Indian Journal of Geo Marine Sciences Vol. 40(5), October 2011, pp.680-686 Stock assessment of the Indian scad, Decapterus russelli (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 fish 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, Alepes 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 .