535 



Abstract — We investigated the migra- 

 tion and behavior of young Pacific blue- 

 fin tuna {Thunnus orientalis) using 

 archival tags. The archival tag mea- 

 sures environmental variables, records 

 them in its memory, and estimates 

 daily geographical locations based on 

 measured light levels. Of 166 archival 

 tags implanted in Pacific bluefin tuna 

 that were released at the northeastern 

 end of the East China Sea from 1995 to 

 1997, 30 tags were recovered, including 

 one from a fish that migrated across the 

 Pacific. This article describes swimming 

 depth, ambient water temperature, and 

 feeding frequency of young Pacific blue- 

 fin tuna based on retrieved data. Tag 

 performance, effect of the tag on the 

 fish, and horizontal movements of the 

 species are described in another paper. 

 Young Pacific bluefin tuna swim 

 mainly in the mixed layer, usually near 

 the sea surface, and swim in deeper wa- 

 ter in daytime than at nighttime. They 

 also exhibit a pattern of depth changes, 

 corresponding to sunrise and sunset, 

 apparently to avoid a specific low 

 light level. The archival tags recorded 

 temperature changes in viscera that 

 appear to be caused by feeding, and 

 those changes indicate that young 

 Pacific bluefin tuna commonly feed at 

 dawn and in the daytime, but rarely at 

 dusk or at night. Water temperature 

 restricts their distribution, as indicated 

 by changes in their vertical distribution 

 with the seasonal change in depth of the 

 thermocline and by the fact that their 

 horizontal distribution is in most cases 

 confined to water in the temperature 

 range of 14-20°C. 



Swimming depth, ambient water temperature 

 preference, and feeding frequency of young 

 Pacific bluefin tuna (Thunnus orientalis) 

 determined with archival tags 



Tomoyuki Itoh 



Sachiko Tsuji 



National Research Institute ol Far Seas Fisheries 



5-7-1 Shlmizu-Ondo, Shizuoka 



Shizuoka, 424-8633, Japan 



Email address (for T Itoh): ltou(3'fra.affrc,go.|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. 101:535-544 (2003). 



Swimming behavior oi Thunnus species 

 and its relation to various environmen- 

 tal factors have been examined mainly 

 by acoustic tracking (e.g. Carey and 

 Lawson, 1973; Laurs et al., 1977; Carey 

 and Olson, 1982; Holland et al., 1990b; 

 Cayre, 1991; Cayre and Marsac, 1993; 

 Block et al., 1997). Acoustic tracking 

 has also been applied to young Pacific 

 bluefin tuna iT. orientalis): to one fish 

 tracked for three hours around Japan 

 (Hisada et al.'), and to six fish tracked 

 for several days each in the eastern 

 Pacific Ocean (Marcinek et al., 2001). 

 Acoustic tracking can monitor fish move- 

 ment, behavior, and even physiological 

 conditions on a time scale of seconds. 

 However, the duration of monitoring any 

 one fish is generally limited to several 

 days at most because of the short life of 

 the tracking transmitter This limitation, 

 together with the high cost of adequate 

 ship-time, generally makes it difficult to 

 monitor the behavior of a large number 

 offish over a long period of time. 



An archival tag is an electronic device 

 that measures environmental variables 

 and records raw or processed data in its 

 memory. The archival tag can monitor 

 animal behavior, its physiological con- 

 ditions, and the several environmental 

 factors that the animal is actually ex- 

 periencing, simultaneously. Data can be 

 collected for a much longer period than 

 with acoustic tracking, if the tags are suc- 



cessfiilly retrieved. Recently, a type of ar- 

 chival tag that can estimate geographical 

 locations has been developed. This type 

 of tag has been applied to southern blue- 

 fin tima T. maccoyii (Gunn and Block, 

 2001) and Atlantic bluefin tuna T. thyn- 

 nus (Block et al., 1998a, 1998b). These 

 reports show the remarkable value of 

 the archival tag data for investigating 

 fish migration and behavior. 



We have implanted archival tags in 

 young Pacific bluefin tuna since 1994 

 to investigate their migration and be- 

 havior This article describes the results 

 obtained from recovered tags and places 

 special emphasis on vertical swimming 

 behavior, preferred water temperature, 

 and feeding frequency. Some insights 

 regarding vertical swimming depth 

 have already been reported in Kitagawa 

 et al. (2000) who used some of the same 

 data. We have described in another pa- 

 per (Itoh et al., 2003) the performance 

 of the archival tag used in the present 

 study and the characteristics of young 

 Pacific bluefin tuna migration based on 

 data from these same tags. 



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, 424-8633, Japan. (In Japanese, 

 the title is translated by the authors.] 



