The seasonal distribution of the longline yellowfin catches shows more pronninent 

 variation than the longitudinal distribution. For instance, June showed a catch peak irrespective 

 of longitude (table 4). A second peak during the December-February period is also evident. 

 This is shown graphically in figures 2 to 4. Figure 2 is a plot of the monthly catches at 160 - 

 165 E. longitude, figure 3 is a plot of the catches at 155 -160 E. longitude, and figure 4 shows 

 the mean catch by month irrespective of longitude. (The two longitudes illustrated in figs. 2 eind 

 3 were chosen because they were the best represented in time.) It is of interest to note that the 

 shapes of the curves for the two longitudes are nearly identical, and that these in turn resemble 

 the curves for all longitudes combined. Furthermore, in each of the three figures there is con- 

 siderable similarity in the shapes of the curves for the two years 1950 and 1951, This relative 

 stability of the pattern of seasonal variation in this portion of the western Pacific indicates that 

 the pattern is real, and furthermore, because it is apparently repeated during two years, the 

 pattern is probably the result of regularly recurring changes in the tuna population. Precisely 

 what factors induce these changes in the population level is unknown. 



Figure 2. --Yellowfin tuna catch per 100 hooks by months for 

 1 -5 N. latitude, 160 -165 E. longitude. Points 

 obtadned from table 4. 



The longitudinal distribution of bigeye tuna in the area under consideration resembles 

 that of the yellowfin in that the differences in abundance associated with longitude appear to be 

 slight and inconsistent (table 4). This is a further indication that the environment over the area 

 under consideration is relatively uniform insofar as its east-west component is concerned. 



The seasonal distribution of bigeye (fig. 5) bears a general similarity to that of the 

 yellowfin in that there appear to be two peaks of abundance, one in June- July- August, and one in 

 Decennber. The latter peak is not well developed as it was in the instance of the yellowfin, but 

 the July peak is very prominent, particularly in 1951. The 1950 peak that corresponds to the 

 July 1951 peak is well developed but occurred 1 month later, in August, and in magnitude is only 

 half as large as the 1950 maximum. As in the instance of the yellowfin, the general regularity 

 of the seasonal distribution of bigeye in the western Pacific just north of the Equator suggests 

 the operation of cyclic phenomena. 



