Table 2. --Proportion of each length group (shown by permillage) 



In the following paragraphs some charac- 

 teristics of the length groups making up the 

 northward-moving albacore will be examined: 



(1) The length groups appearing in the 

 northward-moving albacore number three to 

 five, the number varying from year to year. 

 The only length groups which appear consist- 

 ently throughout the 4 years are Group III and 

 Group IV. In terms of t h e proportion they 

 occupy, all of the groups show wide variations 

 from year to year, the average magnitudes 

 being greater than 50 percent. The fluctuation 

 is particularly conspicuous in Group II, which 

 in some years is an important element and in 

 others does not appear at all. 



(2) The 4-year averages of the modal 

 lengths of each group are respectively 55. 5 

 cm. , 68 cm. , 77 cnn. , 85 cm. , and 92 cm. , 

 but the fluctuations in the values from year to 

 year are great, and the spread between the 

 largest and the smallest extremes is as much 

 as one-half the interval between length groups 

 for all of the groups. The intervals between 

 the several length groups, with the exception 

 of groups I and II, are about 2 cm. smaller 

 than in the case of the southward-moving alba- 

 core (Suda 1954a). The values of the modal 

 lengths themselves are in approxinnate agree- 

 ment with those of the southward-moving alba- 

 core. These facts seem to be ascribable in 

 large part to the characteristics of the growth 

 and also to the nnarked variations fronn year 

 to year. The upper limit of the length range 

 of the pole-and-llne albacore coincides each 

 year at 95-100 cm., but this position is some- 

 times the upper limit of Group IV and some- 

 times the upper limit of Group V, It is thought 

 that this is deternnined rather mechanically and 

 without relation to such things as the positions 

 of the length groups and the range of the dis- 

 tribution, since it is believed that the upper 

 limit of size of fish which can be taken in large 

 numbers by pole-and-line fishing may be in 



this region. In this case, we must consider 

 the possibility that only the comparatively smeill 

 fish of Group V may appear in the catch, 



(3) There is no consistent trend of pre- 

 dominance of any group throughout the 4 years. 

 Cases of predominance of Group III are most 

 numerous, but there are also examples of pre- 

 dominance of Group IV, In most cases the pre- 

 dominant group is overwhelmingly so, but there 

 are also cases in which it does not rise greatly 

 above the others. There are no signs of the al- 

 ternation of dominant groups every other year, 

 as seen in the southward -moving albacore. 



When we consider, over a number of con- 

 secutive years, the length groups which make up 

 the northward-moving albacore, it is difficult to 

 detect any regularity or resemblances in the 

 composition of the length groups from year to 

 year, except for the fact that Groups III and IV 

 appear every year. It is thought that there is a 

 deep connection between these phenomena and 

 the conspicuous fluctuations in the annual catch 

 of the northward-moving albacore.^/ 



Comparison of the Size Compositions of the 



Southward-moving (Longline) Albacore and the 



Northward-moving (Pole-and-Line) Albacore 



As stated in the preceding section, the size 

 composition of the northward-moving albacore 

 shows violent annual fluctuations. When it is 

 compared with that of the southward-moving 

 albacore, some conspicuous points of difference 



5/ 



— According to the data of the Statistics 



and Survey Division of the Ministry of Agricul- 

 ture and Forestry, the albacore landings for the 

 period of May to July of each year were as 

 follows: 1951 - 1, 876. 000 kan /J, 757._26 tons^/, 

 1952 - 11, 556,00 kan /_47, 784. 06_ton£/, 1953- 

 8,428,000 kan /34, 849. 78 t o n s /, 1954- 

 5,841, 000 kan /24, 152.54 tons/. 



18 



