International Council ICES CM 2003/Q:09 for the Exploration Theme Session Q: Regional Long-Term Changes of the Sea in the Spatial Distribution, Abundance, and Migration of Pelagic and Demersal Resources Possible ways of exchange between Asian and American ichthyofaunas in the North Pacific Ocean Alexei M. Orlov Russian Federal Research Institute of Fisheries & Oceanography (VNIRO), 17, V. Krasnoselskaya, Moscow, 107140, Russia [tel: +7 (095) 264-91-43, fax: +7 (095) 264-91-87, e-mail: [email protected]] Abstract Till present only continental slope of the Bering Sea was considered as the way, along which some typical representatives of American ichthyofauna are able to migrate or its pelagic eggs/larvae may be transported to Asian coasts (Pacific halibut Hipposlossus stenolepis, shortraker rockfish Sebastes borealis, arrowtooth flounder Atheresthes stomias, rex sole Glyptocephalus zachirus, sablefish Anoplopoma fimbria). Recent studies showed that exchange between Asian and American ichthyofaunas exists along Kuril and Aleutian Islands. Some species extended their ranges from the Aleutians to Kuril Islands and southeastern Kamchatka (northern rockfish Sebastes polyspinis, dusky rockfish Sebastes ciliatus, arrowtooth flounder, and rex sole) due to recent climatic changes. Some species described from the Aleutian Islands (blacktip snailfish Careproctus zachirus, longfin Irish lord Hemilepidotus zapus, scaled sculpin Archaulus biseriatus, sponge sculpin Thyriscus anoplus, and roughskin sculpin Rastrinus scutiger) were recently found in the Pacific waters off Kuril Islands and are in this area abundant or common. Above species occurred off the Aleutians very rare and are represented mostly by small-sized immature specimens while off the Kurils their adults are very common. Therefore it may be suggested that pelagic eggs or larvae of these species may be transported from the Kuril Islands to the Aleutians by the Western Pacific Gyre waters. Keywords: ichthyofauna, exchange, eggs, larvae, range extension, migrations, transfer, continental slope, Kuril Islands, Kamchatka, Aleutian Islands, Bering Sea Introduction Ichthyofauna of temperate waters of the North Pacific Ocean is characterized by particular originality and represents separate zoogeographic (boreal Pacific) region (Andriashev 1939a). Despite significant similarities, within this region two sub-regions may be distinguished: Asian (Far East) and Oregonian, which fish species compositions essentially differ (Schmidt 1904, 1950; Andriashev 1939b; Fedorov 1978; Allen and Smith 1988). These differences related to different sources of origin of ichthyofaunas in both areas (Indo-West-Pacific for Asian sub-region and East- Pacific for Oregonian one) and to its long existence separately each from other (Schmidt 1948). Representatives of Oregonian ichthyofauna are distributed mostly off the western American coast (California, Oregon, Washington, British Columbia), in the Gulf of Alaska, off the Aleutian Islands, and in the eastern and southern Bering Sea. In Asian waters these species occur only occasionally. In their turn, Asian species are distributed mainly in the northwestern Pacific Ocean (Sea of Okhotsk, western Bering Sea, and the Pacific waters off Japan, Kuril Islands and Kamchatka). These species occur off American coast very rare. It is thought that in the past exchange of ichthyofaunas between Asia and America had mutual character and was realized along Bering Sea continental slope and Aleutian-Kuril arch (Kodolov et al. 1991). In present period only continental slope of the Bering Sea is considered as the main way of such exchange (Novikov 1961). Though Wilimovsky (1964) hypothesized possibility of westward range extension of some Aleutian fishes. Recently it was suggested (Dudnik et al. 1998) that juvenile sablefish Anoplopoma fimbria is able to migrate from the Aleutians in the Kuril Island and Kamchatka waters. Studies conducted during 1992-2002 in the western Bering Sea and the Pacific waters off the northern Kuril Islands and southeastern Kamchatka allowed receiving new data on recent exchange between Asian and American ichthyofaunas. This paper provides new data on distribution of some fishes, inhabiting waters off both Asian and American coasts, and considers possible exchange paths of American and Asian ichthyofaunas. Material and methods This paper is based on catch data obtained from 21 bottom trawl surveys (total over 1,500 bottom trawl stations made during 1992-2002) and numerous bottom trawl hauls conducted during commercial operations from southeastern Kamchatka and northern Kuril Islands area. The investigated area is within 47º30´ N to 52° N, 154º20´ E to 158º50´ E. Samples were collected from three chartered commercial Japanese trawlers (Tomi-Maru 53, Tomi-Maru 82, and Tora-Maru 58). Catch data sampled aboard Japanese trawler Kayo-Maru 28 in the western Bering Sea (168° E – 178° W) during bottom trawl survey and commercial fishing operations in summer 1997 were also used. Bottom trawl surveys were conducted during the daytime, commercial fishing operations were conducted around the clock at depths 76-833 m using a 5-7 m (vertically) by 25-30 m (horizontally) bottom trawl net constructed from 100-120 mm (stretched mesh) polyethylene net. The net was outfitted with steel and rubber ball roller gear in the forward wings. Only successful trawl samples (horizontal and vertical net openings remained within normal range, the roller gear maintained consistent contact with the bottom, the net suffered no or little damage during the tow, there were no conflicts with derelict fishing gear) were used for analysis in the present study. Most hauls were made along isobaths. Hauls with highly variable depths between the start and end of towing were excluded from the analysis. Data on captures of scaled sculpin Archaulus biseriatus, sponge sculpin Thyriscus anoplus, roughskin sculpin Rastrinus scutiger, and longfin Irish lord Hemilepidotus zapus in the southern Bering Sea and off the Aleutian Islands were obtained from electronic fish collection databases of the California Academy of Science, National Museum of Natural History, University of Washington, Scripps Institute of Oceanography, University of British Columbia, Kiel University, British Museum of Natural History, Museum National d’Historie Naturelle, and Museum of Zoology of Hokkaido University that are available via FISHBASE web site (http://www.fishbase.org). Data on captures of above species and of blacktip snailfish Careproctus zachirus, arrowtooth flounder Atheresthes stomias, dusky rockfish Sebastes ciliatus, northern rockfish Sebastes polyspinis, rex sole Glyptiocephalus zachirus, juvenile sablefish Anoplopoma fimbria were taken from published sources (Peden 1979; Nelson 1984; Kido 1985; Matarese and Vinter 1985; Dudnik et al. 1998; Sheiko and Tranbenkova 1998; Poltev and Moukhametov 2000; Chetvergov 2001; Orlov 2001a; Orlov and Moukhametov 2001; Orlov et al. 2001, 2002; Tokranov 2002). Result and Discussion Range extension along the Bering Sea continental slope. Pacific halibut Hippoglossus stenolepis is permanent dweller of the Asian waters. Due to its origin from the northeastern Pacific (Kodolov et al. 1991) and highest abundance off American coast the Asian waters may be considered as the western edge of species range. Condition of gonads, existence of juveniles, adults with developing gonads, spawning and ripe fish are evidence of normal reproduction of Pacific halibut within Asian waters (Orlov 2000). Since species considered is capable to perform lengthy migrations (Kaimmer 2000), adult Pacific halibut may move from American coast in the Asian waters along continental slope of the Bering Sea. It is possible also assume that Pacific halibut abundance within the Asian waters is substantiated due to periodical replenishment by eggs or/and larvae transported by current from the northeastern Pacific. Sablefish Anoplopoma fimbria is an endemic species of the North Pacific. It is typical representative of American ichthyofauna (Novikov 1961; Allen and Smith 1988; Kodolov et al. 1991). This species is most abundant within eastern part of the Pacific Ocean while in the Asian waters sablefish abundance is relatively low and considerably fluctuates in long-term aspect (Sasaki 1984). Since this species is able to perform lengthy migrations (Tuponogov and Kodolov 2001) and its young was never caught in the Bering Sea (Kodolov 1986), it is possible assuming that sablefish, inhabiting the western Bering Sea, is represented by fish migrated from American waters to perform there temporal dependent population (Parin 1988). Capability of arrowtooth flounder Atheresthes stomias to perform lengthy migrations is well known (Shuntov 1966; Novikov 1961). It may migrate in the western Bering Sea from eastern part of the sea along continental slope that may be confirmed by similarity of species size composition in both areas (Orlov 2000). Hypothesis of arrowtooth flounder eggs drift from the northeastern Pacific in the western Bering Sea and eastern Kamchatka waters (Dolganov 2000) are not confirmed yet, because there are no young caught in these areas but only large mature fish represented bulk of catches. Rex sole Glyptocephalus zachirus and dusky rockfish Sebastes ciliatus, in our opinion, are able to penetrate into the western Bering Sea from its eastern part also along continental slope, though not due to active migrations (above species are not good swimmers) but due to gradual range extension during long-term warming.