Around January and February the sardine form great schools 

 in the area centered around Tanegashimaj where they spawn in 

 large numbers „ then gradually move northward along the Japan 

 Sea and Pacific coasts of Japan, reaching the Hokkaido" area in 

 the summer and autunuio This has been the standard pattern, of 

 their migrations in the paste In recent yesro ihe number of 

 sardines on the Tanegashima spawning grounds has shovm a rapid 

 decline and the catch in Japanese coastal waters has also dropped 

 sharplyo At the same time the black tuna fishing in the Satsunan 

 Sea Area has become very poor and has been almost abandoned^ 



Another example is that of the spearfish fishery in the 

 waters e*ast of Taiwanr, This area is known as an excellent 

 ground for these fishes during the northeast monsoon, and the 

 success of the fishery is thought to be intimately related to 

 the abundance of such fishes as the round herrings DecapteruS fl 

 and mackerels which migrate successively into the areao Of 

 course the abundance of these fishes upon which the tunas feed 

 is 5, after all^ controlled by changes in oceanographic conditions,, 

 It goes without saying that all of these various problems are 

 in the end bound up with the productive potential of the oceanj, 

 and they probably cannot be solved except by the method of 

 direct attack referred to abover, However » from the standpoint 

 of the tuna fishery and its present problems ^ and leaving out 

 of consideration these basic questions s, it would be extremely 

 useful if these food organisms could be directly utilized as an 

 indicator of fishing conditions and fishing seasons^ Of coursej, 

 in order to do this it would be necessary to clarify further 

 the mutual relationships between the tunas and these organisms o 

 And even if it were possible to use such food organisms as 

 indicatorsj, if it turned out that their ecology was more com- 

 plex and difficult of investigation than that of the tunaSp 

 they would in actuality be worthlesso It is^, after all, a 

 question of convenience c 



The second case is that of the relationship to the tuna 

 fishery of fishes having ecological characteristics and habits 

 resembling those of the tunaso As exanples of species having 

 such habits we can cite the skipjack^ cybiidSj, Lampris regia, 

 the dolphin, and many sharks,, Among these fishes some have a 

 fairly important significance in the catch of the tuna longline 

 fisheryo The sharks are significant in one respect as a part 

 of the catchj, and in another as pests which damage the fish 

 hooked on the lineSo 



It is known that the migrations of some of these fishes 

 precede those of the tunas ^ others occur at the same time^ and 

 still others follow themo It follows thatj aside from their 

 significance as a part of the catch or as harmful pests^ referred 

 to above, they may be thought to have potential value as actual 

 indicators of fishing grounds and seasonso Butj, although there 

 are knovm to be many fishes which have such a close relationship 



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