300 



Fishery Bulletin 103(2) 



temperature and light level sensors could not be checked. 

 For tag 233, none of the sensors could be verifed because 

 the tag had to be disassembled and destroyed by Lotek 

 personnel in order to recover the data. 



PSAT Tracker algorithm 



The archival tags provided large data sets that allowed 

 for the comparison of the PSAT Tracker algorithm to 

 the manufacturer's light-based geolocation solution. 

 Because longitude estimates generated by PSAT Tracker 

 are constrained by the light-based estimates, these 

 values differed very little from the position estimates 

 from the various tag manufacturers. Although similar, 

 the PSAT Tracker latitude solutions were generally less 

 erratic than those produced from the three light-based 

 algorithms, particularly surrounding the times of the 

 equinoxes (Figs. 5 and 6). The spring and fall equinoxes 

 each produced approximately two months of unreliable 

 latitude estimates for light-based algorithms. 



Pacific bluefin tuna habitat use 



Horizontal movement Tagged bluefin tuna ranged as 

 far north as the California-Oregon border and nearly to 

 the tip of Baja California, Mexico, to the south. Although 

 this distance encompasses 2400 km of coastline, these 

 fish spent the majority of their time in the southern part 

 of the range, best illustrated by a home range analysis 

 of the combined approximately year-long tracks of the 

 three archival tagged bluefin (Fig. 7). Tagged off the 

 northern coast of Baja California, Mexico, these three 

 bluefin moved northward until November, followed by a 

 southward migration to south-central Baja California 

 where they spent the months of January through June 

 (Fig. 8). The two larger archival-tagged fish reached 

 the offshore waters of Oregon before turning south and 

 the smaller fish did not venture north of San Francisco, 

 California. The two larger fish spent much of the winter 

 and spring (January-June) in the coastal 

 bight between Punta Eugenia, Mexico, to 

 the north and Cabo San Lazaro, Mexico, to 

 the south, and the smaller fish had a more 

 dispersed spring range north of Punta Euge- 

 nia. In July all three fish began to move to 

 northern Baja, back into the general area 

 where they were originally tagged and where 

 they were subsequently recaptured (Fig. 8). 

 This general pattern of summer-fall move- 

 ment northward followed by a winter migra- 

 tion southward and a winter-spring holding 

 pattern off south-central Baja California was 

 supported by data from fish with PSATs in 

 years 2000 through 2002 (Fig. 9). 



Although position data for the months of 

 January through June generally placed the 

 tagged bluefin off southern Baja, two of the 

 three fish tagged with archival tags under- 

 went rapid April excursions to the north be- 

 fore returning to the south (Fig. 10). Fish 159 

 traveled 2130 km, one way, before return- 

 ing by 1 May; fish 441 made a similar move 

 but did not go as far north (1285 km) and 

 stopped its southward return 480 km north 

 of its original starting point. The extreme 



