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



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Local time (h) 



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Figure 3 



(A) Track of southern bluefin tuna 1 on 29 April 1992. (B) Track of southern 

 bluefin tuna 2 on 30 April 1992. Speed over the ground (upper graph) and depth 

 of the tuna (lower graph I are plotted against time. The sea bottom is indicated by 

 shading, the solid line represents the bottom of the mixed layer and the dotted 

 lines represent isotherms (°C). The black bar represents nighttime, the unshaded 

 bar, daytime and W = wind speed in km/h. 



surface water in association with a large subsurface school 

 of tuna (Fig. 2C). While traveling to the shelf break, it re- 

 mained near the bottom or just below the mixed layer. A 

 deep sounding was made just after sunset and another 

 just before dawn, the last reaching 180 m. 



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

 nan Reef at 09:16 h on 10 January 1994 (Figs. 1 and 2D). 

 This was the smallest fish tracked in this study. Unlike 

 the others, it was caught on a trolled lure and landed after 

 about a 5-minute struggle. Tracking was discontinued af- 

 ter 30 h due to bad weather This fish was associated with 



large schools for the first five hours of tracking and again 

 for three hours at first light the next day. It made postdusk 

 and predawn dives (Fig. 6A). 



Tuna 8 was released at The Lumps 7 km south of Can- 

 nan Reef at 10:58 h on 12 January 1994 (Figs. 1 and 2D). 

 The fish was followed for 10 h until tracking was halted 

 shortly after sunset. It remained in the upper 20 m for 

 most of the track (Fig. 6B). At 12:50 h it followed the chum 

 line of a pole-and-line vessel. From 14:00 to 16:00 h, it 

 remained at the surface with a large school of tuna before 

 slowing and sounding at a reef. 



