Table 2o Age cori5)osition by fishing grounds 



*Notes Fish with 1, 2^ 3s 



annidi are given as I^ II <, IIIoo, 



According to Udal/j the number of fish taken on a single 

 pole during one hour depends on how well the fish bite and on 

 the density of the school^ and these in turn differ according 

 to what the school is associated witho The distribution of the 

 things with which skipjack schools may be associated varies by 

 type (1), and therefore even though we assume that a school 

 moves to the Northeast from Satsunan^ its character as an object 

 of fishing effort will differ with the difference in fishing 

 groundo Furthermore, the catch per pole per day of fishing 

 depends on the size of the schools and the density of their 

 distribution J, and therefore^, on the general density of fishj 

 as an index of the density of fish the number of fish taken 

 per pole per day of fishing, divided by the number taken by 

 one pole in one hour^ may be usedo The total of fish in a 

 sea area is the product of the surface of the areaj the density 

 of fish, and the duration of the fishing seasono If the total 

 is divided by the average length of the period from the time 

 the schools come into the area until they leave it^ that iSj 

 the period of their stay, the total number of fish which migrate 

 into the sea area during one fishing season can be obtainedo 

 As a measure of the average duration of the stay there should 

 be no objection to taking the maximum value of the number of 

 days elapsing between release and recapture in tagging 

 experiments o 



Therefore s, if we get the nizmber of fish caught per pole 

 per hour from the reports of surveys of skipjack grounds by 

 research vessel^ published in the Reports of Oceanographic 

 InvestigationsH/y and the number of fish caught per pole per 



i/ Udaj Michitakas The Shoals of "Katuwo" and Their Angling » 

 Bullo Japo Soco Scio Fisho 2 (3), 1933c (See po 68 ) 



^ Parts published in (58) - (6?) 



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