Figure l.--Size composition of northward-moving albacore. The solid 

 line represents the length frequency curve (shown by per- 

 millage), and the estimated length groups are shown by 

 the broken line. 



period from summer to autumn are completely 

 lacking, and it is impossible to get a definite 

 grasp of the process of growth. Several 

 growth patterns can be postulated, but the as- 

 sumption that "the series of modes to which 

 the same number has been given shows the 

 growth of a certain age group" gives a value 

 for 1 year's growth that is nearest to the in- 

 tervals between length groups. This hypothesis 

 is thought to be the most adequate, provided 

 that adjacent length groups are considered to 

 be 1 year apart in age. 4./ in this case, the 

 growth of the albacore is not uniform through- 

 out the year, and the rate of growth from 

 summer to autumn turns out to be markedly 



lower. However, it cannot be denied that there 

 is a possibility that a certain age group which 

 has grown as indicated by a certain numbered 

 modal series may in the following longline sea- 

 son (November-December) follow the growth 

 shown by the mode with the next lower number. 

 There is need of some method for ascertaining 

 this. In this case, 1 year's growth would always 

 be considerably greater than the interval be- 

 tween length groups, in fact, it would be nearer 

 to twice that interval. Consequently, there 

 would be very little possibility of adjacent length 

 groups being age groups 1 year apart. If we 

 postulate that growth takes place as indicated by 

 following the series of modes to which the same 



— For the method see my "Size composition of the albacore taken in the North Pacific during 

 the period of southward movement," Bull. Jap. Soc. Sci. Fish. 20(6), 1954. The results of chi- 

 square tests of the fitting of normal distributions to the length frequency curve for northward- 

 moving albacore are as follows: 



Season 



1951 

 1952 

 1953 

 1954 



4/ 



— See my paper previously cited. From the results of separating a number of length groups 



by the fitting of normal distributions on the length frequency curve for longline-caught fish, it 



appears that there is no obstacle to considering adjacent length groups as having a 1-year age 



difference. 



16 



