(5) Autumn low pressure areas and sea conditions and the 

 skipjack fishing grounds of the Northeastern Sea Area 



Wlien the autumn winds begin to blow and the season of the 

 "descending" skipjack starts^ the speed with which the center 

 of gravity of the fishing grounds shifts to the southward is 

 rapid directly after the passage of a low^ but otherwise it 

 shifts slowly c Every time an autumn low passes over this sea 

 area the upper and lower layers of water are either mixed 

 together by the stirring action of the windj or countercur rents 

 are caused by aar cooling;, or cold water from the lower levels 

 is brought up by gyrals =~ at any rate, this mixing action 

 results in a sudden decrease in the temperature di.fferential 

 of the upper and lower layers o In this way the water tempera- 

 ture of the fishing grounds is made tc drop abruptly in steps 

 of 1° - 2°j and with this change the area of the fishing 

 grounds shrinks and the fishing season draws to a close o The 

 year 1932 provided the most severe example of the coming of 

 these autumn lows shortening the fishing season and cutting 

 down the total catch,, This southward retreat of the favorable 

 water temperatures and the corresponding development of the 

 cold currents (flowing southwest) bring the southward movement 

 of the saury o 



(6) Data for the prediction of the abundance or scarcity 

 of skipjack in the Northeastern Sea Ai"ea 



a« There is a tendency for the catch rates in the North- 

 eastern Sea Area to be poor in years when the winter 

 and spring temperatures are low and good in years 

 when temperatures are higho 



Note; In the Zunan and Satsunan sea areas catch rates 

 tend to be good in years with low winter and spring tempera- 

 tures, and poor in years with liigh temperatures o 



bo The trend of ihe catch in the Northeastern Sea Area 

 does not necessarily coincide with the rise and 

 decline of the catch in the Satsunan and Zunan feea 

 areas 



Notes The yearly variations in the catches of the Satsunan 

 and tlie Zunan areas resemble each other o 



Co In the Northeastern Sea Area the abundance or scarcity 

 for the season can to a certain extent be estimated 

 from the amount of fish taken up to the end of June, 



13 



