Spadenose shark, Scoliodon laticaudus (Family: Carcharhinide) locally known as “sandhi” is a common species inhabiting

near shallow coastal waters along the Saurashtra coast. It is exploited by trawls and gillnets throughout the year in fair

abundance. The dietary components of the species were studied and expressed as percentage of numerical composition (CN),

percentage of gravimetric composition (CW) and percentage of frequency of occurrence (F). The major food item in the

stomachs of the species was determined using an Index of relative importance (IRI). Food and feeding analyses confirmed

the carnivorous feeding behavior of this species and the food mostly comprised fishes, shrimps and squids. There was no

evidence of cannibalism. Overall sex ratio was 1.18 that showed the predominance of females over males. As there is limited

information about the biological aspects of this species from Saurashtra coast, the results of the present investigation may

play a vital role in the management of the resource as well as for the efficient exploitation of this species

Fofandi, Mahendra

Koya, Mohammed

Zala, M S

CMFRI Digital Repository

51Observations on selected biological aspects of the spadenose shark(Scoliodon laticaudus Müller & Henle, 1838), landed alongSaurashtra coastMAHENDRA D. FOFANDI, MANGALSINH ZALA AND M. KOYAVeraval Regional Centre of  Central Marine Fisheries Research Institute, Veraval - 362 269, Gujarat, Indiae-mail: fofandimahendra@gmail.comABSTRACTSpadenose shark, Scoliodon laticaudus (Family: Carcharhinide) locally known as “sandhi” is a common species inhabitingnear shallow coastal waters along the Saurashtra coast. It is exploited by trawls and gillnets throughout the year in fairabundance. The dietary components of the species were studied and expressed as  percentage of numerical composition (CN),percentage of gravimetric composition (CW) and percentage of frequency of occurrence (F). The major food item in thestomachs of the species was determined using an Index of relative importance (IRI). Food and feeding analyses confirmedthe carnivorous feeding behavior of this species and the food  mostly comprised  fishes, shrimps and squids. There was noevidence of cannibalism. Overall sex ratio was 1.18 that showed the predominance of females over males. As there is limitedinformation about the biological aspects of this species from Saurashtra coast, the results of the present investigation mayplay a vital role in the management of the  resource as well as for the efficient exploitation of this species.Keywords: Food and feeding habit, Scoliodon laticaudus, Spadenose sharkIntroductionElasmobranchs are caught by trawls, gillnets, hooksand lines and dolnets along the Saurashtra coast. About45% of the total elasmobranchs are landed by trawl net,24.7% by gillnets operated from mechanised boats, 18.2%by nonmechanised gillnets, 9.6% by hooks and lines and2.1% by dolnets. About 65% of batoid fishes and 33% ofthe sharks landings are from the trawlers. The catch andcatch rate of sharks from trawlers have increased over theyears, whereas the catch rate from mechanised gillnetsdeclined over the years after registering a peak during 1985.The elasmobranchs, as a group have been found to bedistributed all along the Indian coast constituting about 6%of the national marine fishery resources. The landingsfluctuated from 26,710 t in 2008 to 29,126 t in 2009 (Anon,2010). There was steady increase in the catches till theseventies. The introduction and expansion of mechanisationof fishing has resulted in substantial increase in the catches.S. laticaudus, Muller & Henle (1838), one of thesmallest tropical carcharhinid sharks is locally known as“sandhi” in coastal area of Saurashtra region. In recentyears,  elasmobranchs have attracted the attention of thefishing industry because of their fins and flesh which havehigh utility value in both export market as well as with inthe country. Sharks are processed for meat which is soldIndian J. Fish., 60(1) : 51-54, 2013frozen or dried, for shark fin soup, leather, liver oil andcartilage for export to  different countries namely Singapore,Thailand, Malaysia, China and others. However,  shark finsare most valuable fetching $60 per 0.5 kg (Cheung, 2003).S. laticaudus is not a fast swimmer and occupies the nearshore region in shallow waters. It is mostly caught in trawlgear as a bycatch.The earlier works on this species were mostly doneon aspects of taxonomy and distribution. Literatureavailable on the biology of this shark species is limited.A study on the description, bionomics and development ofS. sorrakowah, which is now considered a synonym ofS. laticaudus was carried out by Setna and Sarangdhar(1948). The age and growth of S. laticaudus were studiedin Bombay waters by Nair (1976). Devadoss (1984) carriedout a detailed study on the maturity, breeding anddevelopment of this shark off Calicut. Devadoss (1989)also studied the growth and population parameters ofS. laticaudus from Calicut coast. Kasim (1991)  reportedon the shark fishery of Veraval coast with special referenceto population dynamics of S. laticaudus andRhizoprionodon acutus. Unfortunately, no work has beendone on the other aspects of biology like length-weightrelationship, food and feeding habits and sex ratio of thisshark species from the Saurashtra region. Hence an attemptwas made  to fill up the gap which may be helpful for52Mahendra D. Fofandi  et al.devising policy guidelines for managing stock and fisheryof this species along Saurashtra coast.Materials and methodsMulti-stage stratified random sampling method wasadopted for the collection of samples. Every fortnight, atotal of 25 specimens of different size ranges,  werecollected randomly from the trawlers and gillnettersoperating along Saurashtra coast during April 2009 toMarch 2010. Samples were placed into insulated boxes withice and brought to the laboratory for the biological analyses.The total length was measured from the tip of snoutto the tip of upper caudal lobe to the nearest mm and weightto 0.5 g accuracy. The relationship between themeasurements were worked out using the formula of linearregression (Y = a+bX) using regression module of SPSSsoftware (SPSS 10.0, SPSS Inc., Chicago, USA). Thelength-weight relationships were estimated from theallometric formula proposed by Le Cren (1951), separatelyfor both the sexes:W = a L borlog W = log a + b * log LThe feeding intensity was determined by eyeestimation based on the degree of distension of thestomachs. The various stomach conditions based on degreeof fullness expressed as gorged, full, ¾ full, ½ full, ¼ full,trace and empty were studied according to the method givenby Pillay (1952). The dietary components for each stomachstudied were expressed as a percentage of numericalcomposition (CN), percentage of gravimetric composition(CW) and percentage of frequency of occurrence (F)(Hyslop, 1980). The most important food item wasdetermined  using the Index of Relative Importance(IRI %) of Pinkas  et al. (1971) :IRI % = (CN + CW) x FThe month-wise sex ratio was determined andChi-square (χ2) test was performed to test the homogeneityof male and female distribution (Sokal and Rohlf, 1998).ResultsLength-weight relationship A total of 439 (201 males and 238 females) specimensof S. laticaudus in the length range of 22.30 – 68.50 cmwere used for determining the length-weight relationshipseparately for males and females. The regression equationsderived are as follows :Male: log W = -2.3167 + 2.8174 log L ( r = 0.9564 )Female: log W = -2.5407 + 2.9263 log L ( r = 0.9907)Since, there was no significant difference between theslopes at 5% level, a pooled relationship (Fig. 1) wasobtained for males and females as:Pooled: log W = -2.4331 + 2. 9465 log L ( r = 0.9709)Fig. 1. Length-weight relationship of of S. laticaudus (pooled)Food and feedingMonthwise feeding intensity of  S. laticaudusHighest percentage of empty stomachs was recordedin October (78%) and the lowest in January (32%) inS. laticaudus (Fig. 2). Percentage of low feeding (trace and¼ full) varied from 4% in April to 53% in November. Inthe month of October, there was no trace and ¼ fullstomachs observed. Moderate feeding  (½ full and ¾ full)was seen to fluctuate from 1% in August to highest of 49%in December. Percentage of high feeding (full stomachs)also varied considerably from 4% in January to 12% inAugust and there was no gorged stomach observed duringthe  entire study period.Fig. 2. Month-wise feeding intensity of S. laticaudusFood patternsFood and feeding analyses confirmed the carnivorousfeeding behaviour of the species. The diet of S. laticauduscomprised Coilia dussumieri, Trypauchen vagina,Harpodon nehereus, Lepturacanthus savala, Thryssa spp.,Cynoglossus spp., Loligo spp., Solenocera spp., Sardinella spp.,Sciaenids, Sepia spp., Squilla spp., Acetes indicus,53Biology of Scoliodon laticaudusMetapenaeus monoceros, Metapenaeopsis stridulans andParapenaeopsis stylifera.Frequency of occurrenceThe most frequent food item found in the S. laticaudusdiet was digested fish, shrimp and molluscs which wereencountered during almost all the months. During Januaryto September, shrimps were  frequent food item, while  afterOctober, fish species was observed in much of the stomachcontents (Fig. 3).Shrimp was the most dominant group in the stomachcontent of S. laticaudus. Shrimps were found to be dominantamong the food items  in the month of January (83.56%)followed by August (65.69%) (Fig. 3). The lowest valuewas recorded during October (2.06%). The shrimp speciesrecorded includes Acetes indicus, Metapenaeus monoceros,Metapenaeopsis stridulans and Parapenaeopsis stylifera.As evident from the Index of relative importancevalues, the bulk of food was constituted by fish duringOctober to December. Fish was the second dominant fooditem in most of the months. Altogether  five species of fishesoccurred in the gut and C. dussumieri was the mostdominant species encountered. Highest quantity of fish foodin gut content was recorded during November (84.71%)and lowest percentage was recorded in the month of August(2.02%). The fish species  recorded in the gut contentscomprised Trypauchen vagina, Sciaenid spp., Harpodonnehereus, Lepturacanthus savala and  Thryssa spp.Molluscs encountered in the stomach contents ofS. laticaudus include squid and cuttlefish. Highest quantityof squid (Loligo spp.) was recorded during October(16.76%) and December (0.90%). Sepia spp. was recordedin the month of August (4.03%).Crustaceans were chiefly represented by Squilla spp.and was recorded only during August (28.24%) and March(3.74%).Index of relative importance (IRI)The IRI percentage revealed that digested shrimps(46.36%) and fishes (40.15%) contributed more than otherfood items. C. dussumieri (34.62%), ribbonfish (13.57%),Bombayduck (11.79%) and Thryssa spp. (2.64%) were thedominant  food items. Squilla spp. (15.99%), Acetes spp.(14.65%),  Loligo spp. (8.83%) and Sepia spp. (2.50%)stand next to the above list of food items of  S. laticaudus(Fig. 4).Fig. 3. Percentage of frequency of occurrence of food items inS. laticaudusFig. 4. Month-wise percentage index of relative importance offood items in S. laticaudusSex ratioSex ratio was calculated monthly for males andfemales (Table 1). The overall sex ratio was 1.18. Chi squarevalues indicated significant dominance by females in themonths of August 2009, September 2009, November 2009,December 2009 and March 2010 and there was apreponderance of catch of males in the months of April2009, October 2009, and January 2010.Table 1. Month-wise sex ratio of S. laticaudus.Month Sex ratioApril, 2009 0.85August 1.27September 2.4October 0.67November 2.58December 4.56January, 2010 0.75March 1.1Average 1.18DiscussionIn the present study, highest ‘b’ value was arrived atfor females of S. laticaudus followed by males. Theexponential value of 2.926 in females implies that thefemales gain weight at a faster rate in relation to its lengthwhereas the low exponential value compared to female(2.817) observed in males reveals the reverse condition.It may be concluded that during early stages of life, growthrate is allometric. The b value   estimated for the sexes54combined was 2.946. The results  indicated allometricgrowth (b<3) in both  sexes.  The maximum length ofS. laticaudus recorded in the present study was 68.50 cmfor female specimen. However, Mathew (1997) and Nair(1976) recorded maximum length of 66 cm for female and60 cm for male respectively.S. laticaudus has a carnivorous feeding nature andmainly feeds on fishes, shrimps and molluscs (squid andcuttlefish). It is seen that the overall percentage of fishspecies in the stomach of S. laticaudus is high as comparedto shrimps. This indicates that fish is the main componentof their diet and considered to be their preferred food.During the  study period, digested matter which includesfish scales, fish bones and eyeballs often encountered inthe diet, are evidently the remnants of the fish normallyeaten by S. laticaudus. The food items recorded in thepresent study were fishes (C. dussumieri, T. vagina,H. neherus, L. savala, Thryssa spp., Cynoglossus spp.,Sardinella spp., Sciaenids), shrimps (Solenocera spp.,A. indicus, Squilla spp., M. monoceros, M. stridulans andP. stylifera) and molluscs (Loligo spp. and Sepia spp.).Similar food items were also reported by Devadoss (1989).As food items like bottom living fishes namelyCynoglossus spp., Sciaenids  and crustaceans like shrimpsand Squilla spp., observed in the stomach  contents ofsmaller specimens, indicate that S. laticaudus in their earlygrowing years when they are unable to move fast,  seekand prey such bottom living fishes. As they grow andbecome fast swimmers,  they migrate to the pelagic zoneand start actively preying on pelagic fishes likeC. dussumieri, H. nehereus and fast moving molluscs likesquids and cuttlefish.  Cannibalism was not encounteredduring the entire study period. In the present study, theoverall sex ratio observed was 1.18 and females were largerin number than males.S. laticaudus occupies a position high in the marinefoodweb, far from the primary producers and this has itssignificance in the low productivity of its fishery unlikeCoilia, sardines or mackerel.AcknowledgementsThe authors are grateful  to Dr. G. Syda Rao. Director,Central Marine Fisheries Research Institute for extendingall the help and encouragement for carrying out this study.They are also thankful  to the Scientist-in-charge, VeravalRegional Centre of CMFRI for his valuable comments  andsuggestions.ReferencesCheung Gordon C. K. and Chak Yan Chang 2003. Sustainablebusiness versus sustainable environment: a case study ofthe Hong Kong shark fin business,  11:  223-225.CMFRI 2010. CMFRI Annual Report 2010 - 2011.  Central MarineFfisheries Research Institute, Kochi.Compagno, L. 1984. FAO species catalogue. Vol. 4. Sharks ofthe world. An annotated and illustrated catalogue of sharkspecies known to date. Part 2. Carcharhiniformes. FAO Fish.Synop. (125), 4 (2): 251-655.Devadoss, P. 1984. Observations on the maturity, breeding anddevelopment of Scoliodon laticaudus off Calicut coast.J. Mar. Biol. Ass. India, 2: 103-110.Devadoss, P. 1989. Observations on the length-weight relationshipand food and feeding habits of spadenose shark, Scoliodonlaticaudus, Muller & Henle. Indian J. Fish., 36 (2):169-174.Hyslop, E. J. 1980. Stomach analysis - a review of methods andtheir application. J. Fish. Biol., 17: 411-429.Kasim, H. M. 1991. Shark fishery of Veraval coast with specialreference to population dynamics of Scoliodonlaticaudus (Muller and Henle) and Rhizoprionodonacutus (Ruppell).  J. Mar. Biol. Ass. India 33(1/2): 213-228.Le Cren, E. D. 1951. The length-weight relationship and seasonalcycle in gonad weight and condition in the Perch (Percafluviatilis). J. Anim. Ecol., 20: 201-219.Mathew, Joseph, C. and Devaraj, M. 1997. The biology andpopulation dynamics of the spadenose shark Scoliodonlaticaudus in the coastal waters of Maharashtra State,India. Indian J. Fish., 44 (1): 11-27.Nair, K. P. 1976. Age and growth of yellow dog shark S. laticaudusfrom Bombay waters.  J. Mar. Biol. Ass. India, 18(3):531-539.Pinkas, L., Olipham, M. S. and Iverson, I. L. K.  1971. Foodhabits of albacore, bluefin  tuna and bonito in Californianwaters. California Fish Game, 152: 1-105Pillay, T. V. R. 1952. A critique of the methods of study of food offishes. J. Zool. Soc. India, 1: 185-200.Setna, S. B. and Sarngadhar, P. N. 1948. Description, bionomicsand development of Scoliodon sorrakowah (Cuvier),Rec. Indian Mus., 46: 25-53Sokal, R. R. and Rohlf, F. J. 1998. Biometry: the principles andpractice of statistics in biological research. Freeman and Co.,New York, 850 pp.Mahendra D. Fofandi  et al.Date of Receipt : 01.03.2012Date of Acceptance : 09.10.2012

Observations on selected biological aspects of the spadenose shark

(Scoliodon laticaudus Müller & Henle, 1838), landed along

Saurashtra coast

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Observations on selected biological aspects of the spadenose shark (Scoliodon laticaudus Müller & Henle, 1838), landed along Saurashtra coast

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