(1) Such advanced age groups* as seen in 

 the southward migrating fishes do not appear 

 in these which migrate northward, 



(2) Size-composition of the northward 

 migrating ones shows the remarkable annual 

 fluctuation, therefore it is able to say that it 

 is much more unstable than that of the south- 

 ward migrating. 



(3) The dispersionof the length frequency 

 of the northward migrating ones is much more 

 •mall than that of the southward migrating ones. 



Then differences between the two groups 

 seen to be based on ecological differences of 

 them other than the difference of fishing 

 method. In spite of these differences, the 

 author hypothesized that there will be some 

 relations between these two groups on a basis 

 that the body-length of the most dominant size - 

 groups are less than 100 cm in both migrating 

 groups. 



♦Age is not determined; larger than 90 

 cm. (Suda 1954a). 



/end of English summary/ 



The albacore exploited by the longline 

 fishery, which move southward in the autumn 

 and winter between 140 E. and 180 , cease 

 their southward movement each year around 

 March north of the Subtropical Convergence 

 in the vicinity of 28 N. , and in April, while 

 showing some signs of northward movement, 

 they suddenly disappear. As if to take their 

 place, the pole-and-line albacore fishery be- 

 gins, with its main fishing season from May 

 to June. During this period the fishery moves 

 northward between 140 E. and 160°E. The 

 author has attempted to analyze the size compo- 

 sition of these northward-moving albacore ajid 

 also to compare it with the size composition 



of the southward-moving albacore which are 

 taken on longlines (Suda 1954a). The data em- 

 ployed resulted from the studies of landings 

 made by the Nankai Regional Fisheries 

 Research Laboratory at the Tokyo and Yaizu 

 fish marketsi./. 



Size of the Northward-moving Albacore 



According to the data for the period of 1951 

 to 1954, the length range of the northward- 

 moving albacore taken by pole and line is approx- 

 imately 50-100 cm.Z.1 There were almost no 

 specimens over 100 cm. long (solid line in fig. 

 1). However, within this range the lengths show 

 conspicuous changes from year to year. These 

 variations are particularly marked in the fish 

 between 50 cm. and 70 cm. long, which in some 

 years appear prominently and make up an impor- 

 tant element in the albacore catch but in other 

 years hardly appear at all. Fish in the 70 cm. 

 to 100 cm. length range appear every year and 

 are the most stabilized portion of the northward- 

 moving albacore. It is noted that the upper 

 limit of length coincides for all years at about 

 95-100 cm. 



The broken line in figure 1 shows the results 

 of fitting suitable normal distributions to the 

 length frequency curve of the northward-moving 

 albacore^/. Conspicuous variations are shown 

 from year to year in the modal lengths of the 

 several length groups, and it is difficult to de- 

 termine which groups are analogous. In order 

 to make this determination, the size composition 

 by months for the period from November 1950 to 

 July 1954 was obtained and an attempt was made 

 to follow the transition of the modes. Figure 2 

 is the size composition by months of not only the 

 northward-moving albacore but also including 

 the southward-moving fish. In most cases the 

 positions of the modes are not clear for the fish 

 over 90 cm. long, so they have been omitted. 

 As can be seen from figure 2, length data for the 



1/ 



— Measurennents were made as follows: 

 Year Voyage sampling ratio Voyages surveyed 



Fish sampling ratio 



Fish measured 



— In June 1951 some fish 30-37 cm. long were measured, but there was only one large catch 

 of albacore of this size. Their average length (139 fish measured) was 34. 6 cm. , with a standard 

 deviation of 1. 25 cm. 



15 



