Large numbers of the swimming crab Neptumts sanguinolentus are caught and marketed at Kozhikode and the neighbouring places on the West Coast of the Madras State from January to April or.May. It has been obtained in fairly good numbers during these months in the regular departmental catches of fish. Two other species also, N. pelagicus (Linn.) and Charybdis natator (Herbst) have been captured sporadically; but they were always few and did not make any appreciable contribution to the crab fishery at this place during the seasons of 1950 and 1951

Menon, M K

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.. • A Note on the Bionomics and Fishery of the Swimming Crab Neptunus sanguinolenlus (Herbst) on the Malabar Coast* BY M. Krishna Menon, Prawn Research Unit ot The Central Marine Fisheries Research Station, Narakkal. With 3 Text-figures Received 7th January, 1952 I-Introduction II-Breeding IlI----Growfb IV-Age Composition V-Moults VI-Food VII-Sexual Maturity CoNTRN'fS ··t VIII-Proportion and Size of the Sexes IX-Migration X-Fishery XI-Acknowledgement XII-References 'jJ I-Introduction ,., Page 177 178 178 180 .. 180 ISo 182 ... r82 :x:82 183 183 183 Large numbers of the swimming crab Neptumts sanguinolentus are caught and marketed at Kozhikode and the neighbouring places on the West Coast of the Madras State from January to April or.May. It has been obtained in fairly good numbers during these months in the regular departmental catches of fish. Two other species also, N. pelagicus (Linn.) and Charybdis natator (Herbst) have been captured sporadically; but they were always few and did not make any appreciable contribution to the crab fishery at this place during the seasons of 1950 and 1951. The results of the study of this material, collected in the course of the last two years, are embodied in this note. Very little work has been " done on the biology of Indian crabs. Macann's studies (1939) on the land crab Paratelphusa (Barytelphusa) guerini · of Salsette, Miss Naidu's (1951) on Ocypoda pZatytarsis are perhaps the only papers that have been published. Both these species have little economic importance. Prasad and Tampi (I952) have recently published an account of the fishery for .* Published with the permission of the Chief l{esearch-Offic~r, Central ,Marine Fisberies Research Station, Mandapam . • • 178 JOURNAL OF THE ZOOLOGICAL SOCIETY OF INDIA [Vol. 4, No.2 Neptunus pelagicus near Mandapam. It is, therefore, hoped that the· pUblica-tion of this note on a commercial species may be worthwhile. 'Materiill ha$ ooen called d from th hallow w t\:f.S off West HUL usualJ, lip to u d pth of 4 falli-oms, but ~asiaoally lip to a"Oout 8 fathoms al o. Three types. of -nets, the boat seine, the gill net and the ca.st (l t have been used.. t ho bo~ seine Was IDi\11er tban those COtnnlonly useCl in commelcial lShin~' on thls coast. the me&has of the bag -vuying in size from ~ to about I crn,. In taking measurements the disthn;c.e b~hv en the qps of the largest spines bas alont;: beep noted for each individual. II-Breeding In the months of February and March, which usually register the peak of the fishery, numerous berried females have been observed in the market and some have been obtained in our collections as well. In the succeeding months there is a marked fall in their numbers; although a few may be caught even ari late as June. During these months they na:ve ooen f:lrely seen in ollI collections. There is little doubt, therefore, that the breeding period of the species coincides largely with the fishery season and that the maximum numbers breed during these two months. The commercial catches are usually made at about the same depths; but the plankton oolIec ionstoro this a,r~ l)ave seldom contained their larvae in appreci. able numbers. Th6 smaUes arabs c;ap ured in the boa $erne h'Wel a catqpaol'l width .of about I 3"" 4 rum .. even though the meshes of the net are ~mall enougb lohavo caugh much YOounger forms n they were present:in consider bIt:. nUfi').bers in the fishing grounds. These two facts would seem to indicate th<\t hatching- of th eggs takes place etsewlwre. robably ill deep l' water, t110tlgh th l' 1 no po~itive evidene.e for this conclusion. In the a~ence of arwl material notMng about the ~ijrly life history is !tnoWnj btl it is possible tlmt in gene.ral charact~rs the larvae may res:emhl t.bpse of N. pelagici<S de-scrib,-ed by Delsman and De Man (I925). Ill-Growth TVi'O pecllnen. r one of w1tich was avp~ttmtly .in the fini t pos larval ~tage~ and the othth: having a. carapace Width of a.bout 8 mm. weJ.1 obt<1.ined from the marina pl~nkton at !fa !'as. Both of them were reared in the lAboratory. being fed en minced lam meat. which they re clHy accepted. 'rho filit Qne lived for a. month. from ~-It'"48 · to 26-12-48 and reached a carapace width of 11 rom. The-other ~peJiment lns'ecd :£ r a m'ClutQ. and ~o d y~. rr-om 3+49 tQ ~3-2-49 and the iinal size re-aclred was If,.l rom. tJ~ortunaroly the .exact numoor of moulfJ and the increase in size at each w re not recorded at h!i tima. Though th can· ditions were practically in den tical growth in the second experiment was slower '- the increase of abollt 33 mm. being the result of about 50 days' growth . ,1. 4, No.2 e publica-11, usually 30. Three lsed. The rrg on this In taking ;J.lone been le peak of larket and ng months ht even ali collections. s coincides eed during ns; but the in appreci-a carapace lan enough ,Ie numbers hatching of lere is no 'ial nothing l characters an and De lrval stage, :d from the ltory, being Ie lived for of 31 mm. 23-2-49 and r of moults .gh the con-was slower wth. Dec_ .' . ,W52] MENON, M. K: NEPTUNUS SAN&UJNOLENTUS w ,~u fi60 • .. QCQ I~O :wo . .• »: 1(1) 6[1' I) , J~ fa' III 'B 1, >3~ 4 f!l ft~ s~ ~3 · ftS ~3 'UI IItj ,~ 1J1;NG'rH IJiI M IrI fEin·f/G ,-Curl'es IIl:!oWllig- tbo: t llta l .she l~u/!D~W!':. r~r th~' .r; ,4U f95" and I95 r separa tilly f5{1 . .00 · --------1950-1951 Tll:XT-FIG. ~-Curve sh6',Ving the combined. trequ.eucies for J950 an<t 1951 •. J:tlQ JOURNAL OF THE ZOOLOGICAL SOCIETY OF INDIA [Vol. 4, No.2 t.~, ... IV-Age Composition .. Iheresult of Mf ·attljn1p at estimatlng the age composition, ilL the: c'QJ:lectians by prepadn($' curv,eS of tbeir- sire frcqw.mcie's. aro gl\(en below. 'nte graphs ff;l,wn liyp.lOttlng tiW toW· fre.q~eildes f9r the' two seasOils separately a.nil togtlthCII an) shown in, Th.tt.,ftgn'(es I ana~. WJille tilat'for t1fle 195I'season shO\vs only 01l~· pro~ lrunent mode repr~,~llting thE\. Z,t-.25 ~;m. gtO\J,I? thQ~ rQr "1950 n(J the two y6aJ'S ~o.getbe" sho,! two Qther weU-Q,efined rotrd~ (13 ano G) t.o-pre:s~nting the 56-60 mtt1. and 76'£0 lllrn. &f.oulJS re$p~ctiv~y', If the tat&) of growth in their nattll'tLI Cn'~ftonments is c.omparablC' tp that uilderll!-bomtor}t "cooditiOll$ H'l~n Qoth these groll~S may not be o}<l:er than 3-4 or 5 monthsanll prooo.b1y liOlIi!! of the hL,ghc~ grcpttpS likeWt~~ may not be over an year' old. Ev~ al1QWingf r a progr~h" slowing (lown. in grOWUl r~'e. 'tiS p:slla.lly happens. i.t \$- by nQ titeaB certain that tbj! groups nl$llltio:n,ed ab,ov could COllS~!1t of animalS older thag on~ year. Wi~b the data.a.vallable at pms~ • th r fo~. tile method <dOe!!! net pe.rmit l')f any oefil'lite, cOllclusiOBS. II. weu\d se~m, howev r. I:hat ~ large pr~porti{ln of t e eateli!::!! js CQmp.o :cd d£ crabs bdo.ll~j.ng to tho generatioQ pfl)du~d d1.lting file immediately preceding breeding season. V-Mourw The fa t til' t 'growth in th$e :utimals i... nQt a contil1llolijj PJ~ss. ltut is , ffe~led in a sel'i'ps (if l~ps at thp ti)l1f: of m011lting mak s it !;losslMe to &n'iw at some idea s:ta.t1~t.iclm~r of the D1Jmber (jf time'S th~.'le moults tll'ke place. duripg Q partioular period of gro'i\r(h. Fo.r "his purpcse tha:' total number of individuals, for every millimetre increase in si:?;e from 3 rmu. (the smaUest in the col1cctipn) to 60 mrn. "',as C1'I1Cldaleli. The,data for I961: alone were, \JMd in this.. 9.lmn:eotidn. Tb~,se T~~r-:figll're$ \Vij~ p~~tted and fM graph pc pared is shown in Tf.xt~1lgure 3· The curve exhibit , a number (jf mai;1;cs j~'Pf!!s;entit'lg the fonowin~ siY.eS I9. ,if), 3 I 34, 38. 42,,4', 49, 51;, 5-3:~ 57 andS9 • . and thus obvi06~ly mu~lites he disGOlI6nll~ QU ' manner of .Sl'1lwth.. As each inCI'e~e is 'tbe reSult f)f :i 1.no\ll • ibero W~e 1111-paTently XI moults during gt'owth between 1;1 ItIm". <j:Qd 60 mrri. In th' ab3enc:e of any other method, except that of rearing them, to decide v.rhether so many moult~ have actually taken place, it will be necessary to accept this number with some caution. VI-Food The stomach contents of a number of specimens ranging in size from 25 mm. to go mm. have been examined; but it has not been possible to discover any marked change in the diet at different stages of growth except in the size of the Ofg!'ltlisms making up the fQ:Od. As in the e-as¢. cif aU bottom fc:cding erllSt.;iooilJlS c the food consisted of varying amounts of organic matter mixed with sand and • 4. No.2 :ollections ihs drawn ~ether are lone pro-1 the two ?nting the h in their dons then ably some wing for a no means r than one not perm1t oportion of during the cess. but is .le to arrive place during £ individuals le collection) 3 connection. ~ext-figure 3· s 19. 26. 31, Ie discontinu-lere were ap-1 the absence ;her so many this number from 25 mm. discover any :he size of the .ng crustaceans mith sand and II • Dec. 19511] MENON. M. K: NEpTUNUS SANGUlNOLENTUS .. 70 10 IJ HI 26 31 34 39 42 46 49 51 53 57 59 LENGTH IN MM TEXT-FIG. 3-Curve showing the probable number of moults during growth from 13 mm. to 60 mm. l bl mud. Except in two or three, plant material, other than diatoms, was absent and even in the few in which it was present, it was perhaps taken in accidentally along with the other constituents. Among the animal fragments bivavle molluscs and crustaceans, especially amphipods and decapods, predominated. Small gastropods, copepods and polychaet worms also formed an appreciable part of the food of several crabs. Scales and vertebrae of bony fishes and the Cypris larvae of barnacles were also occasionally noticed. • IS::!, JOURNAL OF THE ZOOLOGICAL SOCIETY OF INDIA [Vol. 4, No.2 VII-Sexual Maturity Fully developed spermatozoa have been observed in males measuring about 80 mm. and upwards so that it may be safely assumed that individuals of this sex become mature :when they reach a size of 80-90 mm. Among the berried females captured the smallest measured 78 mm. It is probable, therefore, that the females also attain maturity at about the same size as the males. In the light of what has been stated above in connection with the age composition of the catches, it is quite likely that some individuals of both sexes may become mature in the first year itself. VIII-Proportion and Size of the Sexes The sexes in each day's collection have been usually sorted out separately and their numbers determined, excluding the smallest, whose sex could not be distinguished. Their total number for the entire season has also been calculated. In the 1950 collections males outnumbered females, their proportions being 54.3% arid 45.75% respectively. In the current year, however, the total number of males is less, forming only 46.8%. It has been pointed out by Mackay (1946) in the case of the Pacific edible crab Cancer magister that though the sexes may occur in approximately equal numbers in the total popUlation, due to intem:G fish-ing or their segregation, one may be found in much larger numbers than the other in a particular area. In regard to the maximum size attained by the two sexes, not much disparity has been noticed; the largest males and females obtained so far being 144 mm. and I42 mm. respectively. The number of males and females of 100 mm. and over was also estimated for each year. In 1950 their proportion was 59.1% and 40.9% respectively; for the previous year it is 50.8% and 49..2%. The higher percentage for the previous year is in agreement with the corresponding larger proportion of the total number of males for that year; but during 1951, although the males were less, the proportion reaching the size specified is slightly higher. In view of this, it seems likely that in this species also, the rate of growth of males after reaching maturity may be higher than that of females, as happenes in the case of C. magister. IX-Migration The fact that large numbers of all sizes have been captured in shallow :water near the coast · in the months of January to May, while few or none have been obtained from the same area in most of the other months points to the probabili-ty of an annual migration. During this season young ones seem to ascend into river mouths, as they have been captured from the mouth of the Elathur river, a few miles north of Kozhikode. Panikkar and Aiyyar (1939) have reported the occurniuce of the species in the Adyar backwaters during the period when the 0 bar is open. '_ At other times, when the communication is cut off, they were .absent • ,. 4 No.2-tJ.. 1 , ut lring aoo J.als of this the berri~d ore, that the In the light 'to n of the 5110 corne mature out separately • could not be · en calcula.ted. Ie . ~portions being t 1 number }e to a · Ma.ckay (1946) '1 the sezes ~ay . ten~'" hSP.-eta In ~v the other rs than • Dec. 1952J MENON. M. Ie: NEPTUNUS SANGUlNOLENTUS and they, therefore, think that it is only a casual migrant." The species practically dis~PE ars from the- coastal wuters at West Hill after the monsoon rains start nnd in all likelihood moves into off.t;hore waren. The .European Cl'ab Cancer 'l!agrtrul; ;bas b~ Qbscrved to perform simila.r annual migr iien-5, ,away from the thorn during the autumn and towards th shore ill he ~plin~. Furi.her 'work is required fa confirm this observation as w 11 as to c]etennine the area covered by these migrations. X-Fishery It has been mentioned already that the fishery is of short duration com-mencing in January or February and ending in May. The largest numbers are caught in February, March and probably April. The fishing area does not usua.lly e~tend b~yond 7..a fathoms", a ~ood pa.rt of ilie catch bemg made by ,eClst net in w.ater Dot more than 2-3 fa homs-and the rest in beat seines an(;l gin 1\t1h;. It is s;;).id that some are tal1gbtby hand from belwe6n stones by divem. Practi-clllly th ~ntfro catQ}l f>eelIl.$ ,to be dl~;poscd of ·loCo111y. When ompamd 'to the prawn nshtlty of thi.s co~s.t that of (,."[absappears La be of ]jttle importance at present, as, according to Chidambaram and Raman (1944) the average annual landings amount to only 23 tons. In the absence of any provision to regulate the fishery, there is indiscrimi-nate fishing and large numbers of berried females are also caught. If the capture of such females could be prevented so as to allow most of them to breed normally there Il4'].Y be increasCl in the population. or the crab wbich may lead to an improvement of the fishery. Fishing with the boat seine inevitably leads to the destruction of numerous young, which, if allowed to grow and reach maturity, may be expected to enhance the value of the fishery. XI-Acknowledgement I wish to express my thanks to Dr. N. K. Panikkar, Chief Research Officer, Central Marine Fisheries Research Station, for kindly going through the paper and suggesting ·improvements. XII-References r. CHIDAMBARAM, K. and RAMAN, R. S. V. 1944. Prawn and crab fishing in Madra~. Indian Farming, 6. 2. DELSMAN, H. C. and DE MAN, J. G. 1925. On the 'Radjungans' of the Bay of Batavia. Extrait De Treubia-, 6, 3-4. 3. MACANN, c.. T<J37.. l'to~ Oll, the oommnn ltlnd c~:l.b , Pn"a,tfJU,ht;~a' (Barytelphusa.) guarlnl (M.lM!w) of Salretto. lor,. Bomh. N/i't . IlJsL. 5qc .• at). <1. MACKAY, DONALD, C. G. 1941. The Pacific edible crab. Cancer macister. Bull. Fish. Hes. Bd. Canada, 46. ~. NAIDU, MISS K. G. RAJA BAr 1951. Some stages in the development and bionomi(:s of Ocypoda platytarsis, proc. Ind , Acaci. Sci., Sectio!l B, 33! +I II .. 184 JOURNAL OF THE ZOOLOGICAL SOCIETY 0·' INOlA [Vol. 4, No.2 ' (l. PII"j J ' l~~> N. xl. . q~ J\lVER. ~" G, !9~l'l:> Observations on breeding "in brackish waw!\" anl1D!\13 (l! N~iiJ PrQI). bitt. At;,(lil. SiI., ~j Lon B. O. f. PRiiSAD, !t. R. . :lnd 1".mF!. P . R. So 19~1", An account of the fishery and fishing methods for Neptunus polegicus (Linnaeuc) near :Kla.'I!dapwn.. I. Zocl. Soo. Indid. ,3~ .. • 

A Note on the Bionomics and Fishery of the Swimming Crab Neptunus sanguinolenlus (Herbst) on the Malabar Coast

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A Note on the Bionomics and Fishery of the Swimming Crab Neptunus sanguinolenlus (Herbst) on the Malabar Coast

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