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Aqua culm ral Engineering 5 ~1 9 8 6 1 3 1 3 - 3 2 3

E n g i n e e r in g R e s e a r c h fo r Im p r o v e m e n t o fF r e s h w a t e r P r a w n H a r v e s t Y i el d in H a w a i iC h e e Y . L a m a n d J a w - K a i W a n g

Agricul tura l Engineer ing Department , Univers i ty of Hawai i a t Manoa , HonoluluHa ~ a ii . U SA

A B S T R A C TEngineer ing research for imp roving f reshw ater praw n harves t y ie ld inHa w a i i h a s f o c , l s ed o n t h e d eve lo p m en t o f ma n a g em en t s tr ategie s a n dtechniques . Firs t. a marl ," an d capture m et ho d was devel ope d to est i-m ate ha rvest e ff ic iency. The average harvest e f f ic iency in early co m m er -c ia l p o n d s w a s f o u n d t o b e o n l y 2 4 . 08 %; t h is l ed t o t h e b e l i e f t h a t l o wattd inc ons is tent h arvest y ields were due to low at td inconsL~'tent harveste f fi c ien o ; A n imp r o ved h a n , e s ti n g O , st em w a s t h en d eve lo p ed w h ichpro du ced an average harves t e ff ic iency o f 63"5%. A s tudy was a l so don eto co mp a r e t h e e ffe cts o f d if fe r ent p o n d b a n k g r a ss ma n a g em en t p r a c -t ices o n harves t y ie lds. I t was fo un d tha t reduct ion o f bank grass wi th -o u t a n y o th er ch a n g es i n ma n a g e me n t ca n i n cr ea se t h e y i e ld t o 21 7 9 kgha -1 year - t , wh ich is ah no st 1 "5 t ime s the 1984 s ta te average yield . A nexp erim ent to s tu dy the effects" o f h igher ham'est e f ficien O' on yield is' inprogress.

I N T R O D U C T I O NI n H a w a i i , t h e c o n t i n u o u s s t o c k i n g a n d h a r v e s t i n g s y s t e m f o r 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 m r o s e n b e r g i i c u l t u r e i s p r a c t i c e d . S m a l lj u v e n i l e p r a w n s a r e s t o c k e d i n e a r t h e n p o n d s . A f t e r t h e f ir s t s t o c k i n g ,t h e j u v e n i l e p r a w n s a r e m k x e d w i t h p r a w n s o f d i f f e r e n t s i ze s f r o mp r e v i o u s s t o c k i n g s . H a r v e s t i n g is d o n e a t i n t e r v a l s a n d is c u r r e n t l y 'd o n e b y h a n d - s e i n in g .*Hawai i Institute of Trop ical A griculture a n d H u m a n Resources, Journal Series N o.3 0 0 9 . 31 3Aquac,dmral Engineering 0 1 4 4 - 8 6 0 9 / 8 6 / S 0 3 . 5 0 - E l s e v i e r A p p l i e d S c i e n c ePubl ishers L td , Eng land. 1986 . Pr in ted in G rea t B rita in

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31-~ C . ! ,: L a m , Y . - K . W a n g

Full scale commercial prawn production began in Hawaii in 1969.Growth of the industry' was hampered by the inabiliw of commercialfarms to attain production levels representative of the potential bio-logical productivity of the freshwater prawn. Gibson and Wang (1977)stated that yields ranging from 2225 to 3115 kg ha -t year -~ havebeen demonstrated. Shang (1981) estimated that the break even pro-duction yields for a 40 ha and a 20 ha farm were 1747 kg ha -~year -~ and 1868 kg ha -t year -t. However, the state average yieldswere only 1157"48 kg ha -t year -~ in 1982 (State of Hawaii. 1983),1259.2 kg ha -l year -I in 1983 and 1448.91 kg ha -t year -~ in 1984(K. Lee, personal communication).Freshwater prawn production is far short of the estimated within-state demand of 682-818 tonnes (t) per annum (State of Hawaii,1978). The total freshwater prawn production in Hawaii was 143-34 tin 1982 (State of Hawaii, 1983), 122 t in 1983 and 144.24 t in 1984(K. Lee, personal communication). Thus there is a potential forgrowth of the industry. Industrial growth would have to be motivatedby demonst rated higher profitability. At present, higher profitability ofexisting operations can best be demonstrated by increasing the aver-age yield per hectare per year. The existence of so-called high yieldingponds indicates that the current limiting factor to higher average yieldis most likely not due to a lack of biological know-how. Thus, theresearch focus of the aquacultural engineering group at the AgriculturalEngineering Department of the University of Hawaii, USA, is on thedevelopment of a set of engineering management strategies and tech-niques that will fully utilize existing biological know-how to increasethe average yield per hectare per year.

EXISTING HARVEST YIELDSWhen a grow-out prawn pond is not reaching its productive potential,two simple possible causes come to mind:

(1) Assuming high harvest efficiency, low yields can be attributedto the inability of the pond to produce marketable prawns.(2) Assuming there are marketable prawns in the pond, low yieldscan be attributed to the inefficient harvesting of the marketableprawns.

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Imp rove me nt of reshwater praw n harves t in Haw ai i 3 t 5

0 ' 0 ! 2

F i g . 1 .

3 0 02 8 02 6 02 4 02 2 02 0 01 8 0

.. , 160u l>~ 140t. . 1 2 0I 1 0 0

8 0 -6 0 -4 0 -2 0 4

I t' 0 ! 4 ' 0 1 " 6 ' 0 t 8 ' 1 "0 1 !2 1 -4( t h o u s a n d s )N u m e r ic a l d a t e ( d ay 1 : J a n 2 4 1 9 8 0)H a r v e s t y i e ld o f a p o n d f r o m a c o m m e r c i a l f a r m o n t he N o r t h S h o r e o f

O a h u . P o n d A 8 h i s to r i ca l d a t a 1 9 8 0 - 1 9 8 3 .

Figure 1 shows the harvest yield of a pond from a commercial farmon the North Shore of Oahu. The harvest yields appear to varyrandomly and exhibit drastic changes occasionally. The drasticchanges cannot be explained by natural phenomena like weatherchanges and are most likely due to harvesting variation. Changes innatural phenomena are generally gradual.Assuming low and highly variable harvest yields can be explainedby the two above-mentioned reasons, knowledge of the harvestingefficiency (ratio of the amount of market size prawns harvested to theamount available for harvest) would determine whether they arecaused by the first or second reason. Therefore, it is important toobtain an estimate of the harvesting efficiency.

ESTIMATING HARVEST EFFICIENCYHarvest efficiency can be estimated accurately by draining the pondimmediately following the harvest. The harvest efficiency would be

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3 16 C ~7 Larn, J.-K. Wang~ v e n b y:

E a = } ~ / ( W . + ~ ) * 1 0 0 ( % )w h e r e E d = h a r v e s t e f f i c ie n c y e s t i m a t e d b y d r a i n i n g p o n d ( % ),I,V = w e i gh t o f ha r ves t y i e l d f r om s e i ne ha r v es t (kg), } ~ = w e i gh t o fh a r v e s t y i e ld f r o m d r a i n h a r v e s t ( kg ).

T h i s m e t h o d c a n g i v e a n a c c u r a t e e s t i m a t e o f h a r v e s t ef f ic i e n c y i fa l l t h e p r a w n s a r e r e c o v e r e d d u r i n g t h e d r a i n h a p ' e s t . T h e r e q u i r e -m e n t o f a d r a i n h a r v e s t m a k e s t hi s m e t h o d u n s u i ta b l e f o r fr e q u e n t u sein e i t h e r m a n a g e m e n t o r r e se a rc h .

L a m a n d W a n g ( 1 9 8 5 ) h a v e d e v e l o p e d a m a r k a n d c a p t u re m e t h o df o r e s t i m a t i n g h a r v e s t e f f i c ie n c y w h i c h d o e s n o t r e q u i r e d r a i n i n g ap o n d . L a m a n d W a n g a s s u m e d t h a t t h e p e r c e n t a g e o f m a r k e t s iz ep r a w n s c a p t u r e d i n a h a r v e s t fo l l o w s t h e b i n o m i a l d i s t ri b u t i o n . D u r i n ga h a r v e s t , t h e r e a r e t w o p o s s i b l e o u t c o m e s f o r a n i n d i v i d u a l p r a w n : i tis e i t h e r c a p t u r e d o r n o t c a p t u r e d . T h e f o l lo w i n g a s s u m p t i o n s w e r em a d e :

( 1 ) E a ch i nd i v i du a l t r ia l i s s t a ti s ti ca l ly i n de pe nd en t .( 2 ) I nd i v i dua l tr ia l s a r e d i s c r e t e even t s .( 3) T h e p r o b a b i l i t y o f th e o c c u r r e n c e o f a s u c c e s s ( t h e c a p t u r e o f

an i nd i v i du a l p r aw n ) i n any s i ng l e ha r v es t i s a cons t an t .B a s e d o n t h e s e u n d e r l y i n g a s s u m p t i o n s , a n e s t i m a t e d h a r v e s t e ffi-

c i e n c y , / 5 , i s s a i d t o b e a n e s t i m a t e o f t h e p r o b a b i l i t y o f c a p t u r e o f am a r k e t s iz e p r a w n ( B o x e t a l . , 1 9 7 8 ) . A n e s t i m a t e d h a r v e s t e f f i c i e n c yc a n b e o b t a i n e d b y u si n g a s a m p l e o f m a r k e d p r a w n s . T h e e s t im a t e dha r ve s t e f f i c i ency is g i ven by :

E = ( N c / N t ) * 1 0 0 ( % )w h e r e E = h a r v e st e f f ic i e n c y e s t i m a t e d b y m a r k a n d c a p t u r e m e t h o d(% ), N = n u m b e r o f m a r k e d p r a w n s c a p t u r e d d u r i n g h a rv e st ,N , = n u m b e r o f m a r k e d p r a w n s r e l e a se d i n t o p o n d b e f o r e h a rv e s t.T h e p r a w n s w e r e m a r k e d b y w r a p p in g 1 2" 7 m m ( in t er n a l d i a m e t e r)r u b b e r b a n d s a r o u n d t h e t ail tw i ce . O n l y h a r d - s h e l l e d p ra w n s w e r eu s e d f o r m a r k i n g as t h e r u b b e r b a n d w a s o b s e r v e d t o c o m e o f f w h e na p r a w n m o l t e d . A p p l i c a t i o n o f t h e r u b b e r b a n d a n d p l a c e m e n t o f t h er u b b e r b a n d o n t h e p r a w n t ai l a r e s h o w n i n F i g s 2 a n d 3 , r e s p e c ti v e ly .T h e r u b b e r b a n d s w e r e e a s y t o id e n t if y a n d d i d n o t a f fe c t t h e m o b i l it ya n d n a t u r a l b e h a v i o r o f t h e m a r k e d p r a w n s . T h e r e w a s n o p h y s ic a l

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b T z p r o v em e t , t o f j ; r e s / ; w a t e r y r a '~ ' rz / za r .* . '~ t i :z ! ! ~ ; ; ..~" 3 i

Fig. 2. Applica tio n of the rubbe r band on the prawn tail using a PVC tube.

Fig, 3. Placement of the rubber band on the pr~xvr~,

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3 ! g C . "r7 L a i n , J . - K , ~ ' i k n g

i n ju r y o f t h e p r a w n a n d t h e r u b b e r b a n d s c o u l d b e e a si ly r e m o v e d s ot h a t t h e h a r v e s t e d m a r k e d p r a w n s c o u l d b e m a r k e t e d . A s a m p l e s i z eo f 9 0 m a r k e d p r a w n s w a s s e l e c te d s o t h a t th e h a r v e s t e f f ic i e n cy o f th em a r k e d p r a w n s c o u l d b e a s s u m e d t o b e a p p r o x i m a t e l y n o r m a l l yd i s t r ib u t e d w i t h c o n s t a n t v a r i an c e . M a r k e t s iz e p r a w n s 1 3 0 - 1 4 0 m ml o n g ( m e a s u r e d f r o m t h e p o s t e r i o r e n d o f th e e y e - s t a lk t o t h e t ip o f th et e l s o n ) w e r e u s e d f o r m a r k i n g s i n c e t h e y h a v e b e e n s h o w n t o b eu n a b l e to p a ss t h r o u g h t h e 4 4 . 4 5 m m m e s h n e t u s e d i n h a n d - s e i n in g .T h e p r a w n s w e r e s i z e d b y u s i n g a p l e x i g l a s t u b e , a s s h o w n i n F i g . 4 .T h e e x p e r i m e n t a l p r o c e d u r e s a r e d e t ai le d in L a m a n d W a n g ( 1 98 5 ).

T a b l e 1 s h o w s t il e h a ~ ' e s t e f f i c ie n c i e s e s t i m a t e d b y t h e m a r k a n dc a p t u r e m e t h o d a n d b y h a r v es t i n g a n d d r a in i n g a p o n d . T h e d a t a w e r eo b t a i n e d f r o m 1 0 d i f f e re n t g r o w - o u t p o n d s . A p a i r e d t -t es t w a s u s e dto d e t e r m i n e w h e t h e r t h e d a t a w e r e c o n s i s t e n t w i t h th e n u l l h y p o t h e s i s( H 0) , s o t h a t t h 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 e d b y t h e m a r k a n d c a p t u r em e t h o d a n d b y h a r v e s ti n g a n d d r a i n i n g a p o n d a r e t he s a m e . T h e ts ta ti st ic as s o c i a t e d w i t h H , w a s 1 " 07 a n d P r ( t > 1 0 7 ) = 0 . 1 6 9 . T h e r e -f o r e , th e n u l l h y p o t h e s i s w a s n o t r e j e c t e d . T h e h a r v e s t e f f i c ie n c y d a t a

F i g . 4 . U s e o f p l e x i ~ a s t u b e t o s iz e p r a w n s .

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I m p r o v eme n t o r r e sh wa t er p r aw n h a r v e st i n H a w a i iT A B L E 1

H a r v e s t E f f ic i e n c y E s t i m a t e d b y M a r k an d C a p t u r e M e t h o d a n d byH a r v e s t i n g a n d Draining a P o n d

319

5 ,1 a rk a n d ca p tu re m e t h o d H a r v est i n g a n d d r ai n i n g a p o n dE~ (% ) E d (?4,)24.44 27.48

2.22 9.262-22 5.74

11 . I 1 9 . 0138"89 43.0238-89 39-1622-22 23.4916-67 2 0 ' 0 045.56 38-9525.56 24.67

P aired t - t es t .HI, : E~ = E dD e g r e e s o f f r e e d o m = 9.t value = 1.07.Pr(t> 1.07)=0-169.

i n T a b l e 1 r a n g e d f r o m 5 "7 4 t o 4 3 . 0 2 % , i n d i c a t i n g t h a t h a r v e s t ef fi -c i e n c y o f h a n d - s e i n i n g is h i g h l y v a r i a b le . T h e a v e r a g e h a r v e s t e ff i -c i e n c y w a s o n l y 2 4 - 0 8% , s u p p o r t i n g p r e v i o u s s u s p i c i o n s th a t l o w a n di n c o n s i s t e n t h a r v e s t y i e l d s w e r e d u e t o l o w a n d i n c o n s i s t e n t h a r v e s te f f i c i e n c y .

T a b l e 2 s h o w s d a t a c o ll e c t e d t o o b t a i n a n e st i m a t e o f t h e sa m p l i n gv a r ia t io n . T h e p r o c e d u r e w a s c a r ri e d o u t i n f o u r d if f e re n t p o n d s , a n db e f o r e e a c h h a r v e s t t h r e e sa m p l e s o f 9 0 m a r k e d p r a w n s e a c h (a to ta lo f 2 7 0 m a r k e d p r a w n s ) w e r e r e l e a s e d i n t o e a c h p o n d . T h e t h r e em a r k e d s a m p l e s w e r e d i s t in g u i s h e d b y c o l o r e d r u b b e r b a n d s . T h ep o o l e d e s t im a t e o f s a m p l i n g v a r i a ti o n is 0 . 3 2 3 1 a n d th e s a m p l i n gs t an d a r d d e v i a t i o n is 0 - 0 5 6 8 . T h e e s t i m a t e d s a m p l i n g s ta n d a r d d e v ia -t i o n i s c l o s e t o t h e t h e o r e t i c a l s t a n d a r d d e v i a t i o n o f 0 " 0 4 9 4 , w h i c h i sc a l c u l a t e d w i t h a p v a l u e o f 0 " 3 25 . T h i s s t u d y s h o w s t h a t t h e m a r k a n dc a p t u r e m e t h o d c a n b e u s e d t o e s ti m a t e h a r v e s t e f f ic i e n c y w i t h o u th a v i n g t o d r a i n t h e p o n d . T h e s t u d y a l s o p o i n t e d o u t t h e n e c e s s i t y t od e v e l o p a m o r e e f f ic i e n t a n d c o n s i s t e n t h a r v e s ti n g s y s te m .

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320 C. Y Lain, J.-K. WangTABLE 2Estimation of Sampling Variation Using Th ree M arked Samples in Individual Ponds

Pond Est imated harves t e ff ic ie~wy (%j Average V a ri a n ceSam ple I Sam ple 2 Sample 3

1 25.56 44.45 30'00 33"33 97"55812 24.44 28'8 9 26'67 26"67 4"950653 45"56 43"34 3S 89 42"60 11'536 654 31" 11 27 '78 "~2 " 27.41 15"195 932.50

Pooled sampling variation = (97 '5581 + 4.950 65 -,- 11'52665 + 15-1959)/4= 3 2 . 3 1 0 3 2 5 .Estimated sampling standard deviation = 5-6842171%=0-0568 .p = (33-33 + 26.67 + 42.60 + 27.41 )/4= 32.50 or 0.3250.q = ( l - p ! = 1 - 0 .3 2 5 0 = 0 .6 7 5 0 .Theoretical standard deviation = ~ip*q) /n= ,j(0.3250"0-6750)/90

=0-0494 .

I M P R O V E D N E T H A R V E S T I N G S Y S T E MI m p r o v e d n e t h a r v e st in g s y s t e m s h a v e b e e n d e v e l o p e d b y W i l l i a m s o na n d W a n g ( 1 9 8 2 ) an d L o s o r d o e t a l . (1986) o f th e a q u a c u l t u r a le n g i n ee r in g g r o u p a t t h e A g r i c u l t u r a l E n g i n e e r i n g D e p a r t m e n t o f t heU n i v e r s i ty o f H a w a i i . T h e h a r v e s t e f f i c i e n c y o f t he n e t s y s t e md e v e l o p e d b y L o s o r d o e t a l . ( 1 9 8 6 ) w a s e s t i m a t e d u s i n g th e m a r k a n dc a p t u r e m e t h o d . T h e e s t im a t e o f t he m e a n h a r v e s t e f f i c i en c y w a s6 3 . 5 % a n d t h e s t a n d a r d d e v i a t i o n w a s 5 . 9 % .

E F F E C T S O F H I G H H A R V E S T E F F I C I E N C YT h e w o r k o f M a l e c h a a n d B i g g e r ( 1 9 8 4 ) a n d M a l e c h a e t a l . ( 1 9 8 1 )h a v e i n d i c a t e d t h at l a rg e r p r a w n s s u p p r e s s t h e g r o w t h r a t e o f s m a l l e r

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Im p ro v em en t o f resh w a ter p ra w n h a rves t i n H a w a i i 3 2 1p r a w n s . T h u s h i g h h a r v e s t e ff ic i e n c y w o u l d m e a n h i g h e r g r o w t h r a teo f s u b - m a r k e t s iz e p r a w n s d u e t o t h e a b s e n c e o f t h e la r g e r m a r k e t s iz ep r a w n s . T h e r e s h o u l d a l so b e a r e d u c t i o n i n m o r t a l it y o f m a r k e t s iz ep r a w n s s i n c e t h e r e i s n o a s s u r a n c e t h a t a ll t h e m a r k e t s iz e p r a w n s l ef tb e h i n d i n o n e h a r v e s t w i ll b e p r e s e n t d u r i n g t h e n e x t h a r ve s t. H i g h e rg r o w t h r a t es w o u l d a ls o m e a n m o r e e f fi c ie n t u s e o f f e ed s .A s i m p l e e x p e r i m e n t w as d e s i g n e d to d e m o n s t r a t e t h a t i m p r o v e dh a r v e s t e f f ic i e n c y w o u l d l e a d t o h i g h e r y i e ld u n d e r o t h e r w i s e id e n t i ca lc o m m e r c i a l m a n a g e m e n t p ra c ti ce s ( W a n g a n d L o s o r d o , i n p r e s s .

S ix p o n d s w e r e s e le c t e d f r o m m o r e t h a n a h u n d r e d p o n d s o n al a r g e c o m m e r c i a l p r a w n f a r m l o c a t e d i n K a h u k u , O a h u . T h e s e s L ' ~p o n d s w e r e t h e n p a i r e d a c c o r d i n g t o t h e i r c lo s e n e s s in st o c k i n g d a t e ,s t o c k i n g d e n si ty , a n d r e s t o c k i n g s c h e d u l e . O f e a c h p a i r o f p o n d s , o n ew a s r a n d o m l y s e l e c t e d t o h a v e i ts b a n k g r as s c u t l o w w h i le t he o t h e rw a s l e ft t o t h e n o r m a l b a n k g r a ss m a n a g e m e n t b y t h e fa r m sta ff.

E a r t h e n p o n d b a n k s r e q u i r e g ra s s c o v e r i n g t o c o n t r o l b a n k e r o s i o na n d m a n y f a r m e r s a n d q u i t e a f e w b i o l o g i s t s b e l i e v e t h a t t h e g r a s sc o v e r i n g s h o u l d b e l o n g t o p r o v i d e n o t o n l y e r o s i o n p r o t e c t i o n b u ta l s o a h a b i t a t f o r p r a w n s t o r e d u c e m o r t a l i t y . F r o m a n e n g i n e e r i n gp o i n t o f vie w,, t h e c o n t r o l o f b a n k e r o s i o n r e q u i r e s o n l y t h a t s h o r tg ra s s b e p r o v i d e d . L o n g b a n k g r as s w o u l d i n t e r f e r e w i th t h e h a r v e st -i ng o p e r a t i o n , r e d u c i n g b o t h l a b o r a n d h a r v e s t e f fi c ie n c ie s b y p r o v i d -i n g h i d i n g p l a c e s f o r p r a w n s t o a v o i d c a p t u r e .

F r o m 2 5 O c t o b e r 1 9 8 3 to 31 M a y 1 9 8 4 t h es e p o n d s w e r eh a r v e s t e d 6 0 t i m e s . T h e r e s u lt s a re s h o w n i n T a b l e 3 . A p a i r e d t -t e stw a s u s e d t o d i s c e r n t h e e f f e c t o f b a n k g ra s s c o n d i t i o n s o n h a r v e s ty i e ld s . T h e 3 0 p a i r e d h a r v e s t s w e r e p o o l e d f o r th e p a i r e d t -t es t. T h ea v e r a g e d i f f e r e n c e i n h a r v e s t y i e l d s b e t w e e n p o n d s w h e r e t h e b a n kg r as s w a s c u t s h o r t a n d t h e p o n d s w h e r e n o e f f o rt w a s m a d e t o re d u c et h e g ra s s l e n g t h w a s 2 0 .7 5 1 k g p e r h e c t a r e p e r h a r v e s t w i t h a s t a n d a r de r r o r o f 9 -2 3 1 a n d a c a lc u l a t e d t = 2 a n d P r ( t > 2 ) = 0 .0 5 4 7 . T h e n u l lh y p o t h e s i s t h a t t h e r e w a s n o d i f f e r e n c e i n h a r v e s t y i e l d s b e t w e e n c u ta n d u n c u t p o n d s w a s t h e r e f o r e r e j e c t e d . T h u s t h e r e w a s a f ir st te n t a -t iv e p r o o f o f t h e h y p o t h e s i s t h a t h a r v e s t e f f ic i e n c y s i g n if ic a n t ly a ff e ct st h e h a r v e s t y ie ld . W a n g a n d L o s o r d o w e n t o n t o s h o w t h a t b y s im p l yr e d u c i n g t h e b a n k g r a s s o f t h e g r o w - o u t p o n d s w i t h o u t a n y o t h e rc h a n g e s i n m a n a g e m e n t , th e a n n u a l y i el d c o u l d b e i n c r e a s e d t o 2 1 7 9k g h a - ~ ye a r - ~, w h i c h is a l m os t 1"5 t i me s t he 19 84 s t a t e ave r a ge y i e l d .

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3 2 2 C. E Lain, J. -K. Wang

T A B L E 3H a r v e s t T r i al R e s u l t s

Harvest Po nd Yie ld (k ~ Di fferencedate nu m be r in y ie ld , DiC u t L ) I C U t ( c u t - u n c u 0p o n d p o n d (k g)

( D i - D ):

2 5 O c t 8 3 C 2 6 . C 2 5 6 7 " 5 9 4 4 . 4 5 " "a ' 1 31 6 N o v 8 3 C 2 6 , C 2 5 6 2 " 1 4 6 7 - 5 9 - 5 - 4 42 3 N o v 8 3 C 2 0 . A I 5 6 8 ' 7 2 4 1 . 9 6 2 6 -7 60 7 D e c 8 3 B 1 9, A 2 2 7 7 . 5 6 4 9 - 9 0 2 7 . 6 71 4 D e c 8 3 C 2 6 , C 2 5 6 1 . 2 3 3 2 . 6 6 2 8 "5 82 0 D e c 8 3 C 2 0 . A 1 5 4 8 . 5 3 2 2 .6 8 2 5 . 8 50 4 J a n 8 4 B I 9 , A 2 2 3 0 . 3 9 9 2 -9 9 - 6 2 . 61L J a n 8 4 C 2 6 , C 2 5 6 8 - 0 4 5 5 . 1 t 1 2-9 31 6 J a n 8 4 C 2 0 , A 1 5 1 6" 56 2 6 . 7 6 - 1 0 .2 12 5 J a n 8 4 B 1 9 , A 2 2 8 0 . 7 4 6 1 . 2 3 1 9 -5 00 1 F e b 8 4 C 2 6 , C 2 5 4 8 - 7 6 2 4 . 7 2 2 4 - 0 40 8 F e b 8 4 C 2 0 . A 1 5 5 3 - 3 0 3 6 . 7 4 1 6 . 561 6 F e b 8 4 B 1 9 , A 2 2 6 0 . 3 3 4 5 . 3 6 1 4 .9 72 3 F e b 8 4 C 2 6 , C 2 5 4 5 . 3 6 2 6 -3 1 1 9 .0 52 9 F e b 8 4 C 2 0 , A I 5 7 0 - 53 4 2 . 6 4 2 7 . 9 00 7 M a r 8 4 B I 9 , "~9_ _ 8 6 ' 4 1 8 6 " 8 6 - 0 " 4 51 4 M a r 8 4 C 2 6 , C 2 5 7 0 -3 1 2 5 - 6 3 4 4 . 6 82 2 M a r 8 4 C 2 0 . A I 5 7 5 .5 2 8 5 .0 5 - 9 . 5 32 7 M a r 8 4 B I g , A 2 2 5 4 .8 8 5 7 .8 3 - 2 - 9 50 4 A p t 8 4 C 2 6 , C 2 5 7 5 . 3 0 3 1 -5 2 4 3 . 7 711 A p t 8 4 C 2 0 , A 1 5 6 8 - 49 5 8 . 29 1 0.2 11 8 A p t 8 4 B I 9 , A 2 2 5 4 . 6 6 5 0 . 3 5 4 . 312 5 A p t 8 4 C 2 6 , C 2 5 6 7 . 5 9 3 9 . 92 2 7 . 670 1 M a y 8 4 C 2 0 , A I 5 2 4 .7 2 3 0 .1 6 - 5 . 4 40 4 M a y 8 4 B 1 9, A 2 2 2 7 . 9 0 5 6 . 4 7 - 2 8 ' 5 811 M a y 8 4 C 2 6 , C 2 5 ~ 8 . 1 0 2 9 - 0 3 9 . 0 71 8 M a y 8 4 C 2 0 , A I 5 7 8 . 4 7 7 7 . 5 6 0 -9 12 3 M a y 8 4 B 1 9, A 2 2 3 4 9 3 68 .72 - 3 3 . 7 93 1 M a y 8 4 C 2 6 , C 2 5 5 3 - 3 0 4 6 . 0 4 7 . 2 60 7 J u n 8 4 C 2 0 , A 1 5 4 3 "0 9 4 7 . 4 0 - 4 " 3 1

2 1 7 " 5 61 9 0 ' 9 93 3 7 . 8 23 7 2 . 1 04 0 8 " 0 43 0 5 ' 2 0

5 0 3 8 - 1 62 0 " 7 0

3 4 5 ' 5 91 2 3 . 6 52 4 5 . 2 4

6 6 . 9 14 3 . 4 3

1 1 3 ' 8 53 8 1 ' 0 3

7 7 ' 9 71 3 1 7 - 6 9

3 2 O . 7 7128"38

1 2 5 2 . 4 53 ' 3 5

16"563 7 2 - 1 01 9 0 . 9 9

1 3 6 6 . 0 40 . 4 85 5 . 8 0

1 7 7 8 ' 3 11"25

1 6 1 "0 4S a m p l e s i z e , n = 3 0 .A v e r a g e d i ff e r e n c e i n y i e ld b e t w e e n t h e c u t a n d u n c u t p o n d s , I ) = 8 " 3 8 k g.V a r i a n c e o f t h e d i f f e r e n c e i n y i e l d = 5 2 5 ' 9 8 .S t a n d a r d d e v i a t i o n o f t h e d i f f e r e n c e in y i e ld = 2 2 . 9 3 k g .S t a n d a r d e r r o r o f t h e d i f f e r e n c e i n y i e l d --- 5 0 . 5 6 / ( 3 0 1 , * ( 1 / 2 ) = 9 " 2 3 .

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Improvem ent o f resh water prawn harvest in Haw aii 323A n e x p e r i m e n t to s t u d y t h e e f f e c t o f h i g h e r h a r v e s t e f fi c i en c y o n

y i e ld is i n p r o g r e s s . T h e c u r r e n t n e t s y s t e m h a s a n e s t i m a t e d m e a nh a r v e s t e f fi c ie n c y o f 6 3 - 5 % a n d a n a c c e p t a b l e s t a n d a r d d e v i a t i o n o f5 -9 % . U s i n g t hi s n e t s y s t e m , t h e h a r v e s t e f f i c i e n c y c a n b e i m p r o v e d b yd o u b l e - h a r v e s t i n g a p o n d . I f t h e h a r v e s t e f fi c ie n c y ' is 6 0 % i n e a c hh a r v e s t , th e h a r v e s t e f f ic i e n c y f o r b o t h h a r v e s t s w o u l d b e 8 4 % . T h eo n - g o i n g e x p e r i m e n t w o u l d c o m p a r e t h r e e d i f f er e n t h a r v e s t i n gs c h e m e s w h i c h a r e t h e t r a d i t i o n a l , t h e s i n g l e h a r v e s t i n g w i t h t h eU n i v e r s i t y o f H a w a i i ( U H ) n e t , a n d t h e d o u b l e h a r v e s t i n g w i t h t h e U Hn e t .

R E F E R E N C E SBox, G. E. , Hunter W. G. & Hunter , J . S. (1978) . Statistics fo r Experim enters.Jo h n W i ley an d So n s , New Yo rk.Gib son , R. T . & W ang, J . K. (1977) . A n a l te rna t ive p raw n pr od uc t io n sys tem sdesign in H awai i . Sea Grant Technica l Report , U N IH I-SE AG RA N T-T R 77-05 , Un ivers i ty o f Hawai i , 33 pp .Lain , C, Y. & Wang, J. K. (1985) . Est im at ing harves t e f f ic iency of f reshw aterp rawn s . P r e sen ted a t t h e 1985 Su m m er Meet ing A m . Soc, Ag . Engineers,

E a s t L a n s in g , M i c h ig a n , 2 3 - 2 6 J u n e 1 9 8 5 , A S A E P a p e r N o . 8 5 - 5 0 1 0 .Lo so rdo , T . M. , Wang , J. K., Brook s , M. J. & Lain , C. Y. (1986) . A m ech an-ized se ine harves t sys tem for f reshwa ter p rawns. Aq tm cultu ral Engineering,5 (1 ) , 1 -1 5 .M alecha , S . R. & Bigger, D. (1984) . Th e e f fec t o f the p re-ha rves t s ize g rad ingan d s to ck ro t a t io n in p o n d cu l tu r ed f r e sh wa te r p r awn s , Macrobrachiurnrosenbergii. Presen ted a t the 15th A nn ua l Meeting o f the World Maricu ltureSoc., Van co u v e r , Br i ti sh Co lu m b ia , 1 8 M arch 1 9 8 4.Malecha, S. R. , Polovina, J . & Moav, R. (1981 ) . Mult i-stage rotat ional stock-in g an d h a rv es t in g sy s t em fo r y ea r - ro u n d cu l tu r e o f th e f r e sh wa te r p r awn ,Macrobachium rosenberg i i . UN1HI-SEAGRANT-81-O1, Sea Gran t Co l l eg ePro g ram , Un iv e r s i ty o f H awa ii .Shang , Y. C. (1981) . Freshwater Macrobrachium rosenbergii 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 . Sea Grant M iscel laneous Report , UN IHI-S E A G R A N T - M R - 8 1 - 0 7 , Un ivers i ty o f Hawai i.S ta te o f Hawai i (1978) . Aquacul tzt re D eve lopm ent for Hawaii , D e p a r t m e n t o fP l an n in g a n d E c o n o m i c D e v e l o p m e n t .Sta te o f Hawai i (1983) . S tate o f Ha wa i i Da ta Bo o k , D e p a r t m e n t o f P la n n i n ga n d E c o n o m i c D e v e l o p m e n t .Wang , J . K. & Losordo , T . M. ( in p ress) . The e f fec t o f ear then pond bankgrass on p raw n y ie ld . J. W orld M aric. Soc., 16.Will iamson , M. R. & Wang, J . K. (1982) . An improved harves t ing ne t fo rf r e sh wa te r p r awn s . Aq uacu lmr al Engineer ing , 1 (2) , 81 -91 .