Flatfish landings increased from an estimated 58 t in 2000 to 299 t in 2002, but

declined to 65 t in 2003 and 61 t in 2004 at Cochin. August and September were

the months of peak landings, which were also the peak spawning months. The

optimum length of exploitation was 124 mm. Annual growth coefficient (K) and

L  were 0.79 and 212.5 mm respectively. The resource is being exploited at a

level (E = 0.78) higher than the optimum (Emax = 0.458). Appropriate

management measures are discussed

Nair, Rekha J

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45Indian J. Fish., 54(1) : 45-49, Jan.-Mar., 2007Flatfish fishery off Cochin and some aspects of thebiology and stock of Malabar sole Cynoglossusmacrostomus (Norman)REKHA J. NAIRCentral Marine Fisheries Research Institute, Ernakulam North P.O, Cochin-18.ABSTRACTFlatfish landings increased from an estimated 58 t in 2000 to 299 t in 2002, butdeclined to 65 t in 2003 and 61 t in 2004 at Cochin. August and September werethe months of peak landings, which were also the peak spawning months. Theoptimum length of exploitation was 124 mm. Annual growth coefficient (K) andL? were 0.79 and 212.5 mm respectively. The resource is being exploited at alevel (E = 0.78) higher than the optimum (Emax = 0.458). Appropriatemanagement measures are discussed.IntroductionAmong flatfishes occurring along thewest coast, the Malabar sole Cynoglossusmacrostomus form a major trawl fisheryalong the coastal region from Mulki inKarnataka to Kollam in Kerala.   Thoughthere is no targeted fishery for the spe-cies, it is obtained as a by-catch in shrimptrawls. With the increase in targeted fish-ery for shrimps, this species is also be-ing heavily fished. Market demand forfresh flatfishes is only in the Malabararea; towards South Kerala, the fish isbeing dried and sold through consumermarkets. The fish costs Rs.40 /kg in freshand 50/kg in dried condition. Decayedfish from multi-day  shrimp fishing ves-sels are being dried and sold as ingredi-ent for poultry feed at Rs. 20/kg. Studieson the fishery, biology and stock charac-teristics of flatfishes along the Indiancoasts have been carried out byVivekanandan et al. (2003), Jayaprakash(1998), Khan and Nandakumaran (1993),Grace Mathew et al. (1992), Seshappaand Chakrapani (1983), Victor (1978),Seshappa (1964,1974, 1978) andSeshappa and Bimachar (1955, 1954,1951).The present paper gives an insightinto the flatfish fishery and stock of C.macrostomus based on investigations atCochin from 2000-2004.Materials and methodsData on landings of flatfishes andeffort expended by trawlers were col-lected from weekly observations in thefishing harbours at Cochin andMunambam. To estimate catch (weightand numbers) of each species, the datacollected at the observation centres wereweighted to get estimates for each cen-tre. Samples of the dominant species,C. macrostomus, were collected, length–weight measurements taken and length–weight relationship calculated by themethod of least squares using the46formulaLog W = log a + b Log Lwhere, W = weight in grams, L=length in mm, a = constant and b = expo-nent. Wα was calculated using the Lαvalue and the length–weight relation-ship. For studies on reproductive biology,gonads of female were examined micro-scopically and classified into four stages- immature (Stages I and II), developing(Stages III and IV), mature/ gravid (StageV) and spent (Stage VI). Fishes in StageIII and above were considered for thepurpose of estimating length at firstmaturity. For determination of spawn-ing period, only fishes in Stages V andVI were considered. Length frequencydata were grouped at 5 mm interval toestimate the growth parameters.  Theparameters of growth in length were es-timated following the ELEFAN method(Gayanilo et al., 1988) using the monthlylength frequency data for the years 2000-2004. The estimates of instantaneousmortality (Z) were made using lengthconverted catch curve method (Pauly,1982) with the combined data for fiveyears.The natural mortality rate (M) wasestimated using the empirical formula ofPauly (1980) by taking into account themean annual temperature off Cochin as28.5oC. The fishing mortality F was es-timated as Z – M. The optimum lengthof exploitation (Lopt) was estimated fromthe empirical equation of Froese andBinohlan (2000) using the relationshipLopt = 3 x L? / (3 + M/K)The life span was estimated usingthe equation Tmax = 3/K (Pauly, 1983)To assess the long-term impact offishing, yield per recruit analysis (Y/R)was carried out following Beverton andHolt (1957). From the exploitation ratio,E, the yield (MSY) was estimated. Aver-age standing stock (Y/F) and the annualstock or biomass (Y/U) were estimatedfor the five year period. The exploitationrate, U was estimated as F/Z (1 – e-Z).Recruitment pattern was obtained bybackward projection on the length axisof the set of length–frequency data (sea-sonal growth curve) by using the routineELEFAN II.ResultsThe total annual effort decreasedfrom 14,803 units in 2000 to 2,980 unitsin 2003, but increased to 6,709 units in2004. The catch per unit effort, however,increased from 3 kg in 2000 to 38 kg in2002,  but decreased to 9 kg in 2004. Flat-fish landings increased from an esti-mated 58 t in 2000 to 299 t in 2002, anincrease of 241 t in two years, followedby a drastic decline to 65 t in 2003 and61 t in 2004. Generally, maximum trawleffort was expended in the pre and post-monsoon months (May and August). Dur-ing 2000-04, August and September werethe months of peak production (Fig 1).Landings were poor during the preFig. 1. Seasonal production of flatfishes bytrawlers at Cochin during 2000-2004monsoon months of April - June. During2002 and 2003, however, good landingswere observed during February andMarch also.Fourteen species of flatfishes wererecorded in the fishery. Of these, C.macrostomus dominated the landingsRekha J. Nair47contributing over 65 %, followed by C.macrolepidotus with 18 %. The other spe-cies, which contributed to the fishery,were C. puncticeps, C. bilineatus, C.dubius, Psettodes erumei, Synapturacommersoniana, Bothus myriaster, B.ovalis, Pseudorhombus elevatus, P.javanicus, Aesopia cornuta and Zebriasquagga.A total of 500 specimens rangingfrom 50 -160 mm in total length wereused for the estimation of length –weightrelationship. The data for both sexeswere pooled to get the estimates of a andb. The length –weight relationship for C.macrostomus isLog W = -5.16 + 3 Log LUsing the availability of mature andspent gonads in the samples, the spawn-ing season off Cochin was found to beJanuary –April and August – October,with the peak during August- Septem-ber. The predominant maturity class isStage IV when the commercial fisherycommences after the trawl ban at CochinGrowth parameters were estimatedassuming that the growth in length of thespecies follows von Bertalanffy equation.The length at first capture is 45 mm. Atotal of 5,289 fishes in the range 45 -190mm total length were used for the esti-mation. (Fig. 2).at -0.014. Using these results the VBGFequation for C. macrostomus can be writ-ten asLt = 212.5 (1 – e - 0.79 (1- (-0.014)).Optimum length of exploitation(Lopt) was estimated as 124 mm and themaximum life span Tmax as 3.8 years.Natural mortality M was estimated as1.7. Instantaneous mortality Z was esti-mated using length–converted catchcurve method at 7.78. (Fig. 3).  Using Zand M, fishing mortality F was estimatedat 6.08 and exploitation rate E at 0.78.The cutoff length L’ was estimated at117.5 mm and the mean length in thefishery at 131.5 mm. Using E values, andFig. 3. Length converted catch curve of C.macrostomus at Cochintaking the present average yield at 60 t,the MSY was estimated at 99 t. Thestanding and total stocks were estimatedat 16 t at 126 t respectively.DiscussionThe fluctuations in the landings offlatfish noticed during 2000 - 2004 weresimilar to the results of Jayaprakash(1998). The fluctuations in the flatfishfishery may be attributed to the largescale shoaling of the species in the sur-face and subsurface waters of the inshoreareas in enormous numbers (Jaya-prakash, 1998). In the present study, thepeak production period was during Au-gust and September immediately afterthe monsoon trawl ban, followed Janu-ary -March. The results are differentFlatfish fishery and stock assessment of C. macrostomusFig. 2. Growth of C. macrostomus at Cochin.The growth parameters estimatedwas Lα212.5 mm using Powell –Weatherall plot, K at 0.79 year -1 and to48from those reported by Grace Mathew etal. (1990)  that the peak flatfish land-ings was  during May and June during1984 –1988 at Cochin.  Khan andNandakumaran (1993) also reportedsimilar landing pattern at Calicut.  Itappears that the difference in the monthsof peak landings may be due to changein the fishery pattern after the imple-mentation of trawl ban.Seshappa and Bimachar (1955) ob-served the spawning season of theMalabar sole as September – October offCalicut. . However, in the present study,two spawning seasons (January-April,August-October) were noticed; these re-sults agree with that of Jayaprakash(1998) from the same area. The commer-cial catches consist of fishes in differentmaturity stages and belong to two re-cruitment batches.The length weight relationship for C.macrostomus worked out by various au-thors is given in Table 1. The growth inweight is isometric for this species.Jayaprakash (1998) reported size at firstmaturity to be 97 mm. Results of thepresent study, however, point to a highersize at first maturity (118.5 mm). Simi-larly, results on the length of the fishattained at the end of the first and sec-ond year were higher than that recordedby Khan and Nandakumaran (1993). Thelargest specimen they obtained was 159mm which was much lesser than that ofthe present study.The optimum length of exploitationin the present study point to the fact thatfishes over one year class alone shouldbe exploited. The length at first capturein the trawl (45 mm) is much below theoptimum length as well as the cut offlength. The present exploitation rate Eis much higher than E max; this valuealong with the high F value shows thatthis species is being heavily exploited andthere is need for reducing the trawl ef-fort.AcknowledgementsThe author is thankful to Dr. MohanJoseph Modayil, Director, CMFRI and tothe Head, Marine Biodiversity Divisionfor the facilities, encouragement andguidance and to Dr. E. Vivekanandan,Head, Demersal Fisheries Division forguidance.ReferencesBeverton R.J.H and S.J. Holt 1957. On thedynamics of the exploited fishpopulations. Fishery Investigation Se-ries, London 19: 533 pp.Froese, R and C. Binohlan 2000. Empiricalrelationships to estimate asymptoticlength, length at first maturity andlength at maximum yield per recruit infishes with a simple method to evaluatelength frequency data. J. Fish Biol., 56:758 -772.Gayanilo, F.C Jr., M. Soriano, and D. PaulyTABLE 1. Length weight relationship for C. macrostomus worked out by various authorsArea Sex No. a b AuthorMangalore M 761 0.000004327 3.04 Victor (1978)F 657 0.00001415 2.7886 -do-P 1418 0.000007872 2.9145 -do-Calicut P 150 0.00003759 2.618 Khan and Nandakumaran (1993)Cochin M 340 0.000002194 3.163 Jayaprakash (1998)F 329 0.0000002953 3.10 -do-P 669 0.000002576 3.13 -do-Cochin P 500 0.005737108 3 Present studyRekha J. Nair491988. A draft guide to COMPLETEELEFAN. ICLARM Software Project 2:65 pp.Grace Mathew, M. Feroz Khan and K.Nandakumaran 1992. Present status ofexploitation of fish and shell fish re-sources: Flatfishes and flatheads. Bull.Cent. Mar. Fish. Res. Inst., 45: 197 -204.Jayaprakash, A.A 1998. Studies on the fish-ery, biology and population dynamics offlatfishes (Cynoglossus spp; FamilyCynoglossidae) along Kerala coast. Ph.DThesis, University of Calicut. 307 pp.Khan M.F and K. Nandakumaran 1993.Population dynamics of Malabar soleCynoglossus macrostomus Normanalong Calicut coast. Indian J. Fish., 40(4): 225-230.Pauly, D. 1982. Studying single –species dy-namics in a tropical multispecies context.Theory and Management of TropicalFisheries pp 33 – 70. (Eds) Pauly, D andMurphy C.I, ICLARM, ISIRO.Pauly, D. 1983. Some simple methods for theassessment of tropical fish stocks. FAOFish. Tech. Paper, 234:52 pp.Seshappa, G. 1978. Some observations on thesize distribution and the occurrence ofgrowth rings in the scales of three spe-cies of Cynoglossus at Calicut. Indian.J. Fish., 25 (1 & 2): 188-196.Seshappa, G. 1974. Flatfish resources of westcoast of India. Proc. Sym. Liv. Res. Seasaround India. CMFRI Spec. Publ.: 470 -482. Seshappa, G. 1964. Length frequency stud-ies on the Malabar sole Cynoglossussemifasciatus Day at West Hill, Calicutduring the years 1959 -60 to 1962 -63.Indian J. Fish., 11 (2): 533-546.Seshappa, G and B.S. Bimachar 1955. Stud-ies on the fishery and biology of Malabarsole Cynoglossus semifasciatus Day. In-dian  J. Fish., 2 (1): 180 -230.Seshappa, G and B.S. Bimachar 1954. Stud-ies on the age and growth of the Malabarsole Cynoglossus semifasciatus  Day. In-dian J. Fish., 1 (1 & 2): 145 -162.Seshappa, G and B.S. Bimachar 1951. Agedetermination studies in fishes by meansof scales with special reference toMalabar sole Cynoglossus semifasciatusDay. Curr. Sci., 20:  260 -262.Seshappa G and B.K. Chakrapani 1983.Length frequency distribution inCynoglossus semifasciatus Day on theWest Coast during 1980-81. Indian. J.Fish., 30 (1): 74-86.Victor A.C.C 1978. Length weight relation-ship in the Malabar sole, Cynoglossusmacrostomus Norman. Indian J. Fish.,25(1 & 2): 259 -262.Vivekanandan, E., P.U. Zacharia, M. FerozKhan and Rekha J. Nair. 2003. Flat-fishes In: Mohan Joseph, M andJayaprakash A.A (Eds.) Status of Ex-ploited Marine Fishery Resources of In-dia, CMFRI: 164 – 170.Date of Receipt : 15-06-06Date of Acceptance : 07-08-06Flatfish fishery and stock assessment of C. macrostomus

Flatfish fishery off Cochin and some aspects of the

biology and stock of Malabar sole Cynoglossus

macrostomus (Norman)

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Flatfish fishery off Cochin and some aspects of the biology and stock of Malabar sole Cynoglossus macrostomus (Norman)

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