Report of 

 Grounds Fished by Tuna Boats Operating in the Inner South Seas 



About 1939 the main fishing grounds of tuna boats from Japan operating in 

 the waters around the South Sea Islands were in the area centered at east longi- 

 tude 145° and from north latitude 4° to 10° « Thereafter they shifted gradually 

 eastward and centered at east longitude 150° and north latitude 1° - 2° to 

 5° - 6°. Beginning around January and February of this year the latitude moved 

 southward, whereas the iori;;itude remained nearly the sajie as before » The main 

 fishing ground about '^pril was in the neighborhood of 1° south latitude^, and it 

 was rumored that the fishing boats crossed the equator to carry on their fishing » 

 It then moved gradually northward and the main fishing grounds were located 

 between north latitudes 0'^ and 3° again about Juneo The longitude remained 

 about the same, mainly between 150° and 155°^ and some fishing boats even went 

 out as far as 160°= "i/ith the exception of the fishing grounds in the south 

 latitude below the equator, the fishing grounds are usually centered in the 

 equatorial countercurrent, although they may shift east and westo The fact 

 that yellowfin tuna occupies the top of the list of fish caught is encouraging 

 in that it indicates that a large number of yellowfin tuna inhabit the equa^^- 

 torial countercurrent o The author considers that the fact that the fishing 

 boats p-jssed through the countercurrent and proceeded to the distant south 

 latitudes to conduct their operations was an unavoidable temporary measure due 

 to the j/oor fishing caused by abnormalities in the countercurrent. Let me 

 explain briefly. 



This author and others j, who made oceanographic studies of the waters 

 adjacent to Palau over a period extending through January, February, and iaarch 

 of this year, were truly startled to see that oceanographic conditions were 

 abnormal In short, the results shovjed that the surface water temperature of 

 numerous offshore precis had fall-?r; to i;7°, and that the jvp.ter temperature of 

 the 100-meter stratum, flhich has a ciose bearing upon the occurrence of yellow- 

 fin tuna, had a low average temperature of 18o5° even in the countercurrent » 

 This had a "T^ery bad effect upon fishing in the adjacent .leas and thore was 

 unusually poor skipjack fishing off the shores of Palau. lung fishing along 

 the coast and on bhe seas also slackened markelly and only a i'&K '-una were 

 caught even in the equatorial countercurrent o U^ee "Oceanographic Ch<\nge& and 

 Fishing Conditions in Palau Waters," South Seas Fishery News, Vol. 5, No, 2o) 



At this time the author made a comparative examination of the results 

 during various seasons of the research vessels and fishing boats from Japan 

 which were operating in the neighborhood of 150° „ iie discovered the fact 

 that fishing wns slack e-ren in this 'cvea during practically the same periodo 

 It was eventually surmised that the adverse conditions seen in r,he waters 

 adjacent to Palau exist not only here, but extend to the ?reas far to the 

 easto Thereafter numerous data on tuna fishirg conditions in the vicinity of 

 150° and skipjack fishing conditions during the early part of this year at Truk 

 and Fonape were asse;nbledo "K'hen those -.vere studied, it becairie clear that during 

 the slack period, yellaAifin tuna decrossed and the big-eyed tuna increased in 

 number. Also, a comparatively large number of albacore, which are uncommon in 

 the lower latitudes of island waters, were caught, and skipjack fishing vvas poor 

 even at Truk and Ponnpe, jus.t as it was at Palauo i'he incrc'.se in big-eyed tuna 

 and the large catch of albacore meant low water temperatures in the surface stratum. 



