388 



Fishery Bulletin 105(3) 



tion on surface-oriented behavior of skipjack is relevant 

 to understanding catchability (vertical vulnerability 

 plus spatial vulnerability) by purse-seine vessels and 

 may be useful to incorporate into the standardization 

 of catch and effort data. In addition, this information on 

 occurrence and duration of surface-oriented behavior is 

 useful for evaluating optimal detection periods for the 

 use of remote-sensing techniques for conducting fisher- 

 ies-independent abundance estimation of this species 

 with the use of airborne optical equipment, including 

 LIDAR (light detection and ranging) (Gauldie et al., 

 1997). 



Large-scale studies with archival tags are needed 

 to improve our understanding of skipjack tuna move- 

 ments, behavior, and habitat use, all of which, in turn, 

 will provide useful information for stock assessments 

 of this valuable resource. Elucidating skipjack tuna 

 behavior may also permit the design of optimal fish- 

 ing strategies for this species, including the reduction 



Percent time 

 90 75 60 45 30 15 (I 15 30 45 60 75 90 



14 16 18 20 22 24 

 Temperature ("C) 



30 



Figure 7 



Composite vertical habitat-use distribution for five skip- 

 jack tuna (Katsuwonus pelamis) for all days of behavior 

 unassociated with floating objects. Depth frequencies 

 during the night are represented by the black bars and 

 depth frequencies during the day are represented by 

 open bars; the average ambient temperatures (line of 

 connected dots) are shown within depth intervals. 



of current bycatch levels associated with purse-seine 

 fishing around floating objects. Archival tags are now 

 capable of storing data for multiple years; this capac- 

 ity provides a remarkable opportunity to evaluate on- 

 togenetic changes and the influence of seasonal and 

 annual environmental variability on the behavioral 

 characteristics of tuna. 



Acknowledgments 



This research was made possible through financial con- 

 tributions by the Japan Fisheries Agency, Taiwan Fish- 

 eries Agency, and the United States Tuna Foundation. 

 We are grateful to vessel owners, captains, fishermen, 

 unloaders, industry representatives, and Inter-American 

 Tropical Tuna Commission field office staff in Ecua- 

 dor for assistance in recovering the archival tags. We 

 appreciate the constructive comments on drafts of the 

 manuscript provided by W. Bayliff, E. Calvert, A. Moles, 

 M. Scott, and three anonymous reviewers. 



Literature cited 



Altringham, J. D., and R. E. Shadwick. 



2001. Swimming and muscle function. In Tuna physi- 

 ology, ecology, and evolution. Fish physiology series, 

 vol. 19 (B. A. Block, and E. D. Stevens, eds.), p. 313- 

 344. Academic Press, San Diego, CA. 

 Anonymous. 



2005. Tunas and billfishes in the eastern Pacific Ocean 

 in 2004. Fishery Status Report No. 3. Inter-Am. Trop. 

 Tuna Comm., 119 p. 

 Blank, J. M., J. M. Morrissette, A. M. Landeira-Fernandez, S. B. 

 Blackwell, T. D. Williams, and B. A. Block. 



2004. In situ cardiac performance of Pacific bluefin tuna 

 hearts in response to acute temperature change. J. 

 Exp. Biol. 207:881-890, 

 Block, B. A. 



1991. Endothermy in fish: thermogenesis, ecology, and 

 evolution. In Biochemistry and molecular biology of 

 fishes, vol. 1 (P. W. Hochachka, and T. P. Mommsen, eds.), 

 p. 269-311. Elsevier Publishing, New York, NY. 

 Brill, R. W., and P G. Bushnell. 



2001. The cardiovascular system of tunas. In Tuna 

 physiology, ecology and evolution, Fish physiology 

 series, vol. 19 (B. A. Block, and E. D. Stevens, eds.), p. 

 79-120. Academic Press, San Diego, CA. 

 Collette, B. B., and C. E. Nauen. 



1983. FAO species catalogue. Vol. 2: Scombrids of 

 the world: an annotated and illustrated catalogue of 

 tunas, mackerels, bonitos, and related species known to 

 date. FAO Fish. Synop. 125, 137 p. FAO, Rome. 

 Dagorn, L., P. Bach, and E. Josse. 



2000. Movement patterns of large bigeye tuna (Thunnus 

 obesus) in the open ocean, determined using ultrasonic 

 telemetry. Mar. Biol. 136:361-371. 

 Dizon, A. E., and R. W. Brill. 



1979. Thermoregulation in tunas. Am. Zool. 19:249- 

 265. 

 Dizon, A. E., R. W. Brill, and H. S. H. Yuen. 



1978. Correlations between environment, physiology, 

 and activity and the effects on thermoregulation in 



