4. Oceanographlc Data 



Takayama and Ando (1934, pp 6i 20) • In their Inveatlgatlon of aui^aee water temp- 

 erature! In the seas adjacent to the Pacific coast of Japan, reported that albaoorea were 

 caught when the temperature was 'between 14" and 3l"C. The peak catches, per lon^ line op- 

 eration, were made at a number of different temperatures: 19'^ to 20<'C; 22° to 25°C; and 

 30° to 31°C. The data were not anal7zed by looallty, bat It was shown thatt In general, 

 optimum tegrperatures for al\ species of tunas are highest In the waters off Kyushu and be- 

 come progressively lower in the more northerly sea regions. 



tJda and Tokunaga (1937. pp 297-298), analysing fishing conditions in various alba- 

 core fishing grounds, stated that the optimum catches in the mid-Pacific region were made 

 from December through February when water tenperatures were 17° to 19°Ct with maximum catches 

 obtained at about 18°C. In the coaistal grounds the optimum catches were made from May 

 through June when water tei^eratures were between 18° and 21°C, the maxlmam oatch being ob- 

 tained at about 20°C. 



6. Habits 



The albaoore is generally caught at a depth of about 30 ■ek«rai although it nay be 

 present at levels down to 80 meters. During the spring when water temperatures are rising 

 and small fishi sooh as sardines and anchovies, come to the surface, the albaeoras are seen 

 pursuing these fish. 



Ho detailed studies on the food of the albacore have been ma^e. Klshinouye (1923, 

 p 437) stated that it feeds on pelagic crustaceans and small fish, the typical diet of large 

 pelagic species. Toong albaoores were removed from the stomachs of larger individuals taken 

 near the Bonin Islands on 20 January 1917. 



6. Xeonomlcs 



The edbacore, as previously stated, is an' Important Japanese export item, and In 

 prewar years almost the entire catch was processed, either as frozen albacore or high-grade 

 canned white-meat tuna, for shipment overseas. The waters in which the albaoore Is caught 

 In large amounts are distant from the homeland, and the seas, especially during winter, are 

 extremely rough. Consequently, the talcing of this species Involves expensive operations in 

 terms of fuel and gear. The fish has little market value in Japan. Therefore, the continued 

 success of the fisheries Is dependent upon the re-establlshment of foreign markets. 



ySLLO'rfFIN TUNA. 

 Neothunnus macropterus (Schlegel) 

 Klhada, Ito-shibi, Hatsu, Hoshlbl, Klmejl (immature) 



1. General 



The yellowfln tuna has long been taken In Japsuieee waters during the summer months 

 by circling nets operated In shallow waters for small tuna, and more recently by vessels using 

 long lines to obtain black tuna, marlln, and swordfish. The species, however, did not attain 

 a position of in^iortance In Japanese fisheries until the decade Just prior to the recent war. 



Between 1931 and 1933 survey ships were sent to the South Seas areas under the spon- 

 sershlp of the Bureaui of Fisheries to locate new fishing grounds for the albacore. The sur- 

 veys indicated that the albacore was thinly scattered in this area. Tellowfin tuna, however, 

 was found to be abundant throughout the year in almost all parts of the tropical xone. Vari-! 

 ous fishing companies, with the Intention of beginning large-scale operations for this species, 

 continued Intenolve inveetlgations in all regions of the equatorial rone to determine tht; den- 

 sity of the populations and the best fishing grounds. 



Since the Japanese were only beginning to develop the South Seas fisheries on a 

 large scale Just prior to the beginning of World Wsir II, biological data on the yellowfln 

 tuna are almost negligible. The bulk of the Information herein reported has been supplied 



28 



P-6307 



