Table lo Proportions of large, raediiim, and small 

 skipjack m the catch (19314.) » 



The proportions -varied geographically j small fish being more 

 numerous than large ones on the fishing grounds north of Okinawa 

 and the opposite situation prevailing on the southern grounds 

 ■with large skipjack more plentiful. According to the report of 

 of Kagoshima Prefecture Fisheries E3q)eriment Station for 193Si' ,o 

 the average proportions of the three sizes in the catch for the 

 six years from 1928 to 1933 were 18^ large., 29^ medium;, and ^2% 

 smallo Ihese differ from the proportions in the 19 3i; catchj, but 

 this is thought to be due to the fact that -Uie distinction 

 between the three size categories is not drawn on any definite 

 standard rather than to a change in the composition. If we look 

 at the distribution (fig, 2) of body lengths of the skipjack 

 that are taken, we can perceive a small size group with its mode 

 at 14.6 cm, and a large size group having its mode at 63 cm, 



2° Age of skipjack o It is difficult to use the scales and 

 otoliths for determining the age of skipjack. There are rings 

 formed on the centra of the vertebrae. The number of these rings 

 is extremely great ^ some are broad and some are narrow, some are 

 perfectly and others imperfectly formed^ and they are densely or 

 sparsely distributed. Now some areas can be recognized through 

 the density or sparseness of the distribution, and on the bounda- 

 ries of each area where the rings are densely distributed there 

 are thick and perfectly formed representative rings. Using the 

 first to fifth vertebrae, measurements were made on the surface 

 of the cross section of the distance from the center of the centrum 



-' Kagoshima Prefecture Fisheries Experiment Stations Reports of 

 Cooperative Studies of the Skipjack Fishery s 358 ^ 1935 » 



35 



