which time the above-Tientioned observations were obtainedo Its total catch 

 ratio (number of fish caught per 100 hooks) of tuna and sailfish averaged a 

 mere 0,65 the maximum ratio was l„7o This sea areay judging from past fish- 

 ing survey results, has been an excellent tuna fishing ground, the operation 

 results of the Zuiho Maru compiled during the period between November 1938 

 and March 1939 at 29 stations showing an average catch ratio of UoU, with a 

 maximum of 23 « 



The absence of tuna in the coastal waters of the Palau group was not 

 only noticed during the fishing survey of the Zuiho Maru, but also appeared 

 on the operation records of the medium-sized fishing vessels based at Palau„ 

 The figures obtained are as follows? 



Year Month Average catch ratio 



per operation 



19-iO Oct, 3o7 



Nov„ 4.. 9 



Decc Ael 



19U Jan, 2o3 



Such poor tuna fishing res-alts are believed to be mainly due to "the 

 fact that the temperature of the 100-meter layer of the equatorial counter- 

 current dropped below the minimum water temperature (20 degrees) suitable 

 as a habitat for yellowfin, 



TOien the equatorial countercurrent in the coastal waters of the Palau 

 group shifts southward or when such a phenomenon as a drop in the water 

 tenpsrature of the 100-meter layer occursj we should consider conditions 

 in the countercurrent farther' east. 



We explained previously that when the current area shifted southward 

 in December 19/+0, the countercurrent in the eastern area also shifted some- 

 what to the south as compared_to that of the normal year (see South Sea 

 Fishery ''ew-^ /^Nanyo 3uisan Joho_7, Vol, 4., No„ 3), From the various data 

 listed below, we can deduce that, as in the previous year, the current 

 shifted southward and that the water temperature near the 100-meter layer 

 also droppedo 



(1) By studying the ocean current data obtained during tuna long line 

 fishing tests in Palau waters by the Kiyo Maru (December 1940) and by the 

 Kochi Maru (Decem.ber 1940 to January 1941), the area of the equatorial 

 countercurrent was found to be as followSo The northern limit of the area 

 between 14.5''' to 160° east longitude was roughly as shown on ocean current 

 charts or around 6° to 7° north latitude, but the southern limit shifted 

 southward 2° to 4° so that it was in 0*^ 30" north latitude. 



(2) The average catch ratio of the Kochi Maru during November 1940 was 

 10o7, but even though it operated in the countercurrent area, its catch 

 ratio from December 194C to January 1941 was 2o9o (Surface water tempera- 

 ttires were over 28 degrees. No report on water temperatures of deeper 

 layers, ) 



