Cephalopods caught on the outer Patagonian shelf and its upper and medium slope in relation to the main oceanographic features

Ángel Guerra^{a, *}, Julio M. Portela^b, José Luis del Río^b

Running title: Cephalopods from the Patagonian slope

* Corresponding author at: Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain. Tel. +34 986231939 ext. 180; Fax: +34 986 292762

E-mail address: angelguerra@iim.csic.es (A. Guerra).
1. Introduction
The Southwest Atlantic Ocean (SWA) supports two major cephalopod fisheries. One is focused on the Patagonian long-finned squid Loligo gahi and the other on the Argentine short-finned squid Illex argentinus. Although there is considerable information on these 2 species along the continental shelf within the Argentinean and Uruguayan Exclusive Economic Zones (EEZ) (Nigmatullin, 1989; Basson et al., 1996; Agnew et al., 1998; Haimovici et al.,1998; Bunetti et al., 1999; Agnew et al., 2005; Portela et al., 2010), mainly around the Falkland (Malvinas) Islands (e.g. Arkhipkin et al., 2004; Bazino et al., 2005; Sacau et al., 2005), very little research has been carried out on the High Seas (HS) region. The recently developed Falkland (Malvinas) fishery regularly catches octopuses during survey trawls as does the Falkland Islands Government Fisheries Department (FIGFD) through observers attending commercial trawling operations on the South American continental shelf in the SWA, and research received a further boost when the FIGFD funded a study to identify the octopuses in their fisheries collection (Gleadall et al., 2010). Recently, L. gahi, I. argentinus, Onykia ingens, and Gonatus antarcticus have also been shown to occupy the ecological niche of epipelagic fish on the Falkland (Malvinas) shelf and slope (Laptikhovsky & Arkhipkin, 2010).

Many papers have been devoted to discovering knowledge of the teuthofauna from the Antarctic waters (see, for example, Rodhouse, 1989, and Gleadall et al., 2010, and the literature cited therein). However, little attention has been paid to the cephalopod species from the Argentinean shelf and even less to the biodiversity present in the Patagonian upper and medium slope. Practically the only data available came from the cruises carried out by Rodhouse et al. (1992) devoted to the early life cycle of cephalopods, which surveyed a wide area using RMT8 and Bongo nets, and associated the captures with the major oceanographic features of the SWA.

This paper examines the collection of cephalopod gathered in the cruise ATLANTIS 2009 carried out in the HS of the SWA, including the outer Patagonian shelf and the upper and medium slope, in relation to the main oceanographic features of the SWA. It also aims to contribute to the knowledge of the teuthofauna in the region, the taxonomy of the material collected, as well as its geographical and bathymetric distribution.
2. Study area

The area surveyed was the zone between parallels 44° and 48° South, east of the Argentinean EEZ down to the 1500 m depth contour (Fig. 1), and the depth of the trawls ranged from 107 to 1527 m. The physical oceanography of this area—virtually opposite the Gulf of San Jorge on the Argentinean coast—is complex. We therefore present a schematic scenario, which will allow us to understand the main features that occur in the study area. The major oceanographic features of the SWA are the Brazil Current (BC), the Falkland (Malvinas) Current (FMC), and their confluence region. The BC originates as a branch of the South Equatorial Current (around 08° South) and runs poleward almost parallel to the shelf break. It is tropical in origin and is therefore warm, saline, and relatively oligotrophic. The southern limit of the warm water associated with the BC fluctuates between 36°-38° and 46° South, and is accompanied by the intermittent formation of warm-core, anti-cyclonic eddies (Campos et al., 1995). The encounter between the warm southward flowing BC and the cold northward flow of the FMC, at approximately 38° South, generates a strong thermohaline front: the Subtropical Convergence or Subtropical Zone (STZ). The cool, nutrient-rich FMC branches off the Antarctic Circumpolar Current and flows northward along the Patagonian continental slope. This current flows round both sides of the Falkland Islands before turning northward once again as a single flow, approximately 100 km wide. The FMC is the dominant circulation feature along the Falkland Shelf Break. The sub-Antarctic waters from the FMC flow along the shelf as far north as 32° South before returning south as the Falkland (Malvinas) Return Current and flowing offshore at the confluence zone. The surface water temperatures in the northerly flowing coastal current, between 24° and 33° South, are several degrees lower than the Brazil Current and consist of a mixture of cool water from the FMC and warm water being recirculated from the BC. Brazil Current waters have a temperature of >20.0 °C and salinity of >36.0, while FMC waters have a large temperature range between 4.0 and 15.0 °C, but a narrow salinity signal between 33.7 and 34.1. Because of the large differential between these salinity ranges specified for the Brazil and FM Currents, a large proportion of the water sampled can be expected to have mixed characteristics (Wilson and Rees, 2000 and references therein).

Using the nomenclature for the fronts and zones adopted by Peterson and Whitworth (1989), the three zones south of the STZ associated with the Antarctic Circumpolar Current are, from north to south, the Sub-Antarctic Zone (SAZ), the Polar Frontal Zone (PFZ), and the Antarctic Zone (AZ). These zones are associated with fronts (Fig 2).
3. Material and methods

A multidisciplinary research cruise was conducted by the Spanish Institute of Oceanography (IEO) to assess the biomass of the main commercial fish stocks on the HS of the SWA and to identify Vulnerable Marine Ecosystems (VME). The multidisciplinary bottom trawl survey (ATLANTIS 2009), undertaken between 24 February and 1 April 2009 on board the RV Miguel Oliver, included 132 trawl stations (Fig. 3 Table 1). The survey used a stratified random design with strata boundaries defined by latitude and depth ranges. Scheduled fishing stations (hauls of 30 min) were performed using a LOFOTEN type net fitted with a “Rockhopper” mix train with bobbins and rubber separators, suitable for deepwater fishing over irregular bottoms. The headline height averaged 6.1 m, with a wing spread of 20 m. Mesh size ranged from 160 mm in the upper wings to 40 mm in the cod end liner. Trawling was restricted to daylight hours. The positions of the hauls were randomly chosen prior to starting each stratum survey.

Thirteen depth strata were defined in the study area (Table 1) and were further subdivided into 2571 grids of around 5 square nautical miles (nm²). Finally, 147 hauls were randomly allocated according to the following criteria:

i) The number of hauls in each stratum was proportional to its surface, with a minimum of 2 hauls per stratum; ii) For each stratum, hauls were randomly allocated among all possible grids, excluding those in adjacent squares; iii) When fishing was not possible in a selected grid due to bottom characteristics, the haul was put in the nearest square allowing for bottom trawling.

Only 132 hauls were performed out of the 149 planned, as characteristics of the seafloor hindered bottom trawling, mainly in stratum 7 (1001-1500 m depth). Moreover, 5 of the hauls were considered null for different reasons, such as net breakage or net entanglement. Table 1 shows the scheme of fishing stations by depth stratum and summarizes their main characteristics: depth range (m), surface (nm²), and number of grids per stratum. Hydrographical parameters (sea surface temperature [SST], sea bottom temperature [SBT], and salinity) were collected during the cruise using a CTD-probe.

Catches were sorted immediately after capture. Cephalopods were stored in labelled plastic boxes and frozen at -20 ºC on board. Specimens were taken by the vessel to Vigo (Spain) where the samples were transported to the Instituto de Investigaciones Marinas (IIM, CSIC) marine research laboratory for detailed examination.

After defrosting at room temperature, cephalopods were identified from published guides, and old (e.g. Nesis, 1987; G. Voss, 1978; N. Voss et al., 1998) and recent papers (e.g. Guerra et al., 2000; Lipinski, 2001; Allcock et al., 2004; Vecchione et al., 2005; Gleadall et al., 2010). Total length (TL), dorsal mantle length (ML), and wet weight were measured immediately, and the sex was also determined.

All the material caught on this cruise, except Batoteuthis skolops, which is in the National Museum of Natural History (Washington D.C., USA), has been deposited at the Museo do Mar de Galicia (Vigo, Spain-www.museodomar.com).

Locations of trawls conducted during the ATLANTIS 2009 survey are shown in Fig. 3. The typical range of SST, SBT, and salinity at the different zones, or the oceanographic features cited in the text and Fig. 2 are shown in Table 2.

During the cruise, 90 cephalopod specimens, comprising 16 squids and 5 octopods, were collected. Depth ranges of capture and numbers of hauls with cephalopods catches are shown in Table 3. Cephalopods were present in 71 of the 127 valid hauls (56%) carried out during the cruise. The family of squids best represented was Histioteuthidae with 5 species, while the Octopodidae was represented with 5 species (Table 3). The most abundant squids were of the Gonatus antarcticus Lönngerg, 1898, species (25.5%), followed by Histioteuthis atlantica (Hoyle, 1885) (11.1%). The most abundant octopus species (8.9%) was Muusoctopus eureka (Robson, 1929). G. antarcticus also appears to be the most diverse spatially and was captured at 14 stations (Table 3). However, the distribution of H. atlantica and M. eureka, which appear in 8 stations, respectively, also have a wide geographical area of distribution within the limits of the total area explored.

Size and some other biological data of captured specimens and families (10) of each species are detailed in Table 4.

Table 5 shows the cephalopod distribution caught during this cruise in relation to the major oceanographic features of the study area.
5. Discussion
Six specimens of Brachioteuthidae share the diagnostic characters of Slosarczykovia circumantarctica Lipinski, 2001. This is one of the most common squids in Antarctic waters (Lipinski and Young, http://tolweb.org/Slosarczykovia/24102).

Until now, very few specimens of Batoteuthis skolops Young and Roper, 1968 have been collected (Young & Roper, 1968; Rodhouse et al., 1992; Young and Roper http://tolweb.org/Batoteuthidae/19452). The species is found only in Antarctic and sub-Antarctic waters and little is known of its biology. Due to the interest in our specimen, we plan to present a detailed description and discussion elsewhere.

The taxonomy of the octopuses is still undergoing major revision (see, for example, Norman & Hochberg, 2005) and to date incirrate octopuses have yet to be the subject of a comprehensive study using nucleotide sequence data. Such data are now being collected and research is also under way to provide clear species re-descriptions based upon morphometric data, leading to a much better understanding of the major groups and biodiversity of shallow water octopuses (Gleadall et al., 2010). These authors have described three inkless octopodids from the continental shelf off south-eastern South America. These octopuses are a non-commercial by-catch in the Falkland (Malvinas) fishery. Muusoctopus eureka (Robson, 1929) is one of two common inkless octopuses, is of medium size, with orange-pink skin, and a distinctive pattern of irregular dark markings, interspersed with white spots visible only in living or freshly dead specimens. Eight specimens caught in our cruise belong to this species. Another 4 specimens also captured during our cruise belong to Muusoctopus longibrachus akambei Gleadall et al., 2010.

Two specimens (21-30mm ML) of the Patagonian bobtail squid Semirossia patagonica (Smith, 1881) were caught on the Falkland (Malvinas) shelf by an RMT8 net from the surface to the bottom (Rodhouse et al., 1992). The species have also been collected on the Argentinean shelf (Reid & Jereb, 2005). The records presented here represent an expansion of the geographical range of the species eastwards. According to depth, SST, and SBT (Table 2), our specimens were caught in the STZ, usually located between 35° and 45° South, where the average SST changes from about 12 °C to 7-8 °C (Campos et al., 1995). One specimen of the bobtail Austrorossia mastigophora (Chun, 1915) was also captured in this STZ (45° 46' 30'' South - 60° 27' 29'' West). The known geographical distribution of this bobtail squid was western, southern, and eastern Africa (from Guinea and Somalia to the Cape of Good Hope), but doubtful in Chilean waters (Reid and Jereb, 2005). Therefore, this is the first time that the species is caught in the western part of the South Atlantic Ocean. The Carol bobtail squid Neorossia caroli (Joubin, 1902) was caught south more frequently than the previous bobtail squids (47° 32' 60'' South - 60° 14' 19'' West) and in the deeper, cooler waters (Table 2) of the FMC. This species is represented on the Patagonian slope north of the Falkland (Malvinas) Islands by the subspecies N. caroli jeannae Nesis et al., 2001, while our specimen was recorded much further north than any other until now.

The jewel squids Histioteuthis reversa (Verrill, 1880), H. atlantica (Hoyle, 1885), H. bonnelli (Férussac, 1834), and H. eltaninae N. Voss, 1969 caught are common in the area explored by our cruise, showing an already well-known vertical and geographic distribution inside the FMC (Voss et al., 1998). However, this is the most southern record (45° 13' 52'' South - 59° 24' 04'' West) of Histioteuthis arcturi (Robson, 1948), which had previously only been registered between 28° North and 25° South (Voss et al., 1998).

To date, the known distribution of the squid Slosarczykonia circumantarctica was off Wilkes Land (Australian Antarctic Territory) and in circumpolar Antarctic waters (Lipinski and Young http://tolweb.org/Slosarczykovia/24102). Our findings extend the geographical distribution area of the species towards the north and east of the SWA, occupying the western border of the FMC (from approximately 46° 54' South - 59° 49' West to 45° 17' South - 59° 33' West), at depths ranging from 881 to 1224 m, and SST and SBT between 11.9 and 2.3 ºC, respectively (Table 2).

According to the map of the records of B. skolops provided by Young and Roper (http://tolweb.org/Batoteuthidae/19452), our record is the most northern for this species (44° 30' 22'' - 44° 29' 54'' South).

The glacial cranch squid Galiteuthis glacialis (Chun, 1906) is found throughout the circumpolar Antarctic waters where it is one of the most abundant (Nesis, 1987). According to the map given by Young and Mangold (http://tolweb.org/Galiteuthis_glacialis/19572), our records are the first outside circumpolar Antarctic waters, thus expanding the geographical distribution of the species towards the north, at least until 44° 02' 95'' South. SST and SBT seem to indicate that this species was caught along the western border of the FMC.

Type locality of Graneledone antarctica Voss, 1976 is the Ross Sea (74° 05' 06'' South, 175° 05' 02'' West) (Voss, 1976). However, Kubodera and Okutani (1994) captured 1 specimen at 45° 44' South, 59° 46' West at 858 m depth, which is close to our area of study and within the bathymetric range of our specimens (Table 3). Despite the resemblance of the Kubodera and Okutani specimen to G. antarctica, these authors did not risk identifying it as such. Their argument was that it was captured near the Crozet Islands at such a considerable distance that they hesitate to conclude that the material was conspecific. Nevertheless, the coordinates of capture that the authors give twice (their Table I and on page 214) do not correspond to these islands but to the Patagonian shelf or south-eastern Argentinean EEZ waters, where they also obtained some samples. Our specimens (1 juvenile and 2 immature female, Table 4) share the diagnostic characters of the species. Considering this information, we therefore believe that the species is present off the Patagonian shelf at depths of 1156-1461(Table 3) and from 44º to 47º South. The species was found in the western boundary (59º 25' West) of the FMC, where the SST was 9.7 ºC and the SBT 2.4 ºC (Table 2).

The large-tuberculate octopus Graneledone macrotyla Voss, 1976 was for many years only known by type-locality (54° 43' South, 55° 30' West in 1647-2044 m) (Voss, 1976, 1988). However, the collection studied by Kubodera and Okutani (1994) extended the known distribution of the species to the north of 45° South along south-eastern Argentina, at depths ranging from 858 to 2044 m, which agrees with the latitudinal distribution shown by the present sample (from 45° to 47° South). The western range where this species was caught (59° 32' - 60° 01' West) and the SST and SBT (Table 2) suggest that it inhabits the northern part of the FMC.

Our 4 mature males of Thaumeledone gunteri Robson, 1930 share the main characters given by Allcock et al. (2004). These authors indicated that the distribution of this species is probably restricted to South Georgia and Shang Rocks at a depth of 366-964 m and probably deeper. However, we found this inkless octopus further north, at depths ranging from 855 to 1190 m, with a sea surface temperature of 9.6 ºC, and a sea bottom temperature of 2.6 ºC (Table 3).

Laptikhovsky (2001) reported 32 females of Benthoctopus eureka collected on the Falkland (Malvinas) shelf (48° 40' - 52° 59' South, 56° 51' - 60° 15' West, depth range 125-344 m) during expeditions on board the RV Dorada. Gleadall et al. (2010) are currently proposing a new taxonomic combination for eureka, which is Muusoctopus eureka (Robson, 1929). The species was caught in the same area explored by our cruise. However, the specimens were mainly on the 200 m depth contour (Gleadall et al., 2010), whereas the bathymetric range of the 8 specimens included in this paper was 111 to 1156 m. Therefore, it seems that this species is adapted to a relatively wide range of temperature, possibly from 8 ºC to -0.8 ºC (Tables 2 and 5).

Previously known specimens of M. longibrachus akambei (holotype and paratypes) were caught on different cruises around 49° 22' South and between 59° 10' - 66° 70' West from 147 to 377 m depth off the coastal waters of Argentina (Gleadall et al., 2010). The specimens presented in this paper were captured about 140 nautical miles to the north (46° 53' 98'' South), at a similar western longitude (59° 48' - 60° 39' West), and in deeper waters (428-921 m) (see Table 3).

From a biogeographic point of view our data show that several species, mainly benthic octopuses (Table 5), penetrate the area studied with the plume of cold sub-Antarctic waters and are pushed far into the South Atlantic by the FMC (Fig. 4). This concurs with observations by Strugnell et al. (2008), who showed that the deep-sea lineage had their evolutionary origins in Antarctica. We suggest that sampling in the near future should be attempted on either side of this plume, in regions where there is no Antarctic water, in order to test the presence of cold water-adapted species.

We would like to extend our warmest thanks to authorities of the Spanish Secretaría General del Mar (SGM, General Secretary for the Sea) who owned the research vessel. We are also very grateful to Dr Ian Cleadall for his useful comments on the original manuscript and to María Teresa Fernández Álvarez (IIM, CSIC) for her technical assistance. We would also like to thank the crew of the vessel, the scientific staff, and Raúl Vilela for his assistance with GIS tools.

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