c. It is necessary here to reconsider the 

 fitting of the normal distributions. Naturally 

 the numbers of occurrences at both ends of the 

 distribution are few. Furthermore, in the 

 older groups the scatter or dispersion of the 

 lengths is great. Consequently, sampling 

 error is great, especially in the older groups. 

 Furthermore, the difficulty of estinnating the 

 niodal lengths and the range of distribution of 

 the body lengths is increased, and the length 

 groups overlap each other so that they are 

 difficult to separate. As a result, in the older 

 groups the fitting of normal distributions to 

 the length distribution in itself is unavoidably 

 accompanied by inaccurate results. Actually, 

 if we try taking the coefficient of correlation 

 between the average lengths of group N of a 

 certain year and group N + 1 of the following 

 year^./, the older the age group the smaller 

 the value we get. If we collate these facts 

 with the circumstances set forth in paragraph 

 b, we cannot help thinking that there is a 

 possibility of error in the fitting of normal 

 distributions to the older age groups. 



In conclusion, according to paragraph a we 

 cannot find any facts which would deny that at 

 least in the case of the groups II-IV these length 

 groups are age groups. The results can neither 

 be said to agree nor to disagree but the absolute 

 values of the differences are very small. Con- 

 sequently it appears that there is no great ob- 

 stacle for the present to treating them as age 

 groups. According to paragraphs b and c, in 

 the fitting of the six normal distributions, a 

 possibility of error is indicated in the fitting to 

 the advanced age groups. On the other hand, if 

 there is no error in the fitting of the normal 

 distributions, a doubt is cast upon the assump- 

 tion that the six size groups are age groups. 

 With this sort of results, it is thought that if the 

 size groups postulated for the albacore captured 

 by longline in the North Pacific Ocean are 

 handled as five groups consisting of groups I to 

 IV and an advanced age group above that, there 

 is no obstacle to considering them as age groups. 

 Figure 4 shows the size composition which ap- 

 peared in figure 2 as the 5 length groups, I, II, 

 III, IV and the advanced age group. 



8/ 



— The coefficients of correlation are as follows: 



Group I-II Group II-IU Group III-IV Group IV-V Group V-VI 



+ 0.63 +0.87 +0.64 +0.40 -0.01 



adw-uitcecL uae jAtua 



Figure 4. --Length groups of the albacore caught in the northwestern 

 Pacific during the longline season. 



13 



