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UBC Theses and Dissertations

Performance evaluation of a suspension tray system for the culture of half-shell Pacific oysters, Crassostrea… Wiley, Kent Craig 1982

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PERFORMANCE EVALUATION OF A SUSPENSION TRAY SYSTEM FOR THE CULTURE OF HALF-SHELL PACIFIC OYSTERS, C r a s s o - s t r e a q i g a s IN TREVENEN BAY, BRITISH COLUMBIA by KENT CRAIG WILEY B . S c , The U n i v e r s i t y of G u e l p h , 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of B i o - R e s o u r c e E n g i n e e r i n g ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA J a n u a r y 19.81 © K e n t C r a i g W i l e y , 1981 i i In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department Of A g r i c u l t u r a l Mechanics The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date A p r i l 23, 1982 DE-6 (.3/81) i i i ABSTRACT PERFORMANCE EVALUATION OF A SUSPENSION TRAY SYSTEM FOR THE CULTURE OF HALF-SHELL PACIFIC OYSTERS, C r a s s o s t r e a q i g a s IN TREVENEN BAY, BRITISH COLUMBIA Kent W i l e y M.Sc. U n i v e r s i t y of B r i t i s h C o l u m b i a S u p e r v i s o r : D r . J.W. Z a h r a d n i k The o b j e c t i v e was t o d e s i g n and e v a l u a t e a S u s p e n s i o n o y s t e r t r a y u n i t t o o p t i m i z e c o n d i t i o n s n e c e s s a r y f o r s u c c e s s f u l c o m m e r c i a l c u l t u r e o f o y s t e r s i n B r i t i s h C o l u m b i a f o r t h e h a l f -s h e l l m a r k e t . The s u s p e n s i o n s y s t e m was t e s t e d a g a i n s t M a c N i c o l and N e s t i e r t r a y s p r e s e n t l y u s e d by t h e i n d u s t r y . U n i t s were l o c a t e d i n two s i t e s i n T r e v e n e n Bay. One l o c a t i o n was s h e l t e r e d •and ..calm; t h e o t h e r a n a t u r a l t i d a l raceway w i t h i n t e n s e c u r r e n t f l o w . The p u r p o s e was t o t e s t t h e a b i l i t y of t h e d e s i g n t o p r o v i d e more u n i f o r m g r o w t h , r e t a r d f o u l i n g , be e a s i l y h a n d l e d and be c o m m e r c i a l l y f e a s i b l e t o c o n s t r u c t . A s s e s s i n g t r a y p e r f o r m a n c e was b a s e d on m o n i t o r i n g s h e l l g r o w t h , c o n d i t i o n i n d e x , f o u l i n g o c c u r r e n c e , m a t e r i a l s h a n d l i n g and t h e c a p i t a l c o s t s of t h e s y s t e m s . F i e l d - e x p e r i m e n t a t i o n began i n June and t e r m i n a t e d i n O c t o b e r , 1979. The N e s t i e r u n i t had t h e b e s t s h e ' l l i v g r o w t h i n t h e c a l m e n v i r o n m e n t but d i s p l a y e d v a r i a t i o n i n growth among t r a y s i n t h e s t a c k , s u f f e r e d r e t a r d e d g r o w th i n t h e t i d a l r aceway and had s i g n i f i c a n t b a r n a c l e a c c u m u l a t i o n . The M a c N i c o l p e r f o r m e d on p a r w i t h t h e S u s p e n s i o n s y s t e m e x c e p t f o r v a r i a t i o n s i n g r o w t h due t o v e r t i c a l p o s i t i o n , t h e a c c u m u l a t i o n o f m u s s e l s and l o w e r e d p e r f o r m a n c e a t t h e t i d a l raceway s i t e . S u s p e n s i o n t r a y u n i t s p e r f o r m e d s i m i l a r i l y a t b o t h s i t e s , e x h i b i t e d l e s s v a r i a t i o n i n growth among t r a y s i n a s t a c k , r e t a r d e d f o u l i n g and p r o v e d t h e most e c o n o m i c a l l y f e a s i b l e s y s t e m f o r c o m m e r c i a l u s e . V TABLE OF CONTENTS Page ABSTRACT i i i TABLE OF CONTENTS V L I S T OF TABLES X L I S T OF FIGURES x i i ACKNOWLEDGEMENT x i v INTRODUCTION 1 BACKGROUND 4 BIOLOGY 4 ENVIRONMENTAL REQUIREMENTS AND CONSTRAINTS 7 T i d a l E x p o s u r e 7 S e a s o n a l i t y 7 T e m p e r a t u r e 8 Water V e l o c i t y a n d F o o d A v a i l a b i l i t y 10 S a l i n i t y 13 PH 13 S u b s t r a t e and O v e r c r o w d i n g 14 F o u l i n g , D i s e a s e a n d P r e d a t i o n 15 A) P r e d a t o r s 15 B) F o u l i n g 16 GROWING SYSTEMS 18 THEORY 22 PROPOSITIONS 22 ASSUMPTIONS 23 INFERENCES 23 FUNCTIONAL SPECIFICATIONS 24 t a b l e o f c o n t e n t s c o n t . v i OPERATIONAL FEATURES 25 STRATEGY BEHIND THE DEVELOPMENT OF THE REARING F A C I L I T Y 26 STRUCTURAL CONSIDERATIONS 28 MATERIAL CONSIDERATIONS 30 M e t a l s 30 A. G a l v a n i c A t t a c k 32 B. C r e v i c e A t t a c k 34 C. P i t t i n g , Impingement a n d C a v i t a t i o n 34 D. F o u l i n g and S c a l e F o r m i n g Compounds 35 M e t a l T y p e s 36 A. S t a i n l e s s S t e e l 36 B. N i c k e l A l l o y s 36 C. C o p p e r B a s e A l l o y s 37 D. Aluminum A l l o y s 39 E . C a r b o n a n d Low A l l o y S t e e l s 39 P l a s t i c s 40 A. M e c h a n i c a l B e h a v i o r o f P l a s t i c s 43 B. F a t i g u e A n a l y s i s 44 T y p e s o f P l a s t i c s U n d e r C o n s i d e r a t i o n - 46 A) N y l o n 4 6 B) A B S ( a c r y l o n i t r i l e - b u t a d i e n e s t y r e n e ) 46 C) V i n y l C h l o r i d e P o l y m e r s ( R i g i d ) 47 D) P o l y p r o p y l e n e 4 7 E) P o l y e t h y l e n e 51 M o o r i n g L i n e s 52 The T r a y 54 The S u s p e n s i o n S y s t e m 58 MATERIALS AND METHODS 61 EXPERIMENTAL APPARATUS 61 EXPERIMENTAL DESIGN 66 DATA COLLECTION 71 t a b l e o f c o n t e n t s c o n t . v i i RESULTS 74 QUALITATIVE RESULTS 74 F o u l i n g 74 S h e l l S c a r r i n g 75 M a t e r i a l s H a n d l i n g 78 M a t e r i a l P e r f o r m a n c e 78 QUANTITATIVE RESULTS 80 SHELL LENGTH 80 1. E n v i r o n m e n t Type Vs T r a y S y s t e m 82 2. E n v i r o n m e n t T y p e Vs T r a y S y s t e m 82 Vs V e r t i c a l P o s i t i o n 3. E n v i r o n m e n t T y p e V s T r a y S y s t e m 84 Vs V e r t i c a l P o s i t i o n Vs Time 4. E n v i r o n m e n t Type Vs T r a y S y s t e m 86 Vs Time 5. T r a y T ype 86 6. T r a y Type Vs Time 88 7. V e r t i c a l P o s i t i o n V s T r a y T y p e 88 8. V e r t i c a l P o s i t i o n Vs T r a y T ype 89 Vs Time 9. Time 89 SHELL WIDTH 90 1. E n v i r o n m e n t Type Vs Time 90 2. E n v i r o n m e n t Type Vs T r a y S y s t e m 90 3. E n v i r o n m e n t Type Vs T r a y S y s t e m 92 Vs Time 4. E n v i r o n m e n t Type Vs V e r t i c a l P o s i t i o n 94 5. E n v i r o n m e n t Type Vs V e r t i c a l P o s i t i o n 94 Vs Time 6. E n v i r o n m e n t T y p e Vs T r a y S y s t e m 94 Vs V e r t i c a l P o s i t i o n 7. Time 9 5 8. T r a y S y s t e m Vs Time 95 9. V e r t i c a l P o s i t i o n V s Time 95 10. T r a y S y s t e m Vs V e r t i c a l P o s i t i o n 95 table of contents cont. v i i i 11. Tray System Vs V e r t i c a l P o s i t i o n 95 Vs Time 12. Environment Type Vs Tray System 96 Vs V e r t i c a l Position Vs Time MEAT CONDITION 98 ECONOMICS 98 DISCUSSION 102 QUALITATIVE 102 Fouling 102 She l l Scarring 103 Materials Handling 104 Material Performance 104 Economics 105 QUANTITATIVE 106 Single Factor Interactions 106 1. Environment Type 106 2. Tray Type 106 3. V e r t i c a l P o s i t i o n 107 4. Time 107 Higher Level Interactions 107 1. Environmental Types Related To 107 V e r t i c a l P o s i t i o n In The Culture System 2. Tray System Related To Environmental 108 Location 3. Tray Systems Related To V e r t i c a l 110 Positioning MEAT CONDITION 112 CONCLUSION 114 1. Fouling 114 2. Materials Handling and Economics 114 3. Product Quality 115 table of contents cont. ix 4. Material Performance 115 5. Oyster Growth and Meat Condition 115 REFERENCES 119 APPENDICES Appendix A. ANOVA analysis 12 3 B. Plots of Relationshops To reveal 124 ef f e c t s of factors environment type, tray system, time and v e r t i c a l p o s i t i o n on growth i n s h e l l length. C. Plots of re l a t i o n s h i p s to reveal 147 ef f e c t s of factors environment type, tray system, time and v e r t i c a l p o s i t i o n on growth i n s h e l l width. D. ANOVA for meat condition. 170 E. Secchi disk and water temperature. 171 X LIST OF TABLES page Table 1. C r i t e r i a f or the development of an oyster 3 culture f a c i l i t y Table 2. Chemical composition of P a c i f i c oysters i n B.C. 5 Table 3. Measures of effectiveness. 27 Table 4. Areas of uncertainty. 27 Table 5. C l a s s i f i c a t i o n of t y p i c a l marine environments. 31 Table 6. Corrosion factors for carbon s t e e l immersed 33 i n seawater. Table 7. Differences to be considered when defining the 42 needs of a p l a s t i c s oriented structure. Table 8. The properties of r i g i d PVC. 48 Table 9. The mean length of s h e l l attained i n each of 81 te s t environments(95% confidence l i m i t s ) . Table 10. The mean lengths of s h e l l attained i n each of 81 the v e r t i c a l positions(95% confidence l i m i t s ) . Table 11. The mean lengths of s h e l l attained i n each 83 tray system i n each of the environment types (95% confidence l i m i t s ) . Table 12. The mean lengths of s h e l l attained i n each 87 tray system(95% confidence l i m i t s ) . Table 13. The mean widths of s h e l l attained i n each 91 environment type(95% confidence l i m i t s ) . Table 14. The mean widths of s h e l l attained i n each 91 tray system(95% confidence l i m i t s ) . Table 15. The mean widths of s h e l l attained i n each 91 of the v e r t i c a l tray positions(95% confidence l i m i t s ) . Table 16. The mean widths of s h e l l attained i n each 93 tray system In each of the environment types (95% confidence l i m i t s ) . l i s t of tables cont. x i Table 17. Economic analysis of the h a l f - s h e l l tray 100 culture systems tested(5 t r a y s / u n i t ) . Table 18. Indices of f a v o u r a b i l i t y associated with 118 tray systems tested. x i i LIST OF FIGURES page F i g . 1. Basic anatomical c h a r a c t e r i s t i c s of the 6 P a c i f i c oyster, Crassostrea gigas with the r i g h t valve removed(Quayle, 1969). F i g . 2. Seawater temperatures at a depth of 3 feet 9 i n Ladysmith Harbour, June to September, 1952 and 1953(Quayle, 1969). F i g . 3. Relationship between the standing crop 11 (Abundance) and diatoms and condition f a c t o r of P a c i f i c oysters i n Ladysmith Harbour(Quayle, 1969). F i g . 4. Relationship between length, volume and flow 12 i n the growth of oyster(Crassostrea v i r g i n i c a ) (Turner and Zahradnik, 1975). F i g . 5. Comparitive l o c a l i z e d attack(crevice corrosion 38 and p i t t i n g ) of some important marine a l l o y s as a function of seawater flow conditions(Fink and Boyd, 1970). F i g . 6. Weight l o r s of p l a s t i c samples of various shapes 4 9 incubated with Pseudomonas(Osmon et a l . , 1971). F i g . 7. Weight loss of p l a s t i c samples of various shapes 50 incubated with fungi(Osmon et a l . , 1971). F i g . 8. General arrangement of a single-screw extruder. 55 F i g . 9. The Suspension system. 57 F i g . 10. The assembled Suspension system. 59 F i g . 11. Close-up of the Suspension system and 60 attachment to. the support l i n e s . F i g . 12. The Nestier tray. 62 F i g . 13. The MacNicol tray. 63 F i g . 14. Water q u a l i t y monitoring devices. 64 l i s t of figures cont. x i i i F i g . 15. Davit system for handling the Suspension system. 6 5 F i g . 16. Location of study areas * 67 F i g . 17. The array i n environment 1. 69 F i g . 18. The array i n environment 2. 70 F i g . 19. Mesh siz e a l t e r a t i o n algae c o n t r o l . 76 F i g . 20. A l g a l f o u l i n g occurring on MacNicol trays 77 during the f a l l months. x i v ACKNOWLE DGEMENTS I wish, to thank the S p i r i t Cove Oyster Co-op, the Marine Resources Branch and Celco P l a s t i c s of Coquitlam for providing materials and f a c i l i t i e s to carry out the research. Thanks are also extended to Dr. J.W. Zahradnik and members of the thesis committee for t h e i r p a r t i c i p a t i o n and advice on t h i s research project. 1 INTRODUCTION The N o r t h A m e r i c a n o y s t e r i n d u s t r y began as an i n t e n s e f i s h e r y on t h e e a s t c o a s t . The i n d u s t r y i n i t i a l l y boomed but d e c l i n e s i n n a t u r a l p r o d u c t i o n became e v i d e n t . In 1910 s h e l l f i s h p r o d u c t i o n i n New E n g l a n d was 26,000,000 pounds v e r s u s 400,000 pounds i n 1975 ( T u r n e r and Z a h r a d n i k , 1975). Such a d e c l i n e may be a t t r i b u t e d t o an i n a d e q u a t e u n d e r s t a n d i n g of o y s t e r b i o l o g y and mismanagement of t h e n a t u r a l e n v i r o n m e n t . More s p e c i f i c a l l y , f a c t o r s s u c h a s ; t h e i n c o n s i s t e n c y of n a t u r a l s e t , h a t c h e r y c o s t s , h i g h m o r t a l i t y i n f i e l d p l a n t e d o y s t e r s , t h e l o n g g r o w i n g t i m e a s s o c i a t e d w i t h bottom c u l t u r e , p r e d a t o r c o n t r o l c o s t s , m a t e r i a l s h a n d l i n g , p o l l u t i o n and s o c i a l p r e s s u r e s have c o n t r i b u t e d t o d e c l i n e s i n p r o d u c t i o n . In B r i t i s h C o l u m b i a O s t r e a l u r i d a was t h e o r i g i n a l n a t i v e o y s t e r m a r k e t e d , as e a r l y as 1880 and was t h e o n l y s p e c i e s a v a i l a b l e u n t i l 1903 when t h e e a s t e r n o y s t e r C r a s s o s t r e a  v i r g i n i c a was i n t r o d u c e d . The p r o d u c t i o n of b o t h t h e s e s p e c i e s c e a s e d by 1936 and a c t i o n t a k e n t o r e v i v e o y s t e r i n g l e d t o t h e i n t r o d u c t i o n of t h e P a c i f i c o y s t e r , C r a s s o s t r e a g i g a s i n 1912-1913. T h i s h a r d y s p e c i e s became w i d e l y d i s t r i b u t e d t h r o u g h o u t many of t h e i n l e t s and b ays t o t h e p o i n t of e v e n t u a l l y e l i m i n a t i n g t h e need f o r f u r t h e r i m p o r t a t i o n of J a p a n e s e s e e d . The P a c i f i c o y s t e r c a u s e d a r e s u r g e n c e i n t h e p r o d u c t i v i t y of t h e i n d u s t r y i n B r i t i s h C o l u m b i a ( Q u a y l e , 1969). The b u s i n e s s c h a n g e d from a f i s h e r y t o a g r o u p of c u l t u r a l i s t s . U n f o r t u n a t e l y o y s t e r c u l t u r e i n t h i s p r o v i n c e i s f a c e d w i t h t h e same p r o b l e m s d i s c u s s e d p r e v i o u s l y , but r o o t e d p r i m a r i l y i n t h e a r e a s of 2 m a t e r i a l s h a n d l i n g and b i o f o u l i n g c o n t r o l . The g r o w e r s r e s o r t e d t o t r y i n g a v a r i e t y o f c u l t u r e t e c h n i q u e s t h a t have been p r o v e n s u c c e s s f u l e l s e w h e r e i n an a t t e m p t t o s o l v e t h e p r o b l e m a r e a s . T h i s t r a n s p l a n t a t i o n of t e c h n o l o g y p h i l o s o p h y and a f a i l u r e t o c o n s i d e r c r i t e r i a f o r a f a c i l i t y d e v e l o p m e n t i n t h i s p r o v i n c e ( T a b l e 1) has r e s u l t e d i n many " s o c i o - e c o n o m i c " h e a d a c h e s f o r t h e g r o w e r s . P r o b l e m s f a c i n g o y s t e r c u l t u r e i n B r i t i s h C o l u m b i a r e q u i r e s c i e n t i f i c i n v e s t i g a t i o n r a t h e r t h a n a t r i a l and e r r o r a p p r o a c h t o d e t e r m i n e t h e c a u s e s and f a c i l i t a t e t h e g e n e r a t i o n o f a l t e r n a t i v e s t o be t e s t e d . The p u r p o s e of t h i s r e s e a r c h i s t o d e v e l o p and e v a l u a t e an o y s t e r grow o u t f a c i l i t y a d a p t e d t o t h e b i o p h y s i c o - a q u a t i c e n v i r o n m e n t o f B r i t i s h C o l u m b i a t o a l l o w o p t i m a l economic and e f f i c i e n t c o m m e r c i a l c u l t u r e of o y s t e r s . The o b j e c t i v e s b e h i n d t h e r e s e a r c h i n t o t h e f a c i l i t y d e s i g n a r e t o : - r e d u c e t h e p r o b l e m a r e a s of f o u l i n g , waste a c c u m u l a t i o n and m a t e r i a l s h a n d l i n g - r e d u c e e n e r g y r e q u i r e m e n t s - m i n i m i z e l a b o u r c o s t s - m a i n t a i n a p p r e c i a t i v e r e t u r n s on i n v e s t m e n t by c o n s t r u c t i n g an i n e x p e n s i v e d u r a b l e f a c i l i t y - u s i n g e n v i r o n m e n t a l p a r a m e t e r s t o a d v a n t a g e - p r o v i d e an even d i s t r i b u t i o n o f f e e d - r e d u c e g r o w i n g t i m e t o market s i z e . The f a c i l i t y was d e v e l o p e d i n i t i a l l y u s i n g s y s t e m a n a l y s i s as a d e s i g n p r o c e d u r e and e v a l u a t i n g i t s p e r f o r m a n c e u s i n g o y s t e r g r o w th o v e r t i m e as t h e p r i m a r y i n d i c a t o r . 3 T a b l e 1. C r i t e r i a f o r t h e d e v e l o p m e n t o f an o y s t e r c u l t u r e f a c i l i t y . 1. S I T E SELECTION A) a v a i l a b l e a r e a and a c c e s s i b i l i t y B) f r e s h w a t e r s u p p l y C) e n v i r o n m e n t a l change i n c u r r e d by c u l t u r e c o n s t r u c t i o n D) h y d r o g r a p h i c and h y d r o l o g i c p a r a m e t e r s E) c l i m a t i c c o n d i t i o n s F) p u b l i c h e a l t h c o n s i d e r a t i o n s G) s p e c i e s b i o l o g y 2. MATERIALS A) a v a i l a b i l i t y ( c h o i c e ) B) d u r a b i l i t y C) f o u l i n g r e s i s t a n c e D) c o s t s 3. LABOUR A) a v a i l a b i l i t y B) c o s t C) s k i l l s 4. GENERAL COSTS A) i n i t i a l i n v e s t m e n t B) o p e r a t i n g c o s t s C) r e t u r n s P) m a r k e t i n g 5. LEGAL IMPLICATIONS AND SOCIAL CONSTRAINTS 6. PRODUCTIVITY A) y i e l d B) g r o w t h p e r i o d 4 BACKGROUND BIOLOGY O y s t e r s a r e g r e g a r i o u s , but s e s s i l e i n t h e a d u l t s t a g e and a r e h i g h l y f e c u n d . They have a s h o r t r e p r o d u c t i v e c y c l e , a r e l a t i v e l y f a s t g r o w t h r a t e i f c u l t u r e d p r o p e r l y and an a v a i l a b l e p r o t e i n c o n t e n t ( T a b l e 2). T h e i r p o s i t i o n i n t h e f o o d c h a i n as o b l i g a t o r y h e r b i v o r o u s f i l t e r f e e d e r s a l o n g w i t h i n c r e a s i n g market demands has e l e v a t e d them t o p r o b a b l y t h e most w i d e l y c u l t u r e d a q u a t i c o r g a n i s m . The i n c r e a s i n g demand combined w i t h and an o y s t e r s h o r t a g e has r a i s e d t h e u n i t p r i c e of b o t h s h u c k e d o y s t e r s and o y s t e r s s e r v e d on t h e h a l f - s h e l l . The P a c i f i c o y s t e r i s c h a r a c t e r i z e d by a f l e s h y body e n c l o s e d w i t h i n two s h e l l s o r v a l v e s . The s h e l l s a r e h i n g e d a t t h e a n t e r i o r or umbonal end. The h i n g e a c t s t o s p r i n g t h e s h e l l s a p a r t and t h i s i s o p p o s e d by t h e s i n g l e a d d u c t o r m u s c l e . The f l e s h y body i s e n v e l o p e d by t h e m a n t l e formed of two r i g h t and l e f t l o b e s t h a t f u s e i n t h e a n t e r i o r r e g i o n n e a r t h e mouth. The m a n t l e e x t r a c t s c a l c a r e o u s m a t e r i a l from s e a w a t e r u s e d i n s h e l l d e p o s i t i o n . O y s t e r s f e e d and r e s p i r e s i m u l t a n e o u s l y by e n l a r g e d g i l l s p o s s e s s i n g an e f f i c i e n t c i l i a t e d l a t t i c e - w o r k of g r e a t e l a b o r a t i o n and e f f i c i e n c y t h a t c r e a t e s a p o w e r f u l water c u r r e n t f r o m w h i c h g a s e s a r e e x c h a n g e d and p a r t i c l e s s i e v e d and p a s s e d t o t h e mouth. T h e s e b a s i c a n a t o m i c a l c h a r a c t e r i s t i c s a r e i l l u s t r a t e d i n f i g u r e 1. 5 Average Solids c a l c u l a t e d on moisture-free f l e s h weight (g) Moisture (%) Protein (%) Glycogen (X) Fat {%) Ash (%) Balance Feb. 9 18.90 78.20 47.80 20.50 10.66 8.66 12.36 Apr.12 18.30 79.84 46.65 24.95 12.94 7.62 7.84 May 30 16.72 77.50 47.70 23.80 13.31 6.87 10.32 Aug. 3 11.07 81.47 54.60 11.85 15.75 7.80 10.00 Oct. 3 17.40 80.00 52.20 14.25 11.72 5.78 16.05 Dec. 7 20.10 83.37 49.90 20.05 13.08 8.42 9.45 Feb. 6 20.00 79.89 49.60 19.00 15.27 6.81 9.32 Table 2. Chemical composition of P a c i f i c oysters in B.C.(Balance represents material not accounted f o r , and i s probably the r e s u l t of destruction of some of the carbohydrate by chemical action in the a n a l y t i c a l procedure)(Quayle, 1969). d o r s a l * K U S LEFT MANTLE MARGIN ventrol EXHAIAKT CHAMBER / AN-JS i L E F T MANTLE INHALANT CHAMBER F i g . 1. Basic anatomical c h a r a c t e r i s t i c s of the P a c i f i c oyster, Crassostrea gigas with the r i g h t valve removed(Quayle, 1969). 7 ENVIRONMENTAL REQUIREMENTS AND CONSTRAINTS The P a c i f i c o y s t e r i s a b l e t o w i t h s t a n d wide v a r i a t i o n s i n e n v i r o n m e n t a l c o n d i t i o n s . The o y s t e r i s a b l e t o d e t e c t t h e s e c h a n g e s u s i n g s e n s o r s l o c a t e d on t h e l a b i a l p a l p s ( D w i v e d y , 1973). However, t h e grower s h o u l d be aware of t h e o p t i m a l e n v i r o n m e n t a l r e q u i r e m e n t s o f t h e o y s t e r f o r g r o w t h and d e v e l o p m e n t t o b e t t e r meet optimum c o n d i t i o n s - a t t h e s i t e and i n r e a r i n g f a c i l i t i e s . G rowth, s u r v i v a l and q u a l i t y depend on t i d a l e x p o s u r e , s e a s o n a l i t y of l o c a t i o n , s u b s t r a t e , pH, t e m p e r a t u r e , s a l i n i t y , w a t e r v e l o c i t y , d i s e a s e , p r e d a t i o n , f o u l i n g , d e n s i t y and f o o d a v a i l a b i l i t y . C o l l e c t i v e l y t h e s e f a c t o r s i n t e r a c t t o d e t e r m i n e t h e f a t e of a c u l t u r e d o y s t e r . T i d a l E x p o s u r e Growth r a t e s a r e u s u a l l y l o w e r i n h i g h e r i n t e r t i d a l l e v e l s ( Q u a y l e , 1969). Q u a y l e ( l 9 6 9 ) f o u n d t h a t o y s t e r s e x p o s e d f o r l o n g e r t h a n 5 h o u r s p e r day showed a marked d r o p i n growth r a t e and t h e maximum growth r a t e o c c u r r e d c l o s e s t t o t h e z e r o t i d e l e v e l . M a i n t a i n i n g t h e o y s t e r i n a s u b t i d a l zone or c o n t i n u a l l y submerged a l l o w s c o n t i n u o u s f e e d i n g and improved g r o w t h r a t e . S e a s o n a l i t y Growth i s i n f l u e n c e d by s e a s o n a l and t e m p e r a t u r e c h a n g e s . An e l e v a t e d water t e m p e r a t u r e i n t h e summer r e s u l t s i n i n c r e a s e d f o o d s u p p l y and a v a i l a b i l i t y of c a l c i u m f o r d e p o s i t i o n . T h e r f o r e t h e g r o w t h o f t h e P a c i f i c o y s t e r i n B r i t i s h C o l u m b i a i s 8 e s s e n t i a l l y a summer phenomenon(Quayle, 1969). T e m p e r a t u r e Growth r a t e i s p r o p o r t i o n a l t o t e m p e r a t u r e . Q u a y l e ( l 9 5 1 ) f o u n d t h e P a c i f i c o y s t e r had a h i g h g r o w t h r a t e a t water t e m p e r a t u r e s between 15-19 d e g r e e s C e l s i u s . Q u a y l e a l s o f o u n d t h a t more f o o d and water i s t a k e n i n a t t h e s e optimum t e m p e r a t u r e s . M e d c o f ( l 9 6 l ) a l s o d e t e r m i n e d t h a t i f water t e m p e r a t u r e becomes t o o warm g r o w t h becomes so r a p i d t h a t p o o r l y c u p p e d t h i n s h e l l s r e s u l t . Growth i s " e s s e n t i a l l y z e r o " a t t e m p e r a t u r e s below 10 d e g r e e s C e l s i u s ( B a r d a c h e t a l . , 1972). F i g u r e 2 c o n t a i n s t e m p e r a t u r e d a t a f o r L a d y s m i t h H a r b o u r . I t c a n be u s e d as a f i n g e r p r i n t f o r s i m i l a r t e m p e r a t u r e p a t t e r n s i n t h e i n l e t s a l o n g t h e c o a s t . The optimum t e m p e r a t u r e s f o r gr o w t h o c c u r d u r i n g t h e months of June t o September. F i g . 2. Seawater temperatures at a depth of 3 f e e t in Ladysmith Harbour, June to September, 1952 and 1953(Quayle, 1969). 10 Water V e l o c i t y and Food A v a i l a b i l i t y F e e d i n g r a t e s a r e i n f l u e n c e d by w ater v e l o c i t y and f o o d a v a i l a b i l i t y as w e l l as t e m p e r a t u r e ( W a l n e , 1974). A h i g h c o n c e n t r a t i o n of s u s p e n d e d m a t e r i a l i n t h e form o f s i l t or an "overabundance o f m i c r o - o r g a n i s m s can c a u s e o y s t e r s t o r e d u c e o r c e a s e f i l t r a t i o n . I t i s b e l i e v e d t h a t dense c o n c e n t r a t i o n s of s u s p e n d e d m a t t e r can i n t e r f e r e w i t h t h e pumping p r o c e s s of t h e g i l l s . R i c h a l g a l g r o w t h , p a r t i c u l a r l y a t s i t e s w i t h low f l u s h i n g r a t e s , can r e s u l t i n a b u i l d - u p of b a c t e r i a and a f f e c t t h e o y s t e r ' s g i l l s ( L i p o p s k y and Chew, 1972). The c o n d i t i o n of t h e o y s t e r s i s a l s o l i n k e d w i t h t h e f o o d a v a i l a b i l i t y a t t h e s i t e . S i t e s w i t h h i g h p r i m a r y p r o d u c t i v i t y v a l u e s p r o v i d e an e x c e l l e n t f o o d s o u r c e f o r o y s t e r s . Growth and f o o d r e m o v a l r a t e s . i n c r e a s e w i t h i n c r e a s e d f o o d c o n c e n t r a t i o n ( W a l k e r and Z a h r a d n i k , 1976). F i g u r e 3 • shows t h e improvement i n t h e c o n d i t i o n f a c t o r w i t h i n c r e a s i n g p r i m a r y p r o d u c t i o n of d i a t o m s . The c o n d i t i o n f a c t o r i s t h e r e l a t i o n s h i p between t o t a l volume of whole o y s t e r s and t h e volume of s h e l l c a v i t y . The c o n d i t i o n f a c t o r i s o b t a i n e d by t h e f r a c t i o n : t h e d r y meat w e i g h t d i v i d e d by t h e u n s h u c k e d w e i g h t minus t h e s h e l l w e i g h t and m u l t i p l y i n g t h e e n t i r e e x p r e s s i o n by 1000. The a v e r a g e f e e d i n g r a t e i n c r e a s e s as water f l o w i n c r e a s e s o v e r t h e o y s t e r , s t i m u l a t i n g them t o f e e d more r a p i d l y ( W a l n e , 1974). Water c u r r e n t s a l s o c a r r y away waste, s u p p l y oxygen and d i s t r i b u t e g r e a t e r amounts of f o o d p e r u n i t t i m e . F i g u r e 4 i l l u s t r a t e s t h e r e l a t i o n s h i p of g r o w t h and f l o w r a t e . T h e r e f o r e a grow-out f a c i l i t y l o c a t e d a t a s i t e t h a t t a k e s a d v a n t a g e of t i d a l f l o w and d e s i g n e d t o a l l o w optimum exchange o f w ater 1 i. F i g . 3. Relationship between the standing crop(abundance) of diatoms and condition factor of P a c i f i c oysters i n Ladysmith Harbour(Quayle, 1969). 12 Growth (yr.) F i g . 4. R e l a t i o n s h i p b etween l e n g t h , volume and f l o w i n t h e growth of o y s t e r s ( C r a s s o s t r e a v i r g i n i c a ) ( T u r n e r " and Z a h r a d n i k , 1975TT " — < l u r n e r 1 3 between o y s t e r o y s t e r and e n v i r o n m e n t s h o u l d p r o v i d e b e t t e r g r o w t h . S a l i n i t y S a l i n i t y i n f l u e n c e s t h e g r o w t h and s h e l l q u a l i t y of C r a s s o s t r e a q i g a s . T h e i r o v e r a l l c o n d i t i o n i f h e l d a t s a l i n i t i e s l e s s t h a n 1Oppt f o r more t h a n two weeks w i l l d r o p ( Q u a y l e , 1969). P e r i o d i c f l o o d i n g by major r i v e r s d r a i n i n g i n t o e s t u a r i e s can k i l l an o y s t e r p o p u l a t i o n i f low s a l i n i t y i s p r o l o n g e d ( B u t l e r , 1952; Andrews, Haven and Q u a y l e , 1959). But, t h e P a c i f i c o y s t e r i s a b l e t o w i t h s t a n d s a l i n i t i e s a s h i g h as 33ppt and s u r v i v e f r e s h w a t e r e x p o s u r e up t o 8 h o u r s p e r d a y ( Q u a y l e , 1969). S h e l l q u a l i t y i s a d v e r s e l y a f f e c t e d by extreme h i g h and low s a l i n i t y . C o n d i t i o n s of low s a l i n i t y p r o d u c e a smooth s o f t . s h e l l and h i g h s a l i n i t y p r o d u c e s a h a r d , b r i t t l e s h e l l ( Q u a y l e and S m i t h , 1978). G a m e t o g e n e s i s and spawning i s i n h i b i t e d by p r o l o n g e d s a l i n i t y l e s s t h a n 6 p p t ( B u t l e r , 1949). Q u a y l e ( l 9 6 9 ) r e p o r t e d t h e l e v e l f o r f e e d i n g , g r o w t h and b r e e d i n g i s between 20-30 p p t . S a l i n i t y r e q u i r e m e n t s a r e e a s i l y met i n t h e c o a s t a l w a t e r s o f t h e p r o v i n c e . P r o b l e m s c a n be e n c o u n t e r e d when d e a l i n g w i t h e s t u a r i n e e n v i r o n m e n t s . PH P r o p e r pH i s g e n e r a l l y not a p r o b l e m i n t h e m a r i n e e n v i r o n m e n t s i n c e t h e pH of t h e open ocean r a n g e s between 7.5-8.5 and may d e c r e a s e t o 7.0 or l o w e r i n t i d e p o o l s , bays and e s t u a r i e s due t o d i l u t i o n a n d / o r t h e p r o d u c t i o n of h y d r o g e n s u l p h i d e ( S v e r d r u p , J o h n s o n and F l e m i n g , 1942). The pH r a n g e f o r 1 4 normal growth of C r a s s o s t r e a v i r g i n i c a i s 6.75-8.75 w i t h g r o w th r a t e d r o p p i n g a t a pH below 6 . 7 5 ( C a l a b r e s e and D a v i s , 1966). Low pH . a l s o i n h i b i t s s p a w n i n g ( P r y t h e r c h , 1928). A d u l t A m e r i c a n o y s t e r s ( C r a s s o s t r e a v i r g i n i c a ) kept a t a pH of 4.25 r e m a i n e d open an a v e r a g e of 76% of t h e t i m e but pumped o n l y 10% as much water as c o n t r o l s ; o y s t e r s a t pH 6.75-7.00 i n t i a l l y pumped more v i g o r o u s l y t h a n c o n t r o l s but t h e r a t e l a t e r d e c r e a s e d ( L o o s a n o f f and Tomers, 1947). S u b s t r a t e and O v e r c r o w d i n g S h e l l shape i s i n f l u e n c e d by t h e t y p e of s u b s t r a t e and d e g r e e of c r o w d i n g . A h a r d s u r f a c e p r o d u c e s a f l u t e d , r o u n d and deep shelKQuayle and S m i t h , 1978). O y s t e r s grown d e n s e l y l e a d t o poor g r o w th and m o r t a l i t y due t o a i n h i b i t i o n o f t h e f l o w of p h y t o p l a n k t o n o v e r t h e o y s t e r , waste r e m o v a l and r e n e w a l of o x y g e n . An o v e r p o p u l a t i o n of o y s t e r s i n a s h e l t e r e d bay o r i n l e t i s t h o u g h t t o a f f e c t p r i m a r y p r o d u c t i o n by r e d u c i n g t h e amount of f o o d a v a i l a b l e t o e a c h o y s t e r . Uyeno e t a l . ( l 9 7 0 ) f o u n d t h a t dense a g g r e g a t i o n s of f i l t e r f e e d e r s and t h e i r m e t a b o l i c w a s t e s can l e a d t o l o c a l r e d u c t i o n s i n oxygen and p h y t o p l a n k t o n c o n c e n t r a t i o n s . L a r g e dense c u l t u r e o p e r a t i o n s i n a r e a s h a v i n g l i m i t e d water c i r c u l a t i o n r e l e a s e s u c h l a r g e amounts of e x c r e t o r y p r o d u c t s t h a t t h e y may have t o be moved p e r i o d i c a l l y t o a v o i d s e l f - i n h i b i t i o n of g r o w t h . F a e c e s and p s e u d o - f a e c e s r e q u i r e oxygen f o r b i o d e g r a d a t i o n c a u s i n g low oxygen and h i g h ammonia and t h e p o s s i b i l i t y o f t h e d e v e l o p m e n t of p o i s o n o u s h y d r o g e n s u l p h i d e where s h a l l o w water and poor f l u s h i n g i s p r e s e n t ( K o r r i n g a , 1976). T h i s may a c c o u n t f o r t h e o b s e r v e d 1 5 s l o w e r g r o w t h i n mid s e c t i o n s o f t r a y s or s t r i n g s o f s h e l l s ( K o r r i n g a , 1976). The number o f o y s t e r a r e an i m p o r t a n t v a r i a b l e i n t e r m s of p e r f o r m a n c e and s i z e f o r h a n d l i n g . E s t i m a t i o n of t h e s i z e of an o y s t e r p o p u l a t i o n t h a t an a r e a c a n s u p p o r t s h o u l d be made b e f o r e any l a r g e s c a l e v e n t u r e i s l a u n c h e d . F o u l i n g , D i s e a s e and P r e d a t i o n Under n a t u r a l c o n d i t i o n s o y s t e r s a r e k i l l e d or crowded out by o t h e r m a r i n e a n i m a l s r e d u c i n g q u a l i t y , p e r c e n t s u r v i v a l o r g r o w t h r a t e . In t h e c u l t u r e s i t u a t i o n f o u l i n g c o m p e t i t o r s can i n h i b i t t h e d i s t r i b u t i o n of f o o d t h r o u g h t h e u n i t and i n t e r f e r e with- t h e r e m o v a l of w a s t e s . F o u l i n g , d i s e a s e and p r e d a t i o n d e c r e a s e t h e p r o d u c t i v i t y , compete f o r f o o d and s p a c e and i n c r e a s e t h e r e s i s t a n c e t o f r e e f l o w of w a t e r t h r o u g h t h e f a c i 1 i t y . A ) P r e d a t o r s O y s t e r d r i l l s a r e u n i v a l v e s n a i l s t h a t a c t i v e l y p r e y on s h e l l f i s h . They p o s s e s s an e x t e n d a b l e t o o t h e d r a s p i n g a p p a r a t u s c a p a b l e of d r i l l i n g a h o l e t h r o u g h t h e s h e l l and t e a r i n g a t t h e meat. T h e r e a r e o n l y two s p e c i e s i n B r i t i s h C o l u m b i a and b o t h were i n t r o d u c e d f r o m J a p a n ( O c e n e b r a j a p o n i c a ) and t h e A t l a n t i c c o a s t ( U r o s a l p i n x c i n e r a ). O c e n e b r a j a p o n i c a i s f o u n d i n B oundary Bay, L a d y s m i t h H a r b o u r , C r o f t o n , T h e t i s I s l a n d and Comox(Quayle, 1969). U r o s a l p i n x c i n e r a i s f o u n d i n Boundary Bay o n l y ( Q u a y l e , 1969). D r i l l s do not p ose a s e r i o u s t h r e a t t o t h e i n d u s t r y a t p r e s e n t . . • 16 The b o r i n g sea worm( P o l y d o r a c i l i t a t a ) i s a p o l y c h a e t e h a v i n g a fr e e s w i m m i n g l a r v a t h a t s e t t t l e s on t h e s u r f a c e of o y s t e r s . They make s h a l l o w burrows n e a r t h e s h e l l edge and sometimes may p e r f o r a t e t h e s h e l l . The o y s t e r r e - d i r e c t s growth t o r e p a i r t h e damage. The p a r a s i t i c c o p epod( M y t i c o l a o r i e n t a l i s ) was i n t r o d u c e d from J a p a n w i t h t h e i m p o r t a t i o n of s e e d o y s t e r s . I t i s a m i n u t e o r g a n i s m o c c u r r i n g i n t h e s m a l l i n t e s t i n e of v a r i o u s m o l l u s c a n s p e c i e s u s u a l l y n e a r t h e anus where i t h o l d s i t s p o s i t i o n by s p e c i a l h o o k s . The h i g h e s t r e c o r d e d i n f e c t o n r a t e o f P a c i f i c o y s t e r s i s 20%, but so f a r t h e r e i s no e v i d e n c e t h a t i t c a u s e s m o r t a l i t y or has a s e r i o u s e f f e c t on o y s t e r c o n d i t i o n ( Q u a y l e , 1969). S t a r f i s h pose a s e r i o u s t h r e a t t o b o t t o m c u l t u r e o p e r a t i o n s . The a c t i v e s t a r f i s h p o p u l a t i o n on t h e c o a s t i s made up of t h e o c h r e s t a r ( P i s a s t e r o c h r o c e u s ), t h e p i n k s t a r ( P i s a s t e r b r e v i s p i n u s ), t h e m o t t l e d s t a r ( E v a s t e r i a s t r o s c h e l l i ) and t h e sun s t a r ( P y c n o p o d i a h e l i a n t h o i d e s ). The s t a r f i s h p r o b l e m i s e l i m i n a t e d w i t h o f f - b o t t o m c u l t u r e . T h e r e a r e t h r e e s p e c i e s o f c r a b s t h a t open and f e e d on o y s t e r s and o y s t e r s e e d by c r a c k i n g t h e s h e l l edges w i t h t h e i r c l a w s . They have not p o s e d a s e r i o u s t h r e a t b u t o c c a s i o n a l l y have been d e s t r u c t i v e t o young s e e d . A g a i n , t h e p r o b l e m i s e l i m i n a t e d i n o f f - b o t t o m c u l t u r e . B ) F o u l i n g O t h e r o r g a n i s m s s u c h a s : sea s q u i r t s , shipworms, b a r n a c l e s , m u s s e l s , tubeworms, h y d r o i d s , a l g a e and g a s t r o p o d s compete f o r 1 7 f o o d and s p a c e w i t h the o y s t e r . T h e i r abundance c a n crowd out t h e o y s t e r , a d v e r s e l y a f f e c t s h e l l shape and meat q u a l i t y of t h o s e d e s t i n e d f o r t h e h a l f - s h e l l m a r k e t . At p r e s e n t t h e c o n t r o l of f o u l i n g r e q u i r e s i n t e n s e l a b o u r and m a t e r i a l s h a n d l i n g . An e f f i c i e n t means of f o u l i n g c o n t r o l i s t h e key t o m i n i m i z e l a b o u r and m a t e r i a l s h a n d l i n g i n t e n s e n e s s of h a l f - s h e l l o p e r a t i o n s . 18 GROWING SYSTEMS The P a c i f i c o y s t e r may be grown i n - s i t u or i n l a n d b a s e d c o n t a i n m e n t s w i t h s e a w a t e r pumped i n . The a u t h o r i s of t h e o p i n i o n t h a t l a n d base o p e r a t i o n s m i g h t i n c u r h i g h c a p i t a l c o s t s and o p e r a t i n g e x p e n s e s p r o v i n g t o be u n e c o n o m i c a l i n B r i t i s h C o l u m b i a . I n - s i t u c u l t i v a t i o n e l i m i n a t e s a c e r t a i n d e g r e e of r e l i a n c e upon a d v a n c e d t e c h n o l o g y and t h e back up r e q u i r e m e n t s t h a t must accompany i t . C o s t s c a n be m i n i m i z e d by u s i n g t h e n a t u r a l e n v i r o n m e n t t o i t s f u l l e s t whenever p o s s i b l e . F o r t u n a t e l y use of f o r e s h o r e by o y s t e r c u l t u r a l i s t s i n t h e p r o v i n c e has n o t r e a c h e d a s o c i a l c o n f r o n t a t i o n s t a g e as on t h e e a s t c o a s t o f N o r t h A m e r i c a and i n W a s h i n g t o n and Oregon s t a t e s . I n t h e f u t u r e s u c h p r e s s u r e s may f o r c e t h e use of l a n d b a s e d s y s t e m s . T r a d i t i o n a l l y o y s t e r s have been grown on t h e bottom and s h u c k e d f o r t h e i r meat. The bottom c u l t u r e of o y s t e r s has a l o n g h i s t o r y i n F r a n c e , P o r t u g a l and B r i t a i n . E v e n t u a l l y t h e E u r o p e a n t e c h n i q u e s were t r a n s f e r r e d t o t h e e a s t c o a s t o f N o r t h A m e r i c a w i t h an added d e g r e e of m e c h a n i z a t i o n . In New E n g l a n d c o n s i d e r a b l e i n v e s t m e n t has gone i n t o d r e d g e s , v e s s e l s and d i v e r s f o r b e n t h i c o y s t e r c u l t u r e . The r e c e n t more l u c r a t i v e h a l f - s h e l l t r a d e c a t e r s t o t h e gourmet c u i s i n e o f r e s t a u r a n t s and meat c o u n t e r s . O y s t e r s s e r v e d on t h e h a l f - s h e l l b r i n g a h i g h e r p r i c e t h a n s h u c k e d meat, but t h e grower must a d o p t t e c h n i q u e s t h a t w i l l p r o d u c e a q u a l i t y s h e l l . F o r t h e h a l f - s h e l l m a r k e t , t h e p l a c i n g of s e e d o y s t e r s on t h e b o t t o m i n N o r t h A m e r i c a has n o t been s u c c e s s f u l due t o s t a r f i s h p r e d a t i o n , s i l t a t i o n , i n t e n s e c u l t i v a t i o n r e q u i r e m e n t s 19 and e x p o s u r e t o waves and i c e ( G a l t s o f f , 1956; Shaw, 1962 and E n g l e , 1966). I n t e n s e b o t t o m c u l t u r e e n t a i l s d e c l u s t e r i n g , t h i n n i n g s , t r a n s p l a n t i n g and r e s u l t e d i n a c o m p l i c a t e d c o s t l y o p e r a t i o n . The m a t e r i a l s h a n d l i n g , l a b o u r demands, t h e need f o r " u n u s u a l " t e c h n o l o g y and t h e l o n g g r o w i n g p e r i o d r a i s e q u e s t i o n s as t o t h e v i a b i l i t y o f bottom c u l t u r e . S u b s t r a t e v a r i a b i l i t y , s i l t a t i o n , b e n t h i c p r e d a t o r s , wave a c t i o n and f o u l i n g r e d u c e t h e p o s s i b i l i t i e s o f p r o d u c i n g a q u a l i t y o y s t e r . The b o t t o m c u l t u r e of h a l f - s h e l l o y s t e r s i s not p r a c t i c a l i n B r i t i s h C o l u m b i a . The m a j o r i t y of p r i m e t i d a l f l a t s a r e l o c a t e d i n e s t u a r i n e e n v i r o n m e n t s i n t h e s o u t h w e s t e r n p o r t i o n of t h e p r o v i n c e . U n f o r t u n a t e l y t h e s e a r e a s a r e s u c c u m b i n g t o t h e p r e s s u r e s o f e n c r o a c h i n g i n d u s t r y , and u r b a n i z a t i o n . T h i s has f o r c e d c l o s u r e of many p r o d u c t i v e o y s t e r g r o u n d s due t o p o l l u t i o n by d o m e s t i c and i n d u s t r i a l i n f l u e n c e s . By 1970 a p p r o x i m a t e l y 40% of t h e p r o v i n c e s v i a b l e o y s t e r g r o u n d s were c l o s e d as a r e s u l t o f s u c h p o l l u t i o n ( M a t t h i e s s e n , 1970). Charman and S m i t h (1976) i n d i c a t e d t h a t t h e r e i s l i t t l e s u i t a b l e i n t e r t i d a l g r o u n d r e m a i n i n g and more e x t e n s i v e and e f f i c i e n t use i s p o s s i b l e o n l y by o f f bo t t o m c u l t u r e t e c h n i q u e s . C l e a n o y s t e r g r o u n d must a l s o be b r o u g h t i n t o p r o d u c t i o n f u r t h e r up t h e c o a s t of V a n c o u v e r I s l a n d and t h e m a i n l a n d t o e s c a p e t h e impact of d o m e s t i c and i n d u s t r i a l p o l l u t i o n . T h e r e has been an i n c r e a s i n g i n t e r e s t i n o f f bo t t o m c u l t u r e i n N o r t h A m e r i c a o v e r t h e l a s t d e c a d e due t o t h e l o s s of o y s t e r b o t t o m s , an o y s t e r s h o r t a g e , i n c r e a s e d m arket v a l u e s and t h e c o m m e r c i a l i n t e r e s t i n o y s t e r s e e d p r o d u c t ion(Shaw, 1969). I t r e p r e s e n t s a method of c o n t r o l l i n g p r e d a t i o n , s i l t a t i o n , 20 p e r m i t t i n g t h e f a r m i n g of a g r e a t e r number of a n i m a l s p e r u n i t a r e a . The o f f b o t t o m t e c h n i q u e s p r o v i d e f o r a t h r e e d i m e n s i o n a l use of t h e e n t i r e water column w i t h y i e l d s as much as t e n t i m e s t h a t of b o t t o m c u l t u r e ( Q u a y l e , 1971). S t u d i e s a t Cape Cod, M a s s a c h u s e t t s c o n f i r m e d growth r a t e s were d o u b l e t h a t of b o t t o m c u l t u r e ( C r a s s o s t r e a v i r g i n i c a ), meat q u a l i t y was i m p r o v e d , m o r t a l i t y r e d u c e d , i n c r e a s e d p r o d u c t i o n p e r u n i t a r e a and t h a t s u c h t e c h n i q u e s were e c o n o m i c a l l y f e a s i b l e ( S h a w , 1962; 1963; 1965; Shaw and McCann, 1963). Q u a y l e ( 196-9) f o u n d t h a t C r a s s o s t r e a g i g a s c u l t u r e d o f f t h e bottom r e d u c e d t h e g r o w i n g time t o m a r k e t a b l e s i z e from t h r e e y e a r s t o one t o two y e a r s . A d d i t i o n a l s t u d i e s r e c o n f i r m e d f a s t e r g r o w t h r a t e s , i m p roved meat c o n d i t i o n , h i g h e r p e r c e n t s u r v i v a l and f o r m a t i o n of a w e l l shaped, d e e p l y c u p p e d s h e l l w i t h t h e o f f b o t t o m c u l t u r e of C r a s s o s t r e a g i g a s ( Q u a y l e , 1971)'. T e c h n i q u e s of o f f b o t t o m c u l t u r e may e n t a i l u s i n g v a r i o u s t y p e s o f r a c k s o r t r a y s . Rack c u l t u r e i s p r a c t i c e d i n A u s t r a l i a where i t r e d u c e d t h e p r o b l e m s o f b o t t o m c o n s i s t e n c y , t i d a l h e i g h t l i m i t a t i o n s and t h e p r e d a t o r p r o b l e m s . T h i s t e c h n i q u e i s not p r a c t i c a l i n B r i t i s h C o l u m b i a due t o t h e l a c k of e x t e n s i v e t i d a l f l a t s and t h e p r e s e n c e o f an a c t i v e s t a r f i s h p o p u l a t i o n . T r a y c u l t u r e i s a r e c e n t d e v e l o p m e n t i n N o r t h A m e r i c a on b o t h c o a s t s u s i n g M a c N i c o l , N e s t i e r o r i n d i v i d u a l grower t r a y d e s i g n s . T r a y c u l t u r e o f f e r s p r o t e c t i o n of t h e o y s t e r c r o p and a f a s t e r g r o w t h r a t e i f t h e t r a y s a r e h e l d o f f t h e s e a b e d . P a r s o n s ( 1 9 7 4 ) s u g g e s t e d t h a t t h e water f l o w above and below t h e o y s t e r s grown o f f b o t t o m c o n t r i b u t e s t o t h e f a s t e r g r o w t h . The " a c c e p t e d " p r a c t i c e i s t o s t a c k t r a y s i n l a y e r s of f i v e 21 or s i x s u s p e n d e d i n t h e water column by r a f t o r l o n g l i n e f l o a t a t i o n . The r a f t t e c h n i q u e i s s e l f e x p l a n a t o r y but i t i s wo r t h m e n t i o n i n g t h a t i t r e q u i r e s s h e l t e r e d a r e a s and a f a i r c a p i t a l i n v e s t m e n t i n m a t e r i a l s and a s s e m b l y . The l o n g l i n e t e c h n i q u e i s a means o f e x p l o i t i n g m a r g i n a l a r e a s . I t i s c h e a p e r t o c o n s t r u c t , t o m a i n t a i n and w i t h s t a n d s w e a t h e r i n g . The c a p i t a l c o s t s a v i n g s and g r e a t e r l i f e e x p e c t a n c y compensate f o r t h e d i s a d v a n t a g e of t h e u n i t s p e r h a p s b e i n g h a r d e r t o h a n d l e when i t comes t o l i f t i n g f o r c l e a n i n g , s o r t i n g and h a r v e s t i n g . The e x i s t i n g t r a y d e s i g n s have not been w i t h o u t p r o b l e m s . D i f f e r e n t g r o w t h r a t e s have been known t o o c c u r t h r o u g h t h e v e r t i c a l s e r i e s of t r a y s . F u r t h e r p r o b l e m s have a l s o been e n c o u n t e r e d w i t h b i o f o u l i n g t h a t r e s t r i c t s water c i r c u l a t i o n and s u b s e q u e n t l y f o o d d i s t r i b u t i o n . T h e r e e x i s t e d a d e f i n i t e need f o r a t r a y d e s i g n t o meet t h e demands of f o u l i n g c o n t r o l , a d e q u a t e water c i r c u l a t i o n and be e c o n o m i c a l l y f e a s i b l e t o c o n s t r u c t . 22 THEORY PROPOSITONS 1. The gr o w t h and s u r v i v a l of s h e l l f i s h i s s t r o n g l y d e p e n d e n t on th e f o l l o w i n g f a c t o r s : p o p u l a t i o n d e n s i t y , w ater f l o w r a t e s , c o n t a i n m e n t t y p e , s u b s t r a t e t y p e , f o o d a v a i l a b i l i t y , f o u l i n g a c c u m u l a t i o n , d i s e a s e , p o l l u t i o n , t o x i n s , t e m p e r a t u r e , pH and s a l i n i t y ( L o o s a n o f f and Tomers, 1947; Q u a y l e , 1951; 1969; C a l a b r e s e and D a v i s , 1966; Shaw, 1966; L i p o v s k y and Chew, 1972; Walne, 1974; Walke r and Z a h r a d n i k , 1976 and Q u a y l e and S m i t h , 1978). 2. The c o n t r o l of f o u l i n g a c c o u n t s f o r much of t h e expe n s e i n o y s t e r c u l t u r e ( Q u a y l e , 1969). 3. The o f f - b o t t o m c u l t u r e of o y s t e r s p r o v i d e s a b e t t e r q u a l i t y s h e l l , r e d u c e d t i m e from s e e d t o m a r k e t , f a c i l i t a t e s s t o c k management, r e d u c e d m o r t a l i t y and i n c r e a s e d p r o d u c t i o n p e r u n i t a r e a ( S h a w , 1962; 1966; 1969; Shaw and McCann, 1963; Q u a y l e , 1969; 1971; and T u r n e r and Z a h r a d n i k , 1975). 4. The a c c u m u l a t i o n of f o u l i n g i s dep e n d e n t on t h e v e l o c i t y o f water p a s s i n g o v e r t h e e x p o s e d s u r f a c e ( F i n k and Boyd, 1970 and LaQue, 1975). 23 ASSUMPTIONS 1. A c u l t u r e f a c i l i t y t h a t p r o v i d e s a r e l a t i v e l y f r e e exchange of w a t e r t h r o u g h o u t ( e g a v e r a g e v e l o c i t y h i g h e r t h a n t h a t a t w h i c h f o u l i n g o r g a n i s m s w i l l " s e t " ) w i l l r e d u c e f o u l i n g , improve f o o d d i s t r i b u t i o n p r o v i d i n g f o r b e t t e r growth c h a r a c t e r i s t i c s i n t h e r e a r i n g f a c i l i t y . 2. The major c o n s t r u c t i o n m a t e r i a l s f o r t h e u n i t s c o n s i s t o f : p o l y p r o p y l e n e n e t , s t y r o f o a m and r i g i d PVC w h i c h a r e n o n - t o x i c t o o y s t e r s . INFERENCES 1. G r o w i n g o y s t e r s i n submerged p l a s t i c u n i t s u s i n g l o n g l i n e s u s p e n s i o n , p o p u l a t i o n d e n s i t y can be c o n t r o l l e d and s t o c k i n v e n t o r y m a i n t a i n e d . 2. The f l e x i b l e n a t u r e and " o p e n e s s " o f t h e d e s i g n w i l l a l l o w a r e l a t i v e l y f r e e exchange of water and by l o c a t i n g i n an a r e a h a v i n g d i s t i n c t c u r r e n t a c t i o n w i l l t e n d t o r e d u c e f o u l i n g and improve g r owth c h a r a c t e r i s t i c s when compared t o c a l m e r / s h e l t e r e d e n v i r o n m e n t s and t r a d i t i o n a l methods of t r a y c u l t u r e . 24 FUNCTIONAL SPECIFICATIONS 1. The d e s i g n i s t o p e r m i t r a p i d u n i f o r m g r o w t h , a c o m m e r c i a l l y a c c e p t a b l e s u r v i v a l r a t e and p r o d u c e a m a r k e t a b l e p r o d u c t c o m p e t i t i v e on t h e h a l f s h e l l m a r k e t . 2. A l l o w u t i l i z a t i o n o f t h e m a r i n e e n v i r o n m e n t i n t h r e e d i m e n s i o n s and t h e p h y t o p l a n k t o n p r e s e n t i n t h e upper l a y e r s of t h e water c o l u m n . T h i s p e r m i t s a g r e a t e r y i e l d of o y s t e r s from t h e volume of water o c c u p i e d by t h e s y s t e m t h a n would have e x i s t e d i n t h e n a t u r a l s t a t e . 3. Augment water c i r c u l a t i o n t o . s t a b i l i z e f l o w p a t t e r n s i n and a r o u n d g r o w i n g u n i t s s u c h t h a t "dead" a r e a s a r e m i n i m i z e d . T h i s i s t o p r o v i d e a b e t t e r d i s t r i b u t i o n o f f e e d , waste r e m o v a l and m a i n t a i n s s t e a d y e n v i r o n m e n t a l c o n d i t i o n s . 4. The d e s i g n and t h e m a t e r i a l s o f c o n s t r u c t i o n a r e t o r e d u c e f o u l i n g and p r e d a t i o n below l e v e l s w h i c h have p l a g u e d t h e s t a t e o f t h e a r t t o d a t e . 5. F o r t h e p u r p o s e of management t h e d e s i g n a l l o w s a c c e s s t o i n d i v i d u a l o r g r o u p s of o y s t e r s f o r c l e a n i n g , t h i n n i n g and o b s e r v a t i o n . 25 OPERATIONAL FEATURES 1. The t r a y s a r e t o be l o c a t e d below t h e s u r f a c e a t a d e p t h t h a t a f f o r d s p r o t e c t i o n from waves, t h e a t t a c h m e n t o f f l o a t i n g d e b r i s and m a i n t a i n s an a t m o s p h e r e o f i n c o n s p i c u o u s n e s s a b o u t the o p e r a t i o n . 2. The t r a y d e s i g n i s t o a l l o w an optimum exchange of water between o y s t e r s and t h e e n v i r o n m e n t f o r waste r e m o v a l , oxygen r e n e w a l and p r o v i d i n g even f o o d d i s t r i b u t i o n . 3. The r e a r i n g f a c i l i t y composed of t r a y s s u s p e n d e d i n l a y e r s a r e t o be s t r o n g but f l e x i b l e r e d u c i n g r e s i s t a n c e a g a i n s t f l u i d f o r c e s . The f l e x i b i l i t y a l l o w s t h e s y s t e m t o bend and t w i s t e n h a n c i n g water f l o w . 4. S p a c i n g between t r a y s i s t o be a d e q u a t e enough t o p e r m i t e a s i e r a c c e s s t o o y s t e r s . 5. The o y s t e r s a r e t o be grown i n t h e f a c i l i t y f r o m s e e d (30-40mm) t o m a r k e t a b l e s i z e . S t o c k i n g d e n s i t y i s t o be a t a p o i n t t o r e d u c e t h i n n i n g and d e c l u s t e r i n g . 6. T r a y s a r e t o be s u s p e n d e d s u c h t h a t t h e frame o f e a c h l a y e r o n l y has t o s u p p o r t i t s own w e i g h t . 26 STRATEGY BEHIND THE DEVELOPMENT OF THE REARING F A C I L I T Y The p u r p o s e of t h e r e s e a r c h was t o d e v e l o p a c o n c e p t t h a t would i n c r e a s e e f f i c i e n c y and r e d u c e t h e c o s t s of p r o d u c i n g q u a l i t y h a l f - s h e l l o y s t e r s . I n i t i a l l y a c o n c e p t u a l model was g e n e r a t e d b a s e d on c e r t a i n o b j e c t i v e s , c r i t e r i a and measures of e f f e c t i v e n e s s ( T a b l e 3 ) . The c o n c e p t g e n e r a t e d a r e a s of u n c e r t a i n t y ( T a b l e 4) t h a t became t h e i m p o r t a n t q u e s t i o n s t o be a nswered by t h e f i e l d t e s t s . The d e c i s i o n was made t o b a s e the t r a y on a c i r c u l a r d e s i g n . Frames b a s e d on o t h e r s h a p e s i n v o l v e d numerous j o i n t s and t h e r e f o r e " i n h e r i t " a c o m p l e x i t y i n t h e i r c o n s t r u c t i o n and r e s p o n s e t o s t r e s s . In t h e c i r c u l a r frame s t r e s s i s more e v e n l y d i s t r i b u t e d i n s t e a d o f b e i n g c o n c e n t r a t e d a t c o r n e r j o i n t s . G i v e n t h e p r o p e r f l e x i b l e m a t e r i a l t h e c i r c u l a r frame i s e a s i e r and c h e a p e r t o c o n s t r u c t . The s i z e of t h e t r a y was b a s e d on t h e w e i g h t of o y s t e r s p e r t r a y and t h e m a t e r i a l h a n d l i n g c h a r a c t e r i s t i c s . The d i m e n s i o n a l s p e c i f i c a t i o n s were t o c r e a t e optimum c o n d i t i o n s f o r a s s e m b l y , h a n d l i n g by an i n d i v i d u a l worker and t o m a i n t a i n water c i r c u l a t i o n . A n a l y s i s of water c i r c u l a t i o n was beyond t h e scope o f t h e r e s e a r c h , t h e r e f o r e d i m e n s i o n s were b a s e d on t h e r e p e t i t i v e l i f t i n g and h a n d l i n g c a p a b i l i t y of t h e a v e r a g e human. S i z e was d e c i d e d t o be .91 m e t e r s i n d i a m e t e r , 5.1 cm i n h e i g h t w i t h a 0.5 cm net mesh a t t a c h e d t h e f r a m e . A s i n g l e t r a y had a h o l d i n g c a p a c i t y of .668 s q u a r e m e t e r s . The w e i g h t and d i m e n s i o n a l s p e c i f i c a t i o n s a r e w i t h i n t h e m a t e r i a l s h a n d l i n g 27 Table 3. Measures of effectiveness 1. performance 2. r e l i a b i l i t y 3. maintenance 4. time 5. labour and materials handling 6. cost Table 4. Areas of uncertainty. 1. materials of construction 2. spacing between trays 3. oyster density per tray 4. interactions between oysters environment and culture system 28 r e q u i r e m e n t s s e t down i n t h e b e g i n n i n g of t h e r e s e a r c h . The c i r c u l a r shape r e q u i r e s o n l y a s i n g l e j o i n t and t h e d i a m e t e r i s a maximum s i z e t h a t can be h a n d l e d by a s i n g l e w orker w i t h o u t becoming t o o cumbersome. The 5 . 1 cm h e i g h t was n e c e s s a r y t o p r e v e n t s p i l l a g e of s e e d o y s t e r s , and t h e n e t mesh t o a l l o w exchange of water and c o n t a i n t h e s e e d . The i n d i v i d u a l t r a y r e p r e s e n t e d t h e i n t e g r a l component i n t h e d e s i g n of t h e r e a r i n g f a c i l i t y . To make e f f i c i e n t use of t h e water column a s y s t e m s u s p e n d i n g a number of t h e s e t r a y s v e r t i c a l l y was p r o p o s e d . The s p a c i n g between t r a y s was s e t t o a l l o w a c c e s s t o e a c h t r a y f o r i n s p e c t i o n , c l e a n i n g o r h a r v e s t i n g and o f f e r m i n i m a l r e s i s t a n c e t o w ater f l o w . The tar-get g o a l f o r t h e t r a y a s s e m b l a g e was t o be z e r o m a i n t e n a n c e b e c a u s e o u t a g e t i m e s a r e c o s t l y and maximum p r o f i t goes hand i n hand w i t h maximum r e l i a b i l i t y . A l o n g w i t h t h i s g o a l and t h e d e s i g n c r i t e r i a t h e i n i t i a l c o s t , e f f i c i e n c y i n the i n t e n d e d d e s i g n , t h e p r e d i c t e d l i f e t i m e of t h e p o s s i b l e m a t e r i a l s as i n f l u e n c e d by c o r r o s i o n a l o n g w i t h t h e f u n c t i o n a l i n t e r a c t i o n s of s t r e s s were c o n s i d e r e d . STRUCTURAL CONSIDERATIONS The s t r e n g t h of t h e m a t e r i a l t o be u s e d i n t h e s t r u c t u r e was t h e c r i t i c a l c o n c e r n b e c a u s e t h e d e s i g n must be r e s i l i e n t t o t h e f o r c e s and l o a d s p l a c e d upon i t . S t r e s s d o a d p e r u n i t c r o s s -s e c t i o n a l a r e a ) can c a u s e d e f o r m a t i o n i n t h e form of t e n s i o n , c o m p r e s s i o n o f s h e a r . S t r e s s a r i s e s b e c a u s e of t h e dynamic or s t a t i c l o a d s upon t h e s t r u c t u r e . 29 S t a t i c l o a d i s t h e w e i g h t of t h e s t r u c t u r e p l u s a d d e d l o a d s due t o m a i n t e n a n c e and o p e r a t i o n s . Dynamic l o a d s v a r y w i t h time and a r e a common c o n s i d e r a t i o n i n o f f - s h o r e s t r u c t u r a l d e s i g n . They r e s u l t f r o m t h e s e dynamic f o r c e s and an e s t i m a t e of t h i s r e q u i r e s knowledge of t h e d r a g c o e f f i c i e n t o f t h e s t r u c t u r a l s hape; u n f o r t u n a t e l y many s t r u c t u r e s a r e of t h e form t h a t makes t h e d e t e r m i n a t i o n t o o complex. Wave f o r c e d e t e r m i n a t i o n r e q u i r e s d a t a from l o n g t e r m measurement o f wave d a t a f o r d e s i g n i n g f o r wave h e i g h t , wave s p e c t r u m or i n t e r m e d i a t e sea s t a g e s . These have d i r e c t a p p l i c a t i o n t o an e s t i m a t e of f a t i g u e l i f e of a s t r u c t u r e . I t was e v i d e n t t h a t a dynamic s t r u c t u r a l a n a l y s i s was t o o complex t o be d e a l t w i t h i n t h e r e s e a r c h . The m a t e r i a l s e l e c t i o n p r o c e d u r e f o r t h e s t r u c t u r e was b a s e d upon e x p e c t e d p e r f o r m a n c e i n t h e m a r i n e e n v i r o n m e n t _ and r e s p o n s e t o t h e dynamic and s t a t i c s t r e s s e s t h e s t r u c t u r e was t o be e x p o s e d t o o . 30 MATERIAL CONSIDERATIONS ••-Metals S e l e c t i n g a m e t a l f o r m a r i n e a p p l i c a t i o n r e q u i r e s knowledge of i t s c o r r o s i o n b e h a v i o r . F a c t o r s g o v e r n i n g th e c o r r o s i o n o f m e t a l a r e complex and e a c h e n v i r o n m e n t a l zone s u c h as a t m o s p h e r i c , s p l a s h , t i d a l , immersed, deep ocean o r mud have t h e i r own c h a r a c t e r i s t i c s ( T a b l e 5 ) . D e s i g n of t h e e q u ipment t o be u s e d i n t h e a s s e m b l y must be t a i l o r e d t o meet a s p e c i f i c m a r i n e s i t u a t i o n . Sea w a t e r c o n t a i n s an abundance of h a l o g e n compounds s u c h as c h l o r i d e , b r omide and i o d i d e i o n s whose major e f f e c t on c o r r o s i o n i s p r i n c i p a l l y t h r o u g h t h e i r power t o c a u s e l o c a l i z e d breakdown of o x i d e f i l m s r e s p o n s i b l e f o r p a s s i v i t y and c o r r o s i o n r e s i s t a n c e of m e t a l s s u c h as s t a i n l e s s s t e e l . A s e c o n d e f f e c t i s t h e a b i l i t y of t h e s e i o n s t o form s o l u b l e a c i d i c c o r r o s i o n p r o d u c t s s u c h as f e r r o u s c h l o r i d e w h i c h i n t e r f e r e s w i t h t h e r e s t o r a t i o n of p a s s i v i t y ( L a Q u e , 1975). F o r s e r v i c e i n t h e m a r i n e e n v i r o n m e n t s t r u c t u r a l m e t a l s a r e u s u a l l y p r o v i d e d w i t h a p r o t e c t i v e c o a t i n g c o m b i n e d w i t h c a t h o d i c p r o t e c t i o n t o a c h i e v e optimum c o r r o s i o n c o n t r o l . O t h e r m e t a l s have n a t u r a l p r o t e c t i v e o x i d e f i l m s . T hese f i l m s can p r o f o u n d l y a f f e c t t h e c o r r o s i o n b e h a v i o r of m e t a l s and were i t n o t f o r s u c h f i l m s many common m e t a l s w o u l d c o r r o d e r a p i d l y i n t h e a t m o s p h e r e and w a t e r . O x i d i z i n g a g e n t s c a n sometimes r e t a r d c o r r o s i o n by f o r m i n g t h e s e p r o t e c t i v e f i l m s . Maximum c o r r o s i o n r e t a r d a n c e o c c u r s i f t h e o x i d e f i l m has a s t r u c t u r e w h i c h i s c o h e r e n t w i t h t h a t of t h e u n d e r l y i n g m e t a l i f o x i d a t i o n s t o p s a t 61 Table 5. C l a s s i f i c a t i o n of t y p i c a l marine environments (Fink and Boyd, 1970). Marine Zone D e s c r i p t i o n o r E n v i r o n m e n t Characteristic C o r r o s i o n Behavior o f Steel A t m o s p h e r e (above M i n u t e particles o f sea salt are earned by w i n d . Sheltered surfaces m a y deteriorate more splash) Splash C o r r o s i v i t y varies with height above water, w i n d velocity and d i r e c t i o n , dew cycle , rain-fall, temperature, solar radiation, dust, season, and p o l l u t i o n . E v e n bird droppings are a factor. W e t , well-aerated surface, n o fouling. rapidly l h a n those b o l d l y exposed. T o p surfaces may be washed free o f salt b y r a i n . C o r a l dust c o m b i n e d w i t h salt seems to be particularly corrosive to steel e q u i p m e n t . C o r r o s i o n usually decreases rapidly as o n e goes inland. M o s t aggressive zone for m a n y metals, e.g., steel. Protective coatings are m o r e difficult to maintain than in other zones. T i d a l Shal low water (near surface a n d near shore) C o n t i n e n t a l -s h . i f d e p t h * D e e p ocean Marine fouling is apt to be present to high-water mark. O i l coating from p o l l u t e d harbor water may be present. Usual ly , ample oxygen is available. Seawater usually is saturated with oxygen. P o l l u t i o n , sediment, fouling, velocity, etc., all may play an active role. N o plant fouling, very i . iuch less a n i m a l (shell) fouling with distance from shore. S o m e decrease in o x y g e n , especially in the Pacific, and lower temperature. O x y g e n varies, tending to be m u c h lower l h a n at surface in Pacific but not l o o different in A t l a n t i c . T e m p e r a t u r e near 0 C . V e l o c i t y l o w ; p H lower than at surface. Steel at tidal zone may act c a t h i K l i c a l l y (well) aerated) and receive some protect ion f r o m the c o r r o s i o n just below tidal zone, in case o f a c o n t i n u o u s steel pile. Isolated steel panels show relatively high attack in tidal zone. O i l coating o n surface may reduce attack. C o r r o s i o n may be more rapid than in marine atmosphere. A calcareous scale forms at cathodic areas. Protective coatings and/or cathodic protection may bc used for c o r r o s i o n c o n t r o l . In most waters a layer o f hard shell and other b i o f o u l i n g restricts the available oxygen a t the surface and thus reduces c o r r o -s i o n . (Increased s t r e s s o n structure from weight o f fouling must be provided for). Steel corrosion often less. A n o d e c o n s u m p t i o n is greater to polarize same area o f steel as at surface. Less tendency for protective mineral scale. M u d Bacteria are often present, e.g., sulfate re-d u c i n g type, B o t t o m sediments vary in origin, characteristics, and behavior. M u d is usually corrosive, occasionally inert. M u d - l o - b o t l o m water c o r r o s i o n cells seem possible. Partly e m b e d d e d panels tend to be rapidly attacked in m u d . Sulfides are a factor. Less current than in-scawater is c o n s u m e d to obtain cathodic p o l a r i z a t i o n for buried part o f structure. 32 t h e p r o p e r t h i c k n e s s ( e g . o x i d e s of aluminum and chromium form c o h e r e n t f i l m s on t h e base m e t a l p r e v e n t i n g t h e f o r m a t i o n o f c r a c k s and t h e r e f o r e t h e s e m e t a l s a r e r e s i s t a n t t o c o r r o s i o n ( M e l l a n , 1976). A l o w e r a v a i l a b i l i t y of oxygen w i l l a l s o r e d u c e t h e p r o t e c t i v e e f f e c t of o x i d e f i l m s . W i t h s t a i n l e s s s t e e l oxygen a v a i l a b i l i t y r e t a r d s c o r r o s i o n by d e v e l o p m e n t and r e p a i r of o x i d e f i l m s r e s p o n s i b l e f o r p a s s i v i t y ( L a Q u e , 1975). A s u r f a c e w i t h i n a c r e v i c e ( b e n e a t h a l a p j o i n t r i v e t or washer) h a v i n g l i m i t e d a c c e s s t o d i s s o l v e d oxygen becomes a n o d i c t o t h e s u r f a c e o u t s i d e t h e c r e v i c e a c c e l e r a t i n g c o r r o s i o n w i t h i n t h e c r e v i c e . W i t h p l a i n c a r b o n s t e e l t h e o p p o s i t e e f f e c t i s f e l t where oxygen a c c e l e r a t e s c o r r o s i o n by s e r v i n g as a c a t h o d i c d e p o l a r i z e r ( L a Q u e ; 1975). A. G a l v a n i c A t t a c k Sea w ater i s an e x c e l l e n t e l e c t r o l y t e w i t h s e v e r e c o r r o s i o n o c c u r r i n g when two d i f f e r e n t m e t a l s a r e c o u p l e d t o g e t h e r ( T a b l e 6 ) . I t i s t h e h i g h e l e c t r i c a l c o n d u c t i v i t y of s e a water t h a t p e r m i t s l a r g e a r e a s t o t a k e p a r t i n c o r r o s i o n . One m e t a l i n t h e c o u p l e w i l l become a n o d i c t o t h e o t h e r and g r e a t e r t h e d i f f e r e n c e i n p o t e n t i a l t h e g r e a t e r w i l l be t h e a c c e l e r a t i o n of a t t a c k on t h e a n o d i c member. A s i n g l e m e t a l may a l s o d e v e l o p l o c a l a n o des and c a t h o d e s when f i r s t immersed b e c a u s e of t h e c o m p o s i t i o n a l o r o t h e r v a r i a t i o n s on a m e t a l s s u r f a c e ( F i n k and Boyd, 1970). G a l v a n i c a t t a c k c an be c o n t r o l l e d by c o v e r i n g t h e c a t h o d e w i t h an i n s u l a t i n g b a r r i e r b r e a k i n g t h e e l e c t r i c a l c i r c u i t . Table 6. Corrosion factors for carbon s t e e l immersed i n seawater(Fink and Boyd, 1970). I .H'llN III I -11 it I on Iron .in.l Slivl C h l o r i d e i o n Highly corrosive to ferrous metals. C a r b o n t i e d a n d c o m m o n ferrous metals cannot be passivjtcd. (Sea salt is about 55 percent chloride.) Electrical High c o n d u c t i v i t y makes it possible for anodes c o n d u c t i v i t y and cathodes t o operate over long distance*. thus c o r r o s i o n possibilities arc increased a n d the total attack may be m u c h greater than tlial for the same structure in fresh water. O x y g e n Steel corrosion is eathodically c o n t r o l l e d for the most part. O x y g e n , by depolarizing the cathode, facilitates the attack; thus a high oxygen content increases corrosivi ty . V e l o c i t y C o r r o s i o n rate is increased, especially in tur-bulent flow. M o v i n g seawater may (1) destroy rust barrier and (2) provide more o x y g e n . Impingement attack tends to p r o m o t e rapid penetration. C a v i t a t i o n damage exposes fresh steel surface l o furl her c o r r o s i o n . T e m p e r a t u r e Increasing ambient temperature lends to ac-celerate attack. Healed seawater m a y de-posit protective s o l e , or lose its o x y g e n ; either o r IK>HI actions l e n d t o reduce attack. l i i o f o u l i n g Jlard-ihcl l animal fouling tends to reduce attack b y restricting access o f o x y g e n , liacteria can take part in c o r r o s i o n r e a c t i o n in some cases. Stress C y c l i c stress sometimes accelerates failure o f a c o r r o d i n g steel member. Tensile stresses near y i e l d also promote failure in special situations. P o l l u t i o n Sulfides, which n o r m a l l y are present in p o l -l u l c d seawater greatly accelerate attack o n steel. H o w e v e r , the l o w o x y g e n content o f polluted waters could favor reduced c o r r o s i o n . Silt and sus- l : .rosion o f Hie steel surface by suspended pended matter in the f lowing seawater greatly i n -s c d i m c n l creases the tendency to c o r r o d e . F i l m f o r m a t i o n A • n a l m g o f n u l . or m\t ami ni ineial scale (calcium and magnesium vilts) will i n l e r l c r c w i l h the diffusion o f o x y g e n to the call iode surface, thus slowing the attack. 34 B. C r e v i c e A t t a c k M e t a l s t h a t r e q u i r e p l e n t y of oxygen s u c h as s t a i n l e s s s t e e l and aluminum, t o c o n t i n u o u s l y r e p a i r b r e a k s i n t h e o x i d e f i l m and m a i n t a i n p a s s i v i t y t e n d t o be s u s c e p t i b l e t o c r e v i c e a t t a c k . C r e v i c e s d e v e l o p b e c a u s e o f d e s i g n f e a t u r e s s u c h as g a s k e t s , l a p j o i n t s , under the head o f f a s t e n i n g s , g a s k e t s and under f o u l i n g o r g a n i s m s . The c r e v i c e can be formed between m e t a l and n o n - m e t a l , between two p i e c e s of t h e same m e t a l or d i s s i m i l a r m e t a l s where the e f f e c t c a n be i n c r e a s e d . I f t h e oxygen i n t h e s t a g n a n t water o f t h e c r e v i c e i s consumed b r e a k s i n t h e p a s s i v e f i l m o c c u r a t a h i g h e r r a t e t h a n f r e s h water c a n d i f f u s e i n and r a p i d c o r r o s i o n r e s u l t s . O c c a s i o n a l l y t h e c r e v i c e can ' become a n o d i c and b e c a u s e of i t s s m a l l a r e a w i t h r e s p e c t t o t h e o u t s i d e e x p o s e d sea water s u r f a c e ( t h e c a t h o d e ) i n c r e a s e s t h e r a t e of l o c a l a t t a c k . C. P i t t i n g , Impingement and C a v i t a t i o n P i t t i n g i s a l o c a l i z e d s u r f a c e c o r r o s i o n f a v o r e d by r e l a t i v e l y s t a g n a n t c o n d i t i o n s and t h e p r e s e n c e of heavy m e t a l i o n s s u c h as c o p p e r o r l o c a l d e p o s i t i o n of f o r e i g n m a t t e r . Impingement a t t a c k o c c u r s i n m e t a l s s e n s i t i v e t o s e a w ater c u r r e n t v e l o c i t y . When r a p i d l y f l o w i n g sea water i n a s s o c i a t i o n w i t h b u b b l e s i m p i n g e s a g a i n s t a m e t a l s u r f a c e p r o t e c t i v e o x i d e f i l m s may be d e s t r o y e d and t h e m e t a l l o c a l l y a t t a c k e d . C a v i t a t i o n i s s i m i l a r t o impingement a t t a c k e x c e p t h i g h e r water v e l o c i t i e s a r e i n v o l v e d . Under c o n d i t i o n s of water f l o w b u b b l e s c o l l a p s e on t h e m e t a l s u r f a c e and i f t h e m e t a l s a r e u n a b l e t o w i t h s t a n d t h e combined m e c h a n i c a l and e l e c t r o c h e m i c a l 35 f o r c e s a s s o c i a t e d w i t h t h e hammering e f f e c t o f t h e c o l l a p s i n g b u b b l e s s e v e r e c o r r o s i o n r e s u l t s . C o l l a p s e of t h e s e b u b b l e s p a s s i n g a t a h i g h s p e e d o v e r a s u r f a c e w i l l d e v e l o p low p r e s s u r e s i n s e c t i o n s of a m e t a l s ' s u r f a c e c a u s i n g f l a k i n g of t h e s u r f a c e . D. F o u l i n g and S c a l e F o r m i n g Compounds F o u l i n g i s a major f a c t o r t o be t a k e n i n t o c o n s i d e r a t i o n when d e s i g n i n g m a r i n e f a c i l i t i e s . I t c a n o v e r l o a d a s t r u c t u r e w i t h e x t r a w e i g h t or promote c o r r o s i o n by c r e a t i n g c r e v i c e s w i t h i n w h i c h s u s c e p t i b l e m a t e r i a l s s u c h as s t a i n l e s s s t e e l s w i l l s u f f e r a c c e l e r a t e d a t t a c k . M a i n t a i n i n g a m e t a l s u r f a c e f r e e of f o u l i n g i s n e c e s s a r y when d e a l i n g w i t h s t a i n l e s s s t e e l . P a s s i v i t y o f t h e o x i d e f i l m i s m a i n t a i n e d by k e e p i n g t h e s u r f a c e c l e a n and f r e e o f b i o f o u l i n g and d e p o s i t s . A s e a w ater v e l o c i t y of 1.5 m/s or h i g h e r w i l l p r e v e n t f o u l i n g and promote p a s s i v i t y o f a u s t e n i t i c g r a d e s o f s t a i n l e s s s t e e l ( F i n k and Boyd, 1970). Flow above t h i s c r i t i c a l r a t e g e n e r a l l y must be c o n t i n u o u s or o r g a n i s m s become a t t a c h e d d u r i n g p e r i o d s of no or low v e l o c i t y f l o w ( L a Q u e , 1975). In t h e c a s e of p l a i n c a r b o n s t e e l h a r d s h e l l v a r i e t i e s of m u s s e l s can r e d u c e t h e c o r r o s i o n on s t e e l by r e d u c i n g t h e v e l o c i t y of oxygen c a r r y i n g w a t e r , a c t i n g as a d i f f u s i o n b a r r i e r t o oxygen a t c a t h o d i c s i t e s . The c a t h o d i c s i t e s may a l s o d e v e l o p a c a l c i u m c a r b o n a t e m i n e r a l s c a l e p r o v i d i n g a d d i t i o n a l p r o t e c t i o n . C a l c i u m , magnesium and s t r o n t i u m i n s e a water a l o n g w i t h c a r b o n a t e s can be b e n e f i c i a l i n r e t a r d i n g c o r r o s i o n by o f f s e t t i n g t h e a c c e l e r a t i o n e f f e c t s o f c h l o r i d e s t h r o u g h t h e 3 6 f o r m a t i o n of a d h e r e n t p r o t e c t i v e c a l c a r e o u s d e p o s i t s ( L a Q u e , 1975). These d e p o s i t s have h i g h e l e c t r i c a l r e s i s t a n c e and r e d u c e c u r r e n t f l o w i n l o c a l a c t i o n and g a l v a n i c c e l l s by r e d u c i n g t h e e f f e c t i v e c a t h o d e a r e a ( L a Q u e , 1975). M e t a l T y p e s A. S t a i n l e s s S t e e l S t a i n l e s s s t e e l comes i n t h r e e g r a d e s : m a r t e n s i t i c , f e r r e t i c and a u s t e n i t i c . A sea w a ter v e l o c i t y of 5 f p s or h i g h e r w i l l p r e v e n t f o u l i n g and promote p a s s i v i t y of a u s t e n i t i c g r a d e s of s t a i n l e s s s t e e l . M a r t e n s i t i c and f e r r e t i c g r a d e s a r e not recommended f o r submerged m a r i n e a p p l i c a t i o n ( F i n k and Boyd, 1970). S t a i n l e s s s t e e l s f i n d o n l y l i m i t e d . a p p l i c a t i o n i n t h e m a r i n e e n v i r o n m e n t . They do w e l l where p a s s i v i t y of t h e o x i d e f i l m can be m a i n t a i n e d by b o l d e x p o s u r e of t h e s u r f a c e . These s t e e l s depend on t h e i r p a s s i v e f i l m f o r r e s i s t a n c e t o c o r r o s i o n . E x p o s e d s u r f a c e s or s u r f a c e s w i t h i n a c r e v i c e c a n l o s e t h e i r p a s s i v i t y i n t h e a b s e n c e o f s u f f i c i e n t oxygen t o p r e s e r v e i t . The p o t e n t i a l d i f f e r e n c e between t h e a c t i v e and p a s s i v e s u r f a c e s c a n e x c e e d 500mV, t h e r e f o r e c r e v i c e c o r r o s i o n of s t a i n l e s s s t e e l i s much more s e v e r e than w i t h o r d i n a r y s t e e l ( L a Q u e , 1975). H i g h v e l o c i t y water i s f a v o r a b l e b e c a u s e i t b r i n g s i n oxygen p r o m o t i n g the r e p a i r of b r e a k s i n t h e f i l m . Q u i e t sea w ater can promote p i t t i n g ( f i g u r e 5 ) . B. N i c k e l A l l o y s N i c k e l by i t s e l f d oes n o t have a good r e s i s t a n c e t o sea 37 water e s p e c i a l l y under low v e l o c i t y c o n d i t i o n s . When molybdenum i s a dded i t t e n d s t o v i r t u a l l y e l i m i n a t e l o c a l a t t a c k and t h e a d d i t i o n of chromium f u r t h e r i n c r e a s e s t h e c o r r o s i o n r e s i s t a n c e of t h e m e t a l . T h i r t y t o f o r t y p e r c e n t n i c k e l and 20-30% chromium a l l o y s t i l l d epends on a p a s s i v e f i l m f o r p r o t e c t i o n i n sea w a t e r . T h i s a l l o y t e n d s t o p i t - i n s e a w a t e r ( F i n k and Boyd, 1970). N i c k e l b a s e a l l o y s w i t h 15% more chromium and 10% more molybdenum p r e s e n t ( c a l l e d H a s t e l l o y C) a r e c o m p l e t e l y r e s i s t a n t t o a l l e n v i r o n m e n t s ( F i n k and Boyd, 1 9 7 0 ) ( f i g u r e 5 ) . C. C opper Base A l l o y s The c o p p e r base a l l o y s a r e among the most r e s i s t a n t t o c o r r o s i o n i n t h e m a r i n e e n v i r o n m e n t . The. c u p r o n i c k e l s a r e among th e most r e s i s t a n t and show l e s s t e n d e n c y t o p i t ( F i n k and Boyd, 1970). The p r o t e c t i v e f i l m of c u p r o u s o x i d e f o r m i n g on t h e s u r f a c e of t h e s e a l l o y s p r o t e c t s a g a i n s t c o r r o s i o n and f o u l i n g . A c o r r o s i o n s i t u a t i o n can d e v e l o p w i t h c o p p e r a l l o y s where c o r r o s i o n p r o d u c t s c o n t a i n i n g a h i g h c o n c e n t r a t i o n of c o p p e r i o n s become t r a p p e d w i t h i n a c r e v i c e w h i l e t h e s e i o n s a r e c o n t i n u a l l y b e i n g swept away from s u r f a c e s o u t s i d e t h e c r e v i c e c a u s i n g a c c e l e r a t e d c o r r o s i o n j u s t o u t s i d e t h e c r e v i c e (LaQue, 1975). T h i s d e v e l o p s b e c a u s e a c o p p e r a l l o y s u r f a c e i n c o n t a c t w i t h a s o l u t i o n c o n t a i n i n g a low c o n c e n t r a t i o n of c o p p e r i o n s becomes t h e anode i n a c e l l where t h e c a t h o d e i s a s u r f a c e of t h e same a l l o y i n c o n t a c t w i t h a s o l u t i o n of h i g h e r c o p p e r i o n c o n c e n t r a t i o n ( L a Q u e , 1975). 38 Flow Condition A l i o y Stognont Ouitietnt Uodmi H i j h l c > c v i c « ) Sf**4 Aluminum 2 0 2 4 , 2 2 1 9 , 7 I 7 B 7 0 7 9 . 7 0 7 5 , 1 0 0 5 2014, 6061, X70O2, 5052, 5i54, MOO 5456, 5066, 505Z 508} 9 0 / 1 0 CvNI 7 0 / 5 0 C v N i M o n t i , H I S t o i n l e i t t l t t l i H o t u l l o y C , T I N o otlock i 1 ESI L i M I t or W<x1«iot« Con»ide»ob*« nil fiiiQch o"ock otlock F i g . 5. Comparative l o c a l i z e d a t t a c k ( c r e v i c e c o r r o s i o n and p i t t i n g ) of some important marine a l l o y s as a fu n c t i o n of seawater flow c o n d i t i o n s ( F i n k and Boyd, 1970). 39 D. Aluminum A l l o y s Those a l l o y s c o n t a i n i n g s i l i c o n , manganese and magnesium a r e t h e most r e s i s t a n t t o c o r r o s i o n i n s e a w a t e r ( M e l l a n , 1976). A l l o y s c o n t a i n i n g c o p p e r or z i n c have t h e l o w e s t c o r r o s i o n r e s i s t a n c e ( A l c a n R e p o r t , 1970). The a l l o y s Al-Mg 5052, 5083, 5347 5474(wrought a l l o y s ) and A l c a n A320, 332, A A F 5 1 4 . 0 ( f o u n d r y a l l o y s ) have the h i g h e s t c o r r o s i o n r e s i s t a n c e ( A l c a n R e p o r t , 1970). When d e a l i n g w i t h a l l o y s i t must be kept i n mind t h a t as t h e i r s t r e n g t h i n c r e a s e s aluminum a l l o y s show a t e n d e n c y t o w a r d i n c r e a s e d b r i t t l e m e n t , l o w e r n o t c h t o u g h n e s s and q u e s t i o n a b l e f a t i g u e l i f e ( E v a n and Adamchak, 1972). E. C a r b o n and Low A l l o y S t e e l s A low a l l o y s t e e l o f f e r s no p a r t i c u l a r c o r r o s i o n a d v a n t a g e o v e r c a r b o n s t e e l i n submerged m a r i n e a p p l i c a t i o n s . In most s i t u a t i o n s a r u s t c o a t i n g , c a l c a r e o u s s c a l e o r a l a y e r of f o u l i n g w i l l d e v e l o p i n a few months on t h e s u r f a c e and p r o v i d e an i n t e r f e r i n g p r o t e c t i v e b a r r i e r . V a r i o u s f a c t o r s s u c h as c h l o r i d e i o n s , oxygen, t e m p e r a t u r e , f o u l i n g and s t r e s s can a f f e c t t h e p e r f o r m a n c e o f c a r b o n s t e e l i n the s e a ( t a b l e 6 ) . 40 P l a s t i c s I n t r o d u c t i o n The t e r m p l a s t i c a p p l i e s t o a l a r g e and v a r i e d g r o u p of s y n t h e t i c m a t e r i a l s t h a t a r e p r o c e s s e d by m o l d i n g o r f o r m i n g t o a f i n a l s h a p e . C h e m i c a l l y , p l a s t i c s a r e composed of c h a i n - l i k e m o l e c u l e s of h i g h m o l e c u l a r w e i g h t c a l l e d p o l y m e r s . The p o l y m e r s have u s u a l l y been b u i l t up from s i m p l e r c h e m i c a l s c a l l e d monomers. D i f f e r e n t monomers or c o m b i n a t i o n s of monomers a r e u s e d t o m a n u f a c t u r e a s p e c i f i c t y p e of p l a s t i c . By c h a n g i n g t h e m o l e c u l a r w e i g h t and c h a i n g eometry of a p o l y m e r d i f f e r e n t p r o p e r t i e s c a n be a c h i e v e d . The p r o p e r t i e s c an be f u r t h e r m o d i f i e d by a d d i n g f i l l e r s and p l a s t i c i z e r s ; r e s p o n s e s t h a t r e s u l t from t h e s e m i x t u r e s n e c e s s i t a t e s a r a t h e r b r o a d a p p r o a c h t o e x p o s u r e t o p i n down t h e e n v i r o n m e n t a l a p p l i c a t i o n o f t h e p l a s t i c . I t becomes a m a t t e r of f i n d i n g t h e m a t e r i a l w i t h a l l t h e e s s e n t i a l p r o p e r t i e s wanted f o r t h e p r o d u c t a t t h e l o w e s t f i n a l u n i t c o s t . P l a s t i c s o f f e r many amenable a d v a n t a g e s f o r use i n s t r u c t u r a l d e s i g n . S t r u c t u r a l p l a s t i c s have a h i g h e r s t r e n g t h t o w e i g h t r a t i o t h a n most o t h e r e n g i n e e r i n g m a t e r i a l s . They a r e a t t r a c t i v e i n a p p e a r a n c e and can e a s i l y be made t r a n s l u c e n t or p i g m e n t e d t o g i v e d e s i r e d t i n t s or c o l o u r s t o t h e s t r u c t u r e . The r e s i s t a n c e a s a c l a s s o f m a t e r i a l s t o e n v i r o n m e n t a l c o r r o s i o n i s f a r s u p e r i o r t o a l l but t h e most h i g h l y c o r r o s i o n r e s i s t a n t s t r u c t u r a l m e t a l s ( R i d d e l l , 1973). They o f f e r low w e i g h t , s i m p l e r h a n d l i n g , l o w e r t r a n s p o r t c o s t s and o f f - s i t e p r e f a b r i c a t i o n . The s t r u c t u r a l d e s i g n e r must be aware of t h e v a r i o u s 41 d i f f e r e n c e s a s s o c i a t e d w i t h a p a r t i c u l a r p l a s t i c ( T a b l e 7 ) . P l a s t i c s u n i q u e p r o p e r t i e s a r e q u i t e s e p a r a t e from m e t a l s . M e t a l s and o t h e r hookean m a t e r i a l s used i n s t r u c t u r e s a r e d e s i g n e d w i t h s t r e s s s t r a i n modulus, y i e l d s t r e n g t h and p r o p o r t i o n a l or e l a s t i c l i m i t b e c a u s e t h e s e p r o p e r t i e s a r e r e l a t i v e l y i n d e p e n d e n t of t i m e and t e m p e r a t u r e ( R i d d e l l , 1973). P l a s t i c s , r u b b e r s and e l a s t o m e r s do not have l i n e a r l y r e l a t e d p r o p e r t i e s t o a p p l i e d l o a d s ( G a l a n t i and M a n t e l l , 1965). M a t e r i a l s w h i c h do not c o n f o r m t o a s i m p l e l i n e a r r e l a t i o n s h i p between l o a d and e l o n g a t i o n a r e termed v i s c o e l a s t i c o r non-Newto n i a n ( G a n l a n t i and M a n t e l l , 1965). V i s c o e l a s t i c b e h a v i o r i s p a r t l y e l a s t i c and p a r t l y t h a t of a v i s c o u s f l u i d . I n i t i a l d e f o r m a t i o n o c c u r s i n s t a n t a n e o u s l y ( e l a s t i c r e s p o n s e ) upon a p p l i c a t i o n of l o a d , t h e n i n c r e a s e s a t some d e c r e a s i n g r a t e of t i m e . T h i s i s f o l l o w e d by a s m a l l but c o n t i n u o u s d e f o r m a t i o n ( c r e e p ) w i t h t i m e . Removal of t h e l o a d l e a d s t o i n s t a n t a n e o u s r e c o v e r y , a t i m e d e p e n d e n t r e c o v e r y and some permanent d e f o r m a t i o n . The v i s c o e l a s t i c b e h a v i o r of p l a s t i c s makes s t r e s s s t r a i n d a t a of l i t t l e use i n t h e d e s i g n of p l a s t i c s t r u c t u r e s ( R i d d e l l , 1973). One must have d a t a w h i c h a d e q u a t e l y d e s c r i b e s t h e m a t e r i a l s r e s p o n s e t o l o a d w i t h r e s p e c t t o b o t h t i m e and t e m p e r a t u r e . R e l a t i v e l y h a r d , b r i t t l e and r i g i d p l a s t i c s have f a i r l y c o n s i s t e n t s t r e s s - s t r a i n c u r v e s , but many show v a r i a b i l i t y and a s t r o n g dependence o f s t r e s s - s t r a i n d a t a on t e m p e r a t u r e and l o a d i n g r a t e ( R i d d e l l , 1973). C r e e p r u p t u r e t e s t s a r e t h e o n l y v a l i d c r i t e r i a f o r t h e s t r e n g t h o f p l a s t i c s s i n c e s t r e s s - s t r a i n p r o p e r t i e s s u c h as t e n s i l e and f l e x u r a l s t r e n g t h do n o t p r e d i c t l o n g t e r m r u p t u r e 42 T a b l e 7. D i f f e r e n c e s t o be c o n s i d e r e d when d e f i n i n g t h e n e e d s o f a p l a s t i c s o r i e n t e d s t r u c t u r e . A B C D E F G H I J K L S t i f f n e s s o r f l e x i b i l i t y T e m p e r a t u r e r a n g e i n t h e u s e .S . • e n v i r o n m e n t T e n s i l e r a n g e F l e x u r a l r a n g e Impact r a n g e I n t e n s i t y , f r e q u e n c y and d u r a t i o n o f l o a d S t r e s s c r a c k r e s i s t a n c e Weather and s u n l i g h t r e s i s t a n c e o v e r t i m e D e s i g n l i m i t a t i o n s due t o m a t e r i a l s Methods and e c o n o m i c s M a t e r i a l c o s t / g m / c u cm M a t e r i a l c o s t p e r u n i t s t r e n g t h 43 p e r f o r m a n c e or n e c e s s a r i l y rank m a t e r i a l s i n o r d e r w i t h r e s p e c t t o p e r f o r m a n c e ( R i d d e l l , 1973). Most p l a s t i c s w i l l a l s o a b s o r b m o i s t u r e and as a r e s u l t s u f f e r d e g r e e s of d e t e r i o r a t i o n i n t h e i r p h y s i c a l p r o p e r t i e s ( S m i t h , 1968). The s e n s i t i v i t y of f i b e r s t o m o i s t u r e e f f e c t s i s d e p e n d e n t on t h e c o m p o s i t i o n as w e l l a s t h e g e o m e t r i c a r r a n g e m e n t o f m o l e c u l a r s t r u c t u r e o f t h e f i b e r . T h i s i s a s e r i o u s c o n s i d e r a t i o n f o r a s t r u c t u r e d e s i g n e d f o r m a r i n e a p p l i c a t i o n . The r e s p o n s e s of p l a s t i c i n many r e a l s t r e s s s i t u a t i o n s a r e t o o complex t o be s t r e s s a n a l y z e d and t h e r e f o r e r e q u i r e an e m p i r i c a l a p p r o a c h t o p a r t d e v e l o p m e n t . A. M e c h a n i c a l B e h a v i o r of P l a s t i e s ( B e n j a m i n , 1969) 1. The s t r e s s / s t r a i n c u r v e s a r e n o t u s u a l l y l i n e a r up t o y i e l d . In some c a s e s t h e r e may be no y i e l d a t a l l . T h i s of c o u r s e depends on t h e t y p e of p l a s t i c . F o r example, t h e r m o p l a s t i c s show b r i t t l e f r a c t u r e w i t h a b s e n c e of y i e l d a t low t e m p e r a t u r e s and h i g h e r s t r a i n i n g r a t e s . 2. The modulus of e l a s t i c i t y i n t e n s i o n i s not n e c e s s a r i l y t h e same as t h a t i n c o m p r e s s i o n w h i c h i s t r u e f o r most p l a s t i c s . 3. The modulus o f e l a s t i c i t y i s v e r y low. D e f l e c t i o n s c a n be so l a r g e a s t o s e r i o u s l y l i m i t t h e c a r r y i n g c a p a c i t y o f t h e s t r u c t u r e . T h i s d i s a d v a n t a g e c an be o f f s e t by u s i n g s t r u c t u r a l forms w h i c h g i v e added s t i f f n e s s by v i r t u e of t h e i r s h a p e . 44 4. The m e c h a n i c a l b e h a v i o r of p l a s t i c s i s a f f e c t e d by t h e r a t e o f s t r a i n i n g of t h e m a t e r i a l . At v e r y h i g h s t r a i n i n g r a t e s , t h e t h e r m o p l a s t i c s t e n d t o show b r i t t l e f r a c t u r e w i t h a b s e n c e of y i e l d . I t i s of i n t e r e s t t o n o t e t h a t e x c e p t f o r v e r y h i g h r a t e s o f s t r a i n ( s u c h as i m p a c t ) , t h e m e c h a n i c a l p r o p e r t i e s may be assumed t o be u n a f f e c t e d by t h i s f a c t o r . The e x a c t m e c h a n i c a l b e h a v i o r of p l a s t i c s , even i f f u l l y known o v e r a l a r g e range of s t r a i n i n g r a t e s would not be v e r y u s e f u l . 5. The m e c h a n i c a l b e h a v i o r of p l a s t i c s i s a f f e c t e d by t e m p e r a t u r e . The g e n e r a l a f f e c t s of t e m p e r a t u r e a r e t o r e d u c e t h e e l a s t i c m o d u l i and u l t i m a t e s t r e n g t h of t h e m a t e r i a l . At v e r y low t e m p e r a t u r e s t h e t h e r m o p l a s t i c s show b r i t t l e f r a c t u r e and c a r e s h o u l d be e x e r c i s e d i n t h e i r u s e . 6 . P l a s t i c s c r e e p c o n s i d e r a b l y under l o a d w i t h t i m e . T h i s i s de p e n d e n t upon t h e s t r e s s l e v e l and t h e a m b i e n t t e m p e r a t u r e . Some f i b e r r e i n f o r c e m e n t d e c r e a s e s c r e e p w i t h r e s p e c t t o t i m e . 7. P l a s t i c s show a r e d u c t i o n i n u l t i m a t e s t r e n g t h w i t h t i m e even under s t a t i c l o a d i n g c o n d i t i o n s . 8. The sum t o t a l of a l l t h e p r o p e r t i e s o f a l l p l a s t i c s a r e s u b j e c t t o a l t e r a t i o n d e p e n d i n g upon t h e e n v i r o n m e n t i n w h i c h t h e y a r e i n u s e . . B. F a t i g u e A n a l y s i s Under r e p e a t e d c y c l i c s t r e s s , any m a t e r i a l w i l l f a i l i n 45 t i m e a t s t r e s s e s c o n s i d e r a b l y below i t s s t a t i c b r e a k i n g s t r e n g t h . The f a t i g u e b e h a v i o r of p l a s t i c s i s more complex t h a n t h a t of m e t a l s b e c a u s e of t h e i r v i s c o e l a s t i c i t y . The d e f o r m a t i o n of p l a s t i c s under s t r e s s i s t i m e d e p e n d e n t due t o t h e p r e s e n c e of i n t e r n a l f l o w mechanisms t h a t a r e n e g l i g i b l e i n s t r u c t u r a l m e t a l s . S i n g l e speed t y p e of t e s t s t h a t a r e commonly u s e d t o c h a r a c t e r i z e m e t a l s a r e i n a d e q u a t e f o r p l a s t i c s . A more c o m p l i c a t e d t e s t i n g p r o g r am o v e r much l o n g e r p e r i o d s of t i m e i s r e q u i r e d t o g e n e r a t e t h e n e c e s s a r y d e s i g n d a t a . In t h i s s t u d y t h e a u t h o r d o e s not i n t e n d t o become i n v o l v e d i n s u c h t e s t i n g . The s e l e c t i o n o f m a t e r i a l s and t h e a s s e m b l y i s b a s e d on a v a i l a b l e d a t a of p r e v i o u s i n d u s t r i a l r e s e a r c h . 46 T y p e s of P l a s t i c s Under C o n s i d e r a t i o n S e l e c t i n g a p l a s t i c f o r use i n a submerged m a r i n e a p p l i c a t i o n n a r r o w s th e r e a l m of p l a s t i c s from w h i c h t o c h o o s e . The m a t e r i a l must be r e s i s t a n t t o t h e a b s o r p t i o n of m o i s t u r e , t h e v a r i o u s c h e m i c a l c o r r o s i v e a c t i v i t i e s of sea w a t e r , a b r a s i v e a c t i o n s and m a i n t a i n s u f f i c i e n t s t r e n g t h and d i m e n s i o n a l s t a b i l i t y o v e r a range of water t e m p e r a t u r e s from 2-25 d e g r e e s C e l s i u s . E c o n o m i c a l l y , t h e m a t e r i a l s h o u l d l e n d i t s e l f t o p r e f a b r i c a t i o n and be r e l a t i v e l y low i n c o s t when compared t o a l i f e s p a n of 5-8 y e a r s . A) N y l o n N y l o n i s a t o u g h p l a s t i c h a v i n g e x c e l l e n t r e s i s t a n c e t o wear and c h e m i c a l c o r r o s i o n . I t has a low c o e f f i c i e n t of f r i c t i o n and a t e n s i l e s t r e n g t h i n t h e a r e a of 1 0 0 , O O O p s i ( G a l a n t i and M a n t e l l , 1965). U n f o r t u n a t e l y n y l o n i s -h y g r o s c o p i c and w i l l a b s o r b m o i s t u r e p r o d u c i n g d i m e n s i o n a l c h a n g e s making i t u n s u i t a b l e f o r use i n a r i g i d submerged s t r u c t u r e ( S m i t h , 1968). The m o i s t u r e i t a b s o r b s a c t s as a p l a s t i c i z e r l o w e r i n g s t i f f n e s s , s t r e n g t h and h a r d n e s s . However, i t r e p r e s e n t s a u s e f u l m a t e r i a l f o r any s m a l l s c a l e components i n a s y s t e m . B) A B S ( a c r y l o n i t r i l e - b u t a d i e n e s t y r e n e ) T h i s i s a t o u g h p l a s t i c h a v i n g h i g h r i g i d i t y and impact s t r e n g t h , f a i r c h e m i c a l r e s i s t a n c e and low m o i s t u r e a b s o r p t i o n ( G u i d e t o P l a s t i c s , 1970). The impact s t r e n g t h and low m o i s t u r e a b s o r p t i o n l e a d s t o a s t r u c t u r e w i t h good d i m e n s i o n a l 47 s t a b i l i t y and a b r a s i o n r e s i s t a n c e . However, t h e a b s o r p t i o n of m o i s t u r e i n ABS c a n l e a d t o a r e d u c t i o n i n s t r e n g t h . C) V i n y l C h l o r i d e P o l y m e r s ( R i g i d ) T h e s e a r e c o n s i d e r e d t o be t h e most v e r s a t i l e of p l a s t i c m a t e r i a l s . The v e r s a t i l i t y and wide a p p l i c a b i l i t y of PVC i s due t o a c o m b i n a t i o n of m o derate c o s t w i t h a number of t e c h n i c a l f a c t o r s s u c h a s : good g e n e r a l p r o p e r t i e s as a p l a s t i c i n c l u d i n g c h e m i c a l r e s i s t a n c e , f l a m e r e s i s t a n c e , n o n - t o x i c i t y ( E . P . A . R e p o r t , 1974), s t r e n g t h , m o i s t u r e r e s i s t a n c e and e x c e l l e n t o u t d o o r s t a b i l i t y ( T a b l e 8 ) . R i g i d PVC i s e s s e n t i a l l y c h e m i c a l l y i n e r t . S a l t water does not d e g r a d e i t and i t has been shown not t o be a t h r e a t t o a q u a t i c l i f e ( E P A R e p o r t , 1974). PVC has e x c e l l e n t a g i n g p r o p e r t i e s , r e s i s t a n c e t o p h y s i c a l s t r e s s e s and i m p a c t ; has a h i g h t e n s i l e and f l e x u r a l s t r e n g t h ( B . F . G o o d r i c h C h e m i c a l Company R e p o r t , 1978). I t i s e s s e n t i a l t h a t r i g i d u n p l a s t i c i z e d PVC be u s e d i n a m a r i n e a p p l i c a t i o n . Osmon e t a l . ( l 9 7 1 ) f o u n d t h a t p l a s t i c i z e d PVC i s s u b j e c t t o d e t e r i o r a t i o n by t h e breakdown mechanisms a s s o c i a t e d w i t h th e b u i l d - u p o f m i c r o b i a l g r o w t h ( f i g u r e s 6 and 7) . D) P o l y p r o p y l e n e P o l y p r o p y l e n e i s s u i t a b l e f o r h i g h m o i s t u r e a p p l i c a t i o n s ( G u i d e t o P l a s t i c s , 1970). Water d o e s not permeate t h e p o l y p r o p y l e n e f i b e r s ( G a l a n t i and M a n t e l l , 1965). I t a p p e a r s f r e e of e n v i r o n m e n t a l s t r e s s c r a c k i n g , has a low d e n s i t y , h i g h ASTM Test • Method 7082 8700A 8750 82662 Specilic gravity, =.02 D 792 1.47 1.35 1.38 1.36 Hardness. Rockwell R D 785 107 107 113 Durometcr D t.1 D 785 78 70 80 78 " Compression strength, psi D 695 10.100 8.G00 9.G00 10.100 Flexurnl strength, psi D 790 1G.200 11.500 14.500 16.200 Modulus ot elasticity in tension, psi D 038 410,000 310.000 420,000 410.000 Honl distortion temperature, °F, 264 psi D 648 101 158 162 161 Izod impact strength, (I lb/in notch .nt —<".0°F D 256 — 0.49 0.35 -20 0.01 — — 0.81 + 32 0.99 1.47 0.47 0.99 70 1.75 15.0 0.81 1.75 140 — 10.40 1.2G 100 - 16.30 18.30 — Tensile strength, psi D 038 at -40°F — . 2.000 12.000 — + 32 — 7.600 9,000 — 78 7.100 G.200 7.300 7.100 140 — 3.400 3.G00 — 100 . . . 2.200 2.500 — Coefficient of thermal conductivity D 177 Cal/scc/sq cm/°C/cmx10-4 4.5 4.5 4.2 4.5 Coefficient ol linear expansion, in/in/°F x lO-^ D 696 3.5 5.5 2.9 3.5 Flamrnability D G3!3 All compounds sclf-exlinguishing T a b l e 8. The p r o p e r t i e s o f r i g i d PVC(B.F. G o o d r i c h r e p o r t , 1978) . 20r 20 Percent Weight Loss 10 1 2 3 4 Time (weeks) F i g . 6. Weight l o s s of p l a s t i c samples of various shapes incubated with Pseudomones(OsmoD et a l . . 1971). Percent Weight Loss Time (weeks) F i g . 7. Weight l o s s of p l a s t i c samples of various shapes incubated with fungi(Osmon et a l . , 1971). 51 t e n a c i t y and good a b r a s i o n r e s i s t a n c e ( B r y d s o n , 1975). P o l y p r o p y l e n e n e t has been t e s t e d by UMASS A q u a c u l t u r a l E n g i n e e r i n g Lab i n t h e m a r i n e e n v i r o n m e n t and d i d n o t d e t e r i o r a t e i n s t r e n g t h i n o v e r a y e a r ' s e x p o s u r e t o s a l t w a t e r ( Z a h r a d n i k , 1973). E) P o l y e t h y l e n e P o l y e t h y l e n e i s a p l a s t i c w i t h e x c e l l e n t t o u g h n e s s , b e i n g l i g h t i n w e i g h t and e a s i l y p r o c e s s e d a t a low c o s t ( G u i d e t o P l a s t i c s , 1970). I t p r o v i d e s good f l e x i b i l i t y and c h e m i c a l c o r r o s i o n r e s i s t a n c e . U n f o r t u n a t e l y , t h e p o l y m e r has poor r e s i s t a n c e t o s t r e s s c r a c k i n g ( G u i d e t o P l a s t i c s , 1970). 52 M o o r i n g L i n e s L i n e s a r e r e q u i r e d as an e s s e n t i a l component f o r t h e s u s p e n s i o n of t r a y s . What i s needed a r e l i n e s t h a t w i l l n ot s t r e t c h and p o s s e s s t h e s t r e n g t h and r e s i l i e n c e t o h o l d t h e s y s t e m t o g e t h e r above and below t h e w a t e r . The c h o i c e o f m a t e r i a l s i n c l u d e s c h a i n , m e t a l l i c c a b l e and s y n t h e t i c f i b e r s . C h a i n , b e c a u s e of i t s w e i g h t and low s t r e n g t h t o w e i g h t r a t i o was not c o n s i d e r e d where l i g h t e r g e a r i s r e q u i r e d ( E v a n and Adamchak, 1972). M e t a l l i c c a b l e s a r e s u s c e p t i b l e t o f a t i g u e f a i l u r e s due t o s t r e s s c o r r o s i o n . C a r e must be t a k e n t o a v o i d a b r a s i o n i f p r e m a t u r e f a i l u r e s a r e t o be p r e v e n t e d . Such c a b l e s a r e a l s o v u l n e r a b l e t o d i s s i m i l a r m e t a l oxygen c e l l a t t a c k e s p e c i a l l y n e a r t e r m i n a l f i t t i n g s , c l a m p s and between w i r e s t r a n d s . C a b l e s formed from t w i s t e d w i r e s t r a n d s p r e s e n t many o p p o r t u n i t i e s f o r c r e v i c e c o r r o s i o n w h i c h can be e x p e c t e d t o o c c u r w i t h s t a i n l e s s s t e e l c a b l e s i n sea w a t e r . The a t t a c k o f t e n t a k e s t h e form o f t u n n e l l i n g where i n d i v i d u a l w i r e s t r a n d s s u f f e r i n t e r n a l c o r r o s i o n p r o g r e s s i n g w i t h i n t h e w i r e f r o m t h e f i r s t p o i n t o f a t t a c k . Most s y n t h e t i c f i b e r s a r e immune t o f o u l i n g , d e c o m p o s i t i o n and c an be s e l e c t e d f o r l i t t l e or no m o i s t u r e a b s o r p t i o n . They a r e l i g h t i n w e i g h t and i n t h e m a j o r i t y of c a s e s . a r e p o s i t i v e l y o r n e u t r a l l y b u o y a n t . S y n t h e t i c s a r e i d e a l f o r a p p l i c a t i o n s where shock l o a d i n g and t a u t l i n e c o n s t r a i n t s a r e p r e s e n t b e c a u s e o f t h e i r e l a s t i c c h a r a c t e r i s t i c s . C e r t a i n s p e c i a l b r a i d e d s y n t h e t i c s have been d e v e l o p e d t o combat t h e p r o b l e m o f a l l t w i s t e d rope and c a b l e , t h a t of u n t w i s t i n g under l o a d ( E v a n 53 and Adamchak, 1972). In t h e a p p l i c a t i o n of s y n t h e t i c l i n e s t o t h e o y s t e r s y s t e m a l i n e i s needed t h a t has minimum e l a s t i c i t y and maximum t a u t n e s s t o m a i n t a i n p r o p e r l s p a c i n g between t r a y s . D a c r o n , p r o l e n e ( p o l y p r o p y l e n e ) and m a n i l a may be of v a l u e when l e s s e l a s t i c i t y i s r e q u i r e d ( W i I s o n , 1969). N y l o n can be e l i m i n a t e d b e c a u s e i t s w e t - s t r e n g t h r a t i n g i s 5-19% l o w e r t h a n t h e d r y - s t r e n g t h r a t i n g ( W i I s o n , 1969). D a c r o n rope has an e f f e c t i v e q u a l i t y between wet and d r y w e i g h t s and p r o l e n e r o p e has a w e t - s t r e n g t h r a t i n g w h i c h i s 5% g r e a t e r t h a n i t s d r y -s t r e n g t h (Wi I s o n , 1969). 54 The T r a y The c o n t i n u o u s immersion of t h e t r a y i n the' m a r i n e e n v i r o n m e n t makes i t n e c e s s a r y t o s e l e c t m a t e r i a l s t h a t a r e a b l e t o w i t h s t a n d t h e c o r r o s i o n and a c c u m u l a t i o n of f o u l i n g o r g a n i s m s . The s e v e r i t y of t h e m a r i n e s i t u a t i o n d i c t a t e s t h e e l i m i n a t i o n o f m e t a l s and wood or t h e use of c o s t l y c o a t i n g s . The t r a y d e s i g n i n c o r p o r a t e s o v e r l a p p i n g j o i n t s p r o v i d i n g o p p o r t u n i t i e s f o r s t a r t i n g p o i n t s of c r e v i c e c o r r o s i o n . Based on t h e m a t e r i a l s u r v e y of s t r u c t u r a l m a t e r i a l s r i g i d PVC emerged as t h e b e s t s e l e c t i o n f o r frame c o n s t r u c t i o n . The o n l y l i m i t t o i t s l i f e t i m e under s u c h s e r v i c e i s t h e d e f o r m a t i o n and l o s s o f s t r e n g t h c a u s e d by t h e dynamic and s t a t i c s t r e s s e s t h a t t a k e p l a c e g r a d u a l l y w i t h - t i m e . The l i f e of t h e frame c a n r a n g e ' from 6-10 y e a r s d e p e n d i n g on t h e l o a d i n g r a t e s and t h e c h a r a c t e r of t h e m a t e r i a l s h a n d l i n g p r o c e s s e s . PVC a l s o becomes b r i t t l e w h i l e s u b j e c t e d t o below f r e e z i n g t e m p e r a t u r e s . U n i t s w ould have t o be h a n d l e d d i s c r e e t l y d u r i n g t h e w i n t e r months. W h i l e submerged the p l a s t i c would n o t be s u b j e c t e d t o f r e e z i n g t e m p e r a t u r e s and b r i t t l e b e h a v i o r w o u l d not be a p r o b l e m . R i g i d PVC forms a r e e a s i l y p r e f a b r i c a t e d by hot e x t r u s i o n methods. B a s i c a l l y , t h e p l a s t i c m a t e r i a l i s f o r c e d t h r o u g h an o r i f i c e of t h e d e s i r e d shape and t h e s e c t i o n r e q u i r e d i s o b t a i n e d ! f i g u r e 8 ) . The PVC compound i n g r a n u l a r o r powder form i s c h a r g e d i n t o t h e hopper and f e e d s t h r o u g h t h e h o l e i n t h e b a r r e l i n t o t h e f e e d zone of t h e s c r e w . The m a t e r i a l i s c o n v e y e d f o r w a r d and a t a c e r t a i n s t a g e d e p e n d i n g on t h e n a t u r e o f t h e compound, screw d e s i g n and o p e r a t i n g c o n d i t i o n s ; f u s e s t o a c o n t i n u o u s m e l t . The m o l t e n m a t e r i a l i s f o r c e d t h r o u g h a d i e t o . 55 Hopper Die Barrel | Heaters F i g . 8. G e n e r a l a r r a n g e m e n t o f a s i n g l e - s c r e w e x t r u d e r . 56 form t h e r e q u i r e d shape. The h e a t r e q u i r e d t o m e l t t h e p l a s t i c i s s u p p l i e d by h e a t e r s on t h e b a r r e l of t h e machine and s u p p l e m e n t e d by — t h e s h e a r h e a t g e n e r a t e d by t h e a c t i o n of t h e screw. The d i e s f o r use w i t h r i g i d PVC must be f u l l y s t r e a m l i n e d and f r e e from hang-up p o i n t s ( P e n n , 1971). C o o l i n g , a f t e r t h e e x t r u s i o n emerges from t h e d i e , i s p r o v i d e d by b l o w i n g c o l d a i r o v e r t h e b a r r e l f r o m b l o w e r s s i t u a t e d b e n e a t h t h e machine or by c i r c u l a t i n g c o o l w a t e r . The most c o s t l y a s p e c t of PVC m a n u f a c t u r e i s c u t t i n g t h e d i e ( $ 4 0 / h r ) . One form r e q u i r e s one d i e , t h e r e f o r e t h e number of forms r e q u i r e d i n t h e t r a y must be kept t o a minimum t o r e d u c e c o s t s . R e c t a n g u l a r shaped frames i n v o l v e a minimum of t h r e e d i e s and a s s e m b l y o f numerous j o i n t s . The c i r c u l a r frame r e q u i r e s o n l y one. j o i n t and two d i e s . PVC i s f l e x i b l e enough t o be formed i n t o a c i r c l e and h e l d i n p l a c e by a c o p p e r b u r r r i v e t e d l a p j o i n t - . The t r a y i s composed of a r i g i d PVC f l a t b a r , U - c h a n n e l of PVC and 1.9 cm c o p p e r b u r r r i v e t s ( f i g u r e 9 ) . The s t r i a t i o n s on t h e f l a t b a r a s s i s t i n s e c u r i n g t h e U - c h a n n e l . The n e t mesh i s 0.5cm p o l y p r o p y l e n e w h i c h i s c h e m i c a l l y i n e r t , a l l o w s a f r e e e xchange o f water and i s i n e x p e n s i v e a t 6 c e n t s p e r s q u a r e f o o t . E a c h t r a y r e q u i r e s a n e t mesh t o p t o p r e v e n t s p i l l a g e o f young s e e d s i z e o y s t e r s . 57 Floatation Swivel Iron Triangle PVC Frame ® Conwed Net Support Lines Ballast F i g . 9. The Suspension system. 58 The S u s p e n s i o n System The a s s e m b l e d S u s p e n s i o n system- i l l u s t r a t e d i n f i g u r e 11. L i n e s were of .64 cm p o l y p r o p y l e n e due t o i t s low m o i s t u r e a b s o r p t i o n , h i g h t e n s i l e s t r e n g t h , a v a i l a b i l i t y and r e s i s t a n c e t o c o r r o s i o n and s t r e t c h . C o n n e c t i n g t h e t r a y t o t h e l i n e s was f a c i l i t a t e d u s i n g n y l o n 5 cm c a b l e t i e s ( r e s i s t a n c e t o a b r a s i o n ) and .95 cm c o r r o s i o n r e s i s t a n t snap s w i v e l s . The t r i a n g u l a r s u p p o r t frame t o p p i n g o f f t h e s t r u c t u r e was of p l a i n 1.3 cm c a r b o n s t e e l a n g l e ( f i g u r e 10 and 11). B a l l a s t was added t o p r e v e n t t i p p i n g of t h e u n i t s s i t u a t e d i n a r e a s where c u r r e n t s a r e s u b s t a n t i a l . The g o a l b e h i n d th e s u s p e n s i o n t e c h n i q u e was t o a l l o w i n t e r a c t i o n between t h e f a c i l i t y and t h e e n v i r o n m e n t . The i n c o r p o r a t i o n of s w i v e l c o n n e c t o r s and s p a c i n g between t r a y s was t o enhance t h e p a s s a g e of w a t e r , g r owth and waste r e m o v a l and r e d u c e t h e d r a g r e s i s t a n c e compared t o M a c N i c o l and N e s t i e r t r a y c u l t u r e methods. 59 F i g . 10. The assembled Suspension system. F i g . 1 1 . Close-up of the Suspension system and attachment to the support l i n e s . 61 MATERIALS AND METHODS EXPERIMENTAL APPARATUS The m a t e r i a l s out of w h i c h t h e S u s p e n s i o n u n i t s were c o n s t r u c t e d c o n s i s t e d of c o p p e r r i v e t s , r i g i d PVC, p o l y p r o p y l e n e n e t , p o l y p r o p y l e n e r o p e , n y l o n c a b l e t i e s and g a l v a n i z e d h a l i b u t c l i p s . T h e s e m a t e r i a l s formed t h e s i x t e s t u n i t s o f f i v e t r a y s e a c h ( f i g u r e 1 0 ) . The N e s t i e r t r a y s were s u p p l i e d by Mr. R. P a q u i n of S u n s h i n e S e a f o o d s L t d . ( f i g u r e 1 2 ) . The M a c N i c o l t r a y s were s u p p l i e d by t h e S p i r i t Cove O y s t e r C o - o p ( f i g u r e 1 3 ) . B o t h t r a y t y p e s were m a n u f a c t u r e d out of formed p l a s t i c s . A c c e s s t o t h e t e s t a r e a was a c c o m p l i s h e d u s i n g a 16 f o o t Bombard i n f l a t a b l e e q u i p p e d w i t h a 40 hp o u t b o a r d . Growth was m easured t o t h e n e a r e s t m i l l i m e t e r u s i n g V e r n i e r c a l i p e r s . T e m p e r a t u r e and d i s s o l v e d oxygen were measured u s i n g a YSI Model 57 D i s s o l v e d Oxygen M e t e r i n c o m b i n a t i o n w i t h an i n - s i t u YSI 5739 D i s s o l v e d Oxygen P r o b e . S a l i n i t y was d e t e r m i n e d w i t h a YSI M odel 33 S-C-T m e t e r . The pH was measured u s i n g a Beckman pH m e t e r ( f i g u r e 1 4 ) . N e s t i e r and M a c N i c o l t r a y s were l i f t e d by hand f o r s a m p l i n g and t h e e x p e r i m e n t a l u n i t s were h a n d l e d w i t h t h e a s s i s t a n c e of a p o r t a b l e d a v i t ( f i g u r e 15). The t e s t p o p u l a t i o n of o y s t e r s ( C r a s s o s t r e a g i g a s ) were composed of j u v e n i l e 30mm s e e d o b t a i n e d from P e n d r e l l Sound s p a t f a l l , 1977 u s i n g C h i n e s e h a t c o l l e c t o r s . The sample j u v e n i l e p o p u l a t i o n was c h o s e n r a n d o m l y from a s e e d p o p u l a t i o n of 30,000. The a d u l t p o p u l a t i o n was s e l e c t e d r a n d o m l y from 1000, 2 y e a r o l d 62 F i g . 12. The Nestier tray. F i g . 13. The MacNicol assembly. 6 4 F i g . 15. Davit system for handling the Suspension system. 66 a d u l t s grown i n s u b s u r f a c e t r a y s on s i t e . S i n c e t h e m a j o r i t y of g r o w e r s i n B r i t i s h C o l u m b i a use P e n d r e l l Sound s e e d t h e growth c h a r a c t e r i s t i c s o b t a i n e d i n t h e s e e x p e r i m e n t s a r e g e n e r a l l y a p p l i c a b l e a s b a c k g r o u n d i n f o r m a t i o n f o r c u l t u r e s y s t e m e v a l u a t i o n i n t h e i n d u s t r y . T h i s i d e a h o l d s assumming t h e t e s t p o p u l a t i o n i s o f t h e same g e n e t i c s t o c k a s c o m m e r c i a l s e e d o b t a i n e d i n t h e same a r e a . I t must a l s o be kept i n mind t h a t g r o w t h c h a r a c t e r i s t i c s a r e s i t e s p e c i f i c and t h a t i t i s i n d e e d d i f f i c u l t t o p r e s e n t a g r o w t h p i c t u r e r e p r e s e n t a t i v e of a l l of B r i t i s h C o l u m b i a . EXPERIMENTAL DESIGN E x p e r i m e n t s were c a r r i e d o ut i n t h e f i e l d on t h e o y s t e r l e a s e s of t h e S p i r i t Cove O y s t e r Co-Op and Mr. F r a n k Cameron. The t e s t area's were l o c a t e d i n Okeover I n l e t w i t h i n T r e v e n e n Bay bounded by M a l a s p i n a and Coode P e n i n s u l a s ( f i g u r e 1 6 ) . S i x o p e r a t i o n a l u n i t s of t h e a u t h o r s d e s i g n were c o n s t r u c t e d w i t h f i v e t r a y s p e r u n i t . T h r e e u n i t s were l o c a t e d i n t h e narrow c h a n n e l among t h e I s b i s t e r I s l a n d s , where a s u b s t a n t i a l c u r r e n t f l o w e d . T h i s s i t e i s r e f e r r e d t o as e n v i r o n m e n t 2 i n t h e f o l l o w i n g t e x t . The r e m a i n i n g u n i t s were s e t i n a c a l m e r , s h e l t e r e d a r e a d e s i g n a t e d e n v i r o n m e n t 1. At e a c h s i t e two S u s p e n s i o n u n i t s c o n t a i n e d j u v e n i l e s e e d and t h e t h i r d a s s e m b l y was s t o c k e d w i t h a d u l t o y s t e r s . F o u r N e s t i e r and M a c N i c o l s y s t e m s a l s o w i t h f i v e t r a y s p e r u n i t were l o c a t e d i n e a c h t y p e of e n v i r o n m e n t a l o n g w i t h t h e S u s p e n s i o n u n i t s f o r c o m p a r i s o n . The f i v e t r a y s i n e a c h a s s e m b l y a r e r e f e r r e d t o as v e r t i c a l p o s i t i o n s 1 t h r o u g h t o 5 numbered from t o p t o bottom. F i g . 16. Location of study areas. 68 Two of the f o u r a s s e m b l i e s of each s y s t e m t y p e were s t o c k e d w i t h j u v e n i l e s e e d and t h e r e m a i n i n g two w i t h a d u l t o y s t e r s . The c o m p l e t e a r r a y i n b o t h e n v i r o n m e n t s c a n be v i e w e d i n f i g u r e s 17 and 18. T r a y p e r f o r m a n c e was e v a l u a t e d q u a n t i t a t i v e l y by m e a s u r i n g g r o w th of s h e l l l e n g t h , w i d t h and h e i g h t t o t h e n e a r e s t m i l l i m e t e r , m o n i t o r i n g meat c o n d i t i o n i n d e x and a n a l y z i n g t h e e c o n o m i c s of e a c h s y s t e m . P e r f o r m a n c e was a l s o d e t e r m i n e d q u a l i t a t i v e l y by t h e o c c u r r e n c e of f o u l i n g , m a t e r i a l h a n d l i n g c h a r a c t e r i s t i c s , s y s t e m d u r a b i l i t y , o y s t e r m o r t a l i t y and c o s t s . M a c N i c o l t r a y s were s t o c k e d a t 20 o y s t e r s p e r t r a y . The N e s t i e r s a t 52 and t h e S u s p e n s i o n u n i t s a t 100. T h i s r e p r e s e n t e d a s t o c k i n g d e n s i t y of 70 s q u a r e c e n t i m e t e r s p e r o y s t e r i n e a c h s y s t e m . The e n t i r e e x p e r i m e n t was s e t up as a c o m p l e t e l y r a n d o m i z e d d e s i g n t o be a n a l y z e d by a n a l y s i s of v a r i a n c e u s i n g UBC MFAV. UBC GENLIN was u s e d t o a n a l y z e c o n d i t i o n i n d e x d a t a . The o b j e c t was t o c o n s i d e r t h e e f f e c t o f t i m e , e n v i r o n m e n t t y p e , t r a y s y s t e m and v e r t i c a l p o s i t i o n on t h e p e r f o r m a n c e of t h e t r a y s y s t e m s . P r o c e s s i n g of t h e r e s u l t s by ANOVA i n d i c a t e d w h i c h f a c t o r s and i n t e r a c t i o n t e r m s were s t a t i s t i c a l l y s i g n i f i c a n t . Those f a c t o r s and i n t e r a c t i o n s f o u n d t o be s t a t i s t i c a l l y s i g n i f i c a n t ( a l p h a = . 0 5 ) were f u r t h e r a n a l y z e d f o r e v i d e n c e of p r a c t i c a l s i g n i f i c a n t d i f f e r e n c e s . P r a c t i c a l s i g n i f i c a n t d i f f e r e n c e s were a s s e s s e d by g r a p h i c a l l y p l o t t i n g t h e mean v a l u e s of t h e growth r e s u l t s f o r e a c h f a c t o r and i n t e r a c t i o n t e r m t h a t c o u l d be p l o t t e d g r a p h i c a l l y , o t h e r w i s e mean v a l u e s were a s s e s s e d s e p a r a t e l y . P r a c t i c a l s i g n i f i c a n t d i f f e r e n c e s were 69 F i g . 17. The array in environment 1. F i g . 18. The array i n environment 2. 71 f o u n d i f t h e mean v a l u e s of p l o t t e d l i n e s d i f f e r e d by more t h a n 5 m i l l i m e t e r s . The c o n c e p t of p r a c t i c a l s i g n i f i c a n c e was u s e d t o a s s e s s whether a f a c t o r a n d / o r • i n t e r a c t i o n term i n f l u e n c e d o y s t e r g r o w t h . B a c k g r o u n d e n v i r o n m e n t a l p a r a m e t e r s of t e m p e r a t u r e , S e c c h i d i s k , s a l i n i t y , pH, d i s s o l v e d o xygen, ambient weather c o n d i t i o n s and c h l o r o p h y l l l e v e l s were m o n i t o r e d d u r i n g t h e s a m p l i n g p e r i o d . I n t e n s e s a m p l i n g was c a r r i e d out from June 4 t o O c t o b e r 17, 1979. A f t e r t h i s t i m e u n i t s were l e f t immersed t o o v e r w i n t e r and s u b j e c t t o m o n t h l y e x a m i n a t i o n . Growth measurements and e n v i r o n m e n t a l d a t a were not t a k e n d u r i n g t h e w i n t e r due t o s e v e r i t y and u n p r e d i c t a b i l i t y of weather c o n d i t i o n s and d e p r e s s e d s h e l l g r o w t h i n c o o l e r water t e m p e r a t u r e s . D u r i n g t h e w i n t e r months t h e g o a l was t o o b s e r v e i f the' t e s t u n i t s would h o l d up under t h e s t r e s s of w i n t e r s t o r m s i n t h e a r e a . DATA COLLECTION E a c h t r a y s y s t e m was s u b s a m p l e d a t random f o r s h e l l g r o w t h e v e r y s e c o n d week from June 11 t o O c t o b e r 17, 1979. Subsamples of t e n o y s t e r s were t a k e n from e a c h o f t h e g r o w i n g s y s t e m s , measured and r e t u r n e d t o t h e i r r e s p e c t i v e t r a y s . Growth measurements f o r t h e N e s t i e r and M a c N i c o l t r a y s were t a k e n on .Tuesdays f o l l o w e d by s a m p l i n g of t h e S u s p e n s i o n u n i t s on Wednesdays. On o c c a s i o n due t o i n c l e m e n t weather o r boat m a l f u n c t i o n s s a m p l i n g was not c o m p l e t e d u n t i l T h u r s d a y . C o n d i t i o n i n d e x s a m p l i n g began two weeks a f t e r a d u l t o y s t e r s were s t o c k e d i n t o t h e t r a y s . S t o c k i n g was c o m p l e t e d by June 11. S a m p l i n g t o o k p l a c e e v e r y 2 weeks u n t i l m i d - A u g u s t . Two o y s t e r s 72 were removed from t r a y s i n t h e M a c N i c o l and N e s t i e r s y s t e m s and t h r e e were t a k e n from S u s p e n s i o n t r a y s . O y s t e r were bagged and p l a c e d on i c e f o r 24 h o u r s . O y s t e r s were weighed u n s h u c k e d on a M e t t l e r b a l a n c e t h e n s h u c k e d w i t h t h e a s s i s t a n c e of a microwave, o v e n . Empty s h e l l w e i g h t was t h e n t a k e n and f l e s h was d r i e d a t 110 d e g r e e s C e l s i u s o v e r n i g h t . D r i e d meat sam p l e s were the n w e i g h e d and c o n d i t i o n i n d i c e s c a l c u l a t e d . C o n d i t i o n i n d e x o r c o n d i t i o n f a c t o r was d e f i n e d as t h e r a t i o of w e i g h t o f d r y meat t o volume o f s h e l l m u l t i p l i e d by a f a c t o r of 1000. T r a y s were r e s t o c k e d w i t h marked o y s t e r s of t h e same s i z e and m a t u r i t y t o m a i n t a i n s t o c k i n g d e n s i t i e s i n e a c h t r a y . M a r k i n g of t h e r e p l a c e m e n t o y s t e r s p r e v e n t e d them from b e i n g sampled a t a l a t e r d a t e . E n v i r o n m e n t a l d a t a was r e c o r d e d d a i l y , Monday t h r o u g h F r i d a y , between t h e h o u r s of noon and 1300 h r s d a y l i g h t s a v i n g t i m e ( D S T ) . C h l o r o p h y l l s a m p l e s were t a k e n a t mid-day on Wednesdays of e a c h week from s u r f a c e t o 2x S.D. ( S e c c h i d e p t h ) i f d e p t h p e r m i t t e d u s i n g a 3 l i t r e Nansen b o t t l e . I f t h e d e p t h was s h a l l o w e r t h a n 2x S.D. The sample was t a k e n from t h e s u r f a c e t o 1 meter o f f t h e b o t t o m . The water samples were t a k e n i n i t i a l l y a t j u s t below t h e s u r f a c e f o l l o w e d by 1 meter s a m p l i n g i n t e r v a l s t o t h e a p p r o p r i a t e d e p t h . W i t h minimum e x p o s u r e t o l i g h t t h e c o n t e n t s of e a c h Nansen c a s t was t r a n s f e r r e d t o c o l l a p s i b l e c l e a n e d p l a s t i c water j u g s ( 5 g a l cap) s e t w i t h i n a " d a r k " box. Samples were k e p t c o o l and d a r k i n t h i s c o n t a i n e r and f i l t e r e d w i t h i n 3 h o u r s . The f i l t e r s u s e d were 4.5cm Whatman GF/C g l a s s f i l t e r p a p e r f o l l o w i n g t h e method o u t l i n e d i n S t r i c k l a n d and P a r s o n s , 1972. Upon c o m p l e t i o n of f i l t r a t i o n , 73 f i l t e r s were p l a c e d i n p e t r i d i s h e s ; s t o r e d a t -20 d e g r e e s C e l s i u s u n t i l a n a l y s i s a t a l a t e r d a t e . The c h l o r o p h y l l s were a n a l y z e d by November 1979 as o u t l i n e d i n t h e s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of c h l o r o p h y l l s , S t r i c k l a n d and P a r s o n s , 1972. 74 RESULTS QUALITATIVE RESULTS F o u l i n g A l l t r a y s y s t e m s were m o n i t o r e d f o r f o u l i n g a c c u m u l a t i o n . A " q u a n t i t a t i v e " s t u d y was a t t e m p t e d t o o b t a i n a n u m e r i c a l e s t i m a t e of f o u l i n g b u i l d - u p i n e a c h of t h e e n v i r o n m e n t s s i n c e i t was b e l i e v e d f o u l i n g o r g a n i s m s would have d i f f i c u l t y e s t a b l i s h i n g t h e m s e l v e s where a m o d e r a t e c u r r e n t e x i s t e d ( r a n g e 0-7 k n o t s ) . U n f o r t u n a t e l y , v a n d a l s damaged t h e u n i t s d e s i g n e d t o e v a l u a t e f o u l i n g beyond r e p a i r and t h e e x p e r i m e n t was s t o p p e d . A q u a l i t a t i v e v i s u a l c o m p a r i s o n of f o u l i n g o c c u r r e n c e among t r a y u n i t s , t h o u g h r o u g h i n terms o f s c i e n t i f i c a p p r o a c h t o o b t a i n i n f o r m a t i o n , d i d r e v e a l a s i g n i f i c a n t d i f f e r e n c e i n f o u l i n g a c c u m u l a t i o n i n t h e t r a y s y s t e m s and t e s t s i t e s . The N e s t i e r t r a y s d u r i n g t h e month of J u l y and e a r l y A u g u st s u f f e r e d i n t e n s e b a r n a c l e s e t s . T h i s phenomenon was more a p p a r e n t i n e n v i r o n m e n t 1. D u r i n g t h i s p e r i o d t r a y s y s t e m s were b e i n g d r i e d o u t weekly and r e g u l a r s c r a p i n g of b a r n a c l e s o f f N e s t i e r t r a y s became n e c e s s a r y t o a v o i d e x c e s s i v e b u i l d - u p . B a r n a c l e s e t s on N e s t i e r t r a y s l o c a t e d i n e n v i r o n m e n t 2 were n o t as i n t e n s e . Removal of b a r n a c l e s i n e n v i r o n m e n t 2 was r e q u i r e d o n l y once d u r i n g J u l y and A u g u s t . M u s s e l s e t s were a p r o b l e m i n t h e M a c N i c o l t r a y s from J u l y t h r o u g h September s e t t i n g a t l e v e l s t h a t r e q u i r e d r e m o v a l . M u s s e l s e t s were l i g h t e r i n e n v i r o n m e n t 2. Removal of m u s s e l s was needed o n l y once i n e n v i r o n m e n t 2 compared t o f o u r i n s t a n c e s i n e n v i r o n m e n t 1. 75 F o u l i n g i n t h e S u s p e n s i o n t r a y s was n o n - e x i s t e n t i n b o t h t e s t e n v i r o n m e n t s . F i l a m e n t o u s a l g a e growth d i d o c c u r on t h e topmost t r a y of t h e S u s p e n s i o n s y s t e m w h i l e 1/4" Conwed mesh was u s e d as a c o v e r . E x c h a n g i n g t h i s f o r a 1/2" mesh e l i m i n a t e d t h e a l g a e p r o b l e m ( f i g u r e 1 9 ) . A l g a l g r o w t h d i d not o c c u r on t r a y s s i t u a t e d below t h e t o p t r a y . A l g a l growth was s i m i l a r i n b o t h t e s t e n v i r o n m e n t s . F i l a m e n t o u s a l g a l f o u l i n g d i d become a p r o b l e m a f t e r September 6, among N e s t i e r and M a c N i c o l s y t e m s ( f i g u r e 2 0 ) . A l g a l f o u l i n g was not as s i g n i f i c a n t among S u s p e n s i o n t r a y s . The topmo s t t r a y s i n a l l t h e s y s t e m s were t h e most s u s c e p t i b l e t o a l g a l f o u l i n g . F l o a t i n g d e b r i s s u c h as l e a v e s , b r a n c h e s , t w i g s , l o g s , e t c . , s n a g g i n g on M a c N i c o l and N e s t i e r t r a y s was a p r o b l e m f o r th e d u r a t i o n o f f i e l d e x p e r i m e n t a t i o n . T h i s d i d n o t m a t e r i a l i z e among S u s p e n s i o n u n i t s . S h e l l S c a r r i n g S h e l l s c a r r i n g i s a s h e l l d i s f i g u r e m e n t c a u s e d by t h e gr o w t h of s h e l l i n t o t r a y m a t e r i a l s r e n d e r i n g i t u n s u i t a b l e f o r t h e h a l f - s h e l l m a r k e t . S h e l l s c a r r i n g o c c u r r e d i n M a c N i c o l and N e s t i e r t r a y s w i t h i n t h e two week gap between s a m p l i n g f o r g r o w t h . O y s t e r s i n M a c N i c o l t r a y s t e n d e d t o f u s e w i t h t h e f l a t s i d e w a l l s o f t h e p a r t i t i o n s . O y s t e r s i n N e s t i e r u n i t s would grow s h e l l t h r o u g h t h e c i r c u l a r h o l e s i n t h e t r a y . The two week i n s p e c t i o n r o u t i n e p r e v e n t e d permanent d i s f i g u r e m e n t t h a t would have r e s u l t e d i f th e o y s t e r s had not been p e r i o d i c a l l y i n s p e c t e d . O y s t e r s 1/4 inch mesh F i g . 19. Mesh size a l t e r a t i o n and algae control. 77 F i g . 2 0 . A l g a l fouling occurring on MacNicol trays during the f a l l months. 78 c u l t u r e d i n N e s t i e r t r a y s d i d s t o p gowing t h r o u g h t h e t r a y h o l e s a f t e r 2.5 months. The p r o b l e m c o n t i n u e d i n t h e M a c N i c o l t r a y s up t o t h e end of s a m p l i n g i n O c t o b e r . M a t e r i a l s H a n d l i n g The e a s e w i t h w h i c h u n i t s a r e h a n d l e d was c o n s i d e r e d i m p o r t a n t t o t h e s u c c e s s of a c o m m e r c i a l o p e r a t i o n . B a s e d on t h e h a n d l i n g o f u n i t s f o r a r e s e a r c h o p e r a t i o n one can o n l y s p e c u l a t e as t o t h e s u c c e s s or f a i l u r e s of a c o m m e r c i a l s y s t e m . The M a c N i c o l t r a y s were l i g h t and e a s i l y l i f t e d by a s i n g l e worker p r o v i d e d t h e r e were o n l y 5 t o 6 t r a y s p e r s t a c k . The u n i t s must a l s o be t o t a l l y d i s m a n t l e d f o r a c c e s s t o i n d i v i d u a l t r a y s . The N e s t i e r a s s e m b l y was l i f t e d e a s i l y by a s i n g l e p e r s o n u n t i l o y s t e r s a t t a i n e d n e a r market s i z e . H a n d l i n g became cumbersome and two p e r s o n s w o u l d be r e q u i r e d i n a c o m m e r c i a l s i t u a t i o n . T h i s s y s t e m a l s o r e q u i r e d c o m p l e t e d i s m a n t l i n g f o r i n s p e c t i o n , h a r v e s t i n g or p l a n t i n g . T h i s s y s t e m t o o k l o n g e r t o d i s m a n t l e t h a n t h e M a c N i c o l . The S u s p e n s i o n s y s t e m can be l i f t e d as a c o m p l e t e u n i t of- 5 or more t r a y s and need n o t be d i s m a n t l e d f o r i n s p e c t i o n , h a r v e s t i n g or p l a n t i n g . M a t e r i a l P e r f o r m a n c e The m a t e r i a l s of c o n s t r u c t i o n u s e d i n a l l t h r e e t r a y s y s t e m s s u f f e r e d no d e t e r i o r a t i o n f o r t h e d u r a t i o n o f t h e s t u d y . The PVC and Conwed net m a t e r i a l s c o m p r i s i n g t h e S u s p e n s i o n t r a y d i d n o t s u f f e r any l o s s of s t r u c t u r a l i n t e g r i t y . The 79 p o l y p r o p y l e n e s u s p e n s i o n l i n e s s u f f e r e d no c h a f i n g o r l o s s i n s u p p o r t s t r e n g t h . The t r i a n g u l a r s u p p o r t frame even upon e x a m i n a t i o n i n F e b r u a r y , 1980 showed no s i g n s o f s e r i o u s c o r r o s i o n . The g a l v a n i z e d h a l i b u t s naps t h a t r e p l a c e d t h e s t a i n l e s s s t e e l s w i v e l s i n t h e b e g i n n i n g of t h e s t u d y , would have t o be r e p l a c e d e a c h y e a r . In a c o m m e r c i a l a p p l i c a t i o n t h e use of s u c h snaps would not be n e c c e s s a r y and t r a y s c o u l d be s e m i - p e r m a n e n t l y a f f i x e d t o t h e s u s p e n s i o n l i n e s u s i n g n y l o n c a b l e t i e s . The n y l o n c a b l e t i e s e n d u r e d e x t r e m e l y w e l l and d i d not show any s i g n s o f f r a c t u r e , c h a f f i n g o r d i s c o l o u r a t i o n . 80 QUANTITATIVE RESULTS S h e l l g r o w t h d a t a was examined f o r any u n i q u e d i f f e r e n c e s i n t h e a d d i t i o n of s h e l l l e n g t h , w i d t h and h e i g h t among t h e t h r e e t e s t s y s t e m s and e n v i r o n m e n t t y p e s . The f a c t o r s of e n v i r o n m e n t t y p e , t i m e , t r a y s y s t e m and v e r t i c a l p o s i t i o n were a n a l y s e d s e p a r a t e l y and t o g e t h e r as s o u r c e s of v a r i a t i o n f o r t h e i r i n f l u e n c e on o y s t e r g r o w t h . S h e l l h e i g h t was e l i m i n a t e d as a measure of p e r f o r m a n c e due t o i t s i n s e n s i t i v i t y i n d e t e c t i n g any d i f f e r e n c e s as r e l a t e d t o t h e f o u r f a c t o r s and t h e i r i n t e r a c t i o n s . SHELL LENGTH The a n a l y s i s o f v a r i a n c e and f o l l o w up a n a l y s i s on t h e d a t a by g r a p h i c s and d i r e c t e x a m i n a t i o n o f mean v a l u e s r e v e a l e d t h a t e n v i r o n m e n t t y p e ( T a b l e 9 ) , v e r t i c a l p o s i t i o n ( T a b l e 10) and t h e i n t e r a c t i o n s of e n v i r o n m e n t t y p e v s t i m e , e n v i r o n m e n t t y p e vs v e r t i c a l p o s i t i o n , e n v i r o n m e n t t y p e v s v e r t i c a l p o s i t i o n vs t i m e and v e r t i c a l p o s i t i o n vs t i m e d i d not i n f l u e n c e g r o w t h i n t h e p r a c t i c a l s e n s e ( A p p e n d i x A and B ) . Table 9. The mean lengths of shell attained in each of the test environments(95% confidence limits). Environment 1 2 Mean lengths(mm) 51.0+1.0 49.0+1.0 Table 10. The mean lengths of shell attained in each of the vertical tray positions(95% confidence limits). Position 1 2 3 4 5 Mean length(mm) 49^+1.0 50.0±1.0 51.0±1.0 51.0+1.0 50.0+1.0 82 1. E n v i r o n m e n t Type Vs T r a y System The i n t e r a c t i o n of e n v i r o n m e n t t y p e w i t h t r a y s y s t e m p r o v e d t o be s t a t i s t i c a l l y (Appendirx A) and p r a c t i c a l l y s i g n i f i c a n t ( T a b l e 11). The M a c N i c o l and S u s p e n s i o n s y s t e m s p e r f o r m e d on an e q u i v a l e n t b a s i s i r r e s p e c t i v e of t h e i r e n v i r o n m e n t a l l o c a t i o n . The N e s t i e r t r a y s p e r f o r m e d t h e b e s t i n e n v i r o n m e n t 1, but a t t a i n e d measurements on p a r w i t h t h e o t h e r systems i n e n v i r o n m e n t 2. 2. E n v i r o n m e n t Type Vs T r a y System Vs V e r t i c a l P o s i t i o n T h i s r e l a t i o n s h i p was f o u n d t o be s t a t i s t i c a l l y and p r a c t i c a l l y s i g n i f i c a n t ( A p p e n d i x A & B ) . In e n v i r o n m e n t 1, t h e N e s t i e r t r a y s o u t p e r f o r m e d t h e o t h e r s y s t e m s i n a l l v e r t i c a l p o s i t i o n s ( A p p e n d i x B) a n d . s h e l l l e n g t h measurements d i d not v a r y s i g n i f i c a n t l y due t o v e r t i c a l p o s i t i o n . However, i n e n v i r o n m e n t 2 growth measurements i n a l l v e r t i c a l p o s i t i o n s were s i m i l a r but below t h a t a t t a i n e d i n e n v i r o n m e n t 1. P o s i t i o n e f f e c t s i n M a c N i c o l s y s t e m s were not d e t e c t e d i n e i t h e r e n v i r o n m e n t l o c a l e s e p a r a t e l y . However, i n e n v i r o n m e n t 2 growth i n p o s i t i o n s 1 t h r o u g h 4 were below t h a t a c h i e v e d i n e n v i r o n m e n t 1. L e n g t h measurements a c h i e v e d i n M a c N i c o l t r a y p o s i t i o n s 2 t o 4 i n e n v i r o n m e n t 1 e x c e e d e d l e v e l s i n t h e S u s p e n s i o n s y s t e m ( A p p e n d i x B ) . C o n v e r s e l y , i n e n v i r o n m e n t 2 l e n g t h m e asures i n M a c N i c o l t r a y p o s i t i o n s 1 and 2 were below l e n g t h s n o t e d i n t h e S u s p e n s i o n u n i t s f o r t h e f i r s t two p o s i t i o n s . S h e l l g r o w t h among t h e S u s p e n s i o n t r a y s were s i m i l a r i n b o t h e n v i r o n m e n t s and p o s i t i o n e f f e c t s d i d not become a p p a r e n t . 83 Table 11. The mean lengths(mm) of shell attained in each tray system in each of the environment types(95% confidence limits). Environment 1 MacNicol Nestier Suspension 50.0+1.0 57.0+1.0 47.0+1.0 Environment 2 MacNicol Nestier Suspension 47.0+1.0 52.0+1.0 49.0+1.0 84 3. E n v i r o n m e n t Type Vs T r a y System Vs V e r t i c a l P o s i t i o n Vs Time T h i s f o u r f a c t o r t e r m was f o u n d p r a c t i c a l l y and s t a t i s t i c a l l y s i g n i f i c a n t ( A p p e n d i x A and B ) . T h e r e were few d i f f e r e n c e s between t h e growth p a t t e r n s among t h e c u l t u r e s y s t e m s from e a r l y June t o mid J u l y . O y s t e r growth among t h e t e s t s y s t e m s d e v e l o p e d t h e i r own p a t t e r n s a f t e r t h i s p e r i o d . P o s i t i o n e f f e c t s a p p e a r e d i n M a c N i c o l t r a y s a f t e r mid J u l y . In e n v i r o n m e n t 1, growth i n p o s i t i o n 1 was below t h a t i n o t h e r t r a y p o s i t i o n s . T h i s t r a y a v e r a g e d 2mm/week u n t i l mid A u g u s t and t h e n g r o w t h r a t e i n c r e a s e d t o a p p r o x i m a t e l y 3-4mm/week up t o mid September f o l l o w e d by a r e t u r n t o J u n e - J u l y r a t e s . The t o p t r a y b e c a u s e of i t s slow s t a r t d i d not a c h i e v e measurements o b t a i n e d i n t h e t r a y s b e n e a t h i t ( A p p e n d i x B ) . The r e m a i n i n g p o s i t i o n s i n the s t a c k d i d not d e v i a t e from e a c h o t h e r . Most of t h e o y s t e r s i n t h e v e r t i c a l s e r i e s of t r a y s had i n d i c a t e d a d e c r e a s e i n s h e l l g r o w t h by t h e end of O c t o b e r e x c e p t f o r p o s i t i o n 3 w i t h an i n c r e a s e i n gr o w t h r a t e d u r i n g O c t o b e r ( A p p e n d i x B ) . G e n e r a l l y g r o w t h f o l l o w e d a s t a r t - u p p h a s e ( J u n e t o m i d - J u l y ) f o l l o w e d by i n c r e a s e d g r o w t h r a t e u n t i l e a r l y September, f o l l o w e d by a d e c l i n e i n s h e l l d e p o s i t i o n r a t e . P o s i t i o n e f f e c t s among M a c N i c o l t r a y s i n e n v i r o n m e n t 2 were not a s p r o n o u n c e d , a l t h o u g h p o s i t i o n 1 was s t i l l t h e l o w e s t " a c h i e v e r " . V i s u a l l y from t h e g r a p h s ( A p p e n d i x B ) , d i f f e r e n c e s l a y i n t h e gr o w t h c y c l e o v e r t i m e n ot a p p e a r i n g t o be as e r r a t i c . Growth c u r v e s were more c l o s e l y r e l a t e d and t h e r a t e of s h e l l g r o w t h was more c o n s t a n t from J u l y t o O c t o b e r ( a p p r o x . 2.5mm/week)(Appendix B ) . Growth was m i n i m a l i n O c t o b e r and t h e d e c r e a s e i n growth r a t e was much more v i s i b l e t h a n i n 85 e n v i r o n m e n t 1. Growth 'rates i n e n v i r o n m e n t 2 were l o w e r w i t h r e s p e c t t o e n v i r o n m e n t 1. S h e l l g r o w t h among N e s t i e r t r a y s i n e n v i r o n m e n t 1 a c h i e v e d more f a v o u r a b l e r e s u l t s t h a n t h o s e i n e n v i r o n m e n t 2. Growth r a t e s were l e s s e r r a t i c and measurements up t o September were g r e a t e r t h a n i n e n v i r o n m e n t 2. P o s i t i o n 2 was l o w e r t h a n t h e o t h e r p o s i t i o n s but a c h i e v e d f i n a l l e n g t h measurements c o m p a r a b l e w i t h t h e r e s t of t h e t r a y s i n t h e s t a c k . Growth was s l o w e d from September onward. P o s i t i o n e f f e c t s among N e s t i e r s i n e n v i r o n m e n t 2 were n o t e d from June t o t h e end of J u l y . Z e r o growth o c c u r r e d i n a l l v e r t i c a l p o s i t i o n s from J u l y 10 t o 24. P o s i t i o n e f f e c t s d i s a p p e a r e d d u r i n g a r a p i d g r o w t h p h a s e ( a p p r o x . 4mm/week) from J u l y 24 t o September 6. A f t e r , t h e s e d a t e s p o s i t i o n s 3 and 4 were s i g n i f i c a n t l y h i g h e r t h a n 1, 2 and 5 i n terms of g r o w t h r a t e and l e n g t h o b t a i n e d . A d e c r e a s e d growth r a t e by t h e end of O c t o b e r was n o t c l e a r l y d e f i n e d i n t h i s i n t e r a c t i o n . O y s t e r g r o wth i n t h e S u s p e n s i o n t r a y s were s i m i l a r i n b o t h e n v i r o n m e n t s . Over t h e t e r m of t h e s t u d y p o s i t i o n e f f e c t s were not c l e a r l y d e f i n e d i n e n v i r o n m e n t 2. A t c e r t a i n i n t e r v a l s p o s i t i o n e f f e c t s were a p p a r e n t but t h e s e f l u c t u a t e d t h r o u g h o u t t h e t e r m . However, g r o w t h r a t e i n t h e b o t t o m t r a y d i d d e c r e a s e t o a low l e v e l d u r i n g t h e f a l l m o n t h s ( A p p e n d i x B ) . End r e s u l t s i n b o t h e n v i r o n m e n t s d i d not i n d i c a t e t h e g rowth r a t e had l e v e l l e d o u t by t h e end of O c t o b e r . B e s i d e s t h i s s l i g h t p o s i t i o n e f f e c t t h e o v e r a l l g r o w t h r a t e r e m a i n e d f a i r l y c o n s t a n t i n b o t h e n v i r o n m e n t s f o r t h e d u r a t i o n of s a m p l i n g ( a p p r o x . 3mm/week). The S u s p e n s i o n s y s t e m a l s o d i d not show marked f l u c t u a t i o n s i n 86 g r o w t h r a t e as was t h e c a s e w i t h t h e o t h e r s y s t e m s . 4. E n v i r o n m e n t Type Vs T r a y System Vs Time T h i s r e l a t i o n s h i p was s t a t i s t i c a l l y and p r a c t i c a l l y s i g n i f i c a n t ( A p p e n d i x B ) . Among t r a y s y s t e m s i n e n v i r o n m e n t 1, g r o w t h i n N e s t i e r u n i t s was s u p e r i o r o v e r t i m e . Growth c u r v e s d e s c r i b i n g M a c N i c o l and S u s p e n s i o n t r a y s were c l o s e l y r e l a t e d . Growth r a t e i n t h e N e s t i e r i n c r e a s e d r a p i d l y a f t e r June 26 m a i n t a i n i n g a f a i r l y c o n s t a n t g r o w t h r a t e u n t i l September 6. Growth r a t e s i n o t h e r s y s t e m s d i d not i n c r e a s e s u b s t a n t i a l l y u n t i l J u l y 10 and d i d not match t h e r a t e s a t t a i n e d i n t h e N e s t i e r t r a y s . Growth r a t e s d e c r e a s e d i n a l l s y s t e m s a f t e r September 6 but c u r v e s d i d n o t i n d i c a t e t h a t a p l a t e a u had been r e a c h e d by t h e end o f O c t o b e r . Growth r a t e i n t h e N e s t i e r d i d n o t i n c r e a s e s i g n i f i c a n t l y u n t i l J u l y 24. From September 19 t o t h e end o f O c t o b e r growth measurements i n t h e N e s t i e r were g r e a t e r t h a n i n t h e o t h e r t r a y t y p e s . v G rowth r a t e s i n S u s p e n s i o n t r a y s were s i m i l a r i n b o t h e n v i r o n m e n t s . In e n v i r o n m e n t 2 g r e a t e r l e n g t h s t h a n i n M a c N i c o l t r a y s were a c h i e v e d a f t e r A u g u s t 7. Growth measurements l i n k e d t o e n v i r o n m e n t 2 l o c a t e d M a c N i c o l t r a y s were l o w e r t h a n i n e n v i r o n m e n t 1. M a c N i c o i u n i t s a l s o showed z e r o g r o w t h f o r t h e month of O c t o b e r . The o t h e r s y s t e m s d i s p l a y e d a g r a d u a l d e c r e a s e i n g r o w t h r a t e s s u c h t h a t v i a e x t r a p o l a t i o n , g r o w t h would r e a c h a z e r o r a t e by t h e end of November d e p e n d i n g upon ambient water t e m p e r a t u r e s . 5. T r a y Type Table 12. The mean lengths(mm) of shell attained in each tray system (95% confidence limits). MacNicol Nestier Suspension 48.0±1.0 54.Oil.0 48.0+1.0 • 88 R e s u l t s i n d i c a t e d a s i g n i f i c a n t s t a t i s t i c a l d i f f e r e n c e among t r a y s y s t e m s ( A p p e n d i x A ) . P r a c t i c a l d i f f e r e n c e s d i d not a p p e a r between M a c N i c o l and S u s p e n s i o n u n i t s , but t h e mean s h e l l l e n g t h s among N e s t i e r s y s t e m s were g r e a t e r ( T a b l e 1 2). 6. T r a y Type Vs Time The N e s t i e r t r a y g e n e r a t e d s i g n i f i c a n t l y b e t t e r g r o w t h o v e r t i m e t h a n t h e o t h e r two s y s t e m s ( A p p e n d i x B ) . The M a c N i c o l and S u s p e n s i o n t r a y r e s u l t s were s i m i l a r ( A p p e n d i x B ) . Growth r a t e i n N e s t i e r t r a y s r a n g e d from 0.5 mm/week t o 3 mm/week v e r s u s 0.5 t o 2.6 mm/week i n S u s p e n s i o n and M a c N i c o l t r a y s . S u s p e n s i o n and M a c N i c o l t r a y s d i d a c h i e v e a r a t e of 3.7 mm/week f o r a s h o r t p e r i o d of t i m e . Growth r a t e i n t h e M a c N i c o l t r a y s had begun t o d e c r e a s e t o 0.5 mm/week by m i d - O c t o b e r , however s h e l l was s t i l l b e i n g added among S u s p e n s i o n and N e s t i e r t r a y c u l t u r e d o y s t e r s . S h e l l l e n g t h a t t h e end of O c t o b e r f o r t h e N e s t i e r s t o o d a t 78 mm v e r s u s 69 mm i n t h e o t h e r s y s t e m s . 7. V e r i t i c a l P o s i t i o n Vs T r a y Type Among t r a y t y p e s , a p o s i t i o n e f f e c t a p p e a r e d i n t h e N e s t i e r w i t h t h e s e c o n d t r a y i n t h e column p e r f o r m i n g t h e l o w e s t . S i g n i f i c a n t p r a c t i c a l d i f f e r e n c e s were not d e t e c t e d between M a c N i c o l and S u s p e n s i o n t r a y s or between t h e i r v e r t i c a l p o s i t i o n s ( A p p e n d i x B ) . 89 8. V e r t i c a l P o s i t i o n Vs T r a y Type Vs Time D i f f e r e n c e s were not d e t e c t a b l e i n t h e f i r s t two weeks of t h e s t u d y . Growth r a t e d i f f e r e n c e s s u r f a c e d a f t e r J u l y 10. The g r o w t h c u r v e a s s o c i a t e d w i t h t h e t o p t r a y of M a c N i c o l u n i t s was t h e l o w e s t from l a t e J u l y t o e a r l y A u g u s t . O t h e r t r a y s i n t h e column d i d not show d i f f e r e n c e s ( A p p e n d i x B ) . P o s i t i o n 2 of t h e N e s t i e r was t h e l o w e s t from J u l y 10 t o A u g u s t 7, o t h e r w i s e v e r t i c a l p o s i t i o n d i d n o t a p p e a r as a c o n t r i b u t i n g f a c t o r . Growth r a t e s d e c r e a s e d a f t e r t h e f i r s t week i n September, but o y s t e r s were s t i l l showing an i n c r e a s e i n s h e l l l e n g t h by t h e end of O c t o b e r . The S u s p e n s i o n t r a y s d i s p l a y e d l i t t l e v a r i a t i o n i n growth r a t e a t t r i b u t a b l e t o v e r t i c a l p o s i t i o n . 9. Time S h e l l g r o w t h f o l l o w e d a s i n u s o i d a l t y p e c u r v e ( A p p e n d i x B ) . Growth began w i t h a s t a r t - u p phase from mid-June t o t h e end of t h e month. T h i s was f o l l o w e d by an i n c r e a s e i n g r o w t h r a t e u n t i l e a r l y S eptember. A f t e r t h i s t i m e g r o w t h r a t e t e n d e d t o d e c r e a s e d u r i n g t h e f a l l months. 90 SHELL WIDTH The f a c t o r s of e n v i r o n m e n t t y p e ( T a b l e 13), t r a y s y s t e m ( T a b l e 14) and v e r t i c a l p o s i t i o n ( T a b l e 15) d i d not a c c o u n t f o r any p r a c t i c a l s i g n i f i c a n t d i f f e r e n c e s among g r o w t h i n o y s t e r s h e l l w i d t h . 1. E n v i r o n m e n t Type Vs Time A f t e r t h e s e c o n d week of J u l y s i g n i f i c a n t d i f f e r e n c e s a r o s e between g r o w t h c h a r a c t e r i s t i c s i n t h e two e n v i r o n m e n t s . The growth r a t e s i n e n v i r o n m e n t 1 were h i g h e r from t h e - e n d o f June u n t i l e a r l y September. Growth c u r v e s began t o l e v e l o f f i n b o t h e n v i r o n m e n t s a f t e r t h i s t i m e . Growth i n e n v i r o n m e n t 2 was t h e same as i n e n v i r o n m e n t 1 u n t i l J u l y 10 t h e n t h e growth r a t e d e c r e a s e d l a g g i n g b e h i n d measurements o b t a i n e d i n e n v i r o n m e n t 1 ( A p p e n d i x C ) . D e s p i t e t h i s l u l l i n growth, t h e a c t u a l g r o w t h r a t e s were s i m i l a r i n t h e two l o c a t i o n s . The f i n a l w i d t h measurements were s i m i l a r i n b o t h e n v i r o n m e n t s . 2. E n v i r o n m e n t Type Vs T r a y S y s t e m T h i s i n t e r a c t i o n c o n t r i b u t e d s i g n i f i c a n t l y t o g r o w t h ( A p p e n d i x A ) . O y s t e r s i n N e s t i e r and M a c N i c o l t r a y s i n e n v i r o n m e n t 1 grew b e t t e r t h a n t h o s e i n t h e S u s p e n s i o n u n i t s . E n v i r o n m e n t t y p e d i d not s i g n i f i c a n t l y i n f l u e n c e growth i n t h e S u s p e n s i o n t r a y s . Growth i n N e s t i e r and M a c N i c o l t r a y s were d e p r e s s e d i n e n v i r o n m e n t 2 below l e v e l s i n e n v i r o n m e n t 1 t o a p o i n t where a l l t h e s y s t e m s p e r f o r m e d on a e q u a l b a s i s ( T a b l e 16) . Table 13. The mean widths (mm) of shell attained in each environment type(95% confidence limits). Environment 1 2 Mean width 42.0+1.0 38.0+1.0 Table 14. The mean widths(mm) of shell attained in each tray system (95% confidence limits). MacNicol Nestier Suspension 39.0+1.0 42.0±1.0 39.0±1.0 Table 15. The mean widths(mm) of shell attained in each of the vertical tray positions(95% confidence limits). Position 1 2 3 4 5 Mean width 39.0+1.0 40.0+1.0 41.0±1.0 41.0+1.0 40.0+1.0 92 3. E n v i r o n m e n t Type Vs T r a y System Vs Time Growth c u r v e s of o y s t e r s i n N e s t i e r and M a c N i c o l t r a y s was f a v o u r a b l e i n e n v i r o n m e n t 1 t h a n e n v i r o n m e n t 2. Growth c u r v e s f o r t h e S u s p e n s i o n u n i t s were s i m i l a r i n b o t h e n v i r o n m e n t s ( A p p e n d i x C ) . N e s t i e r t r a y s i n e n v i r o n m e n t 1 had two p e r i o d s of " r a p i d " g r o w t h , one from June 26 t o J u l y 10 and t h e s e c o n d from August 7 t o September 6. A f t e r September 6 g r o w t h r a t e d e c r e a s e d but d i d not show s i g n s of a p p r o a c h i n g z e r o • by t h e end of O c t o b e r ( A p p e n d i x C ) . Growth c u r v e s a s s o c i a t e d w i t h M a c N i c o l and S u s p e n s i o n t r a y s were c l o s e l y r e l a t e d i n e n v i r o n m e n t 1. B o t h s y s t e m s i l l u s t r a t e d a u n i f o r m r a t e from. June 26 t o September 6 f o l l o w e d by a r e d u c t i o n i n growth r a t e . In e n v i r o n m e n t 2 growth was hampered i n t h e N e s t i e r t r a y s u n t i l A u g u s t , t h e p o i n t when g r o w t h r a t e i n c r e a s e d d r a s t i c a l l y and t h e n d r o p p e d a f t e r September 6 ( A p p e n d i x C ) . Growth was s u p e r i o r i n t h e o t h e r two s y s t e m s . Growth c u r v e s f o r M a c N i c o l and S u s p e n s i o n t r a y s i n e n v i r o n m e n t 2 were s i m i l a r e x c e p t g r o w th i n t h e M a c N i c o l t r a y was a p p r o a c h i n g z e r o f a s t e r by t h e end of O c t o b e r . The S u s p e n s i o n t r a y s d i d not i n d i c a t e a l e v e l l i n g o f f or d r o p i n r a t e i n O c t o b e r . T h e i r p e r f o r m a n c e was d e p r e s s e d between August 7 and September 19, a l t h o u g h f i n a l w i d t h measurements d i d not d i f f e r s i g n i f i c a n t l y a t t h e two e n v i r o n m e n t s . Growth r a t e s i n t h e M a c N i c o l t r a y s was d e p r e s s e d i n e n v i r o n m e n t 2. T h e i r f i n a l w i d t h measurements were l e s s i n t h i s e n v i r o n m e n t . G e n e r a l l y , g r o w t h c u r v e s f o r t h e M a c N i c o l and S u s p e n s i o n t r a y s d i s p l a y e d a Table 16. The mean widt±is(mm) of shell attained in each tray system in each of the environment types(95% confidence limits). MacNicol 41.Oil.0 MacNicol 37.0+1.0 Environment 1 Nestier 45.Oil.0 Environment 2 Nestier 40.0+1.0 Suspension 40.0+1.0 Suspension 38.Oil.0 94 more c o n s t a n t growth r a t e o v e r t i m e i n e n v i r o n m e n t 2 t h a n i n e n v i r o n m e n t 1. Growth c u r v e s f o r t h e N e s t i e r t r a y s i n e n v i r o n m e n t 2 were more e r r a t i c t h a n a t t h e o t h e r l o c a t i o n . 4. E n v i r o n m e n t Type Vs V e r t i c a l P o s i t i o n E n v i r o n m e n t 2 seemed t o c a u s e a d e b i l i t a t i n g g r o w t h i n t h e t o p t r a y . P r a c t i c a l d i f f e r e n c e s m a t e r i a l i z e among t h e o t h e r v e r t i c a l p o s i t i o n s e n v i r o n m e n t t y p e ( A p p e n d i x C ) . 5. E n v i r o n m e n t Type Vs V e r t i c a l P o s i t i o n Vs Time A p o s i t i o n e f f e c t d i d not o c c u r i n e n v i r o n m e n t 1 o v e r t h e ter m of t h e s t u d y . Growth r a t e i n p o s i t i o n 1 i n e n v i r o n m e n t 2 was below t h a t of t h e o t h e r v e r t i c a l p o s i t i o n s . Growth r a t e s among o t h e r v e r t i c a l p o s i t i o n s i n e n v i r o n m e n t 2 was m a i n t a i n e d on a u n i f o r m m a g n i t u d e u n t i l t h e end of O c t o b e r . 6. E n v i r o n m e n t Type Vs T r a y System Vs V e r t i c a l P o s i t i o n The M a c N i c o l and S u s p e n s i o n u n i t s d i d n o t d i s p l a y any p r a c t i c a l d i f f e r e n c e s among growth i n v e r t i c a l p o s i t i o n s i n e i t h e r e n v i r o n m e n t t y p e . V e r t i c a l p o s i t i o n s i n N e s t i e r t r a y s i n e n v i r o n m e n t 1 o u t p e r f o r m e d t h e o t h e r s y s t e m s w i t h t h e e x c e p t i o n o f p o s i t i o n 4 w h i c h was o n l y m a r g i n a l l y b e t t e r t h a n t h e M a c N i c o l , p o s i t i o n 4. Growth c h a r a c t e r i s t i c s i n e n v i r o n m e n t 2 were s i m i l a r among t h e t h r e e s y s t e m s . Growth i n N e s t i e r p o s i t i o n s 1,2 and 3 was d e p r e s s e d below t h a t a c h i e v e d i n e n v i r o n m e n t 1. P o s i t i o n s 4 and 5 i n t h e N e s t i e r were s i m i l a r i n b o t h e n v i r o n m e n t s ( A p p e n d i x C ) . e f f e c t on d i d not i n e i t h e r 95 7. Time Growth r a t e s d e s c r i b e d a s i n u s o i d a l c u r v e c o n s i s t i n g of t h e t h r e e p h a s e s as per d i s c u s s i o n f o r s h e l l l e n g t h g r o w t h . 8. T r a y System Vs Time Growth d i f f e r e n c e s among t h e t r a y s s u r f a c e d a f t e r J u l y 24. From t h a t p o i n t , growth r a t e i n t h e N e s t i e r s y s t e m i n c r e a s e d and mean w i d t h s a t t a i n e d were h i g h e r t h a n i n o t h e r t r a y t y p e s . Growth c u r v e s d e s c r i b i n g M a c N i c o l and S u s p e n s i o n u n i t s were a l m o s t i d e n t i c a l ( A p p e n d i x C ) . 9. V e r t i c a l P o s i t i o n Vs Time The g r o w th c u r v e f o r t h e topmost t r a y a p p e a r e d c o n s p i c u o u s l y lower t h a n c u r v e s f o r t h e o t h e r p o s i t i o n s . Growth c u r v e s o f p o s i t i o n s 2 t o 5 were a l m o s t i d e n t i c a l i n a p p e a r a n c e ( A p p e n d i x C ) . 10. T r a y System Vs V e r t i c a l P o s i t i o n E v i d e n c e of an e f f e c t by t h i s i n t e r a c t i o n t e r m d i d n o t o c c u r among t h e M a c N i c o l or t h e S u s p e n s i o n u n i t s , however i t d i d c o n t r i b u t e t o b e t t e r g r o w t h i n N e s t i e r t r a y p o s i t i o n s 4 and 5. P o s i t i o n 1 of t h e N e s t i e r was t h e l o w e s t among t h e s t a c k of t r a y s ( A p p e n d i x C ) . 11. T r a y System Vs V e r t i c a l P o s i t i o n Vs Time P o s i t i o n e f f e c t s a p p e a r e d i n a l l of t h e t r a y s y s t e m s o v e r t i m e . A f t e r t h e f i r s t t h r e e weeks, g r o w t h c u r v e s i n p o s i t i o n 1 of M a c N i c o l u n i t s were l o w e r t h a n c u r v e s a s s o c i a t e d w i t h 96 p o s i t i o n 4. L i t t l e p r a c t i c a l d i f f e r e n c e e x i s t e d between t h e f o u r t h t r a y and r e m a i n i n g v e r t i c a l p o s i t i o n s . P o s i t i o n 1 i n t h e N e s t i e r was t h e l o w e s t w i t h o t h e r t r a y p o s i t i o n s b e i n g c l o s e l y r e l a t e d . A p o s i t i o n e f f e c t s h i f t o c c u r r e d among S u s p e n s i o n u n i t s . A f t e r t h e t h i r d week, p o s i t i o n 1 and 3 were o p e r a t i n g l o w e r t h a n p o s i t i o n s - 2 and 5 u n t i l t h e f o u r t h week. B e g i n n i n g i n t h e f i f t h week p o s i t i o n s 1 and 5 were l o w e r t h a n 4 and 2. B a l a n c i n g t h e t r a y s y s t e m s a g a i n s t e a c h o t h e r , d i f f e r e n c e s between N e s t i e r and S u s p e n s i o n u n i t s a r o s e a f t e r t h e s e c o n d week. From t h a t p o i n t t o t h e end of s a m p l i n g , w i t h t h e e x c e p t i o n of t h e topmost N e s t i e r t r a y , t h e N e s t i e r s y s t e m had t h e more f a v o u r a b l e g r o w t h . A g a i n s t th e M a c N i c o l t r a y t h e f i r s t two p o s i t i o n s r e s u l t s were s i m i l a r , w h i l e p o s i t i o n 3 a c h i e v e d b e t t e r r e s u l t s i n t h e N e s t i e r a f t e r A u g u s t 7, p o s i t i o n 4 a f t e r J u l y 24 and p o s i t i o n 5 a f t e r t h e end o f J u n e . 12. E n v i r o n m e n t Type Vs T r a y System Vs V e r t i c a l P o s i t i o n Vs Time Among N e s t i e r t r a y s i n e n v i r o n m e n t 1 g r o w t h c u r v e s were c l o s e l y r e l a t e d n o t showing any p o s i t i o n d e s c r e p a n c i e s o v e r t i m e . Growth r a t e s d e c r e a s e d a f t e r September 6 t o 19 f o l l o w e d by a s l i g h t i n c r e a s e i n r a t e u n t i l O c t o b e r 2, t h e n l e v e l l i n g o f f . The t o p t r a y i n e n v i r o n m e n t 2 was l o w e r i n p e r f o r m a n c e t h a n o t h e r p o s i t i o n s . T h e r e was l i t t l e d i f f e r e n c e among t h e r e m a i n i n g v e r t i c a l p o s i t i o n s . E n v i r o n m e n t 2 d i d c a u s e more v a r i a t i o n among g r o w t h r a t e o v e r t h e s e a s o n . Growth r a t e s i n e n v i r o n m e n t 1 were not as e r r a t i c ( A p p e n d i x C ) . However, t h e f i n a l w i d t h measures were s i m i l a r i n b o t h e n v i r o n m e n t s f o r t h e N e s t i e r s y s t e m , e x c e p t f o r p o s i t i o n 1 b e i n g lower i n e n v i r o n m e n t 2. 97 M a c N i c o l t r a y s s i t u a t e d i n e n v i r o n m e n t 1 had c l o s e l y r e l a t e d g r o w t h c u r v e s i n a l l p o s i t i o n s and a u n i f o r m growth r a t e from m i d - J u n e t o e a r l y September. In e n v i r o n m e n t 2 t h e c u r v e a s s o c i a t e d w i t h p o s i t i o n 1 was t h e l o w e s t w h i l e o t h e r p o s i t i o n s d i s p l a y e d no s u c h d i f f e r e n c e . S h e l l growth r e m a i n e d a t a c o n s i s t e n t r a t e between end of June t o e a r l y A u g u s t f o l l o w e d by c u r v e s a p p r o a c h i n g z e r o g r o w t h by t h e end o f O c t o b e r . C h a n g i n g p o s i t i o n e f f e c t s were n o t e d i n S u s p e n s i o n u n i t s i n b o t h e n v i r o n m e n t s . Among u n i t s i n e n v i r o n m e n t 1 p o s i t i o n 2 p e r f o r m e d t h e b e s t from J u l y 10 t o September 6 f o l l o w e d by d e c l i n i n g r a t e s i n p o s i t i o n s 1,3 and 5 a f t e r t h i s t i m e . P o s i t i o n s 2 and 4 m a i n t a i n e d a c o n s t a n t r a t e . Growth r a t e i n p o s i t i o n 4 d e c r e a s e d t o z e r o a f t e r September 19 f o l l o w e d by d e c r e a s i n g r a t e s i n p o s i t i o n s 1,2 and 5 a f t e r O c t o b e r 2. Growth was s t i l l o c c u r r i n g i n p o s i t i o n 3 i n O c t o b e r b u t t h e growth c u r v e d i d i n d i c a t e a l e v e l l i n g o f f . The end of t h e s t u d y f o u n d p o s i t i o n 3 g r e a t e r t h a n 1 and l i t t l e d i f f e r e n c e among s h e l l w i d t h s i n o t h e r t r a y p o s i t i o n s . D i f f e r e n c e s a p p e a r e d i n v e r t i c a l p o s i t i o n s of t h e S u s p e n s i o n u n i t s i n e n v i r o n m e n t 2 a f t e r t h e end o f J u n e . T r a y p o s i t i o n s 2, 4 and 5 g r o w t h r a t e s were g r e a t e r t h a n t h e o t h e r p o s i t i o n s and z e r o growth o c c u r r e d i n p o s i t i o n 5 between J u l y 24 and A u g u s t 7. P o s i t i o n s 2 and 4 were a t t h e i r h i g h e s t l e v e l s u n t i l e a r l y September. Growth r a t e s t h e n d e c l i n e d u n t i l O c t o b e r 2. D u r i n g t h e month of O c t o b e r g r o w th r a t e s i n c r e a s e d i n a l l p o s i t i o n s ; p o s i t i o n 1 e s p e c i a l l y i m p r o v e d ( A p p e n d i x C ) . Comparing t h e two e n v i r o n m e n t s p o s i t i o n 3 had t h e l o w e s t g r o w th c u r v e v e r s u s an a b s e n c e of s i g n i f i c a n t d i f f e r e n c e s among t h e o t h e r 98 p o s i t i o n s . Growth r a t e s were g e n e r a l l y u n i f o r m and c o n s i s t e n t i n b o t h 'the e n v i r o n m e n t s . In e n v i r o n m e n t 1 t h e N e s t i e r p e r f o r m e d b e t t e r t h a n t h e S u s p e n s i o n u n i t s a t a l l p o s i t i o n s , w h i l e t h e r e was l i t t l e d i f f e r e n c e between g r o w t h c h a r a c t e r i s t i c s of t h e S u s p e n s i o n and M a c N i c o l u n i t s . In e n v i r o n m e n t 2 p o s i t i o n e f f e c t s were m i n i m a l i n S u s p e n s i o n u n i t s w i t h r e s p e c t t o t h e N e s t i e Y s y s t e m . W i t h t h e e x c e p t i o n of p o s i t i o n 1 i n t h e N e s t i e r t r a y g r o w t h r a t e s between the s y s t e m s . w e r e c l o s e i n m a g n i t u d e . MEAT CONDITION At a 5% l e v e l o f s i g n i f i c a n c e t h e a n a l y s i s of v a r i a n c e d i d not r e v e a l any s i g n i f i c a n t d i f f e r e n c e s among h i g h e r l e v e l i n t e r a c t i o n s i n v o l v i n g two or more f a c t o r s . S t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s were f o u n d o n l y among f a c t o r s of t i m e and t r a y t y p e ( A p p e n d i x D ) . M u l t i p l e r a n g e t e s t s ( N e u m a n - K e u l s and Tukey) r e v e a l e d an i n c r e a s e i n t h e c o n d i t i o n i n d e x from June 21 t o a peak by J u l y 19; f a l l i n g o f f by August 7. The c o n d i t i o n i n d i c e s f r o m J u l y 19 t o August 17 were h i g h e r t h a n t h o s e e n c o u n t e r e d i n June and e a r l y J u l y ( A p p e n d i x E ) . The M a c N i c o l t r a y s s u s t a i n e d a s i g n i f i c a n t l y h i g h e r c o n d i t i o n i n d e x t h a n t h e S u s p e n s i o n or N e s t i e r s y s t e m s . C o n d i t i o n i n d i c e s of N e s t i e r and S u s p e n s i o n s y s t e m s were not s i g n i f i c a n t l y d i f f e r e n t a t a 5% p r o b a b i l i t y l e v e l . ECONOMICS E a c h s y s t e m was b r o k e n down i n t o component c o s t . The 99 M a c N i c o l and N e s t i e r a s s e m b l a g e s r e q u i r e d s i x t r a y s i n e a c h s t a c k . One a d d i t i o n a l t r a y was u s e d as a c o v e r . The p r i c e of N e s t i e r t r a y s was f o u n d t o v a r y d e p e n d i n g upon whether th e p u r c h a s e s o u r c e was c o r p o r a t e o r p r i v a t e . B a s e d upon a c o s t / o y s t e r e v a l u a t i o n , a s s u m i n g a l i f e s p a n of 5 y e a r s f o r e a c h s y s t e m , t h e M a c N i c o l and S u s p e n s i o n a r e t h e c h e a p e s t a t a c o s t of $ . 0 2 / o y s t e r / y e a r v e r s u s $ . 0 4 / o y s t e r / y e a r f o r t h e N e s t i e r s y s t e m . The M a c N i c o l a p p e a r s t h e l e a s t e x p e n s i v e p u r c h a s e , however use of s u c h a s y s t e m would i n v o k e a $ . 0 l / o y s t e r f o r e v e r y hour t h e s y s t e m i s h a n d l e d . H a n d l i n g c o s t s a p p l i e d t o t h e S u s p e n s i o n s y s t e m were e s s e n t i a l l y n i K T a b l e 1 7 ) . Table 17. Economic an a l y s i s of the h a l f - s h e l l tray c u l t u r e systems tested(5 t r a y s / u n i t ) . 1.MATERIALS A. Suspension System PVC f l a t b a r @$1.05/m X 15.2m = $16.00 PVC U-channel §$0.33/m . X 15.2m = $ 5.00 Conwedr Net (a$0.65/m^ X 10.2m2 = $ 6.60 Polypropylene rope V @$0.10/m X 5.6m = $ 0.56 Iron angle h" (3$0.76/m X 2.5m = $ 1:88 Cable t i e s ra$0.30 X 30 = $ 0.90 Swivel (3$2.65 X I = $ 2.65 Styrofoam (3$177/m3 X .03m3 = $ 5.31 #Copper r i v e t s @$0.03 X 10 = $ 0.30 Total $39.20 ,B..McNicol System McNicol tr a y @$1.10 Styrofoam @$177/m3 Center piece §$2.50 X 6 = $ 6.60 X .014m3 = $ 2.50 X I = $ 2.50 Total $11.60 C. N e s t i e r System N e s t i e r tray G>$7.00 - $10.00 X 6 = $42.00 Banding and c l i p s P$3.00 X I = $ 3 . 0 0 Styrofoam @$177/m3 X .014m-3 = $ 2.50 Total $47 - 50.00 table 17 continued 2. HANDLING(labour rate $6/hr and using 2 units) Procedure Suspension McNicol N e s t i e r l i f t i n g d ismantling re-assembly r e - s e t t i n g lOmin 8min lOmin 5min 5min 5min 12min 12min 5mi n 5min TOTAL 18min 25min 36mi n # o f oysters 1000 210 520 $• c o s t / o y s t e r n e g l i b l e .01 .10 system c o s t / o y s t e r •02/yr .02/yr .04/yr (5 y e a r l i f e s p a n ) 1 02 DISCUSSION - QUALITATIVE F o u l i n g The c o m p a c t n e s s of t h e N e s t i e r a s s e m b l y , t h e s m a l l o p e n i n g s and a n g l e d edges on e a c h t r a y p r o v i d e d a f a v o u r a b l e e n v i r o n m e n t f o r b a r n a c l e s . The b a r n a c l e s s e t t i n g i n c r e v i c e s , c o r n e r s and u n der t h e l e d g e s s u g g e s t s t h e s e c r e a t u r e s s ought out and f o u n d t h e dead w a t e r l o c a t i o n s i n t h i s s y s t e m . B a r n a c l e s d i d not s e t i n t h e open a r e a s of t h e t r a y o c c u p i e d by o y s t e r s . The c u r r e n t r e gime i n e n v i r o n m e n t 2 r e d u c e d b a r n a c l e s e t s on t h e N e s t i e r t r a y s below t h a t o c c u r r i n g i n e n v i r o n m e n t 1. The i n t e r t i d a l zone of e n v i r o n m e n t 2 was r e l a t i v e l y f r e e of b a r n a c l e s compared t o e n v i ronment 1. M u s s e l p r e f e r e n c e f o r M a c N i c o l t r a y s i s a d i f f i c u l t phenomenon t o e x p l a i n . I t may be due t o m a t e r i a l of c o n s t r u c t i o n , p e r f o r a t i o n s i z e , d e p t h o r s p a c i n g of t r a y s a n d / o r t h e c i r c u l a t i o n p a t t e r n s t h r o u g h t h e s y s t e m . The a b s e n c e of b a r n a c l e s may be due t o t h e f r e e s w i m m i n g l a r v a e a v o i d i n g t h e m a t e r i a l s of c o n s t r u c t i o n o r t h e e n v i r o n m e n t a l c o n d i t i o n s i n t h e s y s t e m . The more open n a t u r e o f t h e M a c N i c o l t r a y may r e d u c e t h e s t a g n a n t water a r e a s w i t h i n t h e s y s t e m t o e l i m i n a t e b a r n a c l e f o u l i n g . The a b s e n c e of m u s s e l and b a r n a c l e f o u l i n g i n S u s p e n s i o n t r a y s c o u l d be c a u s e d by t h e o p e n e s s o f t h e d e s i g n m a x i m i z i n g t h e e x p o s u r e of a l l s u r f a c e s . The m a t e r i a l s of c o n s t r u c t i o n may p o s s e s s f o u l i n g r e t a r d a n t p r o p e r t i e s t h a t a r e as y e t not documented. 1 03 R e g u l a r d r y i n g of t h e t r a y s e a c h week d i d c o n t r o l a l g a l f o u l i n g on a l l t r a y s . E n d i n g t h e d r y i n g r o u t i n e i n t h e f a l l c a u s e d a l g a e t o b u i l d - u p on N e s t i e r and M a c N i c o l t r a y s . A l g a l f o u l i n g on t h e S u s p e n s i o n t r a y s was n o t a p r o b l e m a f t e r mesh s i z e o f t h e c o v e r was i n c r e a s e d f r o m 1/4 t o 1/2 i n c h . The s m a l l e r mesh s i z e a l l o w e d a l g a l f i l a m e n t s t o weave a b a r r i e r o v e r t h e e n t i r e n e t . The l a r g e r mesh p r e v e n t e d t h e f i l a m e n t s f r o m a t t a c h i n g i n s u c h a manner. The a b s e n c e of a l g a e on l o w e r t r a y s i n t h e s t a c k was p r o b a b l y due t o i n s u f f i c i e n t l i g h t c o n d i t i o n s c a u s e d by t h e s h a d i n g e f f e c t of t h e t o p t r a y . The c o n t r o l of a l g a l f o u l i n g i n t h e S u s p e n s i o n s y s t e m p r e v e n t e d one s o u r c e of r e s t r i c t i n g w a ter c i r c u l a t i o n . A l g a l g r o w t h on t h e o t h e r s y s t e m s p r o b a b l y hampered water c i r c u l a t i o n t h r o u g h t h e t r a y a s s e m b l i e s . The c o n t r o l of f l o a t i n g d e b r i s was a f l o a t a t i o n p r o b l e m . S u s p e n d i n g t h e N e s t i e r and M a c N i c o l t r a y s d e e p e r would have r e d u c e d d e b r i s a c c u m u l a t i o n and a l g a l g r o w t h . The u n i t s were s u s p e n d e d i n s u c h a manner t o meet a s t a t e - o f - t h e - a r t s p e c i f i c a t i o n f o r t r a y c u l t u r e i n B r i t i s h C o l u m b i a . S n a g g i n g of d e b r i s on t h e S u s p e n s i o n s y s t e m was n o t a p r o b l e m . The e n t i r e s y s t e m was s e t d e e p e r i n t h e w a t e r . S h e l l S c a r r i n g The m a t e r i a l h a r d n e s s and t h e f l a t s i d e s o f t h e M a c N i c o l t r a y ; t h e a r r a n g e m e n t of p a r t i t i o n s and h o l e s i z e i n N e s t i e r t r a y s p r o v e d t o promote s h e l l f u s i o n . I f f u s i o n w i t h t h e t r a y p r o c e e d s t o o f a r r e m o v a l l e a d s t o s h e l l f r a c t u r e a n d / o r t h e p o s s i b l e d e a t h of t h e o y s t e r . R e g u l a r i n s p e c t i o n e v e r y 2 weeks 1 04 d u r i n g t h e s t u d y p r e v e n t e d f u s i o n f r o m p r o c e e d i n g t o o f a r . M a i n t a i n i n g s u c h a s c h e d u l e i n a c o m m e r c i a l o p e r a t i o n i s not f e a s i b l e . Growth i n t o t h e t r a y s i d e s o r t h e n e t mesh of t h e S u s p e n s i o n s y s t e m was n e v e r a p r o b l e m . The f l e x i b i l i t y of t h e ne t and t h e s a g g i n g under l o a d e l i m i n a t e d p r e s s u r e d c o n t a c t w i t h the o u t e r t r a y edges and t h e s u p p o r t mesh. M a t e r i a l s H a n d l i n g . The o n l y o b j e c t i o n t o t h e use of M a c N i c o l t r a y s , from a h a n d l i n g v i e w p o i n t , was t h e i r low c a r r y i n g c a p a c i t y p e r t r a y . C o m m e r c i a l o p e r a t i o n s would r e q u i r e l a r g e numbers of t r a y s t o meet p r o d u c t i o n g o a l s . The o p e r a t i o n would be s p r e a d o v e r a l a r g e r a r e a and r e q u i r e s e v e r a l man h o u r s f o r i n s p e c t i o n , h a r v e s t i n g or p l a n t i n g . S i m i l a r p r o b l e m s would a r i s e u s i n g t h e N e s t i e r s y s t e m . The t r a y ' s c a p a c i t y i s g r e a t e r but a l a r g e number of t r a y s would be r e q u i r e d i n a c o m m e r c i a l v e n t u r e . T h i s f a c t , c ombined w i t h a more t i m e l y d i s m a n t l i n g p r o c e d u r e q u e s t i o n s t h e s u c c e s s of t h e s y s t e m f o r c o m m e r c i a l o p e r a t i o n s . S u s p e n s i o n s y s t e m o y s t e r s were r e a d i l y a c c e s s i b l e . E a c h t r a y was d e s i g n e d t o h o l d 100 t o 160 o y s t e r s r e d u c i n g t h e number of t r a y s r e q u i r e d i n a c o m m e r c i a l o p e r a t i o n and a l l o w e d t h e h a n d l i n g of a g r e a t e r number of o y s t e r s p e r u n i t t i m e . M a t e r i a l P e r f o r m a n c e P l a s t i c s a r e an e x c e l l e n t m a t e r i a l f o r m a r i n e a p p l i c a t i o n s i n m a r i c u l t u r e . The g a l v a n i z e d h a l i b u t s naps a t t a c h i n g t h e S u s p e n s i o n t r a y s t o t h e s u p p o r t l i n e s would have t o be r e p l a c e d 105 e a c h y e a r . F o r c o m m e r c i a l use t h e s e c o u l d be s u b s t i t u t e d w i t h n y l o n c a b l e t i e s . The n y l o n c a b l e t i e s e n d u r e d e x t r e m e l y w e l l and showed no s i g n o f f r a c t u r e , c h a f f i n g or d i s c o l o u r a t i o n . The o n l y d e s i g n f a u l t i n t h e S u s p e n s i o n s y s t e m was t h e s a g g i n g of t h e n e t . T h i s p r e v e n t e d f u l l use of t h e g r o w i n g a r e a i n e a c h t r a y . A d d i t i o n a l s u p p o r t o f t h e net mesh s h o u l d be d e s i g n e d i n t o t h e s y s t e m so as not t o i n t e r f e r e w i t h w ater c i r c u l a t i o n . E c onomic s The M a c N i c o l a s s e m b l y was t h e l e a s t e x p e n s i v e from a component c o s t b a s i s , but t h e b e n e f i t s o f c h e a p e r o y s t e r h a n d l i n g c o s t s w i t h t h e S u s p e n s i o n s y s t e m made i t t h e more a t t r a c t i v e p u r c h a s e . . The N e s t i e r t r a y e v o l v e d as t h e p o o r e s t i n v e s t m e n t i n terms of component and m a t e r i a l s h a n d l i n g c o s t . The u n i t s were s e l f -d e f e a t i n g from t h e way t h e y had t o be bound t o g e t h e r . T h e i r a v a i l a b i l i t y i n c o m m e r c i a l q u a n t i t i e s was a l s o d e b a t a b l e a t t h e t i m e o f t h e r e s e a r c h . The S u s p e n s i o n s y s t e m o f f e r e d f a v o u r a b l e c o s t s f o r h a n d l i n g and components. The b e n e f i t of b e i n g a b l e t o h a n d l e a g r e a t e r number of o y s t e r s / u n i t t i m e make t h e i n v e s t m e n t a t t r a c t i v e . 106 QUANTITATIVE The a s s e s s m e n t of t r a y p e r f o r m a n c e was b a s e d upon t h e r e s u l t s f r o m t h e y i e l d v a r i a b l e s o f s h e l l l e n g t h and w i d t h . D i s c u s s i o n s and c o n c l u d i n g remarks a r e b a s e d upon s h e l l l e n g t h and w i d t h g r o w t h p e r f o r m a n c e . S i n g l e F a c t o r I n t e r a c t i o n s 1. E n v i r o n m e n t Type The f a c t o r e n v i r o n m e n t t y p e had l i t t l e i n f l u e n c e upon o y s t e r g r o w t h . E n v i r o n m e n t 2 was a t i d a l raceway and had warmer water t e m p e r a t u r e s d u r i n g t h e months of J u l y and A u g u s t . A c c o r d i n g t o Walne(l974) t h e a v e r a g e f e e d i n g r a t e s h o u l d i n c r e a s e as water f l o w i n c r e a s e s , s t i m u l a t i n g g r o w t h . The a b s e n c e of s u c h a r e s u l t i n t h i s r e s e a r c h c o u l d have been c a u s e d by an o v e r - a b u n d a n c e of m i c r o o r g a n i s m s p a s s i n g o v e r t h e o y s t e r s i n t e r f e r i n g w i t h f i l t r a t i o n . P a r t of t h e c a u s e can be a t t r i b u t e d t o t h e t r a y s s w a y i n g h o r i z o n t a l l y i n t h e c u r r e n t s t r e s s i n g t h e o r g a n i s m s and r e s t r i c t i n g water c i r c u l a t i o n , c a u s i n g a r e d u c t i o n i n f e e d i n g and a s s i m i l a t i o n e f f i c i e n c y . The r e s u l t was an i n h i b i t i v e e f f e c t on t h e growth e n h a n c i n g p r o p e r t i e s of e n v i r o n m e n t 2. 2. T r a y Type The s h e l l l e n g t h y i e l d v a r i a b l e i n d i c a t e d t h a t t h e N e s t i e r t r a y s p r o m o t e d t h e b e s t g r o w t h . R e s u l t s between t h e o t h e r s y s t e m s were s i m i l a r . B e t t e r g r o w t h i n t h e N e s t i e r s y s t e m was due t o i t s s u p e r i o r p e r f o r m a n c e i n e n v i r o n m e n t 1 t h a t b i a s e d t h e 1 07 g e n e r a l c o n c l u s i o n t h a t growth was b e t t e r i n t h i s s y s t e m . 3. V e r t i c a l P o s i t i o n The v e r t i c a l p o s i t i o n i n g o f o y s t e r s i n a column of t r a y s d i d n o t r a d i c a l l y a l t e r g r o w t h . T h i s f a c t o r became i m p o r t a n t i n h i g h e r l e v e l s of i n t e r a c t i o n where t r a y s y s t e m s and e n v i r o n m e n t t y p e were i n v o l v e d i n t h e i n t e r a c t i o n t e rm. 4. Time Growth c u r v e s d e s c r i b e d t h r e e p h a s e s of o y s t e r g r o w t h . I n i t i a l l y , a s t a r t - u p p h a s e ( J u n e 12-26) f o l l o w e d by a p e r i o d of i n c r e a s e d g r o w t h r a t e s . u n t i l e a r l y September; t h e n an i n d i c a t i o n of l e v e l l i n g o f f i n O c t o b e r . The s t a r t - u p p h a s e , where l i t t l e or no g r o w t h o c c u r r e d was l i k e l y due t o a c o m b i n a t i o n of o y s t e r a c c l i m a t i o n t o t h e c u l t u r e s y s t e m , low water t e m p e r a t u r e s and l i m i t e d f o o d . s u p p l y . B a c k g r o u n d e n v i r o n m e n t a l d a t a i n d i c a t e d water t e m p e r a t u r e s were a p p r o x i m a t e l y 12 d e g r e e s C e l s i u s and t h a t s u s p e n d e d p h y t o and z o o p l a n k t o n m a t e r i a l i n t h e w a t e r was l o w ( A p p e n d i x G ) . The i m p r o v e d g r o wth r a t e f o l l o w i n g t h e s t a r t - u p phase was c l o s e l y c o - r e l a t e d t o r i s i n g w a ter t e m p e r a t u r e s and p e r i o d s of l o w e r S e c c h i r e a d i n g s . M e t a b o l i c r a t e s would have i n c r e a s e d i n r e s p o n s e t o t h e c h a n g i n g e n v i r o n m e n t and t h e f o o d s u p p l y was a v a i l a b l e t o f u e l t h e demands of s h e l l g r o w t h . H i g h e r L e v e l I n t e r a c t i o n s . 1. E n v i r o n m e n t a l T y p e s R e l a t e d To V e r t i c a l P o s i t i o n In The 108 C u l t u r e System The g r o w t h c u r v e s d e s c r i b i n g o y s t e r l e n g t h g r o w t h o v e r t i m e were s i m i l a r i n b o t h e n v i r o n m e n t s . However, s h e l l w i d t h growth c u r v e s i n d i c a t e d t h a t e n v i r o n m e n t 2 c a u s e d a s e t b a c k i n J u l y on s h e l l d e p o s i t i o n . The n e g a t i v e i n f l u e n c e o f e n v i r o n m e n t 2 was c l e a r l y c o n c e n t r a t e d on s h e l l w i d t h g r o w th i n v e r t i c a l p o s i t i o n 1 as i n d i c a t e d i n t h e i n t e r a c t i o n term of e n v i r o n m e n t t y p e v s v e r t i c a l p o s i t i o n v s t i m e and e n v i r o n m e n t t y p e v s v e r t i c a l p o s i t i o n . The two f a c t o r t erm, v e r t i c a l p o s i t i o n v s t i m e , f a i l e d t o i n d i c a t e any s i g n i f i c a n t p o s i t i o n d i f f e r e n c e s i n t h e growth p a t t e r n s of s h e l l l e n g t h and w i d t h . T h i s s u g g e s t e d t h a t t h e e n v i r o n m e n t a l t e r m i n t e r a c t e d w i t h t h e f a c t o r of v e r t i c a l p o s i t i o n c a u s i n g t h e p o s i t i o n e f f e c t . The d e s c r e p a n c y between no e f f e c t upon s h e l l l e n g t h and a c l e a r e f f e c t on s h e l l w i d t h g r o w t h r e f l e c t s an a l t e r a t i o n i n t h e a b i l i t y of t h e m a n t l e l o b e s t o s e c r e t e s h e l l d e p o s i t s a l o n g t h e w i d t h a x i s . The r e s u l t was an i m p a i r m e n t of s h e l l w i d t h growth among t o p t r a y s i n e n v i r o n m e n t 2. Ambient c o n d i t i o n s a t t h a t l o c a t i o n c o u l d be a f f e c t i n g m a n t l e p o s i t i o n i n g and i t s a b i l i t y t o s e c r e t e s h e l l w i d t h . I n f o r m a t i o n was s p a r s e about t h e r e g u l a t o r y mechanisms a s s o c i a t e d w i t h s h e l l d e p o s i t i o n , but o b s e r v a t i o n s on growth i n g a s t r o p o d s and l a m e l l i b r a n c h s have shown t h a t s h e l l shape r e s u l t s from t h e p o s i t i o n o f t h e m a n t l e e d g e ( G a l t s o f f , 1964). 2. T r a y System R e l a t e d To E n v i r o n m e n t a l L o c a t i o n The N e s t i e r t r a y d i d n o t p e r f o r m as w e l l i n e n v i r o n m e n t 2 b a s e d on f i n a l s h e l l measurements and g r o w t h r a t e s . E n v i r o n m e n t 109 2 a l s o p r o l o n g e d t h e s t a r t - u p phase i n t h i s s y s t e m u n t i l t h e end o f J u l y and A u g u s t f o r g r o w t h i n l e n g t h and w i d t h . The c o m b i n a t i o n of s m a l l o p e n i n g s , r i g i d - t y p e c o n s t r u c t i o n , t h e t i g h t c o m p a c t n e s s of t h e a s s e m b l y and t h e u n i t s swaying h o r i z o n t a l l y p r o b a b l y i n t e r f e r e d w i t h water c i r c u l a t i o n and s h e l l g r o w t h . A l o n g e r s t a r t - u p phase may r e p r e s e n t an e x t e n s i o n of t h e o r g a n i s m s a d j u s t m e n t t o t h e s t r e s s e s imposed i n e n v i r o n m e n t 2. The l o n g e r s t a r t - u p phase and t h e i n t e r f e r e n c e w i t h water c i r c u l a t i o n d i d n o t a l l o w t h e o y s t e r s i n t h e N e s t i e r s y s t e m t o keep up t o t h e g r o w t h r a t e i n e n v i r o n m e n t 1. Growth i n t h e M a c N i c o l s y s t e m was a d v e r s e l y a f f e c t e d i n e n v i r o n m e n t 2, but t h e s h e l l g r o w t h o v e r t i m e was l e s s e r r a t i c t h a n i n t h e N e s t i e r s y s t e m . The s t a r t - u p phase was n o t p r o l o n g e d i n t h i s s y s t e m . R e s u l t s i n d i c a t e d t h a t w ater c i r c u l a t i o n t h r o u g h t h e M a c N i c o l u n i t s was n o t as s e v e r e l y i m p a i r e d as i n t h e N e s t i e r s y s t e m . A s i m i l a r e x p l a n a t i o n a c c o u n t s f o r t h e lower p e r f o r m a n c e of t h e M a c N i c o l t r a y s i n e n v i r o n m e n t 2, but t h e m a g n i t u d e of t h e e f f e c t s were not as g r e a t . However, i t became c l e a r l y e v i d e n t t h a t t h e M a c N i c o l and N e s t i e r s y s t e m s were more s u i t e d t o t h e c a l m e r e n v i r o n m e n t . Growth r e s u l t s i n t h e S u s p e n s i o n s y s t e m f a i l e d t o i n d i c a t e any d i f f e r e n c e s i n o y s t e r g r o w t h between t h e two e n v i r o n m e n t s i n t e r m s of f i n a l measurements and growth r a t e s o v e r t i m e . R e s u l t s were a t r i b u t e t o t h e o b j e c t i v e of an open d e s i g n t o improve e x p o s u r e o f t h e t r a y c u l t u r e d o y s t e r t o t h e s u r r o u n d i n g e n v i r o n m e n t . The s p a c i n g between t r a y s and t h e use of Conwed n e t was t o a l l o w an u n r e s t r i c t e d exchange of water i n o r d e r t o maximize f o o d a v a i l a b i l i t y and f a c i l i t a t e waste r e m o v a l . I t was 1 10 a n t i c i p a t e d t h a t e n v i r o n m e n t 2 would promote i n c r e a s e d g r o w t h but t h e s w a y i n g of t h e u n i t s i n t h e c u r r e n t n e g a t e d t h e growth e n h a n c i n g c h a r a c t e r i s t i c s :of t h e l o c a t i o n . I t was p o s s i b l e t h a t t h e s y s t e m had a b a f f l i n g e f f e c t on t h e c u r r e n t f l u c t u a t i o n s i n e n v i r o n m e n t 2, r e l i e v i n g t h e o y s t e r f r o m t h e d i r e c t impact of c u r r e n t f l u c t u a t i o n s . R e s u l t s i n d i c a t e d t h a t c o n d i t i o n s f o r gr o w t h were m a i n t a i n e d a l m o s t i d e n t i c a l l y t o t h o s e i n e n v i r o n m e n t 1. The s y s t e m p r o v e d a d a p t a b l e t o m a r g i n a l c o n d i t i o n s . The o n l y d e s i g n p a r a m e t e r t h a t may a c c o u n t f o r t h e a b s e n c e of tota-1 s u p e r i o r g r o w t h p e r f o r m a n c e was t h e s a g g i n g of t h e n et mesh under l o a d c a u s i n g o y s t e r s t o be crowded a t t h e c e n t e r of t h e t r a y . 3. T r a y Systems R e l a t e d To V e r t i c a l P o s i t i o n i n g Growth p e r f o r m a n c e i n t h e N e s t i e r t r a y p o s i t i o n s 1 and 2 were lower w i t h r e s p e c t t o t h e o t h e r v e r t i c a l p o s i t i o n s . P l o t s o f growth o v e r t i m e a l s o i n d i c a t e d t h a t g r o w t h r a t e s i n t h e s e two t r a y s were l o w e r . The M a c N i c o l s y s t e m had a s i m i l a r e f f e c t t h a t was o n l y v i s i b l e o v e r t i m e . C o n s i d e r i n g o n l y v e r t i c a l p o s i t i o n and t h e M a c N i c o l t r a y , t h e mean measurements were s i m i l a r among a l l t h e f i v e v e r t i c a l p o s i t i o n s . Growth c u r v e s o v e r t i m e i n M a c N i c o l v e r t i c a l p o s i t i o n s 1 and 2 were a l s o g e n e r a l l y l o w e r t h r o u g h o u t t h e s t u d y . The t o p t r a y s were j u s t below t h e s u r f a c e and made them s u b j e c t t o t h e s n a g g i n g of f l o a t i n g d e b r i s and a l g a e g r o w t h i n t e r f e r i n g w i t h f o o d a v a i l a b i l i t y a nd waste r e m o v a l c a u s e d by t h e r e s t r i c t i o n of water f l o w . The im p r o v e d g r o w t h c h a r a c t e r i s t i c s among lo w e r t r a y p o s i t i o n s ( v e r t i c a l p o s i t i o n s 3, 111 4 and 5) i s p r o b a b l y due t o l e s s b u i l d - u p of f l o t s a m and lower l i g h t l e v e l s c o n t r o l l i n g e x c e s s i v e a l g a l g r o w t h . A d e q u a t e c i r c u l a t i o n was m a i n t a i n e d . P e r f o r m a n c e d a t a i n d i c a t e d t h a t t h e s e s y s t e m s f a i l e d t o p r o v i d e u n i f o r m growth t h r o u g h a column of t r a y s . S p a c i n g of t r a y s i n t h e S u s p e n s i o n s y s t e m , t h e net mesh r e t a i n e r s and t h e t o p t r a y l o c a t e d 50cm below t h e s u r f a c e seems t o have e n s u r e d an even c i r c u l a t i o n . F l o a t i n g d e b r i s c o u l d n o t a t t a c h and f o u l i n g was c o n t r o l l e d . The r e s t r i c t i o n s of f o u l i n g and d e b r i s t h a t i n t e r f e r e d w i t h o y s t e r growth i n t h e o t h e r t e s t s y s t e m s d i d not o c c u r . P o s i t i o n e f f e c t s were m i n o r . The N e s t i e r t r a y s d i d not cope f a v o u r a b l y w i t h t h e c o n d i t i o n s i n e n v i r o n m e n t 2. V e r t i c a l p o s i t i o n s 1 and 2 were t h e l o w e s t p e r f o r m e r s , g r o w t h r a t e s were more e r r a t i c and not as c o n s i s t e n t o v e r t i m e and l e n g t h g r o w t h c e a s e d c o m p l e t e l y f o r two weeks i n J u l y . The s y s t e m swayed h o r i z o n t a l l y i n t h e c u r r e n t , t h e p r o b l e m s of b e i n g c l o s e t o t h e s u r f a c e and t h e c o m p a c t n e s s of t h e d e s i g n c o u l d have p r e v e n t e d t h e p e n e t r a t i o n of a d e q u a t e w a t e r f l o w i n t o t h e t r a y s . Growth c h a r a c t e r i s t i c s were q u i t e s i m i l a r between the two e n v i r o n m e n t s among l o w e r t r a y s i n t h e N e s t i e r s t a c k . The i m p a c t of t h e e n v i r o n m e n t a l e f f e c t seems t o have been c o n c e n t r a t e d i n t h e t o p t r a y s . In t h e M a c N i c o l u n i t s a c o n s i s t e n t growth r a t e o v e r t i m e , c l o s e l y r e l a t e d growth c u r v e s f o r t h e v e r t i c a l p o s i t i o n s and a d e p r e s s e d g r o w t h i n l e n g t h but not w i d t h i n e n v i r o n m e n t 2 r e a f f i r m e d t h a t t h e c u r r e n t r egime d i d not have as s e v e r e an i m pact upon t h i s s y s t e m p e r f o r m a n c e as i t d i d i n t h e N e s t i e r s y s t e m . Growth was d e p r e s s e d i n t h e t o p t r a y o f t h e M a c N i c o l i n 1 1 2 e n v i r o n m e n t 2, but t h e d i s c r e p a n c y between g r o w t h i n l e n g t h and w i d t h r e i t e r a t e s t h a t c o n d i t i o n s p r o b a b l y a l t e r e d t h e m a n t l e a b i l i t y t o s e c r e t e s h e l l l e n g t h . The c i r c u l a t i o n , f o o d a c q u i s t i o n and waste r e m o v a l p r o b l e m s p o s t u l a t e d as t h e c a u s e f o r hampered growth i n t h e N e s t i e r may not be t h e c a s e i n t h e M a c N i c o l s y s t e m . The p e r f o r m a n c e o f t h e S u s p e n s i o n s y s t e m was s i m i l a r among a l l v e r t i c a l p o s i t i o n s i n e a c h of t h e e n v i r o n m e n t s . P o s i t i o n e f f e c t s were a p p a r e n t i n b o t h s i t u a t i o n s but an a l t e r a t i o n i n which p o s i t i o n ( s ) were on t o p i n terms of g r o w t h p e r f o r m a n c e t e n d e d t o b a l a n c e out i n t h e end r e s u l t . Growth c u r v e s a p p l y i n g t o t h e v e r t i c a l p o s i t i o n s were c l o s e l y r e l a t e d and were g e n e r a l l y c o n s t a n t a t e a c h g r o w t h p h a s e . T h e s e o y s t e r s were not s u b j e c t e d t o t h e c o n d i t i o n s t h a t c r e a t e d a n o m a l i e s i n t h e growth p e r f o r m a n c e s i n t h e o t h e r two s y s t e m s . MEAT CONDITION The c o n d i t i o n i n d e x p r o v e d n o t t o be as s e n s i t i v e t o t h e e f f e c t s of t h e i n t e r a c t i o n s between th e o r g a n i s m , t h e c u l t u r e s y s t e m and t h e e n v i r o n m e n t a l c o n d i t i o n s a t t h e t e s t s i t e s . R e s u l t s d i d i n d i c a t e t h a t t h e t i m e of y e a r and t h e t y p e of c u l t u r e s y s t e m i n f l u e n c e d meat c o n d i t i o n . B a s e d upon e a r l i e r r e s e a r c h by F e d e r a l and P r o v i n c i a l E n v i r o n m e n t M i n i s t r i e s , t h e c o n d i t i o n i n d e x u s u a l l y d e c r e a s e s d u r i n g t h e summer months a f t e r s p a w n i n g has o c c u r r e d i n l a t e J u l y o r A u g u s t . The r e l e a s e of gametes i s i n d u c e d by a m b i e n t water t e m p e r a t u r e s g r e a t e r t h a n 19 d e g r e e s C e l s i u s . Water t e m p e r a t u r e s n e v e r r e a c h e d a warm s t a t e f o r a s u s t a i n e d p e r i o d 1 1 3 o f t i m e i n T r e v e n e n B a y ( A p p e n d i x F ) . N a t u r a l s p a t f a l l d i d not o c c u r i n T r e v e n e n Bay d u r i n g 1979. Meat i n t h e o y s t e r s was plump t h r o u g h o u t t h e summer and o n l y s l i g h t l y " r u n n y " . G o n a d a l m a t e r i a l was e x t e n s i v e l y b u i l t - u p w i t h i n t h e f l e s h and t h e c o n d i t i o n i n d e x was e l e v a t e d f o r t h a t time of y e a r . The s l i g h t d e c l i n e of t h e i n d e x i n A u g u s t c o u l d have been due t o a r e l e a s e of gametes, a l t h o u g h e v i d e n c e of spawning was not o b s e r v e d . The b e t t e r c o n d i t i o n i n d e x v a l u e s a t t a i n e d i n t h e M a c N i c o l t r a y i s somewhat of a p a r a d o x . The M a c N i c o l s y s t e m had t h e p o o r e s t showing i n terms of s h e l l g rowth but s u s t a i n e d a s u p e r i o r meat c o n d i t i o n . S t u d i e s i n B r i t i s h C o l u m b i a and t h e n o r t h w e s t e r n U n i t e d S t a t e s have r e v e a l e d t h a t s u p e r i o r meat q u a l i t y / c o n d t i o n d o e s not n e c e s s a r i l y a c h i e v e s u p e r i o r s h e l l c h a r a c t e r i s t i c s . S h e l l growth has been o b s e r v e d i n e m a c i a t e d o y s t e r s ( Q u a y l e , 1969). I t may be t h a t s h e l l g r o w t h and meat c o n d i t i o n , i n t h i s i n s t a n c e were m u t u a l l y e x c l u s i v e . The a b s e n c e of c o n d i t i o n i n d e x v a r i a b l i t y due t o e n v i r o n m e n t t y p e , v e r t i c a l p o s i t i o n i n g and among two of t h e t r a y s y s t e m s may have i n d i c a t e d a low l e v e l of s e n s i t i v i t y between f l e s h y body g r o w t h and e n v i r o n m e n t a l s u r r o u n d i n g s . I t may f o l l o w t h a t t h e r e s i d e n c e t i m e of f o o d p a r t i c l e s and t h e c i r c u l a t i o n r e g i m e w i t h i n t h e M a c N i c o l t r a y was more c o n d u c i v e t o f l e s h g r o w t h and n o t f o r t h e d e p o s i t of s h e l l m a t e r i a l . 1 1 4 CONCLUSION 1 . F o u l i n g The S u s p e n s i o n s y s t e m d i s p l a y e d s u p e r i o r a n t i f o u l i n g p r o p e r t i e s . F o u l i n g i n t h e S u s p e n s i o n s y s t e m was n e v e r a p r o b l e m f o r t h e d u r a t i o n of t h e r e s e a r c h . T h i s phenomenom may have been due t o p o s s i b l e f o u l i n g r e t a r d a n t p r o p e r t i e s of t h e m a t e r i a l s a n d / o r t h e s y s t e m s d e s i g n . The M a c N i c o l and N e s t i e r t r a y s succumbed t o m u s s e l and b a r n a c l e s e t s r e s p e c t i v e l y . The r e d u c t i o n o f f o u l i n g i n t h e S u s p e n s i o n u n i t s was i n d e p e n d e n t of e n v i r o n m e n t l o c a t i o n . However, e n v i r o n m e n t 2 ( t i d a l raceway) r e d u c e d f o u l i n g i n t h e N e s t i e r and M a c N i c o l t r a y s below t h a t h a v i n g o c c u r r e d i n e n v i r o n m e n t 1. T h e r e f o r e , an a r e a h a v i n g a c u r r e n t a c t i o n may r e d u c e or e l i m i n a t e t h e a t t a c h m e n t of f o u l i n g o r g a n i s m s . The d r y i n g out of a l l t r a y s e a c h week e f f e c t i v e l y c o n t r o l l e d a l g a l growth on t h e N e s t i e r and M a c N i c o l t r a y s . F i l a m e n t o u s a l g a l g r o w t h became e x t e n s i v e i n t h e s e s y s t e m s when th e d r y i n g r o u t i n e was s t o p p e d i n t h e f a l l months. A l g a l g r o w t h on t h e S u s p e n s i o n t r a y s was n e v e r a p r o b l e m once t h e p r o p e r n e t mesh s i z e was u s e d . 2. M a t e r i a l s H a n d l i n g and E c o n o m i c s In c o m m e r c i a l a p p l i c a t i o n s t h e S u s p e n s i o n s y s t e m p r o v e d more f a v o u r a b l e from t h e v i e w p o i n t of m a t e r i a l s h a n d l i n g . The s y s t e m a l l o w e d t h e h a n d l i n g o f a g r e a t e r number of o y s t e r s p e r u n i t t i m e and c o n v e n i e n t a c c e s s t o i n d i v i d u a l o y s t e r s i n an a s s e m b l y . The ease of h a n d l i n g t r a d e d o f f a g a i n s t a s l i g h t l y 1 1 5 more e x p e n s i v e d e s i g n made t h i s s y s t e m w o r t h c o n s i d e r a t i o n t o t h e c o m m e r c i a l grower. 3. P r o d u c t Q u a l i t y O y s t e r s c u l t u r e d i n t h e M a c N i c o l and N e s t i e r t r a y s were pr o n e t o s h e l l d i s f i g u r e m e n t . S h e l l a p p e a r a n c e was not a d v e r s e l y a f f e c t e d among o y s t e r s i n t h e S u s p e n s i o n t r a y s . The S u s p e n s i o n s y s t e m has t h e p o t e n t i a l t o m a i n t a i n an a t m o sphere t h a t can p r o d u c e a more a m i a b l e h a l f - s h e l l p r o d u c t . 4. M a t e r i a l P e r f o r m a n c e R i g i d p l a s t i c s a r e e n v i r o n m e n t . R i g i d PVC r e t a r d a n t p r o p e r t i e s . 5. O y s t e r Growth and Meat C o n d i t i o n The s i n g l e f a c t o r s o f e n v i r o n m e n t t y p e , t r a y s y s t e m and v e r t i c a l p o s i t i o n d i d not i n f l u e n c e o y s t e r g r o w t h . S h e l l g r o w t h c h a r a c t e r i s t i c s were a r e s u l t of h i g h e r l e v e l i n t e r a c t i o n s i n v o l v i n g two or more f a c t o r s . The f o l l o w i n g p o i n t s i l l u s t r a t e t h e c o n c l u s i o n s t h a t were d i s c o v e r e d s u r r o u n d i n g s h e l l g r o w t h i n t h e s y s t e m s t e s t e d . A. The measurement of g r o w t h i n s h e l l h e i g h t was f o u n d t o be a p o or i n d i c a t o r o f p e r f o r m a n c e . B. O y s t e r s e e d s t o c k e d i n c u l t u r e s y s t e m s e x h i b i t e d a s t a r t - u p or a c c l i m a t i o n phase a s s o c i a t e d w i t h t h e b e g i n n i n g s o f s h e l l g r o w t h . C. The t i d a l raceway s i t e had an a d v e r s e e f f e c t upon g r o w t h i n e s p e c i a l l y s u i t e d f o r use i n t h e m a r i n e p r o d u c t s may p o s s e s s some f o u l i n g 1 1 6 s h e l l w i d t h i n t h e t o p two t r a y p o s i t i o n s . D. R e s u l t s i n d i c a t e d t h a t t h e M a c N i c o l and N e s t i e r s y s t e m s a r e more s u i t e d f o r use i n c a l m / s h e l t e r e d e n v i r o n m e n t s . E. The N e s t i e r and M a c N i c o l t r a y s f a i l e d t o a l l o w u n i f o r m growth i n an a s s e m b l y of t r a y s . Growth i n t h e two t o p t r a y s i n t h e N e s t i e r and M a c N i c o l u n i t s were l o w e r w i t h r e s p e c t t o o t h e r r e m a i n i n g t r a y s i n a column. Growth r a t e s were d e p r e s s e d and e r r a t i c o v e r t i m e i n e n v i r o n m e n t 2 among t h e two t o p t r a y s i n t h e N e s t i e r s y s t e m . T h i s impact was l e s s s e v e r e on t h e t o p t r a y p o s i t i o n s of t h e M a c N i c o l t r a y s y s t e m . S h e l l g r o w t h was a l s o e r r a t i c among M a c N i c o l t r a y s l o c a t e d i n e n v i r o n m e n t 2. F. The l o w e r t r a y s i n t h e c o l u m n ( p o s i t i o n s 3, 4 and 5) of t h e M a c N i c o l and N e s t i e r a s s e m b l i e s had s i m i l a r g r o w t h p e r f o r m a n c e a t b o t h t e s t s i t e s . G. The S u s p e n s i o n s y s t e m o f f e r e d u n i f o r m s h e l l g r o w t h i n an a s s e m b l e d column o f t r a y s . H. S h e l l g r o w t h r a t e was not i n c r e a s e d by t h e d e s i g n s p e c i f i c a t i o n s o f t h e S u s p e n s i o n s y s t e m , nor was g r o w t h s t i m u l a t e d t o o c c u r more r a p i d l y under t h e i n f l u e n c e o f c u r r e n t f l o w i n e n v i r o n m e n t 2. I . The M a c N i c o l s y s t e m m a i n t a i n e d t h e h i g h e s t meat c o n d i t i o n i n d e x . Meat c o n d i t i o n i n d i c e s were s i m i l a r between N e s t i e r and S u s p e n s i o n s y s t e m s . J . Growth p e r f o r m a n c e of t h e N e s t i e r s y s t e m i n t h e c a l m e n v i r o n m e n t was b e t t e r t h a n t h e o t h e r t e s t s y s t e m s . Growth p e r f o r m a n c e s were s i m i l a r between M a c N i c o l and S u s p e n s i o n t r a y s a t t h i s s i t e . K. Growth p e r f o r m a n c e of t h e S u s p e n s i o n s y s t e m i n e n v i r o n m e n t 2 1 1 7 was g r e a t e r t h a n t h e o t h e r t e s t s y s t e m s w h i c h were on p a r w i t h e a c h o t h e r . L. G r a p h i c a l p l o t s of s h e l l g r o w t h i n d i c a t e d a d e c l i n e i n s u c h g r o w t h b e g i n n i n g a t t h e end of O c t o b e r . In c o n c l u s i o n t h e d e s i g n s p e c i f i c a t i o n s , o p e r a t i o n a l f e a t u r e s and m a t e r i a l s of c o n s t r u c t i o n of t h e S u s p e n s i o n s y s t e m p r o v e d t o be a more a t t r a c t i v e t r a y c u l t u r e a l t e r n a t i v e i n T r e v e n e n Bay. T a b l e 18 i l l u s t r a t e s i n d i c e s of " f a v o u r a b i 1 i t y " b a s e d upon f a c t o r s d i s c u s s e d t h a t summarize the a t t r a c t i v e n e s s of t h e S u s p e n s i o n s y s t e m h a v i n g t h e l o w e s t t o t a l i n d e x v a l u e . A d d i t i o n a l r e s e a r c h i s r e q u i r e d a t o t h e r t e s t s i t e s i n t h e c o a s t a l w a t e r s of B r i t i s h C o l u m b i a b e f o r e t h e s y s t e m can be s a i d t o be s u p e r i o r f o r use i n most s i t e l o c a t i o n s i n t h e p r o v i n c e . T h i s s u g g e s t i o n seems i n v o l v e d but i s b a s e d on t h e s i t e s p e c i f i c i t y of o y s t e r g r o w t h f o u n d t o o c c u r on t h e c o m m e r c i a l o y s t e r l e a s e s w i t h i n t h e c o a s t a l m a r i n e e n v i r o n m e n t s of B r i t i s h C o l u m b i a . Table 18. Indices o f f a v o u r a b i l i t y associated with the tray systems tested, Tray System Fouling Handling Economics P o s i t i o n Location Material Oysters/tray Total E f f e c t s E f f e c t s Performance McNicol Nestier Suspension 2 3 1 2 3 1 2 3 1 2 2 2 2 1 1 3 14 2 16 1 7 FACTOR 1. Fouling a) high b) medium c) low 2. Handling a) d i f f i c u l t b) e a s i e r c) easy 3. Oysters/tray a) high(63-126) b) medium(31-62) c) low(l-30) 4. Economic Appeal a) high b) medium c) low INDEX VALUE 3 2 1 3 2 1 1 2 3 1 2 3 FACTOR INDEX VALUE 2 1 Position E f f e c t s a) yes b) no Location E f f e c t s a) yes 2 b) no 1 Material Performance a) e x c e l l e n t 1 b) good 2 c) f a i r 3 119 REFERENCES M e a n R e p o r t . 1970. Handbook o f aluminum, 3 r d e d i t i o n . Aluminum Company of Canada L t d . Andrews, J.D., D. Haven and D.B. Q u a y l e . 1959. F r e s h w a t e r k i l l of o y s t e r s ( C r a s s o s t r e a v i r g i n i c a ) i n James R i v e r , V i r g i n i a , 1958. 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P r e l i m i n a r y s t u d i e s on t h e r e l a t i o n between f a e c e s of p e a r l o y s t e r ( P i n c t a d a m a r t e n s i , Dunker) and b o t t o m c o n d i t i o n i n an e s t u a r i n e p e a r l o y s t e r a r e a . ( J a p . ; E n g l . Summary) j . F a c . F i s h . P r e f . U n i v . M i e - T s u , 8: 113-137. Walne, P.R. 1974. C u l t u r e of b i v a l v e m o l l u s c s , 50 y e a r s e x p e r i e n c e a t Conwy. F i s h i n g News L t d . , S u r r e y , England.. 122 W a l k e r , P.N., and J.W. Z a h r a d n i k . 1976. S c a l e - u p of f o o d u t i l i z a t i o n by t h e A m e r i c a n o y s t e r , C r a s s o s t r e a v i r g i n i c a . P r o c . N a t l . S h e l l f i s h . A s s o c . 65: 63-75. W i l s o n , B.W. 1969. E l a s t i c c h a r a c t e r i s t i c s o f m o o r i n g s . I n : T o p i c s i n Ocean E n g i n e e r i n g , C h a r l e s I . B r e t s c h n e i d e r , e d i t o r . G u l f . P u b l . Co. 45p. Z a h r a d n i k , J.W. 1973. P l a s t i c s i n m a r i n e a q u a c u l t u r e and c o a s t a l f i s h e r i e s , Nov. 30, a s t a t u s r e p o r t . A q u a c u l t . E n g i n e e r . L a b . U n i v . Mass. U.S.A. 123 APPENDIX A TABLE A1. ANOVA t a b l e f o r s h e l l l e n g t h . SOURCE DF SUM SQ MEAN SQ F-VALUE PROB E 1 6112.0 6112.0 183.20 0.0 C 8 0.11894E+07 0.14867E+06 4456.3 0.0 EC 8 2374.0 296.75 8.8948 0.35480E- 1 1 T 2 46131 . 23065. 691.35 0.0 ET 2 12597. 6298.4 188.79 0.0 CT 16 13681. 855.06 25.629 0.0 ECT 1 6 5185.4 324.09 9.7142 0.0 P 4 5196.4 1299.1 38.939 0.36789E- 31 EP 4 632. 15 158.04 4.7370 0.81612E- 03 CP 32 2158.2 67.445 2.0216 0.59814E- 03 ECP 32 1408.0 43.999 1 .3188 0.10791 TP 8 3541.1 442.64 13.267 0.38255E- 18 ETP 8 2402.5 300.31 9.0015 0.24103E- 1 1 CTP 64 3706.4 57.912 1.7358 0.27831E- 03 ECTP 64 3252.5 50.821 1 .5233 0.47615E- 02 ERROR 51 30 0. 17115E+06 33.363 TOTAL 5399 0.14689E+07 TABLE A2. ANOVA t a b l e f o r s h e l l w i d t h . SOURCE DF SUM SQ MEAN SQ F-VALUE PROB E 1 15097. 15097. 379.86 0. 0 C 8 0.12287E+07 0.1558E+06 3864.4 0. 0 EC 8 5421 . 1 677.64 17.050 0. 29974E- 24 T 2 14352. 7176.2 180.56 0. 16578E- 75 ET 2 1807. 1 903.55 22.735 0. 14791E- 09 CT 16 6991.1 436.94 10..994 0. 0 ECT 16 6246.8 390.42 9.8236 0. 0 P 4 8056.2 2014.0 50.676 0. 66709E- 41 EP 4 1033.4 258.36 6.5007 0. 32507E- 04 CP 32 3356.4 104.89 2.6391 0. 17572E- 05 ECP 32 2012.9 62.903 1.5827 0. 19767E- 01 TP 8 3410.5 426.32 10.727 0. 44609E- 14 ETP 8 2144.1 268.01 6.7436 0. 78990E- 08 CTP. 64 3756.6 58.696 1.4769 0. 83248E- 02 ECTP 64 3590.4 56.099 1.4115 0. 17523E- 01 ERROR 5130 0.20388E+06 39.744 TOTAL 5399 0.15098E+07 124 1 APPENDIX B P l o t s o f r e l a t i o n s h i p s t o r e v e a l e f f e c t s of t h e f a c t o r s e n v i r o n m e n t t y p e , t r a y s y s t e m , t i m e and v e r t i c a l p o s i t i o n upon g r o w t h i n s h e l l l e n g t h . E n v i r o n m e n t Type E T r a y System T Time C ' V e r t i c a l P o s i t i o n P Time L a b e l D a t e 1 . 1 June 12 2 June 26 3 J u l y 10 4 J u l y 24 5 A u g u s t 7 6 S e p t . 6 7 S e p t . 19 8 O c t . 2 9 O c t . 20 T r a y Code T r a y Type T1 M a c N i c o l T2 N e s t i e r T3 S u s p e n s i o n VERTICAL POSITION R T 1 VERT1CRL POSITION 127 VERTICAL POSITION VS TIME 131 132 133 ENV. 1 VS TRAY SYSTEM VS VERTICRL POSITION 135 MCNICOL TRRY VS VERTICAL POSITION VS TIME TIME LRBEL 137 138 SUSPENSION TRRY VS VERTICAL POSITION VS TIME TIME LRBEL 139 ENV. 1 VS TRRY SYSTEM VS TIME TJME LABEL 140 141 ENV. 1 VS MCNICOL TRRY VS VERTICAL POSITION VS TIME 142 143 f I I I 1 I I 1 I ! 2 3 4 5 6 7 B 9 TIME LABEL 145 ENV. 2 VS SUSPENSION TRflY VS VERTICRL POSITION VS TIME " TIMESLHBEL 147 APPENDIX C P l o t s o f r e l a t i o n s h i p s t o r e v e a l e f f e c t s o f t h e f a c t o r s e n v i r o n m e n t t y p e , t r a y s y s t e m , t i m e and v e r t i c a l p o s i t i o n upon growth i n s h e l l w i d t h . E n v i r o n m e n t Type E T r a y System T Time C V e r t i c a l P o s i t i o n P Time L a b e l Date 1 June 12 2 June 26 3 J u l y 10 4 J u l y 24 5 A u g u s t 7 6 S e p t . 6 7 S e p t . 19 8 O c t . 2 9 O c t . 20 T r a y Code T r a y Type T1 T2 T3 M a c N i c o l N e s t i e r S u s p e n s i o n 149 ENVIRONMENT TYPE VS VERTICAL POSITION CE UJ El E2 0-0 +- + VERTICAL POSITION VERTICAL POSITION VS TIME _| ! ! ! ! 1 , , ! 1 2 3 4 S 6 7 B 9 TJME LRBEL 153 154 155 156 E N V . 2 V S V E R T I C R L P O S I T I O N V S T I M E i 1 1 1 1 1 1 1 1 1 - 2 3 4 5 6 7 B S TIME LRBEL ENV. 1 VS TRAY SYSTEM VS VERTICAL POSITION Tl = 0-0 T2 = +-+ T3 = X-X VERTICAL POSITION E N V . 2 V S T R f l Y S Y S T E M V S V E R T I C A L P O S I T I O N 159 M C N I C O L T R R Y V S V E R T I C A L P O S I T I O N V S T I M E i i i 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 TIME LABEL 160 _t 1 1 1 1 1 1 1 1 1 2 3 4 S 6 7 B 9 TIME LRBEL 161 S U S P E N S I O N T R R Y V S V E R T I C A L P O S I T I O N V S T I M E -1 1 1 1 1 i i — 1 l 1 2 3 4 S 6 7 B 9 TIME LRBEL 162 163 i E N V . 2 V S T R R Y S Y S T E M V S T I M E T i 1 i 1 1 1 1 1 1 i i 3 •< s e i a s TIME LABEL 164 E N V . 1 V S M C N I C O L T R R Y V S . V E R T I C A L P O S I T I O N V S T I M E 1 2 3 4 5 6 7 8 9 TIME LABEL T 1 1 r 1 5 6 7 TIME LRBEL 166 167 E N V . 2 V S M C N I C O L T R R Y V S V E R T I C R L P O S I T I O N V S T I M E ~i 1 1 1 1 1 1 1 i 1 2 3 4 S 6 7 8 9 TIME LRBEL 168 169 E N V . 2 V S S U S P E N S I O N T R R Y V S V E R T I C R L P O S I T I O N V S T I M E •I i i i i i i i i 1 2 3 4 S 6 7 B 9 TIME LRBEL APPENDIX D 170 TABLE D1. ANOVA t a b l e f o r c o n d i t i o n i n d e x . SOURCE DF SUM SQ MEAN SQ F-VALUE PROB E 1 4014.5 4014.5 2.5512 0.11080 C 4 0.12709E+06 31774. 20.192 0.0 T 2 22575. 11287 . 7.1731 0.00084 P 4 8234.7 2058.7 1.3083 0.26571 ERROR 533 0.83870E+06 1573.6 TOTAL 544 0. 10270E+07 APPENDIX E S e c c h i D i s k and Ambient Water Temperature Measurements 174 'Temperature (*c) ro o ro c D C D col or c > WI co fD T3 X cnf Sr 3 3 ro C D m < 3 C D O Environment No. 2 • •—• surface • — o — o i meter x- x- * 2 meter 1 5 3 ° I S " 31 i s 3 i T o 30 i 5 " ' Oct. J u n e J u | y August Sept. 

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