and that the size of the fish taken clearly decreases with the passage of 

 time. Table 6 shows the seasonal changes in the average weight of fish 

 in this sea area by months. 



Table 6. --Mean weight of 

 albacore, by months, for 

 the area of 140°-150°E. 



SI 61 Tt SI 91 101 

 ?6 — 30'M 



At the southern limit of the fishing 

 grounds, which in November is between 

 32 N. and 34 N^ latitu_de, the fish weigh 

 about 3. 5 kan /_30 Ibs^/. Since the fish of 

 this size group are thought to be south of 

 28 N. to 30 N. in March, this means that 

 they travel more than 240 miles south in 

 a period of 4 months. Consequently, the 

 amount of southward miovement in 1 month 

 is on the order of 60 miles or more. It has 

 already been noted that from year to year 

 the modes appear in different lengthclasses, 



but it can be seenfromi 

 figures 7 and 8 that 

 even within a given 

 year the mode does 

 not appear at one 

 fixed position, but 

 that there may be a 

 number of intermedi- 

 ate sizes. It may be 

 thought that with fishes 

 having a snnall annual 

 growth, like the alba- 

 core, there will be 

 overlapping of the 

 length ranges of the 

 various year classes, 

 and this sort of insta- 

 bility in the length 

 classes in which the 

 modes appear in a 

 given year gives rise 

 to various difficulties 

 in using the size com- 

 position to deduce the 

 age of the fish. 



Figure 7. --Albacore length frequency by months 

 in the North Pacific at 140°-150°E., 1949-50. 



67 



The relation- 

 ship between albacore 

 catch rates and surface 



