The yellowfin grounds centered on the EquatoTg the spearfish 

 grounds covering all of the subtropical seas^, and the albacore 

 grounds centered at 30° - 40° north latitude all are subject to 

 restrictions of latitude and all present shifts due to seasonal 

 changes., but they are indeed extensivec Because the fishing methods 

 employ mainly the hook and line^ and because of the spawning habits 

 described below^ it is thought that the propagation of the resource 

 is suitably regulated under natural conditions^ At any rate^, under 

 the conditions obtaining up to the present it is hard to discern 

 any signs of a decline in the resource due to overfishing i, and the 

 yearly fluctuations in the catch may be considered to be mainly con- 

 trolled by changes in the environmentr. 



The foregoing refers to the universality of distribution of 

 the fishing grounds in a horizontal sense^ but it is also necessary 

 to take account of the distribution in deptho In tropical sea areas , 

 where the sea water is highly transparent, solar energy can reach 

 to great depths and the sphere within which marine life can exist 

 is thereby enlargedo It appears that in the tropic seas the range 

 within which the tunas can live extends to far greater depths than 

 has been thought hitherto„ For examplej there are data which show 

 that the yellowfin is present in some abundance at depths as great 

 as 160 meterso (See table 9)o 



It has already been said thatp if we compare the productive 

 potential per unit of sea water^ the cold seas and coastal waters 

 show markedly higher values than the tropic seaso And it has been 

 noted that there is a theory that the density of distribution of 

 fishes in tropical waters is consequently lowc Ifg however^ the 

 range of occurrence is comparedj, that of the tunas is much more 

 extensive than that of the fishes of northern seas or of demersal 

 and coast-dwelling specieso Thus if a comparison is made of the 

 absolute quantity of the resourcej it may be wondered which will 

 be the greater^ the so-called pelagic fishes such as the tuna, or 

 the demersal and coastal fishes? 



Within the limits of present knowledge there is absolutely no 

 way to arrive at an answer to this question, however^, if we take 

 into account the various factors set forth abovep it is impossible 

 to conclude that the tuna resource ^ in tern^ of its absolute quantity p 

 is necessarily inferior to the demersal and coastal fisheso The 

 schools which migrate into Japanese waters \15 J probably represent 

 no more than one branch of the tuna resource of the Indian and 



vlSyl There are people who think that all of the tuna and bonito 

 at least once in their lives migrate into Japanese watersc 

 The author is of the opinion expressed aboveo 



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