WILLIAMS: MODELS OF MIGRATION OF YOUNG SKIPJACK 



those of migrations, tiiere is also a need for a 

 greater input related to the physiology, behavior, 

 and genetics of the species than is presently 

 available. 



The hypothetical nature of certain aspects of 

 the proposed models of skipjack migrations ad- 

 vanced here cannot be denied. However, at this 

 stage in the development of research on the skip- 

 jack resources of the central-east Pacific, a pre- 

 sentation of existing data and ideas on skipjack 

 migrations, in the form of models, appears fully 

 justified. Indeed present research plans were 

 formulated on the basis of the active migration 

 model (the first proposed), although they are 

 equally applicable to testing the other models 

 as well. 



With any of the proposed migration models 

 it is obvious that oceanographic conditions in the 

 central-east Pacific will have a vital controlling 

 effect on the subsequent abundance of skipjack 

 in the eastern Pacific fishery. First, through 

 year-class strength of recruits (spawning suc- 

 cess/larval survival) and second, through the 

 number of recruits actually entering the fishery 

 (migration success) . Not only is it necessary to 

 test the mechanisms of these, and other, migra- 

 tion models, but monitoring and more detailed 

 analyses of inter- and intraseasonal fluctuations 

 in the central-east Pacific environment will as- 

 sist in understanding, and perhaps in predicting, 

 the fishery-independent changes in skipjack ap- 

 parent abundance. 



ACKNOWLEDGMENTS 



It has been a great pleasure to prepare this 

 paper for the Dr. 0. E. Sette dedicatory vol- 

 ume of the Fishery Bulletin, in view of his con- 

 tributions to fisheries biology and oceanography, 

 particularly in the field of tuna research when 

 he was Director of the Pacific Oceanic Fisheries 

 Investigations (POFI) in Hawaii. 



I am grateful to the Director of Investiga- 

 tions of the Inter-American Tropical Tuna Com- 

 mission for permission to use the eastern Pacific 

 skipjack length-frequency data collected and pro- 

 cessed by the Commission. Appreciation is ex- 

 pressed to my colleagues in the Scripps Tuna 



Oceanography Research Program, the Inter- 

 American Tropical Tuna Commission, and the 

 National Marine Fisheries Service for advice 

 and comments during development of the migra- 

 tion models, and to Virginia Moore for the text 

 figures. Thanks are also due to M. Blackburn, 

 E. Forsbergh, G. Sharp, and M. Tsuchiya, who 

 reviewed the manuscript. 



The work was part of the Scripps Tuna Ocean- 

 ography Research (STOR) Program and was 

 supported by the National Marine Fisheries 

 Service under Contracts 14-17-0007-963, 14-17- 

 0007-989, 14-17-0001-2311, and N208-0047- 

 72 (N). 



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