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TWS/91/17

WORKSHOP ON STOCK ASSESSMENT OF YELLOWFIN TUNA IN THE' INDIAN OCEAN, 7-12 OCTOBER. 1991

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GROWTH OF INDIAN OCEAN YELLOWFIN TUNG ESTIMATED FROM SIZE FREQUENCIES DATA COLLECTED ON FRENCH PURSE*SEINERS ,

INDO-PACIFIC TUNA DEVELOPMENT AND MANAGEMENT PROGRAMME (IPTP) - - - ___ - - -

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WORKSHOP ON STOCK ASSESSMENT OF YELLOWFIN TUNA

IN THE INDIAN OCEAN

(Colombo, Sri Lanka, 7 - 12 October 1991)

OF INDIAN OCEAN YELLOWFIN TUNA BTIMATED > ,

FROM SIZE FREQUENCIES DATA COLLECED ON FRENCH PURSE SEINERS

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by Francis MARSAC * 3 ,

INTRODUCXION

The current status of research on Yellowfin tuna growth is open to debate. Two main hypotheses are proposed The first one suggests a high growth rate during the first ages, as commonly observed In most of the species of fish. It la supported by obsewatiom of Wang and Tanaka (1986) and Huang et al. (1973). These authors found growth rates an high an 3.32 to 3.39 an/month for yellowfin ranging between 35 and 92 cm. MarcUle and Stequert (1976) got a 3 admonth rate between 45 and 70 cm; Anderson (1988) estimated a rate of 2.9 . Similar velues were obaewed in the b t e m Pacific (Wild,

and S t h a k e r , 1981) and Weetem PacifIc (Yamanaka,

t The second hypothesh is a two step growth pattem, with a low rate in the young ages and a sudden increase in the intermediate aged, leadhg to 8 common growth trend that can be described by the Von Bertalatif@ growth curve (VBOF). lW was observed in the Atlantic I through tagglng techniqued: 1.4 cm/month for Bsh measuring less than 65 cm FL (Fonteneau, 1980; Bard, 19W Mlyabe, 1984). An analysis canied out from size frequencies data in Vanuatu (SW Pacific) multed in 1.3 cdmonth ra ta between 30 and 50 cm FL (Brouard et aL 1984). A prellmfnary study (Marsac and Lablache, 1985) suggested this growth pattem in

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. the Indian Ocean. Alonger data serles allows now a revision of this analysls.

SOURCE OF DATA AND METHOD

The basic data are the size frequencies samples of the catch made by the French purse seiners between 1984 and 1989. The size spectra extends from 30 to 170 cm. It comprked a part of the size range exploited by the artisanal fishery (smaller fish) and by the longUne fishery (bigger fish). Therefore, these samples represent the bulk of yellowfh sizes exploited in the Indian Ocean.

We used the Bhattachwa method to analyse the modal distribution. 5 )

Fonds Documentaire ORSTOM Cote:8$+83310 Ex: 4 'p , .

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* ORSTOM Biologist, SFA, BP 449, Victoria, Mahe, SEYCHELLES

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RESULTS

Through these data, the population appears as composed of three major groups (fig.1) :

- juveniles (size < 70 cm FL) caracterfzed by well pronounced modes. Though they are caught al l the year round, the maximum occurence is found during the 3rd quarter, in relation with purse seine fishing on logs.

- fish from 80 to 120 cm FL: poorly represented in the catch from 1984 to 1987, they become more abundant in 1988 and 1989. However, they remain in low proportion in the catch compared with juveniles and adults.

- adults (size > 120 cm): well represented but the distinction between the modes is trickllsh due to the combined effects of a slow growth rate, a different growth pattern between males and females and different individual history.

A first vlew of the connection between modes is given on a quarterly basis In figure 2.

More detalled infomation is obtalned on a monthly basis. During the first 21 months of the life cycle, the modal progression suggests a recruitment in the surface fishery in May and June (she between 40 and 42 cm FL). In the yellowfin population, the gonad index reaches peak valdes h m December to March (l3g.3) and larvae should appear during the first quarter (Hassani and Stequert, 1991). The recruits found in May and June would represent a cohort born In the very beginning of the year.

Five cohorts with clear modal progression were relected and their growth pattem compared on the basts of a btrth ln December or January. A graphlc repmentation (fig. 4) points out a good coherence between all of these. The growth ir linear from 6 to 18 months, with an average rate of 1.5 d m o n t h . Then the growth rate increases up to 4 d m o n t h between 20 and 24 montha. Thla mwth m e cannot be modeked along the whole size range. The Von Bertalanffy Growth Function was calculated from 24 months and produced the following estimators :

L - 173.1 an K - 0.65 to - 1.03 gear

Accordlng to the speciac processing applied there, no biological meaning can be given to the parameter to.

An additional analysis focusing on largest shes gives a sllghtly Ngher L -, estimated at 174 cm, with K -- 0.66 (Sabadach, manuscript).

The growth in weight is calculated using the length-weight relatio&hip proposed by Halller (manuscript, W meeting). The curves are presented in figure 5 and a key between age, size and weight in Table 1.

DISCUSSION $ i

The estimation of size at age 1 is in accordance with the she found in the Indian Ocean by Yabuta et al. (1960), based on scale readlngs. The differences appear later and bigger sizes are estimated by the ptesent growth equation.

Thls particular two step growth pattern seems consistent between size frequendes analysis and tagging techniques, while different figures are given by otoliths, scales or vertebrae rings readings. For most of the otoliths readings, small size flsh are in concem and no comprehensive growth equation can be proposed. In the other hand, selectivity is often invocated as a restriction to modal analysis an tagging based results. Since no results on the whole size range are available through direct methods, the growth equation given in this study could be considered as a reasonable hypothesis for this worktng group.

" C Z . jv. . I. * REFERENCES .

ANDERSON, R.C.. 1988 - Growth and migration of Juvenile yellowfin tuna ( Thunnus db8cares) in the central Indian Ocean. COU. Vol. Work Doc, IPTP, TWS/88/21 :

BARD, F.X., 1984 - Croissance de I'albacore (Thunnus albacares) Atlantique d'apks Les d 0 M h de marquage. Rec. Doc. Scf., ICCAT, 20 (1) : 104 - 116.

BROUARD, F., R. GRANDPERRIN et E. CILLAUREN. 1984 - Croissance des jeunes thons jaunes (Thunnus d6auues) et des bonltes ( Kabuwonus pelmi$ dans le Pacifique tropical occidental. Mission ORSTOM de Po@-Vila. Notes et Documents

FONTENFAU, A, 1980 - La croissance de l'albacore de l'Atlantique est. , Rec. Doc. Scl.,

HASSANI, S. et B. STEQUERT, 1991 - Sexual maMty, spawning and fecundity of the

28- 39. 4 3 %

I t d'ochographie, < 10,U " p,

% ICCAT, 9 (1) : 152 - 168. . r

yellowfin tuna (Thunnus al6acares) of the Wertem Indlan Ocean. COU. VOL Wonk DOC, IPTP, TWS/90/68 : 91 - 107.

HUANO, C.C., L. SUN et R.T. YANO, 1973 - Age, growth and population xtructun of Indian yellowfin tuna. X Fhb. Soc. Tafwaa 2 : 16 - 30 (Note consulted In

MARCILLE, J., et B. STEQUERT, 1976 - Etude pn%" de la croissance du llstao ( K 8 t S U w 0 n ~ ~ pelamis) dans l'ouest de l ' o c h Indien. Cah. ORSTOhf (Sk

MARSAC, F., et G. LABLACHE, 1985 - Preliminary study of the growth of yellowfin

O r i g h a l ) .

Oc&Ofl.), 14 (2) : 139 - 51.

estimated from purse seine data in the Westem Indian Ocean. COU. Vol. Work DOC, JPTP. TWS/85/22 i.91- 110.

UCHIYAMA, J.H., et P. STRUHSAKER, 1981 - Age and growth of skipjack tuna, Katsuwonus pelanis, and yellowfin tuna, Thunnus albacares, as indicated by daUy growth increments of sagittae. Fish. BUU., 79 : 151 - 162.

WANG, C.H. et S. TANAKA, 1986 - Development of a multi-cohort analysis method and its application to the Indian Ocean yellowfin tuna. COU. Vol. Work Doc., IPTP, TWS/86/33 : 44 - 51.

WILD, A., 1986 - Growth of yellowfin tuna, í'bunnus albacares, in the eastern Paafic Ocean based on otollth increments. LATTC BdL, 18 : 423 - 479.

Y -.

24 - 1*'30 36 42 48 60 72 84

YABUTA, Y., M. WKINAWA, e t Y. WARASHIN4 1960 - Growth and age of yellowfin tuna. 2. Age determination (scale method). Rep. Nankal Reg. Fish. Res. Lab., 12 : 63 - 74. ~

160 ~ 166

170

YAMANAKA, K.L., 1988 - Estimates of age, growth and spawning of yellowfin tuna in the Puppines as determined from the examination of Increments on saglttal otoliths. 39bme Conf. - Thonibre de I'IAITC, 16 au 18/05/1988, Lake- Arrowhead, Californie.

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I Table 1 - Key between age (month), fork length (can) and weight (Kg) for the Indian Ocean yellowfin tuna. .

I . I

',> I - Length (cm) Weight (Kg)

I 48 53 3.0

18 62 4.6 20 66 5.5 ...........................................

. I . * Qi .- 106 125

* 138 148 1

10.3 23.3 38.5 52.0 64.3 81.5 91.2 98. i

* + the birth date is ret to Januarg 15 th; + the &wth f" 6 to 20 months Is estimated by the apparent progression of ;he modes; t the growth from 21 months ls calculated by the VBOF wlth the following parameters :

, * * , * : ,.i- * I'

- - L- - 173.1 cm K - 0.65 to - 1.03 an (I.e. 12,40 months) ! - - .

t the length-welght relationships ls from Halller (manuscrlpt).

i t .

, j ... ../ ..... . . . . . .

5 10 15 20 25 Temps (en Irimeslres)

F i g . 1 - Quarterly distribution of the size frequencies OfyeIIowfln tuna caught by the French purse seiners in the Westem Indian Ocean. The kquency of each size class is ProPortioMd to the arca of the clrcies (from Sabadach, manuscript)

0 0 1 V C . I S d ... 2vmc-alul -- .

. . . . . . 50 - ...................... . . . . .

. . . . . , l o - i . Y * . . . . . !.. . . . . . : . . . a . . . . . . . . . . . . . . . . .

A i988 : . . .d . .:. . . -p IGS mqen . . . . . . . . . . . . . . . . . . . . . ..... ; ....... m. . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x . .. . . . .

+ . : ” : ’ : . . . . . . . . . . . . . . . . . . . . 0 ................... ..’. .......... .. . . . . . . . . . . . : ......... , I , I I I . ‘ :J., * , F : t I;M A .-.M. . . J J . . A S O N O

Pig. 3 - Monthly means of the gonad index for female yellowfin measuring less than 113 cm (from HassanI and Stequert, 1991).

Estimation of the p;owth by connecting the moda of LcohorU . :

Longueur (cm) 180

I80

140

120

100

ao

80

40

20 O 12 24 38 4a eo

Nois

A : nor. 1984-IQ + B :DEC. 1987 -*- C : JAN. IQ87 -6- D :JAN. 1980 4- E : DEC. 1984

Pig. 4

I( s-.. The cohort A is a pseudo-cohort obtained by combining the yars 1984 to 1969, for ages less than 21 months.

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Growth' in length

24 30 . . 40 eo 72 04 O

Month

Growth in weight - ; . ', ~: l i ' . I I

Weight (Kg) 100

70 -----

12 24 38 40 O0 72 04 O

Month

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