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Indian J. Fish., 47(1) : 1-6, Jan.-Ma r, 2000

P o p u l a t i o n d y n a m i c s o f Labeo calhasu ( H a m i l t o n )i n t h e S y l h e t b a s i n , B a n g l a d e s hM. ALAM, S.M.N. A M N AND A.K. YOUSUF HAROON*Bangladesh Fisheries Research Institute, Riverine Station,Chandpur-3602, BangladeshA B S T R A C T

Population parameters of Labeo calbasu (Hamil ton) were es t imated us ing FiSATsoftware with length-frequency data collected from different a rea s of Sylhe t basin ,north-ea s tern p art of Bangladesh. The von Berta lanffy growth param eters L andK for the species were 49.30 cm and 0.63 / year respectively. The a nn ual ra te ofnatural (M) and fishing (F) mortality were found to be 1.11 and 3.48, respectively.The rate of exploitation (E) was estima ted as 0.76. Recru itmet of thi s speciesinto the fishery takes place during August to October with peak during August-Septem ber. E^j^ was found to be 0.449. T he present investig ation clearly showedthe over fishing (E>0.50) condition for L. calbasu in the Sylhet basin. Therelatio nshi p betwee n the total leng th and body weight was found to be W +0.00927*TL 3.109.

I n t r o d u c t i o nLabeo calbasu (Hami l ton) local lyk n o wn as k a l i b a u s o r k a l i a ra i s am ed i u m s i zed , b o t t o m feed i n g ca rpwh i ch g en e ra l l y a t t a i n s a l en g t h o f 7 1cm an d a we i g h t o f 5 . 5 k g (R ah m an ,

1989). This f i sh i s avai lab le a l l overB an g l ad es h , e s p ec i a l l y i n t h e r i v e r s o fn o r t h eas t e rn r eg i o n (S h af i an d Qu d d u s ,1 9 7 5 ) an d wi d e l y cu l t u red i n p o n d s i nco m b i n a t i o n wi t h o t h e r Gan j e t i c ca rpspecies . I t i s a l so found in Pa kis tan ,In d i a an d M y a n m ar Th i s f is h fo rm sone of the m ajor co mp one nts of thecom me rcia l f ish catch of the Sylhe tb as i n . S p o rad i c wo r k s we re d o n e t os t u d y t h e l en g t h -we i g h t r e l a t i o n s h i p ,condi t ion factor and food and feedingha bi t o f th e Ganjet ic major carp s( J h i n g ra n , 1 9 5 7; Kh an an d S i d d i q u e ,1973 ; S ree P rak as h an d Gu p t a , 1 9 8 6 ) .Th ere i s n o p u b l i s h ed i n fo rm a t i o n o n

t h e p o p u l a t i o n d y n am i cs an d s t o ckas s es s em n t o f t h i s s p ec ie s in B an g l ad e s hes p ec i a l l y f ro m t h e S y l h e t b as i n a rea .T h e p r e s e n t s t u d y w a s t h u s u n d e r t a k e n t o e s t i m a t e t h e k e y p a r a m e t e r sfo r s t o ck a s s es s m en t s u ch a s t h e

asymptot ic l ength (L^) , g rowth coeff ic ien t (K), to ta l m ort a l i t y (Z), na tu ra lmorta l i ty (M), f i sh ing morta l i ty (F) andex p l o i t a t i o n r a t e (E ). Us i n g t h e s e p a ra m e t e r s t h e r e c r u i t m e n t p a t t e r n w a ses t i m a t ed . Th e y i el d p e r r ec r u i t an a l y s i san d t h e v i r t u a l p o p u l a t i o n a n a l y s i s(VPA) were a l so carr ied out .Mate r i a l s an d me th o d s

Len g t h - f r eq u e n cy d a t a o f L . calbasuwere co l lected for tn ight ly f rom theco m m erc i a l ca t ch es a t d i f e ren t l an d i n gs i t e s a ro u n d S y l h e t d i s t r i c t f ro m J an u a ry 19 9 7 t o Decem b er 1 9 9 7 . S am p l es* Corresponding a uthor : E-mail : frirs@bdniail.net

mailto:frirs@bdniail.netmailto:frirs@bdniail.net

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(f L. calbasu were m a i n l y o b t a i n edfrom s ine catche s . Ra ndo m samp les of7 ,048 specim ens we re co l lected . Totall en g t h was m eas u red i n cm b y a m e t rescale ( lmm) s ize s ranging f rom 8 .0 to4 8 . 0 cm . Th e we i g h t was m eas u red i ng by a Sal ter spr ing balance f rom 149ran d o m s am p l es r an g i n g f ro m 7 5 . 0 t o1 ,170 g w i th correspon ding leng th . Th ed a t a were t h en p o o l ed m o n t h -wi s e f ro md i f fe ren t l an d i n g s i t e s an d s u b s eq u en t l ygrou ped in to c lasses of two cm in terv a l s . Th e d a t a were an a l y s ed u s i n g t h eF iSAT (FAO-ICLARM Stock AssessmentTools) as expla in ed in deta i l by Gayani loJ r . et al. (1995) in the computer sof t war e package. Asymptot ic l ength (L^)and growth coefficient (K) of the vonBertalanffy equation for growth in lengthwere e s t i m a t ed b y m e an s o f ELEF A N-I (P au l y an d Dav i d , 1 9 8 1 , S aeg e r an dGay ani lo , 1986) . Add i t ional es t im ate s ofL_ and Z/K valu e w ere o bta ine d byplo t ting T. mi nu s U on L (W etheral l ,1986 as modified by Pauly, 1986), i .e. ,l .-L' + a + bUwh ere , L^ = - a ^ an d Z /K = - ( l + b ) / bwh ere L i s t h e m e an l en g t h , co m p u t edfrom L ' up wa rd , in a g iven le ngth-f requency sam ple whi le L ' i s th e l im i tof th e f i rs t l eng th c lass used incom put ing a value of L .

Th e growth performanc e of L.calbasu p o p u l a t i o n i n t e rm s o f l en g t hg ro wt h was co m p ared u s i n g t h e i n d exof Pauly and Munro (1984) . i . e . ,0' = LogjoK + 2Logio L^

To t a l m o r t a l i t y (Z) wa s e s t i m a t edby leng th conver ted catch curve method.N a t u ra l m o r t a l i t y r a t e (M ) wa s e s t im a t ed u s i n g P au l y ' s em p i r i ca l r e l a t i o n ship (Pauly, 1980) i .e. .

Logjo M = - 0.0066 - 0.279 Logjo L^+ 06543 Logjo K + 0.5634 Logm Twhere L^ i s expressed in cm and T, them e a n a n n u a l e n v i r o n m e n t a l t e m p e r a ture in "C wh ich her e i s 27C.

F i s h i n g m o r t a l i t y (F ) was o b t a i n edby su bt ra ct in g M from Z and explo i t a t ion ra t e (E) w as obta ined f rom F /Z [E= F /Z = F / (F+M)] (Gul land , 1971) .R e c r u i t m e n t p a t t e r n s w a s o b t a i n e d b yb ack w ard p ro j ec ti o n o n t h e l en g t h ax i sof a se t of l ength -f requ ency da ta asdescr ibed in the F iSAT rou t ine . Rela t iveyie ld per recru i t Y/R and b iomass perrec ru i t (R/B) va lue s as a funct ion of Ewere d e t e rm i n ed from t h e e s t i m a t edg ro wt h p a ram et e r s an d p ro b ab i l i t y o fcap t u re b y l en g t h (P au l y an d S o r i an o ,1986) . Th e calcu la t ions wer e c arr ie dout us ing the complete F iSAT sof twarep a c k a g e .

A l e n g t h s t r u c t u r e d V P A of L.calbasu was carried out with L_^=49.30,K=0 .6 3 /y r , M = l . l l , F =3 . 4 8 , a^O. 00 9 2 7an d b =3 .1 0 9 as i n p u t s . Th e to v a l u ewas t ak en a s ze ro .R e s u l t s a n d d i s c u s s i o nGrowth parameters: G r o w t h p a r a m e t e r s o f v o n B er t a l an f fy g ro w t hformula for L. calbasu w e r e e s t i m a t e das L^ = 49.30 cm an d K = 0.63/year. Fort h e s e e s t i m a t e s t h r o u g h E L E F A N - I t h ere sp on se su rface (R^^) w as 0 .165 for th ecu rv e . Th e co m p u t ed g ro w t h cu rv ep r o d u c e d w i t h t h o s e p a r a m e t e r s a r es h o wn o ver i t s r e s t ru c t u r ed l en g t hdis t r ibu t ion in F ig . 1 .

The Powel l -Wetheral l p lo t i s shownin F ig . 2 . The corresponding es t ima tes ofL^ and Z/K for L. calbasu are 49.78 cma n d 1.137, respect ively . This add i t iona le s t i m a t e o f L^ i s s l i g h t ly h i g h e r t h an

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Population dynamics of L abeo ca lbasu

c

4 0

2 0 -

' " ' " I ' J ' ' '1 ' ' 1' I i l " i|i I i r T i I I I I I I ) I I I I I LI I J M 1,1 I Ji I i.r I i l l I . .1 f il l I 1,1 r il l ,Ja n F e b Mar> flpr> May J a n J u l ' flusr ' S e p ' O ct Nov ' DecFig. 1 . Growth curve of Laheo calbasu (Ham il ton ) fi 'oni Sy lhe t bas in wa te rs , Ba ng la desh by E L E F AN Isuper im posed on the leng th - f requency d iag ram (L__=49 .30 cm and K =0 .63 /y r ) .the L^ estim ated throug h EL EFAN-I. the regression was 0.999 (a = 18.27 andThe correlation co-efficient for the b = -4.5 9). The na tu ral mo rtali ty rateregression was 0.989 (a = 23.28 and b was estimated from the emp irical= -0.4 68 ). Calculated growth perfor- equation. P auly (1980) sugges ted th atma nce index (0) was found to be 3.185. this method gives a reas on able value of

9 6

o 7 2Xz.'^0c03 ;i. 2 9 ^ 9

16

iZ0 0

o 0 0 \ ^e 2 9 4 9C u t o f f ( e n g - th . CL';c>nJ

Fig. 2 . Est im ati on of L^ and Z/K using the me tho ds of We thera ll for Labco calbasu (Hamil ton ) in Sy lhe tbas in wa te rs , Bang la desh (e s t ima ted L =49 .738 cm and Z /K=1 .137) .

Mortality: The mortali ty rates M, Fand Z computed were 1.11, 3.48 and4.59 respectively. The catch curveutilised in the estimation of Z isreprese nted in Fig. 3. The darken edquadr i lateral represents the pointsused in calculating Z through leastsquares l ines regression. The blankcircles represent points either not fullyrecruited on nearing to L^ and hence,discarded from the calculation. Goodnessof fit to the descending right handlimits of the catch curve was considere d. Th e co rrelatio n co-efficient for

1 00= 0o o

O S 2 3 -f S

F i g . 3 . L e n g t h c o n v e r t e d c a t c h c u r v e o f Labeocalbasu ( H a m i l t o n ) i n S y l h e t b a s i n w a t e r s ,B a n g l a d e s h .

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201r&

^

^ H -/ /R ^ ..._ L -1 ^ n

F i g . 4 . R e c r u i t m e n t p a t t e r n of Labeo calbasu(Hamil ton ) in Sy lhe t bas in wa te rs , Bang ladesh .

M . T he m e thod of e s t im a t ing M i sw ide ly use d th r oughout t he t r op i c sw he r e t im e se r i e s r e l i a b l e c a t c h a ndeffort d a ta and severa l ye ars of Zva lue s a re not ava i lable . So thede sc r ibe d m e thod i s t he c om m on w a yof es t im at in g M an d F. Th e f ishingm o r t a l i t y r a t e (F ) w a s t a k e n bysu btr ac t ing M from Z and w as found tobe 3.48.Exploitation rate: T he r a t e o fe xp lo i t a t ion ( E ) w a s e s t im a te d a s 0 .76f rom the s tudy a r e a . I t a pp e a r s t h a tthe stock of L. calbasu i n t he Sy lhe tba s in e xc ee d the m a xim um f i sh ingp r e s s u r e (E^^^ = 0.449) an d f ishingmor ta l i ty seem to be of grea t concern(F = 3.48) .

Recruitment pattern: T he r e c r u i t m e n t pa t t e r n ( F ig . 4 ) show s th a t t h i sspec ies wa s recru i ted in th e f isherydur ing A ug ust to October w i th p eakd u r i n g A u g u s t - S e p t e m b e r m o n t h s . I t i sc l e a r f o rm F ig ur e 1 t h a t spa w nings t a r t s i n t he m onth o f M a y .Yield-per recruit and biomass per-recruit: T he r e l a t i ve y i e ld - pe r - r e c r u i ta nd b iom a ss - pe r - r e c r u i t w e r e de t e r mined as a function of L^/L^ and M/Kwer e 0.20 and 1.75, respectively. Fig. 5show s tha t t he p r e se n t e xp lo i t a t i onr a t e ( E = 0 .76) e xc e e ds t h e m a xim umexploi ta t ion ra te of E^^^ = 0 .449 .Virtual population analysis: T h er e su l t s o f t he l e ng th - s t r u c tu r e d V PA ofL. calbasu are show n in Fig. 6 . Valuesfor the mean f i shing mor ta l i ty (F) andthe m e a n e xp lo i t a t i on r a t e ( E ) e s t im a t ed by the ana lys is were 0 .447 and0.287, respec t ive ly. Th e es t im ate dvalues for the exploi ta t ion ra te (E)us ing the l e ng th c onve r t e d c a t c h c ur vea n d VPA we re 0.76 and 0.287, respectively. This indicates that L. calbasus toc ks i n t he Sy lhe t ba s in i s unde r h ighf i sh ing p r e s sur e .

. 2 5 . 5 . 7 5E x p l o i t a t i o n r - l t e . 3 . 7 5i " ta t i on rAteFig. 5 . Rela tive yield-per-re cruit ( left) and biom ass-p er-re cruit (r ig ht) ofLabeo calbasu (Hamil ton ) o f Sy lhe tbas in wa te rs , Bang ladesh (L /L =0 .20 , M/K=1 .75) .

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Population dynamics of 1 ,abeo calbasu

'r H e c a t e rLCr iN i t lo sses f,5^!b,urv Ivors j \

Fig . 6 . Len gth- s t ru c tured v i r t ua l popula t ion a nalysi s of Laheo calbasu (Ham il ton) of Sylh et basinw a t e r s , B a n g l a d e s h .Length-weight relationship: For thes tudy o f t he l e ng th - w e igh t r e l a t i ons h ipa tota l of 149 spec imens of L. calbasuf o r t he i nd iv idua l s r a ng ing in s i z e sfrom 16 to 46 cm in tot al leng th an dw e ig h ing 75 .0 - 1170 .0 g w e r e m e a su r e d .F r om the se , l e ng th - w e igh t r e l a t i o nsh ipwe re es t ima ted , of the form W - aL ' ',u s in g the l oga r i thm ic t r a ns f o r m a t ionLogW = I jOg a + b I .og I 'L, where, a andb a r e c ons t a n t s e s t im a te d by l i ne a rr e gr e s s ion o f t he l og t r a n s f o r m a t ionva r i e t i e s T he r e gr e s s ion t a k e s t heform:Log- W ^ -2 .0 3 30 + 3,109Log TL(r---0.992)Fig. 7 cor responding to , 1)W =- 0 00927 *TL.; i,iu9- ..(2)

Re c r u i tm e nt pa t t e r n o f t he f ishrevea led tha t i t r ecr ui t s into th e f isherya lm ost round tht ; yea r and major

I.Fig. 7. Linearised tonu of lerij'.lli wei;;lit relation shipof Lahco calbasu (llaroihcjn) ofSylheL basin wat e r s , B a n g l a d e s h .

sp aw ni ng occurs in May. I ts f ishingpressure (F = 3.48) i s very high andneed to he reduced for ge t t ing moresus ta in ed prod uct ion . Som e f ishingres t r ic t ion sh ould be imp osed to ge thigher f i sh yie ld f rom tha t bas in.A c k n o w l e d g m e n t s

T he a u thor s e xpr e s s t he i r de e pgr a t i t u de to t he D i r e c to r G e n e r a l ,B a n g l a d e s h F i s h e r i e s R e s e a r c h I n s t i tu te (BFRI) an d the Chief Sc ient i ficO f fi c er o f t h e R i v e r i n e S t a t i o n ,Cha ndpur , BFRI f o r t he i r ke e n in t e r e s ta nd a l l ou t suppor t t ow a r ds t h i s s t udy .T he a u thor s a r e a l so g r a t e f u l t o t hefield staff, f o r t he i r he lp dur ing thesa m pl ing a nd da t a r e c or d ing .R e f e r e n c e sG a y a n i i o , E C . J r . , P . S p a r r e a n d D . P a u l y 1 9 9 5 .

F A O I C L A R M Stock AssesmeiU Tools(FiSAT) User's Manual. F A O C o m p . I n f o .Ser . (F i sher i es) , 8 : 126pp.

G u U a u d , J .A . 1 9 7 1 . E s t i m a t i o n o f m o r t a l i t yr a t e s . A n n e x t o A r c t i c f i s h e r i e s w o r k i n gg r o u p r e p o r t . I C E S C M . D o c . 3 ( m i m e o g r . ).

J l i i n g r a n , V.G. 1 9 5 7 . A g e d e t e r m i n a t i o n o fI n d i a n m a j o r c a r p s (Cirrhina mrigala( H a m . ) b y m e a n s o f s c a l e s . Nature,London, 1 7 9 : 4 6 8 - 4 6 9 .

f O i a n , R . A . a n d A . Q . S i d d i q u e 1 9 7 3 . S t u d i e so n a g e a n d g r o w t h o f R o h u , Laheo rohita( H a m . ) f r o m a p o n d ( m o a t ) a n d r i v e rG a n g a a n d Y a m u n a . Proc. IndianNational Sci. Acad., 3 9 B ; 5 4 2 - 5 9 7 .

P a u l y , D . 1 9 8 0 . O n t h e i n t e r r e l a t i o n s h i p sb e t w e e n n a t u r a l m o r t a li t y . G r o w t h p a r a m e t e r s a n d m e a n e n v i r o n m e n t a l t e m p e r a tur e i n 175 f i sh s tocks . J. Cons. Int.Explor. Mer., 3 9 ( 3 ) : 1 7 5 - 1 9 2 .

F u u ly , D . 1 9 8 6 . O n i m p r o v i n g o p e r a t i o n a n d u s eo f t h e E I E F A N p r o g r a m s . P a r t I I .I m p r o v i n g t h e e s t i m a t i o n o f L_^. Fishhyte,4(1) : 18-20.

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Pauly, D. and N. David 1981. ELEF AN-i BASICprogram for the objective extraction ofgrowth parameters from length frequency data . Meeresforsch, 28(4) : 205-211.Pauly D. and J.L. Munro. 1984 Once more, onthe composition of growth in fish andinve r teb ra te s . Fishbyte, 2(1) : 21 .Pauly D. and M.L. Soriano 1986. Somepractical extensions to Beverton andHolt 's relative jdeld-per-recruit model, p.149-495. In : J.L. Maclean, L.B. Dizonand L.V. Hosillos (Eds.). First Asi anFisheries Forum, Asian Fisheries Society,Manila , Phi l ippines .Rahman A.K.A. 1989. Freshwater Fishes of ofBangladesh. Published by the ZoologicalSociety of Bangladesh. 64/4, Nayapalton,Dhaka-1000, Bangladesh, 364 pp.

Saeger, J . and F.J. Gayanilo. 1986. A revisedand graph ics oriented version of ELEFAN,I and II. Basic programs for use on HP/86/87 microcomputers. Tech. Rep. Dept.Marine Fish., No. 8.Shafi, M. and M.M.A. Quddus 1975. Thelength-weight and length-gir th re la t ionship and condition factor in the carp,Laheo calbasu (Hami l ton-Buchanan) .Dhaka Univ. Stud. Pt. B, XX III (1) : 45-49.Shree Prakash and R.A. Gupta 1986. Studieson the comparat ive growth ra te of threemajor carps of the Govinda lake . IndianJ. Fish., 33(1) : 45-53.Wethera l l , JA. 1986. A new method fores t imating growth and morta l i ty parame ters from length-frequency d ata .

Fishbyte, 4(1) : 12-15.