(3) Compilation of the monthly catch figures for South Sea tuna fish- 

 ing vessels based at Misaki shows that the ratio of the number of big^eyed 

 tuna to the number of yellowfin taken during November and December is 15 

 and 13 per cent respectively, and 38 per cent in Januaryo (The habitable 

 water temperature for big-eyed tuna is lower than that for yellowfin,) 



The island fishing industry, which considers skipjack and tuna as its 

 chief products, finds the phenomenon which results in the lowering of the 

 surface water temperature to 27-28 degrees and the lowering of the 100-meter 

 layer to below 20 degrees not at all to its liking, for this lowering of 

 temperatures is unfavorable to the occurrence of these specieSo The 

 cessation of this phenomenon at the earliest possible moment is hoped for 

 by the industry » 



The detection and clarification of the time of its cessation^ the re- 

 lationship between the southward shift of the equatorial countercurrent and 

 the lowering of water temperature , and the cause of the lowering phenomenon 

 are the problems left for future oceanographlc study. To find an area 

 which meets the requirements of good fishing conditions as to water tempera- 

 ture and other factors and which can serve as a good alternate fishing 

 ground vrtien the equatorial countercurrent, noted for its abundance of 

 yellowfin, shows such a scarcity of fish, is the urgent and vital problem 

 which is assigned to the fishing industry survey. 



Addendum 

 Salinity 



We did not touch on the subject of salinity in this paper because 

 circumstances forced postponement of salinity determinations. The figures 

 on salinities obtained by observation and recorded here are compiled accord- 

 ing to ocean currents, A comparison is made of the vertical distribution 

 of salinities for this year with those for 194-0, The most noticeable 

 differences were seen in the surface layer of the equatorial countercurrent 

 and of the southern equatorial current, and in the 100-meter, 150-meter, 

 and 200=meter layers of the equatorial countercurrent. The salt content of 

 the surface water for this year was about 0,2 per cent higher, while on 

 the other hand that of the middle layer for this year was from 0,2 to 0,4 

 per cent lower, with the difference of 0,4 per cent seen in the 150-meter 

 layer. 



In considering the relationship between salinity and the occurrence 

 of yellowfin tuna, it is regrettable that we do not know the effect of 

 lower salinity on the occurrence of the fish, but we assume that it adds 

 somewhat to the effect of the lower temperature of the water centered 

 around the lOO^meter layer. 



