Holland et a\ : Movements of Thunnus albacares and T obesus near fish-aggregating devices 



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35 



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B 



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DEPTH INTERVAL (m) 



Figure 1 1 



Yellowfin tuna daytime distribution (A) shows two modes, one at 

 the surface and one between 60 and 90 m, which corresponds to the 

 normal position of the interface between the mixed layer and the 

 top layers of the thermocline. Nighttime distribution (B) reflects the 

 tendency of these fish to swim closer to the surface at night. In this 

 and subsequent histograms, bars = standard error. 



The tendency of FADs to bring fish closer to the sur- 

 face was even more apparent in the deeper-swimming 



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DEPTH INTERVAL (m) 



Figure 12 



Daytime distribution of bigeye tuna (A) displays a major mode bet- 

 ween 200 and 240 m, whereas nighttime distribution is much 

 shallower (B), with the predominant distribution falKng between 70 

 and 90 m. 



bigeye tuna, as was dramatically demonstrated by 

 BE8603 which stayed close to S FAD for 6 hours of 

 daylight before moving away at midday. Figure 13 il- 

 lustrates the rapid change of depth that coincided with 



BIGEYE TUNA 8603 



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TIME 



Figure 13 



Plot of the on-FAD and off-FAD movements of bigeye tuna BE8603. Arrow indicates when fish departed R FAD. 



