292 



Abstract— Data recovered from 11 

 popup satellite archival tags and 3 

 surgically implanted archival tags 

 were used to analyze the movement 

 patterns of juvenile northern bluefin 

 tuna (Thunnus thynnus orientalist in 

 the eastern Pacific. The light sen- 

 sors on archival and pop-up satellite- 

 transmitting archival tags (PSATs) 

 provide data on the time of sunrise 

 and sunset, allowing the calculation 

 of an approximate geographic position 

 of the animal. Light-based estimates 

 of longitude are relatively robust but 

 latitude estimates are prone to large 

 degrees of error, particularly near 

 the times of the equinoxes and when 

 the tag is at low latitudes. Estimat- 

 ing latitude remains a problem for 

 researchers using light-based geoloca- 

 tion algorithms and it has been sug- 

 gested that sea surface temperature 

 data from satellites may be a useful 

 tool for refining latitude estimates. 

 Tag data from bluefin tuna were sub- 

 jected to a newly developed algorithm, 

 called "PSAT Tracker," which auto- 

 matically matches sea surface tem- 

 perature data from the tags with sea 

 surface temperatures recorded by sat- 

 ellites. The results of this algorithm 

 compared favorably to the estimates 

 of latitude calculated with the light- 

 based algorithms and allowed for 

 estimation of fish positions during 

 times of the year when the light- 

 based algorithms failed. Three near 

 one-year tracks produced by PSAT 

 tracker showed that the fish range 

 from the California-Oregon border 

 to southern Baja California, Mexico, 

 and that the majority of time is spent 

 off the coast of central Baja Mexico. 

 A seasonal movement pattern was 

 evident; the fish spend winter and 

 spring off central Baja California, and 

 summer through fall is spent moving 

 northward to Oregon and returning 

 to Baja California. 



Tracking Pacific bluefin tuna 



(Thunnus thynnus orientalis) 



in the northeastern Pacific with an 



automated algorithm that estimates latitude by 



matching sea-surface-temperature data from 



satellites with temperature data from tags on fish 



Michael L Domeier 



Pfleger Institute ol Environmental Research 

 901 B Pier View Way 

 Oceanside, California 92054 

 E-mail address: Domeieng'cs com 



Dale Kiefer 



System Science Applications Inc. 



POBox 1589 



Pacific Palisades, California 90272 



Nicole Nasby-Lucas 



Adam Wagschal 



Pfleger Institute of Environmental Research 

 901 B Pier View Way 

 Oceanside, California 92054 



Frank O'Brien 



System Science Applications Inc. 



POBox 1589 



Pacific Palisades, California 90272 



Manuscript submitted 11 June 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



21 December 2004 by the Scientific Editor. 



Fish. Bull. 103:292-306 (2005). 



Current theories indicate the presence 

 of a single stock of northern Pacific 

 bluefin tuna (Thunnus thynnus orien- 

 talis) in the Pacific Ocean. Spawning 

 adults have been recorded only from 

 the western Pacific ( Yamanaka et al., 

 1963; Yabe et al., 1966; Okiyama, 

 1974; Okiyama and Yamamoto, 1979; 

 Nishikawa et al., 1985) but resulting 

 offspring are known to either inhabit 

 the western Pacific or to travel to the 

 eastern Pacific (Sund et al., 1981; Bay- 

 liff, 1994; Itoh et al., 2003a) where 

 they remain for an undetermined 

 amount of time. Although it is believed 

 that only a small fraction of the popu- 

 lation migrates to the eastern Pacific, 

 these fish are the basis for a fishery 

 that occurs from May through Octo- 

 ber. A recent study has documented 

 the migration of an archival-tagged 

 juvenile northern Pacific bluefin tuna 



from the western Pacific to the east- 

 ern Pacific in about two months, where 

 it remained for eight months before 

 being recaptured (Itoh, et al., 2003a). 

 Conventional tagging studies have 

 shown that Pacific bluefin tuna in 

 the eastern Pacific eventually return 

 to the western Pacific where they are 

 believed to remain as adults (Sund et 

 al., 1981; Bayliff, 1994). We provide 

 this cursory summary merely as an 

 introduction to our work, deferring 

 the known details of Pacific bluefin 

 biology to the excellent reviews that 

 have been previously published ( Bay- 

 liff, 1980. 1994; Sund et al., 1981). 

 Work presented in the present study 

 describes the use of electronic tags 

 (pop-up satellite-transmitting archi- 

 val tags and archival tags obtained 

 from fish) and a newly developed sea 

 surface temperature (SST) based geo- 



