pfister 1983 aquacultural-engineering

7/28/2019 Pfister 1983 Aquacultural-Engineering

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Aqua cu l t u ra l Eng i neer ing 2 (1983) 101-118

C a t c h E f f ic ie n c y a n d R e t e n t i v e A b il it y o f C o m m e r c i a lCrawfish Traps-~Vernon A. Pfister and Robert P, Romaire

Fisheries Section, School of Forestry and Wildlife Management,Louisiana Agricultural Experiment Station, Louisiana State University,Baton Rouge, Louisiana 70803, USA

A B S T R A C TThe ca t ch e f f i c iency and r e t en t iv e ab i l i ty o f l O com m erc i a l c rawf i sh t rapswere eva l ua t ed i n com m erc i a l pond s . Trap des igns wi t h t h ree en t rancef unn e l s caugh t s ign i f ican t ly m o re c rawf i sh t han d i d t rap des igns wi t h oneor tw o funnels . Converse ly , the re ten t ive abi l i t y o f the t rap des igns wasi nver se ly r e l a t ed t o t he nu m be r o f en t rance f unne l s .

Traps cons t ruc t ed f ro m P V C p l as t ic - coa t ed w i re caugh t s ign i fi can tl ym o re c rawf ish t han i den t i ca l trap de s igns m ad e f rom ga l van ized wi re ; how -ever , re tent ive abi l i t y o f t raps was not re la ted to cons t ruc t ion mater ia l .The po s ture (ho r i zon ta l versus ver t i ca l ) o f ident ica l ly des igned t raps whe nse t i n t he po nd d i d no t a f f e c t t he ca t ch e f f i c iency nor r e t en t iv e ab i l i ty o ft he traps. Traps wi t h expo sed ba i t caugh t 40 - 4 7% m o re c rawf i sh t han d i dt raps wi t h p ro t ec t ed ba it. A n average o f 84 , 80 a nd 64% o f m a rked c raw-f i sh were re ta ined by t raps a f t er 12 , 24 an d 48 h , respect ive ly .

INTRODUCTIONCulture of red swamp and white river crawfish ( P r o c a m b a r u s c l a r k i iand P r o c a m b a r u s a c u t u s a c u t u s , respectively) is the only large-scale,commercial crustacean aquaculture industry in the continental US. In1981, there were over 23 0 0 0 ha of crawfish cultured in southern

t This study was supported by the Louisiana Agricultural Experiment Station.101Aquacu l t u ra l Eng i neer i ng 0144-8609/83/$03.00 Applied Science Publishers Ltd.England, 1983. Printed in Great Britain


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102 v. A. Pfis ter , R. P. RomaireLouisiana alone (Craft, 1980), and the crawfish industry is burgeoningin Texas, Mississippi and South Carolina. In 1980-1981 over 12-2million kg o f farm-raised crawfish with a wholesale value of t;25 millionwere harvested in Louisiana (Roberts, 1982).

A major constraint to further expansion of the crawfish cultureindust ry is harvesting (Avault, 1980). Crawfish are harvested almostexclusively with baited traps. The traps, which have one or more funnelsthat allow crawfish to enter, are constructed from 1-9-cm hexagonalmesh pou ltry wire to select for marketab le crawfish (greater than 75 mmtotal length). Traps are baited with cut fish, with gizzard shad ( D o r o -s o m a c e p e d i a n u m ) being preferred (Huner e t a l . , 1978). Fishermentypically set be tween 25 and 100 baited traps per hectare, and thecatch is generally emptied a fter 12 or 24 h.

Although numerous trap designs are used for harvesting crawfish,few data are available on the ca tch eff iciency of diff eren t designs. Beanand Huner (1978) investigated the catch eff iciency of several crawfishtraps used in Louisiana. Nicola (1971) and Threinen (1958) describedseveral wire traps used for harvesting wild populations of crawfish( P a c i f a s t a c u s spp. and O r c o n e c t e s spp.) in California and Wisconsin,respectively. Westman e t a l . (1978) evaluated the catchability andretentive ability of several traps constructed from nylon netting for usein harvesting crawfish ( A s t a c u s a s t a c u s ) in Finland. The purpose of thisinvestigation was to evaluate the catch efficiency and retentive abilityof 10 standard commercial trap designs presently used to harvestcrawfish.

MATERIALS AND METHODSTrap designsMajor differences in the 10 trap designs evaluated included varyingnumber of entrance funnels (1-4) per trap, wire used in the trap con-struction (black plastic, black plastic-coated, and galvanized) and theposture of trap when set (vertical or horizontal). Six of the traps werevertical types (i.e. set vertically erect in the water column with thebase of the trap on the pond bottom and the top protruding above thewater surface) and four traps were horizontal types (i.e. set horizontallysubmerged on the pond bottom). All traps were constructed from


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Catch efJ~ciency and retentive ability o f co mm ercial crawfish traps 1031.9-cm hexagonal mesh wire and had a standard inside diameter funnelopening of 4.5 cm. A description of the 10 trap designs follows:S i n g l e - f u n n e l h o r i z o n t a l t r a p ( d e s i g n 1 )This trap was 76 cm long, 51 cm in diameter and con stru cted fromgalvanized wire. One funne l opening (24.5 cm outer diameter X 4.5 cminner diame ter) was forme d. One-half of the opposite end of the trapwas permanently closed. The open portion, used to bait the trap andremove crawfish, was closed with a rubber clamp while the trap was set(Fig. 1).T w o - f u n n e l h o r i z o n t a l t ra p (d e s ig n 2 )This trap was made from galvanized wire, and was identical to design 1except it had two funnel entrances (1 2c m outer dia met er 4.5 cminner diameter), one in each corner of a closed section.T w o - f u n n e l h o r i z o n t a l t r ap , c o a t e d ( d es ig n 3 )This trap was identical in conf igur ation to design 2 except the wire wascoated with black polyvinyl chloride (PVC) plastic (Fig. 2).

Fig. 1. Single-funnel horizontal trap, galvanized wire (design 1).


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104 V. A. Pftster, R. P. Romaire

F i g . 2 . Two-funnel horizontal trap, PVC-coated wire (design 3).

T w o - f u n n e l v e r t i c a l t r a p ( d e s i g n 4 )T h i s t r a p w a s 7 6 c m l o n g, 6 4 c m i n d i a m e t e r a n d c o n s t r u c t e d f r o mg a l v a ni z e d w i r e . T h e b o t t o m o f t h e t r a p w a s c l o s e d a nd f l a t t e n e d , a n dt w o f u n n e l o p e n i n g s ( 1 2 c m o u t e r d i a m e t e r 4 .5 c m i n ne r d i a m e t e r )w e r e i n v e r te d i n to t h e b o t t o m o p p o s i t e e a c h o t h e r. A 6 -4 m m d i a m e t e rm e t a l r o d , 9 1 c m l o n g , w a s c l a m p e d t o t h e s id e o f t h e t r a p w i t h s te e lr in g s a n d h e l d t h e t r a p u p r i g h t w h e n s e t i n t h e p o n d . T h e t o p o f t h et r a p r e m a i n e d o p e n .

T w o - f u n n e l v e r t i c a l t r a p , c o a t e d ( d e s i g n 5 )T h i s t r a p w a s i d e n t i c a l i n c o n f i g u r a t i o n t o d e si g n 4 e x c e p t t h e w i r e w a sc o a t e d w i t h b l a c k P V C p l a s ti c ( F ig . 3 ) .

T w o - f u n n e l v e r t i c a l , c o n e - s h a p e d a n d c o a t e d ( d e s i g n 6 )T h i s t r a p w a s c o n s t r u c t e d f r o m b l a c k P V C p l a s t i c -c o a t e d w i re . T h e t r a pl a y u p r i g h t o n i t s b a s e ( 61 c m d i a m e t e r ) a n d t w o f u n n e l s ( 2 0 c m o u t e rd i a m e t e r 4 . 5 c m i n n e r d i a m e t e r ) p r o t r u d e d i n w a r d f r o m t h e fr in g e o ft h e b a s e . T h e t o p ( 3 3 c m d i a m e t e r ) r e m a i n e d o p e n ( F i g . 4 ) .


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Catch effieieney and retentive ability of commercial crawfish traps 105

Fig. 3 . Two-funnel vertical trap, PVC-coated wire (design 5).

T h r e e - f u n n e l h o r i z o n t a l t r a p , c o a t e d ( d e s i g n 7 )This trap was 79 cm long and 36 cm in diameter and made from blackPVC-coated wire. One end of the trap was closed with wire rings, andtwo funnels (1 4c m outer dia me te r 4-5 cm inner diameter) wereinverted in t he end of the clam ped section. The opposit e end was parti-ally clamped and a single funnel was inverted in the end of the clampedsection. The open end adjacent to the clamped section was fitted with ahinged door to facilitate baiting and rem oval of crawfish (Fig. 5).

T h r e e - f u n n e l v e r t i c a l t r a p , c o a t e d ( d e s i g n 8 )This trap was 76 cm long and 46 cm in diameter and had a frame con-structe d from 6.4 mm diam eter rods. The frame was covered withgalvanized wire which was coated with black tar (Tex aco Net Coat e, anasphalt-base preservati ve).t Thre e funnels (15-5 cm ou ter diame ter X 4-5t The use of a trade name does not imply endorsement by the authors or LouisianaState University.


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106 V. A. Pfister, R. P. Rom aire

F i g . 4 . Two-funnel vertical trap, cone-shaped, PVC-coated wire (design 6).

cm inner diameter) were spaced equidistant from each other and werelocated 5 cm from the trap bot tom . The top of the trap was open(Fig. 6).F o u r - f u n n e l v e r ti c a l t ra p ( d e si g n 9 )This trap was co nstr uct ed from Vexar plastic wire.? The trap layupright on its bot to m (61 cm diameter), and f our entrance funnels(10 cm outer diameter X 4-5 cm inner diameter) protruded inward fromthe base of the trap toward a central baitwell (45 cm long X 10 cmdiameter). The top (20.3 cm diameter) was open.F o u r - f u n n e l v e r t ic a l t r ap ( d e s i g n 1 O )This trap was identical to design 9 except it lacked a central baitwell(Fig. 7).t The use of a trade name does not imply endorsement by the authors or LouisianaState University.


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Catch e f f i c i ency and re t en t i v e ab i l i t y o f commerc ia l c rawf i sh t raps 107

Fig. 5 . Three-fu nnel hor izon ta l t rap , PVC-coa ted wire (design 7) .

Fig . 6 . Thre e-funnel vert ica l t rap , ta r -coa ted wire (design 8) .


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108 V. A. Pfister, R. P. Romaire

Fig. 7. Fo ur-fu nne l vertical trap , Vexar plastic wire (design 10).

C a t c h a b i l i t y studyT h e c a t c h e f f i c i e n c y o f th e 1 0 t r a p d e s i g n s w a s e v a l u a t e d i n t w o c o m -m e r c i a l c r a w f i s h p o n d s w h i c h h a d s u r f a c e a r e as o f 1 4 .6 a n d 1 8 .9 h a ,r e s p e c ti v e l y , a n d a v e r a g ed 0 . 6 m i n d e p t h . T h e p r e d o m i n a n t p l a n t s int h e p o n d s w e r e A l t e r n a n t h e r a p h i l o x e r o id e s , P o l y g o n u n s p p . , L u d w i g i ap e p l o i d e s a n d S e s b a n i a s p p . T h r e e r e p l ic a t e s o f e a c h o f t h e 1 0 t r a pd e s ig n s w e r e r a n d o m l y a s si g ne d a m o n g t h r e e 4 - m w i d e t ra p p i n g l a n es i ne a c h p o n d . T o m i n i m i z e p o s s i b l e t r a p i n t e r a c t io n , t r a p s w e r e s p a c e d1 5 m f r o m e a c h o t h e r ( M o r r i s s y , 1 9 7 5 ) . E a c h t r a p w a s p o s i t i o n e d o nt h e p o n d b o t t o m s o a s n o t t o o b s t r u c t f u n n e l e n tr a n c es .

T r a p s w e r e b a i t e d a t a p p r o x i m a t e l y 1 8 0 0 h w i t h 1 5 0 - 2 0 0 g o f c u tg i z z a r d s h a d a n d w e r e e m p t i e d 1 2 h l a t e r. E a c h t r a p w a s s h a k e n a f t e r i tw a s r e m o v e d f r o m t h e w a t e r t o al lo w n o n - m a r k e t a b l e c r aw f i sh t o fa llt h r o u g h t h e m e s h . T h e t o t a l n u m b e r a n d t o t a l w e i g h t o f c r aw f i sh i ne a c h t r a p w e r e r e c o r d e d . T e n c r a w f i sh w e r e o b t a i n e d a t r a n d o m f r o me a c h t r a p a n d e a c h c r a w f i s h w a s i d e n t i f i e d t o s p e c i e s a n d i ts t o t a l l e n g t h( t ip o f t h e r o s t r u m t o t h e t ip o f t h e t e l s o n ) m e a s u r e d . N o c r a w f i s h w e r e


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Catch e l f i c i ency and re t en t i v e ab i l i t y o f commerc ia l c rawf i sh t raps 109r e t u r n e d t o t h e p o n d s . T h e t r a p p i n g p r o c e d u r e w a s r e p e a t e d b i- w e e k l yf r o m 2 M a r c h t o 1 4 M a y 1 9 8 1 .

J u s t p r io r t o e m p t y i n g t r a p s ( a b o u t 0 6 0 0 h ) d is s ol ve d o x y g e n ( D O )a n d w a t e r t e m p e r a t u r e w e r e m e a s u r e d w i t h a p o l a r o g ra p h i c o x y g e nm e t e r w i t h t h e r m i s t o r i n a s in g le l o c a t i o n 15 c m f r o m e a c h p o n db o t t o m . S e c c h i d i s c v i s ib i li ty w a s m e a s u r e d a t 1 0 0 0 h .

R et ent iv e a b i l i t yT h i s i n v e s t ig a t i o n e v a l u a t e d t h e a b i l i t y o f e a c h o f t h e 1 0 t r a p d e s i g ns t or e ta i n c r a w f i sh o n c e c a p t u r e d . F o u r r e p l ic a t e s o f e a c h o f t h e l 0 t r a pd e s ig n s w e r e a ss i gn e d a t r a n d o m a m o n g f o u r t r a p p i n g l a ne s i n t h e1 4 .6 h a p o n d o n 11 M a y 1 9 81 . T w o o f t h e r e p l i c a te s o f e a c h d e s ig nw e r e b a i t e d a t 1 8 0 0 h w i t h 2 0 0 g o f g i zz a rd s h a d a n d t h e o t h e r t w or e p l i c a te s r e c e iv e d n o b a i t. A f t e r t h e t r a p s w e r e b a i t e d , 2 0 m a r k e dP . c l a r k i i ( ra n ge : 8 4 - 9 6 m m t o t a l l e n g th ) w e r e i m m e d i a t e l y d i s tr i b u t e da t r a n d o m i n t o e a c h o f t h e 4 0 tr a p s. E a c h c r a w f i s h w a s m a r k e d b ye x c i si n g a b o u t o n e - t h i r d o f t h e le f t u r o p o d ( R o m a i r e , 1 9 7 6 ) . T h en u m b e r o f m a r k e d a n d u n m a r k e d c r a w f is h p r e s e n t in e a c h t ra p w a sr e c o r d e d a n d r e t u r n e d t o t h e t r a p a f t e r 1 2 , 2 4 a n d 4 8 h . T r a p s t h a tr e c e i v e d b a i t i n i ti a l ly w e r e r e b a i t e d w i t h 2 0 0 g o f f r e s h s h a d a t 1 2 a n d24 t l .

R E S U L T S A N D D I S C U S S I O NC a t c h a b i l i t y s t u d yH i g h l y s i g ni fi c a n t d i f f e r e n c e s w e r e o b s e r v e d i n t h e e f f i c i e n c y w i t hw h i c h c r a w f i s h w e r e c a p t u r e d f o r t h e 1 0 t r a p d e s ig n s a f t e r 1 2 h (P 0 . 0 5 ; T a b l e 1). T h es i n g l e -f u n n e l t r a p ( 2 = 8 c r a w f i s h a n d 1 7 0 g / t r a p s e t ) c a u g h t s ig n if i-c a n t l y f e w e r c r a w f i s h i n n u m b e r a n d w e i g h t t h a n d i d all o t h e r t ra p


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110 V. A. Pfister, R. P. RomaireT A B L E 1

C a t c h E f f i c i e n c y o f 1 0 C o m m e r c i a l C r a w f is h T r a p D e s ig n s a s E v a l u a te d i n T w oC o m m e r c i a l P o n ds

Trap description Trap Mean Mean Mean Wholesaledesign number weight of total cost

of craw- cr awfi sh length per trapfish~trap (g)/trap (ram) (USdollars,seJ set 1981)

Three - funne l ve r t i c a l(PVC coa t ed ) 8 25 a 2 543 a 87 12 .00

F o u r - f u n n e l v e r ti c a l(Ve xa r ) 10 25 a 471 b 84 17 .00

T w o - f u n n e l v e r ti c al( c o n e - s h a p e d , P V Ccoa t ed ) 6 19 b 340 c 82 6 .57

T w o - f u n n e l v e r t i c al(PVC coa t ed ) 5 18 b 350 c 83 3 .71

Four - funne l ve r t i c a l(Ve xa r , ba i twe l l ) 9 17 bc 337 c 85 18 .50

T w o - f u n n e l h o r i z o n t a l(PVC coa t ed ) 3 17 bc 337 c 83 2 .70

T h r e e - f u n n e l h o r i z o n t a l(PVC coa t ed ) 7 16 bc 353 c 86 3 .75

Two- funne l ve r t i c a l(ga lvan i zed ) 4 15 dc 296 c 84 2 .73

T w o - f u n n e l h o r i z o n t a l(ga lvan ized) 2 12 d 291 c 88 1 .79

S ing l e - funne l ho r i zon t a l(ga lvan ized) 1 8 e 170 d 81 2 .37

1 C a t c h d a t a w e r e b a s e d o n 3 6 o b s e r v a t i o n s f r o m 1 2 -h n o c t u r n a l s e ts .2 Means fo l l ow ed b y t he s ame l e t t e r a r e no t s i gn i fi c an t l y d i f f e r en t ba sed on Du nca n ' smu l t i p l e r ange t e s t , P > 0 .05 (ve r t i c a l com par i so ns on ly ) .

d e s i g n s t e s t e d ( P < 0 - 0 5 ) . T h e m o s t e f fe c t i v e t r a p ( t h r e e - f u n n e l v e r t i c a lt r a p ) c a u g h t t r i p le t h e a m o u n t o f c r a w f i s h ( in n u m b e r a n d w e i g h t ) t h a nd i d t h e l e a st e f f e c t i v e t r a p ( s i n g l e - f u n n e l t r a p ) .


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Catch efficiency and retentive ability of commercial crawfish traps 111Number of entrance funnelsThe catch of crawfish increased significantly as the number of funnelentrances per trap increased from one to three (P < 0-05). Traps withthree entrance funnels (designs 7 and 8) caught 1.2-1.9 times morecrawfish (in weight) than did two-funnel traps (designs 2, 3, 4 and 5)and 2-1-3.0 times more crawfish than the single-funnel trap. Four-funnel traps (designs 9 and 10), however, cap tured no more crawfishthan did three-funnel traps (Table 1). The average catch of crawfish (inweight) in two-funnel traps (designs 2, 3, 4 and 5) was 1.7-2.1 timesgreater than the catch in the single-funnel trap (design 1). Westmanet al. (1978) reported that a crawfish trap with one entrance caughtabout half that of traps with two entrances which agrees with thefindings of this study. Bean and Huner (1978) observed that a trap withsix entrance funnels caught four times more crawfish than did a two-funnel trap.Vertical versus horizontal postureThe average number, weight and size of crawfish caught in two-funnelhorizontal traps (designs 2 and 3) did not significantly differ from thecatch in two-funnel vertical traps (designs 4 and 5) of similar size anddesign ( P > 0.05). Bean and Huner (1978) found no difference in theaverage catch of crawfish between a two-funnel vertical trap and two-funnel horizontal trap of similar design. The three-funnel vertical trap(design 8), however, caught significantly more crawfish (in number andweight) than did the three-funnel horizontal trap (design 7)( P < 0.01)of dissimilar size and design. No difference in the average size of craw-fish captured was noted between the two, three-funnel designs (P > 0.05).The catch efficiency of a crawfish trap was obviously influenced moreby its design than by the posture of the trap when set.Construction materialTwo-funnel traps constructed from black PVC plastic-coated wire(designs 3 and 5; 9~ = 18 crawfish and 344 g/t rap set) caught 30 and18% more crawfish in number (P < 0.05) and weight (0.10 >P > 0.05),respectively, than did two-funnel traps constructed from galvanizedwire (designs 2 and 4; ~ = 14 crawfish and 294 g/trap set). The averagesize of crawfish caught in the PVC-coated traps was (~ = 83 mm totallength) significantly smaller than those caught in galvanized traps


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1 12 V .A . P f i s te r , R . P . Ro ma i re(~ = 86 mm tota l length) (P < 0-05). The plastic coating apparen tlyreduced the diameter of the mesh slightly thereby retaining smallercrawfish that were not held by galvanized wire traps. The increasedcatch of crawfish in PVC-coated traps may also have resulted fromcrawfish being more attracted to black-coloured traps than traps con-structed from lighter-coloured (galvanized) wire. It was also possiblethat metallic elements (such as zinc) in and/or the texture o f thegalvanized coating could have been objectionable to crawfish. Galvan-ized and plastic-coated wire are utilized in cons truc tion o f crawfishtraps to prolong the life of the trap.

B a i t w e l l v e r s u s n o b a i t w e l lThe four-funnel trap without the baitwell (i.e. bait exposed) caught47 and 40% more crawfish per trap in number and weight, respectively,than did the duplicate design with the central baitwell in which the baitwas pro tecte d (P < 0.01). Westman e t a l . (1978) reported that crawfishtraps with pro tecte d bait caught less than one-half the nmnber of craw-fish than did similar traps with exposed bait. When bait was exposed,crawfish were able to masticate more of the material thereby allowing agreater amount of attractants in the bait to be released into the water.In addition, mastication of bait might involve an auditory response thatstimulates crawfish movement toward traps.

S p e c i e s c o m p o s i t i o nP r o c a m b a r u s c l a r k i i comprised 21.7 and 17-2% of the total crawfishcaught in the two ponds, respectively with P . a c u t u s a c u t u s comprisingthe remainder. The percentage of P . c l a r k i i in the catch decreaseddramatically from 40.5% on 16 March to only 15.4% on 14 May (Table2). P . c l a r k i i and P . a c u t u s a c u t u s are generally present together in com-mercial ponds. Although P . c l a r k i i comprises an average of 90% of thecommercial catch from ponds (Huner and Barr, 1980) the proportionof the two species may vary considerably among ponds. Both specieshave been observed to gain dominance in commercial ponds over aperiod of several years; however, the factors which result in one speciesdominating over the other species have not been identified. Many con-sumers consider P . a c u t u s a c u t u s less palatable and therefore lessdesirable than P . c l a r k i i .


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TABLE2

TPcaoRSwmCawsh(Poamucak)Cuebh1TaDg

(Tremn

ohccwcmsohwervcawsh(Pauuauu

Tadcpo

Ta dg

%Pcakncach

1Mch27Mch1A

2A

1Ma

Aa2

e

F

uvc(Vbw

9

53

47

23

20

17

30a

F

uvc(V

1

6!-7

43

60

13

10

27a

Teuvc(ce

8

67

27

10

17

50

20b

Twuhza(ce

3

20

27

10

33

33

17b

Twuvc(ch

ce

6

37

17

10

57

30

14b

Twuvc(ce

5

27

17

17

10

17

13b

Sneuhza(gvz

1

30

17

50

50

13

10b

Twuvc(gvz

4

33

10

83

50

67

17b

Twuhza(gvz

2

40

13

50

0

83

13b

Teuhza(ce

7

37

13

83

17

83

17b

45

20

14

66

14

Aa

3

ln~6.

2MefoowbhsmeeaensgcydeeboD

smperaeP>00(vc

cmsooy


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1 14 V. A . P f i s t e r , R . P . Rom ai reT h e f o u r - f u n n e l t r a p s c o n s t r u c t e d f r o m V e x a r pl as ti c w ir e c a u g h t

m o r e P . c l a r k i i t h a n d i d t h e r e m a i n i n g t r a p d e s i g n s ( P < 0 . 0 5 ; T a b l e 2 ) .N o d i f f e r e n c e w a s n o t e d i n t h e p e r c e n t a g e c a t c h o f P . c l a r k i i a m o n g t h eo t h e r t r a p d e si g ns (P > 0 . 0 5 ). I t is n o t k n o w n w h y t h e f o u r - f u n n e l t r ap sc a u g h t m o r e P . c l a r k i i t h a n t h e o t h e r t r a p d e s i g n s . T h e i n c r e a s e c o u l dh a v e b e e n r e l a te d t o o n e o r m o r e f a c t o r s i n c lu d i n g c o n s t r u c t i o n m a t e ri a l,n u m b e r o f f u n n e l s , t r a p p o s t u r e , t r a p d e s i g n , e t c . U n f o r t u n a t e l y , l i t t l eis k n o w n o f t h e b e h a v i o ra l a n d s o c ia l in t e r a c t i o n s b e t w e e n P . c l a r k i ia n d P . a c u t u s a c u t u s . F u r t h e r s t u d i es a r e n e e d e d t o a s c e rt a in i f m a t e r i a lsu s e d i n t r a p c o n s t r u c t i o n a r e s p e c ie s se l ec t iv e .

W a t e r q u a l i t yW a t e r t e m p e r a t u r e s r a n g e d f r o m a lo w 1 5 .5 C o n 1 6 M a r c h to a h i g h o f2 9 - 9 C o n 1 4 M a y . D i s s o lv e d o x y g e n e x c e e d e d 4 .0 m g / l i tr e o n alls a m p l e d a t e s . W a t e r w a s v e r y t u r b i d i n b o t h p o n d s w i t h S e c c h i d i scv i si b il it ie s o f t e n le ss t h a n 2 0 c m ( r a n g e : 5 - 3 0 c m ) . T u r b i d w a t e r inc o m m e r c i a l p o n d s is g e n e ra l l y i n d ic a t iv e o f a h i g h c r a w f is h p o p u l a t i o nd e n s i t y . T h e c a t c h o f c r a w f i sh d i f f e re d s i g n if i ca n t ly b e t w e e n s a m p l ep e r i o d s ( P < 0 - 0 1) a n d r a n g e d f r o m a m e a n l o w o f 12 c r a w f i s h / t r a p( 2 5 3 g / t r a p s e t ) o n 1 6 M a r c h to a m e a n h i g h o f 22 c r a w f i s h / t r a p( 4 4 0 g / t r a p s e t ) o n 1 1 A p r i l .

N o c o r r e l a t i o n w a s f o u n d b e t w e e n w a t e r t e m p e r a t u r e , D O , S e c c h id i s c v i s ib i li t y a n d t h e c a t c h o f c r a w f i s h ( a v e ra g e d f o r a ll t r a p d e s ig n s )( P > 0 . 0 5 ) . T h i s w a s n o t s u r p ri s in g b e c a u s e w a t e r q u a l i t y m e a s u r e d o ne a c h d a t e w e r e w i t h i n l im i t s c o n s i d e r e d c o n d u c i v e t o g o o d c a t c h e s o fP . c l a r k i i a n d P . a c u t u s a c u t u s ( H o b b s a n d H a l l, 1 9 7 4 ; H u n e r a n d B a r r,1 9 8 0 ) . C r a w f i s h g r o w t h , c h a n g e s i n p o p u l a t i o n d e n s i ti e s , a n d f l u x e s i no t h e r e n v i r o n m e n t a l c o n d i t io n s w e r e p r o b a b l y r es p o ns ib l e f o r t e m p o r a ld i f f e r e n c e s i n c r a w f i s h c a t c h ( M o r r i ss y 1 9 7 5 ).R e t e n t i v e a b i l i t yT h e p e r c e n t a g e o f m a r k e d c r a w f i sh r e ta i n e d b y t h e 10 t ra p d e s i gn s a f t e r1 2 , 2 4 a n d 4 8 h is p r e s e n t e d i n T a b l e 3 . T h e r e t e n t i v e a b i l i t y o f t h e t r a pd e s i g n s w a s i n v e r s e l y c o r r e l a t e d w i t h n u m b e r o f e n t r a n c e f u n n e l s . T h es i n g l e - fu n n e l a n d t w o - f u n n e l h o r i z o n t a l t r a p s (d e s i g n 1, 2 a n d 3 ) , a n dt h e t w o - f u n n e l , v e r t i c al t ra p ( d e s ig n 6 ) r e t a i n e d s i g n i f i c a n t l y m o r e c r a w -f is h a f t e r 1 2 h t h a n d i d t h e f o u r - f u n n e l t r a p s ( d e s ig n s 9 a n d 1 0 ) ( P


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Catch efficiency and retentive ability of commercial crawfish traps 115T A B L E 3Percentage of Marked Proeambarus clarkii Retained in 10 Commercial Trap Designs

After 12, 24 and 48 hTrap description Trap

designAverage % retained 1

12 h 24 h 48 helapsed el ap se d elapsed

Two-funnel horizontal (coated) 3 92 86 80Two-funnel vertical (cone-shaped,coated) 6 90 90 68Two-funnel horizontal (galvanized) 2 91 84 71Single-funnel horizontal (galvanized) 1 89 85 70Three-funnel vertical (coated) 8 88 88 59Two-funnel vertical (coated) 5 82 84 61Two-funnel vertical (galvanized) 4 85 80 40Three-funnel horizontal (coated) 7 79 66 60Four-funnel vertical (Vexar) 10 75 75 54Four-funnel vertical (Vexar,baitwell) 9 71 60 48Average2 84 a 80 b 61 cl n = 4 .2 These means were significantly different based on Duncan's multiple range test,P0 -0 5) . The four-funnel trapsand the three-funnel horizontal trap (design 7) retained significantlyless crawfish after 24 h than did the other trap designs (P < 0.05).

The retentive ability of two-funnel horizontal traps (designs 2 and 3)did not differ significant ly from t wo-fu nnel vertical traps (designs 3and 4) o f similar size and design (P > 0.05). Moreover, the retentiveability of the two-funne l traps const ructe d from galvanized wire (designs2 and 4) did not significantly differ from the two-fu nnel traps con-structed from PVC-coated wire (designs 3, 5 and 6) (P> 0-05). Thenumber of marked crawfish retained by the three-funnel horizontal trapdid not significantly differ from the t hree-funnel vertical trap, nor did


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116 v . A . P f i s t e r , R . P . R o ma i r et h e r e t e n t i v e a b i l i t y d i f f e r b e t w e e n t h e f o u r - f u n n e l t r a p w i t h t h e b a it -w e l l a n d f o u r - fu n n e l t ra p w i t h o u t t h e b a i t w e l l ( P > 0 . 0 5 ). T h e t w of u n n e l , v e r t i c a l t r a p s ( d e s i g n s 4 , 5 a n d 6 ; 2 = 8 4 - 7 % ) , h o w e v e r , d idr e t a i n 1 7 . 2 % m o r e c r a w f i s h a f t e r 2 4 h t h a n d i d t h e f o u r - f u n n e l v e r t ic a lt r a p s ( d e s i g n s 9 a n d 1 0 ; ) ? = 6 7 . 5 % ) .

T h e n u m b e r o f c r a w f is h e s c a p in g f r o m t h e t ra p s i n c r e a se d s i gn if i-c a n t l y a s t h e l e n g t h o f t h e t r a p s e t i n c r e a s e d f r o m 1 2 t o 4 8 h ( P < 0 . 0 5 ;T a b l e 3 ). A n a v e ra g e o f 8 4 % o f t h e m a r k e d c r a w f i s h r e m a i n e d i n t h et r a p s a f t e r 1 2 h , a n d o n l y 8 0 a n d 6 1 % w e r e p r e s e n t a f t e r 2 4 a n d 4 8 h,r e s p e c t i v e l y . T h e a b i l i t y o f t h e 1 0 t r a p d e s i g n s t o r e t a i n c r a w f i s h w a sn o t a f f e c t e d b y t h e p r e s e n c e o f ' fr e s h ' b a i t in t h e t ra p s ( P > 0 . 0 5 ) .

C r a w f i s h w e r e a d e p t a t e sc a p i n g f r o m t r a p s i f s u f f i c ie n t t i m e l a p s e db e f o r e t h e t r a p s w e r e e m p t i e d . T h e p r i n c i p a l e s c a p e r o u t e s i n h o r i z o n t a lt r a p s w e r e t h e e n t r a n c e f u n n e ls . C r a w f i s h w e r e a b le t o e s c a p e f r o mb o t h t h e e n t r a n c e f u n n e l s a n d o p e n t o p s o f v e r ti c al t ra p s . F i s h e r m e ng e n e r a l l y l e a v e t h e t o p s o f v e r t i c a l t r a p s o p e n b e c a u s e it s i g n i f i c a n t l yr e d u c e s t h e t i m e r e q u i r e d t o . e m p t y t h e c a t c h . I n f a c t , c r a w f i s h w e r ef r e q u e n t l y s e e n cr a w l in g o u t f r o m t h e o p e n t o p s o f ve r ti c a l tr a ps .W e s t m a n e t a l . ( 1 9 7 8 ) o b s e r v e d t h a t A s t a c u s a s t a c u s a n d P a c i f a s t a c u sl e n i u s c u l u s w e r e a d e p t a t e sc a p i n g th r o u g h e n t r a n c e f u n n e l s o f t r a psa n d t h e a u t h o r s d e s c r i b e d m o d i f i c a t i o n s i n e n t r a n c e f u n n e ls t h a tm i n i m i z e d c r a w f i s h l os s. A l t h o u g h a n i n c r e a se d c a t c h o f c r a w f i s h w a so b s e r v e d w i t h a n i n c re a s e in t h e n u m b e r o f fu n n e l e n t r a n c e s p e r tr a p ,t h is s t u d y a l s o r e v e a le d a c o r r e s p o n d i n g i n c re a s e i n t h e n u m b e r o f cr a w -f is h e s c a p i n g a s th e n u m b e r o f f u n n e l s p e r t r a p i n cr e a s e d . W e s t m a ne t a l . ( 1 9 7 8 ) a l so r e p o r t e d a n in c r e a se i n r e t e n t i v e a b i l i ty o f c r a w f i s ht r a p s w i t h a d e c r e a s e i n t h e n u m b e r o f e n t r a n c e f u n n e ls .

C O N C L U S I O N SH i g h l y s i g ni fi c a n t d i f f e r e n c e s i n t h e c a t c h e f f i c i e n c y a n d re t e n t i v ea b i l i ty w e r e f o u n d i n t h e 1 0 c o m m e r c i a l c r a w f i s h tr a p d e s i gn s e v a l u a t e di n th i s s t u d y . H o w e v e r , s e v e ra l o t h e r f a c t o r s s u c h a s f i s h a b i li t y , l o n g e v i t ya n d c o s t m u s t b e c o n s i d e r e d w h e n s e l e ct i ng a t r a p d e s ig n f o r c o m m e r -c i al u s e . A t r a p m u s t b e e a s i ly h a n d l e d i n t h e p o n d s . H o r i z o n t a l t r a p sa re o f t e n m o r e d i f f i c u l t t o l o c a t e b e c a u s e t h e y a r e t o t a l l y su b m e r g e dw h e n s et . T h e y m u s t a l so b e l if t e d t o t h e s u r f a c e b y m e a n s o f a na t t a c h e d l in e a n d t h e c l o s e d e n d m u s t b e o p e n e d b e f o r e t h e c ra w f i s h


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Catch e f f i c i ency and re t en t i v e ab i l i t y o f commerc ia l c rawf i sh t raps 117c a n b e r e m o v e d . C o n s e q u e n t l y , f e w e r t r a p s c an b e e m p t i e d p e r u ni tt i m e t h a n c a n v e r t i c a l t r a p s . A l s o , c r a w f i s h o f t e n s u f f o c a t e i n h o r i z o n t a lt ra p s w h e n o x y g e n d e p l e t i o n o c c u r s i n t h e h y p o l i m n i o n b e c a u s e th ec r a w f i s h a re n o t a b l e t o r e a c h o x y g e n a t e d s u r f a c e w a t e r s ( A v a u l t e t a l . ,1 9 7 4 ) . H o r i z o n t a l t r ap s , h o w e v e r , a r e u s e d i n p o n d s w h e r e th e w a t e rd e p t h e x c e e d s 1 m .

T r a p s c o n s t r u c t e d f r o m g a l v a n iz e d w i r e h a v e a c o m m e r c i a l l if e o fo n l y o n e t o t w o y e a r s w h e r e a s t r a p s m a d e f r o m P V C p l a s t i c- c o a te d w i rew i ll g e n e r a l l y l a st f r o m t h r e e t o f iv e y e a r s . I n a d d i t i o n , t r a p s c o n s t r u c t e df r o m P V C - c o a t e d w i r e w e r e m o r e c a t c h e f f i c i e n t t h a n g a lv a n i z ed t ra p s .T r a p s c o n s t r u c t e d f r o m V e x a r p l a s ti c ar e v e r y d u r a b l e a n d c a n b ee x p e c t e d t o h a v e a u s e f u l l i f e i n e x c e s s o f f i v e y e a r s .

T h e c o s t o f a t r a p i s v e r y i m p o r t a n t i n se l e c t in g a d e si g n , e s p e c i a l l yw h e n a l ar ge n u m b e r o f t r a p s m u s t b e p u r c h a s e d . T h e m o s t e x p e n s i v et r a p s w e r e m a d e f r o m V e x a r p l a s ti c a n d P V C p l a s t ic - c o a t e d w i r e ( T a b l e1); h o w e v e r , e x p e n s e m u s t b e w e i g h e d f o r i n cr e a s ed l o n g e v i t y a n dc a t c h a b i l i t y e x h i b i t e d b y th e s e d es ig n s. T r a p s m a d e f r o m P V C p l as ti c -c o a t e d w i r e c o s t a b o u t $ 0 . 9 0 m o r e t h a n g a l v an i z e d w i r e t r a p s o f l ik ed e s i gn ( T a b l e 1). T h e f o u r - f u n n e l V e x a r t r a p s ( d e s i g n s 9 a n d 1 0 ) a n dt h r e e - f u n n e l v e r t i c a l t r a p ( d e s ig n 8 ) a l t h o u g h b e i n g th e m o s t c a t c he f f i c i e n t w e r e a ls o c o n s i d e r a b l y m o r e e x p e n s i v e t h a n t h e t w o - f u n n e lt r a p s ( T a b l e 1 ).

W e b e l i e v e t h a t t h e t w o - f u n n e l , P V C - c o a t e d v e r t i c a l t r a p ( d e s i g n 5 )w a s t h e b e s t o v e r a l l t r a p d e s i g n b a s e d o n t h e c a t c h e f f i c i e n c y a n dr e t e n t i v e a b i l it y , f i sh a b i l i t y , l o n g e v i t y a n d c o s t . F u r t h e r m o r e , i t is m o r ec a t c h e f f i c i e n t t o e m p t y t h e t r a p s a f t e r 1 2 h r a t h e r t h a n 2 4 o r 4 8 h .F u r t h e r r e s e a rc h i s n e e d e d t o d e t e r m i n e t h e r e l a t io n s h i p b e t w e e n th es iz e , s h a p e a n d a n g le o f e n t r a n c e f u n n e l s o f c r a w f i s h tr a p s , a n d t h er e t e n t i v e a b i l i ty a n d c a t c h a b i l i t y o f tr a p s. L i k e w i s e , r e s e a rc h i s n e e d e dt o d e f i n e t h e r e l a t i o n s h i p b e t w e e n c r a w f i s h b e h a v i o u r a l a n d so c ia lp a t t e r n s a n d i f a n d h o w t h e s e p a t t e r n s i n f l u e n c e t h e c a t c h e f f i c i e n c y o fd i f f e r e n t t r a p s d e s i g n s .

R E F E R E N C E SAvault, J . W., Jr , de la Bretonn e, L. W. & Huner, J. (1974). Tw o major problem s inculturing crayfish in ponds: oxygen depletion and overcrowding. Proc . 2nd In t .

C r a y f i s h S y m p . , 2 , 1 3 9 .


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cu l t u r e , 27 pp . ( Unpub l i shed . )Bean , R . A . & Hu ne r , J . V . ( 1978) . A n eva l ua t ion o f s e l ec ted cr awf i sh t r aps andt ra p p i n g m e t h o d s . Proc. 4th lnt . C rayfish Sy rup . , 4, 141.Cr a f t , B . J . ( 1980) . Lou i s i ana i nven t ory o f c rawfi sh f a rm ers - 198 0 . Al exandr i a ,

Louis iana , Uni ted Sta tes Soi l Conserva t ion Service .Ho bbs , H . H . & Ha l l, E . T . ( 1974) . F r e shw a t e r c r ay f ishe s . I n : Pol l u t i on eco l ogy o f

f r e shwa t e r i nve r t ebra t e s , eds . C. W. Har t , J r and S . H. Ful le r , New York ,Academ i c P r e ss I nc .

Huner , J . V. , Bean, R. A. , Mi l tner , M. R. & Wi tz ig , J . (1978) . Crawf i sh ba i t s tudy.P r e sen t ed a t t he A nnua l M ee ti ng o f t he Lo u i s iana Cr awf ish Fa r m er s Assoc i a t ion ,Ba t on Rouge , Lou i s i ana , 6 pp . ( Mi m eogr aph . )

Hune r , J . V . & Ba r r , J . E . ( 1980) . R ed swam p c rawf ish : b i o l ogy and exp l o i t a t i on .Lou i s i ana Sea Gr an t P r og r am , Pub l i ca t i on No . LSU- T- 80- 001 , Ba t on Rouge ,Lou i s i ana S t a t e Un i ve r s i ty , 148 pp .

Mor r i s sy , N . M. (1975 ) . T he i n f l uence o f s am pl ing i n t ens i t y on t he ca t chab i l it y o fm a r r o n , Cherax t enu i m anus ( Sm i t h ) ( Decapod : Pa r a s t ac i dae ) . Austra l ian J . o fM a r i ne a n d F r e s h w a t e r R e s . , 26 , 47 .

Ni co l a , S . J . ( 1971) . Repor t on a new c r ay f i sh f i she r y i n t he Sac r am en t o Ri ve rde l ta . C a l if o r n ia D epa r t m e n t o f F i sh and Gam e . I n land F i she ri e s Adm i n i st r a ti veRepor t No . 71 - 7 , 21 pp .

Rob e r t s , K . J . ( 1982) . Lou i s i ana c r awf i sh f a rm i ng : an econ om i c v iew. P r e sen t ed a tt he Second Na t i ona l Cr awf i sh Cu l t u r e Wor kshop , La f aye t t e , Lou i s i ana , Un i ve r -s i ty o f Sou t hw es t e r n L ou i s iana , pp . 1 - 9 . ( Mi m eogr aph . )

R o m a i re , R . P . ( 1 9 7 6 ) . P o p u l a t i o n d y n a m i c s o f r e d s w a m p c r a w f is h , Procam barusclarki i , in ponds rece iv ing fe r t i l i za t ion and two agr icul tura l forages as supple-me nta l feed . M.S. thes is . Ba to n Ro uge , Lou is iana , Louis iana Sta te Un ivers i ty ,97 pp .

T h r e i n e n , C . W . (1 9 5 8 ) . A s u m m a r y o f o b s e r v at io n s o n t h e c o m m e r c i a l h a rv e s t o fc r ay f i sh in no r t hw es t W isconsin , wi t h n o t e s o n t he l i fe h i s t o r y o f Orconectesvirilis. M adison, W isconsin C onse rva t ion D ep ar tm en t , F i sher ies M gmt . Divi sion ,No. 2 , 14 pp .Wes t m an , K . , Pu r s i a i nen , M. & Vi l km an , R . ( 1978) . A new f o l d i ng t r ap wh i chpr even t s c r ay f i sh f r om e scap i ng . Proc . 4 th In t . Cray f i sh Symp. , 4 , 235 .

pfister 1983 aquacultural-engineering

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