458 



Fishery Bulletin 100(3) 



21 24 



Local time (hours) 



09 



Figure 8 



(A) Track of southern bluefin tuna 12 on 18 January 1994. iB) Track of southern bluefin tuna 13 

 on 19 January 1994. See Figure 7 for legend details. 



of tuna were observed during the whole period that the 

 tracked tuna was near the surface. 



Stomach temperature showed a marked drop initially 

 (presumably it swallowed water on its release) and then a 

 gradual recovery. Temperature reached a peak of 23.8°C, 

 about 4.5°C above ambient temperature, near midnight 

 and then slowly declined throughout the remainder of the 

 night. 



Tuna 14 was released 41 km west of Sceale Bay at 12: 

 26 h on 31 January 1994 (Figs. 1 and 2F). The tuna was 

 lost for about 20 minutes early in the track (Fig. 9A). It 

 had moved south before doubling back and returning 

 to the reef where it had been tagged. At 16:40 h it then 

 swam away with a school of tuna, remaining just above 

 the thermocline and occasionally making excursions to the 

 surface. It made an extended dive after dusk. 



Tuna 15 was released at The Lumps 7 km south of Can- 

 nan Reef at 13:26 h on 1 February 1994 (Fig. 1). It joined a 

 large school of tuna following the chum line of a pole-and- 

 line vessel, but was lost one hour later 



Tuna 16 was released at The Lumps 7 km south of Can- 

 nan Reef at 09:30 h on 2 February 1994 (Figs. 1 and 2F). 

 It was associated with schools initially, but they dispersed 

 at about 1400 h (Fig. 9B). The tag was regurgitated at 15: 

 20 h. 



Time at depth 



The proportion of time spent by tuna in 5-m interval depth 

 strata was plotted by day and night for all tracks combined 

 (Fig. 10). These data indicated that SET are surface-oriented 

 by day in the Great Australian Bight, spending a significant 



