Not to be cited without prior reference to the author

International Council for theExploration of the Sea

C.M. 1993!K:15Shellfish Committee

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THE DIET OF LOLIGO VULGARIS AND LOUGO FORBESI(CEPHALOPODA: LOLIGINIDAE)

IN THE GALICIA WATERS (NW SPAIN).

by

F. Rocha, B.G. Castro, M.S. Gil and A. Guerra

Instituto de Investigaciones Marinas (CSIC). Eduardo Cabello 6. 36208 Vigo. Spain.

ABSTRACT

The stomach comems of 723 Loligo yulgaris and 440 Loligo forbesi caughl in the Galician waters havebeen examined. The diel of both species is described and compared. Loligo yulgaris shows 29 differentitems of prey belonging lO 4 groups (Teleoslei. Crustaeea. CephaJopoda and Polychaeta) and Loligoforbesi 28 different items of prey belonging lO 3 groups (Teleostei. Crustacea and Cephalopoda). Bothspecies cateh similar prey species but in different proportions. Carutibalism was observed in bothspecies. Estimated prey sires were smaller than squid sizes. No differences in feeding habits of malesand females of both species were observed. bUl females seem to increase food intake during maturation.No significanl changes were found in lhe diel of Loligo yulgaris wilhin lhe sire (DML) range studied(65-465 mm). Importance of cephalopods increased and fish decreased in lhe diet of Loligo forbesiwith size (65-685 mm). Diet and food intake variated with seasons in both species.

INTRODUCTION

Loligo vulgaris (Lamarck) and Loligo forbesi Steenstrup are two common cephalopodspecies in Galician Waters (NW Spain). Both squids are caught as by-catch in a multispeciestrawling fisheries and seasonally in an artisanal hand-jigs fishery in Galicia (Guerra er al., inpress). Management of these fisheries can be afford using multispecies models (Mercer,1982). These models require to know the trophic conections among the different speciesincluded in them. Then, a detailed knowledge of the natural diet of the different species ofthe fishery is basic for stablishing these trophic relations.

L. vulgaris and L. forbesi as other loliginid cephalopods are probably very activepredators, playing an imponant role in the trophic web of Galician waters. The biology ofthese species in this area is currently being studied during the course of a EuropeanCommunity project which deals about Stock Dynamics and Recruitment in Fished Populationsof Nonh East Atlantic Squid. As a pan of these biological studies, sampies of stornach

contents of bOlh Loligo were collected for diet detemimitions.The diet of L. vulgaris and L. jorbesi is poorly k.ßown. The only previous studies of

the prey of L. vulgaris in its natural habitat are those by Burukovski er al. (1979) in Central­East AtIantic; Woms (1983) in the Mediterranean Sea; Baddyr (1988) in Tifnit (Morroco),and the preliminary study by Guerra and Rocha (in press) in Galician waters.

Studies of the diet of L.jorbesi were carried out by Martins (1982) mAzores; Gaard(1987) in Farce Bank; Ngoile (1987) arid Howard er: al. (1987) in Scottish waters, and thepreliminary study by Guemi arid Rocha ,(in press) off Galician co<ist.

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In the present paper are descnbed and compared the natural diet of L. vulgaris and L.jorbesi off Galicia (NW Spain), taking into account the effects of sex, size and season in thefeeding of both species. :

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MATERIAL AND METHODSi

The stornach conterlts of 723 L. vulgaris and 440 L. jorbesi caught between February •1991 and December 1992 were eXaniined. SampIes were obtairied from commerciallandingsin vririous Galician ports. For each specimen dorsal maritIe length (DML), weight, sex andrnaturity stage (O-V~ Ngoile, 1987) were noted. Digestive tract was removed and stornachcontents weighed arid stored in alcohol 70° before analysis. .

Prey werc idenÜfied to the lowest possible taxon. Bony fishes arid cephaloPocts wereidentifiect from reference collections,of fish otoliths arid cephalopod beaks arid employirig theguides by Chairie and Duvergier (i934), Schmidt (1934), Chaine (1936), Bauza-Rulhin (1962)arid Härkönen (1986) for otoliths and Clarke (1986) arid Perez-Garichiras (1986) forcephalopod beaks. CrUstacean rerriains were identified from descriptlons and drawings byZarlquiey (1968) and Gonzalez-Gumaran & Mendez (1985). When it was not possible toidentify a prey, arid it was clearly different from otherS, it was placed iri a different categoryand assigned to an arbitrary taxori. !, ., ,

\Vhen it was posible, prey size was estimated frorn fish otoliths and cephalopod beaksand gladius, using equations found in Härkönen (1986) 'arid Clarke (1986) and Perez-Gandanls(1986), respeciively. .

The following indices were used (Castro and Guerra, 1990): ",Occurrence Iridex (OCI): Thc quotient in percentage between the number of stomaehs •

with one type of prey present arid the total number of stomachs examined which containeddebris from. one or several types of prey, each stornach being counted as many times as thenumberof different prey types itcontained., I , ,

Numerical Imporiance Index (NIl): The relationship in percent bCtween the numbCrof individuals in each food category recorded for all stomachs and the total individuals in allfood categories. :,

Emptiness Index (EMI): The riumber of einpty stomachs compaied with the totalnumber of stomaehs as a percentage.: ,

In order to compare the diet of squids of various sizes, analyses were camed outgro,uping, the ariimals of both species into three size categories: DML<200 mrn;200<DML<300 rnrn; and DML>300 rnrn. To determine seasonal variations in the diet,sanipIes were gfouped together by seasons: winter comprising January-March; spring, April­June; summer, July-September; and autumn, October-December.

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Comparison of the diets between different groups of L. vu/garis and L. jorbesi weremade using Chi-square test, grouping types of prey to fulfil the requireinerits of this test(Crow, 1982). EMI and OCI values for different groups of the two species were comparedusing a test of difference between two percentages (Sokai and Rohlf, 1981).

RESULTS

Table 1 shows the preys of L. vu/garis and L. jorbesi. The diet of L. vu/garis wascomposed of29 different prey items belonging to 4 groups (Teleostei, Crustacea, Cephalopodaand Polychaeta), while the diet of L. jorbesi was constituted by 28 differerit prey items of 3groups (Teleostei, Crustacea and Cephalopoda). The 77.0% of L. vu/garis and the 67.6% ofL. jorbesi with food in the stornach had a single prey in the stornach, the rest of the stomachsshowed more than orie prey.

Gastropods, bivalve and remains of algae were also found in the stornach coiitents ofboth species, but they were not considered as prey because their very small size (1-2 mm) ri.ndtheir rariiy.

The diet of each species was ccimpared using Ocurrence (OCI) and NumencalImponance (NIl) Indices (Table 2) by a Chi-square, test. Not significani differerices werefound betweeri both indices in both squid species (X2 = 16.08, df. ",; 12; p > 0.05 for L.vu/garis; X2 = 12.98, df. = i2, p > 0.05 for L. jorbesi). Therefore, arid in order to simplifythe preseritation of the results and the comparisons, only the OCI wäs employed.,

, No significam differences in the diet were found between sexes for L. vu/garis(X2 = 5.19, df. = 5, P > 0.05) and L. jorbesi (X2 =11.32, df. = 7, p > 0.05). Therefore, dietcomparations between squid sizes and seasons were made grouping sexes in both species.EMI was 64.47% anä 61.42% for males L. vu/garis and L.jorbesi, respeciively; these vaIueswere significant higher (p<0.05) than EMI values of femaIes (53.94% and 51.23%,respectively). The EMI was significantly higher in L. vu/garis inmature fernales than inmature ones (p<O.OOI) (Fig. lA). No significant differences were found in EMI values withineach sex in the case of L.Iorbesi, but, similarly to L. vu/garis, mature femaIes of L. jorbesicoriülined food in the stornach more frequeritly, than inmature ones (Fig. 1B). Between sex,mature males of bOlh species presented higher EMI values thari mature females (p<O.OOI aridp<0.05 for L. vu/garis arid L. jorbesi, respectively). No significani differences were found inEMI values for irimature ri.nimaIs of both species (Fig. lA and IB).

The OCI vaIues for each prey cluster and squid size groups are given in Table 3.In the case of L. vu/garis no significant differences were found for the three size groups,using Teleostei and "other prey" (Crustacea~ CephalopOda and Polychaeia) as prey clusters.Teleostei were the main prey for each size group. No significant differences were foundbetween DML<200 mm and 200<DML<300 mm groups of L.forbesi. In this species, the dietof DML>300 mm group was significant different from the 200<DML<300 mm group. Intakeof Teleostei decreased significantly with growth (p<O.OOI). Coritrary, the imponarice ofcephalopods in the diet of L. jor'besi inereased significantly with grOwth (p<O.OOI). Nosignificant differerices were, found in EMI values for size groups of L. vu/garis (p>0.05). EMIvalues of L. jorbesi were significant higher for the two largest size groups being comparedwith the smaUest one (p<O.OOI).

3

•Mature

A

o.JL=~~~~=::Z=:Jf1SE1Y~=;:::Inmature

Maturity stage

70

10

20

30

50

60

~ 40

B

InmatureMaturity stage

.,!

Mature

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Figure 1. Variation of the percentage of empty stomaehs (EMI) in manire arid inmarure malesand females of Loligo vulgaris (A) and Loligo jorbesi (B).

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Figure 2 shows the relationships between size of predator and size of different prey,based on stomach contents of 16 L. vulgaris and 24 L. jorbesi. Length of prey was neverbigger than squid DML. There was not an increase in prey size with squid size for bothLoligo. As consecuence, prey-size relative to squid-size decreased with size-predator.

Prey clusters used to. compare feeding of L. vulgaris and L. jorbesi throughout theseasons of the year are shown in Table 4. Feeding was not homogeneous throughout the yearin both species (p<O.Ol).

In L. vulgaris seasonal heterogenety of diet was due to the difference between autummand winter compared with spring and summer (p<O.05). Teleostei were the main prey duringthe whole year, specially during winter and autumn. During spring and summer the frecuencyof "other prey" (Crustacea, Cephalopoda and Polychaeta) increased with respect to the otherseasons (Table 4). Seasonal differences were due to the summer in the case of L. jorbesi. Inthis species, Teleostei were the main prey during the whole year except during summer, when"other prey" (Crustacea and Cephalopoda) were more important in the diet (Table 4).

EMI values of L. vulgaris (Table 4) were significant lower in winter than in the otherseasons (p<O.05). Summer was the season with the highest EMI value in the case of L.jorbesi(p<O.Ol).

c

8

..cc C c

c

C L. forbesi Ä L. vulgaris

6O,fl-T-v ---------------------------:••:'J"I.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.. '

.'.'.'.. '.. '.'.'.. '

.'.. '.'.'.'.'.'•••-c:::c

•••••• 0... ....•••••• r;t=J 'C Al.

•••••• , l:3 c ........ c ......

A •• ' ....... c

500-

100

f 400­

.~ 300->.e0. 200-

•V o 100 200 300

DML(mm)400 500 600

Figure 2. Relationships between size (DML) of Loligo vulgaris and Loligo jorbesi and sizeof prey found in their stomachs.

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Comparison between both species was made pooling DML<200 mm and200<D~1L<300 mm size groups because not differences were found in their diets (Table 5).DML>300 mm was not considered because L. jorbesi reaches bigger size than L. vulgaris.Diet of both squids were significant differerits (X2 =28.33, df. =8; p < 0.001; Unideritifiedprey were not considered iri this comparison). Differences wem mainly due to the higherfrecuency of Crustaceans (p<O.OOI) and the absence' of Polychaeta (p<O.OOI) in the diet ofL. jorbesi. No significl.mt differences were found in the EMI values of L. vulgaris (58.51 %)compared with L. jorbesi (57.05%). :

DISCUSSION!

, As occur in other cephalopoos (Nixon, 1987)] Teleostei; Cn1stacea ami CephalopOdaare the mairi gfoupS in the diei of L. vulgaris arid L.ljorbesi." , "

L. vulgaris feed mainly on fish (77.36%), crUstacean (6.60%), cephalopods (5.66%)and polychaetes (8.49%) in the Galician wäters. Fish~ Crustacea and Cephaiopoda were alsothc inain prey of L. vulgaris off Central East Atlantic 'areas (BuIukovski ei al.~ 1979; Baddyl-,1988) and L. vulgaris reynaudii off theWest Coast of South Amea (Augustyn; 1991). Fishwas always the domiriant prey, while Crustacea and: Cephalopoda had different imp0narlcein each case. Not Polychaeta were found in those areas.

The diet of L.forbesi consisred in fish (71.84%), cfustacean (17.82%) and cephalopoos(9.19%) off Galiciän coast. Similar rcsuIts were follrid in Scottish watei-S (Ngoile, 1987;Hoviant et al., 1987) and Azöres (Manins, 1982). These authors also descriOOd Polychaetiland Chaetognatha as L. jorbesi prey, which were not found in Galicia.

The range of prey observed in L. vulgaris arid L. jorbesi from Galician waters eloseagreed with that found in other locatioris, the species' belongirig to similar families, but theywere logically characteristics of each geogniphical area stUdied.

The diet of these squids is, based on demersal species like blue whiting(Micromesistius poutaSsou) or silver hake (MerlucciUs merluccius), bui also ihey prey uponpelagic species likc sardine (Sardina pilcJulrdus) or

Jhorse-mackerel (Trachurus rrachurus)

(See Table 1). The most abundarit prey in bOlh squids belonged to the demersal fish familyAinrriodytidae (fable 2). However, L. vulgaris preyed mainly upon pelagic fish in theMediterraneän Sea (Worms, 1983). Thc 35% and the 39% of the dier of L. vulgaris and L.jorbesi. respectively, correspcinded to families comm:ercially exploited in Spain (See NIl inTable 2). Since both liquid species are rehitively abundaOt in the Galiciari waters (in 1991,427tons were fished in the area; from Guerra et al., in press), arid th6ir voraeity - 2-20% of dailyfeeding rate, from data in captivity (Lipinski, 1987 and Hanlon et al., 1989) -, populations ofthese predators may have important effects on prey populations of the area.

Not differences were found in the diet of males and females of Loligo, but the foodintake was higher ii'l mature females than in mature males or lnmanire animals (See Fig. 1).In the case of L. vulgaris, data from Worms (1983) show rio decrease in fOOd intake duringmatUration of females. The minirnun percentage of 'empty storriach corresporided with theanual peak of L. forbesi maturity in the Azores (Martins, 1982). Opposite results have beenpresented for L. opaleseens which reduces iis food ingestion before spawning (Field, 1965,cited by O'Sullivan aIld Cullen, 1983). The increase:of feeding nite of fernales observed inthis study could !Je related with the increasing demand of energy and nutrients for egg production.

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No change in the diet with growth was found for L. vu/garis in the present anaIysis.However, in other areas it has been found a relative increase of fish ingestion.10gether witha decrease of crustacean with gr6wth (Burukovski, 1979; Woms, 1983; Lipinski, 1987). Butcomparison between areas is always difficult because variations in the length of the sampledspecimens and the small size of the sampIes.. It has been observed that the diet of L. forbesi changed with growth. This change was

due to the decrease of fish proportion and the increase of the perceritage of cephaIop6ds.Corici-ary, Ngoile (1987) found an increasing proportion of fish with L. forbesi growth inScottish waters. This discrepance could he due to tne scai-cety of the spedmens bigger than300 mm DML in our sampIes. . ' .

Cannibalism in Lo/igo was OccasionaI. Similar results were reponed by other authors(\VOrlnS, 1983; Lipinski, 1987; Baddyr, 1988). This resuIt contrastwitn the prevalence ofcannibalism in the diet of L. pealei over 200 mm DML observed by Vovk (1983) in theNonhwest Atlantic. Cannibalism has been postulated as a phenomenori associated to squidcrowding on spawning areas (Karpov and CaiIIiet, 1978). As the. spawning of botn Lo/igospecies iri. Galicia occurs in a highly productive area (Fraga, 1981), food inust be highlyavailable dtiring spawning, making cannibalism a rare event.

Seasonal variations in the diet and food intake of hoth Loligo species could beproduced by changes of the fishing ground occurred over the year. DUrlng the erid of thespring, the summer and the start of autumm, L. vu/garis in Galicia is fished inshore byjigging, while during the rest of the year it is caught offshore by trawling. TheSe variationsagree with the observed similarity of the autumm and the winter diet compositionversus thespring arid the summer ones. Moreover, L. forbesi in Galicia is fished inshore by. jiggingdunng the summer arid the start of the autumm; whih~ it is caught by trawling throughout therest of the year. As consequence, the diet of L. forbesi dunng the suriuner was differentrespect to the other seasons of the year.

Overall, L. vuIgaris and L.forbesi seem to be imponant opponimistic predators in theneritic and pelagic communities of Galician waters, feeding inairily on fish, cnistacean andcephalopods.

REFERENCES

Augustyn C.J: 1991. The biomass and ecoiogy of chokka squid Loligo vu/garis reynaudii offthe West Coast of South Africa. S. Afr. TydskT. Dierk. 26(4): 164-181.

Baddyr M; .1988. The, biology of the squid Lo/igo vu/garis in relation to the artisanal fishingsite of Tifnit, Morroco. Doctoral Thesis. Institut Agronomique et Veterinaire Hassan11, Rabat. 93 pp.

Bauza-Rulhin J. 1962. Contribuci6n al estudio de los otolitos de los peces. Bol. R. Soc. Esp.Hist. Nat. (Bio!.). 60: 5-26. .

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. ,Burukovs~i R.N., A.V. Gaevskaya, L.N. Domanevski, Ch.M. Nigmatulin and B.G. Panfilov.

1979. Main Results of Research on Squids Carried out by the AtlantNIRO in theCentral-East Atlantic. I.C.E.S. C.M.19791K:11.,

I

Chaine J. 1936. Recherches s~r les otolithes des pois'sons. Etude descriptive et comparativede la Sagitta des Telt~osteens (3eme partie). Ext. Act. Soc. Linneene Bordeaux. E.Drovillard (Ed.). 88: 262 pp. '

,Chaine J. and J. Duvergier. 1934. Recherches sur les otolithes des poissons. Etude descriptive

et comparative de la Sagitta des Teleosteens.Ext. Act. Soc. Linneene Bordeaux. E.Drovillard (Ed.). 86: 242 pp. :

Castro B.G. and A. Guerra. 1990. The diet of Sepia 'officina/is (Linnaeus, 1758) and Sepiae/egans (D'Orbigny, 1835) (Cephalopoda, Sepioidea) from the RIa de Vigo (NWSpain). Sci. Mar. 54(4): 375-388. !

. I . .'.Clarke M.R. (Ed.). 1986. A handbook for the Identification of Cephalopods Beaks. Clarendon •

Press, Oxford. 273 pp.t

Crow M.E. 1982. Some statistical techniques for analyzing the stornach contents of fish. In:Caillet G.M. and C.A. Simenstad (Eds.). Fish food habits studies. Proceedings of theThird Pacific Workshop, Washington Sea Gm'nt Publ., Univ. Washington. 8-15.

iFraga F. 1981; Upweling of the Galician eoast, Nonhwest Spain. In Coastal Upwelling. F.A.

Richards (Ed.). Amer. Geophys. Union. 176-1,82.I

Gaard E. 1987. An Investigation of the squid Loligo forbesi Steenstrup on Faroe Bank.I.C.E.S. C.M.19871K: 18. I

!

Gonzalez-Gurrlaran E. and M. Mendez. 1985. Crustaceos decapodos de las costas de GaliciaI. Brachyura. Cuadernos de Area de Ciencias Biol6gicas. Sem. Est. Gal. A. do Castro

I .(Ed.). Coruna. Vol. 2. 242 pp.

Guerra A. and F. Rocha. The Life History of!Loligo vu/garis and Lo/igo forbesi •(Cephalopoda: Loliginidae) in Galician WaterS (NW Spain). in press.

II

Guerra A., P. Sanehez and F. Rocha. The spanish fishery for Lo/igo: eurrem trends. in press.II

Härkönen T. 1986. Guide of the otoliths of the fishes of the Nonheast Atlantic. Dandin Ap.5, Sweden. 256 pp. '

Hanlon R.T.; W.T. Yang, P.E. Turk, P.G. Lee and R.F. Hixon. 1989. Laboratory culture andestimated life span of the Eastern Atlantic squid, Lo/igo forbesi Steenstrup, 1856(Mollusea: Cephalopoda). Aquaculture and Fisheries Management. 20: 15-34.

II

Howard EG., M.A. Ngoile and J. Mason. 1987. Loligo forbesi: Its present status in Seottishfisheries. I.C.E.S. C.M.19871K:5. :,

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Karpov K.A. and G.l\1. Caillet. 1978. Feeding dynamics of Loligo opalescens. Calif. Dept.Fish. and Game. Fish. Bull. 169: 45-66.

Lipinski M.R. 1987. Food and Feeding of Loligo vulgaris reynaudii from St. Francis Bay,South Afriea. In: The Benguela and Comparable Ecosystems. A.LL. Payne, J.A.Gulland and K.H. Brink (Eds.). S. Afr. J. Mar. Sei. 5: 557-564.

Martins H.R. 1982. Biological studies of the exploited stock of Loligo /orbesi (Mollusca:Cephalopoda) in the Azorez. J. Mar. Biol. Ass. U.K. 62: 799-808.

Mercer M.C. (Ed). 1982. Multiespecies approaches to fisheries management advice. Can.Spec. Publ. Fish. Aquat. Sei. 59: 169 pp.

Ngoile M.A. 1987. Fishery biology of the squid Loligo /orbesi (Cephalopoda: Loliginidae)in Scottish waters. Ph. D. Thesis, University of Aberdeen. 218 pp.

Nixon M. 1987. Cephalopod diet. In: Cephalopod Life Cycles. Vol.2. Comparative Reviews.P.R. Boyle (Ed.) Aeademic Press. London. 201-220 pp.

Q'Sullivan D. and J.M. Culler. 1983. Food of the squid Nototodarus gouldi in Bass strait.Aus. J. Mar. Fres. Res. 34: 261-285.

Perez-Giindaras G. 1986. Estudio de los Cefa16podos Ibericos: Sistematica y bionomfamediante el estudio morfometrico comparado de sus mandfbulas. Tesis Doctoral37/86.Universidad Complutense de Madrid. 350 pp.

Schmidt W. 1934. Verleichend morphologische studie über die otolithen marinerknochenfische. Arch. Fisch. Wiss. 19(1): 96 pp.

Sokal R. and F. Rohlf. 1981. Biometry. W.H. Freeman and Co. San Franciseo. 859 pp.

Vovk A.N. 1983. Feeding Speetrum of Longfin squid (Loligo pealei) in the North-westAtlantic and its Position in the Ecosystem. NAFQ, Sei. Comm. Studies. 8:33-38.

Worms J. 1983. Loligo vulgaris. In: Cephalopod Life Cycles. Vol.l. Species Accounts. P.R.Boyle (Ed.). Academic Press. London. 143-157 pp.. .

Zariquiey R. 1968. Crustaceos Decapodos Ibericos. Inv. Pesq. 32: pp 510.

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Table 1: Identified prey items in the diet of Lo/igo vu/garis and Lo/igo forbesi in Galician waters from stornach contents analysis.

Prey lIem LoIigo LoIigo Prey llem Loiigo Loligow!qwis fabesi w!qaris forbesi

Teleostei CruslaataClupeidaa. Oecapoda MaalM'a Natantia.

Sardina pi1charctJs X NalantiaA XSpralDJS spratllJs X PrOC8lSidae X

Argeminidaa. Hippolylidae XArgentina sphyraena X X Caidea X

Merlucciidaa. Oecapoda Maaura Aeptanba.Merfuccius merluccius X Brac:hvura A X

Gadida8. Portunidaa XMaamesistius poutassou X X Mfsidaoea. X XGadclJus arg8nleus X Euphausiacea. XTrisopterus sp x Copepoda

Cepolidaa. Calanoidea XCepola maaophthaJma X X MlIlusca

Carangidaa. Cephalopoda.Trach/HUs "achurus X X SepioIidae.

Ammodylidaa. Rondeletiola Ißrlor XGylTll1alTlmOdytes semisquamatus X X Sepielta sp XAm~I8S Dbianus X Loliginidaa.Hyperoplus lanceolalus X LoIigo brbesl X X

Gobidae. Lo/igo Kigans X XAphya minula X X AlIofeutJis subulala XPomatosclJslus sp X Oclopocidae.PomaDsdJistus minutus X Oca1pus vligaris XCrysllllogobius sp X E1tKJone cintJosa XGobiuscuIus lallftscens X J'otfdlaala.

Ca/lIonymidall. PoIyenaela A xCaIIionymus A X X Syllidaa.Calfionymus lyra X Nereis dillftrsico/or XCaIionymus reliculalUs X

Blennidae.B1enniusA XBlennius acellaris X

Atherinidaa.AtherinaA X XAtherina presbyter X

Flat fish. XTeleostIlI A XUnidentified fish X X

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Table 2: Values for the Indices of Occurrence (OCI) and Numerical Imponance (NIl) far eachprey cluster in the stornach contens of Loiigo 1:uiJ;aris and Loiigo /orbesi. No: Total numberof specimens with food in the stomaeh.

Prey Cluster Loligo vulgaris Loligo forbesi

OCI Nil OCI NilTeleostei 78.85 7529 72.67 68.02

Clupeidae 3.37 2.30 2.33 1.74Argentinidae 0.48 0.57 1.16 1.16Menucciidae 4.65 2.91Gadidae 5.29 4.02 6.40 6.98Gepolidae 2.40 2.87 1.16 1.16Carangidae 1.44 1.72 1.74 1.74Ammodytidae 9.62 16.67 6.40 13.95Gobidae 3.37 4.60 6.40 9.30CaJlionymidae 2.40 3.45 8.14 6.98Blennidae 0.96 1.72Atherinidae 3.85 5.17 0.58 0.58Flat fish 0.48 0.57Unidentified fish 45.19 31.16 33.72 21.51

Crustacea 6.73 9.77 18.02 20.93Decapoda Macrura Natantia 1.44 1.74 2.33Decapoda Macrura Reptantia 1.44 1.15 1.16 1.16Mysidacea 0.48 2.87 2.33 1.74Euphausiacea 0.58 1.74Copepoda CaJanoidea 0.58 0.00Unidentified Crustacean 3.37 5.75 11.63 13.95

Mollusca 5.77 6.89 9.30 11.05• Sepiolidae 0.96 1.15Loliginidae 3.85 5.17 5.81 6.40Octopodidae 2.33 4.07Unidentified CephaJopod 0.96 0.57 1.16 0.58

Polychaeta 8.65 8.05

No 300 251

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Table 3: Occurrence Index values for each prey cluster and resuIts of the Chi-square test used für comparison of the diet between size groupsof Lo/igo vulgaris and Loligo forbesi. No: Total specimens number with food in the stomaeh; DML: Dorsal mantle length in Olm; n.s.: Notsignificant; EMI: Percentage of empty stofTIachs.

Prey Cluster SizeGroupDML<200 200<DML<300 DMl>300

Loligo vulgaris

Teleostei 78.51 78.48 81.82Other Prey 21.49 21.52 18.18

No 167 105 28Chi-square 0.031 0.002d.f. 1 1

P n.s. n.s.EMI 58.46 56.97 63.64

Loligo forbesi

Teleoslei 82.93 67.24 56.25

Crustacea 15.85 25.86 9.38Cephalopoda 1.22 6.90 34.37

No 107 53 29Chi-sCJ.Iare 5.86 12.54d.f. 2 2

P n.s. <0.01EMI 45.41 65.36 68.13

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Table 4: Seasonal feeding of Loligo vulgaris and Loligo forbesi. Ocurrence Index (OCI) for each prey cluster. No: Number of specimens withfood in the stomaeh; EMI: Percentage of e,rnpty stomachs.

Prey Cluster Winter Spring Summer Autumn

Loligo vulgaris

Teleostei 90.00 65.45 71.11 88.24Other Prey 10.00 34.55 28.89 11.76

No 46 85 70 99EMI 46.51 60.09 57.58 61.78

Loligo forbesi

Teleostei 79.07 81.97 40.74 73.17Other Prey 20.93 18.03 59.26 26.83

No 62 61 35 31EMI 42.59 44.04 77.27 55.07

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Table 5: Comparison of the diet of Loligo vulRaris and LoliRO forbesi using Occurrence Indexvalues from specimens with D~1L<300 mm. ~o: Total specimens with food in the stomaeh.

Loligo LoligoPrey Clusters vulgaris forbes;

Teleostei 78.49 76.98Clupeidae 2.23 2.88Gadidae 5.91 6.47Ammodytidae 9.14 6.47Gobidae 3.76 7.91Callionymidae 2.69 10.07Other Teleostei 8.06 8.63Unidentified fish 45.70 34.53

Crustacea 5.91 20.14Other Crustacea 2.69 6.47Unidentified Crustacea 3.23 13.67

Cephalopoda 5.91 2.88Polychaeta 9.68 0.00

No 272 160

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