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A major factor influencing the role of U.S. tuna fishing in the ETP is 

 that a CYRA yellowfin conservation program was not adopted for 1980. This 

 situation stemmed primarily from the inability of Mexico, Costa Rica, and 

 the United States to reach agreement on new management and access 

 arrangements for tuna resources in the eastern Pacific. Until an eastern 

 Pacific tuna management regime acceptable to Mexico and Costa Rica can be 

 enacted by the member countries of the lATTC, the U.S. may be forced to 

 concentrate its fishing effort in the areas outside the 200-mile zones of 

 the countries bordering on the ETP. If such becomes the case, the U.S. 

 would lose access to areas from which 65X of its historical catches of ETP 

 yellowfin and skipjack tuna have been taken. Furthermore, since most of 

 the yellowfin tuna caught in the outside areas of the ETP (areas A2 and A3, 

 Figure 1) associate with porpoise, porpoise quotas are likely to be reached 

 earlier in the year, which would severely limit the ability of the U.S. 

 fleet to catch yellowfin in the ETP. 



With exclusive access to highly productive fishing areas in the ETP, 

 the fleets of the coastal nations adjacent to the resource can be expected 

 to continue growing. Much of this growth may be through flag transfers of 

 U.S. vessels otherwise denied access to these areas. 



III. STATUS OF THE STOCKS 



Research on the population dynamics of ETP yellowfin tuna is conducted 

 by the scientific staff of the lATTC. During 1979 the lATTC scientific 

 staff undertook investigations in the following areas: 1) population 

 structure and migration; 2) abundance estimates and their relation to 

 fishing success; 3) size composition and distribution of tunas by time and 

 area; 4) feeding habits; 5) growth studies; 6) tuna/porpoise relationships; 

 and 7) oceanography and tuna ecology. 



I II. A. Stock Structure 



During 1979 the lATTC scientific staff continued its studies on the 

 rates of mixing of individual tuna from different geographic areas of the 

 Pacific. Results of these studies to date are inconclusive. However, 

 tagging experiments indicate that the rate of mixing for yellowfin between 

 the area inside the CYRA and outside the CYRA is low. Therefore, the 

 production model analyses which have been done assume yellowfin tuna in 

 these two areas to be two separate stocks. 



