Population Structure, Mortality Rate and Exploitation Rate of Hilsa Shad (Tenualosa ilisha) in West Bengal Coast of Northern Bay of Bengal, India

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1 World Journal of Fish and Marine Sciences 4 (): 54-59, 202 ISSN IDOSI Publications, 202 DOI: /idosi.wjfms Population Structure, Mortality Rate and Exploitation Rate of Hilsa Shad (Tenualosa ilisha) in West Bengal Coast of Northern Bay of Bengal, India Sachinandan Dutta, Sourav Maity, Abhra Chanda and Sugata Hazra School of Oceanographic Studies, Jadavpur University, Kolkata , India Abstract: The population dynamics of Hilsa was investigated by using FiSAT II software of FAO on length based data, was collected from the three main fish landing centers of West Bengal between June 200 and March 20. The asymptotic length (L8) was mm and the von Bertalanffy Growth Function (VBGF) growth constant (K) was.900 yearg. The total mortality (Z) was.98 yearg and the fishing mortality (F) was 0.73 yearg. The natural mortality (M) of Hilsa Shad was.25 yearg by using Pauly s M empirical equation, where the mean habitat temperature was 27.9 C. FiSAT shows the observed extreme length was mm where predicted maximum length was mm and the growth performance index (2') was The average size group of Hilsa population was observed to be comparatively smaller than that found in Bangladesh water. The exploitation rate (E) was found to be 0.37 (< 0.50). However, the apparent under exploitation of Hilsa population, (though E max=0.555) may switch to overexploitation in future, if sustainable fishing is not implemented. Key words: Population Dynamics % Length Based Data % Mortality % FiSAT II % Overexploitation INTRODUCTION population dynamics of Hilsa from Bangladesh by Rahaman et al. [4], Nurul Amin et al. [5-7], Halder and Estimation of growth and mortality of exploitable Nurul Amin [8], Ahmed et al. [9], Amin et al. [3] species is very important since stock assessment and and Rahman and Cowx [20]. Similar studies had been management rely on these population parameters []. done by Hashemi et al. [2] and Roomian and Jamili [22] Hisha Shad (Tenualosa ilisha) is one of the most common in Iran. The population dynamics of Hilsa has been and important anadromaous fish of West Bengal. It is also comparatively less studied in this part of the country. a very important commercial fish and one of the most In India only few authors researched the population popular fish in Bengali cuisine. Several scientists have dynamic of Hilsa viz. Reuben et al. [23]. In the present worked on different biological aspects of Hilsa Shad viz. study, asymptotic length(l8), growth coefficient(k), Pillay and Rosa [2], Hora [3], Pillay [4, 5], Jones [6, 7], total mortality(z), natural mortality(m), fishing Mathur [8], Bhanot [9], De and Datta [0]. Tenualosa mortality(f), exploitation rate (E), relative yield per ilisha inhabits coastal shelf, estuaries and freshwater recruit(y/r), relative biomass per recruit(b/r), maximum rivers in Indonesia, Sumatra, Myanmar, Bangladesh, India, length, growth performance indexes (2'), requirement Pakistan, Kuwait, Iraq and Iran. Out of these nations, pattern, probability of capture, virtual population analysis maximum Hilsa fishes have been harvested from (VPA) were evaluated by using FiSAT II software Bangladesh. Extensive Hilsa fishing is conducted from package to understand the status of Hilsa population in Bangladesh and comprises 75% of the total world catch of Northern Bay of Bengal of West Bengal coast. New FAOthis species [] and represents about 25% (2,50,000 t) of ICLARM software for (mainly length-based) fish stock the total fish production in Bangladesh [2]. In the recent assessment, the FAO-ICLARM Stock Assessment Tools past, the fishery in inland waters of Bangladesh had been or FiSAT package, integrating the ICLARM s Complete declining, but the total catch has remained stable (about ELEFAN, FAO s LFSA and various other routines, 2,00,000 t annually) due to an increase in catch from the released in mid-992 [24] have been used during the marine sector [3]. Several studies had been done on present study. Corresponding Author: Sachinandan Dutta, School of Oceanographic Studies, Jadavpur University, Kolkata , India. Tel: , Fax:

2 World J. Fish & Marine Sci., 4 (): 54-59, 202 MATERIALS AND METHODS The natural mortality of Hilsa Shad was calculated by using Pauly s M empirical equation [25], where the mean The total length of T. ilisha were measured weekly habitat temperature was 27.9 C. between June 200 and March 20 by using a metric scale from the major marine fish landing centers of West Log0 M = Log0 L Log0K + Bengal viz. Kakdwip, Namkhana and Frasergunje Log0T. (Figure ) for the population dynamics study. The fishes were collected by gill net from the Northern Bay of The fishing mortality rate (F) was then calculated by Bengal. The fishes were randomly selected for its the difference between (Z) and (M) from the equation; measurement. A total of 464 T. ilisha were measured for F = Z-M and the rate of exploitation E was calculated by this present study. The minimum and maximum length was the quotient between fishing and total mortality: E = F/Z 55 mm and 42 mm respectively. [26]. The growth performance index was calculated by Then the data was put month wise into the FiSAT II using the equation of 2 = log K + 2 log L8 [27]. In the in an interval of 50 mm. The analysis was done in FiSAT present study we also estimated the probability of capture II (FAO-ICLARM Stock Assessment Tools) software from gill net selection criteria. One year recruitment (Version.2.2). The von Bertalanffy Growth Function and pattern was also figured out in Hilsa population and the length frequency were plotted based on ELEFAN I which length-structure virtual population analysis was done by is used to understand the seasonal oscillation along with using M, K, L8, Ft parameters as an input in FiSAT-II. the estimation of the L8, K and R n. The predicted maximum length from extreme values was computed. RESULTS AND DISCUSSION Different types of population parameters of Hilsa population were calculated by using the FiSAT II. Growth Parameters: The L8 of mm and K of.9 yearg from K scan (Figure 3) routine were observed by using direct fit of length frequency data in ELEFAN I and the response surface (R n) was found to be for the von Bertalanffy growth curve (Figure 2). The growth performance index (2') was observed to be Rahaman and Cows [20] estimated 2' was 3.47 for marine population of Hilsa and Roomiani and Jamili [22] calculated 2' as 3.4 in Hilsa. The L8 and K values of Hilsa were different from other authors. Nurul Amin et al. [6] recorded L cm and K=0.82 yearg in Bangladesh water while Hashemi et Fig. : Map of Northern Bay of Bengal with three fish al. [2] estimated L8=43.32 cm and K= 0.78 yearg and landing centers. Roomiani and Jamili [22] calculated L8= cm and Fig. 2: von Bertalanffy growth curve for Tenualosa ilisha. 55

3 World J. Fish & Marine Sci., 4 (): 54-59, 202 Fig. 3: K-scan routine for determining the best growth curvature which giving the best value of asymptotic length with growth performance indices in Tenualosa ilisha. Fig. 5: Length-converted catch curve for Tenualosa ilisha in West Bengal Coast. The fishing mortality was observed to be less than the natural mortality that indicates the Hilsa has not been over harvested in West Bengal coast of Bay of Bengal but Nurul Amin et al. [6] estimated M less than F (M=.28 and F=2.49) in Bangladesh water of Bay of Bengal indicating that the Hilsa was over harvested from Bangladesh water. Reuben et al. [23] estimated the exploitation and mortality rate of Hilsa along the northeast coast of India. The natural mortality was and the total mortality was.7. According to them the exploitation rate of Hilsa was The increase in the natural mortality than the fishing mortality may be due to increase in predation rate. Exploitation Rate: The exploitation rate (E) in Hilsa Fig. 4: The cumulative probability of the extreme length. population of Bengal coast was 0.37 and the Emax value recorded as If the value of E would have been more K= 0.77 yearg in coastal water of Iran. In the Ganga- than 0.50 then it could be concluded that the fish is Brahmaputra-Meghna (GBM) basin the Hilsa population overharvested from the particular area during this period was found comparatively at much higher density in [28]. The exploitation rate of Hilsa were 0.66 [4], 0.67 in Bangladesh water because of more freshwater input and male, 0.68 in female, 0.6 in adult and 0.6 in juvenile [8] it was also established [6] that Hilsa population was in Bangladesh water, whereas 0.72 [2] and.8 [22] in overexploited from Bangladesh water. Iranian water. So it is clear that the Hilsa was overfished in Bangladesh and Iran but Hilsa population is yet to rich Maximum Length Estimation: The observed extreme overfishing stage (E max=0.555) in West Bengal, India length (Figure 4) in Hilsa population was 455 mm and the during the study period. predicted extreme length was mm and the range at 95% confidence interval was to Recruitment Pattern: The recruitment pattern (Figure 6) of Hilsa population was significantly high in the primary Mortality Estimation: The total mortality (Z) was.98 breeding season of Hilsa as it indicates the strong yearg from length-converted catch curves (Figure 5), the seasonal recruitment. The prolonged recruitment was natural mortality (M) was.25 yearg and the fishing noticed in June to October with a peak in September, mortality (F) was 0.73 yearg in case of Tenualosa ilisha. which marks the highest amplitude of Hilsa in counts. 56

4 World J. Fish & Marine Sci., 4 (): 54-59, 202 Fig. 6: Recruitment pattern of Tenualosa ilisha in Northern Bay of Bengal. Fig. 8: The virtual population analysis in Tenulosa ilisha in West Bengal coast. Fig. 9: Relative yield-per-recruit and biomass-per-recruit Fig. 7: Logistic selection curve for probability of capture, curves for Tenualosa ilisha from West Bengal showing 25%, 50% and 75% selection length of Coast using the selection ogive option (E 0 = Tenualosa ilisha in Northern Bay of Bengal , E = 0.24, E = 0.555). 50 max Probability of Capture: Probability of capture was 305 and 405 mm and the size class which faced maximum estimated from the type of net (gill net) used for fishing. fishing mortality (F =.47) was 355 mm. From VPA it was From this finding it is estimated that the maximum indicated that the survival rate was highest in 55 mm size probability of capture class size lies between 305 mm and group Hilsa, so the juvenile capture in Bengal coast has 405 mm (Figure 7). The selection length of 25 % or L25 was been less during this study period which indicates that mm, 50 % or L 50 was mm and the 75 % or L75 the Hilsa population is not under immediate threat due to was mm. From the probability of capture analysis overfishing. using selection curve the estimated optimum length of Hilsa (TL, mm) at first capture (Lc = L 50) were 322 and 335 Relative Yield per Recruit and Biomass per Recruit: The mm, TL, respectively for river and marine [20]. relative yield-per-recruit (Y/R) and biomass-per-recruit (B/R) were determined as a function of L 50 /L8 and M/K. Virtual Population Analysis: Virtual population analyses The L 50 /L8 value is 0.35 and M/K value are for (VPA) are very useful tool which allow the reconstruction Hilsa (Figure 9). The Y/R was and the B/R was of the population from total catch data by age or size. In The selection ogive routine of FiSAT-II was used in the this present study we estimated VPA from length based analysis of relative yield per recruit and biomass per data (Figure 8). From this analysis we observe that the recruit analysis (Figure 0) and produced values of maximum numbers of Hilsa Shad were caught between E = 0.507, E = 0.24, E = max 57

5 World J. Fish & Marine Sci., 4 (): 54-59, 202 the authors to conduct the study. We also thank the Eco System for Life, a joint India-Bangladesh initiative by IUCN which facilitated some field studies during 20. We are also thankful to the all field staffs and fishermen for helping us during collection and measurement of the specimens on board and in harbours. REFERENCES Fig. 0: Isopleths, showing optimum fishing activity both in terms of fishing effort and size of first capture (depicted with a star in the central curve) of Tenualosa ilisha. CONCLUSION According to Froese [29] overfishing can be prevented by following certain rules. All of the mature fish population should be caught, those who have attained optimum length but the mega-spawners should not be targeted at all. In this present study, it is observed that the percentage of mature and optimum length size fishes were caught with maximum number and the percentage of mega-spawner catch were found to be minimum. Due to this reason overfishing of Hilsa population could not be established in West Bengal coast during this period, but the E max value of denotes symptoms of overexploitation in near future. If any population is affected by the recruitment overfishing, the population might be seriously hampered to attain the sustainable yield in the long run [30], so the fishing regulation must be strong for Hilsa to make this species sustain for a long time in future. On the other hand, the average Hilsa size found here was quite smaller than Bangladesh, which indicates that it could be a different subspecies or race of Hilsa. Further long term monitoring is required to establish the Hilsa population dynamics, as well as phylogenetic study should be done in the West Bengal coast. ACKNOWLEDGEMENTS The authors are very grateful to the Indian National Center for Ocean Information Services of Ministry of Earth Science, Government of India for funding the Potential Fishing Zone Validation Project which enabled. Fakhri, A., P. Hajeb, A. Shadi, R. Kamalifar and R. Mirza, 20. Growth Parameters and Mortality Rates of Javelin Grunter, Pomadasys kaakan, in the Persian Gulf. World Journal of Fish and Marine Science, 3(4): Pillay, T.V.R. and Jr. Rosa, 963. Synopsis on Biological Data on Hilsa, Hilsa ilisha (Hamilton 882). FAO Fish. Biol. Synops, 25(): -6: Hora, S.L., 94. Life history and wanderings of Hilsa in West Bengal waters. J. Asiatic Society (Sci.), 6(2): Pillay, T.V.R., 955. The biology and fisheries of the Hilsa, Hilsa ilisha (Hamilton): A review. Proceedings of Indo-Pacific Fisheries council, 6(2): Pillay, T.V.R., 958. Biology of Hilsa ilisha (Hamilton) of the river Hooghly. Indian J. Fish, 5: Jones, S., 959a. Fishing method for the Indian shad Hilsa ilisha (Hamilton) in the Indian region (part ). J. Bom. Nat. Hist. Soc., 56(2): Jones, S., 959b. Fishing method for the Indian shad Hilsa ilisha (Hamilton) in the Indian region (part 2). J. Bom. Nat. Hist. Soc., 56(3): Mathur, P.K., 964. Studies on the maturity and fecundity of the Hilsa, Hilsa ilisha (Hamilton) in the upper stretches of Ganga. Indian J. Fish, A(): Bhanot, K.K., 973. Observation on the spawning of Hilsa ilisha (Hamilton) in the Hooghly estuary. Journal of Inland Fisheries Society of India, 5: De, D.K. and N.C. Dutta, 990. Studies on certain aspects of the morphology of Indian shad Hilsa. Indian J. Fish., 37(3): Raja, B.T.A., 985. A review of the biology and fisheries of Hilsa ilisha in the Upper Bay of Bengal. Bay of Bengal Program. BOBP/WP/37. Marine Fishery Resource Management in the Bay of Bengal, pp: Salini, J.P., D.A. Milton, M.J. Rahman and M.G. Hussain, Allozyme and morphological variation throughout the geographic range of the tropical shad, Hilsa Tenualosa ilisha. Fisheries Research, 66:

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