Illex Argentinus: Life Cycle, Population Structure, and Fishery

ICES mar. Sei. Syrap., 199: 425-432. 1995

Illex argentinus: life cycle, population structure, and fishery

P. G. Rodhouse, J. Barton, E. M. C. Hatfield, and C. Symon

Rodhouse, P. G., Barton, J., Hatfield, E. M. C., and Symon, C. 1995. Illex argentinus'. life cycle, population structure, and fishery. - ICES mar. Sei. Symp., 199: 425-432.

Since the establishment of the Falkland Islands Conservation and Management Zone (FICZ) in 1986, catch and effort data for Illex argentinus have been reported to the Fisheries Department of the Falkland Islands Government, and observers have collected biological data aboard commercial vessels fishing within the zone. I. argenti nus are caught in the FICZ between March and lune. Early in the season the fishery is concentrated to the north of the FICZ and later spreads to approximately 52-53°S. By June the fleet has shifted to the northwest of the zone. Catches and catch rates peak early in the season and decline thereafter. Male squid recruit into the fishery at a modal mantle length of about 200 mm and grow to about 300 mm by the end of the season, and females recruit at approximately the same size and grow to some 350 mm. For both sexes this is generally in agreement with data derived from growth increments in the statolith. At the time of recruitment, males are more sexually mature than females. Maturation in both sexes proceeds with growth and most squid migrate out of the fishery about one month before the estimated peak time of hatching of the next generation. Squid maturing early in the season are smaller than those maturing later. Data from the fishery are consistent with the hypothesis that the spawning grounds of I. argentinus are towards the north of the Patagonian Shelf, that eggs and larvae develop in the Brazil Current, and the squid then spread over the shelf to feed, grow, and mature. There is evidence that squid on the spawning migration follow the northerly flow of the Patagonian Current to the west of the Falkland Islands.

P. G. Rodhouse, E. M. C. Hatfield and C. Symon: British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 OET, England [tel: +44(0) 1223 61188, fax: +44(0) 1223 62616], J. Barton: Fisheries Department, Falkland Islands Government, Port Stanley, Falkland Islands.

Introduction Pérez Comas, 1989a, b; Nigmatullin, 1989; Brunetti, 1990a, b; Haimovici and Alvarez-Pérez, 1990). From The ommastrephid squid, Illex argentinus de Castella these data the following outline life history can be nos 1960 (Cephalopoda: Ommastrephidae), occurs over deduced. Most of the stock on the Patagonian Shelf the Patagonian Shelf and slope from about 30°S to 54°S spawns during the winter months, but there is also a at depths from 50 to 1000 m (de Castellanos and Menni, smaller, summer spawning subpopulation (Brunetti et 1969; Roper et al., 1984). It has also been recorded as al., 1991). The spawning grounds have not been identi occasional specimens in association with Martialia hya- fied but winter spawners are thought to lay their eggs to desi at the Antarctic Polar Front to the west of South the north of the Patagonian Shelf in the northern part of Georgia (Rodhouse, 1991). On the Patagonian Shelf it is the Falkland Current or in the Brazil Current (see Peter a short-lived, fast-growing species which attains full sex son and Whitworth (1989) for a review of the regional ual maturity and spawns within one year (Csirke, 1987). oceanography). Summer spawners are thought to spawn The fishery for I. argentinus is pursued mainly by jigging in coastal waters. Young squid, derived from the main vessels (see Hamabe et al., 1983), but squid are also winter spawning, arrive in the northern section of the taken by trawlers. shelf in the austral spring. They spread southwards and Knowledge of the life cycle of I. argentinus is based offshore and then during the summer they move in over largely on fisheries data and material collected from the shelf where the main feeding grounds are located commercial catches and some limited information from and where they are exploited by the commercial fishery. research cruises (Hatanaka et al., 1985; Hatanaka, 1986; Subsequently, in the autumn, they move northwards Koronkiewicz, 1986; Hatanaka, 1988; Brunetti and towards the presumed spawning grounds. Death follows 426 P. G. Rodhouse et al. ICES mar. Sei. Symp., 199 (1995)

48° In this article we review the life cycle and population structure of I. argentinus in the light of these new data from the FICZ.

Materials and methods

50° Catch and effort data for I. argentinus are taken largely from jigging vessels reporting to the Fisheries Depart Falkland Islands ment, Port Stanley, between 1987 and 1989. Biological 51” data were collected aboard fishing vessels by Falkland Islands Government Fisheries observers between 1987 and 1989. Dorsal mantle length (ML) of samples taken 52" from the catch were routinely measured to the nearest 10 mm below and specimens sexed and assigned a matur ity stage (I: juvenile; II: immature; III: preparatory; IV: maturing; V: mature) according to Lipinski’s (1979) scheme. No data are available outside the commercial fishing season, which lasts from February/March to June. This 54 study therefore considers only that part of the life cycle between recruitment into the fishery and commence ment of the spawning migration.

55° 62“ 61" 60 ” 58- 57" 56' 55’ Figure 1. Falkland Islands Interim Conservation and Manage ment Zone (FICZ). Results Distribution of the catch within the FICZ soon after spawning, so the population is mostly com Monthly distribution of the catch within the FICZ for prised of a single cohort derived from the winter the period 1987-1989 is shown in Figure 2. A broadly spawners. There is no evidence that any squid survive similar pattern has been observed in each year. During into a second year. the early part of the season the fishery is concentrated to Growth of post-recruit I. argentinus has been analysed the north of the Falkland Islands. As the season pro from data relating mantle length to age, determined by gresses the catch increases and squid are taken through counting daily growth increments in the statolith (Rod out the FICZ to as far south as approximately 53°S. The house and Hatfield, 1990). As deduced from fishery data major concentrations remain to the north of the Islands. both sexes were confirmed to live for approximately one The fleet subsequently shifts away to the northwest of year. Females grow faster than males but males mature the Zone before the close of the season in June. earlier than females. Hatching dates, back-calculated from age and date of capture, peak in July. Growth in mantle length is best approximated by a linear model Monthly catch and c.p.u.e. during the period the squid are exploited by the fishery Total monthly catch within the FICZ for the period and there is a consistent trend of increasing growth rate 1987-1989 is shown in Figure 3. In each year the catch with date of hatching. has peaked in April and declined thereafter until the end The development of the Patagonian Shelf fishery for I. of the season in June. argentinus, since the early 1970s, has been documented The seasonal distribution of c.p.u.e. within the FICZ by Csirke (1987) and Brunetti (1990c). In 1986 the Falk for the period 1987-1989 is shown in Figure 4. Catch land Islands Government established the Falklands rates increase rapidly to a peak during the early part of Interim Conservation and Management Zone (FICZ), the season and then decline steadily until the end of the which covers an area of 150 miles radius from a point in season. the centre of the Islands, but not including an area in the southwest (Fig. 1) (Anon., 1989). The establishment of an observer programme and reports from vessels Growth licensed to fish in the Zone have subsequently produced Monthly data for the modal length of the male and data on the fishery within the FICZ for the years 1987- female population taken by the fishery for the period 1989. 1987-1989 are shown in Figure 5. For comparison, the CSmr e. yp, 199(1995) Symp., Sei. mar. ICES -10 tonnes • 10-100 tonnes • 100 - 1000 tonnes • > 1000 tonnes lllex argentinus: life cycle, population structure, and fishery and structure, population cycle, life argentinus: lllex

427 Figure 2. Monthly distribution of the catch of Illex argentinus within the FICZ for the period 1987 1989. 428 P. G. Rodhouse et al. ICES mar. Sei. Symp., 199 (1995)

100 • 1 9 8 7 towards an increasing proportion of stage V males by the

■ 1 9 8 8 end of the season. There is a greater proportion of early maturity stage 8 0 A 1 9 8 9 females than males at the time of recruitment into the fishery. Female maturation continues during the course 6 0 x of the season and the population is dominated by matur (/)

Sex ratio Seasonal change in the sex ratio of the catch for the period 1987-1989 is shown in Figure 8. The proportion 2.4 • 1 9 8 7 of males increased in the early part of the season in each ■ 1 9 8 8 year and peaked at the time of maximum catch and A 1 9 8 9 c.p.u.e. Thereafter the proportion of males declined to a _ 1.6 minimum in June.

Discussion O 0.8 Recent fisheries data for I. argentinus from the FICZ are generally consistent with the current concept of the life cycle of this species (Hatanaka et al., 1985). Squid 0.0 usually arrive in the FICZ in February/March and there is generally a rapid increase in both catch and c.p.u.e. JFMAMJ JA followed by a steady decline. The seasonal pattern of sex Figure 4. The seasonal distribution of c.p.u.e. for Illex argenti ratio suggests that females arrive in the FICZ grounds nus within the FICZ for the period 1987-1989 before the males and leave afterwards. The squid first appear in the northern part of the zone and spread southwards as the fishing season progresses. They then linear growth models fitted to size-at-age data for squid retreat towards the northwest of the zone at the end of hatched in July (Rodhouse and Hatfield, 1990) are also the season. This is consistent with a southwards mi given. There is generally close agreement between the gration during the major feeding and growth phase of two methods of assessing growth, although there is some the life cycle, after hatching near the presumed spawn evidence of growth levelling off towards the end of the ing grounds over the northern part of the Patagonian season in the modal length data. Shelf. The southern limit of the feeding migration is apparently the continental slope to the south of the Falkland Islands. As the population approaches full Maturation sexual maturity it appears to seek the northerly flow of Seasonal change in the percent contribution of each the Patagonian Current (see Brunetti et al., 1990) to the maturity stage to the catch for the period 1987-1989 is west of the Falkland Islands (Fig. 9) to assist migration shown in Figure 6. Few males recruit into the fishery back towards the spawning grounds. until they are at stage II and following recruitment Growth of I. argentinus, as determined from analysis maturation continues so that, by June, 40-100% of all of growth increments in the statolith (Rodhouse and males are fully mature (stage V). Over the three years Hatfield, 1990), is generally consistent with shifts in the for which data are available there has been a trend modal mantle length of the population seen in the fisher- ICES mar. Sei. Symp., 199 (1995) Illex argentinus: life cycle, population structure, and fishery 429

400 r 1987 er 1988 Cf 1989 Cf

300

200

a 100 _ l I I 1— j C 0) 4 0 0r 1987$ ■ 1988 $ 1989 9 c CO 300

200

100 j i i i i i I J JFMAMJJ F M A M J JFMAMJ

Figure 5. Monthly modal mantle lengths of male and female Illex argentinus caught in the FICZ during the period 1987-1989. Broken lines represent linear growth models fitted to size at age data for squid hatched in July (from Rodhouse and Hatfield, 1990).

1 9 8 7 cf 1 989 Cf

Figure 6. Seasonal change in percent contribution of each maturity stage of the Illex argentinus catch in the FICZ for the period 1987-1989. 430 P. G. Rodhouse et al. ICES mar. Sci. Symp., 199 (1995)

350 'Cf I 'cf ru "Cf T • 1987 ■ 1988 300 * 1989

250

E 200

$mçn "$ mrç

O 300

J F M A M JJ FMAMJJFMAMJ Figure 7. Seasonal change in the the modal mantle length of each maturity stage of Illex argentinus caught in the FICZ in each month for the period 1987-1989.

1.8 • 1987 ies data from the FICZ and also with similar data given ■ 1988 by Hatanaka (1986). Modelling squid growth is cur 1.6 - A 1989 rently a matter of debate (see Forsythe and van Heuke- lem, 1987; Saville, 1987). Rodhouse and Hatfield (1990) found, that for I. argentinus, a linear model provided the 1.4 best fit to growth data which had been derived by apply ing statolith aging methods to post-recruits. Squid

1.2 growth determined by following the progress of popu O lation modal, or mean, lengths may indicate apparent 2 flattening of the growth curve towards the end of life o 1.0 which is probably due to emigration of larger individuals ra E from the exploited population (O’Dor, 1983; Rodhouse D etal., 1988). 0.8 0) The I. argentinus population departs from the feeding CO 5 grounds in the FICZ by the end of June to commence the 0.6 spawning migration and this is consistent with the peak of hatching activity in July recorded by Rodhouse and Hatfield (1990). Until the spawning grounds have been 0.4 located the time spent on the individual activities of migrating, mating, and spawning and the incubation 0.2 time of the eggs cannot be estimated. It is known that mating rarely occurs on the feeding grounds (Rodhouse and Hatfield, 1990), but two observations support the _L 0.0 _L -jL conclusion of Hatanaka et al. (1985) that the distance J F M A M J Figure 8. Seasonal change in the male:female ratio of the Illex between the feeding and spawning grounds is small. argentinus catch in the FICZ for the period 1987-1989. Firstly, the relatively short time between departure from ICES mar. Sei. Symp., 199 (1995) Illex argentinus: life cycle, population structure, and fishery 431

Antarctic Survey on the life history of Illex argentinus is funded by the Falkland Islands Government.

References Anon. 1989. Falkland Islands Interim Conservation and Man agement Zone Fisheries Report ’87/88. Falkland Islands Government, Stanley. 45 pp. Brunetti, N. E. 1990a. Escala para la identificaciön de estadios de madurez sexual del calamar (Illex argentinus). Frente Marit., 7(A): 45-51. Brunetti, N. E. 1990b. Description of rhynchoteuthion larvae of Illex argentinus from the summer spawning subpopulation. J. Plankton Res., 12: 1045-1057. Brunetti, N. E. 1990c. Evoluciôn de la pesqueria de Illex argentinus (Castellanos, 1960). Inf. Técn. Inv. Pesq., 155:3— 19. Brunetti, N. E., Ivanovic, M. L., Louge, E., and Christiansen, H. E. 1991. Estudio de la biologia reproductiva y de la fecundidad en dos subpoplaciones del calamar Illex argenti nus. Frente Marit., 8(A): 73-84. PRONT- Brunetti, N. E., Ivanovic, M. L., and Rossi, G. R. 1990. Argentine final report of the Southwestern Atlantic Survey by the R/V Kaiyo Maru. Informe INIDEP, 4. 49 pp. FALKLAND ISLANDS Brunetti, N. E., and Pérez Comas, J. A. 1989a. Abundancia, distribueiön y composiciön poblacional del recurso calamar (Illex argentinus) en aguas uruguayo-bonaerenses en mayo, setiembre y noviembre de 1989 y en marzo y mayo de 1987. Frente Marit., 5(A): 39-59. Brunetti, N. E., and Pérez Comas. J. A. 1989b. Abundancia, distribueiön y estructura poblacional del calamar (Illex argentinus) en aguas de la platforma patagonica en diciembre Figure 9. Map of Patagonian Shelf region showing direction of de 1986yenero-febrerode 1987. Frente Marit., 5(A): 61-70. flow of principal currents. Castellanos, Z. A., de, and Menni, R. 1969. Nota preliminar sobre distribueiön de los cephalopodos del Atlantico Sudoc- cidental. Lista de especies incluyendo las del sector antârtico. An. Soc. Cient. Argent., 188: 205-221. the feeding grounds and the calculated time of hatching Csirke, J. 1987. The Patagonian fishery resources and the and, secondly, the large proportion of squid in the FICZ offshore fisheries in the South-West Atlantic. FAO Fish. which are mature by the time they depart to spawn. Tech. Pap., 286. 75 pp. Forsythe, J. W., and Van Heukelem, W. F. 1987. Growth. In Knowledge of the life history of I. argentinus is still Cephalopod life cycles, Vol. 2, pp. 135-156. Ed. by P. R. limited to the period from the arrival of the population Boyle. Academic Press, London. 441 pp. on the feeding grounds, and recruitment into the fishery, Haimovici, M., and Alvarez-Pérez, J. A. 1990. Distribueiön y until the start of the spawning migration when commer maduraeiön sexual de calamar argentino, Illex argentinus cial catches cease. Future research will address the pre (Castellanos, 1960) (Cephalopoda: Ommastrephidae), en el sur de Brasil. Scient. Mar., 54: 179-185. recruitment phase through growth studies and by Hamabe, M., Hamuro, C., and Ogura, M. 1983. Squid jigging surveys of larval distribution in relation to the physical from small boats. Fishing News Books, Farnham, Surrey. 84 oceanography of the Southwest Atlantic and will pp. monitor long-term variability of fecundity in the popu Hatanaka, H. 1986. Growth and life span of short-finned squid lation. It will be important to sample specimens of I. Illex argentinus in the waters off Argentina. Bull. Jap. Soc. Sei. Fish., 52: 11-17. argentinus during and after the spawning migration to Hatanaka, H. 1988. Feeding migration of short-finned squid obtain a fuller understanding of the species’ biology in Illex argentinus in the waters off Argentina. Bull. Jap. Soc. the period immediately leading up to spawning (Hatfield Sei. Fish., 54:1343-1349. et al., 1992; Rodhouse and Hatfield, 1992) and to locate Hatanaka, H., Kawahara, S., Uozumi, Y., and Kasahara, S. 1985. Comparison of life cycles of five ommastrephid squids the position of the spawning grounds. fished by Japan: Todarodes pacificus, Illex illecebrosus, Illex argentinus, Nototodarus sloani sloani and Nototodarus gouldi. NAFO Sei. Coun. Stud., 9: 59-68. Acknowledgements Hatfield, E. M. C., Rodhouse, P. G., and Barber, D. L. 1992. Production of soma and gonad in maturing female Illex We thank Dr G. R. Carvalho and Dr G. Tingley for argentinus (Mollusca: Cephalopoda). J. mar. biol. Ass. UK, reviewing the manuscript. Research at the British 72:281-291. 432 P. G. Rodhouse et al. ICES mar. Sei. Symp., 199 (1995)

Koronkiewicz, A. 1986. Growth and life cycle of the squid Illex Rodhouse, P. G., and Hatfield, E. M. C. 1990. Dynamics of argentinus trom the Patagonian Shelf and Polish squid fishery growth and maturation in the cephalopod Illex argentinus de in the region, 1978-85. Gdynia, Sea Fisheries Institute. 9 Castellanos, 1960 (Teuthoidea: Ommastrephidae). Phil. pages, 14 figures, 12 tables (mimeo). Trans. Roy. Soc. Lond. B., 329: 229-241. Lipinski, M. 1979. Universal maturity scale for the commer Rodhouse, P. G., and Hatfield, E. M. C. 1992. Production of cially important squids. The results of maturity classification soma and gonad in maturing male Illex argentinus (Mollusca: of the Illex illecebrosus population for the years 1973-77. Cephalopoda). J. mar. biol. Ass. UK, 72: 293-300. ICNAF Res. Doc. 79/2/38, Serial 5364. 40 pp. Rodhouse, P. G., Swinfen, R. C., and Murray, A. W. A. 1988. Nigmatullin, Ch. M. 1989. Las especies de calamar mâs abun Life cycle, demography and reproductive investment in the dantes del Atlântico Sudoeste y sinopsis sobre la ecologi'a del myopsid squid Alloteuthis subulata. Mar. Ecol. Prog. Ser., calamar (Illex argentinus). Frente Marit., 5(A): 71-81. 45: 245-253. O ’Dor, R. K. 1983. Illex illecebrosus. In Cephalopod life cycles Roper, C. F. E., Sweeney, M. J., and Nauen, C. E. 1984. Vol. 1, pp. 175-199. Ed. by P. R. Boyle. Academic Press, Cephalopods of the world. An annotated and illustrated London. 575 pp. catalogue of species of interest to fisheries. FAO Fisheries Peterson, R. G., and Whitworth, T. III. 1989. The Sub-Antarc Synopsis 125, Vol. 3. 227 pp. tic and Polar Fronts in relation to deep water masses through Saville, A. 1987. Comparisons between cephalopods and fish of the southwestern Atlantic. J. Geophys. Res., 94: 10817— those aspects of biology related to stock management. In 10838. Cephalopod life cycles, Vol. 2, pp. 277-290. Ed. by P. R. Rodhouse, P. G. 1991. Population structure of Martialia hya- Boyle. Academic Press, London. 441 pp. desi (Cephalopoda: Ommastrephidae) at the Antarctic Polar Frontal Zone and the Patagonian Shelf, South Atlantic. Bull. Mar. Sei., 49: 404-418.