456 



Fishery Bulletin 100(3) 



12 15 18 21 



Local time (hours) 



9 12 15 



Local time (tiours) 



Figure 6 



(A) Track of southern bluetin tuna 7 on 10-11 January 1994. (B) Track of southern blue- 

 fin tuna 8 on 12 January 1994. (C) Track of southern bluefin tuna 9 on 15 January 1994. 

 Shading in the water column represents depth range of tuna schools detected by echo- 

 sounder. See Figure 3 for other legend details. 



sure tag in the stomach ( Figs. 1 and 2E ). This fish was associ- 

 ated with tuna schools for most of the track (Fig. 7B). Most 

 vertical activity was oriented towards the surface, but peri- 

 odic dives were made to or through the thermocline. At night 

 the fish moved slightly deeper but continued to dive at regu- 

 lar intervals. It made an extended dive just after sunset. 



The stomach temperature gradually increased through 

 the night and by 01:00 h was at 28°C, which was 9°C 

 above ambient temperature. At about 01:30 h there was 



a sudden drop in stomach temperature towards ambient 

 temperature and then a gradual recovery that was most 

 likely caused by the swallowing of prey or water (or both). 

 The tag was regurgitated two hours later. 



Tuna 12 was released at The Lumps 41 km west of Sceale 

 Bay at 09:16 h on 18 January (Figs. 1 and 2E). It showed 

 considerable vertical activity similar to tuna 10 and was 

 associated with tuna schools throughout the track (Fig. 

 8A). It made an extended dive just after dusk. 



