to the line of iglanda. There are no fiahing ground* with high catch rates farther to the westward 

 in the Satsunan region except for a few areas of rather high catch rates east of Amami Oahima. 

 The grounds east of Formosa, which had disappeared since December, come back with some 

 catch rates of over 0. 5. 



o o 



The center of albacore distribution in February is 1 or 2 east of that of the broad- 

 bill, but the pattern of distribution is very similar. The albacore grounds in the Kinan sea area 

 are nnore extensive than in January and the fishing appears to be better. 



In the chart for March (k) the center of distribution has moved somewhat north of its 

 position in February and is within the range of 30 to 34 N. , 140 to 147 E. To the southeast^ 

 and separate from this center there is an area of high density of occurrence in the vicinity of 30 

 N. 152 E. It is impossible to determine whether these two areas are connected or whether they 

 are completely separate because of the paucity of data. In the waters west of the Izu Islands, 

 including those around the Ryukyus and Formosa, no areas of high catch rates are to be seen at 

 all. 



The center of distribution of albacore in March appears to be somewhat to the south 

 of that of the broadbill, and in general the density of occurrence appears to have decreased. The 

 albacore grounds in the Kinan sea area have moved somewhat to the south. 



From the foregoing, it appears that the center of distribution of the broadbill, in a 



very general view, is in the vicinity of 140 to 155 E. ,, and that the schools which in October are 



in the vicinity of 42 N. gradually move south with the passage of time. This southward movement 



is accompanied by an extension of the fishing grounds to the east and west, and it appears that 



from January on part of the schools remain in the waters east of the Izu and Ogasawara islands. 



It is unknown whether or not they cross to the westward of this line of islands, but judging from 



o 

 the distribution of catch rates it appears that they do not and the vicinity of 140 E. is considered 



the apparent boundary of their distribution and migrations. As has already been stated, at some 



seasons areas of a fairly dense distribution appear in the waters around Formosa and the Ryukyu 



Islands, but the relationships between the schools appearing in this region and those which occur 



to the east of the line of the Izu and Ogasawara archipelagoes are completely unknown at present. 



Broadbill do appear in the tropical sea area* to the south of the sub tropical line of 

 convergence, but there are no fishing grounds on which concentrated catches of this species are 

 made. However, there are many imnnature fish in this region and larval and juvenile forms 

 appear to occur there, in many cases forming part of the food of other tunas Eind spearfishes. 

 This phenomenon is not as yet well understood, but it probably gives an important clue to the 

 area of reproduction of the broadbill and should be given serious consideration from the point of 

 view of ecology and population studies. In any case, it is worthy of careful note that the fishing 

 grounds of the broadbill swordfish appear to be limited on the south by the subtropical convergence 

 on the west by the line of the Izu and Ogasawara archipelagoes, and on the east by approximately 

 160° E. 



In the foregoing we have attempted to consider the patterns of distribution and 

 migration of each species based on the catch rates, and on this basis there appear to be for each 

 species two types of patterns, the boundaries between which appear to be geographically the 

 subtropical convergence, the area of contact of the Equatorial Countercurrent and the North 

 Equatorial Current, and the line of the Izu and Ogasawara archipelagoes. 



One of these two types of patterns is represented by the striped marlin, which extend 

 over the whole area in the vicinity of 20 to 30 N. , and the black tuna, which occur fronn the 

 vicinity of Luzon to the area of the Kuroshio, In this type dense schools appear over a broad 

 expanse of ocean in an extremely short period of time and then after a very short time disappear 

 agsiin, BO that it is extraordinarily difficult to follow the paths of their migrations. For instance, 

 the catch rate curves for striped marlin all show the highest peak of the year in May in the 

 waters of the Marianas in the vicinity of 20 N. , in Formosan waters, in the waters of the Izu 



165 



