Not to be cited without prior reference to the authors ICES CM 2001/K:15

RECRUITMENT STRENGTH FORECASTING OF THE SHORTFIN (CEPHALOPODA: ) USING SATELLITE SST DATA, AND SOME CONSIDERATION OF THE SPECIES’ POPULATION STRUCTURE.

LAPTIKHOVSKY, V.V., REMESLO, A.V., NIGMATULLIN, CH.M., AND I.A.POLISHCHUK

Atlantic Research Institute of Fisheries and Oceanography (AtlantNIRO), 5 Dm.Donskoy st, Kaliningrad, 236000, Russia. E-mail: [email protected]

INTRODUCTION The Argentine short-fin squid Illex argentinus (Castellanos) inhabits both shelf and oceanic waters off eastern South America between 20° and 55°S, and eastward to 40-45°W. Within this range the population structure is quite complicated. Three major intraspecific groups are recognised by most authors, though with slightly different definitions depending on the material used: Winter-spawning slope group = Southpatagonian stock (SPS), the Winter-spawning shelf group = the Bonaerensis-northpatagonian stock (BNS), and Summer spawning group/stock (SSS) (Brunetti, 1988, Haimovici et al., 1998; Carvalho, Nigmatullin, 1998; Arkhipkin, 2000). The minor Southern Brazil stock (SBS) and Spring Spawning group (SSG) were recognised by Haimovici et al., (1998) and Brunetti (1988) respectively. It is very probable that both of these are extensions of the BNS (Haimovici et al., 1998; Carvalho, Nigmatullin, 1998). A hatching of the most commercially important SPS occurs somewhere between 28° and 38°S. This follows spawning which takes place in July-August on the slope at similar latitudes (Haimovici et al., 1995; Carvalho, Nigmatullin, 1998). Larvae are carried southward by the Brazil Current until they reach the Subtropical Front (Parfeniuk et al., 1993; Santos, Haimovici, 1997; Vidal, Haimovici, 1997). The majority are believed to forage in the southward displacing warm oceanic eddies. After attaining 100-160 mm mantle length they return across the Falkland (Malvinas) Current to the shelf in a wide wave from approximately 38°S to 50°S (Parfeniuk et al., 1993; Carvalho, Nigmatullin, 1998). When growing and foraging on the shelf in January- Marchthe squid gradually move southward to 49-53°S. On maturation, from April to June, they

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shift to the edge of the continental slope and begin to migrate northwards to the spawning grounds assisted by the fair Falkland Current (Arkhipkin, 1993). Reproduction in the BNS is believed to occur on the shelf between 30° and 37°S, mostly in June-July and probably close to the western side of the Brazil-Falkland (Malvinas) Current confluence (Haimovici et al., 1998; Carvalho, Nigmatullin, 1998). Juveniles occur in the shelf waters only and, when foraging in summer and autumn, penetrate southward as far as 46-47°S. On maturation they concentrate on the shelf edge (250-350 m), and then migrate northward to the spawning grounds (Arkhipkin, 2000). Reproduction of the SSS occurs in December-February on the intermediate and outer shelf north of 46°S. The entire life cycle of this group of minor commercial importance occurs within shelf waters (Haimovici et al., 1998; Carvalho, Nigmatullin, 1998). The existence of well-defined stocks, or even cryptic species, was based on evidence of differences in allozyme frequencies (Carvalho, Nigmatullin, 1998). However, recent use of microsatellite loci, which have a greater potential utility for investigating population genetic structure than the allozyme markers used in previous studies, do not confirm the separation (Adcock et al., 1999). The BNS and SPS probably belong to the same stock and represent squid that happened to spend their early stages in different environmental conditions because of larval dispersal after hatching. I. argentinus is one of the most important commercial squid species, with annual catch sometimes attaining as much as 550,000-750,000 MT (FAO, 1997). A multinational squid fishery takes place both in the exclusive economic zones (EEZ) of Argentina and the Falkland Islands and outside of them at 42° and 45-47°S. The bulk of catches in international waters is comprised of winter spawning . It was supposed that fishery fleet between 45° and 47°S yields mostly foraging BNS in April-March and prespawning migrating SPS in May-June (Nigmatullin, Laptilhovsky, 1996). Thus, CPUE in these months could be chosen as indices of the particular groups’ abundance. Satellite sea-surface temperature (SST) data are an easy available source of information, which allows monitoring of the environmental situation over great regions of the world’s oceans. Recently they were successfully applied to forecast the squid, Illex argentinus, fishery within the Falkland Interim Conservation Zone (Waluda et al., 1999). This paper aims to find prognostic relations between satellite SST and this squid’s abundance outside of EEZs, with some consideration of squid migration patterns and population structure.

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MATERIALS AND METHODS To describe SST variability we used data available from the National Center for Atmospheric Research (U.S.A.) that were acquired at a spatial resolution of 1° latitude X 1° longitude and a temporal resolution of 1 months. These SSTs are well correlated with in situ measurements of seas temperature in offshore waters of the Southwest Atlantic (Waluda et al., 1999; Agnew et al., 2000). The following SST checkpoints were chosen: Point 1. 35°30 S, 53°30 W – shelf waters near both BNS and SPS winter spawning grounds; Point 2. 36°30 S, 53°30 W – slope waters near of the winter spawning grounds. Both point (1 and 2) are situated in the region of the Brazil Current activity, near the point of its separation from the shelf edge (35.8±1°C) (Olsson et al., 1988), and SST there probably reflects the current variability; Point 3. 42°30 S, 52°30 W – Brazil-Falkland (Malvinas) Confluence Zone; this point is mostly under the influence of the Brazil Current (Legeckis, Gordon, 1982), and an increase of mean monthly temperature means an increase of the Brazil Current intensity; Point 4. 46°30 S, 60°30 W – shelf waters in the high seas fishery grounds; this point is under influence of mostly Patagonian shelf waters; Point 5. 46°30 S, 59°30 W – slope waters in the high seas fishery grounds; this point is under influence of the Falkland waters only; Point 6. 49°30 S, 49°30 W – Subantarctic front region; a cooling means a shift of the front northwards and an increase of the Falkland Current intensity and vice-versa; Point 7. 50°30 S, 64°30 W – region of the southernmost distribution of the SPS; this point is under influence of the Falkland (Malvinas) Current western branch (Patagonian Current).

Mean monthly indices of abundance were estimated on base of the CPUE of Russian trawler type BMRT in February and May of 1988-1996 at 45-47°S (not 42°S). These two months were chosen for the following reasons. It was supposed that the BNS in February is fully recruited to the fishery, abundance of SSS is very low in comparison with January, and there is still no autumn emigration of the BNS to spawn (Nigmatullin, Laptikhovsky, 1996). In May abundance of the BNS is thought to be insignificant, and the bulk of catches consists of prespawning SPS, which appears there since mid-April. Thus these months are the most representative for showing an abundance of the particular groups.

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RESULTS 1. Indices of abundance in February were positively correlated with these in May of the same year (r=0.65, p=0,01). 2. Indices of abundance in February were negatively correlated with SST at the Point 3 in June (r=-0.62, p=0.02), July (r=-0.57, p=0.03), and August (r=-0.68, p=0.01) of the preceding year (Fig.1A). 3. Indices of abundance in May were negatively correlated with SST at point 3 in July (r=- 0.42, p=0.13), August (r=-0.50, p=0.07), and September (r-0.45, p=0.11) (Fig.1B). Despite p>0.05 (because of the small number observations), we suppose these correlations are worthy of consideration, when the above mentioned correlation (2) will be discussed. 4. Indices of abundance in May were positively correlated with the preceding year’s November temperatures at point 1 (r=0.56, p=0.04) and 2 (r=0.55, p=0.04), as well as with the precedent year’s January temperatures at these points (r=0.60, p=0.03 and r=0.65, p=0.01 respectively) (Fig.2). No such correlations were found for indices of abundance in February. 5. The correlation between SST at both points 1 and 2 during spawning and hatching (May-August) and indices of abundance in May was negative, as might be expected from the results of Waluda et al., (1999). In our case this correlation was low and statistically insignificant (from r=-0.27 to r=-0.44, p>0.05). No such correlation was found for indices of abundance in February. 6. No significant correlation was found between indices of abundance and SST in the previous year at points 4, 5, 6, and 7.

DISCUSSION AND CONCLUSIONS A positive correlation between February and May indices of abundance showed that abundance variations of both the BNS and SPS follow the same pattern. High abundance of one group corresponds to high abundance of the other. Both intraspecific groups probably represent the same stock. At the very least the same factors influence their recruitment. An insignificant negative correlation between SST on the spawning grounds (May-August) and SPS abundance on the high seas in the following year probably would not be worthy of discussion, but Waluda et al (1999) have found a strong negative correlation between this SST in June-July and SPS abundance within Falklands waters. Thus we suppose our weak correlations

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support a hypothesis about the negative influence of temperature at spawning and hatching on winter spawners’ recruitment (Waluda et al., 1999). No hint of the existence of such a correlation was found in the case of the BNS, which represents the bulk of the catches in February and wherelarval and juvenile dispersion is thought to be restricted to the shelf waters. Later, in June-September, low temperatures at point 3 (which means low intensity of the Brazil Current) are also favourable for survival of recruits. An increase in indices of abundance in both February and May is observed if temperatures and Brazil Current intensity were low at the time of larval dispersal in the previous year. Thus low temperatures and low intensity of the Brazil Current during spawning are favourable for both the BNS and SPS hatchling and juvenile survival. It was supposed that the Falkland Current has little impact on the annual migrations of the Falkland-Brazil Confluence Zone. Interannual variability in this region is predominately determined by the strength of the Brazil Current (Vivier, Provost, 1999). Thus it is not surprising that all the correlations were revealed within the zone of this currents activity. Recruitment probably depends mostly on early stages’ survival that happens in Brazil Current. When interacting with the Falkland Current, the Brazil Current produces warm eddies (Legeckis, Gordon, 1982) that move first southward, then eastward (Remeslo, 2000). We suppose that an increase of Brazil Current intensity leads to an increase of juvenile larval transport by eddies into the Argentine Basin. Despite previous suppositions that larval transport by eddies is a normal part of the SPS life cycle (Calvalho, Nigmatullin, 1998), it is seen that intensification of this transport is related to a decrease of SPS abundance both in the Falklands waters and on the high seas. Most juveniles found in the warm eddies would probably die after being transported further south and east off the shelf. A similar situation was found in the northern sibling species, , which reproduces somewhere off Atlantic USA shores, and whose juveniles can cross the ocean to be found around Iceland, Ireland, and even in the North Sea (Nesis, 1987). Slow, meandering, and shifted southward Gulf Stream (a “sibling” of the Brazil Current), is advantageous for this squid survival (Dawe et al., 2000). Similar larvae removal by current eddies provoking a sharp decrease of recruitment was found in anchovy Engraulis capensis, which spawning grounds interact with the Agulhas Current (Duncombe Rae et al., 1992).

An increase in SST on the winter spawning grounds some 5-6 month before squid reproduction is positively correlated with both the SPS and BNS recruitment. High temperatures

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probably act negatively on the larval survival of some fish species, which spawn before Illex, and whose fries and juveniles are fed on by Illex early stages. High temperatures in November are probably favourable for recruitment, because a late intensification of the Brazil Current could create favourable conditions for southward migration of the latest generations of winter hatchlings. Both of the relationships described are doubtful, and not very easy to explain unambiguously. The causative mechanisms between environmental indices and squid are often unclear, as is particular to such heuristic models (Dawe et al., 2000).

ACKNOWLEDGEMENTS We sincerely thank Dr. David Middleton (FIFD, Stanley, Falkland Islands) for valuable help at paper preparation.

REFERENCES Adcock, GJ, Shaw, PW, Rodhouse, PG, Carvalho, GR., 1999. Microsatellite analysis of genetic diversity in the squid Illex argentinus during a period of intensive fishing. Mar. Ecol. Prog. Ser., 187: 171-178. Agnew, D.J., Hill, S., and Beddington J.R. 2000. Predicting the recruitment strength of an annual squid stock: Loligo gahi around the Falkland Islands. Can.J.Fish.Aquat.Sci., 57: 2479- 2487. Arkhipkin, A.I. 1993. Age, growth, stock structure and migratory rate of prespawning short-finned squid Illex argentinus based on statolith ageing investigations. Fish. Res., 16, 313- 338. Arkhipkin, A.I. 2000. Intrapopulation structure of winter-spawned Argentine shortfin squid, Illex argentinus (Cephalopoda, Ommastrephidae), during its feeding period over the Patagonian Shelf. Fish.Bull., 98: 1-13. Brunetti N.E. 1988. Contribucion al conocimiento biologico pesquero del calamar argentino Illex argentinus (Cephalopoda, Ommastrephidae). Tesis Doctoral. Biblioteca de la Fac.Cs.Nat.Museo, UNLP: 135 pp. Carvalho, G.R, Nigmatullin, Ch.M. 1998. Stock structure analysis and species identification. In: Squid recruitment dynamics. The genus Illex as a model, the commercial Illex species and influences of variability: 199-232). Dawe, E.G., Colbourne, E.B., and K.F.Drinkwater. 2000. Environmental effects on recruitment of short-finned squid (Illex ileecebrosus). ICES. J.mar.sci., 57: 1002-1013.

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Duncombe Rae, C.M., Boyd, A.J. and Crawford, R.J.M. 1992. “Predation” of anchovy by an agulhas ring: a possible contributory cause of the very poor year-class of 1989. S.Afr.J.Mar.Sci., 12: 167-173. FAO yearbook of fishery statistics. Catches and landings. 1995. Vol. 80. Rome, FAO, 1997. - 714 p. Haimovici, M, Brunetti, N.E., Rodhouse, P.G., Csirke, J, Leta, R.H. 1998. Illex argentinus. In: Squid recruitment dynamics. The genus Illex as a model, the commercial Illex species and influences of variability: 27-58. Legeckis R., Gordon A.L. Sattelite observations of the Brazil and Falkland currents - 1975 to 1976 and 1978 // Deep Sea Research. 1982. Part A. V. 29. P. 375-401. Nesis, K.N. 1987. of the World. T.H.F. Publication, Neptune City. Nigmatullin Ch.M. Las especias del calamar mas abundantes del Atlantico sudoeste y sinopsis sobre ecologia del calamar (Illex argentinus) // Frente Maritimo, 1989. 5A. P. 71-81. Parfeniuk A.V., Froerman Yu.M., Golub A.N. Particularidades de la distribucion de los juveniles de Illex argentinus en el area de la Deprecion Argentina // Frente Maritimo. 1993. 12A. P. 105-111. Remeslo A.V., 2000. Anticyclonic frontal eddies in the Brazil Current: structure, dynamics, evolution. In: Fisheries and biological researches of AtlantNIRO in 1998-1999. Trudy AtlantNIRO: 56-69. Santos R.A., Haimovici M. Reproductive biology of winter-spring spawners of Illex argentinus (Cephalopoda: Ommastrephidae) off southern Brazil. Scientia Marina. 1997. V. 61. №1. P. 53-64. Vidal E.A.G., Haimovici M. Distribution and transport of Illex argentinus paralarvae (Cephaopoda: Ommastrephidae) across the western boundary of the Brazil / Malvinas Confluence front off southern Brazil. ANU/WSM 1997 Annual Meeting, Santa Barbara (USA), Program and Abstracts. 1997. P. 61. Vivier, F, Provost, C. 1999. Direct velocity measurements in the Malvinas Current J. Geophys. Res.-Oceans, 1999, 104: 21083-21103. Waluda, C.M., Trathan, P.N., and P.G.Rodhouse 2000. Influence of oceanographic variability on recruitment in the Illex argentinus (Cephalopoda: Ommastrephidae) fishery in the South Atlantic. Mar.Ecol.Prog.Ser., 183: 159-167.

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Abundance in February SST, July 50.00 15.00 SST, Aug SST, Jun 45.00 14.00 40.00 A 35.00 13.00 30.00 12.00 25.00 11.00 20.00 SST, deg.C SST, Abundance 15.00 10.00 10.00 9.00 5.00 0.00 8.00

3 4 5 6 7 8 9 0 1 2 3 4 5 6 98 98 98 98 98 98 98 99 99 99 99 99 99 99 1 1 1 1 1 1 1 1 1 1 1 1 1 1

35.00 15.00 14.00 30.00 B 13.00 25.00 12.00 11.00 20.00 Abundance in May SST, Aug 10.00 15.00 SST, Sep 9.00 SST, deg.C SST, Abundance SST, July 10.00 8.00 7.00 5.00 6.00 0.00 5.00 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

Figure 1 Squid abundance and SST in the Point 3.

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35.00 23.5 23 30.00 22.5 25.00 22

20.00 21.5 21 15.00 20.5

10.00 20 SST in January Abundance in May Abundance 19.5 5.00 Abundance Point 1 19 Point 2 0.00 18.5 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

35.00 20.0

30.00 19.0 18.0 25.00 17.0 20.00 16.0 15.00 15.0 10.00

14.0 SST in November Abundance in May Abundance 5.00 Abundance Point 1 13.0 Point 2 0.00 12.0 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

Figure 2. Squid abundance and SST in the Points 1 and 2.

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