i/lfhen we studied the vertical distribution of water temperatures, we found 

 that the surface temperature, which is closely related to skipjack fishing, in 

 many places dropped to almost 27 degrees = From observations made on the Zuiho 

 iiaru during mid-i'^ebruary we discovered that at six out of seven stations the 

 water temperature was down to almost 27 degrees or an average of 27o6 degrees =, 

 Observations made on the Arafura Maru (a chartered survey vessel) during early 

 and mid- February disclosed the fact that two out of eleven stations had water 

 temperatures of 26-27 degrees and seven had temperatures of 27-28 degrees o 

 The average, similarly, was 27o6 degrees ^ This phenomenon was seen along the 

 coast of the Palau groupo The Hakuo iiiaru obtained a water temperature of 27o8 

 degrees during late February^ On the other hand, according to the observations 

 made on the Zuiho Maru during its later voyage (from late February to early 

 iiarch), the number of stations showing water temperature of 2 7-28 degrees 

 diminished and those showing 28-29 degrees increased somewhat o 



The occurrence of surface water temperatures of 2 7-28 degrees in Palau 

 waters (north latitude 0°-10°, east longitude 128°-140°) cannot be called rare. 

 According to the record of the periodic observations conducted at the mouth of 

 Palau harbor during the six years period 1929-1934, these low water tempera- 

 tures generally occurred every year.. The occurrence sometimes covered the 

 entire period from t^anuary to I/iarch and at other times was limited to a part 

 of the period o This occurrence is extremely rare in the high seaso Further- 

 more, if it does appear^ it is localized and does not extend over a wide areao 



The water layer most closely related to the tuna fishery, judging from 

 the mean depth of long line settings, was assumed to be at 100 meters, and 

 the horizontal distribution of water temperatures at the 100-meter layer was 

 determinedo Of the ten stations located in the equatorial count ercur rent area 

 described above, there was only one which showed a water temperature of over 

 20 degrees, and that was 21 o5 degrees » Others were all below 20 degrees and 

 averaged 18o5 degrees » Of the 20 stations in the northern equatorial current, 

 there were five whose water temperatures were over 20 degrees i these five 

 averaged 21 c5 degrees o ^'he other temperatures were all below 20 degrees and 

 averaged 17o8 degrees o Six stations which were assumed to be in the southern 

 equatorial current all showed water temperatures of over 20 degrees j their 

 average was 22 d degrees » Three stations bordering the countercurrent and the 

 southern equatorial current all showed temperatures of over 20 degrees; they 

 averaged 22 „4 degrees » According to these findings, practically all of the 

 100-meter layer of the equatorial countercurrent area showed water temperatures 

 below 20 degrees and all of the 100-meter layer in the southern equatorial 

 current showed water temperatures over 20 degrees » Furthermore, there were 

 more stations in the northern equatorial current which had water temperatures 

 of less than 20 degrees « 



In order to understand the variations of the water temperature of this 

 100-meter layer, we made a rough study of the conditions existing during a 

 normal year. In the northern equatorial current area, water temperatures 

 below 20 degrees 'were occasionally found in the area near the shore, but the 

 water temperatures in the high seas were from 22 to 27 degrees and only rarely 

 belovi 20 degrees o Likev;ise, in the equatorial countercurrent area it rarely 

 fell below 20 degrees and was from 23 to 2 8 degrees » The water temperatures 

 in the southern equatorial current area were all above 20 degrees and averaged 

 about 26 degrees o 



