NOURISHMENT OF CENTRAL PACIFIC STOCKS OF TUNA 

 BY THE EQUATORIAL CIRCULATION SYSTEM 



By Oscar E. Sette 



Pacific Oceanic Fishery Investigations 



Fish and Wildlife Service 



Honohdu, Hawaii 



An extensive program pursued by the Fish and Wildlife Service 

 from its Honolulu laboratory for Pacific Oceanic Fishery Investigations 

 has been directed toward discovery of high-seas fishery resources through 

 study of oceanic productivity. This program, uniting oceanography, 

 biology, and fishery investigation probably has amassed more informa- 

 tion regarding the physical and chemical properties of the upper-level 

 waters, the structure of the upper-level current system, the abundance 

 and distribution of plankton, and the occurrence of harvestable fish 

 in the low latitudes of the east-central Pacific than has been available 

 previously for any mid-ocean area anywhere. 



Up to March 1953 we have occupied 390 hydrographic stations 

 forming 22 sections transverse to the equatorial current system at various 

 longitudes from 140°W. to the 180th meridian (Fig. 1). Most of these 

 have been accompanied by quantitative zooplankton hauls and addi- 

 tional plankton hauls have been made on fishing voyages, making a 

 total of 399. There have been 218 fishing stations, forming 20 transects 

 of the equatorial zone (Fig. 2), as well as several additional patterns 

 of fishing survey over special areas. Hydrographic and fishing trips 

 have provided 4,442 bathy thermograms. Reports have been published, 

 are in preparation, or are planned to cover various aspects at various 

 stages of our progiess. At this time, it is possible to give a broad preli- 

 minary outline of the results as they are now emerging. 



The dominant energy source for equatorial ocean circulation is 

 the trade wind system. In the oceanic portion of the eastern half of 

 the equatorial Pacific, where there is practically no emergent land to 

 impose topographical modifications, the direction and force of the wind 

 govern rather completely the details of the equatorial current system. 

 As a consequence of the circulation there results a chain of biological 

 events that culminate in an abundant stock of equatorial yellowfin 

 tuna, Neothunnus macropterus, Temminck and Schiegel. We shall 

 examine first in cross-section and then in plan view this oceanic equa- 

 torial production system. 



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