D0WD, R.G., E. BAKKEN, and 0. NAKKEN. 1970. A comparison between two s o n i c measuring systems f o r demersal f i s h . J . F i s h , Res. Bd. Canada, 27(4): 737-742. -71-ESTERLY, CO. 1914. The v e r t i c a l d i s t r i b u t i o n and movements of the Schizopoda of the San Diego r e g i o n . Univ. C a l i f . P u b i s . Z o o l . , 13(5)1 123-145. FARQUHAR, G.B. ( e d i t o r ) . 1970. Proceedings of an I n t e r n a t i o n a l Symposium on B i o l o g i c a l Sound S c a t t e r i n g i n the Ocean. Maury Center f o r Ocean Science, Department of the Navy, Washington, D.C. 642 pp. GOLD, B.A. I965. Measurements of volume s c a t t e r i n g from a deep s c a t t e r i n g l a y e r . J . Acoust. Soc. Am., 40: 688-696. HARDY, A.C. and R. BAINBRIDGE. 1954. Experimental observations on the v e r t i c a l m i g r ation of plankton animals. J , mar, b i o l . Ass. U.K., 33s 409-448. HANSEN, W.J. and M.J. DUNBAR. 1970. B i o l o g i c a l causes of s c a t t e r i n g l a y e r s i n the A r c t i c Ocean, p. 508-526. G.B. Farquhar ( e d . ) . i n Proceedings of an I n t e r n a t i o n a l Symposium on B i o l o g i c a l  Sound S c a t t e r i n g i n the Ocean. Maury Center f o r Ocean Science, Department of the Navy, Washington, D.C. HASLETT, R.W.G. 1962a. Measurements of the dimensions of f i s h t o f a c i l i t a t e c a l c u l a t i o n s of echo-strength i n f i s h d e t e c t i o n . J . cons. i n t . e x p l o r . Mer, 27(3): 261-269. , 1962b. Determination of the a c o u s t i c b a c k - s c a t t e r i n g patterns and cross s e c t i o n s of f i s h . B r i t . J . A p p l . Rhys., 13: 349-357. HERLINVEAUX, R.H. 1962. Oceanography of Saanich I n l e t i n Vancouver I s l a n d , B r i t i s h Columbia. J . F i s h . Res. Bd. Canada, 19(l)« 1-37. HERSEY, J.B. and R.H. BACKUS. 1962. Sound s c a t t e r i n g by marine organisms. No. 13, p. 498-539. M. H i l l (ed.) i n The Sea: ideas and observations on progress i n the study of the seas. V o l . 1. I n t e r s c i e n c e , New York. HERSEY, J.B., R.H. BACKUS, and J . HELLWIG. 1962. Sound-scattering s p e c t r a of deep s c a t t e r i n g l a y e r s i n the western North A t l a n t i c Ocean. Deep-Sea Res., 8: 196-210. ISAACS, J.D. and L.W. KIDD. 1953. Isaacs-Kidd midwater t r a w l . S c r i p p s I n s t i t u t i o n of Oceanography, Ref. 53-3. 21 pp. KAMPA, E.M. and B.P. BODEN. 1954. Submarine i l l u m i n a t i o n and the t w i l i g h t movements of a so n i c s c a t t e r i n g l a y e r . Nature, 174: 869-874. LENARZ, W.H. and J.H. GREEN. 1971. E l e c t r o n i c processing of a c o u s t i c a l data f o r f i s h i n g r e s e a r c h . J . F i s h . Res. Bd. Canada, 28(3): 446-447. -72-LEWIS, J.B. 195*1" • The occurrence and v e r t i c a l d i s t r i b u t i o n of the Euphausiacea of the F l o r i d a Current. B u l l , mar. S c i . G u l f . C a r r i b b . , 4: 265-301. LOVE, R.H. 1969. An i m p e r i a l equation f o r the determination of the maximum side-aspect t a r g e t s t r e n g t h of an i n d i v i d u a l f i s h . Naval Oceanographic O f f i c e , Washington, D.C. Ref. No. 69-11. 17 pp. LYMAN, G. 1948. The seas phantom bottom. S c i . Won., 66: 87-88. MARSHALL, J.R. and R.P. CHAPMAN. 1964. Reverberation from a deep s c a t t e r i n g l a y e r measured w i t h e x p l o s i v e sound sources. J_. Acoust. Soc. Am., 36: 164-166. MAUCHLINE, J . and L.R. FISHER. 1969. The b i o l o g y of euphausiids. 453 PP. F.S. R u s s e l l and M. Yonge (eds.) i n Advances i n Marine B i o l o g y . V o l . 7. Academic P r e s s , London. McNAUGHT, D.C. 1969» Developments i n a c o u s t i c plankton sampling. Proc. 12th Conf. Great Lakes Res. I969: 61-68. I n t e r n a t i o n a l Assoc. Great. Lakes Res. MOORE, H.B. 1950. The r e l a t i o n between the s c a t t e r i n g l a y e r and the Euphausiacea.. B i o . B u l l . , 99(2): 181-212. NORTHCOTE, T.G. 1964. Use of a high-frequency echo sounder to record d i s t r i b u t i o n and m i g r a t i o n of Chaoborus l a r v a e . Limnol. & Oceanogr., 9 ( l ) : 87-91. PICKWELL, G.V., R.J. VENT, E.G. BARHAM, W.E. BATZLER, and I.E. DAVIES. 1970. B i o l o g i c a l a c o u s t i c s c a t t e r i n g o f f southern C a l i f o r n i a , B a j a C a l i f o r n i a , and Guadalupe I s l a n d , p. 490 -507 G.B. Farquhar (ed.) i n Proceedings of an I n t e r n a t i o n a l Symposium on B i o l o g i c a l Sound S c a t t e r i n g i n the Ocean. Maury Center f o r Ocean Science, Department of the Navy, Washington, D.C. RINGELBERG, J . 1964. The p o s i t i v e l y p h o t o t a c t i c r e a c t i o n of Daphnia magna St r a u s : a c o n t r i b u t i o n t o the understanding of d i u r n a l v e r t i c a l m i g r a t i o n . Netherlands J . Sea Res., 2(3): 319-406. VIGOUREUX, P. and J.B. HERSEY. 1962. Sound i n the sea. No. 12, p. 476-497. M. H i l l ( e d . ) . i n The Sea: ideas and  observations on progress i n the study of the seas. V o l . 1. I n t e r s c i e n c e . New York. WIEBE, P.H.. 1970. S m a l l - s c a l e s p a c i a l d i s t r i b u t i o n i n oceanic zooplankton. Limnol. & Oceanogr., 15(2): 205-217. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0302442/manifest

Comment

Related Items