MARQUESAS ZONE 



170' 160* 150' 140' 130° 1^0' IIP* 100* 9p° 80' W. 



FIGURE 13. In a paper published during this reporting 

 period, one of our scientists hypothesized that the large 

 I'. S. fishery for skipjack tuna in the eastern Pacific 

 depends upon fish that are spawned in equatorial waters 

 south of Hawaii. The skipjack remain in the fishery area 

 only a short while, returning to the equatorial Pacific to 

 spawn. The Hawaiian skipjack fishery may also depend to 

 some extent on fish spawned in the Equatorial Zone. 



there briefly (no more than a year), and then return to 

 the central Pacific. 



On the basis of subpopulation studies and other evidence, 

 he suggests that the skipjack caught in Hawaiian waters do 

 not comprise a single population unit. He postulates that 

 the central Pacific spawing area can be divided into three 

 adjacent zones, one lying near the latitude of Hawaii, an- 

 other around the Equator, and the third south of the 

 Equator near the Marquesas. The fish spawned in this last 

 zone, he says, probably do not enter the eastern Pacific 

 fishery. He seeks to determine whether the skipjack caught 

 by the U. S. fishery in the eastern Pacific originate for the 

 most part in the Hawaiian or the Equatorial Zone. Several 

 lines of evidence suggest the conclusion that they come from 

 the Equatorial Zone. 



Some of the skipjack in the Hawaiian catch do not orig- 

 inate in Hawaiian waters; whether these come from the 

 same equatorial stock as the eastern Pacific skipjack is not 

 known. There is some direct avidence that the two fisheries 

 are related: two skipjack tagged off Baja California in 1960 

 were caught in the Hawaiian fishery about 2 years later. 

 Another skipjack from Baja California was caught at 

 Christmas Island 16 months after tagging. 



Other .scientists have suggested that the skipjack of the 

 eastern Pacific make long offshore-inshore migrations. What 

 is new about Rothschild's hypotheses is that dimensions 

 have now been postulated for these migrations: they reach 

 from the coasts of the Americas 3,000 miles westward to 

 the equatorial waters south of the Hawaiian Islands. New 

 is the suggestion that the Hawaiian and eastern Pacific 

 fisheries are to some extent drawing on the .same population, 

 with the implication that the "season" skipjack on which 

 the Hawaiian pole-and-line fishery so heavily depends may 

 be those which have escaped the nets of the eastern Pacific 

 fishery earlier in their lives (fig. 13). 



Rothschild offers evidence of fluctuations in year-class 

 strength in the skipjack. This means that Hawaii could 

 well serve as a base from which future eastern Pacific 

 catches could be forecast as they could not be in the fishery 

 area itself. The reasoning is this: Some of the skipjack 

 taken in Hawaii originate in the same Equatorial Zone as do 

 those caught in the eastern Pacific; the Hawaiian catch 

 appears to reflect fluctuations in year-class strength : n 

 knowledge of the mechanisms that affect year — class 

 strength in the central Pacific would provide a lever toward 

 understanding success of spawning in the Equatorial Zone 

 and hence allow estimates of eastern Pacific catches. 



Rothschild's paper is particularly important because he 

 suggests critical tests of the hypotheses advanced. Because 

 adult skipjack at the time of spawning have so far almost 

 completely eluded capture, the next best indicators of recent 



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