recently been published by others (Waldron, 1963; 

 Jones and Silas, 1963; Postel, 1963). 



This paper collates the available evidence per- 

 tinent to the problem of the origin of the exploited 

 groups of skipjack in the eastern and central 

 Pacific Ocean and forwards hypotheses which, I 

 believe, are consonant with such data. Its sec- 

 tions will cover, first, a brief statement of the 

 hypotheses; secondly, the evidence upon which 

 they are based, and finally a discussion of the 

 hypotheses and the sometimes intuitive reason- 

 ing which led to their development. 



The set of hypotheses has been generated from 

 a consideration of a wide variety of data. Many 

 of these data have been published by the Inter- 

 American Tropical Tuna Commission (lATTC) 

 and the Bureau of Commercial Fisheries. Other 

 data have been obtained from the files of the 

 Bureau's Biological Laboratory, Honolulu, and 

 analyzed for this paper. 



The hypotheses are based on a consideration 

 of three conceptual zones from which the skipjack 

 harvested in the eastern Pacific might originate 

 (fig. 1). The hypotheses postulate that large pro- 

 portions of skipjack which enter the eastern Pa- 

 cific fishery originate in the Equatorial Zone. 

 The predominant flow pattern for these fish is 

 suggested in figure 2. Atprerecruitsize(< about 

 35 cm.) skipjack are continually dispersing from 

 the equatorial central Pacific. A large compo- 

 nent moves east toward the coast of the Amer- 

 icas; near the coast, one portion enters the Baja 

 Californiafishery area while another moves into 

 the Central and South American fishery areas. 



Figure 1 . --Schematic representation of the 

 conceptual areas that were evaluated in 

 this paper. 



The skipjack remain in the eastern Pacific for 

 several months and may attain sizes of 55-65 cm. 

 The attainment of this relatively large size (for 

 the eastern Pacific) seems correlated with an 

 offshore spawning movement. This offshore 

 movement terminates in equatorial waters of the 

 central Pacific where spawning occurs. An ap- 

 parent north-south component of movement is 

 superimposed on the generally easterly move- 

 mentof "adolescent" prerecruits to the eastern 

 Pacific fishery and the generally westward di- 

 rection of the eastern Pacific spawning escape- 

 ment. This north-south component may be a 

 general dispersal affected by population density 

 or it may be associated with the seasonal shift 

 of the physical environment (e.g., temperature). 



MEXICAN FISHERY 



CENTRAL AND 

 SOUTH AMERICAN 

 FISHERY 



/ 



SEASONAL 



AND DIFFUSION 



MOVEMENTS 



Figure 2. — Diagram showing the flow of skipjack between the central 

 Pacific and the Mexican and South American fisheries of the eastern 

 Pacific. 



