BULLETIN OF MARINE SCIENCE, 71(1): 97–108, 2002 DISTRIBUTION OF JUVENILE SQUID IN THE SCOTIA SEA IN RELATION TO REGIONAL OCEANOGRAPHY C. I. H. Anderson and P. G. Rodhouse ABSTRACT A total of 211 juvenile and paralarval squid were collected on five research cruises made in the Scotia Sea region during the austral summer (1996–1999). These included specimens of Alluroteuthis antarcticus (Neoteuthidae), Batoteuthis skolops (Batoteuthidae), Brachioteuthis sp. (Brachioteuthidae), Galiteuthis glacialis (Cranchiidae), Gonatus antarcticus (Gonatidae), Mesonychoteuthis hamiltoni (Cranchiidae), Psychroteuthis glacialis (Psychroteuthidae), and a number of small onychoteuthids. The specimens ranged in size from 3.8 to 51.9 mm (dorsal mantle length), and significant differences in the size of the specimens collected were found both between and within species. Water mass type, ocean depth, daylight state and cruise (year) all had significant effects on the overall pattern of catches of squid per trawl under specific circumstances, but no significant differences were found in the pattern of catches of the individual spe- cies. Indications were found that different species favour different water masses, that the near shelf environment may be the most productive for catches of juvenile squid, and that there are interannual differences in the catches of juvenile squid in the vicinity of South Georgia. Overall, although based on a small sample of specimens, this study found that the regional oceanography does influence the distribution of juvenile squid in the Scotia Sea. In the Scotia Sea region, relatively little work has been done on the distribution of paralarval and small juvenile squid (sensu Young and Harman, 1988), and what studies there are have generally been restricted in either temporal or spatial extent (e.g., Rodhouse, 1989; Rodhouse and Piatkowski, 1995). While most work has focussed on the vertical distribution of species within the water column (Rodhouse and Clarke, 1985; Rodhouse and Clarke, 1986; Piatkowski et al., 1994; Rodhouse and Piatkowski, 1995), no multispecies studies from anywhere in the Antarctic have looked at relationships with specific water masses. However, with the increasing emphasis on the ecosystem approach to understanding marine systems (e.g., Murphy et al., 1998), and the recognition of the influence of the physical environment on squid recruitment dynamics (e.g., Waluda et al., 1999), it is clear that investigating these relationships may yield new insights into the ecology of the early life history stages of Antarctic squid. The surface waters of the Scotia Sea can be separated by region on the basis of water masses, each having distinctive temperature-salinity characteristics. These water masses are not static features. They vary in nature seasonally and are advected around Antarctica in the flow of the Antarctic Circumpolar Current (ACC) (Nowlin and Klinck, 1986). Their margins are defined by clear oceanic fronts associated with high velocity current jets, and may develop distinct frontal features such as eddies and meanders (Bryden, 1983). Because of these characteristics, both the water masses themselves and their bound- aries are associated with specific biotic and abiotic conditions which influence the vari- ety and abundance of species found within them (Longhurst, 1998). A clear example is provided by the Polar Front which separates Sub-Antarctic Surface Water from Antarctic 97 98 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 1, 2002 Zone Water (Peterson and Whitworth, 1989), and is associated with an area of seasonally enhanced primary productivity (Longhurst, 1998). This study describes the distribution of paralarval and small juvenile squid collected over a series of cruises in the Scotia Sea during the austral summer, and draws inferences on their relationship to the regional oceanography and other environmental variables, such as water depth and the diurnal cycle. MATERIALS AND METHODS Juvenile squid were collected on five cruises of the British Antarctic Survey research vessel JAMES CLARK ROSS between 1996 and 1999 (Table1). Four of those cruises (JR11, JR17, JR28 and JR38) comprised the Pelagic Ecosystem Studies Group ‘Core Programme’, studying interannual variability in the marine ecosystem immediately to the north of South Georgia. The fifth cruise, the ‘GeneFlow’ cruise (JR26), circumnavigated the Scotia Sea to collect samples for genetic analysis from across the region. A similar methodology was used on all five cruises (see North et al., 1998) and a complete suite of oceanographic data, including temperature and salinity profiles, was col- lected in parallel with the biological sampling. A variety of nets were used to collect specimens, with the majority of successful hauls made by a standard rectangular midwater trawl with an 8 m2 aperture (RMT8), and a neuston net (FNET) (1 m2 aperture) deployed from the foredeck. The only significant difference in methodology between the cruises was that during the ‘Core Programme’ cruises standardized RMT8 net hauls and those targeted at acoustic marks were carried out, whilst on the ‘GeneFlow’ cruise only the latter were used. The standardized net hauls were fished along oblique profiles between the surface and approximately 200 m depth over 30 min periods, while the target net hauls followed a variety of profiles at a range of depths between the surface and 600 m. All the juvenile squid collected were preserved (predominantly in 95–99% ethanol) upon collec- tion, and identified at a later date (using Fischer and Hureau, 1985; Sweeney et al., 1992). Identifi- cations were made to species level wherever possible, and at least to family level in most cases. The dorsal mantle length (ML) of all intact specimens was measured (to an accuracy of approximately ± 0.1 mm) on identification. Only specimens preserved exclusively in ethanol were used in the analysis of mantle lengths. All statistical analyses were performed using Minitab ver. 12.22 (Minitab Inc., 1998), except the G tests (Sokal and Rohlf (1995) with recommended Williams correction (p. 698)) which were calculated by hand (critical values from Rohlf and Sokal, 1995). The mean ML of the specimens caught was compared between the species, using the specimens from all the cruises pooled. For the most abundant species (Brachitoteuthis sp. and Galiteuthis glacialis), the mean ML was also com- pared between cruises for each species separately. The effects of environmental variables on squid catches were investigated using the frequency distributions of (1) total catches of squid in each haul and (2) total catches of each species in each haul. Statistical tests were made examining the effects of water mass type (‘GeneFlow’ data only), daylight state, water depth and, for the ‘Core Programme’ data, cruise (year) and location within the sampling area (see Table 2 for details). RESULTS A total of 211 squid were collected of which 197 could be identified to family or spe- cies level (Table 1). Among the specimens not identifiable to the species level was a neoteuthid (ML 28.7 mm) collected near the Burdwood Bank to the south of the Falkland Islands (at 54.40°S, 56.43°W). This shows some characteristics of Neoteuthis spp. (Sweeney et al., 1992), with a long narrow fin shape and a fin length of 67% ML, but the morphology of the club is closer to that described for Nototeuthis dimegacotyle Nesis and Nikitina 1986 with two greatly enlarged suckers on the manus. 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