Davis and Stanley: Movements of Thunnus maccoyii in the Great Australian Bight 



451 



Figure 1 



Geographic position of southern bluefin tuna tracks in the eastern Great Australian Bight. The number 

 of each fish indicates the start of its track. Symbols along tracks represent hourly positions (open 

 symbol=day, solid symbol=night). 



on the second day could not chum fish to the surface; the 

 fishermen had also observed many tuna at the surface the 

 previous day. 



Tuna 4 was released near Ward Island on 30 January at 

 16:40 h and was tracked for 48 hours. This fish remained 

 within the general area of release until tracking was ter- 

 minated (Figs. 1 and 2B). Vertical behavior is shown in 

 Figure 4B. The fish was associated with surface schools 

 until night on the first day. It was also associated with 

 large numbers of tuna (observed on the echosounder) 

 throughout the night. The surface activity of tuna schools 

 was low throughout the next day. Tuna were observed on 

 the echosounder at the same depth as the tracked tuna 

 throughout the day and next night, but not in the same 

 numbers as the day before. 



Tuna 5 was released on 13 March 1993 at 11:50 h at 

 Rocky Island (Fig. 1). It was tracked for about 4 hours 

 before it was lost. At 1500 h the tracked fish, together 

 with other tuna, followed a pole-and-line vessel that was 

 chumming at the time and that had crossed our path. The 

 fish was temporarily lost but was relocated an hour later, 

 again following the chum line of the pole-and-line vessel. 



Tuna 6 was released at Rocky Island on 14 March 1993 

 at 07:35 h and subsequently tracked for 26 h (Figs. 1 and 

 2C). At 08:15 h the tracked tuna was observed following 

 the chum line of the pole-and-line vessel (Fig. 5B). It was 

 associated with other tuna at or near the surface until 

 about 11:00 h. At 12:00 h the fish moved rapidly offshore 

 at about 2.5 m/s and was tracked to the shelf On reach- 

 ing the shelf break, it remained within a region of warmer 



