UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A new method of determining the efficiency of towed plankton samplers Gilfillan, Edward Smith 1967

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

Item Metadata

Download

Media
831-UBC_1967_A6_7 G54.pdf [ 6.73MB ]
Metadata
JSON: 831-1.0104480.json
JSON-LD: 831-1.0104480-ld.json
RDF/XML (Pretty): 831-1.0104480-rdf.xml
RDF/JSON: 831-1.0104480-rdf.json
Turtle: 831-1.0104480-turtle.txt
N-Triples: 831-1.0104480-rdf-ntriples.txt
Original Record: 831-1.0104480-source.json
Full Text
831-1.0104480-fulltext.txt
Citation
831-1.0104480.ris

Full Text

A NEW METHOD OF DETERMINING THE EFFICIENCY OF TOWED PLANKTON SAMPLERS by EDWARD SMITH GILFILLAN I I I A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE' OF MASTER OF SCIENCE i n the Department of ZOOLOGY and INSTITUTE OF OCEANOGRAPHY We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May, 1967 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag r ee t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l no t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada Depar tment i ABSTRACT In r e c e n t y e a r s i n t e r e s t has i n c r e a s e d c o n c e r n i n g t h e a c c u r a c y w i t h which c o l l e c t i o n s made w i t h p l a n k t o n s a m p l e r s d e s c r i b e t h e s i z e and s p e c i e s c o m p o s i t i o n o f z o o p l a n k t o n i c c o m m u n i t i e s . The i n d i c a t i o n s a r e t h a t e r r o r s a r i s i n g f r o m t h e a v o i d a n c e o f s a m p l i n g d e v i c e s by z o o p l a n k t o n may be i m p o r t a n t , e s p e c i a l l y when p r e c i s e d a t a a r e r e q u i r e d . A model i s p r o p o s e d t o d e s c r i b e t h e p r o c e s s e s by which z o o p l a n k t o n i c o r g a n i s m s e s c a p e or a v o i d a s a m p l e r i n terms o f t h e r a d i u s o f t h e mouth o f t h e s a m p l e r , the speed a t which i t i s towed, t h e e f f e c t i v e s p e e d t h e o r g a n i s m s can a t t a i n i n o r d e r t o e s c a p e , and t h e d i s t a n c e at which" t h e o r g a n i s m s can d e t e c t t h e s a m p l e r . The model i s c a p a b l e o f b e i n g f i t t e d t o f i e l d d a t a t o p r o v i d e a c u r v e o f p e r c e n t a g e c a t c h p l o t t e d a g a i n s t s p e ed o f t o w i n g . The r e s u l t s p r e s e n t e d i n d i c a t e t h a t t h e model g i v e s a good r e p r e s e n t a t i o n o f t h e p r o c e s s e s o f b i o l o g i c a l escapement. I m p l i c a t i o n s o f t h e r e s u l t s a r e embodied i n r e c o m m e n d a t i o n s r e s p e c t i n g t h e d e s i g n o f p l a n k t o n s a m p l e r s . i i TABLE OF CONTENTS Page I n t r o d u c t i o n 1 Concepts and Survey of L i t e r a t u r e 5 The Model 19 M a t e r i a l s and Methods 25 F i e l d Procedure 26 The P l a n k t o n Samplers 29 L a b o r a t o r y Methods 32 Ma t h e m a t i c a l Procedure 37 R e s u l t s . 38 D i s c u s s i o n .59 One-metre C o n i c a l Sampler 69 70-cm N.I.O. Sampler 69 Ca t c h e r . . . . . .71 E x p e r i m e n t a l Samplers . .72 One Square Metre P.O.G. Samplers . . . . . . . .74 P l a n k t o n Sampler Design . . . . < , . . . . .75 Use and U t i l i t y of the Model 77 Ge n e r a l C o n c l u s i o n s 79 REFERENCES 80 APPENDIX I 84 i i i LIST OF TABLES Table S u b j e c t Page 1. Flow Meter Counts (per h a u l ) 10 2. R e s u l t s of F i e l d T r i a l s : August, 1965 One-metre C o n i c a l Sampler . . . . . 53 3. R e s u l t s of F i e l d T r i a l s : J a n u a r y , 1966 M o d i f i e d One-metre C o n i c a l Sampler . . . . . . . 54-4. R e s u l t s of F i e l d T r i a l s : August, 1965 70-cm N.I'.O. Sampler 55 5. R e s u l t s of F i e l d T r i a l s : J a n u a r y , 1966 M o d i f i e d 70-cm.N.1.0. Sampler . 56 6. R e s u l t s of F i e l d T r i a l s : August, 1965 Cat c h e r 57 7. P.O.G. Un p u b l i s h e d R e s u l t s Obtained i n August , .1965- 58 8. Comparison of P o p u l a t i o n E s t i m a t e s i n Numbe'rs/m3 of Water F i l t e r e d 63 9. R e s u l t s of F i f t e e n S u c c e s s i v e Counts of the Number of E u p h a u s i i d s L y i n g w i t h i n l / 2 0 t h of the Area of the Bottom of a D i s h C o n t a i n i n g 1343 E u p h a u s i i d s 86 i v LIST OF FIGURES F i g u r e S u b j e c t Page 1. The k i n e m a t i c b a s i s of B a r k e l e y ' s (1964) model f o r a s s e s s i n g the e f f i c i e n c y of towed p l a n k t o n samplers f a c i n g p. 5 2. Mean f l o w meter counts p l o t t e d a g a i n s t speed of h a u l i n g . 9 • 3. The k i n e m a t i c b a s i s of the model 22 4. The l o c a t i o n of the f i e l d t r i a l s of August, 1965 and J a n u a r y , 1966 27 5a. The one-metre c o n i c a l sampler 33 5b. The one-metre c o n i c a l sampler m o d i f i e d by the attachment of a weight t o i t s b r i d l e s . . . . 33 6a. The 70-cm N.I.O. sampler 34 6b. The 70-cm N.I.O. sampler m o d i f i e d by the removal of the canvas c o l l a r 34 7a. The C a t c h e r 35 7b. The f i l t e r used i n the Catcher 35 8a. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the one-metre c o n i c a l sampler 42 8b. G o o d n e s s - o f - f i t diagram f o r the r e s u l t s o b t a i n e d w i t h the one-metre c o n i c a l sampler 43 9a. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the m o d i f i e d one-metre c o n i c a l sampler . . . 44 9b. G o o d n e s s - o f - f i t diagram f o r the r e s u l t s o b t a i n e d w i t h the m o d i f i e d one-metre c o n i c a l sampler . . . 45 10. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the 70-cm N.I.O. sampler 46 11a. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the m o d i f i e d 70-cm N.I.O. sampler . . . . . . 47 l i b . G o o d n e s s - o f - f i t diagram f o r the r e s u l t s o b t a i n e d w i t h the m o d i f i e d 70-cm N.I.O. sampler 48 V LIST OF FIGURES ( c o n t i n u e d ) F i g u r e S u b j e c t Page 12a. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the Ca t c h e r 49 12b. G o o d n e s s - o f - f i t diagram f o r the r e s u l t s o b t a i n e d w i t h the Ca t c h e r . 50 13a. Percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r the P.O.G. samplers 51 13b. Goodne.ss-of-fit diagram f o r the r e s u l t s o b t a i n e d w i t h the P.O.G. samplers . . . . . . . 52 V i ACKNOWLEDGMENTS I am i n d e b t e d t o a l l of the members of my r e s e a r c h committee f o r t h e i r guidance and encouragement. I would l i k e t o extend my most s i n c e r e thanks t o my r e s e a r c h ' a d v i s o r , Dr. B. Mck. Bary f o r h i s p a t i e n c e , encouragement and c r i t i -c i s m . I would a l s o l i k e to thank Dr. P. A. Dehene1, Dr. I . E. E f f o r d , ' D r . P. H. L e b l o n d , Dr. P. A. L a r k i n , and Dr. G.-L. P i c k a r d , a l l of'whom read and c r i t i c i z e d the manu-s c r i p 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 c r i t i c i s m . R. J . L e B r a s s e u r and-C. D. M c A l l i s t e r of the P a c i f i c Oceanographic Group, Nanaimo, B. C., p r o v i d e d u n p u b l i s h e d d a t a , f o r which many thanks are due. I would l i k e to thank the o f f i c e r s , a n d men- of C.N.A.V. W h i t e t h r o a t and C.N.A.V. S t . Anthony f o r t h e i r c h e e r f u l and generous a s s i s t a n c e i n the g a t h e r i n g of the data . To my w i f e , K a t h e r i n e , whose encouragement d u r i n g the r e s e a r c h and p r e p a r a t i o n of the thesis'made the t a s k much e a s i e r , I o f f e r "my most s i n c e r e t h a n k s . No e x p r e s s i o n of thanks can s u f f i c e • f o r Mrs. E. A. H eilman, w i t h o u t whom none of t h i s would have been p o s s i b l e . INTRODUCTION: The g o a l of the p l a n k t o l o g i s t i s to und e r s t a n d the s t r u c t u r a l and f u n c t i o n a l a s p e c t s of the p l a n k t o n i c community. Because he i s unable to observe t h i s community d i r e c t l y he i s l a r g e l y committed to g a t h e r i n g h i s d a t a ' a t a d i s t a n c e , and f o r i n f o r m a t i o n r e g a r d i n g the s i z e and s p e c i e s c o m p o s i t i o n of the p l a n k t o n i c community, has to r e l y on samples c o l l e c t e d by a v a r i e t y of d e v i c e s . A l t h o u g h pumps, t r a p s , and even purse s e i n e s have been and are b e i n g used t o o b t a i n such samples, almost a l l are c o l l e c t e d w i t h towed p l a n k t o n s a m p l e r s . In the p r e s e n t study s e v e r a l samplers designed to' c a t c h z o o p l a n k t o n r a n g i n g from about one m i l l i m e t r e t o s e v e r a l c e n t i m e t r e s i n l e n g t h are d i s c u s s e d . Almost w i t h o u t e x c e p t i o n p l a n k t o n samplers o p e r a t e by p a s s i n g a l a r g e volume of water through a f i l t e r i n g s u r f a c e . This s u r f a c e , which i s u s u a l l y i n the form of a c o n i c a l n e t , i s expected to r e t a i n much of the p a r t i c u l a t e matter which i s l a r g e r than the mesh a p e r t u r e (Wiborg, 1948). In the s i m p l e s t type of sampler the f i l t e r i n g s u r f a c e i s a t r u n c a t e d cone support e d by a r i n g at the mouth and t e r m i n a t i n g i n a c o l l e c t i n g bucket towards the apex of the cone. T h i s d e s i g n i s b a s i c t o n e a r l y a l l p l a n k t o n s a m p l e r s , but has a number of d i s a d v a n t a g e s . C h i e f of these i s the l a c k of any p r o v i s i o n f o r o b t a i n i n g uncontaminated samples from a p a r t i c u l a r s t r a t u m of the water column, and a g e n e r a l c l u m s i n e s s when u s i n g more than one sampler at a t i m e . However, the b a s i c p r i n c i p l e s of i t s o p e r a t i o n are common t o a l l towed p l a n k t o n s a m p l e r s . Two s o r t s of i n f o r m a t i o n s h o u l d be o b t a i n e d when u s i n g a p l a n k t o n sampler. These'are, f i r s t l y , ' a r e p r e s e n t a t i v e sample of the community or p o p u l a t i o n of a s p e c i e s or group of s p e c i e s of z o o p l a n k t o n p r e s e n t ; and, s e c o n d l y , i n f o r m a t i o n l e a d i n g t o a d e t e r m i n a t i o n of the volume of water f i l t e r e d . A p l a n k t o n sampler may f a i l t o p r o v i d e e i t h e r of these f o r a v a r i e t y of reasons and, i f the inadequacy i s not r e c o g n i s e d , e r r o r s i n the i n t e r p r e t a t i o n of the data may r e s u l t . These e r r o r s can be d i v i d e d i n t o two broad c a t e g o r i e s . F i r s t l y , t h e r e are those sources of e r r o r o r i g i n a t i n g i n t e r n a l l y to the sampler, i n c l u d i n g those a r i s i n g from i n a c c u r a t e d e t e r m i n a t i o n of the volume of water which has passed through the f i l t e r . These e r r o r s can be l a r g e l y over-come by the use of a f l o w meter which has'been c a r e f u l l y c a l i b r a t e d . Losses of c a t c h r e s u l t i n g from e x t r u s i o n of a n i -mals through the meshes of the f i l t e r can be m i n i m i s e d by s e l e c t i n g a f i l t e r which w i l l r e t a i n a l l specimens of the s p e c i e s t o be s t u d i e d . In the second c a t e g o r y are sources of e r r o r o r i g i n a t i n g e x t e r n a l l y t o the sampler, i n c l u d i n g t h o s e ' a r i s i n g i n the e s t i m a t i o n of the s i z e of a z o o p l a n k t o n p o p u l a t i o n because of the non-homogeneous d i s t r i b u t i o n of i t s c o n s t i t u e n t s ( B a r n e s , 1949; Barnes a n d ' M a r s h a l l , 1951; C a s s i e , 1958, 1959). Attempts to compensate f o r the non-homogeneous d i s t r i b u t i o n of z o o p l a n k t o n can be made,' i f n e c e s s a r y , i n the d e s i g n of the sa m p l i n g program. T h i s c a t e g o r y a l s o 3 i n c l u d e s e r r o r s i n the e s t i m a t e s of the s i z e of z o o p l a n k t o n i c p o p u l a t i o n s which may a r i s e from the d e t e c t i o n and avoidance of the s a m p l i n g ' d e v i e e by i n d i v i d u a l a n i m a l s . These e r r o r s are not e a s i l y d e t e c t e d , and they l e a d to n o n - q u a n t i t a t i v e data which can'be troublesome to any program r e q u i r i n g exact i n f o r m a t i o n c o n c e r n i n g t h e ' s i z e of the p o p u l a t i o n of each s p e c i e s i n a community'. Data from s t u d i e s i n the f i e l d b y Sheard (1941), Aron ( 1962 ), Hansen and Anderson ( 1962 ) , Regan ( 1963 ), and Le B r a s s e u r and M c A l l i s t e r - ( 1 9 6 6 ) i n d i c a t e - n o t - o n l y t h a t prob-lems a r i s e from the r e a c t i o n s of z o o p l a n k t o n i c organisms t o the presence of t h e - s a m p l e r , but a l s o t h a t - t h e problems are compounded because the- e f f e c t s of the- r e a c t i o n s v a r y a c c o r d i n g to the v a r y i n g powers' of' p e r c e p t i o n a n d \ l o c o m o t i o n possessed by each s p e c i e s . In t h i s ' c o n n e c t i o n Flemminger and C l u t t e r (1965) have p o s t u l a t e d the e x i s t e n c e of a zone around the p e r i p h e r y of the mouth of the sampler from which-the s p e c i e s of z o o p l a n k t o n they s t u d i e d were a b l e to- escape. B a r k e l e y (1964) has a n a l y s e d t h e - k i n e m a t i c s of t h e ' r e a c t i o n of i n d i v i d u a l a n i m a l s • to" the presence of the-.sampler . In the p r e s e n t study a m a t h e m a t i c a l model, based on B a r k e l e y 1 s a n a l y s i s of the r e a c t i o n of i n d i v i d u a l a nimals t o the presence of a plankton- sampler, i s proposed. T h i s model t r e a t s the p e r i p h e r a l zone of escape as a f u n c t i o n of the speed of h a u l i n g a n d " c a n - b e - f i t t e d t o f i e l d d a ta t o p r o v i d e a C o u r t e s y R. Le B r a s s e u r , P a c i f i c Oceanographic Group, Nanaimo, B r i t i s h C olumbia, Canada. 4 p l o t of p ercentage c a t c h a g a i n s t speed of h a u l i n g . The r e s u l t s of t h i s study i n d i c a t e t h a t the model a c c o u n t s - f o r the major f e a t u r e s of l o s s i n c a t c h r e s u l t i n g from'the d e t e c t i o n and avoidance of the p l a n k t o n sampler by i n d i v i d u a l organisms. r Figure 1. The kinematic basis of Barkeley 's model for assessing the efficiency of a towed plankton sampler. U= the speed of towing, R= the radius of the sampler, X Q = the distance at which organisms can detect the sampler, r Q = the in i t i a l offset of the organism, u= the min imal escape velocity of the organism, p= the or iginal position of the organism, e= the angle at which the organism swims with respect to the axis of the sampler. 5 CONCEPTS AND SURVEY OF LITERATURE: For the purpose of t h i s study b i o l o g i c a l escapement i s d e f i n e d as the avoidance of an a p p r o a c h i n g p l a n k t o n sampler by z o o p l a n k t o n by means of t h e i r own e x e r t i o n s . The con-sequence of b i o l o g i c a l escapement i s u n d e r e s t i m a t i o n of the s i z e of z o o p l a n k t o n i c p o p u l a t i o n s . Another' e f f e c t of b i o l o g i c a l escapement i s t h a t , as a r e s u l t of the v a r y i n g powers of per-c e p t i o n and m o b i l i t y p ossessed by d i f f e r e n t s p e c i e s of z o o p l a n k t o n , the p r o p o r t i o n s of anim a l s caught may not be the same as the p r o p o r t i o n s of those s p e c i e s i n the community. T h i s c o n t r i b u t e s to the s e l e c t i v i t y of a sam p l e r , where s e l e c t i v i t y i s d e f i n e d as the d i f f e r e n t i a l c a p t u r e of one or more s p e c i e s or s i z e ranges of z o o p l a n k t o n . I f B a r k e l e y ' s (1964) a n a l y s i s of the k i n e m a t i c s of b i o l o g i c a l escapement i s c o r r e c t ( F i g . 1) i t i s t o be expected t h a t the number of specimens of a s p e c i e s c a p t u r e d per u n i t volume of water w i l l i n c r e a s e i f the speed of h a u l i n g i s i n c r e a s e d . As the speed of h a u l i n g i s i n c r e a s e d the z o o p l a n k t o n w i l l have l e s s o p p o r t u n i t y t o evade the sampler because they w i l l have l e s s time i n which t o move b e f o r e the sampler over-t a k e s them. T h i s i n c r e a s e i n c a t c h can be expected t o be g r e a t e s t f o r those a n i m a l s which are be s t a b l e t o escape c a p t u r e at the o r i g i n a l speed of h a u l i n g . However, o t h e r f a c t o r s may a f f e c t the e s t i m a t e s of the numbers of each s p e c i e s p r e s e n t ; ^ m o s t l y these o r i g i n a t e i n e r r o r s a r i s i n g i n the c o l l e c t i n g t e c h n i q u e . 6 The u s u a l method of o p e r a t i o n of a p l a n k t o n sampler i s t o pass a l a r g e volume of water through the f i l t e r i n g s u r -f a c e ( n e t ) . One source of e r r o r i s i n the d e t e r m i n a t i o n of the volume of water which has been f i l t e r e d . T h i s volume can be determined e i t h e r w i t h a f l o w meter which'has been c a l i b r a t e d i n the sampler i n which i t i s t o be used, or by assuming t h a t the sampler f i l t e r s some c o n s t a n t f r a c t i o n of the water p r e s e n t e d to i t over the l e n g t h of the tow. I f the volume of water f i l t e r e d i s to be determined by assumption i t i s e s s e n t i a l t o know what the l e n g t h of the tow was and, i n most i n s t a n c e s , what p r o p o r t i o n of the water p r e s e n t e d to the sampler i s f i l -t e r e d . However, the d i s t a n c e t h a t the sampler has moved through the water i s not always easy t o ' d e t e r m i n e . In h o r i -z o n t a l or o b l i q u e h a u l s unknown e f f e c t s of c u r r e n t s s h o u l d be accounted f o r . Even i n a v e r t i c a l h a u l , s h o u l d the s h i p move r e l a t i v e to the w i r e , the d i s t a n c e t h a t the sampler moves through the water i s d i f f i c u l t t o d e t e r m i n e . Another cause of e r r o r s , i n the d e t e r m i n a t i o n of the volume of water which has passed through the sampler, i s c l o g g i n g of the meshes of the f i l t e r , o f t e n by p h y t o p l a n k t o n . When sa m p l i n g i s c a r r i e d out i n p r o d u c t i v e waters c l o g g i n g can be a s e r i o u s problem. When c l o g g i n g o c c u r s the -amount of water f i l t e r e d per u n i t d i s t a n c e may be g r e a t l y reduced. The s e v e r i t y of c l o g g i n g can be reduced by i n c r e a s i n g the amount of open area of the f i l t e r i n r e l a t i o n t o the area of the mouth of the sampler, e.g. by g r e a t l y i n c r e a s i n g the l e n g t h of the sampler, or by i n c r e a s i n g the s i z e of the meshes of the 7 f i l t e r . ( S m i t h , pers . comm.). Because i t i s i m p o r t a n t t o determine the volume of water which has been f i l t e r e d • m a n y p l a n k t o n samplers employ f l o w meters. A f l o w meter c o n s i s t s of an i m p e l l e r , geared to a c o u n t e r , which r e c o r d s the number of r e v o l u t i o n s made by the i m p e l l e r . The use of a f l o w meter i n t r o d u c e s many problems because i t a c t u a l l y measures the l e n g t h of a column of water which has passed through the sampler; not volume. T h e r e f o r e , i t i s n e c e s s a r y to c a l i b r a t e the f l o w meter b e f o r e the number of r e v o l u t i o n s can be c o n v e r t e d to volume f i l t e r e d . The c a l i b r a t i o n i s made by towing the sampler over a known d i s t a n c e both with'and w i t h o u t t h e • f i l t e r i n p l a c e . The r e s u l t s from tows made w i t h o u t t h e : f i l t e r g i v e the c a l i -b r a t i o n w i t h r e s p e c t to d i s t a n c e moved through the water. Comparison of the r e s u l t s g i v e n w i t h and w i t h o u t the f i l t e r g i v e s an e s t i m a t e of the percentage of the water p r e s e n t e d to the sampler which' i s ' a c c e p t e d by i t . What' i s a c t u a l l y measured by the d i f f e r e n c e ' b e t w e e n t h e ' r e a d i n g s o b t a i n e d w i t h and w i t h o u t the f i l t e r i s the r e d u c t i o n i n " t h e v e l o c i t y of f l o w through the sampler•caused by the presence of the f i l t e r , or the l e n g t h of the water•column which'passed•through the sampler at the p o s i t i o n of the f l o w meter. In s m a l l samplers l i k e the Clarke-Bumpus S a m p l e r ' ( C l a r k e and Bumpus, 1950) i n which the i m p e l l e r o c c u p i e s most of the diameter of the sa m p l e r , a good e s t i m a t e of the amount of water which has"passed through the Dr. P. Smith, U. S. Bureau of Commercial F i s h e r i e s , La J o l l a , C a l i f . 8 sampler may be o b t a i n e d . In l a r g e r samplers such as the N.I.O. 70-cm sampler ( C u r r i e and Foxton, 1957) or the one-metre c o n i c a l sampler the f l o w meter o c c u p i e s o n l y a s m a l l p o r t i o n of the mouth of the sampler and the assumption must be made t h a t the f l o w through the sampler' i s everywhere the same as i t i s at the p o s i t i o n of the f l o w - m e t e r . F u r t h e r , f low-meters have t r a d i t i o n a l l y been mounted i n the c e n t r e of the mouth of the sampler. Recent e x p e r i m e n t a l s t u d i e s have shown t h a t the w i r e , and e s p e c i a l l y the t e r m i n a l s h a c k l e ( F i g . 5a) which i s a t t a c h e d to the b r i d l e s of the sampler, c r e a t e a t u r b u l e n t wake which passes i n t o the c e n t r e of the mouth of the sampler ( B a r y , p e r s . comm.). Because the f l o w meter must be, i n a r e g i o n of l a m i n a r f l o w i n o r d e r t o g i v e a c c u r a t e r e s u l t s , the wake may cause c e n t r a l l y mounted f l o w -meters to g i v e i n a c c u r a t e r e s u l t s . E r r o r s i n e s t i m a t e s of the number of organisms per u n i t volume of water r e s u l t i n g from i n a c c u r a t e e s t i m a t e s of the volume of water which has been f i l t e r e d c o u l d obscure the e f f e c t s of b i o l o g i c a l escapement. In F i g . 2 flow-meter r e a d i n g s r e c o r d e d d u r i n g the f i e l d t r i a l s u ndertaken i n the course of t h i s study are p l o t t e d a g a i n s t the speed of h a u l i n g (see Table 1 ) . When the f i e l d t r i a l s were c a r r i e d out the e f f e c t of the t u r b u l e n t wake p a s s i n g i n t o the c e n t r e of the mouth-of the sampler was not a p p r e c i a t e d , and t h e r e f o r e a l l data were o b t a i n e d w i t h Dr. B.. Mck. B a r y , I n s t i t u t e of Oceanography, U n i v e r s i t y of B. C. , Vancouver, Canada . F i g u r e 2 ( f a c i n g ) Mean flowmeter counts p l o t t e d a g a i n s t speed of h a u l i n g . The r e s u l t s f o r the 1-m c o n i c a l sampler, the 70-cm N.I.O. sampler, and the Catc h e r were o b t a i n e d d u r i n g the f i e l d t r i a l s of August, 1965; those f o r the two e x p e r i m e n t a l samplers were o b t a i n e d d u r i n g the f i e l d t r i a l s of J a n u a r y , 1966. X l -m CONICAL SAMPLER 8 70-cm N.I.O. SAMPLER A CATCHER + MODIFIED l-m CONICAL SAMPLER O MODIFIED 70-cm N.I.O. SAMPLER j i i i I l I I 1 1 1— 0 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec 10 Table 1. Flow Meter Counts ( p e r h a u l ) August,1965 Speeds 25 cm/sec 100 cm/sec 200 cm/sec One-metre c o n i c a l , sampler ' - ' 18 .0 16,5 16.5 17.0 14,5 16.5 18,0 17.0 15,0 18.0 18.5 16.0 17,5 17,5 17,0 18,0 17,5 16.0 18,5 .17,0 17,0 17,0 16.5 1.6 ,5 70-cm N.I.O. sampler 6 . 5 9 . 5 9 . 5 9 , 0 8 . 0 9 . 5 7 . 5 8 . 5 Ca t c h e r (50 cm/sec) 7 . 5 8 „ 5 .7 , 5 8 . 0 8 , 5 7 ..5 9 , 0 8 . 0 7 .0 7 „ 0 7 6 5 6 . 5 7 . 5 8 , 0 6 . 0 7 „ 0 6 . 0 8 . 0 8 . 0 9 o 0 8 o 0 8 , 5 7 „ 0 8 . 0 9 , 5 8 „ 5 9 . 0 8 o 5, 9 . 0 9 . 0 9 „ 0 8 , 0 9 . 0 10 . 0 9 , 5 9 , 5 7 . 0 9 , 0 10 , 0 9 ,0 January- 1966 M o d i f i e d one-metre c o n i c a l sampler 19,0 24,0 17,0 14„0 26.5 30,0 2 3 . 5 25 . 0 1:5 . 0 M o d i f i e d 70-cm N.I.O, sampler 15.0 ' 14.0 14,5 15.5 14,0 14.5 15.0 14.0 14.0 11 c e n t r a l l y mounted f l o w m e t e r s . The i m p e l l e r of the f l o w meter used i n the C a t c h e r ( F i g . 7a) (Bary et_ a_l_. , 1958 ) o c c u p i e s n e a r l y the whole d i a -meter of the t a i l p i e c e . The i m p e l l e r of the flowmeter used i n the N.I.O. 70-cm sampler ( F i g . 6a) and i n the one-metre c o n i c a l sampler was about 15 cm i n diameter ( C u r r i e and F o x t o n , 1957). Only l a r g e d e v i a t i o n s i n f l o w such as those caused by c l o g g i n g , can be d e t e c t e d r e a d i l y . In the p r e s e n t study a l a r g e d e v i a t i o n was o b t a i n e d u s i n g the one metre c o n i c a l sampler ( F i g . 5b) when i t was m o d i f i e d by adding a c y l i n d r i -c a l l e a d weight 80 cm i n f r o n t of the mouth of the sampler. I t i s most p r o b a b l e t h a t t h i s d e v i a t i o n was caused by the wake from the weight a f f e c t i n g the f l o w meter. Because the f l o w - m e t e r s i n the two l a r g e samplers were not o n l y i n the t u r b u l e n t zone, but a l s o were unable to monitor more than a s m a l l p o r t i o n of the f l o w through the sampler, the r e s u l t s from them have been used o n l y as an assurance t h a t l a r g e changes i n the volume of water f i l t e r e d per h a u l p r o b a b l y d i d not o c c u r . In the p r e s e n t study the volume of water f i l t e r e d was c a l c u l a t e d by assuming t h a t the samplers f i l t e r e d 100% of the water p r e s e n t e d t o them over the course of the tow. C l o g g i n g i s b e l i e v e d not to have o c c u r r e d . In the f i e l d t r i a l s the samplers were h a u l e d v e r t i c a l l y over a known d i s t a n c e . In the p r o t e c t e d l o c a t i o n i n which they were c a r r i e d out the w i r e never s t r a y e d more than a few degrees from the v e r t i c a l . In the s p e c i a l c i r c u m s t a n c e s of t h i s study the method of assuming 12 a volume f i l t e r e d appears to be the most u s e f u l one. I t i s p r o b a b l e t h a t the samplers d i d not f i l t e r 100% of the water p r e s e n t e d to them, but t h i s i s not i m p o r t a n t because the model b e i n g e v a l u a t e d r e q u i r e s o n l y t h a t some c o n s t a n t p r o p o r t i o n of the water be f i l t e r e d . That a c o n s t a n t volume i s f i l t e r e d over a range of speeds has been demonstrated f o r the C a t c h e r by Bary et a l . (1958) and f o r the Clarke-Bumpus Sampler by T r a n t e r and Heron (196 !5) and by G i l f i l l a n and Pease ( i n p r e p . ) . E r r o r s i n e s t i m a t e s of the number of specimens p r e s e n t per u n i t volume, when a known volume of water has been f i l t e r e d , can a r i s e from two s o u r c e s . F i r s t l y , organisms s m a l l enough to pass through the meshes of the f i l t e r w i l l not be sampled q u a n t i t a t i v e l y . T h i s s i t u a t i o n can be a v o i d e d by c h o o s i n g a f i l t e r w i t h a s m a l l enough mesh a p e r t u r e to r e t a i n i n d i v i d u a l s of a l l those s p e c i e s w h i c h - a r e to be s t u d i e d . However, d e c r e a s i n g the s i z e of the mesh a p e r t u r e i n c r e a s e s the r a t e at which the f i l t e r w i l l c l o g . T h e r e f o r e a compromise i s o f t e n n e c e s s a r y when sampling i n p r o d u c t i v e w a t e r s . A f u r t h e r source of v a r i a t i o n r e s u l t s from the non-homogeneous d i s p e r s i o n o f - i n d i v i d u a l s , or ' p a t c h i n e s s ' , of a s p e c i e s i n the sea ( B a r n e s , 194-9; Barnes and M a r s h a l l , 1951). These patches may be s e v e r a l k i l o m e t e r s i n l a t e r a l e x t e n t ( C u s h i n g , 1954) and have a s u b s t r u c t u r e on the o r d e r of s e v e r a l metres i n a l l dimensions ('Cassie,. 19 58 , 19 59 ). These patches may a l s o be o n l y a few metres i n t h i c k n e s s ( B a r y , 1966). Hauls s e v e r a l hundred metres long w i l l tend to average out the e f f e c t s of the patchy s u b s t r u c t u r e and p r o v i d e a 13 b e t t e r sample of the p o p u l a t i o n p r e s e n t . V e r t i c a l h a u l s w i l l y i e l d the most r e l i a b l e sample when the a g g r e g a t i o n s of zoo-p l a n k t o n are p r i m a r i l y i n h o r i z o n t a l l a y e r s . A f u r t h e r p r e c a u t i o n which s h o u l d be taken t o attempt to reduce the e f f e c t s of p a t c h i n e s s is- t o f o l l o w the same p a r c e l of water r a t h e r than t o sample at the same g e o g r a p h i c a l p o s i t i o n . Few r e l i a b l e d ata c o n c e r n i n g b i o l o g i c a l escapement are a v a i l a b l e i n the l i t e r a t u r e . In many of the r e p o r t e d i n v e s t i g a t i o n s of the problems connected w i t h p l a n k t o n s a m p l i n g , inadequate measures were ta k e n to reduce those o t h e r s o u r c e s of e r r o r which can obscure the e f f e c t s of b i o l o g i c a l escapement'. A c c o r d i n g l y i n t e r p r e t a t i o n - of the r e s u l t s i s d i f f i c u l t at best ( e . g . Hensen, 1895; Kunne, 1933; Gibbons, 1939). A b r i e f r e v i e w of the p e r t i n e n t l i t e r a t u r e i s g i v e n b elow. Winsor and C l a r k e (1940) concl u d e d t h a t e s t i m a t e s of the s i z e of copepod and chaetognath p o p u l a t i o n s g i v e n by a c o n i c a l sampler h a v i n g a mouth opening of 12.5 cm ( a l l samplers such as t h i s one are s u b s e q u e n t l y r e f e r r r e d to i n the t e x t i n the form: 12.5-cm c o n i c a l sampler) were comparable t o those g i v e n by a c o n i c a l sampler w i t h a mouth opening of 75 cm ( i . e . a 75-cm c o n i c a l s a m p l e r ) . Such e s t i m a t e s are open t o q u e s t i o n because the f i e l d t r i a l s not o n l y were c a r r i e d out at a g e o g r a p h i c a l l o c a t i o n r a t h e r than i n a s i n g l e p a r c e l of w a t e r , but the area (Georges Bank) i s one of s t r o n g c i r c u l a t i o n . Thus e r r o r s may have been i n t r o d u c e d by p a t c h i n e s s . 14 Sheard (1941) towed a 70-cm D i s c o v e r y sampler (Kemp and Hardy, 1929) at speeds r a n g i n g from 2 to 6 knots ( k t ) i . e . 1 t o 3 m/sec. As the speed of towing"was i n c r e a s e d , the s i z e of the c a t c h a l s o increased". At 6 k t f i s h up- t o 7,5 cm i n l e n g t h were caught. Fish"were not caught at 2 k t . Sheard a t t r i b u t e d the i n c r e a s e - i n c a t c h and the changes i n the composi-t i o n of the samples c o l l e c t e d at the h i g h e r speeds of towing t o decreased b i o l o g i c a l escapement, Aron (1962) compares'the c a t c h i n g power of an I s a a c s -K i d d midwater t r a w l h a v i n g a 3 f t (,9m) mouth opening and a Clarke-Bumpus sampler ( C l a r k e and Bumpus, 19 50 ) w i t h a: 12.5 cm mouth opening w i t h r e s p e c t t o e u p h a u s i i d s . He s t a t e s t h a t , i n thousands of samples c o l l e c t e d w i t h Clarke-Bumpus Samplers from the North P a c i f i c , e u p h a u s i i d s were v e r y r a r e , w h i l e n e a r l y a l l samples c o l l e c t e d w i t h - t h e - I s a a c s - K i d d midwater t r a w l from the same area were dominated by e u p h a u s i i d s . Hansen and• Anders on' ( 1962 ) compared the c a t c h c o l l e c t e d by a 50-cm c o n i c a l ' sampler and by a 38-cm Hensen sampler ( J e n k i n s , 1901) w i t h t h e ' c a t c h o b t a i n e d ' w i t h a 8 - l i t r e water b o t t l e . E f f i c i e n c i e s were c a l c u l a t e d w i t h r e s p e c t to t o t a l z o o p l a n k t o n p r e s e n t . The c a t c h of the 8 - l i t r e water b o t t l e was t a k e n as 100%. On t h i s b a s i s the e f f i c i e n c y of the Hensen sampler was 65%; t h a t of the 50-cm c o n i c a l sampler o n l y 18%. Regan (1963) i n v e s t i g a t e d the s u i t a b i l i t y of the Clarke-Bumpus Sampler as-ah instrument- f o r - c o l l e c t i n g e u p h a u s i i d s . Regan's data show a tendency toward i n c r e a s e d c a t c h e s at h i g h e r speeds of t o w i n g . The i n c r e a s e i n c a t c h at 15 the h i g h e r speeds becomes g r e a t e r f o r l i f e h i s t o r y stages of i n c r e a s e d age and s i z e and i s g r e a t e s t f o r a d u l t s . Regan's data a l s o show t h a t the average i n c r e a s e i n c a t c h was g r e a t e r by day than by n i g h t . T h i s suggests t h a t v i s i o n may be i m p o r t a n t i n the d e t e c t i o n of samplers by e u p h a u s i i d s . Barnes and T r a n t e r ( 1965:) conducted a s e r i e s of t r i a l s i n o r d e r t o compare the a b i l i t i e s ( i . e . the " c a t c h i n g power") of the A u s t r a l i a n v e r s i o n of the Clarke-Bumpus Sampler ( T r a n t e r , 1966), the I n d i a n Ocean Standard Sampler ( C u r r i e , 1962), and the T r o p i c a l Juday Sampler (J u d a y , 1916) t o c o l l e c t organisms. S t a t i s t i c a l comparison between r e p l i c a t e samples f a i l e d t o show any d i f f e r e n c e which c o u l d be a s c r i b e d to b i o l o g i c a l escapement. Fl e m i n g e r and C l u t t e r (1965) conducted a study d e s i g n e d to f u r n i s h i n f o r m a t i o n about b i o l o g i c a l ' escapement. They sampled two c a p t i v e z o o p l a n k t o n p o p u l a t i o n s w i t h t h r e e c o n i c a l samplers of s i m i l a r d e s i g n , h a v i n g mouth areas i n the r a t i o 1:2:4. These samplers were towed i n a tank on a s p e c i a l l y b u i l t runway at c o n s t a n t speed. The e f f e c t s of two l e v e l s of p o p u l a t i o n d e n s i t y and l i g h t i n t e n s i t y were e v a l u a t e d . In a l l comparisons i n v o l v i n g two samplers the s m a l l e r caught r e l a t i v e l y fewer ani m a l s than the l a r g e r . In the denser p o p u l a t i o n s t h i s t r e n d was a c c e n t u a t e d . The r a t i o s of the c a t c h of the s m a l l e r to the l a r g e r sampler f o r copepods were not a f f e c t e d by l i g h t i n t e n s i t y . The same r a t i o s f o r the c a t c h e s of m y s i d s , which possess compound eyes, were i n c r e a s e d at h i g h e r l i g h t i n t e n s i t i e s ; the d i s p a r i t y between c a t c h e s 16 f o r samplers of v a r y i n g - s i z e was g r e a t e r i n the l i g h t than i n the dark. From these r e s u l t s the a u t h o r s p o s t u l a t e d the e x i s -tence of a zone around t h e • p e r i p h e r y of the-mouth of the sampler from which the a n i m a l s c o u l d escape and t h a t t h i s zone was b r o a d e r i n the l i g h t f o r those animals which d e t e c t e d the sampler by v i s u a l means,- In- t h e p r e s e n t study t h i s concept i s e n l a r g e d upon to t r e a t the w i d t h of a - p e r i p h e r a l zone of escape as a f u n c t i o n of the speed' of t o w i n g . Le B r a s s e u r and M c A l l i s t e r (1966) s t u d i e d the e f f e c t s of the s i z e of the s a m p l e r , - t h e speed of h a u l i n g , and l i g h t i n t e n s i t y on the Catches o f - a wide range of z o o p l a n k t o n i c s p e c i e s . They i n t e r p r e t e d t h e i r r e s u l t s as showing t h a t i n c r e a s -i n g the a r e a of the mouth of the sampler i n c r e a s e d the e s t i m a t e s of p o p u l a t i o n d e n s i t y . I n c r e a s i n g the speed of h a u l i n g a l s o i n c r e a s e d the e s t i m a t e s of p o p u l a t i o n d e n s i t y f o r some s p e c i e s , but not f o r o t h e r s . The i n c r e a s e d c a t c h a s c r i b e d to i n c r e a s e d speed was most pronounced f o r e u p h a u s i i d s . D a r k - c o l o u r e d samplers gave c o n s i d e r a b l y l a r g e r e s t i m a t e s of the s i z e of the e u p h a u s i i d p o p u l a t i o n t h a n - l i g h t c o l o u r e d s a m p l e r s . E s t i m a t e s of the s i z e of the e u p h a u s i i d p o p u l a t i o n were l a r g e r by n i g h t than by day f o r a l l s a m p l e r s . Only the c a t c h e s of e u p h a u s i i d s were a f f e c t e d b y the c o l o u r of the sampler and by changes i n l i g h t i n t e n s i t y . The a u t h o r s c o n c l u d e d t h a t t h e s e r e s u l t s demonstrated; the e f f e c t s i o f b i o l o g i c a l escapement, and t h a t U n p u b l i s h e d m a n u s c r i p t , c o u r t e s y of R. Le B r a s s e u r , P a c i f i c Oceanographic group, Nanaimo, B. C., Canada. 17 f o r e u p h a u s i i d s b i o l o g i c a l escapement was mediated v i s u a l l y . Recent i n v e s t i g a t i o n s ( S m i t h , pers . comm.) have e s t a b l i s h e d t h a t one-metre c o n i c a l s a m p l e r s , which are a c c e p t i n g 95% of the water p r e s e n t e d to them, are preceded by a c c e l e r a t i o n f r o n t s extending'up t o one and o n e - h a l f " m e t r e s i n f r o n t of the mouth of the sampler. L a b o r a t o r y s t u d i e s have shown ( S m i t h , p e r s . comm.) t h a t • o f • c o p e p o d s t e s t e d , stage V Galanus  h e l g o l a n d i c u s are cap a b l e of speeds i n excess of 67 cm/sec f o r d i s t a n c e s up to 7 cm, and L a b i d o c e r a t r i s p i n o s a and L_. a c u t i f r o n s of speeds of 70 and 80 cm/sec r e s p e c t i v e l y f o r d i s -t a n c e s up to 15 cm. The l a r g e copepod E u c h i r e l l a g a l a t e a can swim at a r a t e of 100 cm/sec f o r up t o one and o n e - h a l f metres. The s t i m u l u s which evoked these responses was the i n j e c t i o n of 0.1 ml. of sea water at a v e l o c i t y of 7.5 cm/sec i n t o the sea water medium 5 cm d i s t a n t " from the a n i m a l . Smith has a l s o s a i d t h a t the a c c e l e r a t i o n f r o n t s p r e c e d i n g a p l a n k t o n sampler would p r o b a b l y ' b e ' g r e a t e r than the a c c e l e r a t i o n f r o n t s produced by t h i s r e l a t i v e l y s m a l l j e t of water. In a d d i t i o n t o the l i t e r a t u r e s u rveyed above, concerned w i t h b i o l o g i c a l escapement of z o o p l a n k t o n i c s p e c i e s , t h e r e e x i s t s a l a r g e body of l i t e r a t u r e d e a l i n g w i t h the e r r o r s i n t r o d u c e d i n t o the e s t i m a t e s of the s i z e of l a r v a l f i s h p o p u l a t i o n s by the e f f e c t s of, b i o l o g i c a l escapement ( S i l l i m a n , 1943; A h l s t r o m , 1954; B r i d g e r , 1957 ; C o l t o n , 1958 ; Aron , 1962; Dr. P. Smith, Bureau of Commercial F i s h e r i e s , La J o l l a , C a l i f . 18 I s a a c s , 1965 ; and Pearcy , 1965 ). In a l l of these r e p o r t s the au t h o r s conclude t h a t b i o l o g i c a l escapement i s a s e r i o u s prob-lem i n o b t a i n i n g a r e p r e s e n t a t i v e sample from p o p u l a t i o n s of l a r v a l f i s h . Thus, the evidence f o r the e x i s t e n c e of b i o l o g i c a l escapement i s s t r o n g . However, none of the I n v e s t i g a t i o n s r e p o r t e d i n the l i t e r a t u r e g i v e s any prop e r i n d i c a t i o n of the magnitude of the e r r o r s i n t r o d u c e d by b i o l o g i c a l escapement, o t h e r than the s u s p i c i o n t h a t these e r r o r s may be l a r g e . I t i s c l e a r , t h e r e f o r e , t h a t the p l a n k t o l o g i s t i s i n the d i f f i c u l t p o s i t i o n of knowing t h a t data d e r i v e d from c o l l e c t i o n s may be i n e r r o r , but of not knowing how l a r g e these e r r o r s may be. The p o s s i b i l i t y e x i s t s , a l s o , t h a t c o l l e c t i o n s made w i t h d i f f e r e n t samplers may not be s u b j e c t t o the same e r r o r s . These s e v e r a l c o n s i d e r a t i o n s , namely the e f f e c t s of b i o l o g i c a l escapement of the s i z e and s p e c i e s c o m p o s i t i o n of a sample, have l e d t o the development of a m a t h e m a t i c a l model which d e s c r i b e s b i o l o g i c a l ' e s c a p e m e n t i n such terms t h a t the model can be f i t t e d t o data d e r i v e d from c o l l e c t i o n s made i n the f i e l d t o g i v e an e s t i m a t e of the c a t c h i n g power of a p l a n k t sampler. Evidence i s p r e s e n t e d which i n d i c a t e s t h a t the model i s c a p able of g i v i n g a good e s t i m a t e of the c a t c h i n g power of a p l a n k t o n sampler p r o v i d e d t h a t c e r t a i n assumptions are v a l i d . 19 THE MODEL: B a r k e l e y (1964) has proposed a m a t h e m a t i c a l model ( F i g . 1) which w i l l y i e l d the minimum speed t h a t an a n i m a l must a t t a i n to c o m p l e t e l y escape from a p l a n k t o n sampler under s p e c i f i e d c o n d i t i o n s . These c o n d i t i o n s i n c l u d e the r a d i u s of the mouth of the sampler, the speed at which the sampler i s moving, and the d i s t a n c e a t - w h i c h the a n i m a l s can d e t e c t the sampler. The d e t e c t i o n d i s t a n c e would be d i f f i c u l t t o d e t e r -mine and i s unknown f o r any z o o p l a n k t o n i c organism. In a d d i -t i o n , B a r k e l e y ' s model, a l t h o u g h i t a n a l y z e s the problem of b i o l o g i c a l escapement i n g e n e r a l terms, namely the s i t u a t i o n where a l l the organisms escape from the s a m p l e r , i t i s i n c a p a b l e of d e a l i n g w i t h the s i t u a t i o n where a f r a c t i o n of a z o o p l a n k t o n i c p o p u l a t i o n escapes. In sum, h i s model i n d i c a t e s those s t e p s which must be taken t o m i n i m i s e the e f f e c t s of b i o l o g i c a l escapement, but i t cannot be f i t t e d t o data d e r i v e d from c o l l e c t i o n s made i n the f i e l d , w i t h any s o r t of p l a n k t o n sampler, t o g i v e i n f o r m a t i o n about the performance of the sampler. The model which f o l l o w s i s f o r m u l a t e d i n terms of the same f o u r q u a n t i t i e s c o n s i d e r e d by B a r k e l e y ' s model. However, the f o l l o w i n g model can b e " f i t t e d to f i e l d data to p r o v i d e an e s t i m a t e of the a b i l i t y of a p l a n k t o n sampler to c a p t u r e any z o o p l a n k t o n i c s p e c i e s . In t h i s model the planktom sampler i s r e g a r d e d as f i l t e r i n g some c o n s t a n t p r o p o r t i o n of the water p r e s e n t e d to i t over the range of speeds f o r which the model 2 0 i s t o a p p l y . I m p l i c i t i n t h i s assumption i s the f u r t h e r assumption t h a t the'model i s to a p p l y o n l y i n the absence of c l o g g i n g of the meshes' of the f i l t e r . The k i n e m a t i c b a s i s ' of the model i s shown' i n F i g . 3. The The r a d i u s ' o f ' t h e ' m o u t h of the sampler i s r Q . The speed of t o w i n g i s S^, The' d i s t a n c e at which the a n i m a l s , i_.e_. the ' p o p u l a t i o n of • any spe'c ieis or l i f e h i s t o r y stage - of any s p e c i e s , can d e t e c t the presence of the sampler by any means and respond t o i t i s shown as the p l a n e , x , p e r p e n d i c u l a r to the l o n g i t u d i n a l a x i s ' of the sampler. The d i s t a n c e t o the p l a n e , x, from"the mouth of the sampler i s - assumed t o remain c o n s t a n t as the" speed of t o w i n g i n c r e a s e s . - This ' i s r e a s o n a b l e i n view of the' f a c t t h a t ' t h e sampler f i l t e r s the same amount of water per u n i t • d i s t a n c e - over the range of speeds t o be"used. P o s s i b l y a - more r e a l i s t i c r e p r e s e n t a t i o n ' of the s u r f a c e of r e s p o n s e , x, is' shown by the dashed c u r v e . The b a s i s of t h i s curve i s the r e s u l t • o f a wind t u n n e l study of f l o w through p l a n k t o n samplers' c a r r i e d ' out at the SCOR - ICES-UNESCO symposium on•Zooplankton Sampling Methods h e l d ' i n A u s t r a l i a i n 1965 ( B a r y , p e r s . comm.), The study"showed'that the p r e s s u r e g r a d i e n t s ' p r e c e d i n g the mouth o f ' t h e " sampler a p p r o x i -mate t o t h i s ' form. - The" r e p r e s e n t a t i o n of the s u r f a c e of response shown'by t h e " b r o k e n curve' i s t o a p p l y o n l y when the anim a l s d e t e c t the sampler, by means of the a c c e l e r a t i o n f r o n t s p r e c e d i n g i t , • • Treatment• of- the" s u r f a c e of'response- as' a'plane i s not an i m p o r t a n t d e p a r t u r e from r e a l i t y because t h e r e w i l l be .seme 21 p l a n e , x, i n which i t w i l l appear t h a t a l l the animals have r e a c t e d . T h i s i s t r u e because the model d e a l s w i t h the r e a c t i o n s of a. p o p u l a t i o n • of ani m a l s p r e s e n t e d to the sa m p l e r , and not w i t h the r e a c t i o n s . o f a n y one a n i m a l . F o r the same reason the a n i m a l s ' speed of escape, S^, does not r e p r e s e n t the h i g h e s t speed t h a t any i n d i v i d u a l a n i m a l can a t t a i n . I n s t e a d r e p r e s e n t s the mean- of a l l the components of a l l the a n i m a l s ' speeds p e r p e n d i c u l a r t o the l o n g i t u d i n a l a x i s of the sampler. The w i d t h of the zone around the p e r i p h e r y of the mouth of the sampler from which animals can escape i s p"*", the r a d i u s of the area from which a n i m a l s cannot escape i s r"*" . I f i t is•assumed t h a t ' at any one time the i n d i v i d u a l s of a s p e c i e s a r e - randomly d i s t r i b u t e d a e r o s s the mouth of the sampler, a l t h o u g h not n e c e s s a r i l y throughout the water column, then the p r o p o r t i o n of animals caught can be expressed as the r a t i o of the area of the zone from which animals cannot escape to the area of the mouth of the' sampler. T h i s r a t i o m u l t i p l i e d by 100 can be r e f e r r e d t o as percentage c a t c h (p b e l o w ) . The w i d t h of the zone from which a n i m a l s can escape i s the pr o d u c t of' the' speed t h a t the, a n i m a l s can a t t a i n p e r -p e n d i c u l a r t o the l o n g i t u d i n a l a x i s of the" sampler, S^, and the time t h a t the ani m a l s have i n which to move b e f o r e the sampler o v e r t a k e s them, x/S^. T h i s w i d t h i s a f u n c t i o n of the speed of t o w i n g . The area from which the ani m a l s cannot escape, A , can be ex p r e s s e d as fT times the square of the d i f f e r e n c e between the r a d i u s of the mouth of the sampler and F i g u r e 3 ( f a c i n g ) The k i n e m a t i c b a s i s of the model. s 0 — s p e e d o f t o w i n g s e — m e a n s p e e d o f e s c a p e r Q — r a d i u s o f n e t x — m e a n d i s t a n c e a t w h i c h n e t c a n b e d e t e c t e d b r o k e n l i n e c u r v e — m o r e r e a l i s t i c r e p r e s e n t a t i o n o f x r 1 — r a d i u s o f z o n e f r o m w h i c h e s c a p e i s i m p o s s i b l e ( r 0 - p ) p — p e r i p h e r a l z o n e o f e s c a p e ( b e f o r e n e t c a n o v e r t a k e ) 23 the w i d t h of the zone from which animals can escape. A ^ r r c r - x s / s ) 2 1 1 o e o — ..Equation 1_ when d i v i d e d by the t o t a l a r ea of the mouth of the sampler, A^, and m u l t i p l i e d by 100 y i e l d s e q u a t i o n 2_ which e x p r e s s e d percentage c a t c h , P. P = ( rr ( r - x s e / s o ) 2 / / T r 2 } x 1 0 0 2 : o — E q u a t i o n 2 can be r e a r r a n g e d t o y i e l d : p = (1 - X S /R S ) 2 x 100 3 r e o o — which i s the working e q u a t i o n f o r percentage c a t c h . I f S q i s the o n l y v a r i a b l e i n t h i s e q u a t i o n , 3_, i t i s p o s s i b l e t o s o l v e f o r percentage c a t c h when two or more samples t a k e n at d i f f e r e n t speeds are a v a i l a b l e . S u b s t i t u t i n g a q u a n t i t y , Q, f o r X S e / r S i n e q u a t i o n 3 the b a s i c e q u a t i o n becomes: p = (1 - Q ) 2 4 I f the number of anim a l s a c t u a l l y caught i s r e p r e s e n t e d by B then i t i s t r u e t h a t t h e r e e x i s t s some f a c t o r , z, which i s e q u a l t o P/B. The f a c t o r , z, can be o b t a i n e d p r o v i d e d t h a t S i s the o n l y v a r i a b l e . I f t h i s i s t r u e , then: o J ( z B ) 1 / 2 = 1 - Q = P 5_ from which i t f o l l o w s t h a t : 1 - ( z B ) 1 / 2 = Q 6 24 B e a r i n g i n mind s i n c e Q = xS / r S , then: ° e o o S = x S / r 7 0 e o — which i s an i d e n t i t y . I f i s the o n l y v a r i a b l e i n e q u a t i o n 1_ then the q u a n t i t y QS^  i s c o n s t a n t . T h e r e f o r e , from e q u a t i o n 6_ 1/2 the e x p r e s s i o n S (1 - (zB) ) i s a l s o c o n s t a n t and when two o or more v a l u e s of S q and B are a v a i l a b l e the r e s u l t i n g e q u a t i o n of the form: S n - S .(zB. ) 1 / 2 = S _ - S 0 ( z B . ) 1 / 2 8 01 o l 1 o2 o2 2 — can be s o l v e d f o r z. Once z has been o b t a i n e d P i s c a l c u l a t e d from e q u a t i o n 9_. P = zB 9_ When v a l u e s of P have been c a l c u l a t e d , e q u a t i o n 3_ can be expanded and s o l v e d f o r X S g ( i _ < e _ ' s e e eqn, 10) (X S /R S ) 2 - 2(X S / R S ) + l - p = o 10 e o o e o o The v a l u e s of X S which are c a l c u l a t e d from e q u a t i o n 10 are s u b s t i t u t e d back i n t o e q u a t i o n 3_, from which a p l o t of percentage c a t c h a g a i n s t speed of h a u l i n g i s g e n e r a t e d . T h i s method-of f i t t i n g the model t o f i e l d d a ta i s r e c u r s i v e . The o n l y a b s o l u t e check on the v a l i d i t y of the assumptions made i n the f o r m u l a t i o n of the model i s i n t e r n a l . T h i s i n t e r n a l check i s g i v e n by the v a l u e s of the p r o p o r -t i o n a l i t y c o n s t a n t , z. I f the assumptions made i n the formu-l a t i o n of the model are not v a l i d , z can be expected to vary i n some s y s t e m a t i c manner. I f the assumptions are v a l i d z w i l l be c o n s t a n t . 25 MATERIALS AND METHODS: The f i e l d t r i a l s undertaken i n the course of t h i s study were d e s i g n e d t o y i e l d two s o r t s of i n f o r m a t i o n . The pri m a r y t a s k was to asses s the a b i l i t y of the m a t h e m a t i c a l model to d e s c r i b e the p r o c e s s e s of b i o l o g i c a l escapement. The second-ary t a s k was t o d e t e r m i n e , by means of the model, the magnitude of the e r r o r s a t t r i b u t a b l e t o b i o l o g i c a l escapement which are i n t r o d u c e d i n t o e s t i m a t e s of p o p u l a t i o n s i z e and s p e c i e s c o m p o s i t i o n i n samples c o l l e c t e d by v a r i o u s p l a n k t o n s a m p l i n g d e v i c e s . Every e f f o r t was made i n the d e s i g n of the f i e l d t r i a l s t o ensure t h a t the o n l y v a r i a b l e f a c t o r was the speed at which each sampler was to be h a u l e d through the water. I t was e s s e n t i a l t h a t the speed of h a u l i n g be a c c u r a t e l y known, t h a t the volume of water f i l t e r e d d i d not change from h a u l t o h a u l , and t h a t the same community of z o o p l a n k t o n was sampled by each h a u l . These r e q u i r e m e n t s are b e s t met by v e r t i c a l h a u l i n g of the sampler i n a p a r t i c u l a r body of water at one p o s i t i o n or l o c a t i o n . The d i s t a n c e t h a t the sampler moves through the water as w e l l as the time t a k e n can be a c c u r a t e l y measured. E r r o r s i n t r o d u c e d by the f a i l u r e t o sample the same z o o p l a n k t o n i c community w i t h each h a u l because of the tendency of z o o p l a n k t o n t o form l a y e r l i k e or l e n s l i k e a g g r e g a t i o n s ( B a r y , 1966) and t o perform d i e l m i g r a t i o n s are reduced by v e r t i c a l h a u l i n g . However such p r e c a u t i o n s w i l l be of no a v a i l i f i t i s not p o s s i b l e t o sample from the same p a r c e l of water i n the course 26 of f i e l d o p e r a t i o n s and to keep the w i r e from s t r a y i n g from the v e r t i c a l . An i d e a l l o c a t i o n f o r f i e l d t r i a l s would be a deep, i s o l a t e d b a s i n i n a p r o t e c t e d l o c a t i o n i n which water movements, and t h e r e f o r e movements• of p l a n k t o n i c organisms , would be m i n i m a l . In B. C. c o a s t a l waters an a r e a w h i c h , on p r e s e n t knowledge, i s most l i k e l y t o f u l f i l the a b o v e - r e q u i r e m e n t s i s t h a t p o r t i o n of J e r v i s • I n l e t , B r i t i s h ' C olumbia, Canada, l y i n g o ' o ' between 49 45 N. l a t i t u d e and 49 50 N.' l a t i t u d e and between o ' o • 124 00 W. l o n g i t u d e ' a n d 124 06 W, l o n g i t u d e ( F i g . 4 ) . In t h i s a r ea i s a deep b a s i n w i t h a maximum depth of 732 m (400fm). F i e l d P r o c e d u r e : D u r i n g the t r i a l s every e f f o r t was - made t o sample from the same p a r c e l of water'each day. The s h i p was brought on s t a t i o n each morning and a l l o w e d t o d r i f t w i t h ' t h e t i d e . I f the s h i p was blown b y wind more than'. one - q u a r t er m i l e from the s t a t i o n p o s i t i o n i t " w a s moved back.on s t a t i o n . P o s i t i o n s were t a k e n every hour. I t was seldom n e c e s s a r y t o move the s h i p more than two or t h r e e times each day.- However, s t r o n g winds were e x p e r i e n c e d o n l y once d u r i n g the course of the, f i e l d t r i a l s and, f o r the most p a r t , the weather•was calm. In these c o n d i t i o n s the s h i p was'allowed t o d r i f t w i t h • t h e t i d a l c u r r e n t s , Movement back and f o r t h a c r o s s the- d e s i g n a t e d s t a t i o n p o s i t i o n r e s u l t e d , t o a t o t a l d i s t a n c e : o f ' about o n e - h a l f m i l e . I t i s b e l i e v e d t h a t b y : t h i s ' p r o c e d u r e ' t h e c o l l e c t i o n s of organisms were l i k e l y t o have been from the same p a r c e l of F i g u r e 4 ( f a c i n g ) The l o c a t i o n of the 1965 and J a n u a r y , 1966. S i t e c a t e d by an X. f i e l d t r i a l s of August, of s a m p l i n g i s i n d i -27 28 water d u r i n g any one day. I t c o u l d o n l y be assumed, because the t i d a l c u r r e n t s were demonstrably weak d u r i n g any one day, t h a t from day t o day i n - t h e - c o u r s e of the f i e l d t r i a l s the water body d i d not change a p p r e c i a b l y . The- subsequent a n a l y s i s of the r e s u l t s suggest t h a t t h i s assumption was r e a s o n a b l e . The d e s i g n - o f the f i e l d t r i a l s • w a s • t h e same f o r each sampler. The sampler- was h a u l e d - v e r t i c a l l y - from 4-00 or 500 m, at one of t h r e e speeds , namely, 0.30 m/sec(0.50• m/sec f o r C a t c h e r ) , 1.0 m/sec, or 2.0m/sec. E i g h t r e p l i c a t e h a u l s were made at each speed. I t was p o s s i b l e - t o complete o n l y one h a l f of each s e r i e s w i t h a n y one - s a m p l e r i n one day% T h e r e f o r e each s e r i e s i s a composite of tows made on two r days . • The o r d e r i n which the speeds of h a u l i n g - o c c u r r e d was-randomized each day t o a v o i d s y s t e m a t i c e r r o r s . - The depth t o - w h i c h the sampler descended was determined b y p a y i n g out the w i r e over a m e t e r i n g sheave and c h e c k i n g - t h a t - t h e meter r e t u r n e d to- z e r o when the sampler had been r e t r i e v e d . The t o t a l time r e q u i r e d f o r each h a u l was r e c o r d e d w i t h a sto p watch. Any haul- f o r which the a s s i g n e d speed was• not reached w i t h i n the-. f i r s t • 5 0 m, or which stopped b e f o r e r e a c h i n g - t h e . s u r f a c e , was r e p e a t e d . When the sampler reached the s u r f a c e i t s - f i I t e r ( n e t ) was c a r e f u l l y washed down'using a h i g h - p r e s s u r e j e t of seawater from a hose. The sample"was'preserved- i n 5%, n e u t r a l i z e d forma-l i n . The number-of r e v o l u t i o n s made by t h e - i m p e l l e r o f the f l o w meter was r e c o r d e d . Then -the p r o c e s s was'repeated. The f i r s t s e t of f i e l d t r i a l s was c a r r i e d out i n August, 1965. A second s e r i e s was undertaken i n J a n u a r y , 1966, 29 In which the same procedures were f o l l o w e d except t h a t o n l y t h r e e r e p l i c a t e h a u l s were made at each speed. The P l a n k t o n Samplers: F i v e p l a n k t o n samplers were used d u r i n g the f i e l d t r i a l s . These were s e l e c t e d as b e i n g r e p r e s e n t a t i v e - o f ' t h r e e w i d e l y used c l a s s e s of p l a n k t o n " s a m p l e r s , namely,"the c o n i c a l s a m p ler, the c o n i c a l sampler m o d i f i e d by the a d d i t i o n of an i m p e r v i o u s c y l i n d r i c a l p o r t i o n " a n t e r i o r to the f i l t e r , and the encased hi g h - s p e e d sampler. The s i m p l e s t of these" i s the o r i g i n a l d e s i g n of c o n i c a l sampler ( F i g . 5a) w h i c h c o n s i s t s of a c i r c u l a r r i n g s u p p o r t i n g a c o n i c a l f i l t e r which t e r m i n a t e s i n a bucket i n which the sample c o l l e c t s . The c o n i c a l sampler used i n t h i s s tudy has a mouth di a m e t e r of 100 cm, and i s towed by t h r e e b r i d l e s extend-i n g 80 cm i n f r o n t of the mouth. The f i l t e r i s 305 cm i n l e n g t h . The mesh a p e r t u r e " a p p r o x i m a t e s to 0.7 mm square. D u r i n g the J a n u a r y , 1966, t r i a l s t h i s c o n i c a l sampler was m o d i f i e d by the a d d i t i o n of a c y l i n d r i c a l l e a d weight 15 cm i n d i a m e t e r and 30 cm i n l e n g t h , which was suspended at the apex of the b r i d l e s , 80 cm i n f r o n t of the mouth - of the sampler. In a l l tows w i t h the one-metre c o n i c a l sampler a f l o w meter was f i t t e d i n the c e n t r e of the mouth a p e r t u r e . The 70-cm N.I.O. sampler ( C u r r i e and F o x t o n , 1957) ( F i g . 6a) i s t y p i c a l of a l a r g e c l a s s of p l a n k t o n s a m p l e r s . 30 These samplers are a l l b a s i c a l l y the s i m p l e c o n i c a l sampler m o d i f i e d by the a d d i t i o n of an i m p e r v i o u s , c y l i n d r i c a l p o r t i o n , ahead of the f i l t e r . They can be c l o s e d by . . " s t r a n g l i n g " t h i s c y l i n d r i c a l p o r t i o n . T h i s d e s i g n o r i g i n a t e d w i t h the Nansen sampler (Nansen, 1915). I t was m o d i f i e d i n the d i s c o v e r y samplers (Kemp and Hardy, 1929), i n the Norpac sampler (Marumo, 1958) and a g a i n i n the I n d i a n Ocean Standard sampler ( C u r r i e , 19 63- ) . The N.I.O. sampler used i n the f i e l d t r i a l s has a mouth diameter of 70 cm.. A canvas c y l i n d e r 122 cm i n l e n g t h i s .attached to a sheet m e t a l drum 3 0 . 5 c m i n l e n g t h w hich, i n t u r n , precedes and i s a t t a c h e d to the f i l t e r . The f i l t e r has an a n t e r i o r c y l i n d r i c a l p o r t i o n 100 cm i n l e n g t h f o l l o w e d by a c o n i c a l p o r t i o n 150 cm i n l e n g t h , which t e r m i n a t e s i n a c o l l e c t s i n g b u c k e t . I n . t h e p r e s e n t ' s t u d y a f l o w meter was mounted w i t h i n the mouth of the canvas c y l i n d e r . The a p e r t u r e of the meshes a p p r o x i m a t e s " t o 200 m i c r a square. The f i l t e r i n the sampler, used i n the f i e l d t r i a l s was new. During the J a n u a r y , 1966, t r i a l s t h i s sampler was used w i t h o u t the canvas c y l i n d e r ( F i g . 6b). The r e s u l t s o b t a i n e d w i t h the s t a n d a r d sampler i n i t s o r i g i n a l form i n J a n u a r y , 1966, were the same as those o b t a i n e d i n August, 1965, and'are not r e p o r t e d . The Catc'her (Bary et a l . , 19 58 ) i s t y p i c a l of a f a i r l y new c l a s s , the encased, h i g h - s p e e d p l a n k t o n s a m p l e r s . Other samplers of t h i s type i n c l u d e the G u l f 1 ( A r n o l d , 1959), the G u l f 111 ( G h e r i n g e r , 19520, the G u l f V ( A r n o l d , .1959), and the J e t Net ( C l a r k e , 1964). The Hardy P l a n k t o n Recorder 31 (Hardy, 1936) i s towed at h i g h speeds, but i s i n a l l o t h e r r e s p e c t s d i s s i m i l a r t o the above-mentioned s a m p l e r s . Remarks made below p r o b a b l y do not a p p l y to the Hardy P l a n k t o n R e c o r d e r . In the c o n s t r u c t i o n of a l l of these samplers an o u t e r , r i g i d c a s i n g e n c l o s e s the f i l t e r i n g s u r f a c e , which i s u s u a l l y c o n i c a l . A c o n s i s t e n t f e a t u r e of these samplers i s t h a t the mouth opening i s l e s s i n diameter than the c a s i n g . A r e s u l t of t h i s f e a t u r e i s to reduce the speed of f l o w of the water a f t e r i t has e n t e r e d the mouth and, as a consequence, l e s s e n s the damage done to the z o o p l a n k t o n when they c o n t a c t the f i l t e r . Because of the reduced diameter of the mouth, encased samplers u s u a l l y have a l a r g e r t o t a l a r ea of mesh a p e r t u r e than c o n v e n t i o n a l c o n i c a l s a m p l e r s . Most, but not a l l , of the encased samplers are p r o v i d e d w i t h f l o w meters i n the r e a r p a r t f o r m e t e r i n g the f l o w a f t e r i t has passed through the f i l t e r . F i n a l l y , the c o n s t r u c t i o n of the high-s p e e d samplers i s much more r o b u s t than i s u s u a l l y i n uncased s a m p l e r s . However, the p r i m a r y r a i s o n d ' e t r e of the high-speed samplers i s t h a t i t has l o n g been thought t h a t , i f the speed at which the sampler i s towed i s i n c r e a s e d , z o o p l a n k t o n i c organisms of a wider range of s i z e s and swimming a b i l i t y w i l l have l e s s chance to a v o i d the sampler. Thus the sample c o l l e c t e d i s b e l i e v e d t o be more r e p r e s e n t a t i v e of the com-munity of z o o p l a n k t o n p r e s e n t . The C a t c h e r ( F i g . 7a) c o n s i s t s of a c y l i n d r i c a l f i b r e -g l a s s h o u s i n g 215 cm (84 i n . ) i n l e n g t h and 30 cm (12 i n . ) i n di a m e t e r . T h i s h o u s i n g can be d i s a s s e m b l e d i n t o two main 32 p a r t s . The f o r w a r d p o r t i o n , or 'body', c o n t a i n s the f i l t e r ( F i g . 7b). The a f t e r p o r t i o n c o n t a i n s the f l o w meter and bears s t a b i l i z i n g f i n s a t t a c h e d a t - r i g h t angles' t o i t s o u t e r s u r f a c e . The diameter of the mouth opening i s 22.5 cm (9 i n . ) . The model of the C a t c h e r used i n t h i s study- d i f f e r s from t h a t d e s c r i b e d by Bary e_t a_l. ( 1958 ) i n t h a t the o p e n i n g - c l o s i n g mechanism i s i n the form of a metal d i s c which i s r o t a t e d to open and c l o s e the'mouth" opening , and t h a t the t a i l of the sampler i s of e q u a l diameter t o the body, r a t h e r than reduced to 22.5 cm (9 i n . ) , L a b o r a t o r y Methods: In the l a b o r a t o r y the organisms i n the samples were s o r t e d i n t o f o u r ' g r o u p s . Each of these groups c o n s i s t s of organisms of s i m i l a r s i z e which were p r e s e n t i n numbers l a r g e enough f o r an a c c u r a t e ' a n a l y s i s . They are r e p r e s e n t a t i v e of the medium- to l a r g e - s i z e d - z o o p l a n k t o n . The - f i r s t group con-s i s t e d of copepods of the genus Ca l a n u s . T h i s group was the most numerous; over-90% of the specimens were stage V C_. plumchrus with- a few specimens o f a d u l t Calanus spp , . These specimens range from 4 to 5 mm i n - l e n g t h . The second group was composed of specimens of the copepod Eucalanus b u n g i i v a r . b u n g i i most of which were stage I I I or stage IV cope-p o d i t e s r a n g i n g from 3 to 5 mm i n l e n g t h . The t h i r d group was composed- of specimens of the copepod' Euchaeta j a p o n i c a , most of which-were a d u l t , r a n g i n g from' 5 to- 6 mm i n l e n g t h . T h i s s p e c i e s i s much more r o b u s t , t h a n C.. plumchrus or 33 z~ • Figure 5a. The 1-metre conical sampler rigged as it was used during the field trials of August, 1965. Figure 5b. The 1-metre conical sampler modified by the attachment of a weight to its bridles. The sampler was used as illustrated in the field trials of January, 1966. 34 F i g u r e 6a. The 70 -cm N . I . O . s a m -p le r as it was used i n the f ie ld t r i a l s of August , 1965. — F i g u r e 6b. The 7 0 - c m N.I . O . s a m -p le r modif ied by the r e m o v a l of the canvas c y l i n d e r . The s a m -p l e r was used as i l l u s t r a t ed i n the f ie ld t r i a l s of January, 1966. F i g u r e 7a. The Catcher as it was r i g g e d during the t r i a l s of August, 1965 F i g u r e 7b. The f i l t e r u sed i n the Catcher 36 E.. b u n g i i . The l a s t group i n c l u d e d a d o l e s c e n t and a d u l t specimens of the Euphausacea. Most specimens were a d u l t Euphaus i a p a c i f i c a , r a n g i n g from 10 to 20 mm i n l e n g t h . Every specimen of Euchaeta j a p o n i c a and every e u p h a u s i i d c o n t a i n e d i n the' sample"was' counted, but the numbers of Calanus spp. and E u c a l a n u s " b u n g i i were very l a r g e and i t was n e c e s s a r y t o sub-sample'and e s t i m a t e the' t o t a l s f o r t h e s e . The subsampling t e c h n i q u e was t h a t of B r o d s k i i and Baskakov (1951) (see Appendix 1 ) . In t h i s method the sample i s spread e v e n l y over the bottom of a l a r g e g l a s s d i s h and the t o t a l number of specimens l y i n g over a known f r a c t i o n of the t o t a l a r e a of the bottom- of the d i s h i s counted. The f r a c t i o n of the bottom of the d i s h i s v a r i e d • i n o r d e r t h a t the number of specimens l y i n g i n t h i s - a r e a i s about 100. To t h i s count i s added o n e - h a l f of the number of specimens i n any way b i s e c t e d at the b o u n d a r i e s of the a r e a . T h i s sum i s m u l t i p l i e d by the r e c i p r o c a l of the f r a c t i o n of the t o t a l a r ea to e s t i m a t e the t o t a l number of specimens c o n t a i n e d i n the d i s h . In p r a c t i c e the specimens i n at l e a s t t h r e e d i f f e r e n t areas were counted from each sample. The mean count was used to c a l c u l a t e the t o t a l number of specimens. I f these t h r e e counts d i d not agree w i t h i n 10%, t h r e e more counts were made and the r e s u l t s of a l l s i x counts meaned. In the major-i t y of samples t h r e e counts were s u f f i c i e n t . The specimens of Eucalanus bungi i were too s m a l l t o be r e t a i n e d q u a n t i t a t i v e l y by the one-metre c o n i c a l sampler. T h e r e f o r e o n l y Calanus spp., Euchaeta j a p o n i c a , and 37 e u p h a u s i i d s were counted i n the c o l l e c t i o n s made w i t h t h i s sampler. M a t h e m a t i c a l P r o c e d u r e : The: data o b t a i n e d from the c o l l e c t i o n s made d u r i n g the f i e l d t r i a l s were s u b j e c t e d t o one-way a n a l y s i s of v a r i a n c e ( S t e e l e and T o r r i e , 1960) to determine whether d i f f e r e n c e s noted between catches•made - at d i f f e r e n t speeds were t o be c o n s i d e r e d as r e a l . ' ' " The number of specimens c o l l e c t e d i n each tow was con-v e r t e d t o the percentage of the p r e d i c t e d p o p u l a t i o n of each s p e c i e s which i t r e p r e s e n t e d by the procedure o u t l i n e d i n the s e c t i o n on the model'(pp. 15 to 2 4 ) . E q u a t i o n 10 was s o l v e d f o r each of the 24 p a i r s " o f v a l u e s of perc e n t a g e c a t c h and speed of h a u l i n g t o y i e l d 24 v a l u e s of X S g. A l l v a l u e s o f X S g f o r each c o n f i g u r a t i o n of sampler and" each" s p e c i e s were me'aned and a f i t t e d curve of percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g was" generated from e q u a t i o n 3_. F i n a l l y , an estimate- of the p o p u l a t i o n of. each s p e c i e s p r e s e n t i n the column of- water sampled b y each sampler was o b t a i n e d . T h i s was done by m u l t i p l y i n g the -number of i n d i v i d u a l s of t h a t spe-c i e s c a p t u r e d i n each sampler by t h e • r e c i p r o c a l of the p e r c e n t -age of the t o t a l w h i c h ' t h i s • catch; was c a l c u l a t e d t o r e p r e s e n t . A mean e s t i m a t e d p o p u l a t i o n " s i z e f o r each" s p e c i e s was computed from the data obtained" w i t h each sampler. A program was w r i t t e n i n the Fo r t r a n - IV language f o r an I.B.M. 7040 computer which.performed- a l l the above c a l c u l a t i o n s . 38 RESULTS: Summaries of data d e r i v e d from the i n v e s t i g a t i o n s i n the f i e l d are p r e s e n t e d i n Tables 2 to 7. The raw data are r e p o r t e d i n terms of mean speeds o f , h a u l i n g ("speed c l a s s e s " ) , and mean ca t c h e s of z o o p l a n k t o n , by s p e c i e s or group, f o r each speed c l a s s . The v a l u e s r e p o r t e d f o r the f i e l d t r i a l s of August, 1965, are means of e i g h t h a u l s at each speed; the v a l u e s f o r the f i e l d t r i a l s of J a n u a r y , 1966 v a l u e s are means of t h r e e h a u l s at each speed. The data have been s u b j e c t e d to one-way a n a l y s i s of v a r i a n c e ( S t e e l and T o r r i e , 1960) w i t h speed c l a s s e s c o n s i d e r e d as t r e a t m e n t s . The c a l c u l a t e d v a l u e s of F, _i.e_. t r e a t m e n t mean s q u a r e / e r r o r mean squ a r e , i s r e p o r t e d t o g e t h e r w i t h the expected v a l u e of F f o r s i g n i f i c a n c e at the 95% l e v e l . A l t h o u g h the r e s u l t s of a n a l y s i s of v a r i a n c e i n d i c a t e t h a t i n some i n s t a n c e s the d i f f e r e n c e s between mean" c a t c h e s at d i f f e r e n t speeds are s i g n i f i c a n t and t h a t i n o t h e r i n s t a n c e s the d i f f e r -ences between mean cat c h e s at d i f f e r e n t speeds are not s i g n i f i c a n t , the mean c a t c h i n c r e a s e s w i t h i n c r e a s e d speed of towing f o r every sampler, except the 70-cm N.I.O. sampler i n both c o n f i g u r a t i o n s . F i g u r e 8a shows the r e s u l t s o b t a i n e d by a p p l y i n g the model to data from c o l l e c t i o n s made w i t h the one-metre c o n i c a l sampler. The smooth curves of percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g were ge n e r a t e d by s u b s t i t u t i n g s u c c e s s i v e l y l a r g e r v a l u e s of S^ i n e q u a t i o n 2_ (p. 23). No p o i n t s r e p r e s e n t -i n g p e rcentage c a t c h as c a l c u l a t e d from f i e l d data appear on 39 t h i s p l o t . The degree of agreement between v a l u e s of per-centage c a t c h g i v e n by the f i t t e d curve f o r the c o r r e s p o n d i n g speed of h a u l i n g i s shown i n F i g . 8b. The two g e n e r a l t r e n d s shown by t h e s e - p l o t s ' are t h a t the l a r g e r a n i m a l s ( e u p h a u s i i d s ) are b e s t a b l e to a v o i d the sampler, and.that the s e l e c t i v i t y of the sampler i s much' reduced at the h i g h e r speeds of h a u l i n g . The two c o n s t a n t s , p e c u l i a r t o each s p e c i e s appear i n the t a b l e of' c o n s t a n t s ' a s s o c i a t e d w i t h F i g . 8b. The constant,. X S g, r e q u i r e d to generate" the f i t t e d c u r v e s , i s a measure of the a b i l i t y of a s p e c i e s ' t o escape from t h e ' s a m p l e r . The v a l u e of X S g i s independent of the s i z e of the p o p u l a t i o n of a s p e c i e s sampled by a sampler. T h i s i s not. t r u e of the v a l u e s of z, the p r o p o r t i o n a l i t y c o n s t a n t . Values of z are g i v e n because of the check on the v a l i d i t y of the model which they a f f o r d . The degree of v a r i a t i o n i n the v a l u e s of z i s i n d i c a t e d by the s i z e o f the 95% c o n f i d e n c e l i m i t s upon the mean v a l u e of z. These c o n f i d e n c e l i m i t s are shown both as a b s o l u t e v a l u e s and as-p e r c e n t a g e s of the mean values- of z. I t i s apparent t h a t the c o n f i d e n c e l i m i t s w h i l e q u i t e small,, i n c r e a s e i n s i z e as the number of specimens of a s p e c i e s caught'per h a u l d e c r e a s e s . F i g u r e 9a shows t h e ' r e s u l t s o b t a i n e d by a p p l i c a t i o n of the model to data from f i e l d c o l l e c t i o n s made w i t h the one-metre c o n i c a l sampler i n which the f l o w o f water i n t o the mouth was d i s t u r b e d by t h e ' a d d i t i o n of a body ( w e i g h t ) p r e c e d i n g the mouth ( F i g . 5b). The p r o d u c t s X S g f o r . e a c h group are much, l a r g e r than t h o s e - o b t a i n e d w i t h the u n m o d i f i e d sampler ( F i g . : 8b). These d i f f e r e n c e s i n d i c a t e that; an obvious e f f e c t 40 r e s u l t s from the presence of the body p r e c e d i n g the mouth of the sampler, i.e_. the presence of the body a l l o w s the animals to d e t e c t the sampler at a g r e a t e r d i s t a n c e than when i t i s not p r e s e n t . I t i s c l e a r ( F i g . 9b) t h a t one or more of the assumptions made i n the f o r m u l a t i o n of the model does not h o l d f o r e u p h a u s i i d s . Two m a n i f e s t a t i o n s of t h i s are t h a t not o n l y i s the c o n f i d e n c e i n t e r v a l about the mean v a l u e of z l a r g e , but t h a t the f i t of the p o i n t s r e p r e s e n t i n g f i e l d data to the f i t t e d curve i s poor . The r e s u l t s o b t a i n e d w i t h the 70-cm N.I.O. sampler-( F i g . 6a) are shown i n F i g . 10. There i s l i t t l e doubt t h a t the assumptions made i n the f o r m u l a t i o n of the model are not v a l i d f o r t h i s sampler. T h e r e f o r e no c a l c u l a t i o n s have been per-formed. Flow meter counts show a s l i g h t decrease i n the amount of water p a s s i n g through the s a m pler, per u n i t d i s t a n c e towed, w i t h i n c r e a s i n g speed. T h i s decrease i n the amount of water f i l t e r e d per h a u l would not appear g r e a t enough to account f o r the r e d u c t i o n ' w h i c h o c c u r s i n the c a t c h . A p o s s i b l e a l t e r n a t i v e e x p l a n a t i o n i s t h a t f o r some reason the d i s t a n c e at which zoo-p l a n k t o n i c organisms can d e t e c t the sampler i n c r e a s e s as the speed of h a u l i n g i n c r e a s e s . -The r e s u l t s , shown"in F i g u r e 11a were o b t a i n e d w i t h the. 70-cm N.I.O sampler, m o d i f i e d by the removal of the canvas c o l l a r ( F i g . 6b). The most i m p o r t a n t r e s u l t i s the apparent r e v e r s a l of the t r e n d toward decreased c a t c h at h i g h e r speeds of h a u l i n g t h a t o c c u r r e d when the c o l l a r was p r e s e n t ( F i g . 1 0 ) . 41 The curves are s i m i l a r t o those o b t a i n e d w i t h the one-metre c o n i c a l sampler ( F i g . 8a). F i g u r e 12a shows the r e s u l t s o b t a i n e d by a p p l i c a t i o n of the model to f i e l d data c o l l e c t e d with, the C a t c h e r . I t s h o u l d be noted t h a t the curv e s of percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r Calanus spp. and Eucalanus b u n g i i b u n g i i are superimposed. There i s c o n s i d e r a b l e s c a t t e r i n those p o i n t s r e p r e s e n t i n g p ercentage c a t c h c a l c u l a t e d from the f i e l d d a t a ( F i g . 12b). This s c a t t e r has a c o n s i s t e n t p a t t e r n . The p o i n t s r e p r e s e n t i n g the h i g h - and low-speed h a u l s l i e above the l i n e of p e r f e c t f i t , w h i l e the p o i n t s r e p r e s e n t i n g the h a u l s made at i n t e r m e d i a t e speeds l i e below the l i n e of p e r f e c t f i t . F i g u r e 13 shows the r e s u l t s o b t a i n e d by a p p l i c a t i o n of the model to u n p u b l i s h e d data c o l l e c t e d by the P a c i f i c Oceano-g r a p h i c Group, Nanaimo, B. C. The data were c o l l e c t e d u s i n g two s i m i l a r p l a n k t o n s a m p l e r s . One of the p l a n k t o n samplers was w h i t e ; the o t h e r was dark green.. C o l l e c t i o n s were made w i t h the w h i t e sampler under c o n d i t i o n s of both d a y l i g h t and dark-ness. The r e s u l t s r e p o r t e d h e r e i n are f o r a d u l t e u p h a u s i i d s . They seem to i n d i c a t e t h a t the v i s i b i l i t y of the sampler i s an im p o r t a n t f a c t o r i n d e t e r m i n i n g i t s c a t c h i n g power w i t h r e s p e c t to euphaus i i d s . Group, "Data c o u r t e s y R. L e B r a s s e u r , P a c i f i c Nanaimo, B r i t i s h C olumbia, Canada. Oceanographic 42 ~\ r i 1 1 1 r X o < o « Co/anus spp. X Euchaeta /aponica A Euphausiids 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec 8a 120 43 HO 100 -* 90 -o 80 -i-O 70 r Q 60 UJ < 50 U 3 4 0 i-< 30 o 20 10 \-0 J I L 10 20 30 40 50 60 70 80 90 100 110 120 CATCH (%) FROM FITTED CURVE 8 b Figure 8a (facing) Percentage catch plotted against speed of hauling for the one-metre conical sampler. Figure 8b (above) Goodness-of-fit diagram for the results obtained with the one-metre conical sampler. Key is the same as F i g . 8a. Table of Constants Species (group) X S z 95% confidence l imits Calanus spp. 49.66 0.00011 + .000000017 (0. 15%) Euchaeta japonica 188.76 0.011 + .000016 (1.4%) euphausiids 361.48 0.25 + .000016 (0.66%) 44 45 O H < O Q LU I-< _l O _1 < o 0 10 20 30 40 50 60 70 80 90 100110 120 CATCH (%) FROM FITTED CURVE 9b Figure 9a (facing) Percentage catch plotted against speed of hauling for the modified one-metre conical sampler. Figure 9b (above) Goodness-of-fit diagram for the results obtained with the modified one-metre conical sampler. Key is the same as F i g . 8a. Species (group) Calanus spp. Euchaeta japonica euphausiids Table of Constant s X S e 290.33 511.164 1585. 89 z 95% confidence l imi t s 0.000057 +.000000043 (.0.76%) 0.0051 +.000035 (6.9%) 0.0046 + .0018 (38.8%) ° Calanus spp. X Euchaeta japonica A Euphausiids O £uca/anus bungii bungii -h Chaetognaths _L _L _L 1 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec F i g u r e 10 ( f a c i n g ) R e s u l t s ' o b t a i n e d w i t h the N.I.O. 70-cm sampler. Percentage c a t c h i s p l o t t e d a g a i n s t speed of h a u l i n g . P ercentage c a t c h has been c a l -c u l a t e d o n 1 t h e has i s of the c a t c h at 30 cm/sec as 100%. i 47 T r i 1 r 1 r 100 90 80 70 60 50 40 30 20 10 - A ° Calanus spp. X Euchaeto /aponica A Euphausiids O Eucalanus hung/7 bungii _L _L ± 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec 11 a 48 120 x o I-< o o LU I-< -J ZD O _J < 0 10 2 0 30 40 50 60 70 8 0 90 100 110 120 CATCH (%) FROM FITTED CURVE Mb Figure 11a (facing) Percentage catch plotted against speed of hauling for the modified 70-cm N.I.O. sampler. Figure l i b (above) Goodness-of-fit diagram for the results obtained with the modified 70-cm N.I.O. sampler. Species (group) Calanus spp. Eucalanus b. bungii  Euchaeta japonica euphausiids Table of Constants XS. z e 44.34 0.00019 95.79 0.00051 8.7234 0.017 461.35 0.12 95% confidence limits + .00000012 (0. 62%) + .00000069 (0. 13%) + .0000025 (0. 14%) + .028 (23%) 49 1 r i u < 100 90 8 0 70 6 0 50 40 30 20 I 0 0 o Calanus spp. X Euchaeta japonica A Euphausiids O Eucalanus bungii bungii _i_ 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec 12a 50 0 10 20 30 40 50 60 70 80 90 100 110 120 CATCH (%) FROM FITTED CURVE 1 2 b Figure 12a (facing) Percentage catch plotted against speed of hauling for the Catcher. Figure 12b (above) Goodness of fit diagram for the results obtained with the Catcher. Key is the same as F i g . 12a. Table of Constants Species (group) X S z 95% confidence l imi t s Calanus spp. 155.94 0.0014 + .000012 (0.9%) Eucalanus b . bungii 157.612 0.0054 + .000042 (7.7%) Euchaeta Japonica 95. 716 0. 13 + .00094 (0.68%) Euphausiids 358.17 0.98 + .17 (17%) 51 100 h x o I-< 90 80 70 60 50 40 30 20 10 0 o WHITE X DARK O WHITE - daylight - nig lit 20 40 60 80 100 120 140 160 180 200 220 SPEED OF HAULING cm/sec 3 a Figure 13a (facing) Percentage catch plotted against speed of hauling for the P . O . G . samplers . A l l results are for euph-ausiids . Figure 13b (above) Goodness-of-fit diagram for the results ob-tained with the P . O . G . samplers . Because only two speed c were used a l l points l ie on the line of perfect f i t . Values of X S for the P . O . G . samplers e White sampler-daylight 1189.0 "White sampler-dark 831.0 Dark Green sampler-daylight 421.0 Values of z with confidence l imi t s are not given because only mean catches for each speed class were given. 53 Table 2 R e s u l t s of F i e l d T r i a l s : August, 1965 One-metre C o n i c a l Sampler Speeds of H a u l i n g (cm/sec) 29.39 101.50 206 .02 Calanus spp Mean Catch: Specimens/haul 7841 8258 8312 C a l c u l a t e d F = 0.5091 Tabled F 05 = 2 - 5 7 ( 2 » 2 1 d f ) Euchaeta j a p o n i c a 68 78 84 Mean Catch: Specimens/haul C a l c u l a t e d F = 0.8096 Tabled F n c = 2.57 (2,21 d f ) Euphaus i i d s Mean Catch: Specimens/haul 22 33 37 C a l c u l a t e d F 2.8017 Tabled F _ c = 2.57 (2,21 d f ) . u o S i n c e these are o n e - t a i l e d F t e s t s , t a b l e d F ^ i s used t h r o u g h o u t . 54 Table 3 R e s u l t s of F i e l d T r i a l s : J a n u a r y , 1966 M o d i f i e d One-metre C o n i c a l Sampler Speeds of H a u l i n g (cm/sec) 37.49 81.48 158.30 Calanus spp. Mean Catch: Specimens/haul C a l c u l a t e d F = 1.2474 Euchaeta j a p o n i c a Mean Catch: Specimens/haul C a l c u l a t e d F = 4.1681 Euphaus i i d s Mean Catch: 20 52 342 Specimens/haul 12,331 15,170 16,058 Tabled F = 3.46 (2,6 d f ) 104 131 177 Tabled F Q 5 = 3.46 (2,6 d f ) C a l c u l a t e d F = 30.2068 Tabled F = 3.46 (2,6 d f ) 55 Table 4 R e s u l t s of F i e l d T r i a l s : August, 1965 70-cm N.I.O. Sampler Speeds of H a u l i n g (cm/sec) 30.00 108.0 207.0 Calanus spp. Mean Catch: 6175 4683 3655 Specimens/haul C a l c u l a t e d F = 29.3107 Tabled F . c = 2.57 (2,21 d f ) Eucalanus b u n g i i b u n g i i Mean Catch: Specimens/haul C a l c u l a t e d F = 15.562 Euchaeta j a p o n i c a Mean Catch: 40 38 31 Specimens/haul C a l c u l a t e d F = 3.881 Tabled F n n = 2.57 (2,21 d f ) Euphaus i i d s Mean Ca t c h : Specimens/haul C a l c u l a t e d F - 3.58 1060 834 710 Tabled F = 2.57 (2,21 d f ) 10 Tabled F Q 5 = 2.57 (2,21 d f ) 56 Table 5 R e s u l t s of F i e l d T r i a l s : J a n u a r y , 1966 M o d i f i e d 70-cm N.I.O. Sampler Speeds of H a u l i n g (cm/sec) 31.45 92.00 178.53 Calanus spp Mean Catch: Specimens/haul 4715 508 1 5025 C a l c u l a t e d F = 0.4770 Tabled F Q 5 = 3.46 (2,6 d f ) Eucalanus b u n g i i b u n g i i Mean Catch: Specimens/haul 1581 1871 1835 C a l c u l a t e d F = 4.2874 Tabled T 0 5 = 3 - 4 6 ( 2 > 6 d f ) Euchaeta j a p o n i c a Mean Catch: Specimens/haul 54 56 57 C a l c u l a t e d F = 0.074 Tabled F 0 5 = 3 = 4 6 ( 2 ' 6 d f ) Euphaus i i d s Mean Catch: Specimens/haul C a l c u l a t e d F = 4.5714 Tabled F 0 5 = 3 , 4 6 ( 2 ' 6 d f ) 57 Table 6 R e s u l t s of F i e l d T r i a l s : August, 1965 Catch e r Speeds of H a u l i n g (cm/sec) Calanus spp. Mean Catch: Specimens/haul C a l c u l a t e d F = 31.893 Eucalanus b u n g i i b u n g i i Mean Catch: Specimens/haul C a l c u l a t e d F = 16.631 Euchaeta j a p o n i c a Mean Catch: Specimens/haul No F v a l u e c a l c u l a t e d Euphaus i i d s Mean Ca t c h : .125 .375 ,875 Specimens/haul No F v a l u e c a l c u l a t e d 50.04 120.36 221.41 391 475 660 Tabled F c = 2.57 (2,21 d f ) . u o 102 127 171 Tabled F n c = 2.57 (2,21 d f ) - . u o 5.25 5.725 7.00 58 Table 7 P.O.G. Un p u b l i s h e d R e s u l t s Obtained i n August, 1965 Speeds of H a u l i n g (cm/sec) 100 200 White Sampler ( d a y l i g h t ) Mean Catch: Specimens/haul 1203 2219 White Sampler ( d a r k ) Mean Catch: Specimens/haul 1971 2867 Dark Green Sampler ( d a y l i g h t ) Mean Catch: Specimens/haul 2765 3265 A l l r e s u l t s are f o r ca t c h e s of E u p h a u s i i d s . j 59 DISCUSSION: I f b i o l o g i c a l escapement i s an i m p o r t a n t f a c t o r i n d e t e r m i n i n g the number of z o o p l a n k t o n i c organisms caught by a p l a n k t o n s a m pler, then the number caught c o u l d be expected to i n c r e a s e as the speed of towing i n c r e a s e s because l e s s w i l l escape. The r e s u l t s show, w i t h one e x c e p t i o n , t h a t the number of specimens of any s p e c i e s caught d i d i n c r e a s e as the speed of h a u l i n g i n c r e a s e d . The q u e s t i o n of pr i m a r y importance i s whether these i n c r e a s e d c a t c h e s r e s u l t from d e c r e a s e d ' b i o l o g i c a l escapement. Because of the randomized o r d e r i n which the haulS.i. were made, the depth from which they were t a k e n , and the c o n t i n u e d s a m p l i n g at one l o c a t i o n , i t i s u n l i k e l y t h a t any " c y c l i c a l phenomena such as d i e l m i g r a t i o n s of the organisms - o r . t h e e f f e c t s of the ebb and f l o w of po p u l a - . t i o n s i n a s s o c i a t i o n , w i t h t i d a l c u r r e n t s c o u l d have produced the c o n s i s t e n t l y i n c r e a s e d c a t c h e s at the h i g h e r speeds of h a u l i n g . L i k e w i s e i t i s d i f f i c u l t t o see how any inhomogeneity i n the d i s t r i b u t i o n of the z o o p l a n k t o n i c organisms c o u l d s e l e c t i v e l y i n c r e a s e t h e " c a t c h at the h i g h e r speeds of h a u l i n g . The n u l l h y p o t h e s i s t h a t the mean c a t c h d i d not i n c r e a s e w i t h i n c r e a s e d speed of h a u l i n g was t e s t e d i n the" s t a t i s t i c a l a n l y s i s of the r e s u l t s . ' The t e s t s were set" up so as t o r e j e c t the n u l l h y p o t h e s i s i f the p r o b a b i l i t y of i t s v a l i d i t y was l e s s than 5%. Of the 15 i n s t a n c e s a n a l y z e d - - t h e : n u l l h y p o t h e s i s was r e j e c t e d i n 11 i n s t a n c e s and ac c e p t e d i n 5, However, i n 60 the f i v e i n s t a n c e s where the n u l l h u p o t h e s i s had to be accepted the mean c a t c h i n c r e a s e d as the speed of h a u l i n g i n c r e a s e d . Because i t i s improbable t h a t the a c t i o n of random chance would cause the mean c a t c h t o i n c r e a s e c o n s i s t e n t l y w i t h i n c r e a s e d speed of h a u l i n g , i t may be t h a t the n u l l h y p o t h e s i s had t o be ac c e p t e d because the i n c r e a s e i n c a t c h was s m a l l compared to the v a r i a t i o n i n h e r e n t i n the f i e l d t e c h n i q u e . Another r e l e v a n t p o s s i b i l i t y i s t h a t the samplers f i l t e r e d more water at h i g h e r speeds of h a u l i n g . This i s u n l i k e l y i n view of the r e s u l t s o b t a i n e d by Bary et a l . (1958), T r a n t e r and Heron (1965), and G i l f i l l a n and Pease ( i n prep) where s i m i l a r q u a n t i t i e s of. water were f i l t e r e d , per u n i t d i s t a n c e , over a wider range of speeds than was used i n the p r e s e n t s t u d y . Nor are the i n c r e a s e s i n c a t c h at h i g h speeds p r o p o r t i o n a l l y the same f o r a l l a n i m a l s , w i t h each sampler, as would be expected i f the i n c r e a s e s were a r e s u l t of a l a r g e r volume of water p a s s i n g through the sampler at the h i g h e r speeds. T h e r e f o r e i t may be assumed t h a t the i n c r e a s e d c a t c h e s at h i g h e r speeds of h a u l i n g r e s u l t from more organisms b e i n g c a p t u r e d per u n i t volume of water f i l t e r e d , _i.e_. from a decrease i n b i o l o g i c a l escapement at the h i g h e r speeds of h a u l i n g . I f , as the p r e v i o u s d i s c u s s i o n i n d i c a t e s , the i n c r e a s e d c a t c h e s can be assumed to r e s u l t from decreased b i o l o g i c a l escapement, the a b i l i t y of the model to d e s c r i b e the mechanism of b i o l o g i c a l escapement can be a s s e s s e d . Three sources of i n f o r m a t i o n are a v a i l a b l e as a check on the v a l i d i t y of the model. 61 The most p o w e r f u l of these checks i s found i n the v a l u e s of the p r o p o r t i o n a l i t y f a c t o r , z. A v a l u e of z i s c a l c u l a t e d f o r each comparison between two ca t c h e s of the same s p e c i e s made 'at d i f f e r e n t speeds . I f the assumptions made i n the f o r m u l a t i o n of the model, are v a l i d , these v a l u e s w i l l be c o n s t a n t f o r any g i v e n sampler and s p e c i e s as l o n g as the s i z e of the p o p u l a t i o n sampled does not change. The v a l u e s of z o b t a i n e d from the data c o l l e c t e d i n the course of t h i s s t u d y , w i t h two e x c e p t i o n s , are n e a r l y c o n s t a n t . T h i s i s shown by the r e l a t i v e l y s m a l l 95% c o n f i d e n c e i n t e r v a l s around the mean v a l u e s of z ( T a b l e s a s s o c i a t e d w i t h F i g s . 8b, 9b, l i b , 12b). There i s a p e r s i s t e n t t r e n d toward l a r g e r c o n f i d e n c e l i m i t s on the mean v a l u e s of z as the number of specimens of a p a r t i c u l a r species- i n the sample d e c r e a s e s . Because t h i s o c c u r s i n every i n s t a n c e i t almost c e r t a i n l y r e s u l t s from the f a c t t h a t , i n the f o r m u l a t i o n of the model, the assumptions are s t a t i s t i c a l . That i s , the model d e a l s w i t h the escape r e a c t i o n s of a l a r g e p o p u l a t i o n of z o o p l a n k t o n i c o rganisms; i t i s i n c a p a b l e of d e a l i n g w i t h the escape r e a c t i o n s of a s i n g l e organism. As the number of specimens of a s p e c i e s decreases below a p p r o x i m a t e l y 10 to 50, the a b i l i t y of the model t o p r e d i c t t h e i r escape r e a c t i o n s i s reduced. T h i s e f f e c t shows most c l e a r l y i n the i n s t a n c e of the Ca t c h e r where the t o t a l number of e u p h a u s i i d s caught over 24- tows was o n l y 11 i n d i v i d u a l s . Here the c o n f i d e n c e l i m i t s on the mean v a l u e of z f o r e u p h a u s i i d s are l a r g e . For 'the one-metre c o n i c a l sampler m o d i f i e d by the presence of the weight the numbers of 62 e u p h a u s i i d s caught were l a r g e enough f o r s t a t i s t i c a l a c c u r -acy, but the v a l u e s of z are not c o n s t a n t . T h i s i m p l i e s t h a t one or more of the assumptions made i n the f o r m u l a t i o n of the model i s not v a l i d f o r these organisms, u n l i k e the r e s u l t s o b t a i n e d w i t h the same sampler f o r copepods ( F i g . 9a) which conform t o those o b t a i n e d w i t h the u n m o d i f i e d sampler ( F i g . 8a). E s t i m a t e s of the s i z e of the p o p u l a t i o n s , a f t e r removing the e f f e c t s of b i o l o g i c a l escapement by means of the model, of the same s p e c i e s g i v e n by d i f f e r e n t samplers are another check on the v a l i d i t y of the model. T h i s i s p r o v i d e d t h a t i t can be assumed t h a t the same p o p u l a t i o n was sampled by the s e v e r a l s a m p l e r s . I t i s p o s s i b l e t o make t h r e e comparisons of e s t i m a t e s of the s i z e s of the same p o p u l a t i o n s of z o o p l a n k t o n i c organisms ( T a b l e 8 ) . A comparison of the e s t i m a t e s of the s i z e s of the Calanus spp., Euchaeta j a p o n i c a , and e u p h a u s i i d p o p u l a t i o n s g i v e n by the one-metre c o n i c a l sampler and the Cat c h e r as c a l c u l a t e d from data c o l l e c t e d i n August, 1965 shows t h a t f o r Calanus spp. the e s t i m a t e s d i f f e r by 20%, but t h a t f o r E_. j a p o n i c a and e u p h a u s i i d s the e s t i m a t e s d i f f e r by 100%. However, because the l a t t e r two groups were r e p r e s e n t e d by so few i n d i v i d u a l s i n each sample c o l l e c t e d by the C a t c h e r , i t i s p r o b a b l e t h a t o n l y the e s t i m a t e of the p o p u l a t i o n s i z e f o r Calanus spp. i s v a l i d . The assumption t h a t the same p o p u l a t i o n s of zooplank-t o n i c organisms were sampled by both samplers may not be s t r i c t l y t r u e , f o r the t r i a l s of August, 1965, spread over a 63 Table 8 3 Comparison of P o p u l a t i o n E s t i m a t e s i n Numbers/m of Water F i l t e r e d . August 1965 Calanus spp. Euchaeta j a p o n i c a e u p h a u s i i d s 1-Meter C o n i c a l Sampler 5 3 o i+ 8 .28 .13 Catcher 42.58 .42 .062 January 1966 M o d i f i e d 1-m Sampler M o d i f i e d 70 cm N.I.O. Sampler Calanus spp. Euchaeta j a p o n i c a euphaus i i d s 55.33 . 61 . 68 43.61 . 56 . 5 5 P.O.G. Data ( r e s u l t s f o r e u p h a u s i i d s o n l y ) White Sampler ( d a y l i g h t ) Dark Green Sampler ( d a y l i g h t ) White Sampler ( d a r k ) 92.58 99.45 102.68 Samplers assumed t o f i l t e r 100% of water p r e s e n t e d t o them. 64 two week p e r i o d . But, because of the c l o s e n e s s of the e s t i m a t e s of the s i z e of the Calanus spp. p o p u l a t i o n , i t i s r e a s o n a b l e t o assume t h a t l a r g e changes d i d not occur i n the s i z e s of the p o p u l a t i o n s of o t h e r s p e c i e s . Even i f the data from August, 1965 t r i a l s i s q u e s t i o n a b l e , o t h e r evidence i s a v a i l a b l e from the t r i a l s of J a n u a r y , 1966, and from the data c o l l e c t e d by P.O.G. f o r comparison. I t i s much l e s s l i k e l y t h a t t h e r e were any s i g n i f i c a n t changes i n the s i z e s of the z o o p l a n k t o n i c p o p u l a t i o n s sampled d u r i n g the two days r e q u i r e d to complete the Janua r y , 1966 t r i a l s . The r e s u l t s from the Ja n u a r y , 1966 t r i a l s a l l o w a com-p a r i s o n t o be drawn between the e s t i m a t e s of the s i z e s of the Calanus spp. , Euchaeta j a p o n i c a , and e u p h a u s i i d p o p u l a t i o n s g i v e n by the m o d i f i e d one-metre c o n i c a l sampler and the modi-f i e d 70-cm N.I.O. sampler. For Calanus spp., the s i z e of the p o p u l a t i o n e s t i m a t e d from the c o l l e c t i o n s made w i t h the two samplers agree w i t h i n 20%; f o r Euchaeta j a p o n i c a agreement i s w i t h i n 10%; and f o r e u p h a u s i i d s w i t h i n 20%. A f u r t h e r comparison of the r e s u l t s of the P.O.G. t r i a l s u s i n g white and green samplers by day and by n i g h t i s p o s s i b l e . Here the e s t i m a t e s of the s i z e of the e u p h a u s i i d p o p u l a t i o n g i v e n by the t h r e e samplers of the same b a s i c d e s i g n agree w i t h i n 10% a f t e r the e f f e c t s of b i o l o g i c a l escapement have been removed by means of the model. The e s t i m a t e s of the s i z e of e u p h a u s i i d p o p u l a t i o n g i v e n by the raw data c o l l e c t e d at a speed of h a u l i n g of 100 cm/sec ( t h e s t a n d a r d used) are i n the r a t i o 1:1.67:2.1. 65 These comparisons appear to i n d i c a t e t h a t the r e s u l t s o b t a i n e d by a p p l i c a t i o n of the model t o data c o l l e c t e d w i t h d i f f e r e n t samplers are comparable. That i s , i f sampler A, which i s c a l c u l a t e d t o be 25% e f f i c i e n t w i t h r e s p e c t t o a g i v e n s p e c i e s at speed x, ca t c h e s 25 specimens, and sampler B, which i s c a l c u l a t e d t o be 50% e f f i c i e n t w i t h r e s p e c t t o the same s p e c i e s at speed y, ca t c h e s 50 specimens, the p o p u l a t i o n of t h a t s p e c i e s was 100 specimens per u n i t volume i n both i n s t a n c e s . That i t i s p o s s i b l e t o make such e s t i m a t e s , even though they may be o n l y a p p r o x i m a t e , i s a g r e a t advantage when i t i s d e s i r e d t o compare the c o l l e c t i o n s made w i t h d i f f e r e n t samplers at d i f f e r e n t times and p l a c e s . A t h i r d source of evidence c o n c e r n i n g the a c c u r a c y w i t h which the model d e s c r i b e s the p r o c e s s e s of b i o l o g i c a l escape-ment l i e s i n the agreement between the v a l u e s of percentage c a t c h c a l c u l a t e d from the f i e l d d a t a , and percentage c a t c h taken from the f i t t e d curve of percentage c a t c h p l o t t e d a g a i n s t speed of h a u l i n g f o r e q u i v a l e n t speeds of h a u l i n g . Because the v a l u e s of percentage c a t c h c a l c u l a t e d from the raw data are used to generate t h i s curve the comparison can be expected t o show o n l y gross anomalies' i n the raw d a t a . T h i s i s so because the p o i n t s used t o generate the curve w i l l f a l l on i t o n l y i f the assumptions made i n the f o r m u l a t i o n of the model are j u s t i f i e d . The degree of agreement between p o i n t s r e p r e s e n t i n g p e rcentage c a t c h , as c a l c u l a t e d from raw d a t a , and percentage c a t c h shown the f i t t e d c u r v e s i s i l l u s t r a t e d i n F i g s . 8b 66 t o 13b. For the most p a r t agreement i s very good. The p o i n t s c a l c u l a t e d from the raw data f o r the C a t c h e r f i t the computed curve r e a s o n a b l y w e l l , but w i t h a c o n s i s t e n t p a t t e r n i n t h e i r d i s p e r s i o n . The p o i n t s r e p r e s e n t i n g the c a t c h e s at 50 cm/sec and 200 cm/sec are h i g h and those r e p r e s e n t i n g the c a t c h e s at 100 cm/sec are low. A p o s s i b l e e x p l a n a t i o n f o r " t h i s may be t h a t the hydrodynamic c h a r a c t e r i s t i c s o f " t h e C a t c h e r change between 100 cm/sec and 200 cm/sec. I t i s b e l i e v e d t h a t the C a t c h e r a c c e p t s about 10% more water per u n i t d i s t a n c e at speeds of towing above about 200 cm/sec (4- k t ) ( B a r y , pers . comm.). Th i s i n c r e a s e i n the amount of water f i l t e r e d i s thought to r e s u l t from a v e n t u r i e f f e c t at the a f t e r end of the sampler at the h i g h e r speeds of t o w i n g . Another example, i n which t h e r e i s a g r o s s d e p a r t u r e from the f i t t e d c u r v e , i s t h a t of the r e s u l t s o b t a i n e d f o r e u p h a u s i i d s when towing w i t h the one-metre c o n i c a l sampler preceded by the weight. Here, a g r e a t i n c r e a s e i n the number of e u p h a u s i i d s c a p t u r e d o c c u r s i n the c o l l e c t i o n s made at 200 cm/sec over those made at 100 cm/sec. An i n c r e a s e i n the amount of water f i l t e r e d does not appear to be r e s -p o n s i b l e because the c a t c h e s of Calanus spp. and Euchaeta j a p o n i c a show no such sudden i n c r e a s e . No s a t i s f a c t o r y e x p l a n a t i o n appears p o s s i b l e o t h e r than assuming t h a t f o r some r e a s o n , p r o b a b l y a s s o c i a t e d w i t h the hydrodynamic c h a r a c t e r i s t i c s of the w e i g h t , the e u p h a u s i i d s were e i t h e r much l e s s a b l e to d e t e c t the sampler which does not seem r e a s o n a b l e , or t h a t they were much l e s s a b l e t o escape from 67 the sampler. A l l o t h e r samplers show good agreement between p o i n t s c a l c u l a t e d from the f i e l d d a ta and the curves generated by the model. The s m a l l c o n f i d e n c e l i m i t s on the mean v a l u e s of z and the c l o s e n e s s of the f i t of the p o i n t s c a l c u l a t e d from f i e l d d a ta to the f i t t e d curve demonstrate the c o n s i s t e n c y of the d e s c r i p t i o n of - b i o l o g i c a l escapement g i v e n by the model f o r any one sampler. The q u e s t i o n of the a b s o l u t e a c c u r a c y of the e s t i m a t e s - o f percentage c a t c h i s answered by the comparison of e s t i m a t e s of the s i z e of the same p o p u l a t i o n of z o o p l a n k t o n i c organisms g i v e n by d i f f e r e n t s a m p l e r s . There i s some evidence t h a t samplers w i t h s m a l l e r mouth openings tend to u n d e r e s t i m a t e the s i z e of t h e " p o p u l a t i o n of zooplank-t o n i c organisms sampled ( T a b l e 7 ) . T h i s u n d e r e s t i m a t i o n may r e s u l t from the organisms a v o i d i n g a zone of. t u r b u l e n t water which develops when the l o n g towing w i r e i s : d r a w n v e r t i c a l l y through the water. For any one speed and l e n g t h of w i r e t h i s zone of t u r b u l e n c e would be the same diameter whichever sampler was b e i n g towed. T h e r e f o r e , the f l o w i n t o those samplers w i t h s m a l l e r mouth openings would be r e l a t i v e l y more a f f e c t e d than samplers w i t h l a r g e r mouth openings. I f organ-isms a v o i d the t u r b u l e n t a r e a , the r e s u l t would be to under-e s t i m a t e the s i z e of the p o p u l a t i o n of z o o p l a n k t o n sampled. T h i s e f f e c t would become g r e a t e r as the area of the mouth of the sampler d e c r e a s e d . Because of the many unknown f a c t o r s i t i s not p o s s i b l e t o c a l c u l a t e the exact dimensions of t h i s t u r b u l e n t boundary l a y e r . However, rough c a l c u l a t i o n s 68 ( L e B l o n d , p e r s . comm.) i n d i c a t e t h a t i t c o u l d occupy as much as 30% of the area of the mouth of the 70-cm N.I.O. sampler. The area of the mouth of t h i s sampler i s a p p r o x i m a t e l y one-h a l f t h a t of the one-metre c o n i c a l sampler, so the expected d i s c r e p a n c y i n the e s t i m a t e s of the s i z e of the same zooplank-t o n i c p o p u l a t i o n would be 15%. This i s about the magnitude of the d i s c r e p a n c y t h a t appears t o e x i s t between the e s t i m a t e s of the s i z e of the same p o p u l a t i o n s of v a r i o u s z o o p l a n k t o n i c s p e c i e s g i v e n by these two sa m p l e r s . F u r t h e r a n a l y s i s of Flemminger and C l u t t e r ' s (1965) data ( C l u t t e r , p e r s . comm.) i n d i c a t e s t h a t they may have been a f f e c t e d by a r e g i o n d e v o i d of z o o p l a n k t o n s u r r o u n d i n g the towing w i r e . However, t h i s i n no way i n v a l i d a t e s t h e i r o r i -g i n a l c o n c l u s i o n s c o n c e r n i n g the e x i s t e n c e of a p e r i p h e r a l zone from which z o o p l a n k t o n escape. The f o u r q u a n t i t i e s accounted f o r by the model may not be the o n l y o n e s ' i n v o l v e d i n the p r o c e s s e s of b i o l o g i c a l escapement. However, the evidence i n d i c a t e s c l e a r l y t h a t as lo n g as the assumptions made i n t h e ' f o r m u l a t i o n of the model are j u s t i f i e d , t hese f o u r q u a n t i t i e s appear t o be the ones of major importance i n ' d e t e r m i n i n g the c a t c h i n g power of any gi v e n p l a n k t o n sampler. Now t h a t the r e s u l t s g i v e n by the a p p l i c a t i o n of the model data from f i e l d c o l l e c t i o n s have been shown t o be c o n s i s t e n t not o n l y f o r r e s u l t s o b t a i n e d from any one sampler, but a l s o among s a m p l e r s , i t i s p o s s i b l e t o d i s c u s s the r e s u l t s o b t a i n e d w i t h the i n d i v i d u a l samplers . Dr. P. LeB l o n d , I n s t i t u t e of Oceanography, U.B.C., Vancouver, B. C. 69 One-Metre C o n i c a l Sampler: One of the noteworthy f e a t u r e s of the r e s u l t s from the t r i a l s was t h e " h i g h " e f f i c i e n c y o f " t h e one-metre c o n i c a l sampler. I t a p p e a r s " t h a t ' t h e " o n l y " e s t i m a t e o f the e f f i c i e n c y of a c o n i c a l " s a m p l e r i s that"of"Hansen, and"Anderson (1962). These authors- estimated" the- e f f i c i e n c y • of a" 50-cm c o n i c a l sampler by comparing-the - c a t c h e s i t - made - w i t h - s i m u l t a n e o u s c a t c h e s made u s i n g - a n e i g h t - l i t r e wat er b o t t l e . T h u s ' t h e i r e s t i m a t e of 18% e f f i c i e n c y f o r - t h e 50-cm c o n i c a l sampler i s w i t h r e s p e c t t o the • t o t a l " z o o p l a n k t o n p r e s e n t , i n c l u s i v e of the s m a l l e s t " organisms. ' Therefore,, t h e i r e s t i m a t e i n c l u d e s organisms l o s t ' t h r o u g h - the meshes - of" the - f i l t e r as w e l l as organisms l o s t " a s - a' r e s u l t . o f b i o l o g i c a l - escapement. Because most o f the z o o p l a n k t o n i n the area sampled were very s m a l l , e_.g_. copepod n a u p l i i ,- i t : i s - p r o b a b l e - t h a t - Hansen and Anderson's estimate- of" t h e - e f f i c i e n c y : of: the." c o n i c a l sampler w i t h r e s p e c t to the t o t a l z o o p l a n k t o n : p r e s e n t , as shown by the water b o t t l e , " h a s " n o - r e a l r e l a t i o n - t o the e f f i c i e n c y of the c o n i c a l sampler w i t h : r e s p e c t - t o ' z o o p l a n k t o n l a r g e enough to be r e t a i n e d - c o m p l e t e l y b y the" f i l t e r The r e s u l t s o b t a i n e d i n the p r e s e n t study s t r o n g l y suggest t h a t " t h e one-metre c o n i c a l sampler u s e d - i n - t h i s study i s ve r y e f f i c i e n t at c o l l e c t i n g z o o p l a n k t o n . 70-cm N.I.O. Sampler:. I n t e r p r e t a t i o n of the- r e s u l t s of" the- - f i e l d t r i a l s of the p r e s e n t study i n d i c a t e t h a t , over the range of speeds 70 used, the 70-cm N.I.O. sampler i s not as d e s i r a b l e a p l a n k t o n sampler as the one-metre c o n i c a l s a m pler, p r i m a r i l y because t h e r e i s l i t t l e p o s s i b i l i t y of i m p r o v i n g i t s performance by i n c r e a s i n g the speed at which i t i s h a u l e d . The cause of the s l i g h t r e d u c t i o n i n f l o w through the sampler at speeds of h a u l i n g i n excess of 30 cm/sec i s o b s c u r e . Whatever the cause, the e f f e c t s of the r e d u c t i o n p r o b a b l y are analogous to what occu r s when c l o g g i n g of the meshes of the f i l t e r t a k e s p l a c e . In such c o n d i t i o n s , the r e d u c t i o n i n f l o w can' cause a l a r g e i n c r e a s e i n the magnitude and e x t e n t of the a c c e l e r a t i o n f r o n t s p r e c e d i n g the mouth of the sampler ( S m i t h , p e r s . comm.). The r e s u l t of t h i s e f f e c t i s to enable the z o o p l a n k t o n to d e t e c t the sampler at a g r e a t e r d i s t a n c e . T h i s may be the immediate cause of the r e d u c t i o n i n c a t c h at h i g h e r speeds of h a u l i n g . The more s u c c e s s f u l r e s u l t s of the f i e l d t r i a l s w i t h the 70-cm N.I.O. sampler, m o d i f i e d by removal of the canvas c o l l a r , i n d i c a t e t h a t the d i s t a n c e at which z o o p l a n k t o n i c organisms can d e t e c t the sampler may not change w i t h speed when the canvas c o l l a r i s not p r e s e n t . Whether the s m a l l r e d u c t i o n i n c a t c h at 200 cm/sec over t h a t at 100 cm/sec (T a b l e 4) i s r e a l or an a r t i f a c t of f i e l d or l a b o r a t o r y t e c h n i q u e i s not c l e a r . The curves of percentage Catch p l o t t e d a g a i n s t speed of h a u l i n g f o r the m o d i f i e d 70-cm N.I.O. sampler have been c a l c u l a t e d on"'the b a s i s t h a t t h i s r e d u c t i o n i n c a t c h i s not r e a l . However i t must be borne i n mind t h a t the canvas c o l l a r may not be the e n t i r e cause of 71 the r e d u c t i o n i n c a t c h i n the s t a n d a r d sampler. I t may be t h a t , a n y i m p e r v i o u s c o l l a r ' ahead of the mouth of the sampler may cause a r e d u c t i o n i n f l o w through t h e ' s a m p l e r . I f t h i s \ i s so,,some e f f e c t r e s u l t i n g from the presence of the 30.5 cm metal c y l i n d e r which remained i n p l a c e on the m o d i f i e d sampler c o u l d be e x p e c t e d . The evidence at hand does not appear c o n c l u s i v e r e g a r d i n g any h y p o t h e s i s . In any e v e n t , the 70-cm N.I.O. sampler m o d i f i e d by the removal of the canvas c y l i n d e r from i n f r o n t of the mouth appears t o be more e f f i c i e n t than the s t a n d a r d 70-cm N.I.O. sampler. C a t c h e r : The r e s u l t s based on c o l l e c t i o n s made'with the C a t c h e r f o r Calanus spp. and Euc'alanus b u n g i i b u n g i i are p r o b a b l y a c c u r a t e because the number of specimens of each s p e c i e s which were caught are r e l a t i v e l y l a r g e . Other r e s u l t . s must be r e g a r d e d w i t h c a u t i o n ; too few specimens of Euchaeta j a p o n i c a *e __—_—_-______—- _____ and e u p h a u s i i d s were c o l l e c t e d to g i v e a r e l i a b l e e s t i m a t e of i t s c a t c h i n g power w i t h r e s p e c t to these groups. The r e s u l t s i n d i c a t e t h a t , f o r the range of speeds o f ' h a u l i n g used i n the f i e l d t r i a l s , t he;Catcher- i s l e s s a b l e t o c o l l e c t z o o p l a n k t o n than the one-metre c o n i c a l sampler. E x t r a p o l a t i o n of the curves f o r p e rcentage c a t c h p l o t t e d a g a i n s t . s p e e d of h a u l i n g i n d i -c a t e s t h a t at speeds of h a u l i n g g r e a t e r than 300 cm/sec ( 6 k t ) the C a t c h e r may be an e f f i c i e n t - s a m p l i n g d e v i c e . The low c a t c h i n g - p o w e r of the C a t c h e r a t . t h e low speeds of h a u l i n g may r e s u l t from the t u r b u l e n t zone c r e a t e d by up to 400 m of 7 2 w i r e p r e c e d i n g t h e r e l a t i v e l y s m a l l mouth o f t h e s a m p l e r ; a d d i t i o n a l l y ' b e c a u s e t h e mouth o p e n i n g o f t h e s a m p l e r i s s m a l l e r i t m a y " b e • e a s i e r f o r z o o p l a n k t o n i c o r g a n i s m s t o a v o i d b e i n g c a u g h t . When t h e C a t c h e r i s towed/ h o r i z o n t a l l y , as i t i s d e s i g n e d t o be towed, t h e mouth o f t h e s a m p l e r i s c o m p l e t e l y u n o b s t r u c t e d . t h e r e f o r e • t h e c a t c h i n g power can be e x p e c t e d t o i n c r e a s e somewhat i n c o n d i t i o n s o f ' h o r i z o n t a l t o w i n g . At t h e same t i m e t h e ' r e s u l t s i n d i c a t e t h a t w i t h o u t any i n c r e a s e i n c a t c h i n g power t h e C a t c h e r s h o u l d be e f f i c i e n t a t t h e speeds a t which i t i s u s u a l l y towed (6 k t o r more). E x p e r i m e n t a l " S a m p l e r s : The t r i a l s w i t h t h e m o d i f i e d one-metre c o n i c a l s a m p l e r , m o d i f i e d by t h e p r e s e n c e o f a we igh.t. p r e c e d i n g t h e mouth, were u n d e r t a k e n t o o b t a i n ' a n i n d i c a t i o n o f • t h e d i s t a n c e a t which z o o p l a n k t o n i c o r g a n i s m s a r e a b l e t o d e t e c t t h e p r e s e n c e o f t h e s a m p l e r . I t was assumed t h a t by• s u s p e n d i n g . a body ( l e a d w e i g h t ) some d i s t a n c e (80 cm) i n ' f r o n t o f i t s mouth, th e d i s t a n c e a t w h i c h t h e o r g a n i s m s c o u l d d e t e c t t h e a p p r o a c h -i n g s a m p l e r might b e ; i n c r e a s e d . I f a n y . o f t h e s e l e c t e d s p e c i e s a r e a b l e t o d e t e c t ' t h e u n m o d i f i e d s a m p l e r a t . a d i s t a n c e i n e x c e s s o f 80 cm, t h e n " b y a d d i n g t h e w e i g h t , l i t t l e or no change i n t h e s a m p l e r ' s c a t c h i n g power c o u l d be e x p e c t e d b e c a u s e t h e o r g a n i s m s a l r e a d y would have been a l e r t e d b e f o r e t h e w e i g h t would have r e a c h e d ' t h e m , However i f t h e ' o r g a n i s m s a r e not a b l e t o d e t e c t t h e s a m p l e r a t a. d i s t a n c e o f ,80 cm t h e p r e s e n c e • o f th e weight- c o u l d be e x p e c t e d t o d e c r e a s e i t s c a t c h i n g power by 73 i n c r e a s i n g the d i s t a n c e , X ( F i g . 3 ) , at which the organisms can d e t e c t the presence of the sampler.. Such an i n c r e a s e i n X would e f f e c t an i n c r e a s e i n the product X S g ( e q u a t i o n 10, p. 24). The p r o d u c t s X S^ i n c r e a s e d , on the average, by a f a c t o r of 4.4, w h i c h , because i n a l l o t h e r ways the sampler was not changed, i s a t t r i b u t a b l e t o the presence of the w e i g h t . I t i s not p o s s i b l e to e v a l u a t e t h i s r e s u l t because of the unknown d i s t a n c e at which the organisms were a b l e t o d e t e c t the p r e -sence of the w e i g h t , but i t seems r e a s o n a b l e to assume t h a t organisms are not a b l e to d e t e c t the sampler ( u n m o d i f i e d ) at a d i s t a n c e much i n excess of 80 cm. Thus i t appears t h a t B a r k e l e y ' s (1964) e s t i m a t e of 250 cm f o r the d i s t a n c e at which z o o p l a n k t o n i c organisms are a b l e to d e t e c t the sampler may be excess i v e . The o b j e c t of the t r i a l s w i t h the m o d i f i e d 70-cm N.I.O. sampler was to determine whether the decrease i n f l o w through the s a mpler, at h i g h e r speeds of h a u l i n g , w i t h the concomitant decrease i n the c a t c h i n g power of the sampler r e s u l t e d from i n c r e a s e d r e s i s t a n c e to f l o w through the f i l t e r , or whether i t r e s u l t e d from some p r o p e r t y of the canvas s l e e v e p r e c e d i n g the f i l t e r . The r e s u l t s suggest s t r o n g l y t h a t at l e a s t some of the u n d e s i r a b l e p r o p e r t i e s of the 70-cm N.I.O. sampler at h i g h speeds can be a t t r i b u t e d t o the presence of the canvas c o l l a r . Without the canvas c o l l a r the e f f i c i e n c y of the 70-cm N.I.O sampler approaches t h a t of the one-metre c o n i c a l sampler as i s shown by F i g . 11a. However, a s l i g h t r e d u c t i o n 74 i n c a t c h does occur between 100 and 200 cm/sec. I t i s d i f f i -c u l t t o say whether t h i s r e d u c t i o n i n c a t c h i s r e a l , or whether i t i s an a r t i f a c t of e i t h e r the f i e l d or l a b t e c h n i q u e . The p l o t s of percentage c a t c h a g a i n s t speed of h a u l i n g f o r the m o d i f i e d 70-cm N.I.O. sampler are c a l c u l a t e d on the b a s i s t h a t no r e a l r e d u c t i o n i n c a t c h o c c u r s at the h i g h e r speeds of h a u l i n g . T h e r e f o r e they must be reg a r d e d w i t h a c e r t a i n amount of c a u t i o n u n t i l t h e r e i s s u f f i c i e n t evidence to show whether the r e d u c t i o n i n c a t c h i s , i n f a c t , r e a l , or an a r t i -f a c t . One-Square-Metre P.O.G. Samplers: The r e s u l t s of the P.O.G. t r i a l s i n which wh i t e and dark green, m o d i f i e d , Hensen-type samplers were towed i n c o n d i t i o n s of both d a y l i g h t and darkness permit the a s s e s s -ment of the e f f e c t of the v i s i b i l i t y of the sampler on i t s c a t c h i n g power w i t h r e s p e c t to e u p h a u s i i d s ( a n i m a l s p o s s e s s i n g compound e y e s ) . The samplers used had a mouth area e q u a l t o one square metre. In d a y l i g h t the r a t i o of the product X S g f o r the white sampler t o t h a t of the dark green sampler i s 2.82:1. In darkness the r a t i o i s 1.42:1. These r e s u l t s appear- t o i n d i -c a t e t h a t the c o l o u r may be c o n t r i b u t i n g t o the e f f e c t i v e n e s s , i n terms of c a t c h i n g power, even at n i g h t . That the c a t c h i n g power of the white sampler i n d a y l i g h t s h o u l d be r e l a t i v e l y low seems obvious from the r e s u l t s . P r o b a b l y t h i s i s a t t r i -b u t a b l e to i t s b e i n g r e a d i l y seen, but why the c o l o u r s h o u l d 7 5 c o n t i n u e t o be e f f e c t i v e at n i g h t i s not c l e a r . Perhaps i n darkness b i o l u m i n e s c e n c e from organisms would cause a whi t e sampler t o be more v i s i b l e than a dark green one. However, i t might be e x p e c t e d " t h a t most of the b i o l u m i n e s c e n c e would be g e n e r a t e d when the b i o l u m i n e s c e n t organisms s t r i k e the f i l t e r , i n which'case i t i s d i f f i c u l t to" see why the c o l o u r of the sampler s h o u l d make any d i f f e r e n c e . A comparison between the p l o t of percentage c a t c h a g a i n s t speed of h a u l i n g w i t h r e s p e c t t o e u p h a u s i i d s f o r the dark green P.O.G. sampler, and the same p l o t f o r the one-metre c o n i -c a l s a m p ler, i n d i c a t e s t h a t the P.O.G. sampler i s l e s s a b l e to ca p t u r e e u p h a u s i i d s than the one-metre sampler. I t i n d i c a t e s a l s o t h a t the Hensen-type c o n f i g u r a t i o n i s p r o b a b l y not as good a d e s i g n f o r p l a n k t o n samplers as i s the s i m p l e c o n i c a l sampler. P l a n k t o n Sampler Design: B a r k e l e y ' s (1964-) computations suggest t h a t p l a n k t o n samplers s h o u l d be made much l a r g e r than they are at p r e s e n t i f the c o l l e c t i o n s are to be r e p r e s e n t a t i v e of even the l a r g e r z o o p l a n k t o n i c organisms. His computations are based on the .assumption t h a t z o o p l a n k t o n i c organisms are a b l e t o d e t e c t a sampler one n e t r e i n diameter at a d i s t a n c e of 250 cm. Because the r e s u l t s of the p r e s e n t study i n d i c a t e t h a t z o o p l a n k t o n i c organisms are p r o b a b l y not a b l e t o d e t e c t the presence of a p l a n k t o n sampler one metre" i n diameter at a d i s t a n c e of more than 80 cm, Barkeley's'recommendations need to be r e - e v a l u a t e d . A decrease i n the d i s t a n c e at which . . 7 6; z o o p l a n k t o n i c organisms are a b l e t o d e t e c t the sampler s h o u l d make i t p o s s i b l e - t o decrease the s i z e of the o p t i m a l sampler and y e t keep i t \an e f f e c t i v e t o o l . The r e s u l t s ' of t h i s ' s tudy show t h a t , f o r the range of s i z e s of organisms "• s t u d i e d , plankton- samplers w i t h mouth diam e t e r s of 70 t o 10 0 cm are p r o b a b l y adequate to c o l l e c t r e p r e s e n t a t i v e samples from z o o p l a n k t o n i c communities p r o v i d e d t h a t they are- h a u l e d somewhat f a s t e r - than u s u a l , _ i , e . 150 to 200 cm/sec as'opposed• to the"more usual'100 cm/sec. By an e x t e n s i o n of- t h i s r e a s o n i n g , the p o s s i b l e p e n a l t y p a i d by r e d u c i n g the diameter of the mouth .opening.of a p l a n k t o n sampler may be recompensed-by the' i n c r e a s e i n - t h e number of organisms c o l l e c t e d ' b y - t o w i n g at h i g h e r - s p e e d s . T h i s has been p a r t of t h e ; r e a s o n i n g u n d e r l y i n g the d e s i g n of the h i g h speed s a m p l e r s , but the p r e s e n t - s t u d y appears t o be the f i r s t attempt t o j u s t i f y t h i s ' reasoning, q u a n t i t a t i v e l y . C e r t a i n l y the 23-cm mouth of t h e - C a t c h e r a p p e a r s - t o be u s e f u l , but most o t h e r h i g h s p e e d - s a m p l e r s • ( G u l f I , A r n o l d , 1952; G u l f V, A r n o l d , 1959; J e t Net, C l a r k e , 1964) have-mouth - d i a m e t e r s l e s s than 10 cm. F u r t h e r work - i s - r e q u i r e d - t o determine the e x t e n t t o which t h e - d i a m e t e r of the mouth- opening may be reduced and s t i l l be compensated f o r by i n c r e a s i n g the speed of t o w i n g . From the above: b r i e f - d i s c u s s i o n - c o n c e r n i n g p l a n k t o n sampler d e s i g n i t appears t h a t : f i r s t l y , - e v e r y e f f o r t be made to f a c i l i t a t e the f l o w of water' through- the sampler; s e c o n d l y , the p l a n k t o n 'sampler s h o u l d be made as d i f f i c u l t t o d e t e c t as p o s s i b l e , not o n l y by means of c o l o u r i n g , but by 77 s t r e a m l i n i n g and'making as s m a l l as p o s s i b l e a l l p a r t s which must precede the-mouth of the sampler. F i n a l l y , no m o d i f i -c a t i o n s s h o u l d be made i n the d e s i g n of any p l a n k t o n sampler w i t h o u t thorough t r i a l s to- d e t e r m i n e : w h a t e f f e c t - t h e s e modi-f i c a t i o n s may have on the c a t c h i n g power of the sampler. The Use and U t i l i t y of the, Model: Perhaps' t h e - g r e a t e s t ' u t i l i t y of the model i s to the z o o p l a n k t o n e c o l o g i s t who d e s i r e s - t o ' o b t a i n " d a t a c o n c e r n i n g the s i z e and s p e c i e s c o m p o s i t i o n of the z o o p l a n k t o n i c com-munity which i s q u a n t i t a t i v e . For the purpose of t h i s d i s -c u s s i o n the z o o p l a n k t o n i c - c o m m u n i t y i s - d e f i n e d as those members of the marine community which are p e l a g i c a n i m a l s between the s i z e - l i m i t s of' 0.5 mm- to a-' f e w c e n t i m e t r e s i n l e n g t h . P e l a g i c a nimals l a r g e r than these s i z e - l i m i t s are c o n s i d e r e d t o com-p r i s e the nekton. To say t h a t d ata are q u a n t i t a t i v e ' i m p l i e s t h a t the number of s p e c i e s a n d ' t h e i r r e l a t i v e - abundance' i n the sample are the same as-' i n the: community samp-led and t h a t the volume of water which"'has been' f i l t e r e d i s a c c u r a t e l y known. The problems i n v o l v e d ' in-• d e t e r m i n i n g the'';volume of water f i l t e r e d by the p l a n k t o n sampler have been d i s c u s s e d ' elsewhere (pp. 8 - l l ) i - • . L i k e w i s e the p o s s i b l e - e r r o r s i n t r o d u c e d ' i n t o data as a r e s u l t of the s e l e c t i v i t y of the sampler (p. 5) and e x t r u s i o n of a n i m a l s t h r o u g h ' t h e meshes of the f i l t e r ( p . 3) have been d i s c u s s e d above. 78 Presuming'- t h a t the p r e v i o u s arguments and- c a l c u l a t i o n s are v a l i d , t h e - v a l u e o f ' t h e model to the z o o p l a n k t o n e c o l o g i s t i s t h a t once a-sampler-has'been c a l i b r a t e d ' w i t h ' r e s p e c t to the s p e c i e s " to-be-' i n v e s t i g a t e d s e l e c t i v i t y of' t h e : sampler i s no. l o n g e r a problem' f o r ' s p e c i e s which' the' sampler i s a b l e to c a p t u r e at a l l ' . ' ' Thus' the' zooplankton- e c o l o g i s t need o n l y s e l e c t a samplin g ' d e v i c e - which w i l l c a p t u r e a' few specimens of a l l . the s p e c i e s t c be : s t u d i e d and c a l i b r a t e i t w i t h r e s p e c t to those s p e c i e s - t o o b t a i n - d a t a r e l a t i v e l y f r e e from e r r o r s i n t r o d u c e d " b y b i o l o g i c a l escapement.- The m o d e l - w i l l a l s o be u s e f u l when,it i s ' d e s i r e d ' t o - c o m p a r e ' c a t c h e s made w i t h d i f f -e r e n t samplers at' d i f f e r e n t ' t i m e s . This- i s ' e s p e c i a l l y v a l u a b l when one sampler-cannot'be used'to sample' a l l the s p e c i e s t o be s t u d i e d . Such'a' s i t u a t i o n ' m i g h t a r i s e when both very s m a l l and very l a r g e s p e c i e s ' w e r e t o be s t u d i e d . -However-, • the c a l i b r a t i o n of the- sampler- r e q u i r e s the g r e a t e s t care- i f " a n y b e n e f i t i s " t o a c c r u e ' f r o m ' i t s use. I t must be c e r t a i n t h a t ' t h e s a m e - p o p u l a t i o n ' i s sampled by each h a u l , and t h a t the- volume of water f i l t e r e d d u r i n g each h a u l i s a c c u r a t e l y . known, of- the same. Also, - enough .specimens of each s p e c i e s must'be ; c a p t u r e d by each-haul' to ensure a c c u r a c y i n the c a l c u l a t i o n s . ' 'The lower l i m i t - o n the number of s p e c i -mens c a p t u r e d b y each h a u l i s ' p r o b a b l y from' 10-50. Another i m p o r t a n t a p p l i c a t i o n of the model i s i n the t e s t i n g of e x p e r i m e n t a l s a m p l e r s . H e r e " t h e r use' of' the model s h o u l d enable comparisons t o be made' on' an a b s o l u t e b a s i s between d i f f e r e n t samplers'. Again' every p r e c a u t i o n must be taken to ensure' t h a t ' the - data c o l l e c t e d f u l f i l the re q u i r e m e n t of the model. 79 GENERAL CONCLUSIONS: 1. B i o l o g i c a l escapement can cause d i f f i c u l t i e s i n o b t a i n -i n g a r e p r e s e n t a t i v e ' s a m p l e - f r o m z o o p l a n k t o n i c communities, not o n l y i n the" form" of " l o w e s t i m a t e s " of ".population d e n s i t i e s f o r s i n g l e s p e c i e s , b u t " a s " e r r o r s i n e s t i m a t e s of the s p e c i e s c o m p o s i t i o n of the community. 2. Four quant i t l e s the ;" r a d i u s " of" the; s a m p l e r , the speed at which i t i s towed,"the e f f e c t i v e " s p e e d which- the organisms can a t t a i n ' i n " es"caping r from" the" sampler", and the d i s t a n c e at which the organisms'can d e t e c t the sampler, are c o n s i d e r e d i n the model.' These are p r o b a b l y the• f a c t o r s - of ' prime importance i n d e s c r i b i n g the' p r o c e s s of b i o l o g i c a l escapement. 3. The r e s u l t s g i v e n by the a p p l i c a t i o n of the model to data from c o l l e c t i o n s made i n the f i e l d are not o n l y c o n s i s t e n t f o r data- C o l l e c t e d w i t h any one sampler, but a l s o f o r data c o l l e c t e d with, d i f f e r e n t s a m p l e r s . 4. For the organisms s t u d i e d , samplers h a v i n g mouth d i a -meters of 70 t o 100 cm are p r o b a b l y adequate f o r c o l l e c t i n g a r e p r e s e n t a t i v e sample, p r o v i d e d t h a t they are towed at 150 to 200 cm/sec or more. 80 REFERENCES AHLSTROM, E. H. 19 54. Oceanographic I n s t r u m e n t a t i o n . I l l ; B i o l o g . i c a l I n s t r u m e n t s . Pub Is . Natn . Res . Counc . , Wash., 309 : 36-46. ARNOLD, E. L. J r . 1952. High speed p l a n k t o n s a m p l e r s . I . A high-s p e e d p l a n k t o n sampler (Model G u l f I - A ) . Spec . s c l e n t . Rep U_. S . F i s h W i l d l . Serv .> F i s h e r i e s No . 8 8: 1-6 . ' """" -' 195;9 The G u l f V. p l a n k t o n sampler. C i r c . F i s h . W i l d l . Serv• , Wash., No. 62: 111-113. ARON, W. 1962. Some a s p e c t s of sampl i n g the ma c r o p l a n k t o n . Rapp. P.-v. Reun. Cons . perm . i n t . E x p l o r . Mer, 153: 29-38 BARKLEY, R'. A. 1964 . The T h e o r e t i c a l E f f e c t i v e n e s s of Towed-Net Samplers' as R e l a t e d t o Sampler S i z e and t o Swimming Speed of Organisms. J . Cons . perm . i n t . E x p l o r . Mer, 29: 146-157 . ~ ' ' BARNES, H. 1949. On the volume measurement of water f i l t e r e d by a p l a n k t o n pump, w i t h some o b s e r v a t i o n s of the d i s t r i b u t i o n of p l a n k t o n i c a n i m a l s . J . mar. B i o l . Assn. U. K. , 28 : 651-662 . — ' BARNES, H. and S. M. MARSHALL, 1951. On the v a r i a b i l i t y of r e p l i c a t e p l a n k t o n samples and some a p p l i c a t i o n s of 'co n t a g i o u s s e r i e s ' t o the s t a t i s t i c a l d i s t r i b u t i o n of ca t c h e s over r e s t r i c t e d p e r i o d s . J_. mar. B i o l . Assn. U. K., 30: 233-263. ~~ BARNES, H. and D. J . TRANTER, 1965. A s t a t i s t i c a l e x a m i n a t i o n of the c a t c h e s , numbers, and biomass taken by t h r e e com-monly used p l a n k t o n n e t s . Aust . J . Mar . Fre shw . Res . , 16: 293-306 . ~ BARY, B. McK. 1966. B a c k s c a t t e r i n g at 12 kc/s i n r e l a t i o n to biomass and numbers of Z o o p l a n k t o n i c Organisms i n Saa n i c h I n l e t , B r i t i s h Columbia. Deep-Sea Res. , 13: 655-666. BARY, B. M., J . G. deSTEPHANO, M. FORSYTH, and J . van den KERKHOF. 1958. A C l o s i n g , High-Speed P l a n k t o n C a t c h e r f o r Use i n V e r t i c a l and H o r i z o n t a l Towing. P a c i f i c  S c i . , 1 2 : 4 6 - 5 9 . BRIDGER, J . P. 1957. On e f f i c i e n c y t e s t s made w i t h a m o d i f i e G u l f I I I high-speed townet. J_. Cons . perm. i n t . E x p l o r . Mer, 23: 3 57-36 5. 81 BODSKII, K. A. and G. A. BASKAKOV. 1951. U s k o r e n n y i s c h e t n y i metod o b r a b o t k i z o o p l a n k t o n a . Akademiya Nauk . SS SR , Trudy Usesoyuznogo G i d r o b i o l o g i c h e s k o g o , V o l . 3: 227-238. CASSIE, R. M. 1958. An apparatus f o r i n v e s t i g a t i n g s p a t i a l d i s t r i b u t i o n of p l a n k t o n . N.Z_. J_. S c i . , 1 ( 3 ) : 436-448. 1959. Some c o r r e l a t i o n s i n r e p l i c a t e p l a n k t o n samples. N.Z.J. S c i . , 2 ( 4 ) : 473-484. CLARKE, G. L. and D. F. BUMPUS. 1950. .The p l a n k t o n sampler -an i n s t r u m e n t f o r q u a n t i t a t i v e p l a n k t o n i n v e s t i g a t i o n s . Spec. P u b i s . Am. Soc. L i m n o l . Oceanogr., No. 5, pp. 8. CLARKE, W. D. 1964. The J e t Net, a new high-speed p l a n k t o n sampler. J . mar. Res., 2 2 ( 3 ) : 284-287. COLTON, J . B. 1958. A d a p t a b i l i t y of the Hardy P l a n k t o n Recorder to r e s e a r c h s h i p s t u d i e s . I n : Some problems f o r b i o l o g i c a l survey and t e c h n i q u e s f o r t h e i r s o l u t i o n . Spec . P u b i s . i n t . Comm. NW. A t l a n t . F i s h . , No. 1, p. 277. CURRIE, R. I . 1963. The I n d i a n Ocean Standard Net. Deep -Sea Res., 10: 27-32. CURRIE, R. I . and P. FOXTON. 1957. A new q u a n t i t a t i v e p l a n k -ton n e t . J_. mar . B i o l . Assn. U_.]£.» 36: 17-32. CUSHING, D. H. 1954. S t u d i e s on P l a n k t o n P o p u l a t i o n s . J . Cons. perm. i n t . E x p l o r . M e r , 19: 3-22. FLEMINGER, A. and R. I . CLUTTER. 1965. Avoidance of towed nets by z o o p l a n k t o n . L i m n o l . Oceanogr. 1 0 ( 1 ) : 96-104. GHERINGER, J . W. 1952. An a l l - m e t a l p l a n k t o n sampler (Model G u l f I I I ) . U. _S . F i s h W i l d l . Serv . Spec . S c i e n t . Rep F i s h e r i e s , No. 88: 7-12. GIBBONS, S. G. 1939. The Hensen Net. £. Cons . perm. i n t . E x p l o r . Mer, 14: 242-248. HANSEN, V. Kr. and K. P. Anderson. 1962. Sampling the s m a l l e r z o o p l a n k t o n . Rapp. P.-v. Reun. Cons, perm. i n t . E x p l o r . Mer, 153: 39-4T! ~~ HARDY, A. C. 1936. The c o n t i n u o u s p l a n k t o n r e c o r d e r . D i s c o v e r y Rept.> 11: 457-510. HENSEN, V. 1895. Methodik der u n t e r s u c h u n g e n b e i d e r e x p e d i t i o n . E r g . P l a n k t . - E x p e d . H u m b o l t - S i f t u n g B:1-200 . p l a n k t on-Bd . 1 , 82 ISAACS, J . D. and L. W. KIDD. 1953. I s a a c s - K i d d midwater t r a w l , f i n a l r e p o r t . S c r i p p s I n s t . Oceanogr. Ref. 53-3. Oceanographic Equipment r e p o r t No. 1. JENKINS, J . T. 1901. The methods and r e s u l t s of the German p l a n k t o n i n v e s t i g a t i o n s w i t h s p e c i a l r e f e r e n c e t o the Hensen n e t s . Proc . Trans. L p o o l . b i o l . Soc . , 15: 279-341. JUDAY, C. 1916. L i m n o l o g i c a l A p p a r a t u s . . Trans . Wis. Acad. S c i . A r t s L e t t . , 18:566- 592. KEMP, S. and A. C. HARDY. 1929.. The D i s c o v e r y i n v e s t i g a t i o n s . Objects,, equipment ,. and methods. I I . The s h i p s , t h e i r equipment and the methods used i n r e s e a r c h . D i s c o v e r y Rep . , 1: 151-232 .' ' : ' " KUNNE, C. 1933. W'eitere Untersuchungenzom V e r l e i c h der F a n g f a h i g k e i t v e r s c h i e d e n e r Modelle von v e r t i k a l f i s c h e n d e n p l a n k t o n - n e t z e n . Rapp . P_. -y_. Reun . Cons, perm . i n t . Explor:. • Mer , 8 3:1-35. " " " MARUMO, R. 195.(8 J On the norpac s t a n d a r d p l a n k t o n n e t . Oceanogr. Rep. Japan Met. Agency , 6( 1 ): 45-47. NANSEN, F. 1915. C l o s i n g nets f o r v e r t i c a l h a u l s and f o r h o r i z o n t a l t o w i n g . P u b l . C i r c o n s t . Cons . perm . i n t . E x p l o r . Mer, 67: 1-8. PEARCY , W. G. 1965. Day-night d i f f e r e n c e s i n mid-water t r a w l c a t c h e s of m i c r o n e k t o n . (Paper g i v e n at ICES-SCOR-UNESCO. symposium on Z o o p l a n k t o n Sampling Methods. C r o n u l l a , A u s t r a l i a . ) REGAN, L. 1963. F i e l d - t r i a l s w i t h the Clarke-Bumpus p l a n k t o n sampler. E f f e c t s of coarse and f i n e meshed nets over a range of speeds on e u p h a u s i i d c o l l e c t i o n s . U n i v . B r . Columb"-. I n s t . Oceanogr. Manus c r . Rep . 16 (mimeo) pp. 28. SHEARD , K. 1941. Improved methods of c o l l e c t i n g marine organisms. Rec. S. A u s t . Mus . , 7: 11-14. S I L L I MAN, R. P. 1943.. A study of v a r i a b i l i t y i n p l a n k t o n tow net c a t c h e s of P a c i f i c p i l c h a r d ( S a r d i n o p s c a e r u l e a ) eggs. J . mar. Res., 6 ( 1 ) : 74-83. : STEEL, R. G. D. and J . H. TORRIE. 1960. P r i n c i p l e s and P rocedures of S t a t i s t i c s . M c G r a w - H i l l Book Company I n c . , New York, r9T>0~ : TRANTER, D. J . 1966. the A u s t r a l i a n Clarke-Bumpus sampler and c a l i b r a t i o n t a n k . £.S.I_.R.C_. D i v . F i s h . Oceanogr. Tech. Pap. 19. 83 TRANTER, D. J.' and A, HERON. 1965.. F i l t r a t i o n c h a r a c t e r -. i s t i c s of Clarke-Bumpus s a m p l e r s . Aust . J_. M a r . Freshw. Res. , 16: 2 81-291. .WINSOR, "C. P. and_G. L. CLARKE. 1940.. . A, s t a t i s t i c a l study of : v a r i a t i o n i n the. c a t c h of. p l a n k t o n n e t s . J . Mar. Res . , 3(1) : 1-34. WIBORG, K. F. 1948. Experiments w i t h the Clarke-Bumpus p l a n k t o n sampler and w i t h a p l a n k t o n pump i n the L o f o t e n area i n N o r t h e r n Norway. F i s k . D i r . S k r . , 9 ( 2 ) : 1-22. 84 APPENDIX I The Subsampling Technique: The subsampling t e c h n i q u e of B r o d s k i i and Baskakov (1951) c o n s i s t s of c o u n t i n g the number of specimens of a s p e c i e s or group which l i e w i t h i n a known f r a c t i o n of the area of the bottom of a d i s h . T h i s method depends upon an^even d i s t r i -b u t i o n of the specimens i n the bottom of the dish'. A d i s t r i -b u t i o n which appears even to the eye i s adequate. A l s o the d i a m e t e r of the ( c i r c u l a r ) area t o be counted s h o u l d be s e v e r a l (3-5) times the l e n g t h of the specimens which are t o be subsampled. I f these c r i t e r i a are met the method can p r o v i d e a c c u r a t e and p r e c i s e d a t a . A source of s y s t e m a t i c e r r o r i n the subsampling t e c h n i q u e a r i s e s from the i n t e r a c t i o n between the a n i m a l s which are to be subsampled and the w a l l s of the d i s h . There tends t o be a zone at the j u n c t i o n of the w a l l s and bottom of the d i s h i n which animals are not found. Thus the area i n which the animals are 'evenly '• d i s t r i b u t e d i s s l i g h t l y s m a l l e r than the area of the bottom of the d i s h . The area i n which the a n i -mals are evenly • d i s t r i b u t e d can be termed the e f f e c t i v e area of the bottom of the d i s h . A f u r t h e r source of system-a t i c e r r o r a r i s e s from e r r o r s i n d e l i m i t i n g the area t o be counted. T h e r e f o r e i t i s best to subsample a known number of specimens to determine the exact f r a c t i o n of the e f f e c t i v e a r ea of the bottom of the d i s h which each subsampling area r e p r e s e n t s . T h i s i s done by making 10-20 counts and 85 o b t a i n i n g the mean number of specimens per subsampling a r e a . In p r a c t i c e i t i s d e s i r a b l e t o r e d i s t r i b u t e the specimens b e f o r e each count of, the number w i t h i n the subsampling a r e a . A l s o o n e - h a l f of the number of anim a l s which l i e a c r o s s the boun d a r i e s of the area s h o u l d be added t o the number of anima l s l y i n g c o m p l e t e l y w i t h i n the bo u n d a r i e s of the sub-sampli n g area . Table 9 g i v e s a summary of the r e s u l t s of 15 counts made w i t h a subsampling area n o m i n a l l y e q u a l t o l / 2 0 t h of the area of the bottom of the d i s h . The d i s h c o n t a i n e d 1343 e u p h a u s i i d s . I f the subsampling area had been p r e c i s e l y l / 2 0 t h of the area of the bottom of the d i s h , each subsampling area s h o u l d have c o n t a i n e d 67.15 e u p h a u s i i d s . However, the mean number of e u p h a u s i i d s per subsampling area was 63.8. Th i s i n d i c a t e s t h a t the subsampling area i s a c t u a l l y l / 2 1 s t of the e f f e c t i v e a rea of the bottom of the d i s h . The goodness of f i t of the p r e d i c t e d and a c t u a l numbers of e u p h a u s i i d s i n the d i s h was determined by c a l c u l a t i n g a v a l u e f o r Chi - S q u a r e . C a l c u l a t i o n of Chi-Square on the b a s i s of the subsampling area b e i n g l / 2 0 t h of the area of the bottom of the d i s h gave a v a l u e of 4.66. Th i s i n d i c a t e s v e r y good agreement between the p r e d i c t e d and a c t u a l number of specimens In the d i s h . 86 Table 9 R e s u l t s of F i f t e e n S u c c e s s i v e Counts of the' Number E u p h a u s i i d s L y i n g W i t h i n , l/.20th of the Area of t h Bottom of, a Di s h C o n t a i n i n g 1343 E u p h a u s i i d s Counted , Counted 59 68 61 68 6 3 6 2 62 65 6 0 6 6 T o t a l = 957 Mean = 63.8 Expected number w i t h i n subsampling a r e a = 67.15 Chi-Square = 4.66 P r o b a b i l i t y of a l a r g e r Chi-Square (14 d f ) = .99 Counted 6 4 66 65 5 9 69 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0104480/manifest

Comment

Related Items