The sudden emergence of a fishery and selected aspects of biology and population dynamics of Aluterus monoceros landed

by trawlers at Veraval was studied from January 2008 to December 2009. Total catch of 475 t recorded in September 2009, which increased to 7042 t in October dominated in the trawl landings with a contribution of 29.5%. However, in November and December, the catch decreased sharply to 1374 t and 94 t, respectively. The combined length-weight relationship was log W = -1.50 + 2.694 log L (r = 0.86) (n = 222) indicating allometric growth. Sex ratio was 1:1.05 (n = 129). Females attained sexual maturity at 50.2 cm total length. Zoobenthos, dominated by benthic invertebrates, cnidarians and worms, zooplankton dominated by copepods and nekton dominated by Acetes spp. and clupeid juveniles were the major food items of A. monoceros. The von Bertalanffy growth equation was Lt = 63.53 [1 – e - 0.22 (t + 0.077)]. Natural mortality, fishing mortality

and exploitation ratio were 0.53, 0.58 and 0.52 respectivel

Dhokia, H K

Ghosh, Shubhadeep

Ladani, A A

Mohamed, Gulshad

Polara, J P

Savaria, Y D

Thangavelu, R

Zala, M S

CMFRI Digital Repository

31Sudden emergence of fishery and some aspects of biology and populationdynamics of Aluterus monoceros (Linnaeus, 1758) at VeravalSHUBHADEEP GHOSH, R. THANGAVELU, GULSHAD MOHAMMEDH. K. DHOKIA, M. S. ZALA, Y. D. SAVARIA, J. P. POLARA AND A. A. LADANIVeraval Regional Centre of Central Marine Fisheries Research InstituteMatsya Bhavan, Bhidiya, Veraval – 362 269, Gujarat, Indiae-mail: subhadeep_1977yahoo.comABSTRACTThe sudden emergence of a fishery and selected aspects of biology and population dynamics of Aluterus monoceros landedby trawlers at Veraval was studied from January 2008 to December 2009. Total catch of 475 t recorded in September 2009,which increased to 7042 t in October dominated in the trawl landings with a contribution of 29.5%. However, in Novemberand December, the catch decreased sharply to 1374 t and 94 t, respectively. The combined length-weight relationship waslog W = -1.50 + 2.694 log L (r = 0.86) (n = 222) indicating allometric growth. Sex ratio was 1:1.05 (n = 129). Femalesattained sexual maturity at 50.2 cm total length. Zoobenthos, dominated by benthic invertebrates, cnidarians and worms,zooplankton dominated by copepods and nekton dominated by Acetes spp. and clupeid juveniles were the major food itemsof A. monoceros. The von Bertalanffy growth equation was Lt = 63.53 [1 – e - 0.22 (t + 0.077)]. Natural mortality, fishing mortalityand exploitation ratio were 0.53, 0.58 and 0.52 respectively.Keywords:  Aluterus monoceros, Biology, Fishery, Population dynamics, VeravalIntroductionAluterus monoceros (Linnaeus, 1758), belonging tothe family Monacanthidae and the order Tetraodontiformesis a reef associated subtropical fish occurring in thecontinental shelf down to 50 m depth. It is epipelagic innature and popularly called as the unicorn leatherjacket.It is found solitary or in pairs, occasionally in groups offive or six.  Juveniles are pelagic, often with large jelliesand these bring them close to reefs and adults nest on sandflats adjacent to reefs in deep water or form large schoolsunder weed-rafts (Kuiter and Tonozuka, 2001). It is caughtas by-catch in bottom trawls all over the world (Lopez-Peralta and Arcila, 2002; Khemakorn et al., 2005; Tuanand Mai, 2005). Similar scenario was observed at Veravallanding centre earlier when sparse landings of A. monocerosin bycatch by trawlers were recorded, though only veryrarely. However, from the beginning of 2008, quantum ofcatch gradually increased and this continued upto August,2009. Then suddenly in September, October and Novemberof 2009, their catch increased in such enormous proportionsthat there was targeted fishing for unicorn leatherjacket,which became the sole highest contributor to the trawlcatches of not only Veraval but the entire Saurashtra coast.The price of A. monoceros increased to Rs. 60 and furtherto Rs. 120 per kg. Catches of unicorn leatherjacket wererecorded also in multifilament gillnets during these months.Indian J. Fish., 58(1) : 31-34, 2011There is no published information on the populationparameters and biology of unicorn leatherjacket caughtfrom the Indian waters. The present paper attempts to studythe sudden emergence of the fishery and some aspects ofbiology and population dynamics of Aluterus monoceroslanded at Veraval.Materials and methodsData on catch and effort expended for catchingAluterus monoceros were collected every week from thetrawl (Bhidiya) and gillnet (Old Light House) landingcentres at Veraval during January 2008 to December 2009.The monthly and annual estimates of catches were madefollowing the stratified random sampling design as adoptedby CMFRI. A total of 222 specimens of A. monoceros(length range: 41.0 to 60.9 cm) collected randomly everyweek from trawl landings were sampled for recording totallength (cm) and body weight (g). The length weightrelationship was calculated following the formula W = aLb(Le Cren, 1951). Sex ratio was determined from 129specimens and Chi-square test was performed to test thehomogeneity of male and female distribution. The size atfirst maturity (L50) was determined from 66 femalespecimens by plotting the percentage of mature specimens(stage III and above) against their total length. The foodand feeding intensity from 129 specimens was assessedbased on the distension of their stomach and the volume of32food contained in it and was classified as full, ¾ full,½ full, ¼ full and empty (Ghosh et al., 2009).For estimating the von Bertalanffy growth parametersviz, asymptotic length (Lα) and growth co-efficient (K), themonthly data on length measurements from trawl landingsduring 2008 - 2009 were pooled and grouped into 1 cmclass interval, and analysed using the ELEFAN I moduleof FiSAT software (Gayanilo et al., 1996). Growthperformance index (Ø) was calculated from the finalestimates of Lα and K (Pauly and Munro, 1984). The sizeat first capture (Lc) was estimated as in Pauly (1984) andthe age at zero length (t0) from Pauly’s (1979) empiricalequation, Log (-t0) = - 0.392 - 0.275 Log Lα - 1.038K. Themidpoint of the smallest length group in the catch was takenas length at recruitment (Lr). Natural mortality (M) wasestimated as in Pauly (1980) and total mortality (Z) fromlength converted catch curve (Pauly, 1983) using FiSATsoftware. Fishing mortality (F) was estimated byF = Z - M. Length structured virtual population analysis(VPA) of FiSAT was used to obtain fishing mortalities perlength class. Exploitation ratio (E) was estimated from theequation, E = F/Z.Results and discussionPrior to 2008, there were sparse landings of unicornleatherjacket occasionally as bycatch in trawls to the tuneof less than a tonne annually. The first record of substantialcatch was in January, 2008 when 12.2 t was landed bytrawlers. Subsequently monthwise catch ranging from 1 to18.5 t were recorded between February, 2008 to August,2009. A total catch of 23.6 t was recorded during 2008 at acatch rate of 0.016 kg h-1 forming 0.017% of the trawlnetlandings. The catch increased in 2009 and from January toAugust a total of 41.9 t was recorded at a catch rate of0.056 kg h-1 forming 0.073% of the trawlnet landings.In September, 475 t was landed contributing 2.76% to thetrawl landings (Fig. 1). This increased to 7042 t in Octoberwhen it was the single highest contributor to trawl catchcontributing 29.5%. In November and December, the catchdecreased sharply to 1374 t and 94 t, respectively. Thisspectacular increase in catch could be attributed to the factthat once catch started coming and increasing steadily fromthe early months of 2008 there was targeted fishing for theunicorn leatherjacket. Multiday trawlers of Saurashtra coastoperating in the area of Bombay High around Ratnagiriand Satpatti, employing ribbonfish trawls targeted unicornleatherjacket owing tothe decreasing catch of ribbonfish intrawls. Ribbonfish trawlnets possess large meshed codend(4 - 5 cm) and have large mesh openings in the wing sectionsof the trawl (45 – 60 cm). The multiday trawlers conductedvoyage fishing lasting for 8 – 12 days at depth of 30 – 50 mfor A. monoceros. Each trawler performed, on an average4 hauls per day and carried, on an average 10 to 12 suchShubhadeep Ghosh et al.Fig. 1. Spurt in catch of Aluterus monoceros by trawlers at VeravalFig. 2. Spurt in catch of A. monoceros by gillnetters at VeravalThe mean lengths exhibited an inverse relationship tothe quantum of unicorn leatherjacket caught in trawl nets.The highest mean length of 52.93 cm was recorded in themonth of September and the lowest of 46.19 cm in the monthof October. In October, when the highest catch was recorded,juveniles were exploited in greater amounts and this couldbe an indication of growth overfishing of this species. Thecombined length-weight relationship was log W = -1.50 +2.694 log L (r = 0.86) (n = 222), whichindicated allometricgrowth for the species. This is in contrary to Garcia et al.(1998) who reported on isometric (b = 2.960) growth ofA. monoceros from the Gulf of Salamanca, Colombia. Thisvariation is possibly due to factors related to ecosystem andbiological phenomena like maturity stages, feeding behaviour,competition for food, etc.The overall sex ratio was 1:1.05 (n = 129). Thechi-square values indicated significant (5%) dominance byfemales in the month of September and by males in themonth of October. A. monoceros attained sexual maturityat a size of 50.2 cm total length (Fig. 3) (n = 66). However,gonadal development and sexual maturity in the specieswas observed to commence from 46 cm onwards. Thepercentage of mature and spawning females was 57.1 innets and majority of fish was caught during the night time.A multifilament gillnet fishery for A. monoceros was observedfrom August, 2009 onwards. The catch and catch rateincreased from 2.2 t and 2.45 kg unit-1 in August to a maximumof 78.9 t and 45.26 kg unit-1 in October, after which decreasedto 34.7 t and 15.62 kg unit-1 in November (Fig. 2). There wasno landing of A. monoceros in gillnets in December.33September which decreased to 28.6 in October and to nomature and spawning females in November and December,which is indicative of the fact that the monsoon monthscould be the breeding season of A. monoceros along theSaurashtra coast. Similar views were expressed by Qasim(1973) while studying the maturation and spawning ofmarine teleosts from the Indian waters and concluded thatalong the west coast, spawning takes place during monsoon.Since there was not much difference in the food andfeeding habits of males and females, the data (n = 129) onboth the sexes were pooled. The food items in the diet ofA. monoceros were classified broadly into three majorgroups: zooplankton, zoobenthos and nekton. Zooplanktonand zoobenthos were encountered in the gut of most fishesand nekton was encountered in few. Benthic invertebrates,cnidarians (polyps – corals) and worms dominated thezoobenthos group and were the most important andpreferred food item of A. monoceros. Among zooplanktonfound in gut, copepods dominated followed by decapods.The nonpenaeid prawn Acetes spp. and juveniles of clupeidsconstituted the nekton population found in the gut.Occasionally, seaweeds were also found to be consumedby the unicorn leatherjacket. Lopez-Peralta and Arcila(2002) studying the diet composition of A. monoceros formthe southern continental shelf of Colombia reported onsimilar lines that zoobenthos, zooplankton and nekton werethe major food items. Similar views from north-west Gulfof Mexico were expressed by Pattengill et al., (1997) andfrom south China Sea by Mohsin et al. (1986). The analysisof food items in relation to body size depicted that whileadults fed almost entirely on zoobenthos, juveniles preferredall zoobenthos, zooplankton and nekton. The averagecontribution of fishes in the feeding conditions of fullstomach, ¾ full stomach, ½ full stomach, ¼ full stomachand empty stomach were 6.1%, nil, 12.3%, 20.4% and61.2%, respectively. The intensity of feeding was found tobe more in juveniles than that of in adult mature fishes(Fig. 4). The length of the intestine was found to be on anaverage 3.06 times that of total body length. The relationshipbetween total body length (TL) and intestine length (IL)was log IL = -0.4788 + 1.5628 log TL (r = 0.6) (n = 129),which indicated their omnivory nature and are in fullagreement to the food items encountered in their gut.The growth parameters, Lα and K (annual) estimatedusing the ELEFAN I programme were 63.53 cm and 0.22,respectively at the highest Rn (goodness of fit index) valueof 0.595. Growth performance index φ was 2.95 and t0 wascalculated at -0.077 years. The von Bertalanffy growthequation was Lt = 63.53 [1 – e - 0.22 (t + 0.077)].  Lc was estimatedat 44.91 cm and Lr at 41.4 cm. The mortality rates M, F and Zcomputed were 0.53, 0.58 and 1.11, respectively.Exploitation ratio was 0.52. VPA indicated that main lossin the stock up to 48.5 cm size was due to natural causes.Fishes became more vulnerable to the gear after this sizeand mortality due to fishing increased and eventuallyoutnumbered the natural losses at the highest recordedlength of 60.5 cm. The mean value for fishing mortalitywas 0.15 and the mean value for exploitation ratio was 0.14.AcknowledgementsThe authors are thankful to Dr. G. Syda Rao, Director,CMFRI and Dr. N. G. K. Pillai, former Head, PFD, CMFRIfor the encouragement and the facilities provided.ReferencesGarcía, C. B., Duarte, L. O., Sandoval, N., von Schiller, D.,Melo, G. and Navajas, P. 1998. Length-weight relationshipsof demersal fishes form the Gulf of Salamanca, Colombia.Naga ICLARM Q. (in press).Gayanilo, F. C. Jr., Sparre, P. and Pauly, D. 1996. The FAO-ICLARM Stock Assessment Tools (FiSAT) User’s Guide.FAO computerised information series (Fisheries). No. 8,Rome, FAO, 126 pp.Ghosh, S., Mohanraj, G., Asokan, P. K., Dhokia, H. K., Zala,M. S. and Bhint, H. M. 2009. Trophodynamics andreproductive biology of Otolithoides biauritus (Cantor)landed by trawlers at Vanakbara, Diu along the west coastof India. Indian J. Fish.,  56(4): 261-265.Fishery and population dynamics of Aluterus monocerosFig. 3. Size at first maturity of females (n = 66) of A. monocerosFig. 4. Sizewise feeding intensity (n = 122) of A. monoceros34Khemakorn, P., Kongprom, A., Dechboon, W. and Supongpan,M. 2005. Trash fish: The links between capture fisheriesand aquaculture in Thailand. Regional Workshop on LowValue and “Trash fish” in the Asia - Pacific Region, Hanoi,Vietnam, p. 49-106.Kuiter, R. H. and Tonozuka, T. 2001. Pictorial guide to Indonesianreef fishes, Part 3. Jawfishes - Sunfishes, Opistognathidae -Molidae. Zoonetics, Australia, p. 623-893.Le Cren, E. D. 1951. The length weight relationship and seasonalcycle in gonad weight and condition in the perchPerca fluviatilis. J. Anim. Ecol., 20: 201-219.López-Peralta, R. H. and Arcila, C. A.T. 2002. Diet compositionof fish species form the southern continental shelf ofColombia. Naga, World Fish Centre Q., 25(3&4): 23-29.Mohsin, A. K. M., Ambak, M. A., Said, M. Z. B. M., Sakiam, M.and Hayase, S. 1986. A study on the feeding habits of fishesin the south-western portion of the South China Sea.In: Mohsin, A. K. M., Rahman, R. A. and Ambak, M. A.(Eds.), A study on the offshore water of the Malaysian EEZ.Faculty of Fisheries and Marine Science, UniversityPertanian, Malaysia, 197 pp.Pattengill, C. V., Semmens, B. X. and Gittings, S. R. 1997. Reeffish trophic structure at the Flower Gardens and StetsonBank, NW Gulf of Mexico. Proceedings of the8th International Coral Reef Sympossium, 1:1023-1028.Pauly, D. 1979. Theory and management of tropical multi-speciesstocks. A review with emphasis on the south-east Asiandemersal fisheries. ICLARM Studies and Reviews 1, 35 pp.Pauly, D. 1980. On the interrelationships between naturalmortality, growth parameters and mean environmentaltemperature in 175 fish stocks. L. Cons. Ciem., 39 (2):175-192.Pauly, D. 1983. Length converted catch curves. A powerful toolfor fisheries research in tropics (Part-1). ICLARM Fishbyte,1(2): 9-13.Pauly, D. 1984. Length converted catch curves. A powerful toolfor fisheries research in tropics (Part-II). ICLARM Fishbyte,2 (1): 13-14.Pauly, D. and Munro, J. L. 1984. Once more, on the compositionof growth in fish and invertebrates. Fishbyte, 2(1): 21. Qasim, S. Z. 1973. An appraisal of the studies on maturation andspawning in marine teleosts from the Indian waters. IndianJ. Fish.,  20(1): 166-181.Tuan, V. A. and Mai, B. T. Q. 2005. Trash fish use as a foodsource for major cultured species in An Giang and DongThap provinces, Mekong Delta, Vietnam. RegionalWorkshop on Low Value and “Trash fish” in theAsia - Pacific Region, Hanoi, Vietnam, p. 211-222.Shubhadeep Ghosh et al.Date of Receipt : 26.05.2010Date of Acceptance : 28.02.201135Length-weight relationship of Tor putitora (Hamilton) from Kosi RiverUttararkhand considering different stages of its lifespanN. OKENDRO SINGH, DEBAJIT SARMA AND N. GOPIMOHON SINGH*Directorate of Coldwater Fisheries Research, Bhimtal – 263 136, Nainital, Uttarakhand, India*Department of Statistics and Mathematics, Central Agricultural University, Iroisemba, Imphal, Manipur, Indiae-mail: nosingh2000@yahoo.comABSTRACTThe length-weight relationship of Tor putitora was studied from Kosi River, Ramnagar, Uttarakhand, considering four differentstages of its lifespan. ANCOVA results suggested the existence of two distinct stages of T. putitora with respect to itslength-weight relationship, which do not follow isometric growth. Further, the datasets of two distinct stages were meaningfullyfitted to allometric models with expected value parameters.Keywords: Allometric model, Distinct stages, Expected value parameters, Length-weight relationship, Tor putitoraIntroductionEstablishment of length-weight relationship of fish isa useful indicator for fishery biology studies. It hasenormous advantages as it allows the estimation of theaverage weight of the fish of a given length group bydeveloping a mathematical relationship between length andweight (Beyer, 1987). It is also useful for assessing therelative well being of the fish population (Bolger andConnolly, 1989). Like any other morphometric character,the length-weight relationship can also be used for thedifferentiation of taxonomic units and this relationship isseen to change with various developmental events in lifesuch as metamorphosis, growth and the onset of maturity.Besides this, the length-weight relationship can also be usedin setting yield equations for estimating the number of fishlanded and comparing the population in space and time(Beverton and Holt, 1957). Tor putitora is an endangeredcoldwater fish species that is popular as food fish and assource of recreation for anglers. Many researchers havealready established length-weight relationship of T. putitorafrom time to time. However, a detailed analysis on length-weight relationship of this important species has not beenattempted. The present study aims to develop length-weightrelationship of T. putitora considering different stages ofits lifespan for direct use in fishery assessment.Materials and methodsThe well known allometric model in fishery is defined by:W = aLb     (1)where ‘L’ and ‘W’ represent the length and weight ofthe fish respectively, ‘a’ and ‘b’ are parameters.Indian J. Fish., 58(1) : 35-38, 2011‘Nonlinear estimation procedures’ assuming anadditive error term is recommended for estimating theparameters involved in the above nonlinear model(Venugopalan and Prajneshu, 1998) since the linearisationof the above equation needs multiplicative error assumptionthat tends to be valid when the variability of dependentvariable weight increases with increasing values of weight(Ratkowsky, 1990). However, this does not seem logicalsince variability of weight increases as weight of fishincreases. Further, when we deal with nonlinear estimationprocedures for estimating the parameters, high parametercorrelation may be detected which is indeed undesirable.Ratkowsky  (1990) suggested to use expected valueparameters for choosing the values of the explanatoryvariable in such a way to make the parameter correlationslow. Expected value parameters can be advantageouslyused, as they are nearly unbiased, normally distributed andminimum variance estimators.We can get the expected values from equation (1) bychoosing values L1 and L2 of the explanatory variable L,within the observed range of L as follows:W1 = aL1bandW2 = aL2bSolving these equations, we get( ) ( )2121 LLlog/WWlog11LWa =

Sudden emergence of fishery and some aspects of biology and population dynamics of Aluterus monoceros (Linnaeus, 1758) at Veraval

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Sudden emergence of fishery and some aspects of biology and population dynamics of Aluterus monoceros (Linnaeus, 1758) at Veraval

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