514 



Abstract — We investigated the migra- 

 tion and behavior of young Pacific 

 bluefin tuna (Thunnus orientalis) us- 

 ing archival tags that measure envi- 

 ronmental variables, record them in 

 memor>-, and estimate daily geographi- 

 cal locations using measured light 

 levels. Swimming depth, ambient water 

 temperature, and feeding are described 

 in a companion paper. Errors of the tag 

 location estimates that could be checked 

 were -0.54° ±0.75° (mean ±SD) in lon- 

 gitude and -0.12° ±3.06° in latitude. 

 Latitude, estimated automatically by 

 the tag, was problematic, but latitude, 

 estimated by comparing recorded sea- 

 surface temperatures with a map of 

 sea-surface temperature, was satisfac- 

 tory. We concluded that the archival tag 

 is a reliable tool for estimating location 

 on a scale of about one degree, which 

 is sufficient for a bluefin tuna migra- 

 tion study. After release, tagged fish 

 showed a normal swimming behavioral 

 pattern within one day and normal 

 feeding frequency within one month. 

 In addition, fish with an archival tag 

 maintained weight-at-length similar to 

 that of wild fish; however, their growth 

 rate was less than that of wild fish. Of 

 166 fish released in the East China Sea 

 with implanted archival tags, 30 were 

 recovered, including one that migrated 

 across the Pacific Ocean. Migration 

 of young Pacific bluefin tuna appears 

 to consist of two phases: a residency 

 phase comprising more than 80% of all 

 days, and a traveling phase. An indi- 

 vidual young Pacific bluefin tuna was 

 observed to cover 7600 km in one trav- 

 eling phase that lasted more than two 

 months (part of this phase was a trans- 

 Pacific migration completed within two 

 months). Many features of behavior 

 in the traveling phase were similar to 

 those in the residency phase; however 

 the temperature difference between 

 viscera and ambient temperature was 

 larger, feeding was slightly more fre- 

 quent, and dives to deeper water were 

 more frequent. 



Migration patterns of young Pacific bluefin tuna 

 (Thunnus orientalis) determined with archival tags 



Tomoyuki Itoh 



Sachiko Tsuji 



National Research Institute of Far Seas Fisheries 



5-7-1 Shimizu-Orido, Shizuoka 



Shizuoka, 424-8633, Japan 



E-mail address (for T Itoh): itou@fra.affrcgo.|p 



Akira Nitta 



Japan NUS Co., Ltd. 



Loop-X BIdg., 3-9-15 Kaigan, Minato 



Tokyo, 108-0022, Japan 



Manuscript approved for publication 

 22 October 2002 by Scientific Editor. 



Manuscript received 3 January 2003 

 at NMFS Scientific Publications Office. 



Fish. Bull. 101:514-534 (2003). 



Pacific bluefin tuna (Thunnus orien- 

 talis), a highly migratory species, is 

 mainly distributed in the temperate 

 zone of the northern Pacific Ocean 

 (Yamanaka, 1982; Bayliff, 1994) in con- 

 trast to T. thynnus, which inhabits the 

 Atlantic Ocean (Collette, 1999). 



Current knowledge on the migration 

 of Pacific bluefin tuna is summarized 

 in the following studies: Aikawa ( 1949); 

 Bell ( 1963a ); Okachi ( 1963 ); Orange and 

 Fink ( 1963 ); Nakamura ( 1965 ); Clemens 

 and Flittner ( 1969); Shingu et al. ( 1974); 

 Yorita( 1976); Bayliff( 1980); Yamanaka 

 (1982); Yonemori (1989); and Bayliff et 

 al. (1991). The majority of bluefin tuna 

 spawn in the northwest Pacific Ocean 

 in an area from the Philippines past 

 Taiwan to Okinawa from April to June, 

 and small numbers spawn off southern 

 Honshu in the Pacific Ocean in July and 

 in the Sea of Japan in August (Yabe et 

 al., 1966; Ueyanagi, 1969; Okiyama, 

 1974; Yonemori, 1989; Kitagawa et al., 

 1995). Carried by the Kuroshio Cur- 

 rent, juveniles arrive near the coast of 

 Japan, move northward during sum- 

 mer and early autumn, and then most 

 turn around and move back southward 

 during late autumn and winter along 

 the Japanese coast. During the first 

 few years of their lives, the majority of 

 young fish repeat a similar north-.south 

 seasonal migration. However a small 

 fraction, increasing each year, moves 

 away from the Japanese coast and often 

 reaches the eastern side of the Pacific 

 Ocean, off the United States and Mexico. 



These fish stay in the eastern Pacific 

 Ocean for 1-3 years. Some time later, 

 as mature fish, they gather in the north- 

 west Pacific Ocean to spawn and then 

 disperse after the spawning season. 



This information on Pacific bluefin 

 tuna movements has been accumu- 

 lated through analyses of fishery catch 

 data and tag-recapture data. Fishery 

 catch data are based on different indi- 

 viduals from limited areas where, and 

 particular seasons when, fishing took 

 place. Conventional tagging data pro- 

 vide migration information regarding 

 only two points: release and recapture. 

 Acoustic tracking, another method used 

 for investigating behavior and migra- 

 tion of individuals, can collect detailed 

 information on fish movements and 

 behavior on a time scale of seconds, but 

 the duration of the tracking period of 

 each individual has usually been less 

 than several days in studies of Pacific 

 bluefin tuna (Marcinek et al., 2001; 

 Hisada et al.') as well as in other stud- 

 ies of Thunnus species (e.g. Carey and 

 Olson, 1982; Holland et al., 1990; Cayre, 

 1991; Cayre and Marsac, 1993; Block 



1 Hisada, K., H. Kono, and T Nagai. 1984. 

 Behavior of young bluefin tuna during 

 migration. In Progress report of the 

 marine ranching project 4, p. 1-7. Nat. 

 Res. Inst. Far Seas Fish. Pelagic Fish 

 Resource Division, 5-7-1 Shimizu-Orido, 

 Shizuoka, Shizuoka, 424-8633, Japan. [In 

 Japanese, the title was translated by 

 authors.! 



