2. Transparency 



If we make a comparison of the clarity of the waters of the Northern 

 Equatorial Current and the Equatorial Counter-current, we find that the 

 former has a higher transparency than the latter. In other words, the 

 Northern Equatorial Current is clearer than the Counter-currents This is 

 because the Counter-current contains a great proliferation of diatoms, 

 which are a kind of plant plankton. 



Transparencies of 25 to 35 meters are suitable, and transparencies 

 below this range are the most unsuitable. 



(Transparencies are measured by placing a white disk 30 cm in diameter 

 in the water and finding the limit of its visibility. Of course the 

 clearness or cloudiness of the weather, the hour of the observation, and 

 the angle of the rope on which the disk is lowered must be fully taken 

 into consideration.) 



3. Water temperature 



The temperature of the surface waters in the South Sea islands varies 

 little throughout the year. It remains between 28 and 30 degrees. In 

 the past it has been difficult to locate good fishing grounds by the water 

 temperature, as is done in Japanese waters, and consequently little atten- 

 tion has generally been paid to this factor. However, investigations by 

 the Fisheries Experiment Station of the South Seas Government-General and 

 the results of a study of the poor fishing for yellowfin in Palau waters 

 this year (January, February 19/i.l) have shovm that even within the Counter- 

 current the water temperature at the 100-meter level sometimes drops to 

 below 20° and that this is the greatest cause of poor fishing. Because 

 of this the water temperature in the Counter-current has come to be re- 

 garded as an important oceanographic factor. In the Equatorial Counter- 

 current the 100-meter level, v;hich bears the closest relationship to the 

 tuna longline fishery, usually shows temperatures of 24° or above. When 

 a phenomenon like that which appeared this year arises, it also affects 

 the temperatijres in the surface waters, and when the surface temperature 

 falls to 27° or lower the fishing becomes poor. The coastal waters 

 around the principal islands of the South Seas sometimes show surface 

 temperatures between 27° and 28° for a short time from January to March, 

 and this is a phenomenon which is worthy of attention, 



4. Water color 



The best color is III on Forel's scale. The next best is a color 

 between II and III, followed in order of suitability by II and the shades 

 between III and IV. Color III and the colors between II and III pre- 

 dominate in the Counter-current, and IV is rarely seen. Water color is 

 related to transparency in such a way that higher or lower water colors 

 mean greater or lesser transparency. 



(Ill) Good fishing grounds from the point of view of catch concentration 



