Indian Journal of Fisheries 40 (1,2) : 63-73, March-June 1Q93 Stock assessment of the spiny lobster PanuUrus polyphagus (Herbst) off north-west coast of India P V KAGWADE' Central Marine Fisheries Research Institute, Cochin, Kerala 602 014 ABSTRACT The fishery of PanuUrus polyphagus has demonstraled successive periodic decline and revival. It has been able to survive for over 1 1/2 decades in spite of heavy exploitation. The present yields are 503.5 tonnes for males and 825.4 tonnes for females, while the MSY are 520.365 tonnes for the former and 837.8249 tonnes for the latter. The fishing effort would have to be reduced by 40% to reach the MSY level. Exploitation rate is 0.5096 for males and 0.4925 for females. Protecting the spawners either by banning their capture or by throwing them back into the sea during September, their peak spawning month, has been suggested as a small conservation measure. Miyomoto and Sheriff (1961) conducted half of seventies brought to limelight some preliminary surveys to know the magnitude exploitable rich regions for this valuable of lobster resources to take advantage of the commodity and thus enhanced its foreign lucrative world-wide market for the lobster trade. Export of frozen lobster/lobster tails tails. Chacko and George (1958) and from India increased from 560 tonnes Balasubramanyan et a/.(1960) showed (Rs 406 million in 1979-80 to 1 663 tonnes substantial potentialities for lobsters in the (Rs 2.36 million in 1988-89 (Mohamed and south-west coast of India. Though records Madhavan 1989) thus signifying the of lobsters in the fisheries of Bombay (Rai importance of its fishery. 1993) and India (Chopra 1939) were Two types of lobsters have been available much before this, there was no inhabiting the coastal waters of India. Of attempt to increase their catch or to find the 6 species of spiny lobsters, also known out their availability in any other part of as rock lobsters and all belonging to the the country, because of the limited domestic genus PanuUrus, available in our waters demand. The entry of Indian lobster into 4 and one single species of sand lobster of the foreign market in late fifties led to the genus Themis have been of commercial intensive investigation for the lobster importance. These species are P. resources all over the country. New areas of polyphagus, P. homarus, P. ornatus, P. good fishery potentials for lobsters were versicolor and T. orientalis. The distribution found along the coasts south of Trivandrum and conunercial abundance of each of these and north of Kozhikode in Kerala (George species arc specific (Kagwade et al. 1991). 1967) and Mandapam in Tamil Nadu (Nair P. polyphagus is the .most abundant et al. 1973). The strong urge to develop species, contributing to nearly 3/4 of the commercial fishery for lobsters in the second lobster catch of this entire country. Its fishery has flourished well in Maharashtra and Present address : 'Principal Scientist, Bombay Research Centre of CMFRI, 148 Army and Navy Gujarat in the north-west. The fisheries of Building, Bombay 400 023. the other 3 species oi PanuUrus are of very 63 KAt'JWADf: [Vol,40. I).*i<al view: H, taleral v«wv. 64 March-June 1993] STOCK ASSESSMENT OFSPINY LOBSTER small magnitude and restricted to small mortality (Z) were estimated. The standing areas of Tamil Nadu and Kerala. T. stock and biomass of this species were orientaUs has been landed in good quantities assessed by using length converted by the trawlers in the north-west coast and Thompson and Bell analysis (1934) using in Madras. LFSA programme (Sparre 1987). The status of the lobster fishery in this Jone's method (1979) for different country depended on the prospects of the combinations of L and M/K as inputs in fishery of P. polyphagus because of its cohort and Thomspon and Bell analysis were unique position in relation to its abundance. followed. Much of the biological information is available on this species. Hence, the same Fishery has been chosen for the stock assessment Catch data for 1978-88 from the Central studies. Marine Fisheries Research Institute were used for discussing the fishery. The annual DATA BASE fluctuations in the catch was a common Primary data for all biological studies phenomenon. The catches were lowest (679) were collected from the major landing in 1980, and highest in 1985 with the centres of Sassoon Dock and New Ferry annual average catch of 2 016 t (Table 1), Wharf in Bombay from 1984 to 1988. Data Percentage composition of P. polyphagus on fishery were drawn from the readily in Gujarat, Maharashtra, Kerala and Tamil available published works and from the Nadu are also given in Table 1. Kagwade Fishery Resources Assessment Division of et al. (1991) observed that Gujarat, the Central Marine Fisheries Research Maharashtra and Kerala, each had only one Institute. major centre at Vcraval, Bombay and Calicut respectively. Tamil Nadu had 3 METHODS centres one each at Kanyakumari, Tuticorin Weekly random samples (each of at and Madras. Since the number of years of least 100 specimens) of P. polyphagus were observations varied from centre to centre, drawn at the landing centres Sassoon Dock the annual average catches were taken into and New Ferry Wharf. This number could consideration for this purpose. During the not be adhered to during the lean season. long period of 11 years, data were available Sex-wise total lengths to the nearest million for 3 years at Calicut, 5 years at were measured from the transverse ridge Kanyakumari, 9 years at Vcraval and 11 between supraorbital horns to the tip of years for the rest. The maximum annual telson. The usual techniques were followed average catch for P. polyphagus was in for various biological aspects of the study. Maharashtra (233 tonnes; 71.11%), followed For the stock assessment study during by Gujarat (63 tonnes; 21.12%), Kerala 1984-88 the total number of P. polyphagus (2 tonnes; 0.67%) and Tamil Nadu (0.3 landed each year was estimated separately tonne; 0.1%). for males and females by the length groups. The landings of P. polyphagus in The number of lobsters so obtained were Bombay and Veraval representing used as input for the Jones (1984) length Maharashtra and Gujarat, respectively, cohort analysis. From this instantaneous showed annual lluctuations (Table 2). fishing mortality (F) and instantaneous total Successive periodic decline and revival have 65 KAGWADE [Vol.40, No. 1,2 Table 1. All-India lobster landings and state-wise annual average lobster catch and percentage catch distribution ot P. polyphagus during 1978-88 All-India lobster States Period of Annual average P. polyphagus Year catch (tonnes) observation catch of lobsters (tonnes) Catch (tonnes) 1978 1307 Gujarat 1980-88 147 63.0 21.12 1929 1 135 1980 679 1981 1481 Maharashtra 1978-88 429 233.0 71.11 1982 1764 1983 1300 Kerala 1982-83 8 2.0 0.67 1983-84 1984 3 222 1985-86 1985 4 082 1986 3 057 Tamil Nadu 1978-88 47.3 0.3 0.1 1987 2 562 1988 1587 Table 2. Quarter-wise distribut ion of annual average catch (kg), catch rate (kg, U) and percentage catch of P. polyphagus at Boimba y during 1978-88 Annual Quarter average catch I II III IV Total Kg 76 051 44710 31922 80 721 233 404 KgAJ 6.43 4.56 3.62 5.91 % 32.6 19.1 13.7 34.6 been noticed in its fishery. Similar trend of In Bombay the catch was maximum in the decline and revival was noticed in the All- fourth quarter, followed by the first quarter. India lobster catch also (Table 1). The catch rate in the first quarter was higher P. polyp.Higus, though available all than 5.91 in the fourth quarter. The fishery round the year, displayed seasonal of this species appeared to be the best during abundance in its fishery. Its quarterly October-March. Similar observation was distribution based on the aimual average made by Kagwade et al. (1991) for P. catch during 1978-88 is given in Table 3. polyphagus, Table 3. Annual landings of P. polyphagus in tonnes in Bombay and Veraval during 1980-88 Year Bombay Veraval Total 1980 189 66 255 1981 176 31 207 1982 176 30 206 1983 84 34 118 1984 309 107 416 1985 384 96 480 1986 450 61 511 1987 230 104 334 1988 147 35 182 66 March-June 1993] STOCK ASSESSMENT OFSPINY LOBSTER This species was landed mainly by otter Grov4h parameters derived for adults and shrimp trawls. These were of 16-23 int by von Bertalanffy's growth formula were: with the head rope of varying length. Mesh Males: La, = 537 mm size at the cod-end was 2.5 mm. K = 0.2 to = 0.6037 and Biology Females: LM = 443 mm George (1967) reported the annual K = 0.2231 growth rate for P. homarus by length to = 0.1985 frequency method, and Mohammed and Morphological relationships and George (1971) estimated the length at age conversion factors in P.polyphagus of the same species by tagging experiments. (Kagwade 1987b) showed that each of the Growth under captivity was noted by relationships of carapace length with total Thomas (1972) in P. homarus, Kathirvel length and of abdominal weight with the (1973) in P. polypltagus and Nair et al. total weight was linear while the (1981) in P. homarus, P. ornaUis and P. relationships between total length and total penicillatus. All these growth rates reported weight, total length and abdominal weight, for lobsters were of preliminary nature and carapace length and abdominal weight limited to short time intervals and between were exponential.