Role of Cephalopods in the Diet of the Swordfish, X/Ph/As Glad/Us, from the Eastern Mediterranean Sea

Home , Gladius (cephalopod), Heteroteuthis dispar

BULLETIN OF MARINE SCIENCE, 49(1-2): 312-324, 1991

ROLE OF CEPHALOPODS IN THE DIET OF THE SWORDFISH, X/PH/AS GLAD/US, FROM THE EASTERN MEDITERRANEAN SEA

Giambattista Bello

ABSTRACT The gastric contents of 38 swordfish, Xiphias gladius, from the eastern Mediterranean Sea were examined to study the cephalopod component. Cephalopods were the most abundant prey items (their coefficient of prey frequency = 85.7%). Remains of 20 I cephalopod specimens were found, including loose hard parts, e.g., beaks, gladii, and lenses. Cephalopods belonged to eleven species, all pelagic. Todarodes sagittatus was the predominant food item. Next most abundant cephalopods were Ancistroteuthis /ichtensteinii and Heteroteuthis dispar. All other cephalopod species were ingested occasionally by swordfish. Based on the analyses of the loose beaks mantle length estimations were made and histograms oflower rostral length distribution were generated for T. sagittatus and A. /ichtensteinii. Swordfish are efficient collectors of otherwise rare pelagic animals. Based on the analysis of gastric contents, four cephalopods were recorded for the first time from the area: H. dispar, Onychoteuthis banksii, Histioteuthis bonnellii, Ancistrocheirus lesueurii. Some reflections were made about the local swordfish fishery and the exploitability of pelagic cephalopod stocks.

Swordfish, Xiphic.rs gladius Linnaeus, 1758 (Osteichthyes: Xiphiidae), a cos- mopolitan teleost, is an opportunistic predator which mainly feeds on pelagic species of both vertebrates and invertebrates; the taxon mostly preyed upon is Cephalopoda (see historical resume and results in Toll and Hess, 1981). As noted by Toll and Hess (1981), however, most authors fail to give a complete list of teuthological prey items found in the gastric content of swordfish. Although much work has been done on several aspects of the natural history and fishery biology of X. gladius, a commercially important fish, only one brief note reports a detailed list offood items ingested by swordfish from the eastern Mediterranean Sea (Bello, 1985). This, however, was limited to the examination of prey specimens with soft tissue remains and neglected loose hard parts (gladii, lenses, and beaks). In the present work examination was conducted on the gastric contents of 38 swordfish collected in the Apulian seas (Italy, eastern Mediterranean); they include 16 specimens whose partial analysis was previously reported in Bello (1985). Attention was focused on cephalopods, which represent the most abundant and diverse prey. All types of cephalopod remains were taken into account, including hard parts. The study of swordfish gastric content proved useful in gathering information on the ecology and fishery biology of both swordfish and cephalopods. Additions were made to the knowledge of pelagic cephalopod distribution in the eastern Mediterranean Sea, which is still poorly known (Mangold and Boletzky, 1988).

MATERIALS AND METHODS

The gastric content analysis was conducted on 38 specimens of Xiphias gladius collected by drifting longiine in the south Adriatic Sea, north Ionian Sea, and the Gulf of Taranto (inlet of the Ionian) (Fig. I), during the 1984 to 1986 swordfish fishery seasons. Swordfish ranged in length from 0.80 to 1.75 m (lower jaw to fork). Table I summarizes the swordfish capture data. The fishing season extends from late Spring (May-June) to early Autumn (October-November), with exact dates dependent on swordfish migration and prevailing meteorological conditions. The bottom depth in the fishing zone usually ranges from 500 m to the maximum depth in the Adriatic

312 BELLO: CEPHALOPODS IN THE DIET OF MEDITERRANEAN SWORDFISH 313

.. •'0 N t 't::i

Figure I. South Adriatic and north Ionian Sea. The fishing area is shaded.

(1,223 m) and over 1,700 m in the Ionian Sea and the Gulf of Taranto. Fishing occurs at night; the longline is paid off at evening and retrieved in the morning. Hooks are usually baited with mackerel. Whole swordfish stomachs were preserved at sea in plastic jars containing 10% formalin. In the laboratory the stomachs were cut open and their contents sorted according to taxon. As noted by Hess and Toll(l98l) and Tolland Hess(l98l), cephalopods found in predator stomachs easily lose those taxonomic characteristics usually adopted for identification purposes. Because of this it became necessary to look for other characters for identification, e.g., radula and mandibles. Indeed several cephalopod specimens were represented solely by buccal masses and loose beaks. Beak iden- 314 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2, 1991

Table I. Swordfish collection data (an asterisk marks specimens with empty stomachs)

Fishing zone Harbor Swordfish no. Dale landed South Adriatic Mola di Bari Al to A3 24 July 1984 South Adriatic Savelletri A4 and A5 29 July 1985 South Adriatic Monopoli A6 25 Sept. 1986 North Ionian Leuca 11 31 July 1984 North Ionian Leuca 12 7 August 1984 North Ionian Leuca I3 and 14 28 August 1984 North Ionian Leuca 15 to 18 4 Sept. 1984 North Ionian Leuca 19(*) 7 August 1984 Gulf of Taranto Porto Cesareo GI to GI5 Ist half of September 1984 Gulf of Taranto Porto Cesareo GI6 to GI8 26 May 1985 Gulf of Taranto Porto Cesareo GI9 and G20 28 May 1985 Gulf of Taranto Porto Cesareo G21 14 August 1985 Gulf of Taranto Porto Cesareo G22* and G23* 26 May 1985

tification was performed using available guides including Naef (1923), Clarke (1962, 1986), Mangold and Fioroni {I966), and Voss (\ 969) and by comparisons with examples extracted from whole specimens of known identity. Only Cranchiid beaks were not checked against identified material. Cephalopod remains were measured. Dorsal mantle length (ML) or ventral mantle length (VML) was taken whenever possible, otherwise beak dimensions were measured as suggested by Clarke (1962, 1986). These measurements included lower or upper rostral length (respectively LRL and URL) in teuthoid, lower hood length (LHL) in octopod beaks. Size frequency histograms were made for the lower rostral lengths of Todarodes sagittatus and Ancistroteuthis Iichtensteinii. Dorsal mantle lengths were estimated (EML) from beaks by reference to regression equations reported by Clarke (1986). In taxa lacking such equations a rough estimate was made by simple comparisons with beaks extracted from specimens of known mantle length.

RESULTS Most swordfish stomachs contained some food remains; only three of them (7.9%) were empty. The majority of prey remains consisted primarily of cephalopods and secondarily ofteleosts. In addition, one decapod crustacean chela and some small gelatinous organisms Gellyfish?) were also found. The coefficients of prey frequency are reported in Table 2. The preponderance of cephalopodan prey in the swordfish stomachs is even more obvious when the prey dimension is taken into account. Most fish were small, about 90% of them ranging from 3 to 8 cm in length. The longest teleost was 35 cm long, whereas several ommastrephid squids were longer than that (see results below); the estimated TL for the largest cephalopod, a specimen of Om- mastrephes bartramii, was 60 cm. Teleostan prey volume exceeded that of cephalopods in only five stomachs. Cephalopods remains were attributed to 11 species, all pelagic. The taxonomic list is reported in Table 3. Table 4 summarizes the distribution of prey in swordfish stomachs. The coefficient of prey-cephalopod frequency and the coefficient of cephalopod numerical frequency are reported in Table 5. Heteroteuthis dispar. -- This is the only sepioid and the smallest cephalopod found. Its remains consisted of hard parts only, beaks and possibly lenses, with the exception of a single buccal mass. Ommastrephes bartramii.-According to Bello (1986) this is the only species of Ommastrephes in the Mediterranean Sea. Remains of two specimens of the species were found. First specimen in swordfish no. G6. Slightly digested mantle (ML ~ 10.5 + cm) BELLO: CEPHALOPODS IN THE DIET OF MEDITERRANEAN SWORDFISH 315

Table 2. Coefficients of prey frequency in swordfish stomach, Fp. Fp = nlNp x 100, where N = number of stomachs containing prey of each taxonomic group; Np = number of stomachs containing prey

All specimens Adriatic Sea Ionian Sea Gulf of Taranto Cephalopods 85.7 83.3 87.5 85.7 Teleosts 62.9 33.3 37.5 81.0 Crustaceans 2.9 4.8 Unidentified gelatinous organisms 2.9 4.8

Np 35 6 8 21

with its internal organ and buccal mass. LRL = 2.8 mm, to which an EML of 13.0 cm corresponds. The ratio ilj = 1.12 is lower than the one for T. sagittatus juv. (Clarke, 1986; personal observations). Identification was confirmed by the examination of the radula (cf. Naef, 1923). Second specimen in swordfish no. G9. Pair of large loose beaks. LRL = 12.3 mm; EML = 39.2 cm; ilj = 1.15. Todarodes sagittatus. -As reported by Bello (1985), this is the predominant food item in the diet of swordfish from the eastern Mediterranean Sea (tables 4, 5). Both adult and juvenile squid remains were recovered from the swordfish stomachs. Several loose ommastrephid beaks were tentatively referred to this species because of the darkening pattern of lower beak wings (Clarke, 1986), the shape of the upper rostrum (Mangold and Fioroni, 1966), and the ratio i/j > 1 (Clarke, 1986; personal observations). LRLs ranged from 1.8 to 8.4 mm, to which EMLs ranging from 6.3 to 33.6 cm correspond. Figure 2 gives the lower beak size distribution, which has three modes. The graphs in Figure 3 were generated by splitting the beaks according to their wing darkening stages. At stage B in particular, i.e., isolated spot on the wing, there are two completely separate beak groups (smaller beaks: mean LRL = 4.54 mm, standard deviation = 0.33, EML = 17.7 em; larger beaks: mean LRL = 6.13 mm, standard deviation = 0.62, EML = 24.2 cm). Clarke (1962) shows that the extension of pigmentation to lower beak wing is related to sexual maturity and that wings darken at a smaller size in males than in females. Therefore, the two beak groups in Figure 3B correspond to males and females of the same age group. Consequently the three modes of the overall frequency distribution (Fig. 2) correspond to juveniles of age class 0+ (LRL mode = 2-2.5 mm, EML ~ 9 cm), males (2nd mode) and females (3rd mode) of age class 1. As regards seasonal differences in the beak size distribution, mean juvenile LRL of beaks taken from swordfish caught in late May is 2.24 mm (N = 8), whereas that taken from swordfish caught in September is 2.54 mm (N = 18). The appli- cation of Student's t-test showed that the difference between May and September mean LRL is significant (t = 1.814; df = 24 ....•confidence level> 90%). In this calculation only LRLs less than 3.5 mm were taken into account since the next size class could also include individuals ofthe second size class distribution; thus the real mean LRL for the September specimens should be somewhat higher. Consequently, the corresponding May-September mantle increment (over 10 mm in 3.5 months) is clearly underestimated. Unidentified Ommastrephids. - Two upper and one lower small ommastrephid beaks could not be assigned with certainty to any species. URL = 1.2 and 1.4 mm; LRL = 1.3 mm. 316 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2,1991

Table 3. Taxonomic list of cephalopods found in Xiphias g/adius stomach content

Order Sepioidea Family Sepiolidae Heteroteuthis dispar (Riippell, 1844) Order Teuthoidea Family Enoploteuthidae Ancistrocheirus lesueurii (d'Orbigny, 1842) Family Onychoteuthidae Onychoteuthis banksii (Leach, 1817) Ancistroteuthis lichtensteinii (Ferussac, 1839) Family Histioteuthidae Histioteuthis bonne//ii (Ferussac, 1835) Histioteuthis reversa (Verrill, 1880) Family Ommastrephidae Ommastrephes bartramii (Lesueur, 1821) Todarodes sagittatus (Lamarck, 1798) Family Cranchiidae unidentified Taoniinae Order Octopoda Family Ocythoidae Ocythoe tuberculata Rafinesque, 1814 Family Argonautidae Argonauta argo Linnaeus, 1758

Onychoteuthis banksii. - The only specimen found, a female (ML = 9.7 em), was described in detail by Bello (1990a). Ancistroteuthis lichtenstein ii, - This species is the second most important swordfish food item. ML ranged from about 5.0 to 17.5 em. The LRL distribution graph is reported in Figure 4. The bimodal distribution could suggest the presence of two age classes. Histioteuthis bonnellii.-Remains of two specimens were found in one swordfish. First specimen. Buccal mass alone. LRL = 10.6 mm; wings completely dark- ened; EML = 11.2 em. Second specimen. One upper beak. URL = 4.1 mm; EML = 5 em. Histioteuthis reversa.·- Remains of two specimens were found. First specimen, in swordfish no. A4. One lower beak. LRL = 3.0 mm~ EML = 6.5 mm. Second specimen, in swordfish no. G2. One upper beak. URL = 2.2 mm; EML = 5 em. Ancistrocheirus lesueurii. -Only one lower beak was found. LRL = 6.1 mm; EML = 20.7 em. Cranchiidae spp. - R~:mains of five specimens were found in three swordfish. Two lower beaks in swordfish no. G7. LRL = 4.3 and 4.4 mm. They belonged to the grouping Teuthowenia-Galiteuthis type B (Clarke, 1986). The drawing that most resembles the beaks is that of T. megalops male (Clarke, 1986: fig. 99-B9). Fragments of mantle and arms, and a worn out gladius ~ 16.5 em (cranchiid?)~ two buccal masses in swordfish no. G9. LRL = 3.2 and 3.5 mm. The lower beaks belonged to the grouping Teuthowenia-Galiteuthis type A (Clarke, 1986); they look very much like the photograph of Galiteuthis and the drawing of G. armata (Clarke, 1986: figs. 13-29A and 99-E). BELLO: CEPHALOPODS IN THE DIET OF MEDITERRANEAN SWORDFISH 317 gt,~ .!!:J "w f-

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o 2 3 4 5 6 7 8 9 LRL mm Figure 2. Lower rostrallc:ngth frequency of Todarodes sagittatus beaks found in swordfish stomach contents.

One lower beak in swordfish no. G14. LRL = 1.8 mm. Cranchiid sp. juv.? It looked somewhat like the lower beaks from swordfish no. G9. Argonauta argo. - The examined remains belonged to six specimens. LHL ranged from 2.2 to 5.9 mm; EML from 3.5 to 8.8 cm. Ocythoe tuberculata.--Only one specimen, a female, was found. VML = 6.9 cm.

DISCUSSION Results show that the main source of food for swordfish from the eastern Mediterranean Sea an~pelagic cephalopods. This is in agreement with preliminary data by Cavaliere (1963) and Bello (1985) on swordfish caught in the Mediter- ranean, and with Toll and Hess (1981) on swordfish from the Florida Straits. l Regardless of its size:,the swordfish catches small prey (e.g., Heteroteuthis dispar , juveniles of Todarodes sagittatus) and large prey (e.g., adults of T. sagittatus) (cf. also Stillwell and Kohler, 1985). The statistical analysis of food consumption (Tables 2, 5) is somewhat biased by the wide size range of prey, since small prey items are digested faster than larger ones, and the residence time of prey hard parts in stomachs consequently varies as well. Another source of bias is the fact that swordfish are known to regurgitate stomach contents during and after capture (Tibbo et al., 1961). Nevertheless the ommastrephid squid T. sagittatus is by far the predominant food item, both in terms of number and in terms of weight.

I Some specimens of H. dispar found in swordfish stomachs could be secondary predator remains, i.e., they were present in a predator, probably T. sagirtatus. which was then ingested by a swordfish. This hypothesis is supported by the fact that all H. dispar specimens but one were represented solely by hard parts. whenever H. dispar remains were found those of T. sagirtatus were also present, T. sagirtatus preys upon H. dispar (Bello, I990a). BELLO: CEPHAWPODS IN THE DIET OF MEDITERRANEAN SWORDFISH 321

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o 2 3 4 5 6 LRL mm Figure 3. Lower rostral length frequency of Todarodes sagittatus beaks at different stage of wing darkening. A = transparent wing; B = wing with isolated dark spot; C = wing with advanced darkening. 322 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2,1991

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o 2 3 4 5 LRL mm Figure 4. Lower rostral length frequency of Ancistroteuthis /ichtensteinii beaks found in swordfish stomach contents.

Ancistroteuthis /ichtensteinii and the small sepiolid H. dispar are prey items of less importance. All other cephalopods are only occasionally ingested. Swordfish show a clear diel pattern of vertical movements, going deep during the daylight hours and coming to the surface at night (Carey and Robison, 1981). As regards the feeding depth, several data lead to the conclusion that, at least at night, swordfish feed in the upper layers of the water: T. sagittatus is known to migrate towards the surface at night (Clarke, 1966); the same is true for H. dispar (Roper, 1974) and Onychoteuthis banksii (Roper, 1974; Roper and Young, 1975); Argonauta argo and Ocythoe tuberculata are strictly epipelagic (Voss, 1967). How- ever, the occasional find of deeper living species, such as Histioteuthis bonnellii (in the Mediterranean most abundant between a depth of 100 and 600 m (Mangold and Boletzky, 1987)) and the teleost Sudis hya/ina Rafinesque 1810 (meso- to bathype1agic (Post, 1984)), suggests that X. gladius does occasionally feed in deeper waters. Toll and Hess (1981) demonstrate the heavy swordfish predation upon aggre- gating cephalopods. However, in no gastric content examined during this research were numerous specimens of anyone cephalopod taxon found; the most numerous were 10 specimens of A. /ichtensteinii in one swordfish (A3). On the other hand, four swordfish stomachs contained large quantities of juvenile horse mackerel, Trachurus spp. (36 specimens in A5, 106 in G17, 58 in G18, and 89 in G19), in agreement with the reports of the swordfish habit of preying on schooling fish (Tibbo et al., 1961). The find of a few squids neatly cut into two pieces further supports the hypothesis that the swordfish uses its bill to wound or kill its prey (Tibbo et al., 1961; Toll and Hess, 1981; Stillwell and Kohler, 1985). BELLO: CEPHALOPODS IN THE DIET OF MEDITERRANEAN SWORDFISH 323

It seems that the swordfish, a powerful swimmer, prefers large fast swimming, muscular cephalopods, such as T. sagittatus and A. lichtensteinii in the Mediter- ranean or I/lex in the Atlantic Ocean (Toll and Hess, 1981; Stillwell and Kohler, 1985), and that cephalopod swiftness is no obstacle to swordfish feeding. Thus, it can be stated that X. gladius, in addition to being an opportunistic predator (Toll and Hess, 1981), is also an efficient one. The general distribution of cephalopods in the Mediterranean is not completely known yet, especially in the Adriatic and the eastern basin (Mangold and Boletzky, 1988). In this regard the analysis of predator stomach contents proved to be a very useful tool in enhancing the knowledge of the teuthofauna of the examined area (Clarke, 1966). The occurnmce of O. banksii in the Gulf of Taranto and H. dispar in both the Gulf of Taranto and the Adriatic Sea was recorded for the first time thanks to specimens found in swordfish stomachs (Bello, 1990; in press). New additions to the local fauna are the unidentified cranchiids from the Gulf of Taranto; no cranchiids were reported from this part of the Mediterranean (Man- gold and Boletzky, 1987; Bello, 1987). The one lower beak of an adult Ancis- trocheirus lesueurii is also noteworthy. This species distribution seemed to be limited to the western Mediterranean (Mangold and Boletzky, 1987), where only early juvenile stages were repeatedly collected (Clarke, 1966). In recent times the first Mediterranean adult of A. lesueurii was caught in the Strait of Messina (Bello et al., in prep.). Therefore the specimen reported upon here represents only the second adult from the Mediterranean Sea and the first from the eastern basin. Lastly, some species are not as rare as was thought before: T. sagittatus, O. bartramii, A. /ichtensteinii, and A. argo. Amaratunga (1983) points out the role of cephalopods in marine food webs. Through them an efficient energy transfer occurs from bottom level consumers to large teuthivorous predators. That is also the case of the swordfish. It can be added that all prey-cephalopods of eastern Mediterranean swordfish are species that presently have no commercial interest; in this sense fishermen and swordfish do not compete for prey. The swordfish fishery indirectly exploits the pelagic cephalopod resource. Indeed, the stocks of T. sagittatus and A. /ichtensteinii represent an untapped resource that could be directly exploited by man.2 The decrease in the Apulian swordfish population, due to overfishing, is making an even larger fraction of T. sagittatus and A. /ichtensteinii stocks available to fishermen. Lastly our present knowledge of swordfish food preference can help fishery technicians and fishermen to improve the baiting system for swordfish longline. Apulian fishermen use frozen blue fish, mainly mackerel, as bait; the use of ommastrephid squids would increase the catch. Indeed, in other parts ofthe world fishermen bait the hooks for swordfish with artificial luminescent squids.

ACKNOWLEDGMENTS

I wish to thank two anonymous reviewers for their valuable suggestions and editorial work. Thanks are due to E. Chadd Blackwood for her help with the English.

LITERATURE CITED

Amaratunga, T. 1983. The role of cephalopods in the marine ecosystem. FAO Fish. Tech. Pap. 231: 379-415.

2 The FAO official statistics on Italian catch of T. sagittalus (see for instance Mangold & Boletzky, 1987) are very likely greatly overestimated because of the confusion between T sagittalus and mex caindelii. The lalter species is the one actually fished by boltom trawling. 324 BULLETINOFMARINESCIENCE,VOL.49, NO. 1-2,1991

Bello, G. 1985. Preliminary note on cephalopods in the stomach content of swordfish, Xiphias gladius L., from the Ionian and Adriatic Seas. Rapp. Comm. Int. Mer. Medit. 29(8): 231-232. --. 1986. Catalogo dei Molluschi Cefalopodi viventi nel Mediterraneo. Boll. Malaco!. 22: 197- 214. --. 1987. Elenco dei Cefalopodi del Golfo di Taranto. Atti Soc. Ita!. Sci. Nat. Mus. Civ. St. Nat. Milano 128: 173-179. --. 1990a. Presenza dei cefalopodi Heteroteuthis dispar (RUPPELL, 1844) e Onychoteuthis banksii (LEACH, 1817) nel Golfo di Taranto. Boll. Malaco!. 25: 281-284. --. I990b. The cephalopod fauna of the Adriatic. Acta Adriatica. 31: 275-291. Carey, F. G. and B. H. Robison. 1981. Daily patterns in the activity of swordfish, Xiphias gladius, observed by acoustic telemetry. Fish. Bull. 79: 277-292. Cavaliere, A. 1963. Studi sulla biologia e pesca di Xiphias gladius L. Nota II. Boll. Pesca Piscicolt. Idrobio!. 18: 143-170. Clarke, M. R. 1962. The identification of cephalopod "beaks" and the relationship between beak size and total body weight. Bull. British Mus. Nat. Hist. Zool. 8: 419-480, 10 pits. --. 1966. A review of the systematics and ecology of oceanic squids. Adv. Mar. BioI. 4: 91- 300. --, ed. 1986. A Handbook for the identification of cephalopod beaks. Clarendon Press, Oxford: xiii + 273 pp. Hess, S. C. and R. B. Toll. 1981. Methodology for specific diagnosis of cephalopod remains in stomach contents of predators with reference to the broadbill swordfish, Xiphias gladius. J. Shellfish Res. I: 161-170. Mangold, K. and S.v. Boletzky. 1987. Cephalopodes. Pages 633-714 in W. Fischer, M.-L. Bauchot and M. Schneider, eds. Fiches FAO d'identification des especes pour les besoins de la peche. (Revision I). Mediterranee et mer Noire. Zone de peche 37. Vol. I. -- and --. 1988. Mediterranean cephalopod fauna. The Mollusca, Vol. 12. Academic Press, London and New York: 315-330. -- and P. Fioroni. 1966. Morphologie et biometrie des mandibules de quelques cephalopodes mCditerraneens. Vie Milieu, sCr. A 17: 1139-1196. Naef, A. 1923. Die Cephalopoden. Fauna Flora Golf. NeapeI35(1, I): 863 pp., 19 pits. English trans!., 1972, Smithsonian Inst., Washington D.C., 917 pp. Post, A. 1984. Paralepididae. Pages 498-508 in P. J. P. Whitehead, M.-L. Bauchot, J.-c. Hureau, J. Nielsen and E. Tortonese, eds. Fishes of the north-eastern Atlantic and the Mediterranean. Unesco, Paris, Vol. I. Roper, C. F. E. 1974. Veltical and seasonal distribution of pelagic cephalopods in the Mediterranean. Preliminary Report. Bull. Am. Malacol. Union Inc., May 1974: 27-30. -- and R. E. Young. 1975. Vertical distribution of pelagic cephalopods. Smithson. Contr. Zool. 209: 51 pp. Stillwell, C. E. and N. E. Kohler. 1985. Food and feeding ecology of the swordfish Xiphias gladius in the western North Atlantic Ocean with estimates of daily ration. Mar. Ecol. Prog. Ser. 22: 239- 247. Tibbo, S. N., L. R. Day and W. F. Doucet. 1961. The swordfish (Xiphias gladius L.), its life-history and economic importance in the northwest Atlantic. Bull. Fish. Res. Board Canada 130: 47 pp. Toll, R. B. and S. C. Hess. 1981. Cephalopods in the diet of the swordfish, Xiphias g/adius, from the Florida Straits. Fish. Bull. 79: 765-774. Voss, G. L. 1967. The biology and bathymetric distribution of deep-sea cephalopods. Stud. Trop. Oceanogr. 5: 511-535. Voss, N. A. 1969. A monograph of the Cephalopoda of the North Atlantic. The family Histioteu- thidae. Bull. Mar. Sci. 19: 713-867.

DATEACCEPTED: October 25, 1990.

ADDRESS: Istituto Arion, Casella Posta/e, 70042 Mola di Bari, Ita/y.