42 
Fishery Bulletin 99(1 ) 
146 27 W 
Time (hours) 
8:00 10:00 12 00 14:00 16:00 18:00 20:00 
Figure 2 
Horizontal and vertical movements of yellowfin tuna 2, 100 cm FL. Tracking 
lasted 11 h (December 1995). The period of association between the fish and the 
tracking vessel is shown by the bold line. Arrows indicate the direction of hori- 
zontal movement in the upper graph. 
cular movement around the island. The fish became as- 
sociated with the tracking vessel after traveling half-way 
around the island. The association occurred simultaneous- 
ly with a change in its vertical movement pattern, shifting 
from a movement pattern between the surface and 150 m 
to a surface oriented behavior that kept the fish within a 
few meters of the surface (Fig. 1). As the boat continued 
to move around the island, the fish maintained the asso- 
ciation and swam within 10 m of the surface, except for 
an excursion to 50 m around 07:30. However, this dive oc- 
curred simultaneously with a XBT (expendable bathythe- 
mograph) launch and the fish may have followed the in- 
strument as it went down, a behavior also observed by 
Block et al. (1997). When the tracking vessel reached the 
FAD where the fish had been caught the day before, the 
fish broke its association with the ship and dove, likely to 
join a small tuna school observed on the echo-sounder un- 
der the FAD at around 150 m depth. 
Yellowfin tuna 2 ( 100 cm FL) was captured at 9:00 while 
it was associated with a FAD off Ahe Island (Tuamotu Ar- 
chipelago) and after being followed for 11 h. Immediately 
after its release, the fish returned to the depth at which 
it was caught (between 200 and 250 m) and left the FAD 
heading northwest (Fig. 2). Before 11:00, the fish rose to 
the surface and became associated with the boat; the main 
engine was then shut down and the vessel drifted. Around 
11:15, the boat began to move and the fish followed. The 
fish remained strongly associated with the moving vessel, 
swimming within the first 10 m below the surface until 
16:25, when it began to break off the association, making 
some rapid dives to 70 m. Contact was lost at 18:38, after 
a sudden departure of the fish during a heavy rain squall. 
The fish was briefly relocated at 19:14. 
Yellowfin tuna 3 (108 cm FL) was caught at 07:38, close 
to a FAD located off the island of Tahiti (Fig. 3). After 
release, the yellowfin tuna returned to the depth where 
