The Catch of lunny^ Thurmus Orientalis {T< & S„)„ off KushirOj 

 Hokkaido, in Relation to the v'ertioal Difference in Water -''er.perature 



Synopsis £.\n English/ 



From the thirteen years catch statistics from 1924 to '36 and the 

 records of regular oceanographic observations ^ there is found a negative 

 correlation between the catch per boat of large tunny, weighing above 20 

 kwan (75 kg), and the difference in temperature at the surface and at 50 m 

 depth o 

 [end of English synopsi^ 



The author has previously investigated the relationship between 

 oceanographic conditions and the fishing for tuna v^j gff Kushiro in 

 Hokkaido, and has found that there is a negative correlation between the 

 weight of fish caught per boat per cruise and the vertical difference in 

 water temperature ^ ' o Since that time four years" more data have been 

 added (.fable 1), and it has been decided to make a reexamination of the 

 problem hereo 



Now when we consider the correlation between the number of largep 

 m.edium, v4J ^nd small fish^ which were not treated in the previous reportj 

 and the vertical difference in water temperature (Figure l)j, there is a 

 close correlation for, the large fish„ but for the medium and small fish 

 there is hardly anyo ^ ' According to Table 1 the large (and medium also) 

 clearly tend to decrease o This should be considered a diminution in the 



(1) 



(2) 

 (3) 



(4) 

 (5) 



Kawana^ Takeshi s On the Correlation Between Tuna Jxshing and 

 Oceanographic Conditions., Hokkaido fisheries Experiment Stationp 

 Reports of Fisheries Investigations (3l) 1934^ pp^SOo 



black tuna, kuroshibi , Th'jnnus orientalis (Temiainck & Schlegel)o 



The difference between the surface temperature and the temperature at 

 50 meters o Average for 10 =■ 50 miles off Kushiroo Augusto 



Large fish are over 20 kan \l kan s. 8.2 7 poundgj ^ medium between 10 

 and 20 kan , and small under 10 kano 



The coefficient of the correlation between the number of large fish and 

 the difference in water temperature is r a 0o4li0ol8o The coefficient 

 for the total of weight in kan of larger medium^, and small fish taken 

 per cruise and the difference in water temperature is r s 0o582 i Ool23, 

 so if instead of the number of large fish we take the number of kan or 

 take only the especially large fish among the large group^ it is thought 

 that we can obtain a far higher coefficient of correlationc However, 

 we do not know the number of kan weight for each of the groups of large, 

 small, and medium fish^ 



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