145 E. longitude, that is in the waters around the Mariana Islands, they take on a rather 

 complicated aspect due to the influence of the topography, and northward and southward flowing 

 currents appear. In the extreme western portion of this region, which is at the source of the 

 Kuroshio, the current runs approximately northwest. 



,0 o 



Water temperatures during the northeast monsoon are 26 C. to 27 C. at the 



surface. Temperatures at the 50-nneter level do not differ greatly from the surface, and temper- 

 atures at the 100-meter level are approximately the same. During the southwest monsoon sur- 

 face water temperatures are 28 C. to 29 C. , temperatures at the 50-meter level do not differ 

 greatly from those at the surface, and the temperature at the lOO-nneter level is about 27 C. 



Water color throughout the year is I or II in the Forel scale and the transparency is 

 high, being 35 to 40 meters in most cases. 



During the height of the season of northeasterly winds, rather strong winds blow 

 continuously in the western portion of this region, but it becomes somewhat calnner as one pro- 

 ceeds eastward. During the season of southwesterly winds the sea is generally extrennely calm, 

 but during the typhoon season storms often originate in this area. In this part of the ocean 

 typhoons generally move westward or northwestward and nnany of them pass through the western 

 portion of the region, so care on this point is necessary in operating there. 



The significance and value of this area as a fishing ground is as yet almost completely 

 unknown. Actual fishing operations have been carried on only around the Marianas and data 

 from surveys and fishing experiments are confined almost entirely to that vicinity; consequently 

 it is innpoasible to ascertain the fishing conditions throughout the region as a whole. A tabular 

 summary of these data follows. 



The general overall catch rate is 2.5, and the catch rates are conspicuously low in 

 comparison with those between and 10 N. latitude. 



Table 36. --Fishing conditions in the northern part of the 

 former South Seas Mandate (10 to 20 N. , 

 130° to 170° E. ) 



The reason for the lowering of the catch rates in comparison with the southern portion 

 of the former South Seas Mandate is the decline in the yellowfin catch. The catch rate for 

 yellowfin is about one-sixth that of the former sea area, and even the rate for bigeye tuna is re- 

 duced by about half. On the other hand, the spearfish catch rate is approximately double and 

 there is also a rather conspicuous increase in the albacore catch. Thus it should be noted that 

 not only are the catch rates different as between the two areas, but the composition of the catch 

 is also quite different. This is thought to mean that, as was previously noted for the Indian 

 Ocean region, the distribution of these fishes is controlled more by differences in water systems 

 than by temperature. 



Since the data are almost entirely confined to the period December to February, it is 

 unfortunately not possible to give any explanation of the seasonal chaJiges in fishing conditions. 



72 



