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



519 



130E 



140E 



40°N 



30°N 



20°N 



Figure 3 



Locations estimated by an archival tag with a young Pacific bluefin 

 tuna before (upper panel) and after (lower panel) replacement of the 

 original latitudinal estimate based on day length by one using sea- 

 surface temperature. Locations out of the range of the figure and 

 those for which latitude was not estimated were not drawn in the 

 upper panel. Estimated locations for all days are shown in the lower 

 panel. Open circles in the lower panel are interpolated locations. 



the detailed file (i.e. just before recapture) when compared 

 to the first part of the detailed file (i.e. just after release). 

 The tag manufacturer analyzed this deterioration in the 

 pressure sensors, and expected the sensor characteristics 

 to remain constant after an initial change (if one occurred), 

 and agreed that the early and late pressure data should be 

 treated separately. We assumed that the deterioration oc- 

 curred sometime during the middle period of the time the 

 fish was free, when no record was being kept in the detail 

 file. Recorded depths in the second part of the detail file for 



eight tags with relatively large deterioration detected were 

 corrected by using two regression lines joined at around 30 

 m in real depth for each tag (Fig. 4). 



Effect of the archival tag on fish 



The effect of both the implantation process and the pres- 

 ence of the implanted tag in the fish was investigated by 

 macroscopic observation of recovered fish. Further infor- 

 mation was obtained by comparing the weight at length 



