Itoh et al.: Migration patterns of Thunnus orientalis determined with archival tags 



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The average number of daily feeding events plotted against days after release. 



in an area of 32-37°N, 143-147°E (Fig. 7G). This fish was 

 recaptured by purse seine on 7 June 1996. 



The other fish traveled from the western Pacific Ocean 

 to the eastern Pacific Ocean as follows (Fig. 8). It was re- 

 leased off Tsushima on 29 November 1996 at 55 cm FL and 

 remained for a period within the East China Sea. It moved 

 to the Pacific Ocean on 1 May 1997 and then traveled east- 

 ward straight from a position off the south coast of Kyushu 

 to one off the east coast of Choshi then stayed for a while 

 in an area of 34-39°N, 143-150°E. It moved northeastward 

 from 30 July to 18 August 1997, then stayed in the area 

 40-44°N, 152-163°E. It began the trans-Pacific migration 

 on 11 November 1997 at 41°N, 163°E, and traveled straight 

 to northern California, U.S.A. (36°N, 127°W) arriving on 15 

 January 1998. 



After arriving in the eastern Pacific Ocean, this fish 

 initially stayed in an area of 33-40°N, 122-128°W, then 

 moved southward from 25 February to 3 March, then again 

 stayed in an area of 25-29°N, 116-119°W. It started mov- 

 ing northward on 9 May and reached 40°N, 127°W on 25 

 May, but without staying there moved again southward 

 and reached an area of 25-29°N, 116-120''W on 12 June, 

 close to the place from which it had departed. The fish was 

 recaptured by a recreational fishing vessel on 1 August 

 1998, 610 days after release, off Baja California, Mexico 

 (31°48'N, 117n8'W), at 87.6 cm FL 



The track of this fish consisted of apparently separable 

 segments, five traveling periods and six resident ones. All 

 of the fish that moved out of the East China Sea showed 

 the same type of pattern, staying resident in an area for a 

 relatively long period and then traveling continuously for 

 at least several days in a stable direction. 



The terms "traveling phase" and "residency phase" are 

 used in the following description. If a fish moved continu- 

 ously for more than three days in a stable direction covering 

 more than 700 km in total distance, it was considered to be in 

 a traveling phase — at all other times in a residency phase. A 

 few movements for short periods or short distances (or both) 

 were also observed during periods of a residency phase: a fish 

 resident off the east coast of Hokkaido (40-44°N, 152-163°E) 



shifted eastward gradually within the area during a period 

 of two months (Fig. 8). Another fish resident in the northern 

 area of the East China Sea moved rapidly to the southern 

 area of the East China Sea at the end of December and came 

 back rapidly to the northern area in early May (Fig. 9). In- 

 dividual movements were completed within a few days and 

 the total distances moved were far shorter (380 and 310 km, 

 respectively) than those seen in traveling phases. 



A total of 12 traveling phases were identified in records 

 of six fish (Table 1). The direction of travel stayed constant 

 within each phase, except in one case where a fish com- 

 pletely turned around in the middle of traveling (in the east- 

 em Pacific Ocean in May and June 1998). Daily distances 

 moved during those traveling phases were calculated. To 

 reduce the infiuence of scatter in the estimated locations, 

 three-day running averages of latitude and longitude were 

 used for calculation. Excluding the one trans-Pacific migra- 

 tion phase of exceptional length, 7636 km (66 days), the 

 total distance per traveling phase ranged from about 730 

 to 3406 km (average: 1430 km). The duration of a traveling 

 phase was four to 35 days (average: 17 days) and the dis- 

 tance traveled ranged from 59 to 182 km (average: 104 km). 

 Six residency phases which occurred between two clearly 

 identified traveling phases lasted from 40 to 125 days (aver- 

 age: 81 days). In total, 83% of days were in a residency phase 

 and 17% of days were in a traveling phase. If residency 

 phases for which the beginning or end could not be defined 

 because offish release or recapture were also included, the 

 average duration of residency phases increased to 110 days, 

 and the proportion days belonging to each phase became 

 87% in residency and 13% in traveling phases. 



Comparison of fish behavior and ambient water 

 temperature between traveling and residency phases 



Several points regarding fish behavior, described in detail 

 in Itoh et al. (2003), were compared between all days in a 

 traveling phase and ten days in the residency phase that 

 for four fish immediately preceded the traveling phase. 

 In the case of one fish (no. 241) where data for preceding 



