migrationsofvariousfishspeciesbetweenasianandamericanwaters ...3)-migrations fish.pdf · alcune...

KeywordsIchthyofauna, exchange, eggs, larvae, range exten-

sion, migrations, transfer, continental slope, KurilIslands, Kamchatka, Aleutian Islands, Bering Sea

AbstractUntil now, the continental slope of the Bering Sea

was considered to be the only route by which typicalAmerican fishes or their pelagic eggs or larvae couldreach Asian coasts. These include Pacific halibut Hip-poglossus stenolepis, shortraker rockfish Sebastesborealis, arrowtooth flounder Atheresthes stomias,rex sole Glyptocephalus zachirus and sablefishAnoplopoma fimbria. Recent studies have shown thatexchange between Asian and American fish popula-tions takes place along the Kuril and Aleutian Islands.Due to recent climatic changes, some species haveextended their ranges from the Aleutians to the KurilIslands and as far as south-eastern Kamchatka(northern rockfish Sebastes polyspinis, dusky rockfishSebastes ciliatus, arrowtooth flounder, and rex sole).Some species from the Aleutian Islands, describedearlier, were recently found to be abundant or com-mon in the Pacific waters off the Kuril Islands. Theseincluded blacktip snailfish Careproctus zachirus,longfin Irish lord Hemilepidotus zapus, scaled sculpinArchaulus biseriatus, sponge sculpin Thyriscusanoplus, and roughskin sculpin Rastrinus scutiger. InAleutian waters these species are very rare andmostly represented by small, immature specimens,whereas adults are very common off the Kurils. It issuggested that the pelagic eggs or larvae of thesespecies may be carried by the waters of the WesternPacific Gyre from the Kuril Islands to the Aleutians.

ZusammenfassungBisher galt der Rand des Festlandsockels im Bering-

meer als der einzige Weg, auf dem amerikanischeFische oder ihre pelagischen Eier oder Larven asiatis-che Küsten erreichen können. Zu den betreffenden

Arten zählen der Pazifische Heilbutt Hippoglossusstenolepis, der Nördliche Felsenfisch Sebastes bore-alis, die Pfeilzahnflunder Atherestes stomias, dieAmerikanische Scholle Glyptocephalus zachirus undder Kohlenfisch Anoplopoma fimbria. Nach neuerenForschungen aber findet ein Austausch zwischen asi-atischen und amerikanischen Fischbeständen auchüber die Kurilen- und Aleuteninseln statt. Durch neuereKlimaveränderungen haben einige Fischarten ihrVorkommen von den Aleuten zu den Kurilen und bishin zur südöstlichen Kamtschatkahalbinsel ausgedehnt(Vielstacheliger Felsenfisch Sebastes polyspinis,Bewimperter Felsenfisch Sebastes ciliatus, Pfeilzahn-flunder, Amerikanische Scholle). Einige früher von denAleuten beschriebene Arten gelten neuerdings als häu-fig oder verbreitet in pazifischen Gewässern um dieKurileninseln. Dazu zählen: der Schneckenfisch Care-proctus zachirus, der Drachenkopf (Irische Lord)Hemilepidotus zapus, sowie die DrachenköpfeArchaulus biseriatus, Thyriscus anoplus und Rastrinusscutiger. In aleutischen Gewässern sind diese Artensehr selten und meist nur durch kleine, nicht vollentwickelte Exemplare vertreten, während bei denKurilen erwachsene Exemplare sehr häufig sind. Eswird die Auffassung vertreten, dass pelagische Eieroder Larven der genannten Arten vom Wasser derwestpazifischen Strömungen von den Kurilen zu denAleuten mitgeführt werden.

RésuméJusqu'à présent, le versant continental de la mer de

Bering était sensée être le seul accès, pour les pois-sons typiquement américains ou pour leurs oeufs oularves pélagiques, aux côtes asiatiques. On y dénom-bre le flétan du Pacifique Hippoglossus stenolepis, lesébaste Sebastes borealis, le flet Atheristes stomias,la sole royale Glyptocephalus zachirus et l'Anoplo-poma fimbria. Des études récentes ont montré quel'échange entre populations de poissons asiatiques etaméricaines se passe le long des îles Kouriles et

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aqua, Journal of Ichthyology and Aquatic Biology

Migrations of various fish species between Asian and American watersin the North Pacific Ocean1

Alexei M. Orlov

Russian Federal Research Institute of Fisheries & Oceanography (VNIRO), 17, V. Krasnoselskaya,Moscow, 107140, Russia. E-mail: [email protected]

Accepted: 13.04.2004

1 The paper was presented at the 2003 ICES (International Council for the Exploration of the Sea) Annual Science Conference, 24-27September, Tallinn, Estonia

Aléoutiennes. Suite à de récents changements clima-tiques, certaines espèces ont étendu leur distributiondes Aléoutiennes aux Kouriles et jusqu'au sud-est duKamchatka (le Sébaste nordique, Sebastes polyspi-nis, le Sebastes ciliatus, le flétan Atherestes stomiaset la sole royale). Certaines espèces des îles Aléouti-ennes, déjà décrites, sont devenues récemmentabondantes et communes dans les eaux pacifiquesdes îles Kouriles. On y a dénombré le Careproctuszachirus, le Hemilepidotus zapus, l'Archaulus bise-riatus, le Thyriscus anoplus et le Rastrinus scutiger.Dans les eaux des Aléoutiennes, ces espèces sonttrès rares et le plus souvent sous forme de petitsspécimens juvéniles, alors que les adultes sont trèscommuns au large des Kouriles. On suppose que lesoeufs ou les larves pélagiques de ces espèces sontcharriés par les eaux du courant du Pacifique occi-dental des îles Kouriles aux Aléoutiennes.

SommarioFinora, la scarpata continentale del Mare di Bering

era considerata la sola via attraverso cui i tipici pesciamericani o le loro uova e larve pelagiche potesseroraggiungere le coste dell’Asia. Tra questi ci sono l’hal-ibut del Pacifico Hippoglossus stenolepis, lo scorfanoboreale Sebastes borealis, la platessa dai denti apunta di freccia Atheresthes stomias, la sogliola realeGlyptocephalus zachirus e il merluzzo neroAnoplopoma fimbria. Studi recenti hanno mostratoche scambi di popolazioni ittiche tra Asia e Americaavvengono lungo le Isole Kurili e le Aleutine. A causadi recenti variazioni climatiche, alcune specie hannoesteso la loro distribuzione fino alla fascia sudorien-tale della Kamchatka (quali, lo scorfano settentrionaleSebastes polyspinis, lo scorfano nebuloso Sebastesciliatus, la platessa dai denti a punta di freccia e lasogliola reale). Alcune specie delle Isole Aleutine,descritte in precedenza, sono state rinvenute direcente in grandi quantità nelle acque del Pacifico allargo delle Isole Kurili. Tra queste il liparide Care-proctus zachirus e i cottidi Hemilepidotus zapus,Archaulus biseriatus, Thyriscus anoplus e Rastrinusscutiger. Nelle acque delle Aleutine queste speciesono molto rare e genericamente rappresentate daforme piccole e immature, mentre gli adulti sonomolto comuni al largo delle Isole Kurili. Si ritiene chele uova pelagiche o le larve di queste specie possanoessere trasportate dalle acque della Corrente delPacifico Occidentale dalle Kurili alle Aleutine.

IntroductionThe ichthyofauna of the temperate waters of the

North Pacific Ocean is distinctive and represents adistinct zoogeographic (boreal Pacific) region (Andria-shev 1939a). This region may be divided into theAsian (Far East) and Oregonian sub-regions, eachcontaining essentially different fish species (Schmidt,1904, 1950; Andriashev, 1939b; Fedorov, 1978; Allen

and Smith, 1988). The different fish populations origi-nate from the Indo-west-Pacific and the east Pacificrespectively, and have been separated for a longperiod (Schmidt, 1948). Representatives of Oregon-ian ichthyofauna are distributed mostly off the westernAmerican coast (California, Oregon, Washington,British Columbia), in the Gulf of Alaska, off the Aleut-ian Islands, and in the eastern and southern BeringSea. These species have been found in Asian watersonly occasionally. By contrast, Asian sub-regionspecies are mainly found in the north-western PacificOcean (Sea of Okhotsk, the western Bering Sea, andthe Pacific waters off Japan, the Kuril Islands andKamchatka). These species have only very rarelybeen found off the American coast.

In the past, it was generally believed that theexchange of fish populations between Asia and Amer-ica took place in both directions along the continentalslope of the Bering Sea and the Aleutian-Kuril arch(Kodolov et al., 1991). At present, the main route forsuch exchange is considered to be the continentalslope of the Bering Sea alone (Novikov, 1961). Wil-imovsky (1964) suggested the possibility of a west-ward extension of the range of some Aleutian fishes.More recently, it has been suggested (Dudnik et al.,1998) that juvenile sablefish Anoplopoma fimbria canmigrate from the Aleutians into the waters of the KurilIslands and Kamchatka.

Studies conducted during 1992-2002 in the westernBering Sea and in the Pacific waters off the northernKuril Islands and south-eastern Kamchatka have pro-vided new data on ichthyofauna exchange betweenAsian and American waters. New data on the distrib-ution of some fish species inhabiting waters off theAsian and American coasts is presented here, andthe possible mechanism of exchange between theseareas is considered.

Material and methodsThis paper is based on catch data obtained from 21

bottom trawl surveys (a total of over 1,500 bottomtrawl stations between 1992 and 2002) and numerousbottom trawl hauls conducted during commercialoperations between south-east Kamchatka and thearea of the North Kuril Islands. The total area investi-gated was between 47º30’N and 52°N and between154º20’E and 158º50’E. Samples were collected fromthree chartered commercial Japanese trawlers (Tomi-Maru 53, Tomi-Maru 82, and Tora-Maru 58). Catchdata were also sampled aboard the Japanese trawlerKayo-Maru 28 in the western Bering Sea (168°E –178°W) during bottom trawl surveys and commercialfishing operations in the summer of 1997. Bottomtrawl surveys were conducted during the daytime.Commercial fishing took place around the clock atdepths between 76 and 833 m, using a polyethylenebottom trawl net with a (stretched) mesh of 100-120mm. The trawl mouth, some 25-30 m wide and 5-7 m

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Migrations of various fish species between Asian and American waters in the North Pacific Ocean

high, was rigged with a steel and rubber ball roller.Only samples from successful trawls were used foranalysis in this study. This meant that the horizontaland vertical dimensions of the trawl mouth were withinthe normal range, the roller was constantly in contactwith the bottom, the net suffered little or no damageduring the tow, and no derelict fishing gear wasencountered. Most hauls were made along isobaths.Hauls in which the initial and final depths were verydifferent were excluded from the analysis.

Catch data on scaled sculpin Archaulus biseriatus,sponge sculpin Thyriscus anoplus, roughskin sculpinRastrinus scutiger, and longfin Irish lord Hemilepido-tus zapus in the southern Bering Sea and off theAleutian Islands were obtained from the Fishbaseweb site (http://www.fishbase.org), which containsdatabases from the California Academy of Science(San Francisco, USA), the National Museum of Nat-ural History (Washington D.C., USA), the University ofWashington (Seattle, USA), the Scripps Institute ofOceanography (La Holla, USA), the University ofBritish Columbia (Vancouver, Canada), Kiel Univer-sity (Kiel, Germany), the Natural History Museum(London, UK), the Museum National d’histoireNaturelle (Paris), and the Museum of Zoology ofHokkaido University (Hakodate, Japan). In addition,catch data on the species listed above as well asblacktip snailfish Careproctus zachirus, arrowtoothflounder Atheresthes stomias, dusky rockfishSebastes ciliatus, northern rockfish Sebastes polyspi-nis, rex sole Glyptiocephalus zachirus, juvenile sable-fish Anoplopoma fimbria were taken from publishedsources (Peden, 1979; Nelson, 1984; Kido, 1985;Matarese and Vinter, 1985; Dudnik et al., 1998;Sheiko and Tranbenkova, 1998; Poltev andMoukhametov, 2000; Chetvergov, 2001; Orlov,2001a; Orlov and Moukhametov, 2001; Orlov et al.,2001, 2002; Tokranov, 2002).

Results and Discussion

Range extension along the Bering Sea continentalslope.

The Pacific halibut Hippoglossus stenolepis is a per-manent inhabitant of Asian waters. Due to its origin inthe north-eastern Pacific (Kodolov et al., 1991) andhighest abundance off American coast, the Asianwaters may be considered as the western edge of thisspecies range. Data collected on gonad condition,distribution of juveniles, adults with developinggonads, spawning and ripe fish, are all indicators ofnormal reproduction conditions of the Pacific halibutwithin Asian waters (Orlov, 2000). Since the speciesis considered to be capable of performing lengthymigrations (Kaimmer, 2000), adult Pacific halibutcould migrate from the American coast in Asianwaters and further along the continental slope of theBering Sea. It can also be assumed that the abun-

dance of Pacific halibut in Asian waters is being main-tained by periodical replenishment with eggs and/orlarvae carried by the current from the north-easternPacific.

The sablefish Anoplopoma fimbria is a speciesendemic to the North Pacific. It is a typical represen-tative of American ichthyofauna (Novikov, 1961; Allenand Smith, 1988; Kodolov et al., 1991). This speciesis most abundant in the eastern part of the PacificOcean while in Asian waters its abundance is rela-tively low and fluctuates considerably in the long term(Sasaki, 1984). Since this species is able to performlengthy migrations (Tuponogov and Kodolov, 2001)and its young fish have never been caught in theBering Sea (Kodolov, 1986), it can be assumed thatsablefish inhabiting the western Bering Sea havemigrated from American waters and formed a tempo-rary dependent population there (Parin, 1988).

The ability of the arrowtooth flounder Atheresthesstomias to perform lengthy migrations is well known(Shuntov, 1966; Novikov, 1961). In the westernBering Sea it migrates from the eastern part along thecontinental slope. This may be confirmed by the sim-ilarity of species size composition in both areas(Orlov, 2000). The theory that arrowtooth floundereggs drift from the north-eastern Pacific into the west-ern Bering Sea and eastern Kamchatka waters (Dol-ganov, 2000) has not yet been confirmed, because inmost catches only large mature fish have been found.

In our opinion the rex sole Glyptocephalus zachirusand dusky rockfish Sebastes ciliatus, can also pene-trate the western Bering Sea along the continentalslope from the eastern part, not by active migration(these species are not good swimmers), but bymeans of gradual range extension during long-termperiods of warming. Numerous captures of young rexsole in the western Bering Sea in the late 1990´s(Glubokov, pers. comm.) may indicate environmentalconditions favouring spawning or, because of recentclimatic changes, the survival of eggs carried there bycurrents from the eastern Bering Sea.

This ichthyofaunal exchange route between Asiaand America has long been known and is consideredtraditional (Novikov, 1961; Kodolov et al., 1991). Ourstudies therefore confirm previous findings on theactive migration of Pacific halibut, sablefish, andarrowtooth flounder from the eastern Bering Sea to itswestern part (Fig. 1). Furthermore, data obtainedshow a possible range extension of dusky rockfishand rex sole from the eastern to the western BeringSea along the continental slope.The possibility of shortraker rockfish migration in theBering Sea.

Shortraker rockfish, Sebastes borealis is a speciesendemic to the North Pacific Ocean. It is distributedbetween Japan (39°50´N) and southern California(40°46´N) as far as the Bering Sea. The species is ofcommercial importance off eastern Kamchatka, the

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northern Kuril Islands, the Aleutian Islands region, inthe Bering Sea and the Gulf of Alaska. The shortrakerrockfish has pelagic larvae and juveniles (Matarese etal., 1989). Its life history still requires further study.Important information such as stock structure and thedegree of mixing between populations, required forrational management of the species, is still lacking. Itis still not known if this species performs lengthymigrations or whether there exist discrete popula-tions. An attempt has been made to answer thesequestions in recent publications on the genetics andparasitology of the species (Moles et al., 1998; Ghar-rett et al., 2000), but it is still considered to be a non-migrating (Parker et al., 2000).

Analysis of the size composition of the shortrakerrockfish in the Bering Sea shows maximum abun-dance in the western part. Juveniles are most abun-dant in the eastern Bering Sea whereas very few havebeen caught in the western part (Bakkala et al., 1992;Harrison, 1993; Ronholt et al., 1994; Orlov, 2001b).The shortraker rockfish is long-lived (Beamish andMcFarlane, 1997) with late sexual maturation and lowgrowth rates (McDermott, 1994). There are consider-able fluctuations in abundance and variations in size-age structure from year to year. Taking into accountthe low reproductive rate and the insignificant size ofcommercial catches, we believe the observed sea-sonal and yearly variations in size composition shouldbe attributed to horizontal migration. They cannot beexplained by fluctuations in abundance.

Data on the size composition, benthic juvenile spa-tial distribution and ocean current patterns in theNorth Pacific Ocean (Orlov, 2001b) indicate that in the

Bering Sea, the main spawning area is likely to be thecontinental slope from Cape Navarin and the Com-mander Islands and waters along the north-westernand central Aleutian Islands (Fig. 2). The followingmodel may explain the pattern of shortraker rockfishmigrations. Most larvae originating in the westernBering Sea are carried eastward. Some of them areprobably moved by the Eastern Kamchatka current toeastern Kamchatka and the Kuril Islands, thenthrough straits in the central Aleutian Islands into thePacific Ocean. Some larvae and/or pelagic juvenilesmay linger within quasi-stationary anti-cyclonic eddiesaround sea mountains, near straits and in areaswhere currents meet. These conditions can result inthe formation of local populations that are regularlyreplenished by fish migrating to and from feedingareas. Taking into account the prevailing oceano-graphic conditions, such populations are most likely tobe common in the Aleutian Islands area. In bottomtrawl catches the minimum length of shortraker rock-fish benthic juveniles is about 10 cm, correspondingapproximately to two-year-old fish (Orlov andAbramov, 2001). There is a view that after shortrakerrockfish juveniles settle, the adults remain relativelysedimentary and do not perform any lengthy migra-tions (Barsukov, 1981). However, this conclusion mayonly be valid for small specimens. Recent investiga-tions demonstrate that increase in size is accompa-nied by the onset of migratory behaviour. If smallshortraker rockfish feed mainly on benthic inverte-brates and fishes (Yang, 1996), large fish feed mostlyon squid and mesopelagic fishes (Yang, 1993). Inorder to feed on the latter, shortraker rockfish need to

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Fig. 1. Scheme of distribution of sablefish, Pacific halibut, arrowtooth flounder, rex sole, and dusky rockfish from the east-ern to the western Bering Sea viathrough active migration and range extension of adults, or by the transfer of pelagic fryby currents.

migrate vertically. We suggest that as its sizeincreases, this species is able to migrate horizontallyas well as vertically. In the Bering Sea, adult short-raker rockfish have been caught in deep water farfrom the coast (Balanov and Radchenko, 1995). Theanalysis of size composition in long-line and gill netcatches also substantiates the assumption that short-raker rockfish can migrate horizontally. Oncedeployed, passive fishing gear stays in place for rela-tively long periods. Sporadic movements and themaintenance of considerable distances between indi-vidual fish are characteristic of the spatial distributionof shortraker rockfish (Krieger, 1992). High CPUE’s inlong-line and gill net fisheries may therefore beexplained by the fishes actively moving through thearea where the fishing gear is deployed. The mini-mum length of shortraker rockfish in long-line and gillnet catches is more than 30 cm but mostly 40 to 45cm and larger (Tokranov and Davydov, 1998). Obser-vations from submersible vehicles (Krieger and Ito,1999) showed that this species can swim at 1 km/h,while the average speed of bottom currents in theBering Sea is not more than 0.8 km/h (Stabeno et al.,1999). Comparison of data for the Subarctic Pacificregion currents with the above-mentioned facts sug-gests that shortraker rockfish have to undertakelengthy migrations.Range extensions from the Aleutians to the Kurilsdue to climatic changes.

The possible distribution of American ichthyofaunain Asian waters by means of range extension waspointed out during the second half of the 1990´s. Asharp increase in the abundance of arrowtooth floun-der in the Pacific waters off the northern Kurils andsouth-eastern Kamchatka was noted after 1997 (Fig.

3). In 1994-1995, only accidental captures of largefish had been seen in this area. However, in 1997-1998, catches of arrowtooth flounder in the study areaincreased dramatically. The fish caught were mostlyjuveniles. The maximum number of fish caught wasrecorded in 1997 in the eastern Sea of Okhotsk offKamchatka (Chetvergov, 2001). In this area, arrow-tooth flounder had been found only once in 1996; after1997 its catches substantially decreased. The possi-ble reason for the penetration of the arrowtooth floun-der into the waters of the Kuril Islands and Kamchatkamay be a range extension of the species from theBering Sea along the continental slope. Studies con-ducted in the western Bering Sea during 1990´s(Orlov, 2000) indicated that main arrowtooth flounderaggregations within the Russian EEZ were located tothe east of 180° and to the west of 173° E. Howeverthe catches were very small. Fish caught in this areawere exclusively large fish between 43 and 72 cmlong (mean length 54.8 cm). This means that expan-sion of fish from the Bering Sea cannot be taken asthe cause of observed increase abundance of thearrowtooth flounder off the Kurils and Kamchatka.

Another reason for the increase in abundance of thearrowtooth flounder in the study area may be thetransfer of pelagic flounder yearlings by currents fromadjacent regions. Dolganov (2000) hypothesized thatcurrents may carry the eggs of this species a long wayfrom reproductive areas. This seems doubtful,because at a length of 40-43 mm, arrowtooth flounderjuveniles start to live on the sea bottom (Bouwens etal., 1999a), but in the north-western Pacific juvenilesin bottom catches are frequently 14-18 cm in length(Shuntov, 1966). Catches from the Pacific waters offthe Kurils and Kamchatka did not contain fish of this

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Fig. 2. Hypothetic scheme of shortraker rockfish migrations in the Bering Sea.

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Fig. 3. Map of capture sitesof arrowtooth flounder (redasterisks) off the Kurils andKamchatka, 1992-2002.

Fig. 4. Map of capture sitesof northern rockfish (redasterisks) off the Kurils andKamchatka, 1992-2002.

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Fig. 5. Map of capture sitesof dusky rockfish (red aster-isks) in the north-westernPacific, 1993-2000.

Fig. 6. Map of capture sitesof rex sole (red asterisks)off the Kurils and Kam-chatka in 1998-2001.

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size. Here the minimum length was 28 cm, corre-sponding to an age of 3+ (Bouwens et al., 1999b).

Comparing numbers of caudal vertebrae and gill rak-ers, the arrowtooth flounders caught off the KurilIslands and Kamchatka are very similar to fish from thenorth-eastern Pacific Ocean (Mukhametov and Orlov,2002). Comparisons of fish size composition showedthe similarity between these two areas (Orlov, 2000).Taking all these facts into account, the reason for thesignificant increase in arrowtooth flounder abundanceobserved off the Kamchatka and Kuril Islands is relatedto extension of the species range westward from theAleutians. This results from significant warming of thenorth-western Pacific Ocean in the late 1990´s andconsiderable weakening of the East Kamchatka current(Khen, 1997; Hare and Mantua, 2000). Some rôle ofthe Aleutian-Kuril Islands arch in ichthyofaunaexchange between Asian and American waters haspreviously been noted (Wilimovsky, 1964; Kodolov etal., 1991; Dudnik et al., 1998).

In the second half of the 1990´s considerable num-bers of northern rockfish Sebastes polyspinis wereobserved in catches (Fig. 4). This species was notpreviously recorded in the study area. In 1990´s,northern rockfish was not found in the western BeringSea either. As in the case of the arrowtooth flounder,the size composition of this species in the Pacificwaters off Kamchatka and the Kurils was very similarto that of the Aleutian fish (Orlov, 2000).

Since 1993 dusky rockfish Sebastes ciliatus startedto appear occasionally in catches from Kamchatkaand Kuril Islands waters (Fig. 5). In 1993 and 1996 itwas recorded in catches taken off CommanderIslands; in 1997 it was found in catches made off thesouthern tip of Kamchatka (Cape of Lopatka) (Sheikoand Tranbenkova, 1998), and later it continued to berecorded within the entire study area from 48°16’ N to51°25’ N (Biryukov, Nemchinov, Tokranov, Zolotov,unpubl. data).

Recently, catches of the typically eastern Pacific flat-fish, rex sole, in the Pacific waters off the northernKuril Islands and south-east Kamchatka have becomemore frequent (Fig. 6). There are several possibletheories that might explain these records (Tokranovand Vinnikov, 2000; Orlov et al., 2002). It appears thatrex sole has a continuous distribution from Californiaalong the Gulf of Alaska, the Aleutian Islands and theBering Sea and from the Commander Islands andeastern Kamchatka to the north of the Kuril Islands.The absence of species records before the 1980´sand 1990´s may be due to the fact that the inshorefish fauna of the region has not been studied exten-sively. Catches of rex sole were recently reportedfrom the North Kuril Islands and south-east Kam-chatka (Borets, 1997, 2000; Sheiko and Fedorov,2000), but no documented samples were kept to ver-ify these collections. Because rex sole has pelagic lar-vae and juveniles (Matarese et al., 1989), these may

be carried in the current from the Aleutian Islands orBering Sea to the Kuril Islands. Bottom settlement ofrex sole may occur at lengths of 49-72 mm (Alstromet al., 1984; Matarese et al., 1989). One-year-oldjuveniles of this species about 10 cm long have occa-sionally been caught in British Columbian waters(Hart 1973). Rex sole caught in the Pacific waters offthe northern Kuril Islands and south-eastern Kam-chatka were between 20 and 40 cm long, corre-sponding with an age of 3-12 years (Novikov, 1974).It can therefore be suggested that the fish remain inthe area for several years after bottom settlement,though no individuals under 20 cm long had everbeen caught in the area. For this reason, we doubtthat specimens reported from this area were originallyyoung pelagic fish brought there by currents. We thinkthat rex sole found in the Pacific waters off the north-ern Kuril Islands and south-eastern Kamchatka mayhave originated from the Aleutian Islands or BeringSea as a result of range extension, due to consider-able warming of the north-western Pacific during the1990´s (Hare and Mantua, 2000) and to a weakeningof the East Kamchatka current (Khen, 1997).

Catches of sablefish yearlings in waters off the KurilIslands and Kamchatka became frequent in the 1990´s(Fig. 7). The population status of sablefish inhabitingAsian waters is still uncertain. Kodolov (1986) sug-gested that fish in the Bering Sea and Pacific waters offthe Kuril Islands and eastern Kamchatka are repre-sented by specimens that have migrated from theNortheast Pacific, and that Asian waters represent an“eviction” area for sablefish. Dudnik et al. (1998)assumed that replenishment of sablefish stocks off theKurils and Kamchatka was due not only to the migra-tion of adults from the Bering Sea along the continentalslope, but also to transfer of yearlings by the Aleutiancurrent from the American coast. In contrast, Novikov(1994) considered Asian waters (including the Sea ofOkhotsk) as areas of permanent sablefish distributionand as a part of its wide range in the North Pacific. Yetanother theory (Parin, 1988) explains the existence ofa dependent population of sablefish in the Bering Sea,and its abundance relates to the stock size of popula-tions in reproductive areas. Recent captures of pre-spawning, spawning, and ripe sablefish in Pacificwaters off the Kuril Islands and Kamchatka prove thatspawning takes place in the south-west corner of thearea (Orlov and Biryukov, 2003) which was previouslythought to be a species eviction zone. However, stud-ies of sablefish yearling survival in this area wouldrequire specialized ichthyoplankton surveys, andgenetic studies would be needed to determine thestructure of this sablefish population.

An illustration of range extensions for a number ofAleutian fish species westward to the Kuril Islands ispresented in Fig. 8.Transfer of pelagic eggs and/or larvae from theKurils to the Aleutians by the Western Subarctic Gyre.

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Fig. 7. Map of capture sites of sablefish yearlings (red asterisks) off the Kurils and Kamchatka, 1987-1998.

We believe that fish may move between Asian andAmerican waters, going from the Kuril Islands to theAleutians. This is confirmed by a number of studies.

It is possible to assume that scaled sculpin Archaulusbiseriatus found at Petrel Bank in the Bering Sea byGilbert and Burke (1912) and specimen reportedcaught recently off the Aleutians (Orlov et al., 2001)may have originated from the Kuril Islands becausethey comprised smaller specimens (80.9-129.2 mm),while larger individuals (150-159 mm) were caught offthe northern Kuril Islands. This suggestion is substanti-ated by the fact that the abundance of scaled sculpinoff the Kuril Islands is considerably higher (Fig. 9) thenthat off the Aleutians. In addition to several recent cap-tures reported by Yabe and Sonma (2000) and Orlov etal. (2001), the fish collection of the Zoological Instituteof the Russian Academy of Science (St. Petersburg)contains more than twenty specimens of scaledsculpins collected off the Kuril Islands in 1980´s by A.A. Balanov (Shieko, pers. comm.).

The longfin Irish lord, Hemilepidotus zapus wasdescribed from the southern Bering Sea off the Aleut-ian Islands (Gilbert and Burke 1912). For a long timeit was thought that this species only inhabited watersoff the Aleutian and Commander Islands, wheremostly juveniles less than 173 mm long had beenfound (Peden, 1979; fish collection databases).Recent studies showed that the longfin Irish lord, oneof most abundant cottid species off the central Kurils,is mainly distributed on the underwater plateau south-east of Shiashkotan Island (Fig. 10), mostly as maturefish up to 260 mm long (Tokranov and Orlov, 2001a).Given that the abundance of longfin Irish lord off theKuril Islands is essentially higher than that off theAleutians, it can be assumed there is a periodical driftof large numbers of pelagic yearlings from the Kurilsto the Aleutians, and subsequently wide dispersal ofyoung fish in the latter area. This is supported by peri-odical findings of longfin Irish lord larvae in the south-ern Bering Sea, for instance in 1977, in the 1980´s

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Fig. 8. Hypothetic scheme of range extension of dusky and northern rockfishes, rex sole, and arrowtooth flounder fromthe Aleutians to the Kurils.

Fig. 9. Map of known capture sites of scaled sculpin (red asterisks) off the Aleutians and Kurils.

(Matarese and Vinter, 1985) and in 1992 (Universityof Washington online fish collection database). Thesemay not necessarily have originated in Kuril Islandswaters.

The blacktip snailfish Careproctus zachirus was alsodescribed from the Aleutian Islands (Kido, 1985) fromfour specimens with lengths between 23.6 and 25.2cm. Since then, only a few more captures of thisspecies have been recorded from the area (Orr, pers.comm.). Recent studies have shown that the blacktipsnailfish is reasonably common in the Pacific watersoff the Kuril Islands and Kamchatka (Fig. 11). It hasbeen most frequently observed on the above-men-tioned underwater plateau, where its length variedfrom 19 to 32 cm (Tokranov and Orlov, 2001b).

Until recently, only the waters off the AleutianIslands were considered to be the habitat of theroughskin sculpin, Rastrinus scutiger and the spongesculpin, Thyriscus anoplus (Gilbert and Burke, 1912;Nelson, 1984), where mostly juvenile fish between34.5 and 85 mm and 58 and 121 mm respectively hadbeen caught (Nelson, 1984; fish collection data-bases). Recent studies have shown that the rough-skin sculpin is common in waters off the central Kurils,on the underwater plateau located south-east of Shi-askotan Island. (Fig. 12), where adult fish between100 and 160 mm with a mean length of 120 mm havebeen found (Tokranov and Orlov, 2002). The spongesculpin is also fairly common off the central KurilIslands (Fig. 13), where catches comprised speci-

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Alexei M. Orlov

Fig. 10. Map of known capture sites of longfin Irish lord in the southern Bering Sea and off the Aleutians and Kurils (bluerectangles – larvae, red asterisks – adults).

Fig. 11. Map of known capture sites of blacktip snailfish (red asterisks) off the Aleutians and Kurils.

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Fig. 12. Map of known capture sites of roughskin sculpin (red asterisks) off the Aleutians and Kurils.

Fig. 13. Map of known capture sites of sponge sculpin (red asterisks) off the Aleutians and Kurils.

mens between 84 and 145 mm long, with a meanlength of 112 mm (Tokranov, 1998).

Bearing in mind that most sculpins and snailfisheshave pelagic larvae and juveniles (Matarese et al.,1989), it can be assumed that specimens taken off theAleutian Islands are fish which have been transferredas pelagic juveniles from the Kuril Islands by theWestern Subarctic Gyre (Fig. 14).

ConclusionContrary to the traditional view that exchange

between the Asian and American benthic and bentho-pelagic fish species may only take place along theBering Sea continental slope, new data support thehypothesis that some species may migrate from theAleutian Island waters to the Kuril Islands, easternKamchatka, and even into the Sea of Okhotsk,extending their ranges in a westward direction underthe influence of recent climatic changes in the NorthPacific Ocean. An exchange of American and Asianichthyofauna is also possible in the reverse direction,i.e. pelagic juveniles are carried by currents from thecentral Kuril Islands to the Aleutians. The assimilationof immigrants from other regions seems to be rapid.

AcknowledgementsI would like to thank my friends and colleagues A.I.

Glubokov (Russian Federal Research Institute of

Fisheries and Oceanography (VNIRO, Moscow, Rus-sia), O. A. Nemchinov, I. A. Biryukov (SakhalinResearch Institute of Fisheries and Oceanography,SakhNIRO, Yuzhno-Sakhalinsk, Russia), A. M.Tokranov (Kamchatka Branch of Pacific Institute ofGeography, KB PIG, Petropavlovsk-Kamchatsky,Russia), O. G. Zolotov (Kamchatka Research Instituteof Fisheries and Oceanography, KamchatNIRO,Petropavlovsk-Kamchatsky, Russia), B. A. Sheiko(Zoological Institute, ZIN, St.-Petersburg, Russia),and J. W. Orr (Alaska Fisheries Science Center,AFSC, Seattle, USA) for data providing on capturesand collections of species considered. Finally I greatlyappreciate the assistance and input of Dr. EugeneSabourenkov (Commission for the Conservation ofAntarctic Marine Living Resources, P.O. Box 213,North Hobart, 7002, Tasmania, Australia)

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