Bulletin of the National Salmon
Resources Center, No. 3: 1 1- 14
December 2000

Easternmost Record for Ocean Distribution ofMasu Salmon (Oncorhynchus masou)
Kazumasa Ohkuma"', Shigehiko Urawa"', Yasuhiro Ueno**,and Nancy D. Davis*3* 'Research Division, National Salmon Resources Center, Fi yheries Agency of Japan,
2-2 Nakanoshima, Toyohira-ku, Sapporo 062-0922, Japan(ohkuma@salmon affrc.go j p )*2HachinoheBranch, Tohoku National Fisheries Research Institute,Hachanohe, Aomori 031-0841, Japan*'School of Aquatic and Fishery Sciences, University of Wa Thington
Box 355020, Seattle, W A 981 95-5020, USAAbstract. - Masu salmon (Oncorhynchus masou) was caught in the central North Pacific Ocean(46'00' N, 180'00') on June 27,1998 during a high-seas salmonid research cruise by the R/V Wukatukemaw. The species was identified by morphological and genetic analyses. The capture location was far
to the east from the previously recorded catches of masu salmon in the North Pacific Ocean (45-5OoN,
157-162'E). The masu salmon was a maturing male (age 1.I), whose fork length was 540 mm and bodyweight was 2,460 g. Considering the location and date of capture, it is likely that the fish had strayedfrom its usual distribution and wandered far eastwards to the mid Pacific Ocean.

Key words: masu salmon, ocean distribution, easternmost record, central North Pacific Ocean

Introduction

Materials and Methods

Masu salmon (Oncorhynchus masou) are distributed
along the Asian side of the North Pacific Ocean andtheir ocean distribution are usually limited to the Sea of
Okhotsk, Sea of Japan, and coastal waters along thePacific side of northern Japan (Kato 1991). Catches ofonly three specimens of maw salmon have been previously recorded in offshore waters of the western North
Pacific Ocean (4S-SO0N,157-162"E;Fig. 1; Machidori
et al. 1978). During a high-seas salmonid researchcruise by the R/V Wakatake maru, a salmon, tentatively identified as a maw salmon, was caught in the central North Pacific Ocean far to the east of the previously known ocean distribution of these fish. The specimen
was shipped to the National Salmon Resources Centerand positively identified as a maw salmon by morphometric and electrophoretic analyses.

The specimen was caught by drifting surface gillnet
on June 27, 1998 in the central North Pacific Ocean(46'00'N, 180°00') during research salmon fishing
operations of the R/V Wakatake maru (Fig. 1). The surface seawater temperature was 7.3"C. The fish wascaught in the 72 mm mesh panel of a research gillnet
consisting of ten different mesh sizes ranging from 48
mm to 157 mm. In addition to this specimen, 5 sockeye(0.nerka), 26 chum (0.keta), 6 pink (0.gorbuscha),
159 coho (0. kisutch), and 3 chinook salmon (0.
tshawytscha), and 13 steelhead trout (0.mykiss) werecaught at the same location (Ueno et al. 1998). Thespecimen was frozen in the round at -40°C, and shippedto the National Salmon Resources Center for species
identification.
After thawing the specimen, morphometric charac-teristics were observed, measured, and counted (TableContribution A No. 17 from the National Salmon
Resources Center.
02000 National Salmon Resources CenteI1). Scales were collected from the INPFC-preferredarea for age determination. The heart was removed andanalyzed by gel electrophoresis for malate dehydrogenase (sMDH-B1,2; Aebersold et al. 1987) to compare
the band patterns with those of known examples ofOncorhynchus (pink, chum, sockeye, coho, chinook,さけ・ます
資押管理センター川報 BuH ． Natl

Rep. HOkkaido Salmon Hatchery, t7: 1‑98
Kat0, F. 1991. Life histories Of masu and amago
salmon (Oncorhynchus
masouand Oncorhynchus
rhodurus). In Pacific salmon lifehistories (edited byC. Gro0t and L. Margolis). UBC Press, Vancouver
pp. 447‑520.
Machidori, S., and F. Kat0. 1984. Spawning
populations and marine life Of masu salmon (Onc0‑rhynchus masou). Int.N. Pac. Fish. COmm. Bul1., 43:1‑138.
Machidori, S., T. Okazaki, S. It0, and J. Ogasawara.
masou) found in1978. Masii salmon (Oncorhynchus
the offshore waters fn the northwestern NOrth Pacif‑iC Ocean. Bul1. Far Seas Fish. Res. Lab., I6: 1‑7. (InJapanese with Englishsummary.)
Masuda, M., K. Amaoka, C. Araga, C. Uyen0, and T.
YOshin0. 1984. The fishes Of the Japanese Archi‑pelag0. TOkai Univ. Press, TOky0, xxii + 437 p.
Matsubara, K. 1955. Gyorui no keitai to kensaku ‑ 1.

1shizakiShoten,TOky0. 788 p. (InJapanese.)
Semk0,R. S. 1956. SOme new information On themasu salmon, (0. masou) along west Kamchatka.
ZO01. J.,37 (?). (Translationseries Of USSR Reports

sMmonReSourCCSCenter， NO3， 2000

On NOrth Pacific Ocean Fisheries, 3).
Uen0. Y., N. D. Davis, M. Sasaki, and T. It0. 1998.

Japan‑U.S.co0perative high‑seassalmonid researchaboard the R/V Wakatake

maru

from June 9 to July25, 1998. (NPAFC DOc. 326) National ResearchInstitute Of Far Seas Fisheries, Shimizu. 55 P.

サクラマスの 海洋分布の 最東 記録
大熊― 正 ・浦和茂彦 ・上野康弘・NmCyD・DaViS

若竹丸による 北洋さけ・ます 調査期間中の 1998 乍h 月
27 日に中耶北太平洋 (46 。 N ， l80 。 )において漁獲された角が，形態および遺伝 的分析によりサクラマス と同定された． このサクラマスは 年齢 l． l の成軌 雄で ，体長は 540mm，体重は2 ， 460g

であ った・

このサクラマスの採捕 場所はこれまで 知られた本種の 海洋分布城(45‑50 。 N ， 157‑162。 E) からはるかに 離れていた． 採捕場所と時期を 考慮すると， このサクラマスは 中部北太平洋に誤って 迷い込んだと 用、われる ．