Cephalopoda: Loliginidae)

BULLETIN OF MARINE SCIENCE, 49(1-2): 309-311, 1991

PRELIMINARY STUDY ON THE FEEDING BY LOLIGO GAHI (CEPHALOPODA: LOLIGINIDAE)

Angel Guerra, Bernardino G. Castro and Marion Nixon

ABSTRACT The stomach contents of 13 specimens of Loligo gahi. captured off the Falkland Islands, were examined, The squids had all fed upon one species of crustacean belonging to the genus Euphausia. The weight of the stomach contents was between 4.5 and 8.0% of the total wet body weight. Several stomachs contained eyes from as many 96 to 244 individuals of this crustacean. The results shows that this species has a type and food intake similar to other loliginids and ommastrephids from temperate and boreal waters. Loligo gahi is fished in considerable quantity from these waters and its feeding habits indicate that it has an important influence on the krill, playing an important role in the trophic web of the ecosystem in these waters.

The recent decline of fisheries in some areas has resulted in many Spanish trawlers fishing off the eastern coasts of the Falkland Islands. This has developed into a directed fishery for Loligo gahi. In 1986 some 90,000 tons were caught (Patterson, 1987). This squid is captured in depth of 160-300 m in waters of6- 10°C. The catches are frozen on board ship at -40°C, stored in 10 kg blocks in holds kept at - 20°C, and brought back to Vigo (NW Spain). The investigation of the diet of cephalopod will enable us to understand better the importance of these extremely efficient carnivores in the food web of the sea. As far as we know, this preliminary study is the first investigation of the feeding of this species in these waters.

OBSERVATIONS AND CONCLUSIONS One hundred and twenty eight squids, captured in March 1987 off the Falkland Islands, were examined in Vigo. They were defrosting in tap water at room tem- perature; all were in good condition and all belonged to the same species, Loligo gahi d'Orbigny, 1835. The identification was made from the diagnosis given by Brakoniecki (1984). The animals ranged from 125 to 187 mm dorsal mantle length (DML). Males were all fully matures and females maturing (Lipinsky, 1979), placing them all within the size range of sexually mature (maturing) animals of this species (Hatfield et al., 1990). They showed very similar stomach fullness and stages of digestion of the prey. The digestive tract was removed from 13 specimens (7 males and 6 females) randomly taken from the total sample and the entire contents examined. The stomach in most cases was distended, but the oesophagus and intestine were empty. The contents of the stomach of each squid was weighed (Table 1). The food material present in the stomach of every specimen was found to belong to a single unidentified euphausiid species. Euphausiids, together with shrimps and prawns, form a considerable part of the diet of other loliginid squids (Nixon, 1987). At least some of the euphausiids eaten by Loligo gahi were mature and bearing eggs, and presumably of 45-50 mm total length, as the reconstructions made using entire cephalotorax and abdomens found have shown. The euphausiid remains in the stomachs of the squids were in fragments and showed some maceration. The fragments were all in the same stage of digestion. Adult euphausiids eaten

309 310 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2. 1991

Table I. Thirteen spedmens of Loligo gahi are arranged in descending order of dorsal mantle length (DML), together with the total wet weight (W), the antero-posterior length of the buccal mass (LBM), the sex and the stage of maturation for each. The wet weight of the stomach contents (WSC) of each is given and shown as a percentage of its total body weight (W)

LBM DML W(g) Sex Maturation WSC(g) % (WSC/WTB) (mm) 187 112.7 a mature 7.52 6.67 15.9 170 118.1 a mature 7.78 6.58 15.5 168 95.4 a mature 6.01 6.30 15.7 164 93.1 a mature 4.19 4.50 15.3 159 80.7 a mature 7.16 8.87 15.2 lSI 71.7 !i! maturing 4.83 6.16 15.0 144 79.9 !i! maturing 5.67 7.10 14.9 143 70.3 !i! maturing 3.76 5.35 14.9 142 71.6 !i! maturing 4.37 6.20 14.9 139 69.4 a maturing 6.10 8.79 14.8 131 58.7 !i! maturing 3.07 5.23 14.8 126 52.0 a mature 3.43 6.10 14.6 125 55.0 <;> maturing 4.83 8.78 14.5 would have been three times the antero-posterior length of the buccal mass (14.5- 15.9 mm, Table 1) of L. gaM. Thus it is certain that euphausiids are bitten into fragments short enough to enter the buccal cavity, and ofa diameter small enough to enter the oesophagus as in other loliginids (Bidder, 1950) and in Sepia (Guerra et al., 1988). The wet weight of the stomach contents ranged from 3.07-7.78 g, and formed from 4.5-8.87% of the total body weight (Table 1). Several stomachs contained many euphausiid single eyes, the number ranging from 192 to a maximum of 488, representing 96 to 244 individuals. This shows certainly that Loligo gahi is capable of capturing euphausiids in considerable numbers. An estimation of the time expended in the capture can be made on the basis of data of other teuthoids. Kier (1982) followed the capture of panaeid shrimps by L. pealei in the laboratory with a high speed camera. The tentacular strike was rapid, 15-35 msec, and the total time from the first sight of prey was 1.6-6.5 sec in all. In the sea a school of Illex illecebrosus was filmed whilst capturing and feeding on a surface swarm of Meganychtiphanes norvegica. These small euphausiids were caught with the swiftly ejected tentacles of the squid, an attack taking less than 2 sec (Nicol and O'Dor, 1985). Therefore, feeding on a swarm of euphausiids, L. gahi could capture 244 specimens taking between 6 and 26 min. It is not possible to assess the daily food consumption of Loligo gaM, but the stomach contents formed 4.50-8.97% of the total wet weight. This may be com- pared with the average daily intake of L. opalescens of 4-29%, with an average of 14.9%, under laboratory conditions in a temperature of 13°C or more (Yang et al., 1986). Also with the daily ratio of L. pealei (3.2-3.8% wet weight/day) estimated by Vinogradov and Noskov (1979), and with the daily ratio (9-10%) obtained by Macy (1980 in 1982) in the same species under laboratory conditions. This brief study shows that the feeding habits of Loligo gahi in the cold waters of the Falkland Islands are similar to those of other coastalloliginids living in temperate waters and ommastrephids (Illex illecebrosus) from boreal ones. Further detailed investigations of the species and size prey taken through the seasons and of the life cycle of L. gahi, together with the daily food intake and the rate of conversion of the squid are needed to determine the influence of this species on the trophic web of th~: ecosystem in which it lives. GUERRAETAL.:FEEDINGBY LOLlGO GAHI 311

ACKNOWLEDGMENTS

We would like to thank M. T. Fernandez for her technical assistance.

LITERATURE CITED

Bidder, A. M. 1950. The digestive mechanism of the European squids Loligo vulgaris, Loligoforbesi, Alloteuthis media and Alloteuthis subulata Q. J. Micros. Sci. 91: 1-43. Brakoniecki, T. F. 1984. A full description of £Oligo sanpaulensis Brakoniecki, 1984 and redescription of Loligo gahi d'Orbigny 1835, two species of squid (Cephalopoda: Myopsida) from Southwest Atlantic. Bull. Mar. Sci. 34: 435-448. Guerra, A., M. Nixon and B. G. Castro. 1988. Initial stages of food ingestion by Sepia officinalis (Mollusca Cephalopoda). J. Zool. Lond. 214: 189-197. Hatfield, E. M. C., P. G. Rodhouse and J. Porebski. 1990. Demography and distribution of the Patagonian squid (£Oligo gahi d'Orbigny) during the austral winter. J. Const. Int. Explor. Mer 46: 306-312. Kier, W. M. 1982. The functional morphology of the musculature of squid (Loliginidae) arms and tentacles. J. Morph. 172: 179-192. Lipinski, M. 1979. Universal maturity scale for the commercially important squids. (Cephalopoda: Teuthoidea). ICNAF Res. Doc. 79/2/38, Ser. 5364:1-40. Macy, W. K. 1980. The ecology ofthe common squid Loligo pealei LeSueur, 1821 in Rhode Island waters. Ph.D. thesis, University of Rhode Island, Kingston. 236 pp. --. 1982. Feeding patterns of the long-finned squid, Loligo pealei in the New England waters. BioI. Bull. 162: 28-38. Nicol, S. and R. K. O'Dor. 1985. Predatory behaviour of squid (Illex illecebrosus) feeding on surface swarms ofeuphausiids. Can. J. Zool. 63: 15-17. Nixon, M. 1987. The diets of Cephalopods. In P. R. Boyle, ed. Cephalopod life cycles, Yol. II. Academic Press: 201-219. Patterson, K. 1987. Fishery events in the Falklands. New Scient. 114: 44-48. Yinogradov, Y. I. and A. S. Noskov. 1979. Feeding of short-finned squid, Illex illecebrosus, and long-finned squid, Loligo pea lei, off Nova Scotia and New England, 1974-75. ICNAF Sel. Pap. 5:31-36. Yang, W. T., R. F. Hixon, P. E. Turk, M. E. Krejci, W. H. Hulet and R. T. Hanlon. 1986. Growth, behavior, and sexual maturation ofthe market squid, Loligo opalescens, cultured through the life cycle. Fish. Bull. U.S. 84: 771-798.

DATEACCEPTED: September 24, 1990.

ADDRESSES:(A.G. and B.G.C.) Instituto Investigaciones Marinas, Eduardo Cabello 6. 36208 Vigo. Spain: (M.N.) 60 Norfolk Road, New Barnet, Hertfordshire EN5 5LT, England.