(2) Underlined figures represent occasions when the fish were 

 particularly smallo 



(3) "Size of yellowfin" is the average of the yellowfin in the 

 day's catcho 



According to table 13 5 at this season in this area yellow- 

 fin of 30 to 40 kilograms predominatep with fish of around 35 

 kilograms being most numerous™ In spite of the fact that the 

 area surveyed was only 120 miles from east to west and 180 

 miles from north to souths it appears that from time to time 

 fish of remarkably small size were takai ^ and on the days when 

 such fish were taken the catch rate took a sudden dropo On 

 the whole, one can detect a tendency for the fish taken to 

 become somewhat smaller and for the catch rate to gradually 

 become lower with the passage of time^ In order to make the 

 data of table 13 easier to visualize, they are presented 

 graphically in figure 27o 



Whether or not the phenomena described in the foregoing 

 are due merely to chance cannot be ascertained because there 

 are no other data with which to make a comparisono According 

 to Dro Kishinouye, the black tuna taken at the beginning of 

 the fishing season are large, and with the passage of time they 

 gradually become smallero No clear explanation can be given 

 of the significance of the fact that among the schools of fish 

 of about 35 kilograms weight, whic?i are thought to be all of 

 about the same age groupp there suddenly appear from time to 

 time fish of markedly smaller sizes, but it is thought that 

 they may represent fragments of a number of schools which 

 successively passed through this sea area„ 



The validity of the above remarks is open to doubt, but 

 at any rate the phenomerxa described in the foregoing probably 

 give some hint as to the movements of the schools in this area. 



It is said that if you go to the seas of the low latitudes, 

 you can catch yellowfin at any time, but the data presented 

 above show that the fishing conditions are by no means always 

 the sameo In other words, even in these latitudes a fishing 

 season can be discerned, however, this fishing season differs 

 in some respects from that of the high latitudes o In waters 

 which seasonal changes place outside the limits of distribu- 

 tion of tuna, there is no catch at all except during the fishing 

 season, while in the lovf latitudes the change is expressed 

 simply in terms of an increase or a decrease in the catch rate. 



As was shown in table 3j, the value and significance of 

 the fishing grounds vary remarkably from one area to another,, 

 Some remarks on this sort of variation are to be set forth in 

 the following section, but it shows that even in waters of the 



94 



