rs, hovirever, -•he tuna Icrigline fishery 

 has daveloped witn rapid stride, ... ;:he fis!-"-!^^ grounds have 

 been expanded, it lias become evif^.-v': that fi^/i-.:.c 3rounds are 

 not Gcnfined to areas having the scrt of "opogrc^'y described 

 above. For example, the v.-aters IOC <= 200 niilec v'^^t of tb3 

 Riilippines, which are among the deepest in t'—; , . possess 

 excellent fishing grounds at certain seasons, i.i ;>;s ise the 

 aibacore grounds east of Cape Koji^-ia and ths yellov.-_'in grounds 

 near the Equator are located right out in the middle of the 

 open sea, and it is difficult tc s ee how they may be relf:tec 

 to the configuration of the sea bottom or the position of land 

 masses. 



Tj-is situation seems extremely natural, if we take into 

 account the migratory character of the tunas. If we only had 

 the requisite knowledge of the seasons and routes of their 

 migrations, :Ye could tell directly -Ahen the fishing would be 

 good and which areas could be developed as fishing grounds, 

 without any reference to the topography. 



In short, such topographically defined fishing grounds 

 are an extremely limited part of the total potential tuna long- 

 lining grounds. On the other hand, the fishing grounds which 

 lie along the naths of migration are highly mobile and extremely 

 generalized in character. This is not to say that the fishing 

 grounds possessed of the type of topography described above have 

 little significance and value. The point is that each type of 

 ground has its particular characteristics. 



iv. Relationship tc other marine life. 



In a broad sense, all of the marine animals living vj-ithin 

 the range inhabited by the tunas are related to then in some 

 way, and by extension bear some relationship to the fishery. 

 It must not, however, be thought thax a. great problem, such as 

 these relationships present, can be studied thoroughly in a:iy 

 short period of time. Furthermore, corisidering it as an actual 

 problem, the knowledge which we have been able to gain up to 

 the present is really insignificant, \ie will consider here only 

 two or three exomples which are thought to have an especially 

 direct connection with the tuna fisliery. 



The first example is that of the marine animals which are 

 es.ten by the tunas. It may be thought that, other oceanograp-ii- 

 cal factors being equally favorable, an area where food organisms 

 are abundant will have superior possibilities as a fishing ground 

 over one where such organisms are scarce. The type of fishing 

 ground described above, where resident schools are found on sJioals, 

 is evidence of this sort of superiorit;,-. Among the fishing grounds 

 in Japanese home waters, the black tuna grounds off Tanegashima 

 and in Hokkaido' waters may be considered, from one point of view, 

 to have exactlv this same sort of sigrj.f icanoe. 



104 



