Consequently, it can be thought that the sex ratio will have a great 

 effect on the size composition. The size of fish in August, as shown in 

 table 1, is especially large, and it is thought that these albacore have a 

 high proportion of males. 



A noteworthy point about these albacore is the development of 

 their gonads. As early as June individuals are noted in which the nnales' 

 gonads weigh more than 200 granns and those of the females more than 

 400 grams. The presence in July of males with gonad weights of 300 

 grams and females with gonad weights of 400 to 500 grams is thought to 

 indicate that the development of the gonads has progressed somewhat 

 since June. In August 1937 the Shizuoka Prefecture research vessel 

 Fuji Maru reported gonad weights of 260 grams fronn the waters west 

 of Midway Island; judging from the position of the fishing grounds, these 

 are thought to have been albacore occurring south of the Subtropical Con- 

 vergence. The albacore which move south into the area south of the 

 Convergence and spread widely over the South Seas waters are thought 

 gnerally to have well-developed gonads at this season, and it is imagined 

 that their spawning is carried on over broad areas of the South Seas com- 

 pletely separated from the main fishing grounds . However, no completely 

 ripe eggs have as yet been encountered, so we have no definite proof of 

 spawning. 



As for the condition of the gonads of albacore occurring in areas 

 north of the Subtropical Convergence, those taken west of Midway Island 

 were all extremely immature, with gonad weights below 50 grams for 

 both males and females. The results of investigations made in March 

 at 28°N. to 30°N. , 145°E. to 160°E., showed very few of the females 

 above 90 cm. in length to have ovaries weighing more than 100 grams, 

 and these fish are thought not to move northward but to continue south. 

 More than 90 percent of the specimens examined had gonad weights of 

 less than 100 grams and were extremely innmature. Studies of the alba- 

 core taken by pole-and-line fishing in May and June show only immature 

 fish. 



2. Waters north of 10 N. and west of the line of islands 



These are the albacore around Okinotorishima. For May catch- 

 rate values of about 1.0 are indicated. From June on some albacore 

 continue to appear in this sea area, and it looks as if albacore always 

 occur there throughout the year. It will be noted, however, that the alba- 

 core catch rates in this area are high from November to February, in 

 seasonal contrast to the southward-moving albacore east of the line of 

 islands. Nothing is known of the size composition of the albacore which 



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