1931o — This was a Tear of rather low surface tenperaturesc IfLthin 

 100 utiles both currents had three branches apiece » Water ten^eratures 

 at the kO to 100-B»Bter levBls showed oarkedly low readings, laeaning that 

 toe vertical distribution of the warn current was extremely thin, 



1932, — IMs was a year of generally low water teii5>eratureso Ihe 

 coastal streaa of the cold current heading southward from Erimosaki was 

 straag, and the third branch of the warm current did not pass north of 

 the Erimo station line. The Erimo line had lower temperatures in AiJgust 

 than in July, later temperatures on the Eriiao line were lower than those 

 on the Krishiro line (July - Novaaber). 



17. Oceanographic Conditions and the Fishing Situation 



a. Vertical Differential in later Tenmeratures and Fishing Conditions 



The results of observaticns aade in August, 10 to 50 miles south of 

 Xushiro, have been takan. In conparing the ten5)erature differentials for 

 the s-irfaoe and levels from 10 to 2X meters, the yearly changes are 

 greatest as between the surface and the 50-meter level, so this will be 

 taken as representative., If the total landings are taken for the amount 

 of the catch, the figure is likely to be affected by the number of boats 

 engaged in the fishery, while if we take the average catch per boat it 

 is likely to be controlled by the nuncer of cruises made or by temporary 

 changes in the nuoi)er of boats putting in to the port, and in either case 

 the figures will be lacking in accuracy = !Ilierefore we have taken the 

 average catch per cruise = Since in the case of the Kushiro boats one 

 cr-i.ise is generally equivalent to one night, this is probably the most 

 reasonable = 



^e result is that in years whan the veartical differential in 

 water tesperature is .qwaTi the fishing is good, and when the differential 

 is great the fishing is poor, 



Ihe phenoB»enon of a small vertical temperature differential off 

 tushiro means either that the wara current is not strong, so that its 

 force does not extend all the way to the E.ijriles, or that the cold cur- 

 rent is net strong, so that it does not reach to west of Kushiro, and 

 thus the ccmtact of the two cijrrents is in the waters near Kushiro = 

 In that case the center of the tuna schools is within the operating 

 radius of the boats based at Kushiro and consequently they find good 

 filling. Biis theory is also confirmed by the fact that when the vertical 

 differential in water temperatures at the Hoshappusaki line and at the 

 BriBOsaki line is cospared with the amount of the landings at Kushiro, 

 the correlation is not dosee 



!!hese facts are shown by table 9 and figure lie Ihe coefficient of 



correlation is r = -O^^l^ 



18 



