30° 



20° 



Figure 1„ Equatorial Hydrog raphic Crui seSo Our method 

 of investigating high seas fishery resources is to first understand 

 the seas in which the fish have to make their living. Since January 

 1950 we have crossed and recrossed the ocean area lying south of the 

 Hawaiian archipelago along the tracks shown in this chart, taking 

 temperatures, salinities, phosphates, and plankton samples at 60- 

 mile intervals along the solid lines „ 



From these observations and measurements we have 

 been able to determine the general circulation features as shown on 

 the next figure. Also, we learned where the surface waters are en= 

 riched, undoubtedly providing more abundant food for the tuna„ 

 These surveys have shown that the oceanic conditions change with 

 time and the indications are theit these changes nnay be on the order 

 of but a few days. 



