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Fishery Bulletin 100(4) 



tuna are caught throughout the day near the surface by 

 both handhne and longhne fisheries between October and 

 December (Hisada, 1973). A second explanation for some 

 of the unassociated type-2 behavior is that the fish were 

 still possibly associated with a FAD but were making af- 

 ternoon excursions into the DSL, foraging for food. 



Occasionally bigeye tuna make dives in excess of 500 

 m (Fig. 7 and Table 2). The durations of the deep diving 

 events are not correlated (r=0.0008, P>0.05) with body 

 size. Moreover, there appear to be two types of deep dives 

 (Table 2). One may be for predator avoidance. The fish 

 descend and then ascend rapidly back to the depth at 

 which it had been previous to the dive. The second type 

 may be a foraging behavior, where prolonged time is spent 

 at greater depths, up to 1000 m. Deep dives to 1000 m or 

 more have also been reported from archival tag data for 

 bigeye tuna in the Coral Sea (Gunn and Block, 2001) and 

 for Atlantic bluefin tuna (Block et al., 2001a; Block et al., 

 2001b). 



Bigeye tuna exhibiting behavior associated with floating 

 objects ( Fig. 6 and Table 2) generally remain above the ther- 

 mocline, but they still show a diel shift in depth distribu- 

 tion. They remain at about 6 m, on average, deeper during 

 the day than at night (Fig. 6). Stomach content analysis of 

 FAD-associated bigeye tuna in the eastern Atlantic Ocean 

 by Menard et al. (2000) showed that 82.7'7r of the stomachs 

 were empty, where as only 25% of the stomachs of bigeye 

 tuna unassociated with floating objects were empty. They 

 concluded that FADs do not have a trophic function. How- 

 ever, the observed excursions to depths of about 300 m for 

 a few hours at about 1800 h for four consecutive days by 

 a FAD-associated bigeye tuna (Fig. IB) may be related to 

 foraging for prey in association with the DSL. 



Parin and Fedoryako (1999) stated that tunas associate 

 with floating objects only temporarily because there are in- 

 sufficient food resources in the vicinity of these devices. We 

 found that residence times and total times spent at FADs 

 are limited (Table 2). Our observations do not support the 



