losordo 1986 aquacultural-engineering

7/28/2019 Losordo 1986 Aquacultural-Engineering

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Aquacultural Engineering 5 (1 9 8 6 ) I - 15

A M e c h a n i z e d S e i n e H a r v es t S y s t e m fo r F r e sh w a t erP r a w n s *

T ho m as M . Loso rdo ,~ Jaw-Kai Wang,~ - M ark J . Br ook s ,~ andC h e e Y i n L a m t

. A g r i cu l tu ra l E n g in ee r in g D ep ar tmen t , . f .A n imal S c ien ces D ep ar tmen t .U n iv e r s i ty o f H aw ai i . H o n o lu lu , H aw ai i 9 6 8 2 2 , U S A

A B S T R A C TThis paper descr ibes new deve lopments in a se lec t i ve harves t sys tem f o r

f r e s h wa t e r p r a wn s . Th e n e t s y s t em ca n b e p u l l ed e i t h e r m ech a n i ca l l y o rby hand . I t pro duc ed a cons i s t en t l y h igh harves t e f fi c i ency an d y ie ld .Th e s y s t em i n ch l d ed a l o w co st , l ig h t we i g h t p r o t o t )p e b o o m d es i g n edt o r ep l ace t h e h a r vest c rew i n t h e p o n d . C o m p o n en t s o f th e n e t sy s temwere a t tache d to each o ther by ny lon f i sh n e t z ippers . The z ippers werea l so used as a c los ing mechanism to increase harves t e f f i c i ency . Them ea n h a r ves t e ff ic i en cy o f m a r ke t a b l e p r a w n s o f t h e n ew s y s t em i near then produ ct ion po nd s was es t im ated to be 63"5%.

I N T R O D U C T I O NT h e c o m m e r c i a l p r o d u c t i o n o f t h e f r e s h w a t e r p r a w n M a c r o b r a c h i u mr o s e n b e r g i i i n H a w a i i w a s b e g u n i n t h e e a r l y 1 9 6 0 s ( S t a t e o f H a w a i i ,1 9 7 8 ) . In 1 9 8 3 , a p p r o x i m a t e ly 9 6 h a o f w a t e r s u r f a c e a re a w e r e in c o m -m e r c i a l p r o d u c t i o n o n 2 1 i n d i v i d u a l s i t e s . F o u r m a j o r f a r m s m a k e u pa p p r o x i m a t e l y 8 4 h a o f t h e p r o d u c t i v e a r e a ( S ta t e o f H a w a i i, 1 9 8 3 ) .

R e g a r d l e s s o f t h e f a r m s i z e , o n e o f t h e m o s t c o s t l y a c t i v i t i e s i n v o l v e di n p r a w n g r o w - o u t o p e r a t i o n s i s s e l e c t i v e h a r v e s t i n g o f m a r k e t s i z ep r a w n s w i t h n e t s ( F u j i m o t o e t a l . , 1 9 7 7 ) . G i b s o n a n d W a n g ( 1 9 7 7 ) e s t i -m at ed t hat t he t rad i tiona l ne t - ha rves t ing o per at ion requ ired 7"5 m an-h o u r s p e r 0 .5 h a p o n d , a c c o u n t i n g f o r a p p r o x i m a t e l y 9 % o f t h e to ta lf arm operat ing cos t . S imi lar ly , Shang ( 1981) se t harves t ing labor requ ire -* J o u r n a l S e r i e s N o . 2 9 5 8 , T h e H a w a i i I ns t it u te o f T r o p i c a l A g r i c u l tu r e a n d H u m a nR e s o u r c e s .

IAquacultural Engb~eering 0 1 4 4 - 8 6 0 9 / 8 6 / S 0 3 . 5 0 - - E l se v ie r A p p li e d S c ie nc ePubl ishers L td , Eng land . 1986 . Pr in ted in Great Br i ta in


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2 7". M. Lo so rd o , J . -K . Wang. M. J . Br oo ks , C . Y . La inm e n t s at 7-5 m a n - h o u r s p e r p o n d p e r h a r v e s t, a b o u t 5 - 7 % o f t h e t o ta lo p e r a t i o n a l c o s t , a n d 1 6 - 3 7 % o f a ll f a r m l a b o r c o st s.Whi le the t r ad i t iona l ne t -ha rves t ing opera t ion i s l abor in tens ive , i t sha rves t e f f i c iency has be en low. H arv es t e f f i c iency is de f ined as then u m b e r o f m a r k e t s i z e p r a w n s c a u g h t i n a s i n g l e h a r v e s t i n g o p e r a t i o nd i v id e d b y t h e t o t a l n u m b e r o f m a r k e t s i ze p r a w n s p r e s e n t e d i n t h e p o n dpr io r to ha rves t ing .

P e t e r s o n ( 1 9 8 2 ) d e s c r i b e d t w o m e t h o d s o f n e t h a r v e s t in g p r a w n s f ro mr e c t a n g u l a r p r o d u c t i o n p o n d s . H e f o u n d t h a t h a r v e s t ef fi ci e n ci e s r a n g e df r o m 6 - 2 3 % w i t h a n o v e r a ll a v e r a g e o f 1 5 % . L a m a n d W a n g ( 1 98 5 ), i n as tudy on es t ima t ing ha rves t ing e f f i c ienc ies on the same fa rm (asP e t e r s o n 's s t u d y ), f o u n d h a r v e s t in g e f fi c ie n c i es f r o m 2 - 4 6 % w i t h ana v e r a g e o f 2 3 %. T h i s d a t a is s i g n if ic a n t a s f a r m e r s a n d r e s e a r c h e r s h a v e ,i n t h e p a s t, c o n s i d e r e d h a r v e s t i n g e f f ic i e n c y t o b e b e t w e e n 5 0 - 7 5 %( G i b s o n a n d W a n g , 1 9 77 ; P o lo v i n a a n d B r o w n , 1 9 7 8; Wi l l i a m s o n a n dWang, 1982) .Wi l l i amson and Wang (1982) , in an e f fo r t to inc rease ha rves t e f f i -c iency and reduce l abor , des igned , f abr ica ted and f i e ld - te s ted a ' f i r s tg e n e r a t i o n ' m e c h a n i z e d s e i n e h a r v e s t n e t s y s te m f o r t h e H a w a i i a n p ra w ni n d u s t r y . T h e n e t s y s t e m c o n s i st e d o f a m o n o f i l a m e n t n y l o n s e i n e -n e ta n d a r ig i d P V C h a r v e s t g r a d e r b o x b e t w e e n t h e p r i m a r y n e t w i ng s . T h e

n e t s y s te m w a s p u l le d t h r o u g h t h e p o n d b y p r im e m o v e r s u t i li z in g amul t ip le l ine b r id le sys tem to pu l l on the l ead l ine and f loa te r l ine .V a r i a t i o n s o f t h e s y s t e m w e r e f a b r i c a t e d a n d u s e d o n t w o m a j o r f a r m sf r o m 1 9 7 9 t o 1 9 8 0. T h e s y s t em s d id n o t c o m e i n t o w i d e u se b e c a u s e o ft h e t i m e r e q u i r e d t o s e t u p a n d m o v e t h e c o m p l i c a t e d b r i d l e s y s t e m( R i e t o w , p e r s o n a l c o m m u n i c a t i o n ) a n d s u s p e c t e d d a m a g e t o p r a w n sharves ted in heav i ly s i l ted pond s (Wal lace, pe rso na l c om mu nica t ion) .A ' s e c o n d g e n e r a t i o n ' m e c h a n i z e d n e t s y s t e m w a s d e v e l o p e d b yA m f a c A q u a t e c h - H a w a i i , a n o w d i s c o n t i n u e d p i l o t f a r m o p e r a t i o n o nt h e i s l a n d o f K a u a i . T h e A m f a c s y s t e m c o n s i s t e d o f a N o . 1 8 t w i n e m u lt i-f i l a m e n t n y l o n s e i n e - n e t w i t h a c e n t e r - m o u n t e d n e t h a r v e s t b a g . T h es y s te m w a s p u l le d f r o m e a c h e n d w i th a p ri m e m o v e r a n d d e p e n d e d o n al a r g e n u m b e r o f b o t t o m l i n e l e a d w e i g h t s a n d a d o u b l e l e a d l i n e w i t h ane t ~sk i r t ' in be tween to secure an adequa te sea l wi th the pond bo t tom.W h i l e t h e n e t a c h i e v e d h a r v e s t e ff ic i en c i es f r o m 6 6 t o 7 0 % i n n e wpon ds , i t d id no t pe r fo rm well in heav i ly s i lt ed o lde r po nd s w i th e rod edb a n k s .T h i s p a p e r d e s c r i b e s a " th ir d g e n e r a t i o n ' m e c h a n i z e d h a r v e s t n ets y s t e m t h a t c o u l d b e u s e d i n h a r v e s t i n g b o t h n e w a n d o l d p r o d u c t i o np o n d s . I t c a n b e p u l le d e i t h e r m e c h a n i c a l l y o r b y h a n d a n d p r o d u c e scons i s ten t ly h igh ha rves t e f f i c ienc ies and y ie lds .


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A m e c h a n i z e d s e in e h a r v es t s y s t e m f o r f i' e s h w a t e r p r a w n s 3P r a w n s a r e b e n t h i c o r b o t t o m - d w e l l i n g a n i m a l s , a n d a s a r es u lt t h e

mos t c r i t i c a l f ac t o r i n ne t s y s t em des i gn i s i t s ab i l i t y t o ma i n t a i n a goods ea l b e t w e e n t h e n e t s y s te m a n d t h e p o n d to p r e v e n t p r a w n s f r o m e l u d -i n g c a p t u r e .

T h e r e a r e t h r e e m a j o r c a u se s f o r p o o r s e al s b e t w e e n n e t s a n d p o n d s :1. P o n d irregtdari ties: A s t h e p o n d a g e s , i t a c c u m u l a t e s m u d a n d s i l t .

L a r g e ' b u ll ' m a l e p r a w n s a n d " tr as h " f is h, su c h a s c o m m o n t il ap i a,c a n m a k e d e e p d e p r e s s i o n s i n t h e s of t m u d a n d s ilt. A n o t h e r c a u s eo f d e p r e s s i o n s i n t h e b o t t o m is t h a t o f t h e f o o t - p r i n t s o f t h e h a r v e s tc re w . O l d e r p o n d s a r e a ls o l ik e ly t o h a v e s e v e r e b e r m e r o s i o nc a u s e d b y w i n d d r i v e n w a v e a c t io n .2 . L o n g b a n k g ra ss : D u e t o t h e c o n t i n u e d b e l i e f b y m a n y f a r m e r s t h a tl o n g b a n k g r a s s i s n e c e s s a D ' f o r g o o d p r o d u c t i o n , g r a s s i s o f t e nk e p t a t e x t r e m e l y lo n g l e n g th s p r o t r u d i n g i n t o p r o d u c t i o n p o n d s .T h e p r e s e n c e o f s u c h g r a s s t e n d s t o l if t t h e l e a d i n g e d g e o f t h e n e ts ys t em ' s bo t t o m l ine . U n l e s s t he g r a s s i s cu t o r l i f ted ou t o f the w ay ,it is i m p o s s i b l e t o a c h i e v e a g o o d s ea l.3 . I m p r o p e r p u l l in g f o rc e s : M o s t h a n d - p u l l e d s e i n e - n e t s i n H a w a i iw e r e d e s i g n e d t o b e p u l l e d b y a h a r v e s t c r e w , u s i n g t h e i r f e e tc u r l e d i n s i d e t h e b o t t o m l in e . T h e c r e w is u su a l ly s p a c e d a t re g u l a ri n t e r v a l s a l o n g t h e s e i n e . W h e n t h e c r e w e n c o u n t e r s e x c e s s i v ea m o u n t s o f b o t t o m s ilt o r m u d , t h e y o f t e n w il l l if t w i t h t h e ir f e et o rt hey w i ll pu l l t he ne t by t he f l oa t e r l ine . T h i s s i t ua t i on i s e s pec i a l l yc o m m o n d u r i n g t h e n e t ~c lo sin g' o p e r a t i o n . T h i s o p e r a t i o n r e q u i r e st h a t t h e t w o e n d s o f t h e n e t b e ' cl os ed " t o g e t h e r a n d r e m o v e d f r o mt h e p o n d w i t h o u t l o s in g t h e s e al a g a in s t e i t h e r t h e b o t t o m o r h e r i n .A s t h e n e t i s g r a d u a l l y m o v e d o n l a n d , t h e p r a w n s a r e c r o w d e dn e a r o r i n t o t h e h a r v e s t b a g . H o w e v e r , p r i o r t o e n t r y i n t o t h e b a g ,t h e d e n s e l y c o n c e n t r a t e d p r a w n s c a n e s c a p e i n l ar g e n u m b e r s w i tht he s l i gh t e s t l i ft ing o f t he ne t .

F o r a m e c h a n i z e d n e t s y st e m p u l l e d fr o m t h e p o n d b e r m , t h e pu l li ngf o r c e a t t h e e n d o f t h e r o p e h a s a v e r ti c a l c o m p o n e n t t h a t m a y c a u s e l if t-i n g o f th e b o t t o m l e a d l in e in th e a r e a w h e r e t h e p o n d b o t t o m i n te r se c t st h e b e r m . T h i s a r e a is c o m m o n l y c a ll e d t h e "to e' o f t h e p o n d a n d iss u s p e c t e d t o b e a n a r e a w h e r e p r a w n s e l u d e c a p t u r e d u e t o a p o o r s ea l.

O P E R A T I O N A L A N D D E S IG N C O N S ID E R A T IO N SN e t p u l li n g s y s t e m sI n o r d e r t o m a i n t a i n a g o o d s e al , i d e a l ly th e o n l y f o r c e a p p l i e d t o t h e n e tb o t t o m l i n e s h o u l d p a r a l l e l t h e p o n d b o t t o m . I n p r a c t i c e , i t m e a n s t h a t


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4 7-. M. Los ord o , J . -K . Wang . M . J . Bro oks . C . K La inl o n g l in e s n e e d t o b e u s e d t o p u ll t h e n e t b o t t o m l in e to m i n i m i z e t h ea n g le b e t w e e n t h e p u ll in g l i n e a n d t h e p o n d b o t to m .

I n t h e i m p r o v e d n e t s y s t e m , 1 8 "3 m ( 6 0 -f t) r o p e t e t h e r s a r e a t t a c h e d t oh a r n e s s e s , w h i c h a r e t h e n u s e d t o a p p l y p u l l i n g f o r c e s t o t h e b o t t o m l e a dlin e. T w o p e r s o n s w e a r i n g h a r n e s s e s t h e n w a lk b a c k w a r d s in t h e p o n dp u l l i n g t h e n e t , fo l l o w i n g t h e t o e o f th e p o n d . D i s r e g a r d i n g t h e c a t e n a r ye f fe c t, t h e f o r c e t r i a n g l e p r o d u c e d b y a n 1 8 " 3 m ( 6 0 - f t) t e t h e r ( s e e F ig . 1 )p u l l e d a t w a i s t h e i g h t ( a b o u t 7 6 . 2 c m o r 3 0 i n ) p r o d u c e d a f o r c e e q u a l t o9 9 % o f t h e a p p l i e d f o r c e i n a d i r e c t i o n p a r a l le l to th e p o n d b o t t o m a n dw i t h a v e r ti c a l f o r c e e q u a l t o o n l y 4 % o f t h e a p p l i e d f o r c e .

M e a s u r e m e n t s t a k e n d u r i n g h a r v e s ti n g o p e r a t io n s i n d ic a t e d t ha t e v e nin m o d e r a t e l y s i lt e d p o n d s , p u l l in g f o r c e s r a r e l y e x c e e d 3 11 -4 N ( 7 0 lb )a n d a r e u s u a l l y l e ss t h a n 1 3 3 . 4 N ( 3 0 lb ). T h u s , t h e l if t in g f o r c e s o n t h el e a d l in e o f t h e n e t s h o u l d n o t e x c e e d 1 3 .3 N ( 3 lb ) a n d is m o r e l i k e ly t ob e a b o u t 5 "6 N ( 1 . 2 5 Ib ). T h u s , l e ss w e i g h t w a s n e e d e d t o k e e p t h eb o t t o m l e a d li n e s e a l e d a g a i n s t th e p o n d b o t t o m a n d t h e r e s u lt a n t li g h te rb o t t o m l in e w a s l e ss li k e ly t o d i g i n to t h e p o n d - b o t t o m m u d .

I n a n e f fo r t to r e d u c e h a r v e s t l a b o r a n d to m a k e it e a s i e r to h a r v e s te x t r e m e l y s il ty p o n d s , a l o w c o st p r o t o t y p e b o o m s y s t e m w a s u s e d t or e p l a c e t h e h a r v e s t c r e w i n t h e p o n d ( s e e F ig . 2 ).

T h e b o o m w a s c o n s t r u c t e d o f li g h t w e i g h t p e r f o r a t e d 3 -8 c m ( 1} in )s q u a r e t e l e s c o p i c e n g i n e e r i n g t u b i n g w i th a tr a d e n a m e o f T e l e s p a r ( U n i s t ru t C o r p o r a t i o n , H o n o l u l u , H a w a i i ). T h e h o r i z o n t a l b o o m a n dv e r t ic a l a r m w e r e g i v e n r ig i d i ty b y th e u s e o f t e n s i o n m e m b e r s m a d e o f0 "3 c m (,~ i n) d i a m e t e r ( 7 1 9) g a l v a n i z e d v i n y l - c o a t e d c a b l e s . T h e b o o mh a s a t o t a l l e n g t h o f 4" 6 m ( 1 5 f t) a n d e x t e n d s a p o p r o x i m a t e l y 3 -0 m( 10 f t) t o t h e s id e o f t h e p r i m e m o v e r . A t t h e p o n d - e n d o f th e b o o m , a

F x : F C o s g : ( o - 9 g ) ( F )f l o a t e rl i n e F y : F 'S i n e = ( 0 . 0 4 ) ( F )

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m u d l i n e ~ ? Fx 'W = 1-751bsFig. 1. N et pulling force triangle.


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A m e c h a n i z e d s e i n e h a r v e s t s y s t e m _to r r e s h w a t e r p r u w n st e l e s co p i n g v e rt ic a l a r m s e c t io n e x t e n d e d d o w n i n t o th e p o n d a n d w a sa d j u s t e d t o r e a c h a p p r o x i m a t e l y 1 5 -2 c m (6 in ) f r o m t h e b o t t o m . At e t h e r w a s a t t a c h e d t o t h e v e r t i c a l a r m e n d a n d e x t e n d e d h o r i z o n t a l l yb a c k t o t h e n e t ' s b o t t o m l in e. M o s t o f t h e f o r c e s a c t i n g o n t h e v e r ti c ala r m a r e i n t h e h o r i z o n t a l d i r e c t i o n p a r a ll e l to th e p o n d b o t t o m . T h e s ef o r c e s w e r e t r a n s f e r r e d t o t h e p r i m e m o v e r b y t h e c a b l e r u n n i n g f r o mt h e b o t t o m o f t h e v e rt ic a l a r m t o a s h o r t h o r i z o n t a l b o o m a t t a c h e d t o t h ef r o n t o f t he p r i m e m o v e r .N et d es ignT h e n e t w a s o f t h e b o t t o m s e in e o r b e a c h s e in e t y p e w i th a c e n t e rm o u n t e d h a r v e s t b ag . T h e b a g c o u l d b e s i de m o u n t e d o r n o t u s e d at all.

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Fig. 2. L o w cost prime mover mounted boom system. {Drawing not to scale.~


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6 7-. M . L o s o r d o . J . - K . W a n g , M . Z B r o o k s , C . K L a i nT h e p r i m a r y "w in gs" ( s e i n e - n e t s to e a c h s i d e o f t h e c e n t e r b ag ) w e r e

18-3 m (60 f t) lon g a nd 1-8 m (6 f t) d ee p . T h e ne t ha s 3 .8 cm (11 in )s t re t c h ( 1-9 c m o r ~ i n s q u a re ) k n o t t e d e y e m e s h m a d e f r o m N o . 9 m u l t i-f i l a m e n t n y l o n t w i n e . T h e n e t t i n g w a s h u n g i n s u c h a w a y t h a t 4 5 - 7 m( 1 5 0 f t) o f n e t t i n g m a d e 3 0 -5 m ( 1 0 0 ft) o f s e i n e , a n d w a s t ie d t o t h ef l o a t e r l i n e a n d l e a d l i n e e v e r y f o u r t h m e s h . T h e f l o a t l i n e w a s m a d e o f1 -0 c m (~ in ) d i a m e t e r b r a i d e d p o l y p r o p y l e n e w i t h 11 o z b u o y a n c y( S B - 6 ) f l o a t s a t t a c h e d e ve r2 ,' 3 8 .1 c m ( 15 i n ) o n c e n t e r . T h e b o t t o m l in eo r l e a d l i n e w e r e l ' 0 c m (~ i n) b r a i d e d p o l y p r o p y l e n e ; h o w e v e r , it h a s a2 8 s t r a n d ( e a c h s t r a n d is a 1"0 c m o r ~ i n d i a m e t e r s p u n - p o l y e s t e r r o p e )s y n t h e t i c " m u d l i n e ' a t t a c h e d t o t h e l e a d l i n e to p r e v e n t t h e n e t f r o mc u t t i n g in t o t h e m u d . T h e l e a d l in e h a s 5 5 g s p li t l e a d w e i g h t s ( N o . 8 S P L -1 ) a t t a ch ed ev eN ' 61 - 0 cm ( 24 in ).

F o u r a u x i l i a ~ " s e i n e w i n g s c a n b e a d d e d t o t h e p r i m a l " w i n g s a sn e e d e d t o i n c re a s e t h e l e n g t h o f th e s e i n e w h e n u s e d in w i d e r p o n d s . T h ea u x i l i a ~ w i n g w a s 9"1 m ( 3 0 f t) l o n g a n d o f i d e n t i c a l c o n s t r u c t i o n a s t h ep r i m a r y w i n g s e x c e p t f o r t h e a d d i t i o n o f a 3 8-1 c m ( 15 in ) d e e p n e t " sk ir t'a t t a c h e d b e l o w t h e m u d l i n e w i th a l ig h t c h a i n o n t h e b o t t o m l in e o f t h esk i r t . These sk i r t s , running the fu l l l eng th of the auxi l i a ry wings , , , , , ' e r ed e s i g n e d to p r e v e n t l os se s o f p r a w n s w h i c h w o u l d n o r m a l l y e sc a p e w h e nt h e m u d l i n e i n a d v e r t e n t l y l os t c o n t a c t w i th t h e b o t t o m o r b e r m o f t h ep o n d d u r i n g t h e p u l l in g o p e r a t i o n .

Fig. 3. Harvest bag with zipper attachment.


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A mechanized seine harvest system fbr ffeshwater prawns 7T he ha r ves t bag w as 4 - 6 m ( 15 f t ) l ong by 1 . 5 m ( 5 f t ) w i de and w as

t ap e r e d i n de p t h f r om 1 .8 m ( 6 ft) a t i t s op en i n g t o 0 -9 m ( 3 ft) a t t heb a c k . ( T h e t a p e r a l l o w e d f o r t h e p r o d u c t t o b e c a r r i e d d o w n t h e p o n dr a t h e r t h a n t h ro u g ja t h e b o t t o m m u d . ) T o m a k e t h e b a g , 4 . 4 c m (1~ i n )s t r e t c h (2 .2 c m o r ~ i n s q u a r e ) N o . 9 m u l t i f i l a m e n t n y l o n n e t w a s s e w e dt o 1 .0 c m (3 i n) b r a i d e d p o l y p r o p y t e n e r o p e w i t h 3 1 1 .8 5 g ( l l - o z ) f l o a t e r sa t t a c h e d e v e r y 3 0 - 5 c m ( 1 2 in ). T h e b a g h a d n o t o p f o r e a s y a c c e s s t o t h ep r o d u c t .A l l c o m p o n e n t s w e r e a t t a c h e d t o e a c h o t h e r t h r o u g h f i s h n e t z i p p e r sp r o d u c e d b y Y K K ( U S A ) In c . ( C i n c in n a t i. O H ) . T h e n y l o n z i p p e r s w e r es e w n o n t o t h e v e rt ic a l p e r i m e t e r r o p e s o f t h e s e i n e w i n g s a n d t h e o p e n -i ng o f t he ha r ves t bag ( F i g . " t, . T h e z i p p e r s w e r e a l s o u s e d t o p r o v i d e ac l o si n g m e c h a n i s m f o r t h e n e t s y s t e m a s o n e h a l f o f a z i p p e r w a s s e w nt w o m e s h e s a b o v e t h e m u d l i n e o v e r t h e e n t ir e l e n ~ h o f th e p r im a W a n daux i l i a r y w i ngs ( s ee F i g . 4 ) .

H A R V E S T O P E R A T I O N P R O C E D U R E ST h e m u l t is t ra n d s y n t h e ti c m u d l i n e d e p e n d e d l ar ge ly u p o n t h e ab s o r p -t io n o f w a t e r f o r n e g a t iv e b u o y a n c y a n d s h o u l d b e i m m e r s e d in w a t e r f o ra t l e a s t 4 h p r i o r t o t he f i r st ha r ve s t o f t he day .

Fig. 4. M ultistrand mu dlinewith zipper for closingprocedure.


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8 T . M . Lo sor do . J . -K . W ang , M . J . B rooks ' . C . E La i nT h e n e t s y s t e m c o n s i s t e d o f f i v e p i e c e s : t w o p r i m a r y w i n g s , t w o

a u x il ia ~ , w i n g s, a n d t h e h a r v e s t b a g. T h e c o m p o n e n t s w e r e u n l o a d e d,an d s p a c e d a r o u n d o n e e n d o f th e p o n d b e f o r e a h ar v e st . T h e b u n d l e s o fn e t w e r e t h e n u n t i e d a n d s t re t c h e d o u t o n t h e b a n k a n d j o i n e d a t t h ez i p p e rs , a n d t h e t e t h e r s w e r e a t t a c h e d t o th e m u d l i n e a t t h e p o i n t w h e r et h e au ,,d lia ry a n d p r i m a l , w i n g s c o n n e c t . T h e t e t h e r s w e r e t h e n a d j u s t e di n l eng t h t o e i t he r 7 "6 m ( 25 f t) o r 18"3 m ( 60 f t) f o r pu l l i ng bv ha r v es tb o o m ( F ig . 7 ) o r h a r v e s t c r e w w i t h h a r n e s s e s ( F ig . 5 ). re s p e c t i v e l y . T h es e t -u p p r o c e d u r e r e q u i r e d a p p r o x i m a t e l y 10 t o 15 m i n b e f o r e e a c hh a r ve s t. T h e h a r v e s t c r e w m e m b e r s t h e n t o o k u p t h e i r p o s it i o n s a s i n d i-c a t e d b y F ig . 6 ( a) ( F ig . 6 r e p r e s e n t s a p r i m e m o v e r a n d o n e h a r n e s so p e r a t i o n f o r d e m o n s t r a t i v e p u r p o s e s ).W h e n h a r v e s t i n g u s i n g t w o p r i m e m o v e r s o u t f i t t e d w i t h h a r v e s tb o o m s , t h e t e t h e r s w e r e a t t a c h e d t o t h e h a r v e s t b o o m ' s v e r t i c a l a r m ,w h i c h w a s m o v e d f o r w a r d a t a r a te o f a p p r o x i m a t e l y 6 . 4 m (2 1 ft) r a in - t.T h e t w o h a r v e st c r e w m e m b e r s i n t h e p o n d a t ta c h e d t h e e n d s o f t hea u xil ia ry ' s e i n e w i n g m u d l i n e t o t h e i r a n k l e ( c l o s e st t o t h e b e r m ) , a t t a c h e dt h e fl o a te r l in e to t h e b o o m a n d w a l k e d d i r e c t ly b e h i n d t h e b o o m a l o n gw i t h t h e p r i m e m o v e r ( F i g . 7 ) . T h e s e c r e w m e m b e r s w a l k e d a l o n g t h ep e r i m e t e r o f th e p o n d , h o l d i n g th e i r le g a n d n e t e n d c l o s e to t h e w a t e rl in e o f th e p o n d a n d u s in g t h e ir f re e h a n d s t o m o v e g r as s a n d o t h e r b e r mo b s t r u c t i o n s a w a y f r o m t h e w a t e r l i n e ( F ig . 8 ). T h e s e c r e w m e m b e r s a ls od i r e c t e d t i le f o r w a r d s p e e d o f t h e p r i m e m o v e r a c c o r d i n g t o t h e e ff o rt sr e q u i r e d t o m a i n t a i n a g o o d s e a l w i th t h e p o n d b e r m .U p o n r e a c h i n g t h e e n d o f t h e p o n d , o n t h e s i d e w h e r e c l o si n g w o u l do c c u r , t h e t e t h e r w a s d e t a c h e d f r o m b o t h t h e n e t a n d t h e b o o m . T h em u d l i n e w a s f i rm l y p r e s s e d i n t o t h e b o t t o m s ilt f r o m t h e t o e o f th e p o n d

Fig. 5. Harv esters' positions withou t prime mo ver.


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,-1 m e c h a n i z e d s ei ne harve.5 " s"c~gem fo r F~e_vhwa~er pr a wv, s ~at ha -v~ - 3 t ' .. - r"~w r~ ,gmD:2r "

i i . . . . . . i " ' !]

,~7=,,-~- i i / : 2 ~6 O f t t ~ t , ~ e r ,/ ?

i ~ ~ p ' 6 O f t p r , i m a r , yI ~ , . ~ _ ? ' ; i s ~ ln w i n g] L _ 4 _ ~ ~ _ _(~ .: . _ ~ _ ~ ! - Jt a ) ~ ~ i ' h a r ' v c s t b a g, , , j j

F i g . 6 .

~ t

i , i i~-~ N(b )

i " ~ - _ " t ~ " ~

,!; I l l ~-x2

itL ;

' . i~ . . . . . . . . .

H a r v c s t i n g o p e r a t i o n w i t h o u r p r i m e m o v c r . : a p u l l i n g t h e n e t , ( b ) c losin g ,o p e r a t i o n . ( c) z i p p i n g t h c n c t ' s m u d l i n e s t o g e t h e r .

H a r v e s t e r' s p o s i t i o n w i t h pr im e m o v e r a n d b o o m .i g . 7 .


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10 1-. M , Lo so rd o , J . -K . ~2~ng, M. J . Br oo ks , C E L arn

F i g . 8 . P u l l i n g t h e n e t ,

up to the top of the berm. The two harvest crew members from this sidethen moved to the other side of the pond to assist in moving the netsystem around the end of the pond to the point where the other net wingwas set (Fig. 6(b)). This operation can be done with the prime moverpulling the net. However, if there seems to be a large quantity of prawnsin the net and/or an extremely hard or un-silted bottom, the closingoperation should be done entirely by hand to minimize mudline liftingand associated losses of prawns.

When the net ends were brought together at the point of closing, theharvest crew took up positions as indicated in Fig. 6(c). One personremained on the pond bank, one stood behind the harvest bag in thepond, and two members remained inside, the perimeter of the net andperformed the net zipping operation. The zippers that were attached justabove the mudlines were brought together, joined and zippered closed.When the two members zipping moved away from the bank, both crewmembers at each end of the net sytem exerted a pulling force on the netas the net wings were zipped together. The lead person pulled the net'smudlines together clearing both debris and prawns from between themudlines. The second person performed the actual zipping of the nettogether (Fig. 9). The zipping operat ion usually requires 7-10 min. Timecan be taken at this point to allow for self-sorting of the under marketsize prawns through the net's mesh.


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A m e c h a n i z e d s e i n e h a r v e s t s } 's te m f b r f i' es h w a t e r p r a w n s I !

Fig. 9. Zippingthe mudlines together.

F i g . 1 0 . Removing the net from the pond.

U p o n c o m p l e t i o n o f t h e z i p p i n g p r o c e d u r e t h e n e t c a n b e g r a d u a l l yr e m o v e d f r o m t h e w a t e r w h i le k e e p i n g t h e p r a w n s b a c k in th e w a t e r ( F ig .1 0). A s t h e n e t' s w i n g s e c t io n s w e r e c o m p l e t e l y r e m o v e d , t h e p r a w n sw e r e m o v e d i n t o t h e h a r v e s t b a g w h i c h i s d e t a c h e d f r o m t h e w i n g s b yu n z i p p i n g a n d le ft in t h e w a t e r f o r a p e r i o d o f a p p r o x i m a t e l y 1 0 - 1 5 m i nt o ag a i n a l l o w t h e a n i m a l s t o s e lf s o r t. W h i l e t h is w a s o c c u r r i n g t h e n e tc o m p o n e n t s w e r e g a t h e r e d a n d l o a d e d f o r t r a n s p o r t t o t h e n e x t h a r v e s t


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1 2 7-. M . L o s o r d o . J . - K . B a n g . M . J . B r o o k s , C . ~ . L a i ns i t e . The ent i re harves t operat ion , not inc lud ing hand sor t ing , r equ iredf rom i i t o 1~ h .

A f t e r t h e s e l f - s o r t i n g p e r i o d , t h e p r o d u c t c a n b e d i p n e t t e d f r o m t h eh a r v e s t b a g a n d e i t h e r h a n d s o r t e d a t p o n d s i d e o r t r a n s p o r t e d d i r e c t l yto the farm l ive h old ing faci li ty .

S Y S T E M E \ L 4 , L U A T I O NT h e h a r v e s t in g p r o c e d u r e , a s a d e s c r i b e d h e r e , w a s d e v e l o p e d d u r i n g 1 5h a r v es t o p e r a t i o n s a t t h e A m O r i e n t A q u a f a r m 5 4 - h a c o m m e r c i a l p r a w np r o d u c t i o n f a c i l i t y , b y U n i v e r s i t y p e r s o n n e l . F o l l o w i n g t h e d e v e l o p -m e n t a l p e r i o d , t h e n e t a n d b o o m s y s t e m ,,,,'a s m o v e d t o t h e K a h u k uP r a w n C o . ( K P C ) 1 2 " 5 -h a fa rm f o r d e m o n s t r a t i o n a n d f i e ld e v a l u a t i o n .

T h e n e t a n d b o o m s y s t e m w a s e v a l u a t e d u s i n g t w o t e s t p a r a m e t e r s :ha~ 'e s t y i e ld ver sus t he prev ious f i ve harves t y i e lds us ing t he f arm'ss t andard ne t harves t ing operat ion , and t he e s t imat ed harves t e f f i c i encya s m e a s u r e d b y t h e m a r k a n d c a p t u r e m e t h o d d e v e l o p e d b y L a i n a n dW a n g ( 1 9 8 5 ) .

Tab le t r epresent s t he re su l t s o f t he har~ 'e s t ing operat ions comple t edin s e v e n p o n d s a t th e K P C f a rm . T h e n u m b e r s in t h e p a r e n t h e s e s a re t h e

T A B L E lC o m p a r i s o n o f H a r v e s t Y i e ld s

P o n d P r e v i o u s h a r v e s ts , l b s ( '% o f t o t a l y i e h l ) U H n e t 7 o t a ln o . s y s t e m y i e h t ,

1 2 3 4 5 lbs21 156 186 109

(162) (19"3) (113~13 lS 0 12 2 181_1(16 '1) (10 .9) ( 1 6 115 99 113 171(11 '4) (13"0) (19-7

16 120 133 139(11 '3) (12-6) (13-1

4 64 64 111(8 .4) (8 .4) ( 1 4 - 619 175 144. 24 4

(13 . 4 ) ( l l . O ) (18 -7 :14 73 142 199

(7.1! (13-8) !119"3

10 1(1t) '5)2 0 2( 1 8 ' t168( 1 9 . 3

2 12{2 0 - 0157(20 .7?3 1 9( 2 4 - 4173

I6 -8 ;

143( 14-87199

17-8)124

14 '3)195(18 .4)149( 19 -6196( 15.02 4 7( 2 3 - 9

2 7 0: 2 8 . 0 )2 3 3(2t).9)194(22"3)

2 5 92 4 . 5 )214(28 .2)2 2 7(17.4)198

19.2',

9 6 5100 )1161oo)8 6 9(1oo)

1 0 5 8(100 )7 5 9(1oo)

1 3 0 5( I 0 0 )1 0 3 2(lOO)


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,A mec / ta t t i c , ed se in e harve . ; t ~>'s :em o r f r e sh wa te r pr aw ns I 33 0 [

~.~2 0>

1 0= P o n d 4

. = P o n d 1 3, = P o n d 1 4

' . = P o n d 1 , 5? = P o n d 1 6 = P o n d 1 9,~ = P o n d 2 1

0 I 2 3 4 5 uHnetHacvest sequence

F i g . 1 1 . C o m p a r is o nof harvest y i e l d s .

p e r c e n t a g e s o f t h e t o t a l o f t h e s i x h a r v e s t y i e l d s t h a t t h e s i n g l e h a r v e s ty i e l d re p r e s e n t s . W h e n d i s p l a y e d in g r a p h i c f o r m in F ig . 11, a d i f f e r e n c eis c l e a r ly s e e n b e t w e e n t h e p r e v i o u s h a r v e s t o p e r a t i o n s a n d t h e y ie l d s o ft h e n e w n e t an d b o o m s y st em ( U H n et) .T h e e v a l u a t i o n o f t he e s t i m a t e d h a r v e s t e f fi c ie n c y w a s p e r f o r m e d insix p o n d s . T w o o f t h e o p e r a t i o n s w e r e c a r r ie d o u t b y U n i v e r s i ty p e r s o n -n e l w h i l e t h e r e m a i n i n g f o u r t e s t s w e r e p e r f o r m e d u s i n g t h e f a r m ' sr e g u l a r h a r v e s t c r e w o p e r a t i n g t h e n e w s y s t e m . T h e r e s u lt s o f t h e h a r v e s te f f ic i e n c y e s t i m a t i o n a r e p r e s e n t e d in T a b l e 2 . T h e m e a n h a r v e s t e ff i-c i en cy a s i nd i c a t ed bv t he s i x f i e l d t ri a ls w as 63"5%.D u r i n g t h e t e s ti n g a n d e v a l u a t i o n p e r i o d , a n u m b e r o f a r e a s f o ri m p r o v e m e n t in th e n e t s y s te m d e s i g n w e r e n o t e d A s e c o n d n e t s y s te mis c u r r e n t y b e i n g f a b r i c a t e d w i t h t h e f o l l o w i n g m o d i f i c a t i o n s .T h e n e w s e i n e - n e t w i n g s w i ll b e 9 0 ft lo n g , e l i m i n a t i n g t h e n e e d f o ra u x i li a ry w i n g s. E a c h w i n g w il l h a v e a c o n t i n u o u s 9 0 ft z i p p e r a b o v e t h e


14/15

1 4 T . M . L o s o r d o , J . - K , W a r lg . M . J . B r o o k s , C , ~ : L a r nT A B L E "~

H a r v e s t E f f i c i e n c y E s t i m a t eP o n d n o . H a r v e s t y i e l d E s t i m a t e d h a r v e s t H a r v e s t c r e w

Ib~ e ~ 7( ie n cy i ':'~,~1 3 2 3 3 6 3 U H

4 2 1 4 6 1 U H9 I 9 3 6 6 K P C

19 ~ - -. , / ~ .~ K P C1 4 1 9 8 - 7 3 K P C1 6 1 7 9 6 3 K P C

m udl ine (ve rsus the cu r ren t th ree 30 t~ z ippers ) to fac i l it a te an ea s ie rc los ing p rocedure . To avo id p rawn losses over the f loa te r l ine , thef loa te r s wi l l be spaced c lose r toge ther . The ou t s ide 60 f t o f each wingwi ll have the f loa t s spac ed eve ry 12 in on cen te r . T he rem ain ing 30 f t o fthe wing wil l hav e f loa t s spaced a t 9 in on cen te r . Th e se ine -ne t eye s izewi ll be inc rea sed to 1 in s t re tch m esh an d the cen te r m ou nte d harves t bagwil l be e l im ina ted . The two 90 ft wings wil l be z ipped d i rec t ly a t thecen te r , a ha rves t bag cou ld be a dd ed i f a va r ia t ion in mesh s izes isrequ i red fo r p ra w n se l f so r t ing .

S U M M A R Y A N D R E C O M M E N D A T I O N SA ' t h i r d g e n e r a t i o n ' m e c h a n i z e d h a r v e s t n e t s y s te m h a s b e e n s u c c e s s fu l lyd e v e l o p e d a n d t e s t e d f o r t h e H a w a i i a n p r a w n i n d u s t r y . T h e s e i n e - n e ta n d b o o m s y s t e m w a s c a p a b l e o f r o u t i n e l y c a t c h i n g 6 3 % o f t h e a v a il a b lem a r k e t s i z e p r a w n s i n h e a v i l y s i lt e d a n d e r o d e d p r o d u c t i o n p o n d s . W h i l edoubl ing p rev ious ly repor ted har~ 'es t e f f i c ienc ies , the ne t a l so s ign i f i -c a n t l y r e d u c e d b o t h t h e t i m e a n d e f f o r t r e q u i r e d b y t h e t r a d i t i o n a lh a r v e s t in g m e t h o d c u r r e n t l y e m p l o y e d b y th e i n d u s tr y .

A C K N O W L E D G E M E N T ST h i s s t u d y h a s b e e n s u p p o r t e d b y t h e A q u a c u l t u r e D e v e l o p m e n tP r o g ra m , D e p a r t m e n t o f L a n d a n d N a t u r a l R e s o u r c e s, S t a te o f H a w a i i( G r a n t N o . 1 6 5 8 9 ) a n d t h e U n i v e r s i t y o f H a w a i i N a t i o n a l S e a g r a n tP r o g r a m ( G r a n t N o . A / R - 1 5).


15/15

A m ech anize d seine harvest system ~or freshwater praw ns 15T h e a u t h o r s w i s h t o a c k n o w l e d g e t h e c o n t r i b u t i o n s o f t i m e "a nd f ac il i-

t i e s m a d e b y K a h u k u P r a w n C o . , A m O r i e n t A q u a f a r m a n d P r a w n s o fH a w a i i , In c . i n t h e t e s t i n g o f t h e n e t s y s t e m .

G r a t i t u d e i s e x t e n d e d t o L i s a B r o w n , S a l l y H i g a a n d J o a n n eK u r o s a w a f o r e f f or ts i n th e d e v e l o p m e n t o f t his p a p e r .

R E F E R E N C E SFuj imoto , M. , Fu j imu ra , T . & K ato , K. (1977i . A n id io t ' s gu ide to p raw n p onds .In : S h r im p a n d P r a w n F a r min g i n t h e ~ t~ 's te rn He mi s p h er e , eds J . A. Han sonan d H . L . Go o d win , Do wd en , Hu tch in so n & Ro ss , I n c . , S t r o u d sb u r g ,Pennsy lvan ia .G ibso n, R . -17. & W ang, J . K. (1977) . A n al terna t ive p raw n pr od uc tio n system sdesign in Haw ai i. S e a G r a n t T e c h n i c a l R e p o r t U N [ H I - S E A G R A N T - T R - 7 7 -05. Un ivers i ty o f Haw ai i.Lain , C. Y. & W ang, J . K. (1985) . Es t im atin g harve st ing eff ic iency of f reshw aterp r awn s . P r e sen ted a t t h e S u m m er M ee t in g o f t h e Am er i can So c ie ty o f Ag ri -cu l tu r a l En g in ee r s , Eas t Lan s in g , Mich ig an , 2 3 - 2 6 Ju n e 1 98 5.Pe terson , J . J . (1982) . Freshwater p rawn harves t ing : a compar ison o f th reem e t h o d s . P r o c . Wo r ld M a r i cu l t u r e S o t . , 13, 104-19.Po lov ina, J . & Brow n, H. (1978) . Popu la t ion dyn am ics and pro duc t ione c o n o m i c s . Proc. L~'brld M aricu l t t tre Soc, , 9 ,3 9 3 - d ~0 4 .Rie tow, Al lan , S ., Pres iden t , Prawns o f H awai i , Ki lauea , Hawai i. Persona l com -m u n ica t io n .Shang, Y. C. (1981) . Freshwater M a c r o b r a c h i u m r o s e n b e r g i i p r o d u c t i o n i nHawa i i. p r ac t ice s an d e co n o m ics . S ea Gr a tz t M i s ce l l a n eo u s R ep o r t . U N IH I -S E A G R A N T - M R - 8 1 - 0 7 , Univers i ty o f H awai i .S t a te o f Hawa i i (1 9 7 8 ). A q u ac u l tu r e D ev e lo p m en t fo r Hawa ii: A ssessm en t s andr eco m m en d a t io n s . Aq u acu l tu r e P lan n in g Pr o g r am , Ho n o lu lu , Hawa ii.S t a t e o f Hawa i i ( 1 9 8 3 ) . Un p u b l i sh ed f a r m su r v ey , Dep a r tm en t o f Lan d an dN a t u r a l R e s o u r c e s , A q u a c u l t u r e D e v e l o p m e n t P r o g r a m , p r e p a r e d b vK endr ic k K. F . Lee .Wal lace , J . . Manager , AmOrien t Aquafarm, Kahuku . Hawai i . Persona l com-

m u n ica t io n .W il liamson , M. R. and Wang , J . K. { 98 2) . A n im pro ved harves t ing ne t fo r f resh-wa te r p r awn s . A q u a c l z l t t tr a l E n g in eer in g , I (2) , 81-91.

losordo 1986 aquacultural-engineering

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