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Amen'can flag vessels fishing in the eastern Pacific in 1979 totaled 

 110,919 mt (51X of total carrying capacity of all flag vessels), made up of 

 approximately 98% seiners, 2% baitboats, and < 1% jigboats by capacity. By 

 number, the fleet was composed of 138 purse seiners, 28 baitboats and 3 

 jigboats. 



The U.S. fleet usually fishes the CYRA for yellowfin and skipjack 

 tunas from January to the closure of the CYRA. When the CYRA closes to 

 yellowfin fishing, the majority of the larger purse seiners move either to 

 areas outside the CYRA or to the Atantic Ocean. Smaller purse seiners, 

 baitboats, and jigboats continue to fish the CYRA for skipjack tuna and 

 species of tuna (bluefin or albacore) other than yellowfin. 



The U.S. commitment to the conservation of skipjack and yellowfin tuna 

 stocks in the eastern Pacific is indicated by its membership in the lATTC. 

 The monetary commitment of the U.S to the lATTC was $1,607,000 in 1979, or 

 approximately 93% of the 1979 lATTC contributions ($1.7 million) from 

 member countries. 



III. STATUS OF STOCKS 



III. A. Stock Structure 



Skipjack tuna are distributed across the Pacific in tropical and 

 sub-tropical latitudes, usually in waters exceeding 20° C at the surface. 

 They occur commonly from about 40° N to 40° S latitude in the western 

 Pacific, and from about 30° N to 30° S in the eastern Pacific. Their 

 distribution is probably influenced by the temperature of the prevailing 

 currents, which are warm and poleward- flowing in the west, and cold and 

 equator-ward in the east. 



The population structure of skipjack in the Pacific Ocean is not 

 well understood. One hypothesis proposes that all skipjack in the Pacific 

 belong to one population that is spawned in the equatorial regions west of 

 140° W longitude, that the young fish migrate poleward into the fishing 

 areas, and that the older fish return to the equatorial regions to spawn. 

 Another more recent hypothesis suggests that there may be at least two 

 subpopulations of skipjack in the Pacific Ocean: the western Pacific 

 subpopulation, and the central and eastern Pacific subpopulation. Recent 

 tagging studies conducted by the South Pacific Commission have shown 

 extensive migrations of skipjack in the south and equatorial Pacific Ocean. 

 When the analyses of these data are complete, the population structure of 

 this species will probably be more clearly understood. 



There appear to be two main groups of skipjack in the eastern 

 Pacific: a northern group off the west coast of Baja California, in the 

 Gulf of California, and around the Revillagigedo Islands; and a southern 

 group from off Central America to off northern Chile. In most years 

 skipjack are excluded from the southern coast of Mexico by a cell of warm 



