age-groups IV and above, so if we seek the survival rate from the 

 con?30sition at Palau during the autumn peak season by the method 

 previouslyZ/ used for the yellowtail^ it comes out „Sho^ 



For those species of the tunas which have roughly the same 

 range of distribution and which resemble each other in making 

 large seasonal migrationSj for which estimates have hitherto been 

 made J the survival rate is o75 for the black tuna, o57 for the 

 yellovrfin tuna^ and 066 for the albacore£/,, but if we take into 

 consideration the fact that the highest age-group in the catch 

 is Vl3/ for the skipjack, while it is X for the black tuna,, IX 

 for the yellowfin^ and VIII for the albacore^ we can probably say 

 that the value obtained above as the survival rate for the skipjack 

 is fairly reliable „ 



Effective clues for the deduction of the catch rate are found 

 in the records of tagging experiments » Mth the skipjack^ 318 

 fish were released from 193h to 1939 in the Satsunan area, 10 in 

 the Kinan area, and 162 in the Izu archipelago of which 7? Ij 

 and 2 respectively were recaptured within 20 days and close to 

 the point of release 5, while of 92 fish released in the Ogasawara 

 area two were recaptured 53 and $Q days later in the Northeastern 

 regiono In the same period^ I53IO fish were released in the 

 Northeast, but not one of them was recap tiired-^S/o Accordingly, 

 the proportions recaptured are o022 for Satsunan, dOO for Kinan, 

 0OI2 for Zunan, and 0OOIJ4 for Ogasawara^Northeasto Since not one 

 of the fish released in the Northeastern Sea Area was captured, 

 it can be seen that the nearer the fish are to the northern 

 extremity of their migration, the stronger is the effect of the 

 handling in connection with capture and taggingo It is thought, 

 therefore, that it is inappropriate to use the rate of recapture 

 to establish the catch rate for Ogasawara-Northaasto Then if we 

 divide the number of fish taken by the number- that mi^ate into 

 the area to get for each fishing ground a numerical value in 



.>M» larEP », /^ 



'^ If we take £> as the survival rate, then ^j^^^g - ^~r 



I0I9 

 2ol9 



2^M. - o^ky 



^ Tauchi, Morisaburo§ On the Stock of Yellowtailo Bullo Japo 

 Socc Scio Fisho 9 (U)? 19hO. 



W The records of taggings are in Reports of Oceanographic 



Investigations (5U), (55), (57), (^8 .59 ,61 ,63 ,65 , 

 and the records of recapture are in (54)9 (57;.9 (59;, (>oi;, (.ojj^o 



30 



