unquestionably change with the changes in the movements of sardines and 

 squid dependent on the changes in oceanographic conditions o The increasing 

 size of the fish as one goes farther north means that one must take into 

 consideration the fact that the larger tuna are, as set forth in a later 

 section, more adaptable to water temperatures than the medium and small 

 fish, together with the fact that the larger the fish the greater is its 

 speed of raigrationo 



b. Favorable Tenperatures 



Time of first catch and water tenperatures 



If we present the surface water temperatures measured by survey vessels 

 at the time of the first catches, we find that on July 2, 1926, 30 to ^0 

 miles south of Erimosaki, when a school of large t\ma was sighted, it was 

 12o2°C to 13.6°C, and on July 11, 1927, 20 miles south of Urakawa the 

 Sanyo Maru, which had sighted a school of large tuna, found a temperature 

 of 13.5°C. Similar records taken by fishing vessels are lloO°C for the 

 place where the first catch was made on June 20, 1927, 60 miles southwest 

 of Erimosaki (off Shiriyasaki), l6oO C where the first catch was made on 

 June 27, 1928, 3$ miles southwest of Erimosaki, and lii„$°C where the first 

 catch was made on June 27, 1929, 30 miles southwest of Erimosaki o Thus 

 the water temperatures on the grounds where the first catches are made, 

 which in normal years are about 30 miles south of Erimosaki, are about 

 lii°Co The first catches are made at higher temperatures in warmer years 

 and at lower ones in colder years, but a zone of water of over 12°C 

 should be sought » 



Peak season and water temperatures 



There have been few years in which the fishing grounds off Kushiro 

 have shown water temperatures higher than 20oO°C, and the lowest recorded 

 is about 13.0°C, like the temperatures of 1926o Generally the range 

 is llioO°C to l8,0°Co Ten miles south of Hitokappu on Etorofu Island 

 on August 2U, 1927, the SanyC Maru sighted a large school of tuna in 

 water of 9<.9°C, and on September 2k of the same year kO miles south of 

 Hitokappu a large school of tuna was sighted in water of 12o5°Co Since 

 1927 was a warm year, in normal years the fish must move northward in 

 the Chishima area through zones of water of 10oO°C or colder o 



Aid of the season and water temperatures 



Although there are no observations of water tenperatures at the end 

 of the season, there must be times when good fishing is found at 

 ten5)eratures of around 10.0 Co 



11; 



