rndianJournale^Fisheries39 (\2) •• A2~64, March, June 1992
Stock assessment of silverbellies of India with particular reference to Andhra Pradesh and Tamil Nadu
V SRIRAMACHANDRA MURTY', M SR]NATH^ P UVINGSTON', Y APPANNA SASTRY* and S SRINIVASARENGAN'
Central Marine Fisheries Research Institute, Cochin, Kerala 682 014
ABSTRACT
Along Indian coasts, the silveifoellies are exploited by trawl and aitisanal gears but bulk of the landings are obtained by tiawlt which operate up to SO m depth. During 1979-83, the estimated annual average silvetbelly landings were 69 000 tonnes, whereas during 1984-88 these were 62 000 tonnes. Maximum silveibelly landings were obtained in Tamil Nadu which contributed 70.5% ol total all-India silverbelly landings followed by Andhra Pradesh (9%), Kerala (8.4%), Kamataka (6%) and other sutes (6.1%). Out of 20 species of silveibellies, known to occur in the seas around India, LeiogiuUhus bindus and Secutor insidiator were most dominant along Andhra Pradesh and northern Tamil Nadu coasts, together contributing to 64% and SS% respectively of tilveibeUy landings. Along southern Tamil Nadu, L. joiusi and L. dussumeri were most dominant together forming about 60% of silvetbelly catch in the region. The available information on the biology of different species from several localities along Indian coast was reviewed.Parameter s of growth and mortality of dominant species were estimated. Stock assessment was made separately for L. bindus and 5. insidiator and then mixed fisheriesassessmen t made for these two species combined from Andhra Pradesh and itonhem Tamil Nadu. From southern Tamil Nadu coast, stock assessment was made forL.jonesi and L.dussumieri separately and combined. Along Andhra Pradesh coast, the effoit level was found greater than the'one yielding MSY in the existing fishing grounds. In noitheiti Tamil Nadu there was scope to increase the fishing effort to get MSY. In southern Tamil Nadu yield can be increased by about 1.5% through increasing the effort by 40%. The assessment of yield of Z.. bindus and 5. insidiator in relation to cod end mesh size of trawl along Andhra Pradesh showed the need to reduce the cod end mesh size by about 40%. In northern Tamil Nadu also more or less similar situation existed. In southern Tamil Nadu, the MSY corresponded to the existing cod end mesh size and, therefore, did not warrant any change in the latter.
The fishes of the family Leiognathidae, considered as trash fish at certain places, the popularly called as silverbellies or ponyfishes, quantities landed make them important both are among the important demersal fishes con- from fishery and management point of view, tributing to the fisheries along Indo-west Silverbellies are known to be more abundant Pacific region. Though these are small and are in shallower regions in the sea (James 1973; Pauly 1977a, b; Filial and Dorairaj 1985; Present address: 'Senior Sdentisi. ^Scientist Sudarsan et al. 1988; Sivaprakasam et al. ^'"SSdection Grade), Karwar Researeh Centre 1991) up tO abOUt 40 m depth though they aie ofCMFRi, Post Box No. 5. Karwar. North Kanara, available in depthsof 100-150 malso(Sudar- Kamataka. san et al. 1988). These fishes are known to ^Scientist (Selection Grade). Visakhapatnam Res- undertake diumal vcrUcal migrations staying eareh Centre of CMFRI, Andhra University P O, . .L i. .. j • j .• j Visakhapamam 530 003. ' at the bottom dunng day ume and moving up *SdenUst (S-2), Madras Research Centre of CMFRI, to Surface and subsurface waters during nights 68/1,4th Floor, Greams Road. Madras 600 006. (Venkatraman and Badrudeen 1974, Murty
42 March, June 1992] STOCK ASSESSMENT OF SILVERBELUES
1986b). A lot of work has been done on groupwise/specicswise landings made by the various aspects of these fishes as evidenced by Central Marine Fisheries Research Institute two bibliographies exclusively on these fishes for the years 1984-88 were used for the (PaulyandPauly 1981, James era/. 1992). In present study. Further, the estimates of catch India an estimated 53 876 tonnes of silvcrbel- for each maritime state pertaining to the lics landed during 1990 (Anonymous 1991) period 1979-88 were also used. whiQh formed 5.7% of the total demersal fish Detailed data on effort and catch were and 2.5% of total marine fish landings. collected for 18 days in a month and on Total 20 species of silverbcUies are species composition, length composition and known from India and a lot of work on dis biology of dominant species for 4-8 days tribution, taxonomy, biology and fishery has every month from the trawl landing centres at been done (Arora 1952; Balan 1967; James, Visakhapalnam, Kakinada, Madras and Man- 1967, 1969. 1973, 1975. 1986; Pillai 1972; dapam. These data of 1984-88 formed the Vcnkatraman and Badrudccn 1974; James major input for this study. and Badrudccn 1975.1981.1986,1991; Rani For stock assessment. Leiognathus bin- Singh and Talwar 1978a, 1978b; Annam and dus and Secular insidialor from Andhra Dharmaraja 1981; Kurup and Samuel 1983; Pradesh and northern Tamil l4adu-Pon- MiJrty 1983, 1991; Jayabalan 1985. 1986, dichcrry; and L.jonesi and L. dussumieri from 1988a, 1988b; Jayabalan and Ramamoorlhy southern Tamil Nadu were selected because 1985a. 1985b. 1985c, 1986; Pillai and these species were most dominant in these Dorairaj 1985; Vivckanandan and Krish- regions and determined the success or namooFlhy 1985; James et al. 1987; Reuben failure of silverbclly fishery in the respective et al. 1989 and Srinalh 1989). Population areas. dynamics of dominant species from particular Species composition and length frequen localities have ..also been studied (Vcnkat cy distribution: At each of the above four raman era/. 1981;Murty 1985.1986a.l986b. trawl landing cenu-cs. samples were collected 1991 and Kiu-lhikeyan et al. 1989). An allempt from different boats and brought to the is made here to study tlic dynamics of the laboratory for taking data on species composi exploited silverbclly resources making u&c of tion, length composition and biology. Total data obtained during 1984-88 on dominant length was considered for length frequency spccicsof the group from Andhra Pradesh and and other studies. The data on species com Tamil Nadu coasts. The results arc presented position and ksngth composition collected on inihis paper. each observation day were first weighted respectively to the estimated total catch of the MATI:RIAI.S AND Mirriions group and species obtained on that day and Data obliiincd from trawl landings only such estimates in a month were pooled and were considered. Bulk of the silverbclly land then raised to the estimated catch of the month ings in India were obtained from Tamil Nadu- as per Alagaraja (1984). The monthly es Pondichcrry and Andlira Pradesh and con timates were pooled to get quarterly and an siderable data were generated from this nual estimates. To obtain estimates of total region. The stock assessment in the present catch (weight) of each species as well as catch study was, therefore, restricted to this region. (numbers) at length also of each species, the The estimates of districiwisc and gear- diita oblained at the observation centres were wise effort and di.slrictwisc, gearwisc and sullably weighted to get estimates for each
43 UmrYEFAL [Vol. Sf. No. 1.2
A - Leiagnaihm biruMis. II. L. jonesL. C\ L. di4SSMmieri. I). Secuior imsuilalGr..
44 Maidi, June 1992] STOCK ASSESSMENT OF SILVERBELUES
State. As the data on production from each Estimation of von Bertalanffy growth district were available in the form of quarterly parameters: The parameters of growth in estimates, the monthly estimates from each length were estimated following the ELEFAN observation centre pooled for each quarter method (Pauly and David 1981, Gayanilo et (January-March: I quarter, April-June: II al. 1988); the estimates were made using the quarter. July-Septemben III quarter. Oc monthly length frequency distribution of tober-December: IV quarter) were weighted catch of the species, separately from each of to get quarterly estimates. F(x this purpose, the four centres. In the data of each year, the data obtained at Visakhapatnam were different starting lengths and 'samples' were raised to those obtained in the northern dis used and best fit values were taken. Thus, 2-4 tricts of Srikakulam, Vijayanagaram and sets of growth parameters in each year from Visakhapatnam together, and those from each centre were obtained for each species. Of Kakinada to the data obtained in the remaining all such estimates in all the five years, the coastal districts (East Godavary, West smallest and largest LK values and their as Godavary. Krishna. Guntur. Prakasam and sociated K values were selected from each Nellore) of Andhra Pradesh (Fig. 1). The centre for all further studies. The results ob former is referred as northern Andhra Pradesh tained by using the largest L. and its as and the latter as southern Andhra Pradesh. In sociated K were referred to as having been Tamil Nadu-Pondicherry (Fig. 2), the data obtained by using 'higher parameters' and obtained at Madras were weighted to tliose of those obtained by using the smallest LK and Madras, Chengalpattu, South Arcot and Pon- its associated K by 'lower parameters'. dicherry together and those obtained at Man- Mortality rates: The estimates of in dapam (Mandapam. Pamban and Rames- stantaneous total mortality rate (Z) were made waram) to the ones from the southern coastal using length-converted catch curve method districts of Thanjavur, Pudukkottai, Ramana- (Pauly 1982) using the data of all the fiveyear s thapuram (presently Muthuramalingam and pooled and the LFSA package of Sparre Ramanathapuram). Tirunelveli (presently
Chidambaranar and Kattabomman) and Kopasokud) Kanyakumari. These two areas arc referred to stAapoiem as northern Tamil Nadu (A in Fig.2) and ikkallopeta Bhtmunlpatnam southern Tamil Nadu (B in Fig. 2) respective Visakhapatnam ly. Stock assessment was done separately with these sets of data. For Andhra Pradesh, the two estimates were pooled to get estimates for the state because thei species dealt with from the two regions were the same. For Tamil Nadu- Pondicherry, however, the species dealt with were not same from the two centres as the dominant species were different in the two regions. The estimates obtained, therefore, were treated separately. Fig. 1. Map of coastal districts of Andhra Pradesh. 1, Biology: The results of detailed studies Srikakulam; 2, Vijayanagaram; 3, Visakhapat made on aspects of biology of particular nam; 4, East Godavary; 5, West Godavary; 6, species were taken from published work. Krishna; 7, Guntur, 8, Prakasam; 9, Nellore.
45 MURTYFf/U,. [Vol. 39, No. 1,2
Tamil Nadu, south Tamil Nadu) in each year were pooled for the five years (1984-88) and average annual values obtained; these were used as input for the study. Yield and biomass at different effort levels were estimated by the length-converted Thompson and Bell (1934) analysis (Sparre 1985, Murty 1989) and the programme MIXFISH of LFSA package of Sparre (1987). In each species, the yield and biomass at different effort levels were first estimated separately using the statistics ob tained with the help of 'lower' and 'higher' growth parameters. The average of the values corresponding to each effort level were then obtained and were considered in this study. The assessment of different species was Pig. 2. Map of coastal districts of Tamil Nadu and done~separately and combined from each Pondicherry. 1, Chcngalpatlu and Madras; 2, region of Andhra Pradesh and Tamil Nadu. South Arcot; 3, Pondicherry (U.T.); 4, Than- Yield and cod end mesh size: Trawl data javur, 5, PudukkoUai; 6, Muthuramalingam; 7, alone were considered for this purpose. For Ramanathapuram; 8, Chidambaranar, 9, Kat- labomman; 10, Kanyakumari. studying the effects of changes in cod end mesh size on the yield, the following proce (1987). The natural mortality rate (M) was dure was adopted using thedata of each region estimated using the empirical formula of in Andhra Pradesh and Tamil Nadu- Pauly (1980) and then the fishing mortality (F) Pondicherry: as Z-M. For each species from each centre a. For each species the present tc values estimates of mortality rates were made (corresponding to Lc values as stated separately using both the sets of growth above) were taken. These values in each parameters. species were decreased and increased by Lengths at recruitment and first capture: the same factor (as 10%, 20% The mid point of the smallest length group in . 150% 200% of present tc). the catch during the five-year period was b. Using these resultant tc values, the taken as length at recruitment (L,). The present F and other required parameter lengths corresponding to the first values in tlie values, the Beverton-Holt (1957) yield- descending limbs of the length-converted per-recruit (Yw/R) analysis was made. catch curves (with bolh the sets of growth c. Taking the value of yield-pcr-recruit parameters separately) were taken as lengths (Yw/R) at current F and tc and the value at first capture (Lc). of annual average yield of the species Yield and biomass: The data on catch during 1984-88, the recruitment in num (numbers) at length of each species at each bers (R = Y + Y/R) was estimated. centre weighted to total catch of the species of d. The Yw/R at each tc in each species as the rcgion(north Andhra, south Andhra, north obtained at 'b' above, was weighted by
46 March, June 1992] STOCK ASSESSMENT OF SILVERBELLffiS
the value of R obtained in 'c' above to were estimated as 49 000 tonnes and 54 OCX) obtain values of yield in weight at dif tonnes respectively (Anonymous 1991). ferent tc values (i.e. percentage of present Catches in different states: The silverbel tc). ly landings in different maritime states and e. In each species, the yield corresponding union territories during the decade 1979-88 to different tc levels was first estimated showed that maximum landings were ob separately using the statistics obtained tained in Tamil Nadu (70.5%) followed by with 'lower' and 'higher' growth Andhra Pradesh (9%), Kerala (8.4%), Kar- parameters and averages of yield cor nataka (6%) and others. The maximum es responding to each tc level were then timated landings in any year were about obtained and used for this study. 62 000 tonnes in Tamil Nadu in 1983, fol f. The values of yield at different tc levels lowed by 11500 tonnes in Karnataka in 1986, for different species in each region were 9 900 tonnes in Andhra Pradesh in 1981, and pooled to get the combined yicld-mesh others (Table 1). Thus the southeast and south curves for the species considered. west coasts contribute to over 90% of silver The results pertaining to the two belly landings in India. regions in Andhra Pradesh were pooled Districtwise landings: In Andhra Pradesh and those pertaining to northern Tamil (Fig. 4.A), maximum silverbelly production Nadu-Pondichcrry and southern Tamil Nadu was obtained in Srikakulam district with an were treated separately for reasons stated nual average of 2 100 tonnes during 1986-88 earlier. forming 35% of total si/verbclly landings in RESULTS Andhra Pradesh. This was followed by East Godavary (1645 tonnes, 27.7%), Ncllore (992 Fishery tonnes, 16.7%), Visakhapatnam (709 tonnes, Along Indian coasts, the silverbcUies are 11.9%),Prakasam (234 tonnes, 3.9%),Guntur exploited by trawl and a variety of artisanal (170 tonnes, 2.9%), Vijayanagaram (51 ton gears such as shore seine, boat seine, gillnet, nes, 0:9%), West Godavary (23 tonnes, 0.4%) etc. However, these fishes are caught in large quantities by trawls which are operated in shallower regions up to 50 m depth. AlHndia silverbelly catch: The landings in India during 1979-88 (Fig. 3) showed that they ranged from about 53 000 tonnes (1985) to 92 000 tonnes (1983). During the firsthal f of 1979-88 period, the average annual land ings were estimated at 69 000 tonnes whereas during the second half of this period the same was 62 (XX) tonnes. Though the fluctuations in the annual landings were not very large (ex cept 1983), with the annual average during 1979-88 at 69 000 tonnes, the landings 1979 1981 1983 1985 1987 showed a declining trend. In fact, in 1989 and Fig. 3. Estimated annual landings of silverbellies in 1990, the annual silverbelly landings in India India during 1979-1988.
47 MVRTY ETAL. [Vol 39. No. 1.2
and Krishna (20 tonnes, 0.3%) districts. In I Srikakulam and Vijayanagaram there was no trawling and maximum silverbelly production was obtained by boat seine followed by shore »n r^ »n ^ 1—' rl CO ^ •3 I 00 00 TT '
NO'* iTfio
» o — M to t m >0 r- 00 Trawl fishery: In Andhra Pradesh, com I ^N & ^K ^' ^ mercial trawlers of three different sizes rang-
48 March, June 1992] STOCK ASSESSMENT OF SILVERBELLIES
180-
^ 96
- 12. I
Q LJ OC Z Z O I S 5 2 iS ^ ? S Fig. 4. Average distiiawise landings of sUvetfaelliei during 1986-88. A. In Andhra Pradesh (SKK: Srikakulam, VU: Vijayanagaram, VIS: Visakhapamam, EGD: East Godavaiy; WGD: West Godavaiy, KRI: Krishna, GUN: Guntur, PRA: Prakasam, and NEL: Nellore district). B. In Tamil Nadu-Pondicheny [MAD: Madras, CHE: Chengalpattu, SAR: South Arcot, PON: Pondicheny, TAN: TTianjavur, PUD: Pudukkotui, RAM: Ramanathapuram (presently Mulhuramalingam and Ramanathapuram), TNL: Tinmelveli (presently Chidambaranar and Kattaboniman), and KKI: Kanyakumari districts].
ing from 10 to 11.4 m OAL operated in the mostly conducted during day time up to depth range 5-50 m during greater part of the depths of about 50 m. In the southern districts year and during November-February in particularly along Ramanathapuram coast dq)ths extending up to 80 m. Most of the boats both night and day fishing was carried out returned the same day but some conducted regularly up to depths of about 40 m. In this fishing continuously for 2-4 days . Shrimp region silverbelly was used for human con trawl with cod end mesh size of 15-20 mm sumption and a small quantity was reduced to was operated by all these boats. Silverbelly fish meal. was considered as a 'trash' fish and used most Seasonal variation in silverbelly land ly in poultry feed. ings: The quarterly catch estimates (as per In Tamil Nadu-Pondicherry, the trawlers centage of each year) from the northern (9.8-11.0 m OAL) operated shrimp trawl with Andhra Pradesh, southern Andhra Pradesh, a cod end mesh size ranging from 15 to 25 northern Tamil Nadu and southern Tamil mm. In the northern districts, fishing was Nadu during 1985-88 are shown in Fig. 5.
49 MVRViETAL (VcL39,Nal,2
and northern Tamil Nadu also, but in small 'quantities. L.jonesii however, is known from the southern Tamil Nadu coast only. Biology Various aspects of biology of different species were studied from different localities along Andhra Pradesh and Tamil Nadu and on one species (jLebgnathusbindus)tKm Kerala. The results are briefly given below for each Fig. S. Seasonal (quarterly) variations in catches of sil- species. verbcllics. Lebgnathus bindus: According to Balan (1967), this fish spawns off Calicut in relative There were year to year variations in periods ly deeper waters during December-Febniary. of peak landings in the four regions. However, The length at first maturity was estimated as the second quarter was the peak period in 87 mm and fecundity as ranging from 4 950 northern Andhra Pradesh, first quarter in to 7 735 in fisheso f the length range 98-114 southern Andhra Pradesh and third or fourth mm. Copepods were the most dominant food quarter in both the regions of Tamil Nadu. item followed by polychaetes, cladocerans, Species composition: Out of 20 species of larval bivalves and larval crustanceans; silverbcUies known to occur in the Indian seas phytoplankton occurred in stomachs frequent (James and Badrudeen 1991) most of them ly during monsoon period. occur in varying proportions in the Palk Bay From Kakinada, Murty (1983) reported and Gulf of Mannar along southern Tamil that this species is a fractional spawner Nadu coast. Off^he coasts of Andhra Pradesh releasing the ova in at least two spawning and northern Tamil Nadu, 9-12 species con acts during the course pf one year, this tribute to the fishery. Along Andhra Pradesh species spawns almost throughout the year coast, Leiognalhus bindus was the most with a peak during December-February. The dominant species forming 40% of silverbelly length at first maturity was estimated to be catch followed by Secular insidiator (24%); 80 mm. all other species together formed the rest According to James and Badrudeen (36%). Along northern Tamil Nadu coast also (1986) the spawning is continuous in batches these two species were most dominant over prolonged period along southeast coast together forming about 55% of silverbelly of India. catch; among these two, 5. insidiator was This species exhibits sexual dimorphism. more abundant. These two species occurred The males have a black spot under the pectoral along southern Tamil Nadu coast also but in negligible quantities. In this arcaL.jonesi was fin near its base which is absent in females the most dominant species forming 44% of (Jayabalan and Ramamoorthi 198Sa). silverbelly catch. The other important species Leiognathus dussumieri: According to was L. dussumieri which formed about 15% James and Badrudeen (1981), this species of silverbelly catch followed by other releases the ova in batches during shorter species. L. dussumieri occurred along Andhra periods and spawns in the Gulf of Mannar during April-May and November-December.
50 Much. June 1992] STOCK ASSESSMENT OF SILVERBELLIES
The length at first maturity was estimated at and between fecundity and fish weight as 78 mm in males and 83 mm in females. The Log F = 0.8056 -t- 2.3838 log W. maximum length recorded was 161 mm. According to James and Badrudeen According to Pillai (1972), this species (1986), this species spawns in batches in quick spawns off Tuticorin during prolonged period. succession over a short poiod. The fecundity was .estimated to range from Secutor insidiator: I^Ilai (1972) estimated the 5 400 to 32 500 with an av^age of 14 300. fecundity from Gulf of Mannar as ranging Leiognathus brevirostris: In the Palk Bay from about 7 250 to 15 700 with an average of and Gulf of Mannar this species spawns 10620. throughout the year with peaks during May- According to Jayabalan and Ramamoor- June and October-November (James and thi (1985b), this species spawns during Badrudeen 1975). The lengths at first maturity March-April and July-November in the sea were estimated as 68 mm in males and 63 mm off Porto Novo. The length at first maturity in in females and fecundity 3 650-16 240 in males was estimated as 79-82.5 mm and in fishes of the length 106-132 mm. The maxi females as 81-82.5 mm. The relation between mum recorded length was 142 mm. Diatoms, fecundity and total length was determined as: copcpods, Lucifer, nematodes and poly- Log F =-5.2479+ 4.50 log L chaetes were important food items. and between fecundity and total weight as: Leiognathus jonesi: James (1986) gave a detailed account of the biology of this species Log F = 2.3155 -f 1.3806 log W. from Palk Bay and Gulf of Mannar. It was Murty (1991) reporting on the biology of concluded that spawning takes pl^ce S, insidiator from Kakinada stated that the throughout the year with individual fish spawning is throughout the year with a peak spawning at least twice in a year, the during January-March. There was predomi prolonged spawning period was also indicated nance of males up to 87 mm group and of by the occurrence of smaller fisho f the length females above this length group. The maxi range 14-39 mm round the year. Length at mum length in the fishery was 117 mm and first maturity was determined at 70 mm in length at first maturity of females was es males and 75 mm in females. Fecundity was timated as 90 mm. estimated to range from about 700 to 39 800 Gazza minuta: Pillai (1972) estimated the in fisheso f the fork length range 65-104 mm. fecundity as ranging from about 7 950 to Maximum length recorded was 152 mm. The 28 430 with an average of 13 530 in the Gulf most important food items were Plewosigma, of Mannar. Triceratium, Coscinodiscus, nematodes, From Porto Novo, Jayabalan (1988b) copcpods and foraminifcrans. determined the spawning period as August- Leiognathus splendens: From Porto February. The length at first maturity in males Novo, Jayabalan (1986) reported that spawn was estimated as 99 mm and in females as 102 ing takes place ahnost throughout the year mm. Fecundity was estimated as ranging from with two peaks during April-May and Oc about 11 650 to 26 750 in 15 fishes of the tober-December. Length at first maturity was length range 110-114 mm. estimated as 89-90 mm in males and 89-94 The results, therefore, show that silver- mm in females. The relationship between bellies are fractional spawners spawning fecundity and total length was determined as: throughout the year with one or two peaks or Log F = ^7.4897 + 6.6970 log L over longer durations each year; the estimates
51 MmYETAL [VaL39.Na.l,2
Laiognathus bindus, Visakhapatnam 1987 Stock assessment Growth parameters: The smallest and largest L^ values and their associated K values of the four species under study along with the corresponding Phi values (Paidy and Minuo 1984) are shown in Table 2; the cw- respcNiding length frequency (restructure(0 data with growth curves are shown in figures 6-9. In L. bindus (Table 2). the estimated Leiognathus bindus, Madras 120:
120
E Secutor insidiator, Visakhapatnam 1988
B 100:,
S 60
Fig. 6. Reiuuctured length frequency data 20- (ELEFAN1) and growth curvei ot Ltiogiialhia bindus. Viiakhapatnam 1987: U. = 151 mm. tC ^ 0.95 per year, SS=9. SL=65 mms Vifakhapat~ S. insidiator, Visakhapatnam 1987 nam 1987: L^ = 163 mm, KsO.95 per year, 1O0' SS=7, SD=45 mm; Kakinada 1988: L«=154 mm, K=0.77 per year, SS=9, SL=30 mm} 60 Kakinada 1988: U.=16S mm, K=0.70 per year, SS=10,«L=100 mm. 20
of length at first maturity are within 63-102 -JLl.2 52 Much. Jime 1992] STOCK ASSESSMENT W Sn^VERBELUES Secutor inskialor, Kakinada 1987 lier by Murty (1986a) wereclosa* to the values of this study but those estimated fiom Calicut 100 "" t (Pauly and David 1981), Samar sea (Silvestre , 1986) and Java sea (Dwiponggo et al., 1986) 50- [^ were different the values of LK were much smaller (Tables 2 and 3). O-I In LJoned (table 2), the L« values were S. insidiator, Kakinada 1988 slightly larger than Lniax known. While the Leiognathus yonesi, Rameswaram 1988 120 60' OJ r^-T L. jonesi, Ramaswaram 1984 120- 60 OJ r L dussumieri, Pamban 1984 140 1 ] jT 70 ^41 \ IM^II Ills IJi 1 ' 1 ' r-"—1 r l_pj r^"f Fig. 8. Reitfuctured length fieqaency data (ELEFAN 1) and growth curvet of Secutor in L. dussumieri, Parrban 1986 sidiator. Kakinada 1987: U = 12S mm. K = 140 1.06 per year, SS s 1, SL = 8S nun; Kakinada 1988: L_ = 130 mm, K = 0.85 per year, SS = 7, SL s 65 mm; Madru 1986: U, = 125.5 mm, K 70 . = 1.22[ffcryear, SS = 9. SL = 80mm: Madrai 1987: U.= 138 mm. K = 1.30 per year. SS = 4, SL - 65 mm. ITlTiTriTnT Fig. 9. Reitructured length frequency data values of L. and K in both the sets ranged (ELEFAN 1) and growth curvei of Leiognathus fiom 151 mm to 167 mm and from 0.70 to 0.% jontai. Rameiwaram 1988: L_= 155 mm, respectively. The maximum known length of K=0.70 per year, SS=3, SL=SO mm; Runes- this species was 1S5 mm (Anonymous 1977) waram 1984: L«= 160 mm, K=0.6 per year, SS=1. SL=70 mm. Leiognathus dussumieri. from Madias. The estimated values within Pamban 1984: U. = 162 mm, K=1.2 per year, each set (lower or higher) were found to be SS=7, SL=85 mm; Pamban 1986: U= 175 close to each other. The values estimated ear mm, K=0.80 per year, SS=:7, SL=60 mm. 53 Table 2. Estimated values of growth panmeters, mortality rales, lengths and ages at enliy md first capture of different species of silveibelly as used in the present study (the ^ Values are also shown) Species Locality K^ Loga Logb U. K Z M F «r •c M/K (phi) Lower L^ and related K and other parameters Leiognalhus Visakhapamam 130 -4.77709 2.96182 151 0.95 4.14 2.05 2.09 0.087 0.275 2.34 116 bmdus Kakiiuda 142 -4.77709 2.96182 154 0.77 5.26 1.78 3.48 0.152 0.412 T26 131 Madras 155 -4.77709 2.96182 153 0.90 5.22 1.98 3.24 0.172 1.022 232 2.20 L.jonesi Rameswaram 152 -5.20211 3.2167 155 0.70 5.36 1.67 3.69 0330 0.961 2.23 238 L. dussumieri Pamban 161 -5.02993 3.1136 162 1.20 6.70 2.35 435 0.250 0.630 2.50 1.96 Secular Visakhapamam 119 -5.73713 3.43654 120 120 4.88 2J5 2.33 0J158 1.052 2.24 113 2 iiisiduuor Kakinada 117 -5.73713 3.43654 125 1.06 4.69 233 136 0.279 1.100 2.22 120 Madias 120 -5.73713 3.43654 125J 1.22 5.67 2.55 3.12 0334 1.011 2.28 2.09 1 Higher L^ and related Kand other parameters L.bindus Visakhapamam Samei •s above 163 0.95 4.72 ZOl 2.61 0.080 0.257 2.40 112 Kakinada n 165 0.70 5.43 1.64 3.79 0.155 0.412 2.28 134 Madias n 167 0.96 7.44 2.01 5.43 0.147 0.814 2.43 109 LJonesi Rameswaram n 160 0.60 4.95 1.50 3.45 0372 1.076 2.19 150 L-dussuimeri Pamban ti 175 0.80 5.46 1.76 3.70 0343 0.851 2.39 120 S. insidiator Visakhapamam " 130 0.85 5.28 1.99 3.29 0.332 1310 2.16 134 Kakinada fl 130 0.85 4.36 L99 137 0.332 1.291 116 234 Madras 138 130 8.72 2.59 6.13 0.279 0.810 139 1.99 Note: All lengths in mm, weights in grains and ages in years. The Z values are those obuined by length-oonveited catch curve method; Log a and b are constants < g. of length-weight leiationship. 4 values are calculated f estimates of Venkatraman et al. (1981) were timated yield of these two species is 3 680 close to the estimates of this study, those ob tonnes. Hence, the increase in yield by tained by Karthikeyan et al. (1989) were not decreasing the effort by 20% will not be sig so (Table 3); the L. was much smaller than nificant these estimates. In northern Tamil Nadu (Fig. 11.A), the In L. dussumieri the L« was closer to the maximum yield of 1 860 tonnes of L. buidus U.X (Table 2). corresponds to 120% of present effort In 5. In 5. insuUator the estimates obtained insidiator the yield increases to about 2 270 were close to each other (Table 2). The lone tonnes at 200% of present effort. The com earlier estimate (Murty 1991)wasclosertothe bined yield of these two species increases to present estimated values (Tables 2 and 3). 4 100 tonnes at 200% of present effort The Mortality rates: Taking the two sets of present yield of these two species is estimated parameters (Table 2), the total mortality rates to be 3 930 tonnes. Thus, a 100% increase in were estimated using the length-converted effort can resulti n about 4% increase in yield. , catch curve. In L. bindus, the estimated values In southern Tamil Nadu (Fig. 12) the of Z varied from 4.14 to 5.26 under 'low» yield of L. dussumieri increases to 5 720 ton pioameters* and from 4.72 to 7.44 under nes at 200% of present effort whereas the 'higho' parameters* (Table 2). In L.Jonesi, the MSY of 16 500 tonnes of L. jonesi cor- Z values were 4.95 and 5.36 under 'higher' respdnds to 120% of present effort The max and 'lower' parameters respectively. In L. imum combined yield (tf 22 100 tonnes of dussumieri, they were 5.46 and 6.70 (Table 2). these two species corresponds to 140% of In 5. tnsidiator under 'lower parameters', the present effort The estimated yield of these Z values varied from 4.69 to 5.67 mid from species during the stu4y period was 21 800 4.36 to 8.72 under 'higher parameters' at dif tonnes. Thus a 20% increase in effcHt will ferent centres (Table 2). result in about 1.3% increase in yield of the The estimated values.of natural mortality two species and 40% increase in effort will rate (M), under both the sets of parameters increase the yieU byabout 1.5%. ranged from 1.64 to 2.05 in L. bindus, from Cod end mesh size c^ trawl and yield: In 1.50 to 1.67 in L.Jonesi, from 1.76 to 2.35 in Andhra Pradesh, the yiekl of L. bindus in L. dussunueri and from 1.99 to 2.59 in S. creases up to 200% of present tc. In 5. in- insidiator. The M/K values (Table 2) in all the ^diator, on the other hand the MSY cones- cases showed that they were well within the ponds to 60% of the presenttc (Fig. 10.B).The range of 1.0-2.5 (Beverton and Holt 1959) situation thus, shows that under the current known in fishes. effort level there is need to reduce the cod end mesh size by 40% to get MSY ctf one ^;)ecies Effort and yield: In Andhra Pradesh, and to increase the same by at least 100% for maximum yield of about 2 500 tonnes of L. another q)ecies. The combined maximum bmdus is obtainable at 60% of the present yiekl of the two species, however, cor effm whereas the yield of S. insidiator in responds to 60% of pvsent tc. This implies creases to I 560 tonnes at 200% of present that the present cod end mesh size which is effort The mixed fisheries assessment of already small (15-20 cm) has to be reduced these two qiecies showed that maximum yield further by 40% (to 9-12 mm). This reduction of 3 700 tonnes will be obtained at 80% of the can only result in 1-6% increase in yield. present eff(»t (Fig. lOA). The present es 53 Table 3. Parameters of growth, mortality, lengths and ages at entiy and first capture of different silverbelly species from Indo-Pacific region Species Area/Locality Source L,. I^(per tg L, t, I^ M (mm) year) (year) (mm) (year) (mm) Leiognalhus Kakinada, India Murty 1986 158.4 0.58 -0.024 17 0.18 57.0 0.75 5.20 1.50 3.7 2.16 bindus Samarsea SavestnEl986 121.0 0.98 0 - - 4.28 2.21 2.07 2.16 Java Dwiponggo 125.0 1.38 0 50.3 - 8.84 2.83 - 2.33 elal. 1986 Calicut, India Pauly and. 122.0 1.3 ~ 2.29 David 1981 L.jonesi Mandapam, India Venkatraman 161.20 0.528 0.111 48 0.56 3.20 2.28 0.92 2.14 elal.l9S\ Mandapam, India Karthikeyan 146.62 0.917 0 15 5.26 1.25 4.01 2.29 e L. elongatus Malaysia Chan and 135.00 0.80 0 3.10 1.80 1.30 2.16 Uew 1986 L.leudsaa Samarsea Silvestie 1986 137.00 0.93 0 3.86 2.12 1.74 2.24 i Java Dwiponggo 135.00 1.80 0 47.6 6.15 3.31 2.84 2.52 e< In northern Tamil Nadu (Fig. 11. B) the MSY corresponds to 80% of present tc forL. blndus and to 60% of present tc for S. in- sidiator. The combined maximum yield of these two species corresponds to 60% of S present tc. Here also, the implicatirai is reduc tion in cod end mesh size by 40% which results in 13% increase in yield. N In southern Tamil Nadu (Fig. 13) the MSY of the two species corresponds to present tc only suggesting that under the present effort level and in the present fish ing grounds, mesh regulation is not neces Ji § o sary. DISCUSSION Two species (L. bindus and 5. insidialor) 8 were considered for the study from Andhra Pradesh and northern Tamil Nadu coasts and two other species (L.jonesi and L. dussumieri) from southern Tamil Nadu. As these species 3 -I i = formed about 60% by welight of silverbelly catches in the respective regions, assessment ON ^ Si o of these species could b6 taken as nearly ^ reflecting the situation in the silverbelly 8 8 8 8 fisheries of the regions. J E s The problems in arriving at realistic es timates of groNvth parameters and the conse — o quent need to take into account at least two OS . OA ' I - 00 sets of growth parameters (lowest and highest L« and related K) from among many sets of 00 d u ^ ^ Oi values estimated and the types of conflicting management options one would encounter in mixed fisheries assessments, have been dis cussed in the paper on threadfin breams in this I issue. As these are common to most of the o g multi-spccics/mixcd fisheries, they are not I I dealt with here. By the very abundance of silverbellies, a both in terms of number of species as well as I quantities landed, and the species dominant in I the fishery, the southern Tamil Nadu is dis I tinct and requires separate treatment for 57 MURTYfiTA^ [VaL39.Nal,2 Andhra Pradesh 3960 r 8100 3960r 3520 ' 20 40 60 80 100 120140 160180 200 20 40 60 80 100 120 140 160180 200 Effort as % of present tc as % of. present FigvlO. Yield of Leiagnaihia blndus and Seeutor iiaidiatmr from Andhra Pradesh. A. At different effoit levels expressed as percentage of present effoit. B. At different tg levels expressed as percentage of present t^ (the small vertical lines oo the curves indicate MSY in the present fishing ground and the long venical lines the current effort or tc levels and yields). flsheries management Northern Tamil Nadu quired to harvest MSY but the levels of effoit and Andhra Pradesh, however, do not show required to get the same w»e different in both greater difference with regard to the species the species. In southern Tamil Nadu, in both composition and dominant ispecies. The as the species (Fig. 12), increased effort was sessments were, however, tceated separately necessary to get MSY but at difterent mau- for the three regions due to the above reasons mum levels. The combined assessment of the and mainly because the fisheries management two ^)ecies (in each region) lead to a still is within the administrative control of mari different situation in that the effort cor time states. responding to maximum combined yield was The Thompson and Bell long-term different from the effort conesponding to forecast in Andhra Pradesh indicated the need MSY of CQnstituent species. A more or less to decrease the present effort level for one similar situation was seen in case of yield- species and increase the same for anotha mesh curves of the species from the three species in the same fishery to get MSY (Fig. regions making the task of formulating effec 10.A). In northern Tamil Nadu (Fig. 11.A), tive management measures difficult. If all situation was that increased effort was re other species in the mixed fishery are also 58 March, June 1992] STOCK ASSESSMENT OF SILVERBELUES Northern Tamil Nadu 4600 4600 4140 5850 '•140 3680 • 5200 3680 3220 4550 •g 3220 2760 - - 3900 I 2760 E >2300 - 3250 2300 ! 1840 2600 S1840 1380 - 1950 > 1380 920 1300 460 650 20 40 60 80 100 120 140160 180 200 20 40 60 80 100 120 140 160 180 200 Effort as % of present tc as % of present Fig. 11. Yield of Leiognalhia bindus and Secular insidialor from nonhem Tamil Nadu. A. At different effort levels expressed as percentage of present effort. B. At different t^ levels expressed as percenuge of present tc. considered, the situation will only become importance of stock assessment lies in making more complex. This is the realproble m faced available strategies for regulating fisherieso f in fisheries resources management particular several species stocks so that the fishery ly in tropical countries like India. While managers can select the strategy mostrequired knowledge of the biological interactions be for the industry. In the case of silverbelly tween specifcs contributing to the multi- resources considered here, the present effort species/mixed fisheries is essential for can be maintained in the present fishing effectively formulating regulatory measures, grounds, because in cases where increase in on the basis of available knowledge, the only effort to get MS Y is warranted, the increase in option appears to be fit is to regulate the effort yield will be very marginal and can result in" at a level where MSY (or MS^) of the most reduction in catch rates. Only in Andhra economically important species is obtained. Pradesh there is need to decrease the effort by As long as the effort is stabilized at a required about 20%; here also the increase in yield and level (in the well-defined fishing grounds), the catch rates is not significant.warranting such yield of all the species including the targctted a reduction in effort. Though the analysis in species, also gets stabilized as long as the certain instances indicated the need to reduce steady state assumption is fulfilled. Thus the cod end mesh size of trawl net, particularly in 59 MURTY£7AL [VoL39.No.l.2 Soii.thern Tamil Nadu 24 r 80 100 120 200 Effort as % of present Fig. 12. Yield of l^eiognathus jonesi and L. dussumieri at different effort levels expressed as percentage of present effort in southern Tamil Nadu. northern Tamil Nadu, such a regulation will where active fishing both by mechanized and not result in substantial increase in yield and non-mcchahized gears is taking place. Con even if so, the contribution will be from much siderable caution is necessary before any ef smaller fish (of the already small, considered fort increase in the present fishing grounds is as trash fish) not valued by the industry in any thought of because of its possible impact on significant manner. other resources. Moreover, silvcrbclly land It is known that silverbcllics arc predo ings are showing declining trends in recent minantly inhabitants of shallower regions years. 60 STOCK ASSiaSMILNTOl- SILVIiRBEUJIiS Southern Tamil Nadu 40 60 80 100 120 140 160 180 200 tc as % Of present Fig. 13. Yield of Leiognalhus jonesi and L. dussumieri at different tc levels expressed as pereenuge of present t^ in soulhem Tamil Nadu. ACKNOWLEDGEMENTS the course of analysis of data at the Computer We thank Dr P S B R James. Ex-Director. Centre; the authors are thankful to them. CMFRI, Cochin, for encouraging the study. 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