equatorial region were located in the same 

 positions as in the early months of 1954 (fig. 8). 

 This is also true in the western Pacific, where 

 the modes were similar in 1950 and 1951. 



Intrayear Size Variation 



A progression of modes from month to 

 month during the growing season would be ex- 

 pected inaclosed population if the modes repre- 

 sent year classes. However, there is no pro- 

 gression in the length-frequency distributions of 

 male and female equatorial yellowfin taken by 

 longline gear in the central area (fig. 7). Another 

 good tinne series with data segregated by sex is 

 available for the period January 27 through June 

 15, 1954 (fig. 8). Again there is little or no 



modal progression. One item of interest is 

 the change in relative numbers of the two size 

 groups (fig. 8); in January-February the 

 snnaller sizes (90-120 cm.) (upper panels) 

 predonninated, while during March-April the 

 larger fish (130-170 cm.)were most numerous 

 in the catch. This change in the relative num- 

 bers of the dominant sizes probably reflects 

 the fact that the earlier sample was taken 

 closer to land, for as pointed out in Shomura 

 and Murphy (1955), samples fronn the vicinity 

 of islands contain a higher percentage of snnall 

 fish than those from well offshore. 



It can be seen in figure 9 that the modal 

 groups (with the sexes connbined) do not pro- 

 gress in the western Pacific either, though 



1950 



1951 



I I I M I I I n I M I I I I 



62 72 82 92 102 112 122 132 142 152 162 172 52 62 72 62 92 102 112 122 132 142 152 

 LENGTH IN CENTIMETERS 



Figure 9. --Length-frequency distributions of yellowfin measured on 

 Japanese mothership expeditions, 140 E. to 179 E. longitude. 



