UBC Theses and Dissertations

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UBC Theses and Dissertations

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

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A STUDY OF THE RELATIONSHIP BETWEEN ZOOPLANKTON AND HIGH-FREQUENCY SCATTERING OF UNDERWATER SOUND  R i c h a r d 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 t h e Department o f ZOOLOGY and INSTITUTE OF OCEANOGRAPHY  We a c c e p t t h i s t h e s i s a s conforming t o t h e r e q u i r e d standard  THE UNIVERSITY OF BRITISH COLUMBIA O c t o b e r , 1971  In  presenting this  thesis  in p a r t i a l  fulfilment of  an advanced degree at the U n i v e r s i t y of B r i t i s h the L i b r a r y s h a l l I  f u r t h e r agree  make i t  freely available  that permission  for  the requirements f o r  Columbia,  I agree  r e f e r e n c e and  f o r e x t e n s i v e copying o f  this  that  study. thesis  f o r s c h o l a r l y purposes may be g r a n t e d by the Head of my Department o r by h i s of  this  representatives. thesis  for  It  financial  i s understood that gain s h a l l  written permission.  Department  of  The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada  Columbia  copying o r p u b l i c a t i o n  n o t . b e allowed without my  i Chairmen:  Dr. B. McK.  Bary, Dr. A. G.  Lewis  ABSTRACT  Q u a n t i t a t i v e v o l u m e - s c a t t e r i n g measurements were compared t o the d i s t r i b u t i o n of e u p h a u s i i d s i n S a a n i c h I n l e t , B r i t i s h S c a t t e r i n g was  r e c o r d e d a t 42,  107,  and 200  kHz  Columbia.  from the depths o f  h i g h e u p h a u s i i d c o n c e n t r a t i o n s , and 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 were determined. 11  kHz  No s c a t t e r i n g from e u p h a u s i i d s was  echo-sounder.  r e c o r d e d by a  D a i l y v a r i a t i o n s i 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(Az), g e n e r a l l y compared w e l l w i t h v a r i a t i o n s i n the concentration of euphausiids.  The d a i l y b e h a v i o u r of the h i g h -  f r e q u e n c y s c a t t e r i n g layer., and t h e r e f o r e m(az) o f e u p h a u s i i d s , was w e l l as t h e presence  i n f l u e n c e d by moonlight  and the c o n c e n t r a t i o n  and weather c o n d i t i o n s as  o r absence of an o x y c l i n e i n the  inlet.  In the absence of an o x y c l i n e c o n d i t i o n s would have been c l o s e r t o c o n d i t i o n s i n the open ocean.  Under these  circumstances  e u p h a u s i i d c o n c e n t r a t i o n s and m ( i z ) were low i n the mornings and g r a d u a l l y i n c r e a s e d throughout layer consolidated.  the day;  the h i g h - f r e q u e n c y  scattering  D u r i n g t h e evening m i g r a t i o n , the l a y e r became  more d i f f u s e , and the number of e u p h a u s i i d s per c u b i c metre decreased. The  s c a t t e r i n g c r o s s - s e c t i o n , O ( c m ) , of a e u p h a u s i i d 3  found t o i n c r e a s e w i t h the average increased frequency.  d r y weight and  F o r each c r u i s e 0 was  approximately  o f magnitude a p a r t a t the t h r e e f r e q u e n c i e s . ranged IO  - 4  from 4.81  x 10"5  t o 5.21  x 10~3  (200  l e n g t h , and  The  -  (42  with order  v a l u e s of CT ( i n  kHz), 5 . 4 9  (107 kHz), and 2.30 x IO"? t o 3.67 x 10 5  one  x 10  kHz).  - 6  was  cm )  t o 3.99  2  x  ii  TABLE OF CONTENTS Page I.  II.  INTRODUCTION  1  MATERIALS AND METHODS  8  F i e l d Work  8  Laboratory Analyses:  Biological  16  Laboratory Analyses:  Acoustic  17 20  Mathematics and Theory . . . . . . . . . . . . . .  III.  27  RESULTS  27  D i e l V a r i a t i o n s During Each C r u i s e 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  Cruise Averages  IV.  V.  VI.  43  DISCUSSION  51  SUMMARY AND CONCLUSIONS  66  REFERENCES  '.  67  i i i L I S T OF TABLES Table 1.  2.  3.  4.  5.  6.  7.  Subject  Page  C r u i s e numbers, dates a n d t h e presence o r a b s e n c e o f a n 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  Times o f moonset, s u n r i s e , sunset, moonrise, moon p h a s e , a n d 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  W e a t h e r 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  T o t a l r a d i a t i o n f o r each hour i n l a n g l e y s a t D e p a r t u r e B a y , 1969  36  P o t e n t i a l s c a t t e r e r s other than euphausiids c a u g h t 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 the high-frequency s c a t t e r i n g l a y e r  . .  42  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  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 , a n d mean l e n g t h o f e u p h a u s i i d s f r o m t h r e e samples from each c r u i s e . . . . .  50  iv  LIST OF FIGURES Figure 1.  2.  Subject  Page  Chart o f S a a n i c h I n l e t w i t h l o c a t i o n s o f t h e mooring buoys and t h e b i o l o g i c a l s a m p l i n g a r e a  ....  9  A c h a r t - p a p e r r e c o r d of the a c o u s t i c i n f o r m a t i o n r e c o r d e d on magnetic t a p e  1^-  B l o c k diagram o f t h e s h i p - b o a r d r e c o r d i n g a p p a r a t u s f o r t h e a c o u s t i c r e c o r d i n g s on magnetic t a p e . . . . .  15  B l o c k diagram o f t h e l a b o r a t o r y equipment f o r t h e acoustic analyses  18  5.  Diagram o f t h e e x p e r i m e n t a l model  22  6.  Temperature and oxygen d i s t r i b u t i o n s a t t h e buoys on t h r e e c r u i s e s  7.  C r u i s e 69/3. D a i l y v a r i a t i o n s i n m(Az)(a) and e u p h a u s i i d c o n c e n t r a t i o n s (b) ....  33  C r u i s e 69/8. D a i l y v a r i a t i o n s i n m ( a z ) ( a ) and euphausiid concentrations ( b ) .  33  C r u i s e 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.  C r u i s e 69/22. D a i l y v a r i a t i o n s i n m ( i z ) ( a ) e u p h a u s i i d c o n c e n t r a t i o n s (b)  34  3.  4.  8.  9. 10.  11. 12.  13.  14.  15.  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 e u p h a u s i i d c o n c e n t r a t i o n s (b)  C r u i s e 70/3. D a i l y v a r i a t i o n s i n m(4z)(a) e u p h a u s i i d c o n c e n t r a t i o n s (b)  m(Az)(a)  28  and  m(Az)(a)  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 n i ( i z ) ( a ) euphausiid concentrations ( b ) , . . . . . .  C r u i s e 70/8. Daily variations in euphausiid concentrations ( b ) .  Saanich  and 38 and 38  and 40 and 40  Average v a l u e s o f t h e s c a t t e r i n g c r o s s - s e c t i o n , o ( c m ) , o f a e u p h a u s i i d f o r each c r u i s e a t 42, 107 and 200 kHz  45  Average v a l u e s o f t h e s c a t t e r i n g c r o s s - s e c t i o n , <j(cm ), o f a e u p h a u s i i d f o r each c r u i s e a t 200 kHz and the average d r y weight o f a e u p h a u s i i d f o r each c r u i s e  47  3  16.  3  V  LIST OF FIGURES Figure 17.  18.  19.  20.  21.  22.  (continued)  Subject  Page  The a v e r a g e 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 , ra(iz), f o r each c r u i s e a t 200 kHz and t h e t o t a l weight o f e u p h a u s i i d s t h a t c o r r e s p o n d t o t h e volume d e f i n e d by ra(Az)  48  Echograms a t 11, 4 2 , 107, and 200 kHz d u r i n g t h e day when moored a t t h e buoys ( c r u i s e 68/35» 5 December 1968)  52  Echograms 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 m i g r a t i n g t o the surface i n the evening as r e c o r d e d a t 42 and 200 kHz when moored a t the buoys and an 11 kHz r e c o r d from t h e same t i m e p e r i o d ( c r u i s e 68/35» 5 December, 1968) . . . Echograms a t 200 kHz t o show t h e b e h a v i o u r o f 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 . . . . . . . . . . . . Echograms o f t h e morning d e s c e n t o f t h e s c a t t e r i n g l a y e r s r e c o r d e d a t 11, 4 1 , 107, a n d 200 kHz when t h e s h i p i s moving ( c r u i s e 68/35> 5 December,  58  59  1968).  61  Echogram a t 200 kHz d u r i n g b i o l o g i c a l s a m p l i n g operations w i t h a depth t r a c e o f the sampler, p l u s a chart r e c o r d o f the temperature v a r i a t i o n s d e t e c t e d ' by a t h e r m i s t o r on t h e sampler and recorded a t the time o f sampling .  62  vi ACKNOWLEDGMENTS The a u t h o r w i s h e s t o thank t h e many p e r s o n s who have helped during t h i s study.  S p e c i a l t h a n k s must go t o my a d v i s o r s ,  D r . B.McK. B a r y f o r s u p p o r t i n g t h e p r o j e c t t h r o u g h i t s p r e l i m i n a r y s t a g e s and s u p p l y i n g t h e equipment needed f o r t h e work, and D r . A.G, L e w i s f o r h e l p i n c o m p l e t i n g t h e s t u d y and c r i t i c i z i n g t h e m a n u s c r i p t . T h i s work was s u p p o r t e d by t h e Defense Research Board o f Canada t o whom I owe s p e c i a l t h a n k s . I am a l s o i n d e b t e d t o D r . H.D. F i s h e r , D r . P.H. L e B l o n d , D r . T,R, Parsons and D r . R.W. S t e w a r t f o r t h e i r h e l p f u l s u g g e s t i o n s and  criticisms. Many people d e s e r v e thanks f o r h e l p i n g w i t h t h e many a s p e c t s  of t h e p r o j e c t .  Mr. Wayne Ross and Ross L a b o r a t o r i e s , I n c . f o r t h e  c a l i b r a t i o n s o f t h e echo sounders and t h e i r c o n t i n u e d i n t e r e s t i n t h e p r o j e c t ; C a p t a i n C M a c a u l a y and t h e o f f i c e r s and crew o f t h e C.S.S. V e c t o r f o r t h e i r h e l p and a s s i s t a n c e d u r i n g t h e c r u i s e s ; Mr. D a v i d 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 h e l p on t h e c r u i s e s , i n t h e d a t a r e d u c t i o n , and f o r k e e p i n g t h e a u t h o r a l e r t on many o c c a s i o n s ; D r . R.W. S t e w a r t , D r . P.H. L e B l o n d and Mr. Ken Denman f o r a d v i c e and h e l p w i t h t h e t h e o r y and mathematics;  M r , Don Hume f o r  h e l p w i t h t h e e l e c t r o n i c s ; Mr. Bob Johns and M i s s 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 t h e m a n u s c r i p t ; a n d M i s s Diane DeBruyn, M r s . M a r i o n J o n e s , M r s . Dorothy James, and M i s s M a r i o n Canty f o r h e l p 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  t h e o r y on f o o d c h a i n s i n t h e marine  environment r e q u i r e s a c c u r a t e e s t i m a t e s o f t h e s t a n d i n g s t o c k and d i s t r i b u t i o n (patchiness) of plankton.  W h i l e p h y t o p l a n k t o n can be  r e l a t i v e l y e a s i l y d e t e r m i n e d from c h l o r o p h y l l a a n a l y s e s , z o o p l a n k t o n c o n c e n t r a t i o n s , b o t h i n terms o f a b s o l u t e numbers and t h e degree o f p a t c h i n e s s i n a w a t e r column, a r e much more d i f f i c u l t t o o b t a i n . The use o f h i g h - f r e q u e n c y echo sounders c o u l d 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 t h o s e organisms w h i c h a r e p o t e n t i a l sound s c a t t e r e r s . Three groups o f z o o p l a n k t o n which a r e i n t h e s e a i n h i g h numbers f i t i n t o t h i s c a t e g o r y ; t h e s e a r e copepods, e u p h a u s i i d s , and amphipods. A l l t h r e e groups a r e major f o o d organisms f o r f i s h e s i n t h e marine environment. Fishermen began u s i n g echo sounders t o l o c a t e h e r r i n g i n s h a l l o w w a t e r as e a r l y as 1930. l a y e r a t mid-depths (100  The e x i s t e n c e o f a sound s c a t t e r i n g  m t o 1000  m) i n deeper w a t e r was  s t u d i e d n e a r the end o f World War I I .  first  Marine a n i m a l s were s u g g e s t e d  as the sound s c a t t e r e r s when i t was n o t e d t h a t t h e "Deep S c a t t e r i n g L a y e r " (D.S.L.) m i g r a t e d towards t h e s u r f a c e a r o u n d s u n s e t and t o deeper depths around s u n r i s e . r e s u l t s t h r o u g h 1962  A r e v i e w o f most s t u d i e s and t h e i r  i s g i v e n by Hersey and Backus (1962).  A more  r e c e n t summary o f papers i n t h e f i e l d i s found i n F a r q u h a r (1970). The r e l a t i o n s h i p between z o o p l a n k t o n and s o n i c s c a t t e r i n g has not been a d e q u a t e l y s t u d i e d i n t h e p a s t .  Besides f i s h e s , several  -2t y p e s o f organisms have been s u g g e s t e d a s p o s s i b l e s c a t t e r e r s o f sound a t f r e q u e n c i e s c e n t e r e d a r o u n d 12 kHz. These i n c l u d e e u p h a u s i i d s and o t h e r c r u s t a c e a n s (Boden, 1950S Moore, 1950), p h y s o n e c t i d s i p h o n o p h o r e s (Barham, 1963» 1966), and s q u i d s (Lyman,  1948).  Some i n v e s t i g a t o r s have found h i g h c o n c e n t r a t i o n s o f  z o o p l a n k t o n from t h e d e p t h s where s t r o n g s c a t t e r i n g was r e c o r d e d . The c r u s t a c e a n E u p h a u s i a p a c i f i c a , f o r example, was r e p o r t e d t o be t h e 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 d e p t h s o f a s o n i c s c a t t e r i n g l a y e r r e c o r d e d a t 12 kHz (Boden and Kampa, 1965). In r e c e n t y e a r s s t u d i e s o f t h e D.S.L. have branched o u t 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 i n t e r e s t has been w i t h f i s h e s .  kHz r a n g e ) , and t h e p r i m a r y  Most a u t h o r s have c o n c l u d e d t h a t  f i s h e s a r e t h e most l i k e l y s c a t t e r e r s o f sound a t f r e q u e n c i e s around 12 kHz (Hersey and B a c k u s , 1962).  The g a s - f i l l e d f l o a t s o f  p h y s o n e c t i d s i p h o n o p h o r e s a p p e a r 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 t h e organisms have o n l y been caught s p o r a d i c a l l y from d e p t h s where t h e 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  e u p h a u s i i d s h r i m p would be t h e s c a t t e r i n g agent a t f r e q u e n c i e s around 12 k H z . B a r y (1966b) compared t h e v e r t i c a l d i s t r i b u t i o n o f both e u p h a u s i i d s and amphipods w i t h t h e l o c a t i o n o f a 12 kHz s c a t t e r i n g l a y e r i n S a a n i c h I n l e t , B r i t i s h C o l u m b i a . Because he found no c o n s i s t e n t r e l a t i o n s h i p between t h e r e c o r d e d s c a t t e r i n g and t h e biomass o r numbers p f specimens, he c o n c l u d e d t h a t z o o p l a n k t o n  -3organisms o f l e n g t h s up t o 2 cm were n o t c a u s i n g b a c k s c a t t e r i n g o f s u f f i c i e n t i n t e n s i t y t o be r e c o r d e d a t t h i s d e p t h . S a a n i c h I n l e t , B a r r a c l o u g h and H e r l i n v e a u x  (1965) found  Also i n high  c o n c e n t r a t i o n s o f hake ( M e r l u c c i u s p r o d u c t u s ) a t t h e d e p t h s 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 s p o r a d i c use o f echo-sounders a t f r e q u e n c i e s g r e a t e r t h a n 30 kHz i n s t u d i e s o f t h e 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 t h e d i s t r i b u t i o n s . o f e i t h e r zooplankton concluded  or fishes.  B a r r a c l o u g h , L e B r a s s e u r , and Kennedy  (1969)  t h a t s h a l l o w s c a t t e r i n g l a y e r s r e c o r d e d a t 200 kHz i n t h e  P a c i f i c p r o b a b l y r e s u l t e d from z o o p l a n k t o n , p r i m a r i l y l a r g e copepods, i n c o n c e n t r a t i o n s up t o 150  p e r cubic meter.  used i n a l a k e by N o r t h c o t e  (1964) t o r e c o r d  A 200 kHz sounder was the d i s t r i b u t i o n of  Chaoborus l a r v a e , b u t t h e e x i s t e n c e o f a gas bubble i n t h e head o f 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), u s i n g  v a r i o u s f r e q u e n c i e s g r e a t e r than  12 kHz t o s t u d y p l a n k t o n 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 s t r e n g t h s were p r o p o r t i o n a l t o t h e biomass o f z o o p l a n k t o n i c t a r g e t s when t h e p r o p e r f r e q u e n c y was u s e d . corresponded  A t 200 kHz s c a t t e r i n g r e c o r d s  t o b i o l o g i c a l c a t c h e s c o n s i s t i n g p r i m a r i l y o f Daphnia s p .  He s u g g e s t s t h a t t h e use o f v a r i o u s f r e q u e n c i e s would make i t p o s s i b l e t o separate zooplankton  s p e c i e s w i t h o u t b u b b l e s ( a s Daphnia)  from t h o s e w i t h b u b b l e s ( s u c h a s C h a o b o r u s ) .  I n h i s s t u d y , back-  s c a t t e r i n g s t r e n g t h s were d e t e r m i n e d s e m i - q u a n t i t a t i v e l y by u s i n g a r e f l e c t a n c e spectrophotometer  on t h e g r a p h i c a l r e c o r d s .  Hansen and  Dunbar (1970) have shown t h a t t h e e x i s t e n c e o f a 100 kHz s c a t t e r i n g l a y e r i n t h e A r c t i c corresponded  with the accumulation  o f thecosomatous  pteropods. B a r y ( p e r s . comm.) a n d B a r y and P i e p e r (1970) have r e p o r t e d that the depth d i s t r i b u t i o n o f euphausiids Columbia, corresponded This high-frequency  i n Saanich I n l e t , B r i t i s h  t o t h e d e p t h o f a s c a t t e r i n g l a y e r a t 200 k H z .  s c a t t e r i n g l a y e r and t h e maximum 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 were l o c a t e d a t a d e p t h s h a l l o w e r than t h e 12 kHz scattering layer.  F i s h e s and p h y s o n e c t i d s i p h o n o p h o r e s were caught  o n l y r a r e l y from t h i s h i g h - f r e q u e n c y  scattering region.  Numerous measurements have been r e p o r t e d on t h e t a r g e t s t r e n g t h s (analogous  t o t h e s c a t t e r i n g c r o s s - s e c t i o n ) o f many  f i s h e s ( s e e f o r example C u s h i n g e t a l . , 1963? H a s l e t t , 1962 a , b; Love, I 9 6 9 ) .  Few v a l u e s have been r e p o r t e d f o r p l a n k t o n .  Beamish  (1969) lowered an echo-sounder t r a n s d u c e r and hydrophone a r r a y i n t o a high-frequency He c o n c l u d e d  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.  t h a t , a t 102 k H z , t h e a c o u s t i c c r o s s - s e c t i o n o f a  e u p h a u s i i d was 1.35 x 10*"^ c m . 3  V o l u m e - s c a t t e r i n g measurements a t l o w f r e q u e n c i e s 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 r e p o r t e d by many authors.  F o r example, v o l u m e - s c a t t e r i n g measurements a t 12 kHz  have been r e p o r t e d by B a t z l e r and Vent (196?) and P i c k w e l l e t a l . (1970) . V o l u m e - s c a t t e r i n g measurements o v e r a w i d e r band o f f r e q u e n c i e s ( l - 30 k H z ) , u s i n g p o i n t charges a s sound s o u r c e s , were shown i n t h e papers o f Chapman and M a r s h a l l (1966), G o l d (1965), H e r s e y , 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 , a s w e l l a s s i g n a l p r o c e s s i n g , have  been developed  u s i n g these same f r e q u e n c i e s ; the major i n t e r e s t  i n t h e s e 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, a n d L e n a r z and Green, 1971). A g r e a t d e a l o f 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 S a a n i c h I n l e t , w h i c h i s l o c a t e d on t h e e a s t c o a s t o f 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 t h e s e s t u d i e s f o r a number o f r e a s o n s . The maximum depth o f t h e i n l e t i s 235 ra» i f has a l a r g e p o p u l a t i o n o f e u p h a u s i i d s , and appears t o s e r v e a s a n u r s e r y f o r s t o c k s o f d o g f i s h , h e r r i n g , and hake ( B a r r a c l o u g h and H e r l i n v e a u x , 1 9 6 l ) . As a r e s u l t o f a number o f f a c t o r s i n c l u d i n g a l a c k o f c i r c u l a t i o n i n the i n l e t , a s h a l l o w s i l l d e p t h , and a l o w f r e s h w a t e r r u n - o f f , an o x y c l i n e around 100 m i s p r e s e n t d u r i n g most o f t h e y e a r  (see  H e r l i n v e a u x , 1962, f o r a d i s c u s s i o n o f t h e p h y s i c a l oceanography of S a a n i c h I n l e t ) .  When p r e s e n t , oxygen c o n c e n t r a t i o n s below t h e  o x y c l i n e a r e l e s s t h a n 0.5 m l / l , and t h e bottom waters may be completely anoxic.  The o x y c l i n e s t o p s t h e downward m i g r a t i o n o f  e u p h a u s i i d s b u t n o t t h e f i s h e s ; t h u s t h e two p o p u l a t i o n s a r e o f t e n separated  vertically. The 12 kHz s c a t t e r i n g l a y e r i n S a a n i c h I n l e t and i t s  r e l a t i o n t o the h y d r o g r a p h i c p r o p e r t i e s o f t h e water column, and t o p l a n k t o n and f i s h d i s t r i b u t i o n s have been d i s c u s s e d by B a r y (1966 a , b , 1967)* B a r y , B a r r a c l o u g h , and H e r l i n v e a u x (1962), and B a r r a c l o u g h and H e r l i n v e a u x ( l 9 6 l , 1 9 ° 5 ) .  I n i t i a l s t u d i e s o f 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 z o o p l a n k t o n and f i s h d i s t r i b u t i o n s have been d i s c u s s e d by B a r y and P i e p e r (1970); t h e 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 o f e u p h a u s i i d s have been r e p o r t e d by Beamish (1969).  -6-  In previous studies i n Saanich I n l e t , s c a t t e r i n g was recorded g r a p h i c a l l y by echo-sounders mounted i n the h u l l s of ships (except f o r Beamish, 1970).  While the g r a p h i c a l records were  adequate to show s c a t t e r i n g l a y e r depths, they d i d not enable the measurement of back-scattering i n t e n s i t i e s , v a r i a t i o n s i n s c a t t e r i n g 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 a l s o not  considered.  The r e s u l t was that records were not very u s e f u l i n comparing scattering intensities. The purpose of the present study was to continue the work i n Saanich I n l e t with more exacting techniques using echosounders w i t h hull-mounted transducers.  The echo-sounder systems  were c a l i b r a t e d and ten c r u i s e s were completed from September I968 to March 1970.  Signals r e f l e c t e d from the s c a t t e r i n g layers  were recorded on magnetic tape.  From these recorded s i g n a l s the  back-scattered a c o u s t i c i n t e n s i t y was c a l c u l a t e d . The volumes c a t t e r i n g c o e f f i c i e n t and the acoustic cross-section of the s c a t t e r e r s was then determined.  The volume-scattering  coefficients  and the acoustic cross-sections were then compared to b i o l o g i c a l c o l l e c t i o n s taken during the same c r u i s e s . The study was  intended  to show q u a n t i t a t i v e l y the r e s u l t s of using various sound frequencies to study marine organisms and to b e t t e r define the r o l e of  zooplankton  i n s c a t t e r i n g . I t was a l s o hoped that the r e s u l t s would show whether or not the echo sounder could be used t o ( 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 o b s e r v a t i o n s on s e a s o n a l , d a i l y , and changes i n numbers o f z o o p l a n k t o n  (in situ).  climatic  -8-  II.  MATERIALS AND  METHODS.  F i e l d Work. The s t u d y was  c a r r i e d out i n S a a n i c h I n l e t on t h e  s o u t h e a s t c o a s t o f Vancouver I s l a n d , B r i t i s h Columbia ( F i g . l ) . The a r e a sampled was  i n t h e immediate v i c i n i t y o f two mooring  buoys l o c a t e d i n t h e c e n t e r o f t h e i n l e t . i n f o r m a t i o n was  The q u a n t i t a t i v e a c o u s t i c  c o l l e c t e d w h i l e moored t o the two buoys; t h e  b i o l o g i c a l c o l l e c t i o n s were t a k e n from t h e a r e a j u s t west o f t h e buoys. The d a t a were c o l l e c t e d from September 1968 March 1970.  Ten, two-week c r u i s e s were completed  p e r i o d (Table l ) .  through  during t h i s  Because o f changes i n the a c o u s t i c - r e c o r d i n g 1968)  procedures the f i r s t two c r u i s e s (September and December  have not been used f o r t h e q u a n t i t a t i v e p a r t of t h i s s t u d y ; t h e y were, however, u s e f u l f o r q u a l i t a t i v e o b s e r v a t i o n s and  calibration  data. Hydrographic  s t a t i o n s were o c c u p i e d a t f o u r l o c a t i o n s  i n t h e i n l e t ( F i g . l ) a t the b e g i n n i n g of each c r u i s e t o some oceanographic  parameters  determine  which might have a f f e c t e d t h e  b u t i o n s of the z o o p l a n k t o n and n e k t o n . i n c l u d e d t e m p e r a t u r e , s a l i n i t y and  The measurements t a k e n  oxygen.  B i o l o g i c a l and a c o u s t i c i n s t r u m e n t s were checked 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 .  and b i o l o g i c a l i n f o r m a t i o n was  and  The o r d e r i n which t h e a c o u s t i c a l  collected varied.  T h i s depended on  a v a i l a b i l i t y of t h e r e c o r d i n g equipment and t h e use of t h e a r e a by t h e R o y a l Canadian Navy.  distri-  sampling  F i g u r e 1. ( f a c i n g ) Chart of S a a n i c h I n l e t w i t h l o c a t i o n s of t h e mooring buoys, t h e b i o l o g i c a l s a m p l i n g a r e a , and t h e hydrographic s t a t i o n s .  -10-  TABLE 1 C r u i s e numbers, d a t e s , and t h e presence o r absence o f an o x y c l i n e around 100 m i n t h e w a t e r column.  Cruise  Dates  Oxycline P r e s e n t o r absent  68/31  23 September - 4 O c t o b e r , 1968  Absent  68/35  25 November - 5 December, I968  Present  69/3  29 J a n u a r y - 9 F e b r u a r y , I969  Present  69/8  1-13  Present  69/14  7 - 2 0 June, 1969  Present  69/22  25 J u l y  Absent  69/25  15-26  69/27  28 O c t o b e r - 7 November, I969  Present  70/3  20 - 30 J a n u a r y , 1970  Present  70/8  17 - 26 March, 1970  Present  A p r i l , 1969  - 8 A u g u s t , 1969 September, I969  Absent  -11The p r i m a r y b i o l o g i c a l s a m p l e r was t h e i n s t r u m e n t e d C a t c h e r I I (CAT) ( B a r y 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 d e p t h .  The f i l t e r s ( n e t s ) used were e i t h e r 2.5 o r 16  mesh/cm (mesh opening 2.16 mm o r 0.47 mm).  An i n s t r u m e n t package  on t h e CAT e n a b l e d measurements t o be r e c o r d e d ( t h r o u g h o u t a l l tows) on t h e d e p t h , t e m p e r a t u r e , number o f f l o w meter r e v o l u t i o n s , and the r a t e o f f l o w t h r o u g h t h e n e t .  The volume o f w a t e r f i l t e r e d  was c a l c u l a t e d from t h e r e c o r d e d f l o w meter c o u n t s .  The s i g n a l from  t h e depth t r a n s d u c e r on t h e i n s t r u m e n t package was t r a n s f o r m e d a t t h e s u r f a c e a n d i n t e r f a c e d t o a Ross* echo-sounder.  T h i s produced  a t r a c e o f t h e sampler d e p t h on the echogram d u r i n g t h e s a m p l i n g operations.  The d e p t h t r a c e was a d j u s t e d a t t h e s t a r t o f each  c r u i s e t o the s c a l e o f d e p t h a s shown by t h e 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 o b t a i n e d w i t h a 6 - f o o t I s a a c s - K i d d midwater t r a w l (IKMT) ( I s a a c s and K i d d , 1953).  The IKMT  c o u l d not be c l o s e d and, t h e r e f o r e , c o l l e c t i o n s from one d e p t h may have c o n t a i n e d specimens from s h a l l o w e r d e p t h s .  The depth-temperature  i n s t r u m e n t package was a l s o a t t a c h e d t o t h i s s a m p l e r . B i o l o g i c a l samples were t a k e n m a i n l y from t h e depths o f the high-frequency ("zooplanktonic") s c a t t e r i n g l a y e r .  Collections  were a l s o t a k e n from t h e r e m a i n d e r o f t h e w a t e r column.  Tows were  p r e d o m i n a n t l y d u r i n g t h e daytime ( i . e . s u n r i s e t o s u n s e t p e r i o d s ) ; o c c a s i o n a l tows were a l s o made d u r i n g t h e n i g h t .  The samplers were  towed a t speeds o f 5 ± 1 k t s ( 9 . 3 km/hr) f o r t h e CAT and 3.5 ± 1 k t s (5.5 km/hr) f o r t h e IKMT.  The s a m p l i n g d u r a t i o n f o r t h e CAT tows  *Ross L a b o r a t o r i e s , I n c . , S e a t t l e ,  Washington.  -12-  was from 2-14 minutes, depending on t h e abundance o f zooplankton a t the sampling d e p t h .  IKMT tows were m a i n t a i n e d " a t d e p t h " f o r a  d u r a t i o n o f 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 p r e s e r v e d on the s h i p i n 5$ formalin buffered with tetraborate sampled  (borax).  C o l l e c t i o n s were sub-  on board i f t h e approximate volume o f specimens was g r e a t e r  than 8 oz (232 m l ) .  Large decapods, cephalopods, f i s h e s , and f i s h  l a r v a e were removed b e f o r e sub-sampling. Three, Ross " F i n e l i n e " echo-sounders were used t o r e c o r d the s c a t t e r i n g . kHz.  These o p e r a t e d a t f r e q u e n c i e s o f 42, 107,  and 200  An 11 kHz Simrad t r a n s d u c e r , operated w i t h a Simrad EH^R  t r a n s c e i v e r / r e c o r d e r o r a G i f f t ( G D R - T ) t r a n s c e i v e r / r e c o r d e r , was a l s o used.  A l l t r a n s d u c e r s were h u l l mounted f o r t h e r e c o r d i n g s used t o  examine the s c a t t e r i n g .  Comparative echograms from t h e f o u r sounders  were made w h i l e moored a t the c e n t r a l buoys, d u r i n g the b i o l o g i c a l c o l l e c t i o n s , and d u r i n g the h y d r o g r a p h i c c a s t s .  Comparative  soundings  were conducted a t t h e buoys f o r 24 hours on e v e r y c r u i s e t o observe the d i e l change i n t h e s c a t t e r i n g  layer.  Q u a n t i t a t i v e a c o u s t i c i n f o r m a t i o n was a l s o c o l l e c t e d from a l l f o u r sounders.  C a l i b r a t i o n o f t h e echo-sounder systems f o r t h i s  purpose was c a r r i e d out by Ross L a b o r a t o r i e s , I n c . i n November 1968 i n Lake Washington.  C a l i b r a t i o n checks were t h e r e a f t e r conducted  on the systems a t t h e s t a r t o f a l l  subsequent c r u i s e s .  The sounders  were a l s o m o d i f i e d t o o b t a i n t h e r e t u r n s i g n a l b e f o r e i t had been a l t e r e d t o s u i t the r e q u i r e m e n t s o f t h e g r a p h i c r e c o r d e r .  The g a i n  c o n t r o l s on the Ross sounders were changed t o permit t h e use o f a  -13-  c a l i b r a t e d , stepped  gain c o n t r o l .  T h i s g a i n c o n t r o l c o u l d be  v a r i e d c o n t i n u a l l y between s t e p s 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 t h e f o u r sounders were r e c o r d e d on magnetic tape f o r l a t e r a n a l y s i s i n t h e l a b o r a t o r y (F'ig. 2 ) . Such r e c o r d i n g s were t a k e n o n l y w h i l e moored t o reduce s h i p n o i s e ( e l e c t r i c a l ) and t o reduce t h e p o s s i b i l i t y o f i n t e r f e r e n c e due t o water m o t i o n and a i r - b u b b l e s produced when t h e s h i p was underway. A b l o c k diagram o f t h e s h i p b o a r d a p p a r a t u s i s shown i n F i g . J. W h i l e t a p i n g was i n p r o g r e s s , a l l f o u r echo-sounders were t r i g g e r e d s i m u l t a n e o u s l y by t h e t r i g g e r p u l s e from t h e 107 kHz Ross r e c o r d e r . monitored  The t r i g g e r p u l s e and t h e f o u r r e t u r n echoes were  by a T e k t r o n i x model 5^9 s t o r a g e o s c i l l o s c o p e and r e c o r d e d  on f i v e channels  o f an Ampex model FR-1300 tape r e c o r d e r .  These  were r e c o r d e d a t a t a p e speed o f 30 i n c h e s / s e c , u s i n g FM r e c o r d and reproduce modules.  W h i l e r e c o r d i n g t h e s i g n a l r e t u r n s from  t h e s o u n d e r s , t h e p u l s e d u r a t i o n o f 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 t h e Ross sounders were t u r n e d o f f .  The beam a n g l e ( h a l f - p o w e r p o i n t ) f o r  t h e Ross sounders was 5° x 10° and f o r t h e Simrad was 22° x 22°. S i g n a l p r o c e s s i n g by t h e Ross system b e f o r e r e c o r d i n g on t h e magnetic tape was t o a m p l i f y , r e c t i f y , and t a k e t h e envelope of t h e a c o u s t i c return ( f i l t e r ) .  The s i g n a l from t h e Ross t r a n s c e i v e r had a  dynamic range o f 0.5 t o 100 v o l t s . the tape r e c o r d e r was ± 1 . 0  S i n c e t h e r e c o r d i n g range o f  v o l t s , t h e r e t u r n e d s i g n a l s were  a t t e n u a t e d by a t h r e e p o s i t i o n a t t e n u a t o r t o f i t t h e r e q u i r e m e n t s t h e tape r e c o r d e r and t o b e s t r e c o r d s c a t t e r i n g from t h e a r e a o f interest.  of  -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 i n f o r m a t i o n r e c o r d e d on magnetic t a p e . Due t o t h e slow response t i m e o f the g r a p h i c r e c o r d e r t h e f i n e d e t a i l p r e s e n t on t h e tape i s not shown.  imi] 60  200 kHz 80  ipitaiiilit  100  107 kHz  :  " CRUISE 69/ 3 Tape 7 pas 0 >' J. 23 20 nrW/ line 0702 hr» 5 Feb 69  50  metres  30  metres  0  metres  -15-  F i g u r e 3 . ( f a c i n g ) B l o c k diagram o f t h e s h i p - b o a r d a p p a r a t u s f o r a c o u s t i c r e c o r d i n g s on magnetic t a p e .  recording  trigger  Ross 107 kHz graphic recorder trigger pulse  "return  Transceiver  7  output pulse  trigger Ross 200 k H transceiver  signal  200 k H ,  z  return echo  Transducer  return signal Atten  Ross 107 k H transceiver  107 k H ,  z  return signal  Atten Ross 42 k H transceiver  42 k H ,  z  Tektronix 549 storage oscilloscope  return signal Atten  Simrad 11 k H transceiver  11 k H  z  z  return signal -**\ FM record  mode trigger  Ampex FR 1300 tape  recorder 30 ips  FM repro-  J?^?  mode  -16-  A c o u s t i c i n f o r m a t i o n was r e c o r d e d on tape f o r a p e r i o d of a p p r o x i m a t e l y  two minutes once every o t h e r hour, u n l e s s t h e  r e c o r d i n g s i t u a t i o n was such t h a t f i s h e s were o b s c u r i n g the h i g h frequency at  scattering layer.  These tape r e c o r d i n g p e r i o d s s t a r t e d  s u n r i s e w i t h the downward movement o f the l a y e r , and c o n t i n u e d  until  the l a y e r had m i g r a t e d  Laboratory Analyses; Plankton  t o t h e s u r f a c e near  sunset.  Biological  c o l l e c t i o n s o b t a i n e d i n the f i e l d were  i n the l a b o r a t o r y and s o r t e d i n t o t h e f o l l o w i n g groups: amphipods, decapods, chaetognaths, cephalopods and f i s h e s .  medusae,  counted euphausiids,  siphonophores,  The e u p h a u s i i d s , o f major i n t e r e s t i n  t h i s study, were s o r t e d i n t o " 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 c l a s s e s o f mean l e n g t h 0,6, 1.2,and 1.8 cm.  Amphipods  were s e p a r a t e d by s p e c i e s where p o s s i b l e , and i n t o l a r g e r taxonomic groups where s p e c i e s 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 specimens were low.  o r the number o f  Decapods were s e p a r a t e d i n t o p a s i p h a e i d s ,  s e r g e s t i d s , and m i s c e l l a n e o u s decapods.  Chaetognaths and medusae  were not s u b d i v i d e d , nor were siphonophores  w i t h t h e e x c e p t i o n of  p h y s o n e c t i d siphonophores.  l a r v a e were measured  for  F i s h e s and f i s h  t h e i r s t a n d a r d l e n g t h and the f i s h e s which were n u m e r i c a l l y  abundant were  identified.  A f t e r i n i t i a l s o r t i n g , p o r t i o n s o f s e l e c t e d samples o f euphausiids and  (10 from each s i z e group) were i d e n t i f i e d , measured,  the f r e e z e - d r i e d weight determined.  i n t h e f r e e z e - d r y e r ( V i r T i s Research, b e f o r e b e i n g weighed. water f i l t e r e d  The e u p h a u s i i d s were l e f t  G a r d i n e r , N.Y.) f o r 10 hours  The number o f organisms p e r c u b i c meter o f  f o r the CAT c o l l e c t i o n s was  determined.  Collections  -17of f i s h e s were p r i m a r i l y from the IKMT. b o t h by the CAT  and  F i s h l a r v a e were c o l l e c t e d  IKMT.  Laboratory Analyses t  Acoustic  In o r d e r 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 r e c o r d e d v o l t a g e s ( t h e v o l t a g e i s p r o p o r t i o n a l pressure),  i t was  v o l t a g e and  acoustic  n e c e s s a r y t o i n t e g r a t e the s i g n a l o f b o t h  the square o f the v o l t a g e o v e r the a r e a of  (high-frequency s c a t t e r i n g l a y e r ) .  the u s u a l t h i c k n e s s  the  interest  To s i m p l i f y a n a l y s e s of  d a t a , a s t a n d a r d i n t e g r a t i o n i n t e r v a l o f 20 m was was  to  the  s e l e c t e d as  this  of the 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 i n  Saanich I n l e t . To a v o i d the n e c e s s i t y and  of a n a l o g - t o - d i g i t a l  conversion  d i g i t a l i n t e g r a t i o n , an a n a l o g computer, d e v e l o p e d a t  the  I n s t i t u t e o f Oceanography, U n i v e r s i t y of B r i t i s h Columbia, employed f o r i n t e g r a t i o n o f t h e r e c o r d e d a c o u s t i c The  f r e q u e n c y response o f the  integrators  was 4),  signal (Fig.  i n the a n a l o g computer  c o u l d not handle t h e t h r e e h i g h e r f r e q u e n c i e s used i n t h i s experiment which n e c e s s i t a t e d  a reduction  of the tape r e c o r d e r from 30  i n the t a p e speed f o r the r e p r o d u c e mode i n c h e s / s e c (30  speed slowed by a f a c t o r of 8 ) . 20 m d e p t h i n t e r v a l was Two, and  Thus t h e  i p s ) t o 3^ i p s ( i . e . tape integration period  c a l c u l a t e d t o be 220  variable-time-delay  to stop i n t e g r a t i o n .  The  t r i g g e r s were d e v e l o p e d t o s t a r t  f i r s t t r i g g e r ( t ^ ) , i n i t i a t e d by 0  i n t e g r a t i o n p e r i o d which corresponded t o the t o p of t h e The  the  msec.  tape-recorded t r i g g e r s i g n a l ( t ) , determined the s t a r t of  scattering layer.  for  second t r i g g e r (t£)  was  the  the  high-frequency  set f o r a constant  -18-  Figure 4 . ( f a c i n g ) B l o c k 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 .  Variable time delay trigger  trigger pulse Ampex FR 1300 tape recorder 3 % i p s FM reproduce  o o X  0-21  I  mode  X N  j  Tektronix 549 storage oscilloscope  o  -J  220 m sec time delay trigger  ro X  X N  /off trigger for a n a l o g computer  Analog computer x /p 1  / x or y*x  2  y*y  or  yv  Sanborn two pin chart recorder  -19i n t e r v a l o f 2 2 0 msec and t u r n e d o f f t h e i n t e g r a t o r s a t t h e end of t h i s t i m e p e r i o d . the f i r s t t r i g g e r  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  (t^).  In t h e i n i t i a l t a p i n g , t h e s i g n a l t h a t went onto t h e magnetic tape was a m p l i f i e d and/or a t t e n u a t e d w i t h a p p r o p r i a t e c o m b i n a t i o n s so t h a t peak v o l t a g e s 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 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 p r e s e n t 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 t h e 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 , p r e s e n t o n l y d u r i n g some c r u i s e s , t h e r e p r o d u c e d s i g n a l was passed by two d i o d e s i n s e r i e s b e f o r e a r r i v i n g a t the a n a l o g computer.  The e f f e c t o f t h e d i o d e s was t o d r a i n any  s i g n a l g r e a t e r t h a n 1 . 2 v o l t s o f f t o ground. The a n a l o g computer was used here o n l y a s an i n t e g r a t o r o f t h e r e c t i f i e d v o l t a g e o r o f t h e square o f t h e v o l t a g e . The system i n t e g r a t e s o n l y two s i g n a l s a t a time (X and Y ) , so t h a t s i x r u n s were needed t o o b t a i n t h e v a l u e s f o r each d a t a b l o c k ( i . e . two minute t a p i n g p e r i o d ) . the same time p e r i o d .  each,  The echoes used i n each r u n were from  A f t e r t h r e e echoes had passed from t h e  s t a r t o f each r u n ( d a t a b l o c k ) , t h e 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 . N u m e r i c a l v a l u e s o f t h e i n t e g r a t i o n s were r e a d o f f o f a d i g i t a l v o l t meter ( H e w l e t t - P a c k a r d }  3 4 4 0 A  D.V.M., 3443A h i g h - g a i n  auto-range u n i t ) and were a l s o r e c o r d e d on a two c h a n n e l B r u s h c h a r t r e c o r d e r (model 2 2 0 ,  C l e v i t e Corp.).  The s i g n a l s were  m o n i t o r e d by t h e s t o r a g e o s c i l l o s c o p e t o check t h e r e p r o d u c e d  -20s i g n a l s and t o make c e r t a i n t h a t t h e 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 t h e p o r t i o n o f t h e 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 desired. The i n t e g r a t e d v o l t a g e s were then used t o o b t a i n t h e 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 h i g h - f r e q u e n c y ( o r "zooplanktonic")  scattering layer.  Since  i t was n o t p o s s i b l e t o  r e c o r d any s c a t t e r i n g from 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 r e g i o n on t h e 11 kHz Simrad echo-sounder, n u m e r i c a l  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 o f 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 strength, or i t s a b i l i t y t o s c a t t e r  sound from an i m p i n g i n g O  T  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 ,  d e f i n e d by Hersey and Backus ( 1 9 6 2 ) , i s  is = A where I  (i)  i s t h e i n t e n s i t y ( e r g s / s e c / c m ) o f t h e s c a t t e r e d wave 3  g  at a distance  z (cm) from t h e s c a t t e r e r , 0 (cm ) i s t h e s c a t t e r i n g 3  c r o s s - s e c t i o n , and I i s t h e i n t e n s i t y o f t h e i m p i n g i n g  acoustic  wave. If there  i s more t h a n one s c a t t e r e r i n t h e a c o u s t i c  beam, t h e 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 , m(Az), i s d e f i n e d by  Hersey and Backus (1962) a s  m(Az,f) = Ncr(f)  (2)  -21where N i s t h e number o f s c a t t e r e r s i n t h e volume d e f i n e d by A z and t h e beam a n g l e , and a i s t h e s c a t t e r i n g c r o s s - s e c t i o n o f t h e s c a t t e r e r which w i l l v a r y w i t h t h e f r e q u e n c y ( f ) used. l i q u a t i o n 1 can be m o d i f i e d t o i n c l u d e more than one s c a t t e r e r , where I s now r e f e r s t o the t o t a l i n t e n s i t y o f the s c 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 g i v e n by A l b e r s (1965) t o be  I = El  where p i s t h e root-mean-squared  (4)  (rms) a c o u s t i c p r e s s u r e ( d y n e s / c m ) , 2  jo i s t h e d e n s i t y o f t h e water (gms/cm ) and c i s t h e sound v e l o c i t y 3  i n the water  (cm/sec).  The e x p e r i m e n t a l s i t u a t i o n f o r t h e 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 a n g l e o f t h e sounders i s d e f i n e d by  t h e h a l f - p o w e r p o i n t s ; t h i s v a l u e i s f o r t h e f u l l a n g l e and i s shown i n t h e f i g u r e as 2-©-. The depths o f r e c o r d e d s c a t t e r i n g a r e from z± t o %2 (  i n  c m  ) measured from t h e t r a n s d u c e r f a c e , and t h e  mean depth o f t h e r e c o r d e d 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 r e c o r d e d as a f u n c t i o n o f t i m e , t h e depth can a l s o be w r i t t e n as  z = ct or t = £ c  -22-  Figure 5.  (facing)  Diagram o f t h e e x p e r i m e n t a l model.  transducer Om z = 1m  -23where c i s t h e v e l o c i t y o f sound i n cm/sec, and t i s t h e t i m e 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 t h e depths z-^ t o Z2 ( o r t]_ t o t 2 ) can be w r i t t e n a s r 2  1 I  where p  s  =  s  t  to-t-, 1  1  J  t-, p *  L_s;  3  dt  , .  (5)  i s t h e r e c o r d e d rms p r e s s u r e o v e r t h e 20 m i n t e r v a l ( t h e  p r e s s u r e i s d e t e r m i n e d from t h e r e c o r d e d v o l t a g e s by t h e c a l i b r a t i o n v a l u e s a t 1 m below t h e t r a n s d u c e r ) . S i m i l a r l y t h e a c o u s t i c i n t e n s i t y ( s e e e q u a t i o n 4) a t 1 metre from t h e s u r f a c e - t h e c a l i b r a t i o n depth) i s  (6)  I = ^  where p i s t h e c a l i b r a t e d a c o u s t i c p r e s s u r e a t 1 m from t h e transducer. To c a l c u l a t e t h e v a l u e f o r t h e a c o u s t i c i n t e n s i t y o f t h e i n c i d e n t wave r e a c h i n g t h e s c a t t e r e r , i t i s n e c e s s a r y t o c o r r e c t f o r d i s p e r s i o n o f t h e wave w i t h i n c r e a s i n g d e p t h .  Since  calibration  o f t h e sounders i s a t 1 m, t h e change i n a r e a s i s g i v e n by t h e r a t i o A /A o r c  TTT TTT  2 c  2  (z " (  z  c  tan 0 )  tan 0 )  2  2  (7)  -24where z  Q  i s t h e d e p t h o f c a l i b r a t i o n (lOO cm) and z i s t h e mean  d e p t h o f t h e 20 m i n t e r v a l ( i n cm). E q u a t i o n ( 6 ) t h e n f o r t h e i m p i n g i n g wave i s  I  2  „2  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 ( a z ) , can be w r i t t e n as  m  (  I  4  ) = ^  z  . 4TT(Z-100)  Z  3  2  (  9 )  c  where  = _1  I  J  1  /p dt 2  Frequency-dependent l o s s e s due t o a b s o r p t i o n were c a l c u l a t e d by t h e f o r m u l a g i v e n by V i g o u r e u x and Hersey  (1962,  from H o r t o n 195?) • Thus, (9) i s m o d i f i e d t o r e a d  m(Az)  = ll . 1  . 4tr(z-100) z  2  . 2<<X'l) E  (10)  c  where a i s t h e a b s o r p t i o n i n db/m and X i s t h e d i s t a n c e i n m. The v a l u e m(^z) then i s t h e sum o f t h e s c a t t e r i n g c r o s s s e c t i o n s o f a l l organisms i n t h e volume d e f i n e d by t h e beam a n g l e and t h e 20 m depth i n t e r v a l .  -25-  The volume o f t h a t s e c t i o n o f t h e cone c u t by Z j and Z2> i n cubic metres, i s  V = V -V 2  = l/3ro:2 2 " l/3iWi Z! 2z  1  = l/3-rr t a n 0 ( z  3 2  (ll)  3  - Z] ) 3  where z-^ i s t h e upper depth o f t h e l a y e r ( i n m e t r e s ) and Z2 i s t h e l o w e r depth o f t h e 20 m i n t e r v a l . 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 s d e t e r m i n e d b i o l o g i c a l c o l l e c t i o n s made by t h e CAT.  from t h e  The t o t a l number o f  e u p h a u s i i d s i n t h e volume c o r r e s p o n d i n g t o m(&z) i s N = V  n  where n i s t h e number o f e u p h a u s i i d s p e r m  (12) 3  and V i s t h e volume  -26-  in m . 3  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  euphausiid i s  N  of  -27III.  RESULTS. The main oceanographic  feature affecting the d i s t r i b u t i o n  of e u p h a u s i i d s i n t h e i n l e t was an o x y c l i n e w h i c h , i f p r e s e n t , was found a t a d e p t h o f around 100 m.  An example o f c o n d i t i o n s i n t h e  i n l e t when t h e o x y c l i n e was p r e s e n t 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 o c c u r r e d i n t h e i n l e t ( T a b l e l ) between  c r u i s e s 69/l4 and 69/22 (June t o t h e end o f J u l y ) and F i g . 6b shows t h e oxygen d i s t r i b u t i o n a t t h e end o f 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) t h e o x y c l i n e was n o t a s s t r o n g a s b e f o r e ; oxygen c o n c e n t r a t i o n s were g r e a t e r than 0.5 m l / l i n t h e bottom w a t e r s o f t h e i n l e t .  I n January  and March 1970 ( c r u i s e s 70/3 and ?0/8) t h e o x y c l i n e had r e - f o r m e d . 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 The d a i l y v a r i a t i o n i n t h e 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 , ITI(AZ),  and 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 (from t h e CAT tows u s i n g  the 10 mpi n e t u n l e s s o t h e r w i s e s t a t e d ) a r e i n c l u d e d 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 t h e times of s u n r i s e , sunset,  m o o n r i s e , and moonset f o r t h e dates when a c o u s t i c r e c o r d i n g s o r b i o l o g i c a l c o l l e c t i o n s were t a k e n .  Weather c o n d i t i o n s and c l o u d  cover f o r these p e r i o d s a r e found i n T a b l e  3.  There was a g e n e r a l r e l a t i o n s h i p between m(Az) 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 (see F i g s . 7-14).  and t h e  The presence o r  absence o f t h e o x y c l i n e , m o o n l i g h t , and c l o u d c o v e r appeared t o a f f e c t the d i s t r i b u t i o n of euphausiids.  Conditions during the  e i g 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-  F i g u r e 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 t h e S a a n i c h buoys on t h r e e c r u i s e s . The t e m p e r a t u r e p l o t was drawn from a bathythermograph s l i d e and t h e 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) C r u i s e 69/81  a s t r o n g o x y c l i n e was  present.  (b) C r u i s e 69/22; t h e i n l e t had been f l u s h e d . T h i s was shown by t h e r e l a t i v e l y h i g h oxygen c o n c e n t r a t i o n n e a r the bottom of t h e i n l e t . ( c ) C r u i s e 69/275 t h e o x y c l i n e had a l m o s t r e f o r m e d .  Temperature (°C)  Oxygen concentration (ml/L)  Temperature (°C)  Oxygen concentration (ml/L)  Temperature (°C)  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 p h a s e , a n d 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 . N a u t i c a l Almanac, (a)  Times (P.S.T.) were c a l c u l a t e d  from t h e  a o r b ( c o l u m n 3) r e f e r t o d a t e s when e i t h e r  acoustic  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 .  Cruise  Date  69/3  Feb.  69/8  69/14  69/22  April  June  July Aug.  69/25 69/27  Moonset  4 5 6 7  0830  Oct.  Jan.  Mar.  Moon Phase  E f f e c t on Plankton  1702 1703 1705 1707  1918 203.I  full full  possible possible possible possible  1839  0011 0220 0351  Sunset  0857 0910  0726 0725 0723 0722  7 a 9 a 12 b 13 b 14 b  0729 0938 1350 1509 1626  0527 0522 O516 0514 0512  1842 1846 1848  1850  0408 0424  17 a 19 b  2229 2312  0355 0355  2006 2007  0553 0754  new  30 b 31 b 1 b 5 a  0555 0722  0429 0431 0433  2045  2102 2116 2225  full full  0437  1942 1940 1938 1934  0053 034?  0545 0549  1759 1754  1647 1725  II36 1306  0642 0644 0653 0655  1645 1642 1633 I632  1844 2047  0743 0742 0737 0736  0438 0608 0458 . 0606 0514 0604 0544 0558 0608 0555  29 31 5 6  a a/b b b  a a a/b b  22 a 23 a 27 28  70/8  Moonrise  Sunrise  Sept.22 b 24 a  Nov.  70/3  a or b  b b  18 a 19 a 20 b 23 b 24 b  0844  0844  1352  1443 1455  0806 0828  0925 0938  2146  2303  3/4 3/4  3/4 1/2 1/4 1/4 new  1/4  ?  7 unlikely unlikely unlikely unlikely unlikely  3/4 1/2  possible possible possible possible  3/4  unlikely  full  7 possible possible  0240  3/4 2/3 1/2 1/4  1640 1642 1648 1650  1628 1740  full full  possible possible  2214  2/3 1/2  18 09 1811 1812  1313 1426 1536 1905 2017  1817 1819  0129  2325  7 7  7 7  3/4  ?  f f f f  7  u u u u  ll ll ll ll  possible possible possible  -30-  TABLE 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  collected.  Cruise  Date  69/3  Feb.  69/8  69/14  69/22  Apr.  A c o u s t i c (a) or B i o l o g y (b)  Time (P.S.T.) 1200  Cloud Cover 10/10 10/10 9/10 1/10 10/10 10/10  4 5  a a/b  6 7  b b  7 9  a a  12  b  13  b  14  b  1426 0840 1206 1413 1737 0546  15  b  0845  17  a  0300  19  b  0641 1102 1200  10/10  30 31  b b  0700  1/10  0731  0  1  b  5  a  1117  1400  1233  0714 1438 0843 1000  1300 1231  0955  2/10  10/10 .10/10 10/10 10/10 10/10  3/10 4/10 8/10 6/10 2/10 1/10 0 0 0  0850  1522 0750 1038  0602 0702 1500 1800  1/10 1/10 10/10 10/10  Mist Hazy, b r i g h t Drizzle P a r t i a l l y overcast L i g h t l y overcast Heavy o v e r c a s t Drizzle Drizzle  Hazy Sunny Sunny Sunny Sunny S l i g h t l y hazy Thin overcast - c l e a r Sunny Sunny Sunny Sunny Clear  -  hazy hazy hazy hazy  -31Acoustic or Cruise  Date  69/25  Sept. 22  Biology  (a) Time (P.S.T.) (b) 0845  b  1308 1?24  0405  Oct.  29  31 Nov. 4  a b  5  a b b  6 70/3  Jan.  a b b  27  70/8  28 M a r . 18  19  a  20  b b  23 24  0502 0602 1102  8/10 10/10 10/10  0522 1343 1317 0920 1656  10/10 10/10 10/10 10/10 lO/lO  0818 1018  8/10 6/10  1214  8/10 3/10  0600  0615 1500  22  23 26  10/10 10/10 10/10  0300  24  69/27  Cloud Cover  0849  0830 0926 1102 1342 0622 1700 2230 06 33 1735 0812  0838 1507 0506 1012  M i s t and f o g Hazy - b r i g h t Showers Partly cloudy Partly cloudy  Overcast - r a i n Overcast - d r i z z l e Overcast - f o g Mist - rain Overcast - Occ. r a i n  C l e a r , dark Thin clouds  10/10 lO/lO 5/10 10/10 7/10 5/10 3/10  1/10 0 0  1/10 1/10 10/10 10/10  9/10 0 0  Heavy o v e r c a s t Sunny Occ. s p r i n k l e Sunny Sunny Sunny  Clear Clear  Overcast Clear Clear  showers  -32The a c o u s t i c and b i o l o g i c a l d a t a from c r u i s e s 69/3» 69/8, and 69/14 (Fig,7-9)  a l l showed t h e e f f e c t o f t h e absence o f m o o n l i g h t and o f t h e  presence o f an o x y c l i n e .  The c o n c e n t r a t i o n s o f e u p h a u s i i d s ( a s  r e f l e c t e d by both m(Az) and t h e number o f e u p h a u s i i d s / m ) 3  i n t h e morning f o l l o w i n g s u n r i s e . was complete  were l o w  I n c r u i s e 69/3 ( F i g . 7) c l o u d c o v e r  and t h e r e was no e f f e c t from m o o n l i g h t , w h i l e i n c r u i s e s  69/8 and 6 9 / l 4 t h e moon was a t an e a r l y s t a g e .  Thus, t h e absence o f  m o o n l i g h t r e s u l t e d i n a m i d n i g h t d e s c e n t and few e u p h a u s i i d s were found near t h e s u r f a c e a t dawn.  As downward m i g r a t i o n o c c u r r e d , t h e c o n c e n t r a -  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 l o w e r l i m i t 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 was determined by t h e depth o f t h e o x y c l i n e . The e f f e c t o f f i s h i n 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 was shown on c r u i s e 69/3 ( F i g . 7 ) .  F i s h echoes were observed b o t h on  the echograms ( i . e . s o l i t a r y echoes t h a t remained under t h e echo-sounder beam f o r a p e r i o d o f time and appeared a s h o r i z o n t a l l i n e s on t h e echogram) and a s l a r g e " s p i k e s " on t h e t a p e - r e c o r d e d 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 n o t t o t a l l y , c o n f i n e d t o t h e v a l u e s a t 42 kHz.  V a l u e s o f m(Az)  f o r 42 kHz appear h i g h i n most i n s t a n c e s and one  v a l u e (1200 h o u r s ) s u r p a s s e s t h e v a l u e a t 107 k H z . U n f o r t u n a t e l y , t h e 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 , p l u s the e f f e c t o f t h e v a r i a b i l i t y  of t h e b i o l o g i c a l d a t a , have made t h e 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 d u r i n g 69/8 ( F i g . 8) a t f i r s t appear t o show an i n c o n s i s t e n c y between t h e 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, 1 4 ) .  W h i l e b o t h show a low c o n c e n t r a t i o n e a r l y i n t h e  -33-  F i g u r e 7. ( l e f t ) C r u i s e 69/3. D a i l y v a r i a t i o n s i n m(Az)(a) and e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  F i g u r e 8. ( r i g h t ) C r u i s e 69/8. D a i l y v a r i a t i o n s i n m(Az)(a) and e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  Time (P.S.T.)  Time  (P.S.T.)  -34-  F i g u r e 9« ( l e f t ) C r u i s e 69/lk. Daily variations i n m(iz)(a) and e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  F i g u r e 10. ( r i g h t ) C r u i s e 69/22. and e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  D a i l y v a r i a t i o n s i n m(Az)(a)  Time (P.S.T.)  Time ( P . S . T . )  -35morning, t h e p a t t e r n s r e v e r s e from 1100 t o 1800 h o u r s .  The weather  d a t a , 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 i n g periods (Table 3).  these  On A p r i l 7» 1 2 , 13> and 14 t h e s k y was o n l y  p a r t i a l l y o v e r c a s t 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 c r u i s e s 6 9 / 3 and 6 9 / l 4 .  The one a c o u s t i c v a l u e taken on  A p r i l 7 appears t o a g r e e w i t h t h e 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, t h e s k y was o v e r c a s t a n d by 1300 hours had become h e a v i l y o v e r c a s t (see a l s o s o l a r r a d i a t i o n measurements a t D e p a r t u r e Bay, Table 4 ) .  The echograms from t h i s p e r i o d show t h a t w h i l e p a r t o f t h e  high-frequency  s c a t t e r i n g l a y e r remained a t a c o n s t a n t d e p t h , a n o t h e r  p a r t moved up i n t h e w a t e r column d u r i n g t h e h e a v i l y o v e r c a s t c o n d i t i o n . U n f o r t u n a t e l y , tows were n o t conducted t o determine which p a r t o f t h e l a y e r moved upwards a n d which p a r t 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 b e f o r e w i t h r e s p e c t t o t h e l a c k o f b i o l o g i c a l The  observations.  s l i g h t decrease i n m(Az) a f t e r 0700 hours was n o t t y p i c a l but was  p r o b a b l y due t o weather c o n d i t i o n s d u r i n g t h i s p e r i o d w h i c h showed an i n c r e a s e i n haze and t h e r e f o r e a p o s s i b l e d e c r e a s e i n l i g h t  intensity.  C r u i s e 69/22 ( F i g . 10) was unique i n a number o f ways. a 3/4 o r f u l l moon was p r e s e n t u n t i l a f t e r s u n r i s e .  First,  T h i s appears t o  have helped t o m a i n t a i n t h e i n t e g r i t y o f t h e l a y e r a t t h e s u r f a c e a t n i g h t and d u r i n g t h e morning m i g r a t i o n .  Thus b o t h h i g h v a l u e s o f  U ( A Z ) and h i g h c o n c e n t r a t i o n s o f e u p h a u s i i d s morning.  were observed i n t h e  Second, t h e o x y c l i n e had d i s a p p e a r e d  migration of the euphausiids  and no l o n g e r  i n t o deeper w a t e r s .  hindered  As t h e y reached  daytime d e p t h s , t h e c o n c e n t r a t i o n s , and m(Az), d e c r e a s e d .  Then, t h e  l a y e r g r a d u a l l y re-formed throughout t h e day u n t i l t h e e v e n i n g  -36-  TABLE 4 T o t a l r a d i a t i o n f o r each hour (L.M.T. ) i n l a n g l e y s a t Departure  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, C a n a d i a n D e p a r t m e n t o f Transport).  April Hour  October  7  9  1 3 8 28 48 61 66 66 63 53 40  2 8 12 20  27 9  29  31  5  November 6  1 2  3 4  5  6  7 8  9 10 11 12  13 14  15 16 17 18  19  1  19 27 25 18  19 15  0 0 1 2 2 3  5  0 1 4 8  9 19 12  6 2 1  17 13  7  +  3 1  0  +  10  6 1  2 12 18 26  1 2 3 6 10  10  4 4 . 2 1  19 9 5  20 21 22  23 24  *Departure  Bay i s a p p r o x i m a t e l y  +L.M.T.; l o c a l mean t i m e .  38 m i l e s n o r t h o f S a a n i c h  Inlet.  4 3 1  -37m i g r a t i o n a g a i n r e s u l t e d i n d i s p e r s i o n . The o t h e r unique f e a t u r e o f t h i s c r u i s e was t h e presence o f l a r g e numbers of s m a l l  euphausiids  w h i c h was shown by t h e d i f f e r e n c e i n c a t c h e s from t h e 10 mpi (mesh p e r i n c h ) n e t and t h e 4 0 mpi n e t . 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 a l m o s t i d e n t i c a l t o 69/22.  The o x y c l i n e was s t i l l a b s e n t ; however,  weather c o n d i t i o n s (10/10 o v e r c a s t , see Table 2) negated t h e p o s s i b l e e f f e c t o f t h e moon t o h o l d t h e h i g h - f r e q u e n c y during the n i g h t .  s c a t t e r i n g l a y e r together  Thus the r e s u l t s from t h e p e r i o d p r i o r t o 0900 showed  low numbers and a l o w 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 6 9 / l 4 .  The b i o l o g i c a l d a t a from t h i s c r u i s e were o f f u r t h e r i n t e r e s t  i n two r e g a r d s .  F i r s t , 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 was h i g h e r  below t h e f i r s t 20 m o f t h e h i g h - f r e q u e n c y i n t e r v a l ) than i n i t .  s c a t t e r i n g l a y e r (20 m  The upper p o r t i o n was used i n t h i s  instance  because o f p o s s i b l e l o s s e s o f a c o u s t i c i n t e n s i t y due t o a b s o r p t i o n and s c a t t e r i n g o f t h e sound a s i t passed through the l a y e r .  the f i r s t part of  The second p o i n t was t h e tremendous i n c r e a s e i n t h e concen-  t r a t i o n o f e u p h a u s i i d s a s t h e y were stopped a t t h e s u r f a c e upon m i g r a t i n g upwards around sunset ( i . e . 95/m a t 1800 hours and 668/m 3  3  a t t h e s u r f a c e a f t e r m i g r a t i n g - 1900 h o u r s ) . 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 d u r i n g any o t h e r c r u i s e . The o x y c l i n e d u r i n g 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 t h e r e was s t i l l oxygen a t  t h e bottom o f t h e i n l e t ( 0 . 5 m l / l ) .  E u p h a u s i i d c o n c e n t r a t i o n s 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 t h e o x y c l i n e was p r e s e n t .  There were maximal c o n c e n t r a t i o n s i n t h e l a y e r  around 1100 h o u r s , w i t h l o w e r numbers d u r i n g m i g r a t i o n p e r i o d s .  -38-  F i g u r e 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 e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  F i g u r e 12. ( r i g h t ) C r u i s e 69/27. and e u p h a u s i i d c o n c e n t r a t i o n s ( b ) .  D a i l y v a r i a t i o n s i n m.Az)(a)  Time  (P.S.T.)  Time (P.S.T.)  -39There was a p o s s i b l e e f f e c t o f m o o n l i g h t on t h e p l a n k t o n t h e n i g h t b e f o r e t h e 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 t h e n i g h t p r i o r t o t h e 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 full,  overcast).  S i m i l a r l y , as reported i n c r u i s e  t h e r e was an i n c r e a s e d c o n c e n t r a t i o n a f t e r t h e e u p h a u s i i d s  69/25,  reached  the s u r f a c e f o l l o w i n g t h e e v e n i n g m i g r a t i o n ; t h e e u p h a u s i i d s  then  d i s p e r s e d i n t h e w a t e r column. The a c o u s t i c d a t a 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 t o be s i m i l a r t o t h a t d i s c u s s e d f o r c r u i s e 69/8.  The r a d i a t i o n d a t a ( T a b l e 4)  from D e p a r t u r e Bay i n d i -  c a t e t h a t c o n d i t i o n s on O c t o b e r 31 and November 5 (two o f t h e t h r e e 5th  a c o u s t i c r e c o r d i n g p e r i o d s ) were s i m i l a r t o those on November and 6th  when t h e b i o l o g i c a l s a m p l i n g  occurred.  On O c t o b e r  however, t h e r a d i a t i o n v a l u e s were much l o w e r . w i t h part of the high-frequency  29,  T h i s was a s s o c i a t e d  s c a t t e r i n g l a y e r r i s i n g i n t h e water  column; 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 t h e v a l u e s o f m ( i z ) d e c r e a s e d o v e r t h e 20 m i n t e r v a l . concentration of euphausiids  The d a i l y v a r i a t i o n i n t h e  t h e n c o u l d 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 November 5» and d i f f e r e n t from those r e c o r d e d r e l a t i o n s h i p i s seen i n F i g .  on O c t o b e r 29;  this  12.  D u r i n g c r u i s e s 70/3 s t a b l e feature i n the i n l e t .  on O c t o b e r 31 and  and ?0/8  t h e o x y c l i n e was a g a i n a  D u r i n g c r u i s e 70/3  t h r e e a c o u s t i c r e c o r d s were t a k e n .  ( F i g , 13)  only  T h i s was due t o t h e presence o f  large schools of f i s h i n the high-frequency  scattering region.  U n f o r t u n a t e l y , these t h r e e d a t a p o i n t s do n o t i n d i c a t e much about the n a t u r e o f t h e s c a t t e r i n g d u r i n g t h i s p e r i o d .  However, t h e  -40-  Figure 13. ( l e f t ) 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 ) .  Figure 14. ( r i g h t ) Cruise 70/8. D a i l y v a r i a t i o n s i n m(&z)(a) and euphausiid concentrations ( b ) .  •.  200 k H  V  z  107 kH, 42 •  kH  z  January 22  I  ® January 23  200 k H 107 k H 42 k H -i  1  r  z  z  z  • March 18 ©March 19  •  January 27  •  March 20  o  January 28  o  March 24  O  40  O  40  mpi net  mpi net  layer at surface -  1000  1200 Time  1400 (P.S.T.)  1600  1800  2000  0500  0700  0900  1100 Time  1300 (P.S.T.)  1500  1700  1900  -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 t o 69/3  and 69/8  morning hours.  concentrations  The  e u p h a u s i i d s were i n low  during  the indicating  the absence of moonlight d u r i n g the n i g h t ( t h e moon a t t h i s time only ^ f u l l ) .  A f t e r the morning p e r i o d , the data  l e v e l i n g o f f i n the c o n c e n t r a t i o n of The  r e s u l t s of c r u i s e 70/8  indicate  except  f o r March 23.  (March 1970,  F i g . 14) showed the  The  Moonlight  (Table 2)  d i d not seem t o have d u r i n g the a c o u s t i c r e c o r d i n g  have had an e f f e c t when b i o l o g i c a l sampling  peak value of m(az)  a t 1200  h i g h number of e u p h a u s i i d s however, t h i s was  c o l l e c t e d a t 1100  hours.  i n the e a r l y morning hours and  w i t h the suggested  The  one  low  values  increase i n  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  e f f e c t of the moonlight as mentioned  S c a t t e r e r s Other Than A list  the s l i g h t  t o the  Unfortunately,  not s u b s t a n t i a t e d v e r y w e l l i n t h a t only  concentration of euphausiids  occurred.  hours appeared t o correspond  b i o l o g i c a l c o l l e c t i o n showed a h i g h c o n c e n t r a t i o n . of m(^z)  the volume-  A l l days d u r i n g t h i s p e r i o d were c l e a r  a f f e c t e d the d i s t r i b u t i o n of euphausiids p e r i o d s , but may  a  euphausiids.  b e s t r e l a t i o n s h i p between e u p h a u s i i d c o n c e n t r a t i o n s and scattering coefficient.  was  earlier.  Euphausiids  of o t h e r p o t e n t i a l sound s c a t t e r e r s caught i n the  s c a t t e r i n g l a y e r i s given i n Table  5->  As shown i n the t a b l e ,  p a s i p h a e i d shrimp, s e r g e s t i d shrimp, mysids, cephalopods, amphipods, and  physonectid  enough t o add f i s h was  siphonophores do not appear t o be i n numbers l a r g e  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 .  Although  only  one  caught (69/25) by the samplers used, n e i t h e r sampler i s  thought t o be very s u c c e s s f u l i n c a t c h i n g t h e l a r g e r f i s h e s . l a r v a e were not caught on c r u i s e s  69/3* 69/8, 70/3» o r ?0/8.  Fish Larvae  TABLE 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 than 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 which 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 . E x c e p t f o r amphipods, numbers l i s t e d a r e t h e number o f samples which c o n t a i n e d a p a r t i c u l a r organism; t h e average number p e r sample i s i n p a r e n t h e s e s .  No. o f Samples  Fish Larvae  Physonectid Siphonophore Nectophores  Mysids  Sergestids and Pasipaeids  Cephalopods  •0  0  0  -  -  --  2(1)  0  -  3(4)  CAT IKMT  27 1  0 0  0 0  Kl)+ 0  0 0  2(1) 0  3(1) 0  CAT IKMT  6  0  -  0  0  -  4(3)  0  KD  0 . 9 *  CAT IKMT  28 3  0 0  CAT IKMT  11 2  0 1(1)  2(2) 2(2)  CAT IKMT  24 2  0 0  1(2) 0  70/3  CAT IKMT  18  0  0  -  -  -  -  -  70/8  CAT IKMT  26 2  0 0  0 0  0 0  2(1) 0  Iruise  Sampler  c9/3  CAT IKMT  11  69/8 69/14 69/22  69/25 . 69/27  Fishes  -  -  3.2  -  0.4  -  -  -  -  -  16(3) 3(8)  0 0  0 0  0 0  M2)  0.4*  0 0  1(1) 1(2)  2(1)  0.9  0 0  0 0  0  KD  7.3  0  0  -  0  -  2.0  2(1) 0  0 0  3.0  0.  0 1(1) 0 0  *Amphipod counts from 10 mpi n e t c o l l e c t i o n s o n l y . +0ne p h y s o n e c t i d pneumatophore was a l s o f o u n d i n one sample  -  Av. No. Amphipoc p e r m"  KD KD  -  -  -43were few i n numbers d u r i n g 69/25 and 69/2? and p r o b a b l y d i d n o t add s i g n i f i c a n t l y t o t h e s c a t t e r i n g . F i s h l a r v a e caught d u r i n g c r u i s e 69/14 were m a i n l y f l a t f i s h ( w i t h o u t a swimbladder) and t h e eulachon ( T h a l 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 t h e f i s h l a r v a e were m a i n l y t h e eulachon (37%)» hake (Merluccius productus, (10$).  3^%), L i p a r i s f u c e n s i s (15%)» a n d f l a t f i s h  Both t h e e u l a c h o n a n d 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 o f sound.  Due t o t h e t e c h n i q u e s  used t o r e c o r d t h e 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 n o t add s i g n i f i c a n t l y t o t h e s c a t t e r i n g a t  107 a n d 200 kHz. C r u i s e Averages The average v o l u m e - s c a t t e r i n g are l i s t e d i n Table 6.  c o e f f i c i e n t s f o r each c r u i s e  Averages a r e l i s t e d f o r the 0800 - 1600 hour  i n t e r v a l , f o r t h e p e r i o d from one hour a f t e r s u n r i s e t o one hour b e f o r e s u n s e t , and f o r a l l v a l u e s a f t e r t h e l a y e r l e f t t h e s u r f a c e i n t h e morning t o b e f o r e i t r e a c h e d t h e s u r f a c e i n t h e e v e n i n g . Means a r e l i s t e d f o r t h e t h r e e f r e q u e n c i e s .  T - t e s t s were r u n  comparing the means o f t h e t h r e e f r e q u e n c i e s  (42 v s 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 a r e n o t e d a t t h e 5% o r 1% l e v e l s  (Table 6 ) . The  s c a t t e r i n g cross-section of a euphausiid a t the three  f r e q u e n c i e s 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 o f v a l u e s (o, i n c m ) , 2  as shown i n t h e f i g u r e s (0800 - 1600 hour a v e r a g e ) , t o 3.67 x 10-5 (LL2 k H z ) , 5.49 x 10~ 4.81  x 10"  5  t o 5.21 x 1 0  - 3  6  i s 2.30 x IO"?  t o 3.39 x IO ' - (107  (200 k H z ) .  -  4  kHz),  -44TABLE 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 , JI(AZ), over d i f f e r e n t t i m e intervals.  V a l u e s a t 42 kHz were o m i t t e d from t h e average i f t h e y were  > t h e v a l u e s a t 107 kHz ( i n d i c a t i n g f i s h were making t h e v a l u e t o o l a r g e ) . Cruise 69/3 69/8  Time I n t e r v a l 0800-1600 0713-1747 0800-1600 0631-1630 0631-1930  Av. H I ( A Z ) 42 kHz  107 kHz  -  .590  * *  5.84 4.99 5.21  *  0800-1600 0700-1800 0500-2000  .485 .5^7 .499  *•* •** **  4.48 ^.95 3.99  0800-1600 0700-1700 0600-1900  .897 .861 1.05  * -**  3.89 3.83 3.90  0800-1600 0700-1606 0600-1802  4.88 3.99 3.71  69/27  0800-1600 0800-1626  3.61 3.53  70/3  0842-1234  1.40  70/8  0800-1600 0800-1720 0642-1820  69/14  69/22  69/25  .533 .599  .532  10.2 5.36  1.17  .0448 1.78 1.73 1.59  Av. m ( i z ) 200 kHz  A V . m(A.z)  * *  ** *•*  •** *•*  **  74.6 63.0 69.8 68.8 71.4 56.1 61.7 64.8 64.1  13.3 11.4 10.6  * *  98.6 79.8 8O.7  15.0 13.8  * *  92.7 94.0  •*  33.0  3..01 **  * *-*  4.99 4.74 4.05  *-  **  *-•*  48.2 45.4 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 t h e 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 t h e 1% l e v e l .  -45-  F i g u r e 15. ( f a c i n g ) Average v a l u e s o f t h e s c a t t e r i n g c r o s s - s e c t i o n , a ( c m ) , o f a e u p h a u s i i d f o r each c r u i s e a t 4 2 , 107, and 200 kHz. 2  -46F o r c r u i s e 69/22 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 was c a l c u l a t e d f o r samples t a k e n w i t h t h e c o a r s e mesh n e t (10 mpi) and the f i n e mesh n e t (40 m p i ) .  As would be e x p e c t e d , 0 d e c r e a s e d as  the average s i z e o f t h e organisms became s m a l l e r (more s m a l l e u p h a u s i i d s were caught i n t h e f i n e mesh n e t ) . The mean d r y weight o f a e u p h a u s i i d 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 t h e p l o t o f G a t 200 kHz. The g e n e r a l shape o f t h e two c u r v e s i s s i m i l a r , e s p e c i a l l y f o r t h e c r u i s e s where t h l a r g e r v a r i a t i o n s o f e u p h a u s i i d d r y weight were o b s e r v e d .  The  e u p h a u s i i d s c o l l e c t e d on 6 9 / l 4 , f o r example, had t h e g r e a t e s t average d r y weight as w e l l a s t h e l a r g e s t v a l u e f o r O. In F i g . 17 t h e 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 , m ( A z ) , i s p l o t t e d f o r each c r u i s e a t 200 k H z . The t o t a l weight o f e u p h a u s i i d s t h e o r e t i c a l l y c o n t a i n e d i n t h e volume d e f i n e d by m(az) i s also plotted.  T h i s v a l u e o f 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 t h e mean d r y w e i g h t t i m e s t h e t o t a l number o f e u p h a u s i i d s p r e s e n t i n t h e volume ( t o t a l number i s t h e average number p e r m  3  t i m e s t h e volume d e f i n e d by t h e beam a n g l e and t h e ' 2 0 m i n t e r v a l ) . T h i s p l o t shows a c l o s e r e l a t i o n s h i p between t h e t o t a l weight and IH(AZ) b u t , a s b e f o r e ( F i g . 16), weight a r e apparent.  v a r i a t i o n s i n C and average d r y  The p o i n t o f m a j o r i n t e r e s t i n t h i s comparison  i s t h e two v a l u e s c a l c u l a t e d f o r t h e t o t a l d r y w e i g h t from c r u i s e 69/22.  One p o i n t was c a l c u l a t e d based on t h e c o l l e c t i o n s from t h e  10 mpi mesh n e t ( c o a r s e ) 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 n e t ( f i n e ) .  The t r e n d i n t h e v a l u e s f o r m ( i z )  showed a g r a d u a l d e c r e a s e from c r u i s e s 69/8 t o 69/l4 t o 69/22.  -47-  F i g u r e 16. (facing) Average v a l u e s o f t h e s c a t t e r i n g c r o s s s e c t i o n O ( c m ) , o f a e u p h a u s i i d f o r each c r u i s e a t 200 kHz, and the average d r y weight of a e u p h a u s i i d f o r each c r u i s e . 2  -48-  F i g u r e 17. ( f a c i n g ) The 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 , m(Az), f o r each c r u i s e a t 200 kHz, and t h e t o t a l w e i g h t of e u p h a u s i i d s t h a t c o r r e s p o n d t o t h e volume d e f i n e d by M(AZ) ( t h e beam a n g l e and t h e 2 0 m d e p t h i n t e r v a l ) .  Average m ( A z , 200 k H ) 0800 - 1600 hours z  Average total weight of euphausiids / volume defined by m ( A z )  in grams  -49The  b i o m a s s ( w e i g h t ) o f e u p h a u s i i d s b a s e d on t h e 10 m p i  net  collections  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 showed a r e v e r s a l o f t h i s Euphausia all  trend.  p a c i f i c a was  t h e most abundant e u p h a u s i i d  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)»  r a s c h i i was weight  t h e second  most a b u n d a n t .  of the euphausiids  collections  The  w h i l e Thysano'essa  average l e n g t h and  i s a l s o shown i n T a b l e  on  7.  dry  -50TABLE 7  Species composition, mean dry weight and mean l e n g t h of euphausiids from three samples from each c r u i s e .  Cruise  % Euphausia pacifica  % Thysanoessa raschii  Other  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 o n l y .  Mean Dry Weight (mg)  Mean Length (mm)  -51IV.  DISCUSSION.  B a r r a c l o u g h , L e B r a s s e u r , 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 h i g h c o n c e n t r a t i o n s o f copepods.  McNaught (1969) has suggested  t h a t Daphnia was a n  adequate s c a t t e r e r o f sound i f t h e p r o p e r f r e q u e n c y was used (200 k H z ) . S i m i l a r l y , Bary ( p e r s . comm.) and Bary a n d P i 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 r e c o r d e d a t 200 kHz was found a t depths where l a r g e numbers o f e u p h a u s i i d s were c o l l e c t e d i n S a a n i c h ( p e r s . comm.) a l s o s u g g e s t s t h a t t h i s h i g h - f r e q u e n c y  Inlet.  Bary  scattering layer  was a l s o r e c o r d e d a t 107 kHz a n d 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 r e c o r d e d a t t h e h i g h f r e q u e n c i e s and a s s o c i a t e d w i t h z o o p l a n k t o n were not r e c o r d e d on a n 11 kHz,  Simrad  echo-sounder which was used c o n c u r r e n t l y ) . R e s u l t s o f t h e p r e s e n t s t u d y s u p p o r t t h e work o f B a r y ( p e r s . comm.) and Bary and P i e p e r (1970),  Echograms from t h e f o u r echo-  sounders a r e shown i n F i g . 1 8 . These echograms show a n a r e a o f h i g h f r e q u e n c y s c a t t e r i n g (55-75 m) on t h e 42, 107, and 200 kHz echo-sounders, but not on t h e 11 kHz echo-sounder.  A f i s h l a y e r c e n t e r e d around 85 m  i s shown on a l l echograms. The  v a l u e s f o r t h e 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),  f o r the t h r e e f r e q u e n c i e s ( 4 2 , 10?, 200 kHz) were u s u a l l y an o r d e r o f magnitude a p a r t , t h e v a l u e f o r ITI(AZ) a t 200 kHz a l w a y s b e i n g t h e  largest.  Only d u r i n g p e r i o d s when t h e r e were l a r g e numbers o f f i s h i n 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 d i d t h i s r e l a t i o n s h i p change; i n a few i n s t a n c e s v a l u e s o f U ( A Z ) were l a r g e r a t 42 kHz t h a n a t 107 kHz (see c r u i s e 69/3 a t 1100 h o u r s , F i g . 7 a ) .  On most c r u i s e s t h e average  - 5 2 -  F i g u r e 18. ( f a c i n g ) Echograms a t 11, 4 2 , 107, and 200 kHz d u r i n g t h e day when moored a t t h e buoys ( c r u i s e 68/35, 5 December 1968).  •  -53m(Az)  f o r t h e t h r e e f r e q u e n c i e s 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 o t h e r ( T a b l e 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 d r y w e i g h t o f e u p h a u s i i d s  c a l c u l a t e d t o be i n  t h e same volume as t h a t w h i c h d e f i n e d m(<az) ( F i g . 1 7 ) . 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 e u p h a u s i i d s f o r most o f t h e sound s c a t t e r i n g . euphausiids  Values  This  were r e s p o n s i b l e  o f t h e d r y weight o f  from c r u i s e 69/22 c a l c u l a t e d from 1 0 mpi net  mesh) samples were more c l o s e l y c o r r e l a t e d w i t h m(az)  (coarse  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 e u p h a u s i i d  increased  w i t h an i n c r e a s e i n t h e d r y weight ( F i g . 16) and an i n c r e a s e i n length (Table 7 ) . ( F i g . 15). cm . 2  The  The  v a l u e s of O a l s o i n c r e a s e d w i t h  v a l u e o f a a t 107 kHz f o r J u l y I 9 6 9 was  T h i s compares w e l l w i t h 1.35  x 10"^  cm  2  frequency 3.0  10"^  x  c a l c u l a t e d by  Beamish ( 1 9 6 9 ) u s i n g 102 kHz f o r t h e same time p e r i o d i n I 9 6 8 (also i n Saanich  Inlet).  O t h e r p o t e n t i a l s c a t t e r e r s o f sound were r a r e l y caught i n the 20 m h i g h - f r e q u e n c y  s c a t t e r i n g zone ( T a b l e 5 ) .  Cephalopods,  mysids and decapods were c o l l e c t e d i n o n l y a few samples and t h e s e i n s t a n c e s the numbers o f organisms were l o w .  in  Physonectid  s i p h o n o p h o r e s were i d e n t i f i e d from o n l y two samples from a l l c r u i s e s ; i n these two  samples o n l y one n e c t o p h o r e per sample was  found.  L a r v a l f i s h e s were caught on about h a l f o f the c r u i s e s , but i n h i g h numbers o n l y on two  cruises.  Of t h e s e f i s h l a r v a e  c o l l e c t e d , t h e hake and t h e e u l a c h o n were the m a j o r c o n s t i t u e n t s and both o f t h e s e c o n t a i n swimbladders and a r e t h e r e f o r e good  -54-  scatterers  of  sound.  although neither  F i s h e s w e r e o n l y f o u n d i n one  s a m p l e r u s e d i n t h i s s t u d y i s t h o u g h t t o be  good c o l l e c t o r of a d u l t eulachon. effect  By  fishes  maximizing the  of s o l i t a r y ,  such as  materials  and  The  In  c o n c e n t r a t i o n of  cruise  the  data are  euphausiids, i n  thie v a l u e s o f m ( A z ) .  Variations  one  conditions  ( o r s o l a r r a d i a t i o n measurements), the  different of an  oxycline  around 100  70/8,  14).  l i m i t the  and  Fisher,  1969)0.  results in  time of  weather  moonset,  general patterns presence or  present  (cruises the  69/3,  from absence  high-frequency  s t o p p e d by,  the  oxycline  layers,  d e n o t e d by  or the  discontinuity  of  scattering  ( F i g s . 7,  s e p a r a t i o n of  e u p h a u s i i d s (see  69/8,  concentration  the  migration of  in  general,  i n c r e a s e d as  was  water types which are  was  probably 6 9 / 2 7 ) ,  and  Discontinuity  to  i n the  reported  m.  oxycline  m(az)  l a y e r r e a c h e d , and 13,  Variations  high-  concentration  to variations  appeared to r e s u l t from the  When t h e  e u p h a u s i i d s and  have been a t t r i b u t e d  moon.  cruises  69/14, 70/3,  the  quantitative  i n the  d u r i n g any  phase o f the  larvae  situations  same d e p t h s a s  l a y e r have been compared t o 3  corresponded to  and  or f i s h  r e c o r d i n g s f o r the  (number/m ) c o l l e c t e d ; the  The  the  taken.  frequency s c a t t e r i n g  7-14.  or  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 ) , of the  of e u p h a u s i i d s  a  scattering,  methods).  f i s h s c h o o l s were p r e s e n t i n the  a n a l y s e s were not  c  salmon, hake,  recorded planktonic  high-frequency s c a t t e r i n g , acoustic  Figs  the  high-amplitude echoes from f i s h e s  have been m i n i m i z e d (see where l a r g e  collection  8,  9,  different  l a y e r s , are  known  f o r example M a u c h l i n e  -55The  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 w a t e r s became oxygenated (Fig. 6).  I n t h e absence o f a n o x y c l i n e ( c r u i s e s 69/22, 69/25)  t o h i n d e r downward m i g r a t i o n , 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 went deeper i n the w a t e r column a n d was d i s t r i b u t e d o v e r a w i d e r depth i n t e r v a l . I(AZ)  As a r e s u l t , 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  remained l o w a l l m o r n i n g .  The l a y e r g r a d u a l l y reformed  d u r i n g the day, t h e 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 and 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 b e i n g maximal i n t h e l a t e a f t e r n o o n (1500-1600 h o u r s , c r u i s e 69/22} 1400 h o u r s , c r u i s e 69/25). p a t t e r n p r o b a b l y most c l o s e l y resembles  This  that i n oceanic s i t u a t i o n s ,  a l t h o u g h such work u s i n g t h e h i g h f r e q u e n c y sounders has n o t been c a r r i e d o u t i n t h e open ocean. The presence  o f s t r o n g m o o n l i g h t d u r i n g the n i g h t appeared  t o m a i n t a i n t h e i n t e g r i t y o f the l a y e r n e a r the s u r f a c e on c e r t a i n cruises.  I n such cases p a r t o f the p o p u l a t i o n o f e u p h a u s i i d s  remained n e a r the s u r f a c e a l l n i g h t i n s t e a d o f p a s s i v e l y s i n k i n g ( m i d n i g h t s i n k i n g a s d e s c r i b e d by C u s h i n g , 1 9 5 l ) .  T h i s e f f e c t was  shown on c r u i s e s 69/22 and d u r i n g the b i o l o g i c a l c o l l e c t i o n s o f c r u i s e 70/8 ( F i g s . 10, 1 4 b ) ,  In these instances t h e concentration  of e u p h a u s i i d s ( F i g s . 10b, 14b) and ITI(AZ) ( F i g , 10a) was h i g h i n the e a r l y morning p e r i o d when t h e l a y e r was m i g r a t i n g from t h e s u r f a c e down t o i t s daytime d e p t h .  I n t h e absence o f a m o o n l i g h t  "cue" f o r t h e e u p h a u s i i d s t o remain n e a r t h e s u r f a c e d u r i n g t h e n i g h t , midnight s i n k i n g occurred.  I n t h e s e cases few e u p h a u s i i d s  were i n t h e n e a r - s u r f a c e w a t e r s b e f o r e s u n r i s e and t h u s t h e concent r a t i o n s , and m ( a z ) , were l o w d u r i n g t h e morning, downward m i g r a t i o n s .  -56The w e a t h e r 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 o f the . e u p h a u s i i d s b e s i d e s masking t h e e f f e c t o f m o o n l i g h t .  The e f f e c t  o f submarine i l l u m i n a t i o n on t h e movement o f s c a t t e r i n g l a y e r s has been r e p o r t e d by a number o f a u t h o r s and B a c k u s , 1956; Kampa and Boden, 1954).  (see f o r example C l a r k e Clarke  (l9?0) and  L e w i s (l95^) have a s s o c i a t e d t h e d i s t r i b u t i o n o f e u p h a u s i i d s a particular The  with  isolume. e f f e c t o f weather on the h i g h - f r e q u e n c y  scattering  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 b o t h c r u i s e s t h e weather was sunny p a r t o f  the t i m e and h e a v i l y o v e r c a s t a t a n o t h e r ;  surface  illumination  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 d u r i n g On c r u i s e 68/9 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  periods. ITI(AZ)  these  and  were h i g h i n t h e m o r n i n g , the e u p h a u s i i d s b e i n g compressed  a g a i n s t the o x y c l i n e . the day.  On sunny days the v a l u e s remained h i g h d u r i n g  I n t h e presence o f a h e a v i l y o v e r c a s t s k y , the  and submarine i l l u m i n a t i o n d e c r e a s e d , and p a r t o f the  surface  high-frequency  s c a t t e r i n g l a y e r moved upwards i n t h e w a t e r column ( i . e . the l a y e r became more d i f f u s e ) .  T h i s r e s u l t e d i n a d e c r e a s e d 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  in distribution  and r e d u c e d c o n c e n t r a t i o n a t any one d e p t h has a l s o been r e p o r t e d by M a u c h l i n e and F i s h e r (1969). The 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 migrated  from the  s u r f a c e t o depth a r o u n d morning t w i l i g h t and then back t o t h e s u r f a c e a t dusk i n a manner d e s c r i b e d by B a r y (1967) and Cushing (l95l).  The r a t e o f a s c e n t d u r i n g 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 h o u r s , c r u i s e 68/35, 5 December, 1968,  -57Fig. 19).  T h i s v a l u e i s l e s s t h a n t h e average swimming speed o f  a e u p h a u s i i d (90 m/hr) determined  e x p e r i m e n t a l l y by Hardy and  Bainbridge (1954). The Cushing  "morning r i s e " o f t h e p l a n k t o n was d i s c u s s e d by  (1951) f o r many s p e p i e s of organisms i n c l u d i n g  euphausiids  ( p a r t i a l l y based on d a t a on e u p h a u s i i d s by E s t e r l y , 1914, and L e w i s , 195*0.  E s t e r l y found much l a r g e r numbers o f N y c t i p h a n e s  s i m p l e x n e a r t h e s u r f a c e between 4 and 6 a.m. than d u r i n g any o t h e r p e r i o d o f t h e day.  Lewis (195*0 p r e s e n t e d d a t a which  t h a t a morning r i s e o c c u r r e d w i t h Euphausia Stylocheiron carinatum.  suggested  tenera but not with  M a u c h l i n e a n d F i s h e r (1969) were unable t o  show t h e morning r i s e w i t h Meganyctiphanes n o r v e g i c a o r Thysanoessa r a s c h i i and c o n c l u d e d t h a t t h i s p r o b a b l y r e s u l t e d from  insufficient  data. A s e r i e s o f 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 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 was observed d u r i n g c r u i s e 69/25 and t o a l e s s e r e x t e n t d u r i n g c r u i s e 70/8. Both r i s e s , however, o c c u r r e d b e f o r e n a u t i c a l t w i l i g h t and appeared t o be c l o s e l y r e l a t e d t o t h e t i m e o f t h e moonset [/the moon on 25 September ( c r u i s e 69/25) was a f u l l moon and t h e s k y was o n l y 4 / l 0 o v e r c a s t ; on 18 March ( c r u i s e 70/8) t h e r e was a 3/4 f u l l moon a n d t h e 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 o v e r c a s t s k y , and a moon which r o s e a t 0129  and s e t a t 1 4 4 3 ) .  The p l a n k t p n descended d u r i n g t h e n i g h t and d i d  not r i s e i n t h e morning; t h e o n l y n o t i c e a b l e e f f e c t o f s u n r i s e appeared t o be a c o n s o l i d a t i o n o f t h e l a y e r .  -58-  F l g u r e 1 9 . ( f a c i n g ) Echograms 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 m i g r a t i n g t o t h e s u r f a c e i n t h e evening a s r e c o r d e d a t 42 and 200 kHz when moored a t t h e buoys, and an 1 1 kHz r e c o r d from the same time p e r i o d ( c r u i s e 68/35* 5 December I 9 6 8 ) .  42  metres  ROSS  -59-  F i g u r e 20. ( f a c i n g ) Echograms a t 200 kHz t o show t h e b e h a v i o u r 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 a r o u n d morning t w i l i g h t . The g a i n s e t t i n g s on t h e sounder were v a r i e d b u t t h e t i m e - v a r i a b l e g a i n (TVG) was t h e same on a l l f o u r o c c a s i o n s . The TVG was s e t f o r these recordings'; a t v a l u e s w h i c h were hoped t o produce a l i n e a r response w i t h d e p t h ( i . e . t o c o r r e c t f o r a b s o r p t i o n and s p h e r i c a l spreading l o s s e s ) .  -600n c r u i s e 69/22 t h e moon a g a i n r o s e i n t h e e v e n i n g (2225 h o u r s ) and s e t a f t e r s u n r i s e (1352). and t h e s k y l / l O o v e r c a s t . the h i g h - f r e q u e n c y  The moon was 2/3 f u l l  The moon seemed t o have k e p t p a r t o f  s c a t t e r i n g l a y e r n e a r t h e s u r f a c e a t n i g h t 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 m i g r a t e downwards.  No morning r i s e was apparent a l t h o u g h  this  c o u l d have been obscured by t h e l a r g e numbers o f f i s h e s a t t h e surface a t t h i s The  time.  o n l y e v i d e n c e o f a "morning r i s e " ( C u s h i n g , 1951) o f  the p l a n k t o n found i n t h i s s t u d y 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 l e n d support  t o t h e work o f  R i n g e l b e r g (1964), who s u g g e s t e d t h a t i t was t h e r a t e o f change o f l i g h t i n t e n s i t y which was t h e s t i m u l u s f o r m i g r a t i o n , r a t h e r t h a n the s e a r c h i n g f o r an optimum i s o l u m e .  The main argument a g a i n s t  R i n g e l b e r g * s t h e o r y i n t h e p a s t has been i t s f a i l u r e t o e x p l a i n the pre-dawn r i s e o f t h e p l a n k t o n . One  o f t h e l a r g e s t problems i n t h i s s t u d y has been t h e  v a r i a b i l i t y of the b i o l o g i c a l data. for  T h i s can be seen i n t h e v a l u e s  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 a s shown i n F i g s . ? - l 4 b , and i n  the echograms ( F i g s . 21, 2 2 ) . C a s s i e , 1959) a g g r e g a t i o n hydrographic aggregation  I n a few i n s t a n c e s ( f o r example  o f zooplankton  has been a s s o c i a t e d w i t h  f e a t u r e s b u t , more f r e q u e n t l y , t h e r e a s o n f o r such has n o t been shown.  M a u c h l i n e and F i s h e r (1969) have  r e p o r t e d t h a t e u p h a u s i i d swarms have been observed f o r a number o f s p e c i e s , i n c l u d i n g Euphausia p a c i f i c a .  M a u c h l i n e a l s o has r e p o r t e d  (from M a r r 1962) t h a t E u p h a u s i a superba a g g r e g a t e s i n t o dense swarms o r " p a t c h e s "  i n a l l phases o f i t s l i f e c y c l e ,  -61-  F i g u r e 2 1 . ( f a c i n g ) Echograms of t h e morning d e s c e n t o f t h e s c a t t e r i n g l a y e r s r e c o r d e d a t 11, 4 2 , 107, and 200 kHz when t h e s h i p was moving ( c r u i s e 68/35> 5 December 1968).  -62-  F i g u r e 22. ( f a c i n g ) Echogram a t 200 kHz d u r i n g b i o l o g i c a l s a m p l i n g o p e r a t i o n s w i t h a depth t r a c e of t h e s a m p l e r , p l u s a c h a r t r e c o r d o f the t e m p e r a t u r e v a r i a t i o n s d e t e c t e d by a t h e r m i s t o r on t h e sampler and r e c o r d e d a t the t i m e of s a m p l i n g .  metres Or- -^L  /<5*5  10SS  CAT opened ® CAT closed  ICll  20  *— Sampler depth  40  Flow  (CAT) trace  Temperature  60  r v  i  «5  80  70/8  100  L  2 0 0 kHz Ross  i  24 March 1970  -63P a t c h i n e s s i n S a a n i c h I n l e t , a s r e c o r d e d by t h e 200 kHz echo-sounder,  i s shown i n F i g s . 21 and 22.  A t r a c e o f t h e tempera-  t u r e v a r i a t i o n a t t h e d e p t h o f t h e 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 n o t e t h a t t h e temperature  d e c r e a s e s from 9.2°C t o 8.?°C a s t h e gear moves from an a r e a where no " p a t c h " o c c u r s t o an a r e a where a " p a t c h " e x i s t s . The s i z e o f a " p a t c h " can be determined from t h e echogram ( F i g . 22).  S u b j e c t i v e l y , one can choose a s y m m e t r i c a l " p a t c h " which  i s 15 m deep.  The h o r i z o n t a l dimension i s t h e n c a l c u l a t e d t o be  around 500 m i n d i a m e t e r ( c a l c u l a t e d b o t h by t h e echo-sounder/beam a n g l e / p a p e r speed method and by t h e r e v o l u t i o n s o f t h e f l o w meter i n t h e CAT d u r i n g t h e b i o l o g i c a l s a m p l i n g p e r i o d ) .  Due t o t h e beam  a n g l e o f t h e echo sounder, h o w e v e r , " p a t c h e s " l e s s t h a n about 15 m i n d i a m e t e r would n o t be d i s c e r n i b l e a t t h e s e depths u n l e s s t h e " p a t c h e s " were w i d e l y s e p a r a t e d .  Thus, a s y m m e t r i c a l 15 m aggrega-  t i o n o r " p a t c h " , a s d e s c r i b e d by Wiebe (1970), might n o t be d i s c e r n ible.  Such " p a t c h e s " , however, would be e v i d e n t i f t h e echo-sounder  t r a n s d u c e r were lowered t o depths n e a r t h a t o f t h e " p a t c h " . A c o l l e c t i n g / e c h o - s o u n d e r system a s d e s c r i b e d i n t h i s t h e s i s p r o v i d e s an e x c e l l e n t e x p e r i m e n t a l system t o l o o k i n t o t h e p a t c h i n e s s problem.  The a d d i t i o n o f a s a l i n i t y s e n s o r t o t h e  e l e c t r o n i c s package o f t h e CAT would a l l o w s i m u l t a n e o u s measurements t o be r e c o r d e d on h y d r o g r a p h i c p a r a m e t e r s , a l o n g 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 s t r e n g t h s and t h e b i o l o g i c a l c o l l e c t i o n s .  In order  to avoid 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 t h e s c a t t e r i n g o r d i s t r i b u t i o n o f organisms,  -64a h i g h - r e s o l u t i o n bathyphotometer s h o u l d be added t o  determine  submarine i l l u m i n a t i o n a t depths where t h e organisms a r e  found.  The need f o r c o n c u r r e n t d a t a 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 hydrographic  different  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 d a t a shown i n F i g s . 7-14 b e t t e r i f t h e y had been c o l l e c t e d s i m u l t a n e o u s l y .  would be much A l a r g e number  of parameters s h o u l d be r e c o r d e d c o n c u r r e n t l y t o reduce t h e problems r e s u l t i n g from v a r i a b i l i t y , i n t h e environment. o b s e r v a t i o n s must n e c e s s a r i l y be undertaken  Thus,  multi-parameter  i n future studies;  such s t u d i e s s h o u l d be a b l e t o a d e q u a t e l y handle t h e v a r i o u s parameters which a f f e c t t h e p h y s i o l o g y and b e h a v i o r , and t h e r e f o r e t h e e c o l o g y , of the  organisms.  High-frequency  ( g r e a t e r t h a n 50 k H z ) , 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 s t u d y i n g t h e e c o l o g y o f the euphausiids.  A l t h o u g h 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 a t t h e o t h e r c r u s t a c e a n s , t h e y w i l l p r o b a b l y be l e s s u s e f u l t h a n f o r s t u d y i n g t h e e u p h a u s i i d s w h i c h t e n d t o s h o a l o r swarm (Mauchline and F i s h e r , 1959)  and a r e t h e r e f o r e more l o c a l i z e d i n  t h e w a t e r column. I n c r e a s e d knowledge about the e u p h a u s i i d s , 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 h e l p i n a s s e s s i n g f o o d s t o c k s i n t h e ocean.  E u p h a u s i i d s a r e known t o be t h e main s u p p l y f o r such  e c o n o m i c a l l y i m p o r t a n t f i s h e s as h e r r i n g , m a c k e r e l , and some s p e c i e s of salmon.  In f a c t , t h e e u p h a u s i i d s a r e thought t o be o n l y second  i n importa.nce  t o t h e copepod as t h e b a s i c a n i m a l f o o d i n t h e s e a ,  -65and i n some a r e a s t h e y exceed t h e numbers o f 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 g r e a t d e a l of commercial  i n t e r e s t has  been shown i n t h e p o s s i b i l i t i e s o f h a r v e s t i n g e u p h a u s i i d s , p a r t i c u l a r l y t h e l a r g e a n t a r c t i c s p e c i e s , E u p h a u s i a superba ( B u r u k o v s k i y , 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  a n i m a l s i s t o 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 o f 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 t h e u n d e r s t a n d i n g o f such  problems.  -66V.  SUMMARY AND CONCLUSION.  Euphausiids  caused sound s c a t t e r i n g a t f r e q u e n c i e s o f  42, 107, and 200 kHz b u t n o t a t 11 kHz. volume-scattering high-frequency  Daily variations i nthe  c o e f f i c i e n t , ID(AZ) a s d e t e r m i n e d from the zone o f  s c a t t e r i n g , corresponded t o v a r i a t i o n s i n t h e  concentration of euphausiids  c o l l e c t e d from the same d e p t h s .  V a r i a t i o n s i n the p a t t e r n s o f 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 t o the presence o r absence o f an o x y c l i n e a t 100 m i n the i n l e t and s e c o n d a r i l y t o m e t e o r o l o g i c a l  effects.  When the o x y c l i n e was p r e s e n t , downward m i g r a t i o n stopped a t o r near the t o p o f the o x y c l i n e .  I n these  instances, the v e r t i c a l  range o v e r which t h e e u p h a u s i i d s  were d i s t r i b u t e d was compressed.  The  was h i g h a l l day, a s was  concentration o f euphausiids  m(Az);  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 , and u ( d z ) , d e c r e a s e d d u r i n g t h e evening  migration. In the absence o f a n o x y c l i n e , m i g r a t i o n o c c u r r e d t o  g r e a t e r depths i n t h e w a t e r column and t h e d i s t r i b u t i o n o f e u p h a u s i i d s occurred over a wider v e r t i c a l range. was  The c o n c e n t r a t i o n a t depth  low i n the m o r n i n g , and t h e n g r a d u a l l y became h i g h e r t h r o u g h o u t  the day.  The a c o u s t i c d a t a showed t h i s p a t t e r n b e t t e r t h a n t h e  b i o l o g i c a l d a t a , t h e b i o l o g i c a l d a t a showing a g r e a t e r e f f e c t o f patchiness.  The p a t t e r n shown i n the absence o f an o x y c l i n e  p r o b a b l y b e s t d e s c r i b e s most o c e a n i c The layer  [JII(AZ),  situations.  general d a i l y nature o f the high-frequency  scattering  and the e u p h a u s i i d c o n c e n t r a t i o n 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 o r absence o f m o o n l i g h t and w i t h t h e  -67weather c o n d i t i o n s . "cue"  The p r e s e n c e o f s t r o n g m o o n l i g h t a c t s a s a  f o r a t l e a s t part o f the population of euphausiids  remain n e a r t h e s u r f a c e d u r i n g t h e n i g h t .  and t h e s e  Thus l a r g e r numbers o f  e u p h a u s i i d s , a s shown by t h e zone o f h i g h - f r e q u e n c y  scattering,  were observed d u r i n g t h e m o r n i n g m i g r a t i o n p e r i o d s when preceded by a m o o n l i t n i g h t , t h a n when preceded by a n i g h t w i t h l i t t l e o r no m o o n l i g h t . 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 p r e s e n t .  In s i t u a t i o n s without t h e 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 t h e w a t e r column;  t h e i r r e l a t i v e c o n c e n t r a t i o n remained unchanged.  W i t h reduced  i l l u m i n a t i o n and t h e presence o f an o x y c l i n e o n l y p a r t o f t h e p o p u l a t i o n moved upwards r e s u l t i n g i n d i s p e r s i o n o f t h e h i g h frequency s c a t t e r i n g l a y e r . euphausiid  I n t h i s c a s e , b o t h m(az)  and t h e  concentration decreased. V a l u e s 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 ( c m ) , o f a 3  euphausiid  i n c r e a s e d w i t h t h e f r e q u e n c y o f sound u s e d ; t h e v a l u e s  a t t h e t h r e e f r e q u e n c i e s f o r each c r u i s e were about one o r d e r o f magnitude a p a r t .  These v a l u e s ranged from 4.81 x 10~5 t o 5»21 x 10"3  (200 k H z ) , 5.49 x I O "  6 t  0  t o 3.67 x 10"5 (42 k H z ) .  3,99  x  1 0  -4  ( 7 k H z ) , and 2.30 x 10~7 1 0  F o r a l l f r e q u e n c i e s , O was l o w e s t  for  c r u i s e s where t h e average d r y weight and l e n g t h o f a e u p h a u s i i d were s m a l l and i n c r e a s e d a s t h e average s i z e and w e i g h t o f a euphausiid  increased. The  net  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  c o l l e c t e d w i t h a 10 mpi  ( c o a r s e , 2.16 mm opening) showed b e t t e r agreement w i t h 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 , !H(AK), t h a n catches w i t h 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 o f  -68s m a l l (<10 mm i n l e n g t h ) e u p h a u s i i d s were p r e s e n t .  T h i s would be  expected s i n c e t h e l a r g e e u p h a u s i i d s a r e much b e t t e r s c a t t e r e r s o f sound ( l a r g e r o ) . A "dawn r i s e " i n t h e p l a n k t o n r e s u l t i n g from s u n r i s e was not observed.  I n two i n s t a n c e s a r i s e i n t h e p l a n k t o n towards  t h e s u r f a c e o c c u r r e d j u s t p r i o r t o downward m i g r a t i o n and appeared t o be a s s o c i a t e d w i t h moonset. An echo-sounder system such a s t h e one used i n t h e p r e s e n t s t u d y appears t o be e x t r e m e l y w e l l s u i t e d f o r s t u d y i n g t h e problem of p a t c h i n e s s w h i c h has plagued marine e c o l o g i s t s f o r y e a r s . 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