7/28/2019 Edling 1985 Aquacultural-Engineering

1/9

Aquacu l tu ra l Eng ineer ing 4 (1985) 247-255

A P r e li m i n a r y R e p o r t o n a M e c h a n i c a l C r a w f i s hH a r v e s t i n g U n i tR o b e r t J . E d l i n g a n d T h o m a s B . L a w s o n

Agricultural E ngineering D epartm ent, Louisiana Agricultural Exp erimen t Station,Louisiana S tate University Agricultural Ce nter, Ba ton R ouge, Louisiana 70803, U SA

A B S T R A C TThe commerc ia l c rawf i sh i ndus t r y i n Lou i s iana i s rap id l y e xpand ing .Because cur ren t harve s t i ng me thods a re l abor i n t ens i ve and expens i ve , ana u t o m a t e d m e c h a n i c a l h a r v e st e r w a s d e v e lo p e d .

T h e a u t o m a t e d h a r v e st e r is b a se d o n h ig h d e n s i t y t r ap p i ng w i t h f r e q u e n tt rap mo vem en ts . A l inear m ov e i rr igator , w hich i s ada pted to large areas ,was u sed a s a chass i s . Movemen t o f t he harves t e r was con t ro l l ed au to -ma t i ca l ly . The ma ch ine l ow ered t raps f o r a p re se t t rapp ing t ime , l i f t ed ande m p t i e d t h e t r ap s a n d m o v e d a p r o g r a m m e d d i s t a n ce b e f o r e r e s e t t in g t h etraps.

I n a c o m p a r i s o n t e s t, t h e m a c h i n e e q u a l e d o r e x c e e d e d t h e e f f ic i e n c y o fs t a nd a r d t r a p p i n g m e t h o d s . L i t t l e m e c h a n i c a l d i f f i c u l t y w a s e x p e r i e n c e dwi th the harvester .

I N T R O D U C T I O NL o u i s i an a p r o d u c e s o v e r 9 0 % o f t h e c r a w f is h c u l t u r e d i n t h e U n i t e dS t at e s. T h e r e a r e a n e s t i m a t e d 4 0 5 0 0 h a d e v o t e d t o c r a w f i s h f ar m i n g i nL o u i s i a n a , a n d t h e i n d u s t r y i s e x p a n d i n g r a p i d l y ( d e la B r e t o n n e , 1 9 8 3 ) .A l t h o u g h o v e r 9 0 % o f t h e c r a w f i s h p r o d u c e d a r e c o n s u m e d lo c a ll y ,m o r e w i d e s p r e a d m a r k e t s a r e e x p e c t e d t o d e v e lo p , a n d c ra w f i s hf a r m i n g a p p e a rs t o h a v e a b r i g h t f u t u r e i n L o u i s ia n a a n d o t h e r s o u t h e r ns t a t e s .

T h e l a r g e s t e x p e n s e i n c r a w f i s h f a r m i n g i s h a r v e s t i n g . F r o m 4 0 t o6 0 % o f t h e g r os s r e c e i p t s a r e a s s o c i a t e d w i t h h a r v e s ti n g . C r a w f i s h a r ec u r r e n t l y h a r v e s te d u s i n g b a i t e d w i re t r a p s m a n u a l l y p l a ce d in t o p o n d s

247Aquacu l tu ra l Eng ineer ing 01 44 -86 09 /85 /$0 3 .3 0- Elsev ie r Applied SciencePublishers Ltd, England, 1985. Printed in Great Britain

7/28/2019 Edling 1985 Aquacultural-Engineering

2/9

248 R. J . Ecl l ing, T. B. Lawsona t d e n s i t i e s o f 2 5 - 1 0 0 t r a p s h a -1 . T h e m o s t p o p u l a r t r a p is c y l i n d ri -c a ll y s h a p e d a n d h a s t w o e n t r a n c e f u n n e l s a t t h e b o t t o m . T h e t r a p s a r ea p p r o x i m a t e l y 4 5 c m i n d i a m e t e r , 9 1 c m t a ll a n d a r e m a d e o f 1 .9 c mh e x a g o n a l m e s h r u b b e r - c o a t e d c h i c k e n w i r e. O t h e r c o n f i g u r a t io n s a r ea l so u s e d ( L a w s o n a n d W h e a t o n , 1 9 8 2 ) . T h e t ra p s a r e b a i t e d w i t ha p p r o x i m a t e l y 2 0 0 g o f c u t f is h , u s u a l l y g i z z a rd s h a d ( D e r o s o m ac e p e d i a n u m ) . T h e c a t c h is n o r m a l l y e m p t i e d a n d t h e t r a p r e b a i t e d o n c ea d a y . T h e m o s t e f f i c i e n t h a r v e st in g m e t h o d s e m p l o y i n g b o a t s , a rec a p a b l e o f e m p t y i n g 2 0 0 t ra p s o r m o r e p e r h o u r ( H u n e r a n d B a rr , 1 9 8 0 ).

R e s e a r c h h a s s h o w n t h a t p r o d u c t i o n c a n b e i n c r e a se d b y h a r v e st in g7 5 - 1 0 0 t r a p s h a -1 t h r e e t i m e s d a i ly (P f is t e r, 1 9 8 2 ) . H o w e v e r , t h e l a b o rr e q u i r e m e n t s a s s o c i a t e d w i t h s u c h f re q u e n t , h ig h d e n s i t y t r a p p in g ise x c e s s iv e . T h e r e f o r e , a m e c h a n i c a l h a r v e s t i n g s y s t e m r e q u i r i n g o n l yl im i t e d l a b o r w o u l d b e o f va l u e t o t h e c r a w f i sh f a r m i n g i n d u s t r y .

H A R V E S T E R D E S I G NT h e a u t o m a t i c h a r v e s te r d e si gn i s b a s e d u p o n h i gh d e n s i t y tr a p p i n gw i t h f r e q u e n t t r a p m o v e m e n t s a n d se t t im e s o f s h o r t d u r a t i o n . T h et ra p p i n g m e t h o d u s es a t r a p d e n s i t y o f 4 3 5 - 1 0 0 0 t ra p s h a -1 w i t h a6 - 6 0 m i n s e t t im e . C o n v e n t i o n a l t r a p p in g m e t h o d s u s e a t r a p d e n s i t yo f 2 5 - 1 0 0 t r a p s h a -1 w i t h a 2 4 h s e t t im e . A f t e r e a c h s e t o f t h e a u t o -m a t i c h a r v e s t e r t h e c r a w f i s h i n t h e t r a p s a r e d u m p e d m e c h a n i c a l l y . A st h e c r a w f i s h a r e b e i n g d u m p e d , t h e e n t ir e m a c h i n e m o v e s t o a n e w p r o -g r a m m e d p o s i t i o n , a n d t h e tr a p s a re r e s e t o n t h e p o n d b o t t o m . T h em a c h i n e t r a p p i n g m e c h a n i s m w i ll b e d e s c r i b e d f ir st , fo l l o w e d b y ad e s c r i p t i o n o f t h e m a c h i n e c o n t r o l a n d c h a ss is t h a t c a r ri e s t h e m u l t i -t r a p h a r v e s t i n g m e c h a n i s m .

F i g u r e 1 is a s c h e m a t i c o f a p a r t i a ll y r a i s e d t r a p . A t t h e e n d o f a p r o -g r a m m e d s e t t i m e 0 - 7 5 k W e l e c tr ic m o t o r r o t a t e s a s h a f t to w h i c h t h el if t c a b l e s a r e c o n n e c t e d . T h e t r a p t r a v e l s u p t h e t e l e s c o p i n g a r m s a n dr o t a t e s o n a h o r i z o n t a l s h a f t a t t h e t o p o f t h e t ra p s u p p o r t t h a t isc o n n e c t e d t o t h e s id e o f th e f u n n e l . R o t a t i o n c o n t i n u e s u n ti l th e t r a pis i n a n in c l i n e d p o s i t i o n , a t w h i c h t i m e t h e c r a w f i s h e a s i ly t u m b l e o u to f th e t r a p a n d f al l t h r o u g h t h e f u n n e l i n t o t h e t r a n s p o r t p i pe . A p p r o x i -m a t e l y 1 51 l i te r o f w a t e r m i n -1 c o n t i n u a l l y f l u s h e s t h e p i p e , c o n v e y i n gt h e c r a w f is h t o a h o l d in g a r e a at th e e n d o f t h e p i pe . T h e m a c h i n e t h e nm o v e s a p r e - d e t e r m i n e d d i s ta n c e b e f o r e t h e t ra p s a r e l o w e r e d . T h e

7/28/2019 Edling 1985 Aquacultural-Engineering

3/9

A preliminary report on a mechanical crawfish harvesting unit 249

Fig. 1. Schematic of a partially raised trap, showing: trap entrance (A), trapsupport with telescoping arms (B), lift cables (C), funnel (D) and pipe that trans-ports the crawfish (E).

electric motor connected to the lift cables is reversed, and the traps arelowered, returning to a vertical position and ont o the pond bott om.

The traps used with the harvester were cylindrica lly shaped, 53 cm indiameter and 122 cm tall with an open top. They were designed toallow the crawfish easy entrance into the trap from virtually anydirection. The entrance opening on each trap was a 5 cm wide slit ex-tending 270 degrees around the circumference of the trap at the base.The quarter of the trap nearest the pipe was left as wire mesh to createa slide area for the crawfish to aid in dumping. The bait was impaled ona large pin clipped to the trap bottom.

It was possible to program the machine to lift the traps at set timeintervals ranging from 2 min to 4 h and move a distance of up to 12 mduring the 4 min allowed for crawfish to empty from the traps. Datafrom an earlier model indicated that 4 min was sufficient time for thetraps to empty.

A 2-span Valmont Ranger linear move irrigator was used to supportthe traps and other necessary harvesting equipment. One span measured33 m and the oth er 39 m. The irrigator spanned a 0.8 ha p ondmeasuring 72 m by 134 m. A levee for the center tower wheels of the

7/28/2019 Edling 1985 Aquacultural-Engineering

4/9

250 R. J. Edling, T. B. Lawsonirrigator was constructed in the center of the pond, thus dividing thepond into 2 cells approximately equal in size. Eighteen traps were sus-pended 3 m apart beneath the irrigator: 10 traps on the 39 m span and8 traps on the 33 m span. Irrigators with as many as 20 spans areproduced, therefore the machine concept is adaptable to much largerponds.

The irrigator was electrically controlled by a 10 kW generatorpowered with a 4 cylinder air-cooled diesel engine. The drive motorsoperated on a 3-phase 480 volt system; controls and safety circuits were110 volts. The speed of the irrigator was controlled by a percentagetimer. Since linear movement is at a constant speed (approximately 2 mrain-l), the percentage of each minute that the motors operate controlthe speed. The crawfish harvesting system was operated by the electricalsystem of the irrigator and was designed to be easily attached to anddetached from the irrigator. Figure 2 shows the machine with the trapsin the set position and Fig. 3 shows the traps in the raised position.

Fig. 2. Machinewith traps in the set position.

7/28/2019 Edling 1985 Aquacultural-Engineering

5/9

A preliminary report on a mechanical crawfish harvesting unit 251

F i g . 3 . Machine with traps in the raised position.

R E S U L T S A N D D I S C U S S I O NI n it ia l t e s t in g o f t h e m a c h i n e b e g a n i n m i d - M a r c h , 1 9 8 2 ( M o r g a n , 1 9 8 2 ) .T h e o b j e c t i v e o f t h e t e s ts w a s t o d e t e r m i n e i f t h e m a c h i n e c o u l d a tt a inh a r v e st s c o m p a r a b l e t o c o n v e n t i o n a l h a r v e s ti n g m e t h o d s . T h e m a c h i n e -h a r v e s t e d p o n d a n d a p o n d s i m i la r i n c h a r a c t e r i s t ic s t o t h e m a c h i n e -h a r v es t ed p o n d w e r e lo c a t e d a t t h e L S U B e n H u r A q u a c u l t u r e R e s e a r c hC e n t e r i n B a t o n R o u g e , L o u i s ia n a . F i f t y t r a p s w e r e i n s ta l l e d in a g r idp a t t e r n in t h e n o n - m a c h i n e - h a r v e s t e d p o n d f o r c o m p a r i s o n , r e p r e s e n t in ga r e l a t iv e l y d e n s e t r a p c o n c e n t r a t i o n o f 7 5 t r a p s h a -1. T h e s t a n d a r d t r a p sa n d t h e m a c h i n e t r a p s b o t h w e r e b a i t e d w i t h c u t f is h. S ta n d a r d t ra p sw e r e e m p t i e d a n d r e b a i t e d e a c h m o r n i n g ; t h e m a c h i n e w a s r u n f o ra b o u t 6 h e a c h d a y . W a t e r te m p e r a t u r e a n d d i s s o lv e d o x y g e n w e r er e c o r d e d d a i ly in th e m a c h i n e - h a r v e s t e d p o n d . T w e n t y c ra w f i s h w e r er e m o v e d d a i ly f r o m e a c h s i de o f t h e m a c h i n e - h a r v e s t e d p o n d a n dw e i g h e d . T h e t e s t w a s r u n f o r a 1 0 d a y p e r i o d . R e s u l t s a r e s h o w n inT a b l e 1 .

7/28/2019 Edling 1985 Aquacultural-Engineering

6/9

252 R. J. Edling, T. B. LawsonA p a i r e d t - te s t w a s u s e d t o a n a l y z e a n d c o m p a r e t h e t o t a l d ai ly

m a c h i n e c a t c h w i t h t h e c o n t r o l c a t c h . T h e r e w a s n o s i gn i fi c a ntd i f fe r e n c e b e t w e e n t h e t o t a l d a i l y w e ig h t s o f m a c h i n e c a t c h a n d c o n t r o lc a t c h - h o w e v e r , t h e c o n t r o l c a t c h c r a w f i s h w e r e l ar g er . T h e 1 0 t r a p s id eo f t h e p o n d y i e l d e d 2 . 5 ti m e s m o r e t h a n t h e 8 t r a p si de , e v e n t h o u g h i tw a s o n l y 1 .2 t im e s l a r ge r . T h e a v e r a g e d a i ly w e i g h t o f 2 0 c r a w f i s h w a sa l s o g r e a t e r f r o m t h e 1 0 t r a p s i d e ( 0 . 4 3 k g ) t h a n t h e 8 tr a p s i d e ( 0 . 2 8k g ) . T h e s e d i f f e r e n c e s m a y b e r e l a te d t o w a t e r q u a l i t y e f f e c ts - h o w e v e r ,t h e s p e c i fi c r e a s o n f o r t h e d i f fe r e n c e s h as n o t b e e n d e t e r m i n e d b e c a u s ew a t e r q u a l i ty m e a s u r e m e n t s o t h e r t h a n d is s ol ve d o x y g e n a n d w a t e rt e m p e r a t u r e w e r e n o t m a d e .

T o e s t i m a t e t h e p o t e n t i a l o f t h e m a c h i n e , a n e c o n o m i c a l a n al y si s w a sm a d e ( M o r g a n e t a l . , 1 9 8 2 ). B e c a u s e a s s u m p t i o n s m a d e w e r e s u b j e c t t oq u e s t i o n , t h e r e s u lt s o f t h e a n a ly s is c a n o n l y b e c o n s i d e r e d p r e l im i n a r ya n d p r o v i d e a fi rs t e s t i m a t e c o n c e r n i n g t h e e c o n o m i c a l f e a s i b il it y o f th em a c h i n e . A r e a s o n a b l e p a y b a c k p e r io d o f 5 -9 y e a r s w a s i n d ic a t e d b yt h e a n a ly s is . H o w e v e r , t h e a n a l y si s w a s b a s e d o n a n n u a l p r o d u c t i o nl ev e ls o f 1 6 8 0 k g a n d 2 0 2 0 k g h a -1 a n d o n a n a v e ra g e m o v e m e n ts p e e d o f 0 . 3 m r a in -1. T h e 0 . 3 m m i n -1 a v e r a g e m o v e m e n t s p e e d w a so b t a i n e d b y a s s u m i n g a 6 . 0 m m o v e w i t h a s e t t i m e o f 2 0 m i n . U s in gt hi s m o v e m e n t d i s ta n c e a n d s e t t i m e t h e m a c h i n e t o o k a b o u t 6 h t oh a r v e s t t h e t e s t p o n d s . W i t h o u t t h e a b o v e t w o c o n d i t i o n s t h e fe a si -b i l i t y o f t h e m a c h i n e is q u e s t i o n a b l e . T h e r e f o r e , t h e p r i m a r y o b j e c t i v eo f f u r t h e r t e s ts c o n d u c t e d w a s t o d e t e r m i n e t h e v a l id i ty o f t h e s ea s s u m p t i o n s .

F o l l o w i n g c ra w f is h p o n d m a n a g e m e n t r e c o m m e n d a t i o n s , t h e t w o -c e ll re s e a r c h p o n d w a s d r a in e d i n J u n e o f 1 9 8 2 a n d h a n d - s e e d e d w i t hp r e - s o a k e d r ic e a t a r a t e o f a p p r o x i m a t e l y 1 1 2 k g h a -1 . A g o o d s t a n dw a s o b t a i n e d , a n d t h e p o n d w a s f l o o d e d i n O c t o b e r w h e n c o o l e r f al lw e a t h e r b e g a n . D i p n e t s a m p l e s in N o v e m b e r i n d i c a t e d a g o o d p o p u l a -t i o n o f s m a l l c r a w f i s h . D i s s o l v e d o x y g e n b e l o w 1 -0 m g l it e r -~ w a se x p e r i e n c e d o n 1 N o v e m b e r a n d t h e m a c h i n e w a s u s ed t o a e ra te .H a r v e s t b e g a n in m i d - J a n u a r y . E a r ly y i e ld s w e r e s m a ll d u e t o th e s m a l ln u m b e r o f l ar ge c r a w f i s h a n d t h e l o w a c t i v i t y o f t h e c r a w f is h in w a t e rb e l o w 1 3 C .

B e c a u s e o f t h e i n a c t i v i t y a s e t t i m e o f 1 h w a s u s e d i n s t e a d o f t h e 2 0m i n s e t t i m e . T h e l a rg e r s e t t i m e m e a n t i n c r e a s e d t i m e t o h a r v e s t t h et e s t p o n d , f r o m 6 to 1 8 h . F r e q u e n c y o f h a r v e st in g w a s a ls o a l te r e d t om a i n t a i n t h e 0 . 3 m m i n -1 a v e ra g e l o n g t e r m m o v e m e n t s p e e d . B y t h e

7/28/2019 Edling 1985 Aquacultural-Engineering

7/9

TABLE1

Rusfomh1TCmpnEomeaC

oaHvMeh

De

Mhcahvn

1rasd

8rasd

Tm

D

CchTm

D

Cch

(C

(rare-1

(kg

(C

(rare-1)(kg

Cno

hvn

TadyCdy

cach(kgcach(kg

2 c

2Mac

25

30

1

20

60

4

1

2

~

2Mac

23

32

1

20

55

4

1

1

2Mac

10

75

1

10

79

5

1

1

~

2Mac

15

90

1

10

90

5

1

1

2Mac

10

10

6

14

10

4

1

1

,~

2Mac

12

96

7

10

10

3

1

1

3Mac

10

72

6

10

82

3

9

8

:~

3Mac

20

67

8

20

76

3

1

1

1A

20

54

7

20

62

3

1

1

=

2A

25

7

9

20

76

3

1

1

Ta

9

3

1

1

~ 13

7/28/2019 Edling 1985 Aquacultural-Engineering

8/9

254 R. J . Edl ing, T. B. Lawsonend o f January production increased substantially. The weather turnedcool the first week of February and yields decreased due to reducedcrawfish activity. The bait was changed from carp ( C y p r i n u s c a r p i o ) toshad the fourth week of February due to the unavailability of carp. Inaddit ion, low dissolved oxygen conditions (below 1.0 mg l iter -1)occurred at that time. Stunting, as indicated by small size, muddy craw-fish appearance and reduced crawfish activity occurred at the end ofFebruary. Except for infrequent high yields, the production of theponds never returned to acceptable production levels. Although manyexplanations have been suggested, it is thought that the low dissolvedoxygen conditions gave rise to stunting, reduced yields and lack of asuccessful harvest with the machine. Plans are being made to providebette r aeration in the future.

In addition to aeration there was also a problem with maintainingthe average assumed speed of 0.3 m min -1. Following the economicanalysis assumptions of area covered with the machine (Morgan e t a l . ,1982), the machine on the test pond was to be active only one-fourthof the time; Le. one 6 h trapping period per day or one 18 h trappingperiod every 3 days. Calculating average production over 120 days at amodera te production level of 1300 kg ha -~ gives a daily production of10-8 kg or 32.4 kg every 3 days. Data taken were only in frequent lyabove these values, even early in the season before stunting becameevident. There were not enough crawfish getting trapped in the allottedtime to indicate that the machine was economically feasible.

Mechanically, the machine worked fairly well. Some trouble wasexperienced in correcting damage to the guidance mechanism thatoccurred when the guidance cable was accidently broken. The liftmechanism also needs to be improved because the pickup cable tendsto bind between the pulley and pulley housing when the cable is slack,leading to cable breakage. Originally, each trap had a pickup cable oneach side, however, it was difficult to maintain the same tension in eachcable. One cable was removed, but problems continued . Finally, a smallrope was used, but again difficulties were experienced. Work will con-tinue toward a solution to this minor problem.

CONCLUSIONSThe prototype crawfish harvesting model shows promise althoughadditional work is needed. It is felt that a mechanical crawfish harvester

7/28/2019 Edling 1985 Aquacultural-Engineering

9/9

A pre l iminary rep or t on a mech anical crawf ish harves t ing uni t 255can be developed that will be successful and will be adopted by thecommercial crawfish industry. If successful, an automated crawfishharvesting system will save the farmer many dollars which wouldordinarily go towards trap materials, bait and labor.

REFERENCESde la Bretonne, L. (1983). Production Statistics and Market Predictions, Crawfish

Tales, 2 (3) pp. 8-9.Huner, J. V. & Barr J. E. (1980). R e d S w a m p C ra w fis h: B i o l o g y a n d E x p l o i ta t i o n ,Sea Grant Publication No. LSU-T-80-001, Louisiana State University, Center forWetland Resources, Baton Rouge, LA.

Lawson, T. B. & Wheaton, F. W. (1982). Pond culturing of crawfish in the southernUnited States. A quacul tural Engineer ing , 1 (4), 311 - 17.

Morgan, K. L. (1982). An automated system of harvesting crawfish using a linearmove irrigator. MS Thesis, Louisiana State University, Baton Rouge, LA.Morgan. K. L., Edling, R. J. & Musick, J. A. (1982). A mechanical crawfish harvester.Lou i s i ana Agr i cu l t u re , 26 (2), 4-5.

Pfister, V. A. (1982). Evaluation of selected crawfish traps and trapping techniquesin Louisiana. MS Thesis, Louisiana State University, Baton Rouge, LA.Roberts, K. J. (1980). Louisiana Crawfish Farming, An Economic View. CooperativeExtension Release, Louisiana State University, Baton Rouge, LA.