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Fishery Bulletin 100(4) 



in those regions, compared to the daytime depths of the 

 equatorial EPO (Maynard et al., 1975; Tont, 1976; Davies, 

 1977; Kuznetsov et al., 1982; Fiedler et al., 1998; Josse et 

 al., 1998). Farr and Best (1998) reported that DSL distri- 

 butions are related to mesoscale oceanographic features, 

 defined by flow and temperature variability, and are most 

 commonly observed at the pycnocline. 



Geographic variation in DSL depths throughout the 

 Pacific are possibly related to isolumes of the associated 

 micronekton, and can potentially be estimated from the 

 light level data recorded by the archival tags attached to 

 bigeye tuna. Variation in daytime DSL depths is probably 

 a function of light penetration (which is regulated by bio- 

 logical production) and absorption of light by chlorophyll 

 and phaeopigments (Tont, 1976). 



The behavior of bigeye tuna is strongly influenced by 

 the presence of drifting FADs within their habitat. Be- 

 cause of this behavior associated with FADs, even though 

 it is for relatively short periods, bigeye tuna are highly 

 vulnerable to capture by purse-seine vessels. Estimates of 

 bigeye tuna residence times and percentages of total time 

 associated with drifting FADs, along with estimates of 

 FAD densities, could be used to evaluate vulnerability to 

 capture by the surface fishery. There is a critical need for 

 conducting a large-scale tagging program in the EPO fo- 

 cused on bigeye tuna — a program where conventional tags 

 are used for estimating size-specific mortality and mixing 

 rates and archival tags are used for evaluating fine-scale 

 movements, behavior, and habitat selection. 



Acknowledgments 



We are grateful for invaluable advice and assistance pro- 

 vided by B. Block, T Booth, M. Braun, R. Brill, J. Gunn, 

 R. Hill, P. Hooge, and T Williams. We are thankful to B. 

 Blocker and the crew of Her Grace for their performance in 

 fishing and tagging operations. We are indebted to vessel 

 owners, captains, fishermen, unloaders, and industry 

 representatives for returning recovered archival tags. We 

 thank Juan Gracia for his assistance with tagging and the 

 lATTC field office personnel for recovering archival tags. 

 We also wish to thank B. Bayliff, R. Brill, R. Deriso, G. 

 Watters, and two anonymous reviewers for constructive 

 comments on drafts of the manuscript. 



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