Tuna and billfish production from the Indian coastal waters, Lakshadweep and

Andaman and Nicobar islands during the period 1985-'99 averaged 40,204 t. The

contribution by E.affinis, Athazard, T.tonggol, K.pelamis and T.albacares (young

ones) were 18,5041,6,8521,3,093 t, 3,3921 and 2,2111 respectively. Drift gill net

was the major gear employed in the coastal tuna fishery. The length frequency data

collected on the above species during 1990-'98 at seven centres along the Indian

coast were analysed employing FiSAT programme to estimate their growth and

mortality parameters, exploitation rates and relative yield per recmit

Ajith Kumar, T T

Balasubramanian, T S

Bhaskaran, M M

Dhokia, H K

Elayathu, M N K

Ganga, U

Gopakumar, G

Kasim, H M

Kemparaju, S

Koya, K P Said

Kunhikoya, V A

Manimaran, C

Manojkumar, B

Muthiah, C

Nasser, A K V

Pillai, N G K

Pillai, P P

Sivadas, M

Yohannan, T M

CMFRI Digital Repository

Management of Scombroid Fisheries Editors N.G.K. Pillai N.G. Menon P.P. Pillai U. Ganga ICAR CENTRAL MARINE FISHERIES RESEARCH INSTITUTE (Indian Council of Agricultural Research) Post Box No. 1603, Tatapuram P.O. Kochi-682 014, India Stock assessment of coastal tunas in the Indian seas RRPillai, N.G.K.PiUai, C.Muthiah, T.M.Yohamian, H.Mohamad Kasim, G.Gopakumar, K.P.Said Koya, B.Manojkumar, M.Sivadas, A.K.V. Nasser, U.Ganga, H.KJ)hokia, S.Kemparaju, M.M.Bhaskaran, M.N.K. Elayathu, T.S.Balasubramaniam, C.Manimaran, V.A.Kunhikoya and T.T.Ajith Kumar Central Marine Fisheries Research Institute, Kochi ABSTRACT Tuna and billfish production from the Indian coastal waters, Lakshadweep and Andaman and Nicobar islands during the period 1985-'99 averaged 40,204 t. The contribution by E.affinis, Athazard, T.tonggol, K.pelamis and T.albacares (young ones) were 18,5041,6,8521,3,093 t, 3,3921 and 2,2111 respectively. Drift gill net was the major gear employed in the coastal tuna fishery. The length frequency data collected on the above species during 1990-'98 at seven centres along the Indian coast were analysed employing FiSAT programme to estimate their growth and mortality parameters, exploitation rates and relative yield per recmit. In the present study, the growth parameters Uo and K, length at first capture (L )^, and mortality rates are given. Along the coastal waters of India the exploitation rate (E) of E.affinis varied in different states, being 0.86 along Kerala-Kamataka belt, 0.77 in Gujarat and 0.75 in Tamilnadu. Based on Y/R the optimum exploitation rate (E ) ofE.affinis is 0.4 only indicating that the current exploitation level of this species in coastal waters is relatively high. The exploitation rates of A.thazard, T.tonggol and T.albacares were 0.72, 0.3 and 0.81 respectively with (E ,) being 0.40, 0.42 and 0.37 respectively for these three species, indicating that tnere is further scope for increasing the exploitation of T.tonggol in the coastal waters while others are being exploited relatively at a high rate in recent years. INTRODUCTION Tunas constitute one of the economically important marine fisher-ies resources and during 1985-'99, their production from Indian seas fluctu-ated between 24,287 t (1987) and 53,662 t (1992) with an average annual production of about 40,2001 forming 3.6 % of the total pelagic fish produc-tion. The status of exploitation of coastal tunas occurring in the Indian seas in recent years has been dealt with elsewhere (Pillai et at., 2000). The stock assessment of tunas occurring in the Exclusive Economic Zone (EEZ) of India has been attempted earlier (Silas and Pillai, 1985; James et at., 1993; Yohannan et al, 1993 and Pillai et at., 1993). After the published studies based on data during the period 1984- '88, considerable changes in the trend of production were recorded since 1989, making it imperative to carry out a re-examination of the population parameters, status of exploitation and stock assessment of tunas from the Indian seas. MATERIALS AND METHODS The statewise and all India tuna landings data for the period 1989-125 Management of Scombroid Fisheries '98 were taken from NMLRDC of CMFRI. Length frequency data collected from six major fish landing centres along the west and east coasts of India during the above period formed the basis of the estimates. Data collected from Veraval has been raised to the average annual catch of Gujarat and from Mangalore and Malpe to Kamataka state. Data collected from Kochi, Calicut and Vizhinjam were pooled and raised to the average annual catch of Kerala and from Tuticorin raised to the catch of Tamilnadu . Growth parameters were estimated based on the pooled data for the states of Kerala, Karnataka and Goa (west coast) and Tamilnadu (east coast). Length con-verted catch curve method (Pauly, 1984) was used to obtain estimates of total mortaUty(Z) while the natural mortality (M) was estimated using Pauly's (1980) method, the average water temperature being taken as 28.5°C. The exploitation ratio (U) was estimated using the equation U= F (l-e-^)/Z. The annual total stock was estimated by the equation YAJ where Y is the average annual catch of the particular species. Relative yield per recruit (Y/R) was estimated as given in ELEFAN module of FiSAT which indicated the maxi-mum exploitation rate (E ^) and optimum exploitation rate (E ^  ) . RESULTS The growth parameters Lmand K (annual) of different species estimated by ELEFAN (Table 1) and mortality rates obtained by the catch curve analysis (Figs. 1,2, 3,4) were as follows : h. ^OPOM A b s o l u t * «v« <||*MPS> Fig. 1. Length converted Catch Curve analysis of E. afflnis. (Input parameters Lo 89.0 cm K=0.9yr ') Z=5.85 E=0.8 Absolut* «ro (uo«rs> Fig. 2. Length converted Catch Curve analysis of A. (hazard. (Input parameters Uo 54cm K=0.87yr ') Z=4.4 E=0.70 t" 1 * • f- 4 Fig. 3. Length converted Catch Curve analysis of T. albacares. (Input param-eters L«, 172 cm K=0.39yr ') Z=3.10 E=0.81 ' a 1 a 3 Aboeluto Mro <yoai*s> Fig. 4. Length converted Catch Curve analysis of T. tonggol. (Input param-eters La 92.5 cm K=1.2yr ') Z=1.86 E=0.40 126 Stock assessment of coastal tunas in the Indian seas Table 1. Estimated growth parameters and mortality rates Species L«,(cm) K( annual) Z M L(cm) E-affinis 89.0 0.90 Athamrd 54.0 0.87 Tdbacares 172.0 0.39 T.tonggd 92.5 1.2 5.85 4.40 3.1 1.86 4.90 3.20 2.5 0.7 0.98 1.20 0.6 1.2 0.8 0.7 0.8 0.3 44 35 104 681 i ' rff"" • 1 a Absolut* as* <w»«rs> 16 5 12 Absolut* avs <yoars> SB /«15 "^10 .L B — T ^ 2 Absolut* as* invars) Fig. 5. State-wise Catch Curve analysis of E.affinis fishery (A) Kerala E=0.86; (B) Kamataka E=0.86 (C) Gujarat E=0.77 127 Management of Scombroid Fisheries Based on the growth parameters the lengths at age for different species have been esimated as follows: Species E.affinis A.thazard T.albacares T.tonggol LooCcm) 89.0 54.0 172.0 92.5 K( annual) 0.90 0.87 0.39 1.20 Length (cm)! I II 52.8 31.4 55.5 64.6 Parameters such as E^, E ^^ and Exploitation assessing the status of exploitation of different given below: Species E.affinis A.thazard T.albacares T.tonggol E Opt 0.35 0.42 0.40 0.40 E max 0.7 0.9 0.7 0.9 present E 0.80 0.70 0.81 0.40 74.3 44.5 93.2 84.1 at age (years) III IV 83.0 86.6 50.0 52.3 118.6 135.9 89.9 91.7 ratio (U) were studied for species of tunas which are Av.annual total stock (t) (at start ofyear)(Y/U) 23,130 9,788 2,764 10,310 The coastal tunny E.affinis is the most intensively exploited coastal tuna species followed by A.thazard .The exploitation of E.affinis is relatively high in the south-west coast comprising the states of Kerala and Kamataka (E=0.86) compared to Gujarat in the north-west (E= 0.77) and Tamilnadu (E=0.75) on the south-east coasts (Fig. 5). DISCUSSION The morphological and reproductive characteristics, population sizes and genetic frequencies of species are adjusted to their environments by natural selection and species inhabiting different environments show differ-ent patterns of life history characteristics (Adams, 1980). The relationship between habitat, ecological strategies and population parameters has been termed as r and K selection (Macarthur and Wilson, 1967 ) with a K strate-gist species having a large Loo and low K from the von Bertalanffy growth equation, large body size and delayed maturity and an r selected species having small Loo and high K values, small body size and early maturity (Adams, 1980). While no species are r or K selected in an absolute sense, fisheries based on more r selected species are likely to be of a boom and bust nature but those based on more K selected species will be characterised by relatively stable population sizes and catch levels. However, once these fish-128 Stock assessment of coastal tunas in the Indian seas eries are overfished it would take a long time for stocks to rebuild (Adams, 1980). The K value of the various tuna species vary between 0.4 and 1.2 indicating a relatively slow growth pattern and the need to evolve appropri-ate exploitation strategies. James et al. (1993) estimated the length at first maturity (LJ of E.ajfinis , A.thazard and A.rochei at 44, 32 and 23 cm respectively. In the present study the length at first capture (L )^ of the various species studied like oi E.ajfinis, A.thazard, T.albacares and T.tonggol were 44, 35, 92 and 68 cm respectively which indicates that except perhaps for E.ajfinis all other species have an opportunity to spawn at least once before they are captured, reducing the risk of recruitment and growth overfishing to occur. FAO (1993) while discussing the reference points (RP) used in fish-ery mangement, like maximum sustainable yield (MSY), reports that they are mostly useful for assessment of single stocks and less applicable to highly migratory resources such as tunas.This is because often, multiple fisheries occur at different locii on the overall migratory routes of tunas and these local fisheries are seasonal and very short. Therefore declines in catch rate with time and size cannot be unambiguously attributed to fishing as opposed to migration. Yohannan et al. (1993) also observed that environmental con-ditions and forage availability are key factors in deciding the availability and abundance of tunas. As regards the tuna fishery in Indian waters, non availability of catch- effort and length frequency data from the whole range of distribution of a particular species of tuna mainly because this fishery is limited to the small scale sector and there is seasonality in the availability of various species, pose difficulties in arriving at conclusions regarding the growth and mortality estimates and stock structure. Therefore a practical approach would be to consider each fishing location to be assessed as favouable or unfavourable in relation to a size based RP and the optimal size at first capture (L )^ as judged from the yield per recruit analysis which will ensure that a certain spawning biomass survives to replenish the fished stock. Also it is desirable that while estimating the exploitation rate and optimum yield of tunas, both commercial fishery and exploratory survey data are con-sidered to arrive at meaningful conclusions. REFERENCES Adams, P.B. 1980. Life history patterns in marine fishes and their conse-quences for fisheries management. Fish. Bull.,78(1):1-11. FAO, 1993. Reference points for fishery management: their potential appli-cation to straddling and highly migratory resources. FAO Fish. Circ., 864, 52 p. James, P.S.B.R., P.P.Pillai, N.G.K.Pillai, A.A.Jayaprakash, G.Gopakumar, H.Mohamed Kasim, M. Sivadas and K.P. Said Koya.1993. Fishery biology and stock assessment of small tunas. In: D.Sudarsan and 129 Management of Scombroid Fisheries M.E.John (Eds.) Tuna Research in India. Fishery Survey of India, Bombay, p. 123-148. Pauly, D. 1980. On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stocks. J.Cons. C/£M.,39(3): 175-92. Pauly, D. 1984. Fish population dynamics in tropical waters: a manual for use with programmable calculators. ICLARM Stud. Rev., 8,325 p. Pillai, PP , K.R Said Koya, N.G.K.PiIlai and A.A. Jayaprakash. 1993. Fish-ery and biology of yellowfin tuna occurring in coastal fishery in In-dian seas. In: D.Sudarsan and M.E.John (Eds.) Tuna Research in India , Fishery Survery of Indian, Bombay, p. 23-38. Pillai, PR, N.G.K. Pillai, C. Muthiah, T.M. Yohannan, H. Mohamad Kasim, G. Gopakumar, K.P. Said Koya, B.Manoj kumar, M. Sivadas, A.K.V. Nasser, U.Ganga, H.K.Dhokia, S.Kemparaju, M.M.Bhaskaran, M.N.K.Elayathu, T.S.Balasubramaniam, C.Manimaran, V.A. Kunhikoya and T.T.Ajith Kumar. 2000. Status of exploitation of coastal tunas occurring in the Indian seas. National Workshop on Scombroids , 19-20 September 2000, CMFRJ, Kochi (MS). Silas, E.G. and RRPillai. 1985. A critique on National Tuna Fishery. Bull. Cent. Mar. Fish. Res. Inst., 36: 118-19. MacArthur, R.H. and E.O.Wilson. 1967. The theory of island biogeogra-phy. Princeton Univ.Press.Princeton, NJ, 203p. Yohannan,T.M., RRPillai and K.RSaid Koya. 1993. Fishery, biology and stock assessment of skipjack tuna in Indian seas. In: D.Sudarsan and M.E.John (Eds.) Tuna Research in India. Fishery Survey of India, Bombay, p. 77-96. 130 

Stock assessment of coastal tunas in the Indian seas

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Stock assessment of coastal tunas in the Indian seas

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