the middle ten days of August Group C appears about 100 miles off Kinkazan, 

 and in the first ten days of September it moves offshore and joins the 

 mixed groups of A and B, At the same time Group D is added and from the 

 first ten days of September to the end of the fishing season the ratio 

 of each group in the mixed catch does not differ markedly either at the 

 northern or southern limits of the fishing grounds, along the coast or 

 at the offshore side, nor at the center of the grounds nor at their 

 periphery, a nearly uniform ratio of mixture being maintained with the 

 four groups thoroughly mixed in the northern section. 



It cannot be deduced from the weight data alone whether these four 

 different weight groups are due to differences in age or whether the 

 migrating schools belong to different strains, but according to Aikawav2; 

 the skipjack schools of the Northeastern sea area are composed of a 

 Satsunan strain and an Ogasavrara strain, the former, with a condition 

 factor of 2^0 - 2/!>..4., making up about B0% of the total, while the latter 

 has a condition factor of 13,0 - 18. 80 Both groups are composed almost 

 exclusively of fish in their fourth or fifth year. Another study of the 

 skipjack of Palau waters(3) shows a range of sizes for each year^class 

 from fish of the year to those in their eighth year. 



Now assuming that we are dealing with a strain of fish from the 

 Zunan area and another from the Ogasawaras, if we reverse the formula^^) 

 f = ^ X 1,000 to get the body length from the weight and the condition 

 factor, and deduce the age of each group, groups A and B, regardless of 

 which strain they -belong to, fall into the length categories of fourth-year 

 fish for Group A and fifth-year fish for Group B, If Group C is assigned 

 to the Satsunan strain, it is composed of second-year, and if to the 

 Ogasawara strain, of third-year fish„ Group D, whichever strain it may 

 be assigned to, falls into the category of third-year fish. Even though 

 groups C and D are treated es rather lean representatives of the 

 Ogasavrara strain, they cannot be regarded as fourth-year or fifth-year 

 fish. It is considered that the four groups A, B, C, and D do not arise 

 from differences in the strains from which they come, but rather that they 

 show age classes. 



Similar data are lacking for the southern areas outside of the North- 

 eastern sea area and the weights of the whole catch are not clearly known, 

 but the results of an investigation of the catches of about 50 vessels 

 reporting on the fishing situation to the Central Fisheries Station show a 

 weight composition for the schools like that given in Table lo In general 

 May and June are the peak season, and in the Zunan and Ogasawara areas a 

 considerable catch continues to be made around July - October, the peak 

 season in the Northeastern area, while an extremely small catch is made 

 during the winter season of January - April and November - December. 



(2) Aikawa, Hiroaki„ aai. Jap, Soc. Sci„ Fish. 6 (l), 1937. 



(3) Aikawa, Hiroaki. Bull, Jap. Soc. Sci„ Fish. 7 (2), 1938. 

 (4.) Kimura, Kinosuke. Bull. Jap, Soc, Sci. Fish. 6 (2), 1937, 



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