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An antipodal link between the North Pacific and South Atlantic Oceans?
ARTICLE IN PRESS Deep-Sea Research I 57 (2010) 1009–1011
Contents lists available at ScienceDirect
Deep-Sea Research I journal homepage: www.elsevier.com/locate/dsri
An antipodal link between the North Pacific and South Atlantic Oceans? Alexander I. Arkhipkin n, Vladimir V. Laptikhovsky, Paul Brickle Falkland Islands Government Fisheries Department, PO Box 598, FIPASS, Stanley, FIQQ 1ZZ, Falkland Islands
a r t i c l e in fo
abstract
Article history: Received 29 March 2010 Received in revised form 7 May 2010 Accepted 17 May 2010 Available online 24 May 2010
We report on the extraordinary findings of several endemic species of North Pacific deepwater fish and squid on the continental slope of the Falkland Islands in the Southwest Atlantic, namely the giant rattail grenadier Albatrossia pectoralis (Macrouridae), pelagic eelpout Lycodapus endemoscotus (Zoarcidae) and squid Gonatopsis octopedatus (Gonatidae). These deepwater dwellers might have moved more than 15,000 km from their common species ranges with Pacific Deep Water along the western slopes of both Americas and through the Drake Passage. Our findings provide further evidence of the possible role of deepwater currents in the dispersal of bathypelagic and benthopelagic animals from one polar region to another across various climatic zones of the world ocean. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Zoogeography Species range extension Albatrossia pectoralis Lycodapus endemoscotus Gonatopsis octopedatus North Pacific Southwest Atlantic
1. Introduction Species ranges of marine pelagic animals spread within various climatic zones of the world oceans. The range limits of planktonic animals usually coincide with mesoscale or macroscale oceanic gyres and other oceanographic structures (Beklemishev, 1981), whereas nektonic animals are capable of migrating across oceanographic structures and thereby contribute to resource exchange among neighbouring marine ecosystems (Loreau and Holt, 2004). Wherever pelagic species have discontinuous ranges, their populations live mostly in homologous habitats (Beklemishev, 1981), as for example the squid Ommastrephes bartramii which inhabits temperate pelagic waters of both hemispheres (Nesis, 1985). Animals living further poleward from temperate zones are generally endemic to either the Arctic or Antarctic, except for large cetaceans and sharks that are able to perform latitudinal migrations across temperate and tropical zones within one ocean. Another exception is obligatory deepwater benthopelagic animals that have cosmopolitan distributions in abyssal waters of the world oceans (including subpolar regions), such as abyssal grenadier Coryphaenoides armatus and blue antimora Antimora rostrata (Cohen et al., 1990). Rarely have stray deepwater benthopelagic fish been found in the hemisphere opposite to their common species ranges. One finding of a large Patagonian toothfish, normally inhabiting the South Atlantic, has
n
Corresponding author. Tel.: + 500 27260; fax: + 500 27265. E-mail address: aarkhipkin@fisheries.gov.fk (A.I. Arkhipkin).
0967-0637/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2010.05.004
been reported in the North Atlantic near Greenland which might have travelled in deep water across the equator (Møller et al., 2003). Another large predator of the Southern Ocean, Patagonian hake Merluccius australis, has been found in the northern Pacific near Japan (Abe and Funabashi, 1993). The aim of the present paper is to report on our recent astonishing findings of deepwater marine fish and squid known previously only from the North Pacific, in antipodal locations of the Southwest Atlantic. We discuss how they might have appeared at least 15,000 km from their previously known species ranges.
2. Materials and methods The Fisheries Department of the Falkland Islands has been carrying out research surveys and analyses of commercial catches on the Patagonian Shelf and slope around the Falkland Islands since 1987. To date, samples have been analysed from 488 hauls made between 500 and 1500 m using bottom and semipelagic trawls onboard both research and chartered survey fishing trawlers. Additionally, catches have been examined of 5185 commercial longline sets for Patagonian toothfish. A total of 273 species of fish and invertebrates have been identified from these samples. Recently, some of these deepwater catches have brought animals previously unknown in the Southwest Atlantic. A deepwater research trawl survey conducted on the northern side of Burdwood Bank with a semi-pelagic net (R/V Dorada, station 2489, 19 July 2006, 531440 S 591060 W–531440 S 591010 W,
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998–1008 m depth) brought up a small pelagic eelpout of ca. 15 cm total length (Fig. 1A). It was identified as the North Pacific deepwater slipskin Lycodapus endemoscotus Peden and Anderson, 1978 (Zoarcidae) by one of the leading specialists in zoarcid fish, Dr. M.E. Anderson (SAIAB, J.L.B. Smith Institute of Ichthyology, Grahamstown, South Africa). During another survey on deepwater grenadiers, a small squid (11.5 cm mantle length, immature female) was recovered from a bottom trawl conducted south of the Falkland Islands (F/V Manuel Angel Nores, station 162, 21 November 2007, 531240 S 591250 W–531220 S 581220 W, at 1391–1396 m depth). It was identified as the North Pacific gonate squid Gonatopsis octopedatus Sasaki, 1929 (Gonatidae) (Fig. 1B) and later confirmed genetically (Dr. A. Lindgren, University of California, Santa Barbara, USA, pers.com), marking the first finding of the genus in the southern hemisphere. A grenadier of the genus Albatrossia (Macrouridae) of 81.5 cm total length, was caught during the longline fishery for Patagonian toothfish on the eastern side of Burdwood Bank (F/V CFL Pioneer, station 123, 29 March 2000, 531430 S 571490 W, 1666 m depth) (Fig. 1C). The age of this grenadier was estimated to be 13 years using growth increment counts on its otoliths. It was assumed initially that the specimen represented a new species of Albatrossia based on the otolith shape (Brickle and Laptikhovsky, 2002). However, a further comparison of this fish with two specimens of A. pectoralis generously sent by a grenadier specialist, Dr. T. Iwamoto (California Academy of Sciences, San Francisco, California, USA), did not reveal any morphological differences. No differences were also found between otoliths of the Falkland specimen and similar sized A. pectoralis from the Bering Sea (kindly provided by Dr. Alexey Orlov, VNIRO, Moscow, Russia). The initial assumption about possibly new species had been made by comparing the otoliths from our specimen with those of smaller fish and therefore not taking into account ontogenetic variability in otolith shape (Brickle and Laptikhovsky, 2002). Thus, we re-identified our specimen as a giant rattail A. pectoralis (Gilbert, 1892), a common deepwater dweller of the North Pacific. All specimens are stored in the reference collection of the Falkland Islands Fisheries Department.
Fig. 1. Three North Pacific deepwater benthopelagic species caught in antipodal locations near Burdwood Bank of the Southwest Atlantic, (A) deepwater slipskin Lycodapus endemoscotus (total body length of 15 cm), (B) gonatid squid Gonatopsis octopedatus (dorsal mantle length of 11 cm), and (C) giant rattail Albatrossia pectoralis (total body length of 81.5 cm).
3. Results and discussion It is notable that all three species encountered for the first time in our samples in the Southwest Atlantic have their species ranges in the North Pacific. The giant rattail A. pectoralis is an endemic grenadier occurring along the continental slope of the North Pacific from Honshu, Japan (Shinohara et al., 1996) to northern Baja California, Mexico (Clausen, 2008). Among thirteen species of pelagic slipskins of the genus Lycodapus, eleven species are endemic to the North Pacific, one is found off Chile, and another one, Lycodapus antarcticus, occurs in the Southern Ocean (Anderson and Fedorov, 2004). The species which was found in our samples, Lycodapus endemoscotus, has been known from the Okhotsk Sea to the northern Baja California, with only one specimen caught recently off Peru (Anderson, 1989). Subpolar and temperate waters of the North Pacific are thought to be the centre of the adaptive radiation of the abundant pelagic squid of the family Gonatidae, with all five species of the genus Gonatopsis being endemic to the area. Only one species of the family, Gonatus antarcticus, is widely distributed in the Southern Ocean (Nesis, 1997). What do these species have in common except for the fact that they were captured in antipodal locations to their previously known species ranges? First, all of them are deepwater animals, whose common habitat is in waters of greater than 600–1000 m depth. Second, they have benthopelagic lifestyles, i.e. they are associated with water layers off the bottom but do not utilise the substrate. Third, none of them are known to be active migrants like the tunas and whales. It seems quite unlikely that these species might be introduced to their alien habitats via ship ballast waters as has occurred with the notorious invasion of the ctenophore Mnemiopsis leidyi to the Black Sea (Vinogradov et al., 1989). Among 32 fish species (none of them deepwater) introduced by the ballast water transport worldwide by the year 2000, the majority were represented by nearshore gobies and blennies that seek refuge and spawn in crevices and therefore may hide in ballast intake grades of ships. The survival of both pelagic fish (such as clupeoids) or pelagic eggs and larvae of benthic fish (such as pleuronectids) in ballast tanks was close to zero (Wonham et al., 2000). One of our species encountered, the giant rattail A. pectoralis is characterized by deepwater spawning with eggs, larvae and alevins developing in bathypelagic layers (Orlov and Tokranov, 2008). In the northern part of their species range alevins of A. pectoralis may occur in mesopelagic waters (Endo et al., 1993) with one possible larva even taken at the surface near San Juan Island, Washington, USA (Busby, 2005). Nothing is known yet about spawning habits of L. endemoscotus. However, it was observed that the congener L. mandibularis spawn on the bottom and their eggs are negatively buoyant (Ferry-Graham et al., 2007). Gonatid squid have been found brooding their egg masses in bathypelagic waters (Seibel et al., 2000). Therefore for our deepwater species, the chances of them appearing in ship ballast tanks at any ontogenetic phase are miniscule as the ship water intakes are close to the surface. In an unlikely event of their appearance in the ballast tanks (A. pectoralis larva?) they would hardly have any chance to survive a long journey across tropics in stale and warm ballast waters. On the other hand, these deepwater fish and squid might be transported by deepsea currents. Deepwater circulation in the Pacific indicates possible transport routes of bathypelagic and benthopelagic animals from the North Pacific to the Southwest Atlantic (Fig. 2). The dense deep waters of the South Pacific move to the North Pacific in the western part of the ocean and circulate there (Reid, 1997). The return outflow of the Pacific Arctic Intermediate Water spreads southward from the North-eastern Pacific in the eastern part of the ocean below the main thermocline
ARTICLE IN PRESS A.I. Arkhipkin et al. / Deep-Sea Research I 57 (2010) 1009–1011
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Pioneer in fish and squid sampling. We are grateful to Drs. M.E. Anderson, A. Lindgren, T. Iwamoto and A. Orlov for their valuable help in identification of our specimens. We also thank Dr. Andreas Winter (Fisheries Department, Falkland Islands) for his comments and suggestions on the earlier draft of the manuscript.
References
Fig. 2. Possible migratory route of deepwater benthopelagic species from the North Pacific with Pacific Arctic Intermediate Water, Pacific Deep Water and Upper Circumpolar Deep Water through the Drake Passage into the Southwest Atlantic.
(Aken, 2007). A part of this outflow turns westward and joins the northern cyclonic gyre, whereas another part mixes with Pacific Deep Water (PDW), continues southward, crosses the equator, and then moves further south along South America under the northbound Humboldt Current. Finally, this flow mixes with Upper Circumpolar Deep Water to pass through Drake Passage to the Southwest Atlantic (Reid, 1997). The movement of PDW is slow (Aken, 2007), so it may take a few years for long-lived fish or even several generations for short-lived squid to migrate the whole way. It is notable that such transport is only possible for deepsea dwelling animals. Species that migrate to bathypelagic layers for only part of the day during their diel vertical migrations (like for example jumbo squid, Dosidicus gigas; Nigmatullin et al., 2001) spend the rest of the day in upper water layers. These species are therefore restricted in their range distributions by the presence of upper water layers that meet their habitat requirements. This is possibly one of the main reasons why jumbo squid, despite its recent large range extension to temperate waters of both hemispheres in the Eastern Pacific (Zeidberg and Robinson, 2007; ˜ez et al., 2008), has not penetrated to the Southwest Atlantic Iba´n through the Drake Passage which is occupied by cold waters of the Antarctic Circumpolar Current. It is quite likely that the recent appearance of Gonatopsis octopedatus in the Southern Hemisphere repeated the evolutionary pathway made in Pleistocene by the North Pacific ancestors of Gonatus antarcticus (Nesis, 1997). Our findings provide evidence of the possible role of deepwater currents in dispersal of bathypelagic and bathy-benthopelagic animals from one polar region to another across various climatic zones of the world ocean.
Acknowledgements We acknowledge the assistance of the crew of the research vessel Dorada and fishing vessels Manuel Angel Nores and CFL
Abe, T., Funabashi, M., 1993. A record of a merlucciid fish from off Ibaraki Prefecture, Japan. Uo 42, 1–8. Aken, van, H.M., 2007. The deep flow in the Southern, Indian, and Pacific Oceans. In: The Oceanic Thermohaline Circulation: an introduction. Springer-Verlag, New York, pp. 79–102. Anderson, M.E., 1989. Records of rare eelpouts of the genus Lycodapus Gilbert in the North and Southeastern Pacific Ocean, with an addition to the California marine fish fauna. Calif. Fish Game 75 (3), 148–154. Anderson, M.E., Fedorov, V.V., 2004. Family Zoarcidae Swainson 1839—Eelpouts. Calif. Acad. Sci. 34, 58 Annotated Checklists of Fishes. Beklemishev, C.V., 1981. Biological structure of the Pacific Ocean as compared with two other oceans. J. Plankton Res. 3 (4), 531–549. Brickle, P., Laptikhovsky, V., 2002. New records of deep-sea fishes from the waters around the Falkland Islands. J. Fish Biol. 60, 492–494. Busby, M.S., 2005. An unusual macrourid larva (Gadiformes) from San Juan Island, Washington, USA. Ichthyol. Res. 52, 86–89. Clausen, D., 2008. The giant grenadier in Alaska. In: Orlov, A., Iwamoto, T. (Eds.), Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries, American Fisheries Society Symposium, vol. 63, pp. 414–450. Cohen, D.M., Inada, T., Iwamoto, T., Scialabba, N., 1990. FAO Species Catalogue, Vol. 10. Gadiform Fishes of the World (Order Gadiformes), an annotated and illustrated catalogue of cods, hakes, grenadiers and other gadiform fishes known to date, FAO Fisheries Synopsis, no. 125, vol. 10, FAO, Rome. Endo, H., Yabe, M., Amaoka, K., 1993. Occurrence of the macrourid alevins of genera Albatrossia and Coryphaenoides in the northern North Pacific Ocean. J. Ichthyol. 40, 219–226. Ferry-Graham, L.A., Drazen, J.C., Franklin, V., 2007. Laboratory observations of reproduction in the deep-water zoarcids Lycodes cortezianus and Lycodapus mandibularis (Teleostei: Zoarcidae). Pac. Sci. 61 (1), 129–139. ˜ ez, C.M., Arancibia, H., Cubillos, L., 2008. Biases in determining the diet Iba´n of jumbo squid Dosidicus gigas (D’Orbigny 1835) (Cephalopoda: Ommastrephidae) off southern-central Chile (341S–401S). Helgol. Mar. Res. 62, 331–338. Loreau, M., Holt, R.D., 2004. Spatial flows and the regulation of ecosystems. Am. Nat. 163 (4), 606–615. Møller, P.R., Nielsen, J.G., Fossen, I., 2003. Patagonian toothfish found off Greenland. Nature 421, 599. Nesis, K.N., 1985. Oceanic Cephalopods: Distribution, Life Forms and Evolution. Nauka Press, Moscow. Nesis, K.N., 1997. Gonatid squids in the subarctic North Pacific: ecology, biogeography, niche diversity and role in the ecosystem. Adv. Mar. Biol. 32, 243–325. Nigmatullin, Ch.M., Nesis, K.N., Arkhipkin, A.I., 2001. A review of the biology of the jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae). Fish. Res. 54 (1), 9–19. Orlov, A.M., Tokranov, A.M., 2008. Some ecological and biological features of giant and popeye grenadiers in the Pacific waters off the northern Kuril Islands and Southeastern Kamchatka. In: Orlov, A., Iwamoto, T. (Eds.), Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries, American Fisheries Society Symposium, vol. 63, pp. 225–260. Reid, J.L., 1997. On the total geostrophic circulation of the Pacific Ocean: flow patterns, tracers, and transports. Prog. Oceanogr. 39 (4), 263–352. Seibel, B.A., Hochberg, F.G., Carlini, D.B., 2000. Life history of Gonatus onyx (Cephalopoda: Teuthoidea): deep-sea spawning and post-spawning egg care. Mar. Biol. 137, 519–526. Shinohara, G., Endo, H., Matsuura, K., 1996. Deep-water fishes collected from the Pacific coast of northern Honshu, Japan. Mem. Nat. Sci. Mus., Tokyo (29), 154–185. Vinogradov, M.E., Shushkina, E.A., Musayeva, E.I., Sorokin, P.Y., 1989. A newly acclimated species in the Black Sea: the ctenophore Mnemiopsis leidyi (Ctenophora: Lobata). Oceanology 29 (2), 220–224. Wonham, M.J., Carlton, J.T., Ruiz, G.M., Smith, L.D., 2000. Fish and ships: relating dispersal frequency to success in biological invasions. Mar. Biol. 136, 1111–1121. Zeidberg, L.D., Robinson, B.H., 2007. Invasive range expansion by the Humboldt squid, Dosidicus gigas, in the eastern North Pacific. Proc. Natl. Acad. Sci. USA 194, 12948–12950.
Contents lists available at ScienceDirect
Deep-Sea Research I journal homepage: www.elsevier.com/locate/dsri
An antipodal link between the North Pacific and South Atlantic Oceans? Alexander I. Arkhipkin n, Vladimir V. Laptikhovsky, Paul Brickle Falkland Islands Government Fisheries Department, PO Box 598, FIPASS, Stanley, FIQQ 1ZZ, Falkland Islands
a r t i c l e in fo
abstract
Article history: Received 29 March 2010 Received in revised form 7 May 2010 Accepted 17 May 2010 Available online 24 May 2010
We report on the extraordinary findings of several endemic species of North Pacific deepwater fish and squid on the continental slope of the Falkland Islands in the Southwest Atlantic, namely the giant rattail grenadier Albatrossia pectoralis (Macrouridae), pelagic eelpout Lycodapus endemoscotus (Zoarcidae) and squid Gonatopsis octopedatus (Gonatidae). These deepwater dwellers might have moved more than 15,000 km from their common species ranges with Pacific Deep Water along the western slopes of both Americas and through the Drake Passage. Our findings provide further evidence of the possible role of deepwater currents in the dispersal of bathypelagic and benthopelagic animals from one polar region to another across various climatic zones of the world ocean. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Zoogeography Species range extension Albatrossia pectoralis Lycodapus endemoscotus Gonatopsis octopedatus North Pacific Southwest Atlantic
1. Introduction Species ranges of marine pelagic animals spread within various climatic zones of the world oceans. The range limits of planktonic animals usually coincide with mesoscale or macroscale oceanic gyres and other oceanographic structures (Beklemishev, 1981), whereas nektonic animals are capable of migrating across oceanographic structures and thereby contribute to resource exchange among neighbouring marine ecosystems (Loreau and Holt, 2004). Wherever pelagic species have discontinuous ranges, their populations live mostly in homologous habitats (Beklemishev, 1981), as for example the squid Ommastrephes bartramii which inhabits temperate pelagic waters of both hemispheres (Nesis, 1985). Animals living further poleward from temperate zones are generally endemic to either the Arctic or Antarctic, except for large cetaceans and sharks that are able to perform latitudinal migrations across temperate and tropical zones within one ocean. Another exception is obligatory deepwater benthopelagic animals that have cosmopolitan distributions in abyssal waters of the world oceans (including subpolar regions), such as abyssal grenadier Coryphaenoides armatus and blue antimora Antimora rostrata (Cohen et al., 1990). Rarely have stray deepwater benthopelagic fish been found in the hemisphere opposite to their common species ranges. One finding of a large Patagonian toothfish, normally inhabiting the South Atlantic, has
n
Corresponding author. Tel.: + 500 27260; fax: + 500 27265. E-mail address: aarkhipkin@fisheries.gov.fk (A.I. Arkhipkin).
0967-0637/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2010.05.004
been reported in the North Atlantic near Greenland which might have travelled in deep water across the equator (Møller et al., 2003). Another large predator of the Southern Ocean, Patagonian hake Merluccius australis, has been found in the northern Pacific near Japan (Abe and Funabashi, 1993). The aim of the present paper is to report on our recent astonishing findings of deepwater marine fish and squid known previously only from the North Pacific, in antipodal locations of the Southwest Atlantic. We discuss how they might have appeared at least 15,000 km from their previously known species ranges.
2. Materials and methods The Fisheries Department of the Falkland Islands has been carrying out research surveys and analyses of commercial catches on the Patagonian Shelf and slope around the Falkland Islands since 1987. To date, samples have been analysed from 488 hauls made between 500 and 1500 m using bottom and semipelagic trawls onboard both research and chartered survey fishing trawlers. Additionally, catches have been examined of 5185 commercial longline sets for Patagonian toothfish. A total of 273 species of fish and invertebrates have been identified from these samples. Recently, some of these deepwater catches have brought animals previously unknown in the Southwest Atlantic. A deepwater research trawl survey conducted on the northern side of Burdwood Bank with a semi-pelagic net (R/V Dorada, station 2489, 19 July 2006, 531440 S 591060 W–531440 S 591010 W,
ARTICLE IN PRESS 1010
A.I. Arkhipkin et al. / Deep-Sea Research I 57 (2010) 1009–1011
998–1008 m depth) brought up a small pelagic eelpout of ca. 15 cm total length (Fig. 1A). It was identified as the North Pacific deepwater slipskin Lycodapus endemoscotus Peden and Anderson, 1978 (Zoarcidae) by one of the leading specialists in zoarcid fish, Dr. M.E. Anderson (SAIAB, J.L.B. Smith Institute of Ichthyology, Grahamstown, South Africa). During another survey on deepwater grenadiers, a small squid (11.5 cm mantle length, immature female) was recovered from a bottom trawl conducted south of the Falkland Islands (F/V Manuel Angel Nores, station 162, 21 November 2007, 531240 S 591250 W–531220 S 581220 W, at 1391–1396 m depth). It was identified as the North Pacific gonate squid Gonatopsis octopedatus Sasaki, 1929 (Gonatidae) (Fig. 1B) and later confirmed genetically (Dr. A. Lindgren, University of California, Santa Barbara, USA, pers.com), marking the first finding of the genus in the southern hemisphere. A grenadier of the genus Albatrossia (Macrouridae) of 81.5 cm total length, was caught during the longline fishery for Patagonian toothfish on the eastern side of Burdwood Bank (F/V CFL Pioneer, station 123, 29 March 2000, 531430 S 571490 W, 1666 m depth) (Fig. 1C). The age of this grenadier was estimated to be 13 years using growth increment counts on its otoliths. It was assumed initially that the specimen represented a new species of Albatrossia based on the otolith shape (Brickle and Laptikhovsky, 2002). However, a further comparison of this fish with two specimens of A. pectoralis generously sent by a grenadier specialist, Dr. T. Iwamoto (California Academy of Sciences, San Francisco, California, USA), did not reveal any morphological differences. No differences were also found between otoliths of the Falkland specimen and similar sized A. pectoralis from the Bering Sea (kindly provided by Dr. Alexey Orlov, VNIRO, Moscow, Russia). The initial assumption about possibly new species had been made by comparing the otoliths from our specimen with those of smaller fish and therefore not taking into account ontogenetic variability in otolith shape (Brickle and Laptikhovsky, 2002). Thus, we re-identified our specimen as a giant rattail A. pectoralis (Gilbert, 1892), a common deepwater dweller of the North Pacific. All specimens are stored in the reference collection of the Falkland Islands Fisheries Department.
Fig. 1. Three North Pacific deepwater benthopelagic species caught in antipodal locations near Burdwood Bank of the Southwest Atlantic, (A) deepwater slipskin Lycodapus endemoscotus (total body length of 15 cm), (B) gonatid squid Gonatopsis octopedatus (dorsal mantle length of 11 cm), and (C) giant rattail Albatrossia pectoralis (total body length of 81.5 cm).
3. Results and discussion It is notable that all three species encountered for the first time in our samples in the Southwest Atlantic have their species ranges in the North Pacific. The giant rattail A. pectoralis is an endemic grenadier occurring along the continental slope of the North Pacific from Honshu, Japan (Shinohara et al., 1996) to northern Baja California, Mexico (Clausen, 2008). Among thirteen species of pelagic slipskins of the genus Lycodapus, eleven species are endemic to the North Pacific, one is found off Chile, and another one, Lycodapus antarcticus, occurs in the Southern Ocean (Anderson and Fedorov, 2004). The species which was found in our samples, Lycodapus endemoscotus, has been known from the Okhotsk Sea to the northern Baja California, with only one specimen caught recently off Peru (Anderson, 1989). Subpolar and temperate waters of the North Pacific are thought to be the centre of the adaptive radiation of the abundant pelagic squid of the family Gonatidae, with all five species of the genus Gonatopsis being endemic to the area. Only one species of the family, Gonatus antarcticus, is widely distributed in the Southern Ocean (Nesis, 1997). What do these species have in common except for the fact that they were captured in antipodal locations to their previously known species ranges? First, all of them are deepwater animals, whose common habitat is in waters of greater than 600–1000 m depth. Second, they have benthopelagic lifestyles, i.e. they are associated with water layers off the bottom but do not utilise the substrate. Third, none of them are known to be active migrants like the tunas and whales. It seems quite unlikely that these species might be introduced to their alien habitats via ship ballast waters as has occurred with the notorious invasion of the ctenophore Mnemiopsis leidyi to the Black Sea (Vinogradov et al., 1989). Among 32 fish species (none of them deepwater) introduced by the ballast water transport worldwide by the year 2000, the majority were represented by nearshore gobies and blennies that seek refuge and spawn in crevices and therefore may hide in ballast intake grades of ships. The survival of both pelagic fish (such as clupeoids) or pelagic eggs and larvae of benthic fish (such as pleuronectids) in ballast tanks was close to zero (Wonham et al., 2000). One of our species encountered, the giant rattail A. pectoralis is characterized by deepwater spawning with eggs, larvae and alevins developing in bathypelagic layers (Orlov and Tokranov, 2008). In the northern part of their species range alevins of A. pectoralis may occur in mesopelagic waters (Endo et al., 1993) with one possible larva even taken at the surface near San Juan Island, Washington, USA (Busby, 2005). Nothing is known yet about spawning habits of L. endemoscotus. However, it was observed that the congener L. mandibularis spawn on the bottom and their eggs are negatively buoyant (Ferry-Graham et al., 2007). Gonatid squid have been found brooding their egg masses in bathypelagic waters (Seibel et al., 2000). Therefore for our deepwater species, the chances of them appearing in ship ballast tanks at any ontogenetic phase are miniscule as the ship water intakes are close to the surface. In an unlikely event of their appearance in the ballast tanks (A. pectoralis larva?) they would hardly have any chance to survive a long journey across tropics in stale and warm ballast waters. On the other hand, these deepwater fish and squid might be transported by deepsea currents. Deepwater circulation in the Pacific indicates possible transport routes of bathypelagic and benthopelagic animals from the North Pacific to the Southwest Atlantic (Fig. 2). The dense deep waters of the South Pacific move to the North Pacific in the western part of the ocean and circulate there (Reid, 1997). The return outflow of the Pacific Arctic Intermediate Water spreads southward from the North-eastern Pacific in the eastern part of the ocean below the main thermocline
ARTICLE IN PRESS A.I. Arkhipkin et al. / Deep-Sea Research I 57 (2010) 1009–1011
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Pioneer in fish and squid sampling. We are grateful to Drs. M.E. Anderson, A. Lindgren, T. Iwamoto and A. Orlov for their valuable help in identification of our specimens. We also thank Dr. Andreas Winter (Fisheries Department, Falkland Islands) for his comments and suggestions on the earlier draft of the manuscript.
References
Fig. 2. Possible migratory route of deepwater benthopelagic species from the North Pacific with Pacific Arctic Intermediate Water, Pacific Deep Water and Upper Circumpolar Deep Water through the Drake Passage into the Southwest Atlantic.
(Aken, 2007). A part of this outflow turns westward and joins the northern cyclonic gyre, whereas another part mixes with Pacific Deep Water (PDW), continues southward, crosses the equator, and then moves further south along South America under the northbound Humboldt Current. Finally, this flow mixes with Upper Circumpolar Deep Water to pass through Drake Passage to the Southwest Atlantic (Reid, 1997). The movement of PDW is slow (Aken, 2007), so it may take a few years for long-lived fish or even several generations for short-lived squid to migrate the whole way. It is notable that such transport is only possible for deepsea dwelling animals. Species that migrate to bathypelagic layers for only part of the day during their diel vertical migrations (like for example jumbo squid, Dosidicus gigas; Nigmatullin et al., 2001) spend the rest of the day in upper water layers. These species are therefore restricted in their range distributions by the presence of upper water layers that meet their habitat requirements. This is possibly one of the main reasons why jumbo squid, despite its recent large range extension to temperate waters of both hemispheres in the Eastern Pacific (Zeidberg and Robinson, 2007; ˜ez et al., 2008), has not penetrated to the Southwest Atlantic Iba´n through the Drake Passage which is occupied by cold waters of the Antarctic Circumpolar Current. It is quite likely that the recent appearance of Gonatopsis octopedatus in the Southern Hemisphere repeated the evolutionary pathway made in Pleistocene by the North Pacific ancestors of Gonatus antarcticus (Nesis, 1997). Our findings provide evidence of the possible role of deepwater currents in dispersal of bathypelagic and bathy-benthopelagic animals from one polar region to another across various climatic zones of the world ocean.
Acknowledgements We acknowledge the assistance of the crew of the research vessel Dorada and fishing vessels Manuel Angel Nores and CFL
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