Edwards: Associated tunas and dolphins in eastern tropical Pacific 



689 



does not solve the problem that dolphins apparently 

 must locate not only the same type of prey as large 

 yellowfin tuna, but quite a bit more of it during any 

 given time-period. Following tuna does not appear ade- 

 quate to fulfill dolphin schools' energy requirements. 

 This fundamental difference in food energy require- 

 ments may be the single most important biological 

 factor underlying the association. Oceanographic 

 conditions (the shallow mixed layer) set the stage; 

 energetics requirements (hydrodynamics and foraging 

 patterns) appear to constrain the roles. Although the 

 definitive answer has yet to be demonstrated quan- 

 titatively, the energetics-based hypotheses presented 

 here are at least consistent with currently available 

 data. The tuna-dolphin association may be a conse- 

 quence of a combination of oceanography, hydro- 

 dynamics, foraging energetics, and life-history 

 characteristics, i.e, a consequence of the ecology of the 

 association's components. 



Acknowledgments 



This study could not have been completed without 

 generous sharing of data, time, and constructive ad- 

 vice by helpful individuals from, but not limited to, the 

 National Marine Fisheries Service, Southwest Fish- 

 eries Science Center, and the Inter- American Tropical 

 Tuna Commission. This work was completed while the 

 author was a National Research Council PostDoctoral 

 Research Associate at the Southwest Fisheries Science 

 Center, La Jolla, CA. 



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