The mechanism of alternate-year- cycles 

 has been examined on the basis of assump- 

 tions A, B, and C, which had been thought 

 to have the strongest validity. As a result 

 it has been shown that the majority of the 

 elements forming this mechanism lie in 

 the fact that there is a marked variation 

 every other year in t h e amount of the 

 schools regarded as age groups, and it 

 also has been pointed out that there is a 

 possibility that the displacements of the 

 modes regarded as age groups are 

 contributory to this mechanism. 



Based in the same way on assumptions A, 

 B, and C and chiefly from the point of view 

 of the carrying on of future studies, we 

 have considered the time of appearance of 

 the alternate-year cycle and the mechanism 

 which gives rise to it. It has thereby been 

 made clear that the time is anterior to the 

 development of age group a, but it has not 

 been possible to show whether (a) it arises 

 gradually in the course of the process of 

 growth, or (b) whether it is determined at 

 once at one particular stage. However, in 

 a general manner of thinking it should be 

 said that (b) has the greater possibility, 

 and it is also thought correct to ascribe the 

 time to the early stages of life. This is 

 also in agreement with hypothesis ( 1 ) . 

 Even though we assume that the matter is 

 decided at once in the early stages of life, it 

 is hard to think that the mechanisnn arises 

 in a simple form, and in handling the 

 matter of recruitment it is thought that 

 there is a necessity for considering the 

 problem of the mechanism for replenish- 

 ment in at least the North Pacific, South 

 Pacific, and Indian oceans. 



It cannot be determined whether or not 

 alternate-year cyclical phenomena will 

 continue hereafter, but assuming that they 

 do continue, it is anticipated that in further 

 developing future bigeye studies these phe- 

 nomena will provide an important starting 

 point and a key to the consideration of 

 various matters. 



Bigeye Studies. II. A Consideration of the 



Size Composition of Bigeye Taken 



on Pole and Line* 



By 



Misao Honma and Tadao Kamimura 

 Nankai Regional Fisheries Research Laboratory 



/English title and summary/ 



Biology of the Big-Eyed Tuna, Parathunnus 



mebachi (Kishinouye) - II. A Consideration 



on the Size Composition of the Big-Eyed 



Tuna Caught by Pole and Line 



The present paper deals with analysis of 

 length frequency of the young big-eyed tuna 

 caught by pole and line. Especially a relation- 

 ship between the fishing localities and the dis- 

 crepancy in the mean length which was evident 

 in the same modal group has been discussed. 



1. Data used for the study are the 

 measurement of body length obtained from 

 nunnbers of samples and the pertaining infor- 

 mation furnished by fishing boats at two ports 

 during the period from June to July 1953. 



2. In the length fr 

 modes, A and B, wer 

 throughout the samples 

 mean value of each s 

 examined nearly in the 

 findings have led the wr 

 that modal group A ma 

 unit different from gr 

 length frequency. 



equency two dominant 

 e recognized not only 

 (Fig. 2) but also in the 

 chool from Ito 17 

 sanne period. These 

 iters to an assumption 

 y form an independent 

 oup B in regard with 



3. As no uniformity in the length frequency 

 has been found among the samples belonging to 

 the same group (Table 1), correlation between 

 the mean length of the groups and fishing lo- 

 cality has been examined, substituting the size 

 composition sorted by fishing cruise for that by 

 school of fish, because few data on the latter 

 were available for this purpose. 



As a result it was found that the mean 

 length of the fish in both groups A and B was 

 small in the western area of the fishing grounds 

 and tends to become greater as one goes east 

 (Table 2, Fig. 3). 



♦ Published in 1955 in the Bulletin of the 

 Japanese Society of Scientific Fisheries 20(10): 

 863-69. Contribution No. 64 of the Nankai 

 Regional Fisheries Research Laboratory. 



36 



