Indian Journal of Geo Marine Sciences Vol. 40(5), October 2011, pp.680-686

Stock assessment of the Indian scad, (Ruppell, 1830) from Mumbai waters

Nalini Poojary 1*, L.R. Tiwari 2 & S.K. Chakraborty 3 1,3 Central Institute of Fisheries Education, Panch Marg, Versova, Andheri (West), Mumbai 400 061, India. 2Maharshi Dayanand College of Arts, Science and Commerce, Parel, Mumbai – 400 012, India *[E-mail: [email protected]]

Received 13 July 2010; revised 5 February 2011

Present study consists the Growth, mortality and the stock assessment of Decapterus russelli . ‘L ∞’ was estimated as 277 mm and ‘K’ as 1.237/year. The t o estimated by VBGF plot was – 0.3443 year. Growth in length of D. russelli described -1.237{t-(-0.3443)} following von Bertalanffy growth equation as, L t = 277[ 1-e ]. Longevity was estimated to be 2.42 years. Total mortality rate (Z), natural mortality rate (M) and fishing mortality (F) were estimated to be 6.66, 2.1 and 4.56 respectively. In this study, Z/K was found to be 5.38 indicating that the stock of D. russelli is presently mortality dominated in Mumbai waters. Exploitation rate (U) was calculated as 0.6838 and the Exploitation ratio (F/Z) as 0.6847. Thompson and Bell long- term prediction analysis indicated that there is no decline in yield of D. russelli even if the fishing effort is doubled. Present level of fishing has no deleterious effect on the fishery of D. russelli

[Keywords: D. russelli , Indian Scad, Stock assessment, growth, mortality]

Introduction Maharshtra 5 has been given in table 1 which shows Caranigids are a part of pelagic fishery and a steady decline. constitute 7% of annual marine landing in India. The average contribution of D. russelli in the year They include 25 genera and 140 species. They 2004-2008 towards the total marine catch of India particularly support the fishery in Andhra Pradesh, was 1.11% and 0.94% to the total marine catch of Tamil Nadu, Kerala and Karnataka 1. Of the 35 species Maharashtra and 25.67% to the total carangid that commonly occur along the Indian coast, landing of Maharashtra 6. So far there is no catch data Megalaspis cordyla , Decapterus russelli, exclusively for D. russelli from Mumbai landing djeddaba , Selar crumenophthalmus , Caranx spp., and centres. They are observed between October to Scomberoides spp. mainly constitute the fishery in February in the landing centres of Mumbai. Maharashtra 2. D. russelli is caught as a by-catch D. russelli is one of the important species in the throughout the year along the north-west coast of trawl catches of Mumbai coast and accounts for India using mainly trawlers with cod end mesh sizes almost 40% of the total carangid catch 7. They are ranging from 15 mm to 20 mm depending on the consumed fresh as well as cured in brine and seasons of operation, in the depth range of 55 -90 m. sun dried. It is also utilized as raw material to Decapterus spp. formed the most dominant group prepare fish meal 8. Since the prices of quality among the 20 species caught in the various cruises fish are sky rocketing, attention should be paid to conducted by the FORV Sagar Sampda 3. In 1976-85 the effective utilization of D. russelli. It is a and 1986-95 the increase in annual carangid landing commercially important fish in Kerala, Tamil Nadu, of India were to the tune of 59.1% and 67.3% Andhra Pradesh, Karnataka and Gujarat. Though the compared to their preceding decades and their average catch of D. russelli is poor in Mumbai, pricewise landings were 39,247 t and 1,44,164 tonnes 1. In the it is very remunerative. successive years the landings have decreased from Proper management strategy needs to be in place 1,96,868 t in 1995 to 1,21,863 t in 2006 4,5 . The same after ascertaining the present status of the species. trend has been seen in the annual landings of Investigations on Stock assessment studies of D. russelli in India which dropped from 1.03,063 t in D. russelli from east and west coasts of India has been 1995 to 39,409 t in 2006 4,5 . The landings from reported by few authors 19,23,24 . Age, growth and NALINI et al .: STOCK ASSESSMENT OF THE INDIAN SCAD 681

Table 1—Total marine landings and total scad landings (in tonnes) in Maharashtra from 1985-2008 4,5 (in tonnes) Year Total marine catch Total carangid landing Total scad landing % of scad to total % of scads to total marine landings carangid landings 1985 3,35,809 5,583 1,383 0.41 24.77 1986 3,15,218 11,491 2,319 0.74 20.18 1987 2,85,208 6,872 2,351 0.82 34.21 1988 3,15,244 13,868 4,390 1.39 31.66 1989 3,62,330 22,452 9,494 2.62 42.29 1990 3,45,724 14,215 8,768 2.54 61.68 1991 3,84,162 9,668 3,893 1.01 40.27 1992 3,27,695 11,311 5,947 1.81 52.58 1993 3,33,003 11,112 3,444 1.03 30.99 1994 3,23,828 17,477 3,554 1.10 20.34 1995 3,16,462 18,626 3,705 1.17 19.89 1996 3,39,148 9,526 2,188 0.65 22.97 1997 3,90,067 12,261 4,954 1.27 40.40 1998 4,15,741 8,326 352 0.08 4.23 1999 2,97,032 6,144 735 0.25 11.96 2000 3,68,222 7,947 1,122 0.30 14.12 2001 3,95,966 11,984 1,552 0.39 12.95 2002 4,49,599 13,847 1,088 0.24 7.86 2003 4,15,094 19,247 1,439 0.35 7.48 2004 3,50,712 12,548 1,584 0.45 12.62 2005 2,67,003 7,096 852 0.47 12.00 2006 3,34,451 7,155 858 0.44 11.99 2007 3,19,470 6,311 674 0.43 10.68 2008 3,58,746 6,241 660 0.39 10.58 mortality studies of D. russelli from Mumbai was presented by Jaiswar et al. 9 but so far no assessment of the stock of D. russelli from Mumbai waters has been carried out. Present study was taken up to examine the intensity of its exploitation and assesses the present status of the resource.

Materials and Methods Length frequency data was collected weekly from New Ferry Wharf, Sassoon Docks and Versova landing centre of Mumbai from Sept 2004 to May 2007. The percentage of D. russelli landed at New Ferry Wharf was 90 % and the remaining 10% was from Sassoon Dock and Versova landing centre. Fishing grounds of Mumbai have been depicted in Fig. 1. Weight of fish was measured to the nearest gm at the landing centre itself. Length was measured from the tip of the snout to the end of caudal fin (total length) to the nearest mm. Total catch of the species on the day of observation was noted. Weekly length frequency data collected for D. russelli were raised to the day’s catch and then to monthly catch and subsequently to the annual 10 catch by following the method of Sekharan . Monthly raised values were fed into FiSAT Figure 1—Fishing grounds of trawlers operated from New programme to analyze various parameters. To study Ferry Wharf 682 INDIAN J. MAR. SCI., VOL. 40, NO. 5, OCTOBER 2011

the growth parameters results from Gulland and Results and Discussion Holt plot 11 employing FiSAT was used. Longevity Age and growth was estimated from the equation t = 3/k 12 and max Data of size composition during the different also by inverse Bertalanffy’s equation. months for three years was pooled and is shown in Total mortality coefficient (Z) was estimated by 17 11 Table 2. Method of Bhattacharya which is contained length converted catch curve method and natural in the FiSAT software package was applied and mortality was calculated by Pauly’s empirical 13 subsequently the values of L ∞ and K were estimated equation , Fishing mortality rate was estimated by 11 by Gulland and Holt . The values ‘L ∞’ 277 mm and Z-M. The exploitation rate (U was estimated by the ‘K’ (1.237/year) thus obtained by Gulland and Holt 11 U = (F/Z) * (1- e –z) formula 14 and the exploitation 14 (Fig. 2) were considered for further calculations in ratio was estimated as E = F/Z . Length at first estimating population parameters. Present values are capture (L c50 ) was calculated by selection ogive method determined by applying probability of capture to the length frequency distribution. Relative yield per recruit (Y’/R) and biomass per recruit (B’/R) was calculated employing FiSAT package. The length structured Virtual Population Analysis (VPA) 15 of FiSAT was used to assess the fishing pressure on different length groups. Input parameters used were L∞ = 277 mm, K = 1.237/yr, M = 2.1, a = 0. 001922, and b = 3.29 obtained from the length-weight relationship. The terminal fishing mortality was assumed as 0.55 as D. russelli is a small sized fish with higher chances of being preyed upon and also appears to be slightly overexploited 9. Stock and potential were assessed by length based Thompson and Bell Predictive model 16 . Figure 2—Gulland and Holt Plot

Table 2—Table showing size composition during the different months Length range Sept Oct Nov Dec Jan Feb Mar April May June 30-39 1 40-49 1 50-59 10 60-69 5 70-79 4 80 - 89 1 33 90 - 99 5 2 29 100 - 109 2 29 12 2 66 1 110-119 58 32 2 3 34 120 - 129 2 3 41 35 33 20 28 4 8 130 - 139 4 5 10 32 88 76 51 18 11 140 - 149 7 17 32 37 71 73 92 66 16 1 150 - 159 18 43 55 44 127 105 129 136 63 8 160 - 169 84 98 56 29 64 160 122 100 136 7 170 - 179 70 116 116 64 40 134 198 159 165 11 180 - 189 44 50 136 168 64 96 313 156 549 15 190 - 199 21 38 93 190 74 79 423 138 1228 19 200 -209 22 14 57 157 42 20 206 64 757 31 210 - 219 17 10 44 82 14 2 96 22 239 41 220 - 229 1 14 34 11 2 30 8 48 12 230-239 1 2 7 1 43 240-249 1 3 250-259 3 2 260-269 2 1 1 NALINI et al .: STOCK ASSESSMENT OF THE INDIAN SCAD 683

within the range values observed by Mansor 18 and general range of M/K for was 1-2.5. The M/K very close to the estimates made by Manoj Kumar 19 ratio for D. russelli was calculated as 1.69 which falls 20 and Widodo . The t o estimated by VBGF plot within the suggested range. This also indicated that was– 0.3443 year. The growth in length of D. russelli the value of the estimated ‘M’ is reasonable. The is described following von Bertalanffy growth fishing mortality coefficient (F) was calculated by the equation as, relationship of F = Z-M and it was estimated as 4.56.

-1.237{t-(-0.34)} The exploitation rate (U) was calculated as 0.6838 Lt = 277[ 1-e ] and the Exploitation ratio (F/Z) as 0.6847. Estimates Using the von Bertalanffy’s growth formula of mortality parameters from this study are closer to (VBGF), the lengths attained by D. russelli were the work of Jaiswar et al .9 who studied the species 193 mm, 252 mm and 269 mm at the end of 1, 2 and from Mumbai waters indicating that this species still 3 years respectively indicating that the growth was continues to be mortality dominated. The variations rapid in the first year. The longevity was calculated as with the work of other authors may be due to different 2.42 years. The maximum length recorded during the L∞ and K values and also to the difference in location period of study was 261 mm and the corresponding and year of study. age was estimated as 2.30 years. Stock assessment 23 Mortality Using Beverton and Holt’s Method , the Total mortality coefficient (Z) was estimated as frequency, cumulative frequency and cumulative 6.66 and Natural mortality (M) as 2.1. The mortality percentages were calculated which gave the L c 50 parameters estimated by other authors is tabulated in (Length at which 50 % of the fish become vulnerable table 2. In this study, Z/K was found to be 5.38 which to gear) as 186.9 mm and t 50 was calculated as 0.9075 indicated that the stock of D. russelli is presently years. The probability of capture by trawl selection highly mortality dominated (>2) in Mumbai waters. analysis was estimated as 183.28 mm There was not The natural mortality coefficient (M) estimated by much difference in the L c 50 values obtained by both Pauly’s empirical formula 13 was 2.1. Natural mortality methods and trawl selection analysis being more (‘M’) may vary within the species in different areas as accurate the same was taken for calculation of relative it is dependent on density of predators and yield and yield – isopleth. competitors whose abundance is influenced by fishing The input data for the knife-edge selection was 22 activities . D. russelli being a small fish would be Lc50 /L ∞ as 0.613718 and M/K as 1.69. The knife-edge preyed upon by the predators of small/mediuim size selection indicated that at E 0.1 the Y/R is 0.007869 g. in their juvenile stage and by larger predators during wheras E 0.5 , Y/R is 0.03310 g. However at E max of 1.0 their adulthood . This being a pelagic fish, the mean the Y/R is 0.464 g at which the biomass stood at zero. sea surface temperature of 28.2°C also fits for a The present E as obtained by F/Z was found to be pelagic fish like D. russelli better. Thus, the M 0.68. The selection ogive (Fig 3) shows maximum estimated by Pauly 13 was taken for further Y/R at E of 0.606. The yield isopleth diagram shows calculations. Beverton and Holt 22 suggested that the that eumetric fishing can be done at E = 0.55 and

Figure 3—Selection ogive for D. russelli 684 INDIAN J. MAR. SCI., VOL. 40, NO. 5, OCTOBER 2011

Lc/L ∞ = 0.45 (Fig 4) The length cohort analysis economic yield in terms of value is obtained at shows that the F for this species has shown an F- factor of 1.2. The net revenue generation for increasing trend for the large size groups. The chief the yield showed a decline from the f-factor of 1.30 reason for this may be that for the smaller size groups Table 4. Though there is no decline in the catch by the death is mainly due to natural causes and smaller Table 4—Thompson and Bell Yield - Stock Prediction size groups are discarded and hence are not for D. russelli represented in the fishing ground. The Thompson and f - factor Yield (10 Λ 7) Biomass (10 Λ 7) Value (10 Λ 8) 16 Bell predictive model (Table 3 and Fig 5) shows that 0.00 0.0000000 203.600082 0.000000 at the present level of fishing (F=1.0) the biomass has 0.10 37.1874695 174.560562 47.345753 declined to 79.39 t as compared to a virgin biomass of 0.20 64.3727036 152.249268 80.695450 203.6 t. At the present level of fishing the yield is 134 0.30 84.3255844 134.921463 104.090530 t which is 38% of SSB. The predictive model also 0.40 99.0225143 121.311874 120.386971 0.50 109.8806381 110.497475 131.611115 describes the results of increase in the efforts and 0.60 117.9211502 101.800507 139.205780 proportionate increase in the catches. The maximum 0.70 123.8834839 94.720444 144.201782 0.80 128.3056183 88.885254 147.337738 0.90 131.5807953 84.016777 149.144211 1.00 133.9976501 79.905533 150.003082 1.10 135.7690582 76.392929 150.189850 1.20 137.0529022 73.358040 149.903336 1.30 137.9664459 70.707977 149.287201 1.40 138.5706177 68.370979 148.402145 1.50 138.9709167 66.291069 147.388870 1.60 139.2312469 64.424400 146.318573 1.70 139.3589325 62.736286 145.184509 1.80 139.3835449 61.199039 144.015762 1.90 139.3279572 59.790478 142.833221 2.00 139.1839142 58.492596 141.610519 2.10 139.0254517 57.290688 140.454544 2.20 138.8254242 56.172684 139.312164

Figure 4—Yield isopleths diagram for D. russelli 2.30 138.5730591 55.128513 138.159500 2.40 138.3230133 54.149773 137.071869 2.50 138.0504608 53.229401 136.006119 2.60 137.7606049 52.361359 134.964798 2.70 137.4573822 51.540493 133.949249 2.80 137.1440735 50.762375 132.960266 2.90 137.8231354 50.023144 131.997925 3.00 136.4966125 49.319427 131.061981 3.10 136.1661530 48.648308 130.151978 3.20 135.8198090 48.007145 129.247452 3.30 135.4910278 47.393650 128.396149 3.40 135.1592712 46.805756 127.565201 3.50 135.8257904 46.241631 126.754562 3.60 134.4915928 45.699608 125.964081 3.70 134.1575928 45.178200 125.193428 3.80 133.8243561 44.676067 124.442177 3.90 133.4798737 44.191967 123.692192 Figure 5—Thompson and Bell analysis for D. russelli 4.00 133.1576233 43.724789 122.989273 Table 3—Mortality parameters given by other workers from India

Location/ Author L∞ K Z M F U E Kakinada, East coast of India 21 232.3 1.08 6.65 1.90 4.75 0.70 0.71 N.W. Coast of India Jaiswar et al .1 (40 mm – 220 mm) 240 1.42 7.75 2.63 5.1 0.65 0.66 East coast of India/ Reuben et al .20 221 0.71 2.83 1.35 1.48 - 0.52 N.W. Coast of India/ Reuben et al 20 299 0.45 2.85 0.83 2.02 - 0.71 S.W. Coast of India/ Reuben et al. 20 248 0.78 3.88 1.26 2.62 - 0.68 Malabar S.W. coast of India 16 (65 mm – 242 mm) 271.2 1.22 3.79 2.08 1.71 - 0.49 Present investigations (34 mm - 261 mm) 277 1.237 6.66 2.1 4.56 0.6838 0.6847 NALINI et al .: STOCK ASSESSMENT OF THE INDIAN SCAD 685

increasing the effort, the returns are not remunerative. 2 Jadhav D J, Chavan B B, Sawanth A D, Josekutty C J, Moreover, making any suggestions on change of Sarang J D & Thakurdas, Unusual landing of Alepes djeddaba (Forskal) and Megalaspis cordyla (Linnaeus) by efforts is futile as this is landed as a by-catch of purse seiners at New Ferry Wharf, Mumbai. Mar. fish. Infor. shrimp trawl. Tech & Extn , 179 (2004) 17. In present study, the knife-edge procedure gave 3 Sivakami S, Nair P N R, Jayaprakash A A, Kasim M, E of 1.00, whereas the selection ogive procedure Yohannan T M, Sivadas M, Said Koya K P & Seetha P K, max Distribution and abundance of carangids along the EEZ of gave E max of 0.606. The E value calculated using F/Z India, In: Proc. of the Second Workshop on Scientific Results is 0.68. The basic assumption of knife-edge selection of FORV Sagar Sampada , edited by V. K. Pillai, S. A. H. is that fishes below the length at first capture will not Abidi, V. Ravindran, K. K. Balachandran & V. V. Agadi, be retained by the net while selection ogive method (Department of Ocean Development, New Delhi) 1996, pp. 347-361. assumes that probability of capture (retention) of any 4 CMFRI, Annual reports . (Central Marine Fisheries Research fish is function of its length. In practice knife edge Institute, Cochin) 1985-2008. selection rarely occurs therefore E of 0.606 by 5 CMFRI, Marine fish landings in India 1985- 2004 estimates selection ogive appears to be more reasonable. The and trends. ( Central Marine Fisheries Research Institute, yield isopleth diagram indicates the L /L values Cochin) 2005, pp. 120. c ∞ 6 Poojary N, Studies on the Biology and Stock Assessment of (mesh size) on y-axis, the exploitation ratio on the Decapterus russelli (Ruppell 1830) from Mumbai waters. X-axis and the yield. The diagram shows at E of 0.55 Ph.D. Thesis, (University of Mumbai), 2009, pp. 277. and L c/L ∞ of 0.45 the optimum yield could be 7 Tamhane A V, On Occurrence and biology of Indian Scad, obtained. The present E = 0.68 which is slightly high. Decapterus russelli (Ruppell, 1830) off the North West coast of India, M.Sc. thesis (University of Mumbai), 1996, pp.150. It is also observed that the present L c is 183 mm and if 8 Bal D V and Rao K V, Marine fisheries of India, (Tata Mc- at Lc/L ∞ of 0.45 the L c would be 124 mm which is far Graw-Hill Publishing Company Limited, New Delhi), less than the length at maturity of 156 mm 6. 1984, pp. 212. 9 Jaiswar A K, Chakraborty S K, and Swamy R P, Studies on Conclusion the age, growth and mortality rates of Indian scad Decapterus russelli (Ruppell) from Mumbai waters. Fish. The rate of growth of D. russelli is rapid in the first Res . 53:3(2001) 303-308. year. Stock of D. russelli is presently mortality 10 Sekharan K V, On oil sardine fishery of the Calicut area dominated in Mumbai waters. However, fishing during the year 1955-56 to 1958-59. Indian J. Fish ., 9A: mortality has decreased in comparison to the previous 2 (1962) 679-700. 11 Gulland J A & Holt S J, Estimation of growth parameters for reports. Probability of capture for trawl selection was data at unequal time intervals. J. Cons. CIEM ., 25(1) 1959, derived as 183 mm. Though E of 0.55 and Lc /L ∞ 47-49. value of 0.45 are ideal for fishing, mean length at first 12 Pauly D, Some simple methods for the assessment of tropical capture to be maintained at present level of 183 mm fish stocks. FAO Fish. Tech. Pap ., 234(1983) pp. 52 13 Pauly D, On the interrelationships between natural mortality, for long term sustainable yield. There is no decline in growth parameters and mean environmental temperature in the catches even if efforts are increased to 1.8. 175 fish stocks. J. Cons. CIEM , 39:2(1980) 175-192. However, F-factor of 1.8 is not advisable as the catch 14 Beverton R J H & S J Holt, On the dynamics of exploited is not remunerative. Fishing may be continued at the fish populations. Fish Invest. Minist. Agric. Fish ., Food G. B. present level. It must be emphasized that compilation (2 sea fish) 1957, 19: pp. 533. 15 Jones R, Assessing the effects of changes in exploitation of such species study may ultimately serve as an input pattern using length composition data (with notes on for multispecies approach which will immensely VPA and cohort analysis). FAO Fish.Tech.Pap., 256 benefit the management of the resources. (1984) pp.118.

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