The average annual catch of Fenneropenaeus indicus in the trawl landing of

Puthiappa, Kozhikode was 197 t with a CPUE of 15 kg. Peak fishing period was

April-May. About 28% of the average annual shrimp catch was constituted by F.

indicus. The stock assessment studies indicated that the fishery is still underexploited

and the effort can be increased to obtain the maximum sustainable

yield

Sarada, P T

CMFRI Digital Repository

383Fishery and stock assessment of Fenneropenaeusindicus (H.Milne Edwards) from Kozhikode, southwest coast of India.P.T. SARADAResearch centre of Central Marine Fisheries Research Institute, Calicut,Kerala - 673 005, IndiaABSTRACTThe average annual catch of Fenneropenaeus indicus in the trawl landing ofPuthiappa, Kozhikode was 197 t with a CPUE of 15 kg. Peak fishing period wasApril-May. About 28% of the average annual shrimp catch was constituted by F.indicus. The stock assessment studies indicated that the fishery is still under-exploited and the effort can be increased to obtain the maximum sustainableyield.Indian J. Fish., 53(4) : 383-388, Oct.-Dec., 2006IntroductionFenneropenaeus indicus forms one ofthe most commercially important speciesdue to its large size, quality meat andhigh export value. As a result,exploitation of this resource is intenseboth from estuary and sea.  Puthiappaharbour at Kozhikode is one of the majortrawl landing centers of North Keralacoast and observation on the shrimpfishery from here gives a general picturefor the Malabar area. Prawn fishery ingeneral have been dealt with from Keralaby Anon (1975), from Malabar area byPanikkar (1937), and from Kannur coastby Kuthalingam (1970). Aspects onbiology, growth and populationcharacteristics of F.indicus were studiedfrom Cochin and Alleppey coast byGeorge (1961) and George et al. (1963);and from Ambalapuzha by Kurup andRao (1974). Maturation and spawning ofthis species from south-west coast havebeen dealt with by Rao (1968). Populationdynamics and stock position of thespecies from Kakinada have been studiedby Lalithadevi (1986) and from east coastby Rao et al. (1995). However publishedwork on the Indian white shrimp fisheryfrom Kozhikode coast especially on stockposition is lacking.In view of its importance in thefishery and absence of any publishedinformation on this species from thisarea, the present study was undertakenbased on the data collected  during theperiod,  August 2002 - July 2004 fromthe trawlers landed at Puthiappa. In thispaper besides the fishery, the populationdynamics covering the aspects such asstock, MSY etc of the species have beendescribed.Materials and methodsData on catch, effort and speciescomposition of shrimp fishery were384P.T. Saradacollected twice in a week from Puthiappalanding center during 2002-03 and 2003-04 and the days’ catch was estimated tothat month. Random samples ofF.indicus were collected twice in a monthand analysed for size and maturitycondition sex-wise. As the main gearoperated for shrimps was trawl, the datacollected from shrimp trawl was used forthis study. To avoid break in data in Julydue to the ban on trawling, August toJune was taken as one year. FISATcomputer program and stock assessmentmanual (Sparre and Venema, 1992) wereused for calculating the populationcharacteristics and stock assessment.The details of methodology used are givenin the respective aspects under result.ResultsAnnual catch, effort and CPUETrawlers contributed 96 % of thetotal shrimp catch of this center and therest by discovala (minitrawl) and ring net(mini purse-seine). The indigenous gearswere operated mainly during monsoonseasons. In 2002-03 the total shrimpcatch by trawl net was 889 t with a CPUEof 58.4 kg. This formed 6.7% of that gear’scatch. Among the 11 species of shrimpscaught during this period, F.indicus wasthe dominant species (27.9%) followed byMetapenaeus dobsoni (27.7%) andParapenaeopsis stylifera (25.5%). In thenext year, 2003-04, the shrimp catchdeclined to 505 t with a CPUE of 46 kg.The effort expended had also reducedfrom 15233 units to 10961 units. But thepercentage of shrimps in the total catchincreased to 6.9. This year M.dobsonidominated (46.9%) the catch followed byF.indicus (28.9%) and P.stylifera (16.6%).The annual average shrimp catch was697 t and the CPUE was 52 kg.In the case of F.indicus, the catchwas 248 t and the CPUE was 16.3 kg in2002-03. But in 2003-04, the catchdeclined to 146 t reducing the CPUE to13.2 kg. The average annual catch ofF.indicus for the period, August 2002 –June 2004 was 197 t and the CPUE was15 kg. The annual average percentage ofF.indicus was 28.2Seasonal catch, effort and CPUEThough the shrimp fishery was fromAugust to June, the F.indicus fishery wasonly from October to June with a peakduring April-May. The catch of F.indicusin 2002-03 showed a gradual increasefrom October to May. From an initialcatch of 327 kg in October it increased to99.5 t in May and then it decreased inJune. Corresponding with the catch, theCPUE also showed a continuous increasefrom October (0.28kg) to May (42.17kg).In 2003-04, the catch showed widefluctuation. It increased from 3 kg inOctober to 27.8 t in January. But thecatch decreased in the following twomonths and recorded 8.6 t in March. Thecatch then increased to a maximum of39.6 t in April. Again it showed adecrease in the next two months. Just asthe catch, the CPUE also fluctuated.October recorded the minimum CPUE(0.01 kg) but June recorded themaximum (32.12kg) followed by April (26kg). The average monthly catch of thesetwo years showed a gradual increasefrom October (165 kg) and reached themaximum in May (64 t). The averagemonthly CPUE also showed a similarpattern of fluctuation with a minimumin October (0.2kg) and a maximum inMay (30.81 kg) followed by April(30.72kg). Percentage composition ofF.indicus in total shrimp catch during2002-03 varied from 2.1 in October to59.4 in May. In 2003-04, it varied from20.7 in November to 57.4 in April. Thepercentage of F.indicus in the averagemonthly shrimp catch varied from 2.1 inOctober to 53.7 in April.385Fishery and stock assessment of Fenneropenaeus indicusEstimation of growth parametersThe maximum length recorded was170 mm for males and 180mm forfemales. The asymptotic length (L!) wascalculated by using Powell-Wetherallmethod (Wetherall et al., 1987) and thevalue was 178.8 mm in males and 183mm in females. The growth constant (K)was calculated by using ELEFAN as 1.4for males and 1.2 for females. Onapplying von Bertalanffy growthequation based on these values and onassuming ‘to’ as ‘0’, females reached totallength  of 128 mm in the first year and168mm in the second year. Malesattained a length 133 and 168 mmrespectively for first year and secondyear.Estimation of mortality ratesTotal mortality coefficient (Z) wasestimated from linearized lengthconverted catch curve. The ‘Z’ wasestimated as 6.6 for males and 6.7 forfemales.Natural mortality coefficient (M)(Rikhter and Effanov, 1976) was 1.5 forfemales and 1.7 for males. The age ofmassive maturation (the age at which50% of the population matures –Tm50)was calculated as 0.8 for males and 0.9for females. The Lm 50 (size at firstmaturity) was at 118mm in males and123mm in females.Fishing mortality (F) was calculatedas 4.9 in males and 5.2 in females.Trawl net selectivityThe gear selectivity was found outfrom the ascending limb of lengthconverted catch curve. The age and sizegroup thus obtained at first capture(t50% and L50%) in males were 0.73years and 116-120 mm respectively. Infemales, these values were 0.9 years and121-125 mm respectively.Virtual population analysis:Virtual population analysis wasdone by using Jones’ length - based cohortanalysis. Here, the terminal F/Z wasassumed to be 0.5. The fishing mortalityand total mortality were maximum in thesize group of 126 –130 mm (males) and131-135 mm (females). Mean number ofF.indicus (number of survivors) in the seaand their biomass for the period 2002-2004 were 329.063 million and 95 trespectively for males and 536.84 millionand 155t respectively for females.Prediction analysisThe future yields and stock biomasslevels were predicted by using thepredictive models such as yield perrecruit model and Thompson and Bellmodel.Beverton and Holt’s yield per recruitanalysis:The values taken for the analysis ofmales were K=1.4, to =0, Tc=0.73,Tr=0.37, W! = 33.6, M =1.7, Z = 6.6 andpresent F= 4.9. The values taken forfemales were K=1.2, t0=0, Tc=0.9,Tr=0.3, W! = 37.2, M= 1.5, Z=6.7 andpresent F= 5.2.The yield per recruit for the presentF was 5.03 g in male and 4.29 g in female.Y/R curve for different fishing mortalitiesdid not show a maximum but after acertain stage the rate of increase of Y/Rbecame very slow and that was taken asthe F-MSY. Thus obtained F-MSY(relative) in males was 7 and females was8.5.The corresponding yield per recruitswere 5.1 and 4.38 g. As the Y/R – curvedid not have a maximum, the averagebiomass per recruit (B/R)were alsocalculated and plotted along with Y/R. Itshowed that for F. indicus, the biomasscorresponding to the optimum F- level (F-MSY) was 5.41 % and 4 % of the virgin386stock biomass (Bv) of male and femalerespectively (Fig.1)Thompson and Bell modelLength based Thompson and Bellmodel was also used to predict the yieldand stock biomass by size group as afunction of fishing mortality. Theanalysis used 14 different F-array byraising the F-value with 14 factorsstarting from zero to 2.6. The present F-factor was taken as 1. The presentaverage annual yield was 96.1 t in malesand 100.9 t in females. The total yieldwas 197 t. The mean biomass availablefor the factor -1 was 47.4 t in males and75.7 t in females and the total was 123.1t. The virgin stock biomass was 345.3 t(148.5 t male and 196.8 t female). Theyield was maximum (MSY) for the F-factor 1.6 in the case of males and 2 inthe case of females and the yields were97.9 t and 109.2 t respectively. The totalyield (males and females combined) forfactor 1.6 was 205.6 t and it wasmaximum (206.9 t) for the F-factor 2.0and the corresponding mean biomasseswere 98.9 t and 90.4 t. (Fig. 2).October to June with a peak in April-May. Though in the average annualshrimp catch this species formed 28 %,during April - May, it formed more than50% of the shrimp catch. The increase inF.indicus catch compared to earlier yearswas mainly due to the introduction ofmulti-day trawlers fishing in deepergrounds and the catch was mainlyconstituted by large sized F.indicus.The age and growth study showedthat males grew to133 mm in the firstyear and females to 128 mm, whereas inthe second year both the sexes reached168 mm. Males grew faster than femalesand it reached L! earlier. The ‘K’ valueof males (1.4) was higher than females(1.2)  which is also observed by Kurupand Rao (1974), though Jayawardane(2002) and Lalithadevi (1986) observeda higher value of ‘K’ for females .In theP.T. SaradaFig.2. Yield and biomass curve of the length-based Thompson and Bell analysisFig.1. Yield per recruit and Biomass perrecruit curve of F.indicus as a functionof F012345670 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.2 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10FYield /recruit(g) & Average Biomass/recruitFemaleMaleY/RB/RPresentF-  F-MSY0501001502002503003504000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4F - factorYield  and  Mean biomass (t)femaleMalePresent FF-MSYTotal biomassTotal yieldBiomassYieldDiscussionF. indicus is one of the mostcommercially important species ofshrimps. It occurs in trawl catch frompresent study majority of the male catch(82%) was caught between the sizegroups of 103 and 133 mm and the age ofwhich varied from 7 months to11.6months. In the case of females 84 % ofthe catch was caught between the sizegroups of 103 mm and 138 mm. The ageof this size groups ranged from 8 to 14months. But the age of massivematuration was at 9.6 months in maleand 11 months in female. The size at firstcapture was also at the age of 9 months387in male and 11months in female whichmeans more than half of the catch (male-52% and female- 61%) did not get theopportunity to spawn at least once beforecapture.The mortality studies showed thatthe natural mortality is slightly higherin males than females but the fishingmortality is higher in females. In the caseof species caught by trawlers, which arehaving low K-value will have lower M-value but the F-value will be higher (EJF,2003). The present natural mortality was1.7 for males and 1.5 for females.Jayawardane et al. (2002) had reporteda natural mortality of 1.73 for both malesand females by using the same method.In the present study total mortality wasestimated as 6.6 and 6.7 for males andfemales respectively. Though the valueof Z seems to be high, the predictionstudies such as yield per recruit andThompson and Bell model revealed thatthe fishing level is below optimum. Theyield per recruit analysis indicated thatfishing mortality (fishing effort) could beincreased from the present level of 4.9 to7 in males and 5.2 to 8.5 in females.Thompson and Bell model also showedthat the present level of fishing is belowoptimum and to obtain maximumsustainable yield fishing effort can beincreased by 1.6 times in male and twotimes in female. When the yield of malesand females were pooled, the maximumyield was obtained at F- factor 2.0. Thebiomass at the current level of fishing is22.3% of the virgin biomass. The biomassat the MSY level (B-MSY) is 14.8% of thevirgin biomass. This study shows thatthere is scope to increase the fishingeffort twice to get the MSY.AchnowledgementsI express my gratitude to Dr.MohanJoseph Modayil, Director, CMFRI, Kochi;Dr.E.V.Radhakrishnan, Dr.G. Nanda-kumar, Dr. M.Srinath and  Dr.P.N.Radhakrishnan Nair.ReferencesAnonymous 1975. Studies on marine prawnbiology and resources. 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Growth and populationdynamics of the Indian white prawnPenaeus indicus H.M.Edwards fromKakinada. Proc. Indian. Acad. Sci., 96(5):529-639.Panikkar, N. K. 1937. The prawn industry ofMalabar coast.  J. Bombay. Nat. Hist.Soc., 39 343-53.Rao,P.V. 1968. Maturation and spawning ofthe penaeid prawns of the south westcoast of India .FAO Fish .Rep., 57 (2):285-302.Rao, G. Sudhakara,V. T.Subramanian,M.Rajamani, P.E.S.Manickam and G.Maheswarudu 1995. Populationdynamics of Penaeus spp. in the eastFishery and stock assessment of Fenneropenaeus indicus388coast of India.  Indian J.Fish., 40: 1-19.Rikhter, V. A. and  V. N. Effanov 1976. Onone of the approaches to estimation ofnatural mortality of fish populations.ICNAF Res. Doc., 76/VI/8: 12pSparre, P. and  S.C.Venema 1992.Introduction to tropical fish stockassessment. FAO FishTech.Pap., 306/1:376p.Surendranatha Kurup, N. and P.VedavyasaP.T. SaradaRao 1974. Population characteristics andexploitation of the important marineprawns of Ambalapuzha, Kerala. IndianJ.Fish. , 21 (1):183-210.Wetherall, J. A., J. J. Polovina  and S.Ralston,1987. Estimating growth and mortalityin steady state fish stock from lengthfrequency data. ICLARM Conf. Proc.,(13):53-74.Date of Receipt : 27-10-05Date of Acceptance : 22-7-06

Fishery and stock assessment of Fenneropenaeus indicus (H.Milne Edwards) from Kozhikode, south west coast of India

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