dj.rect proportion to the catch ratio and calculate the catch 

 rate for Japanese waters on the basis of the proportion of 

 recaptures on the grounds south of Ogasawaray we get olO = o30o'*»* 



The above value does not seem too unsuitable as a catch rate 

 for sbipjack in view of the rates of dO for black tuna and o29 

 for yellowfin that have been deduced previouslyoS/ 



To suininarize the above: (1) After the skipjack have spent 

 their juvenile period in the region of the South Sea Islands, 

 they make a great migration beginning in early summer along the 

 Kuroshio through the waters off Japan proper,, part of them as 

 fish of age-groups II and IV but most of them as age-group III„ 

 After reaching the waters off Northeastern Japan., they turn 

 back south with the autumn and thereafter appear to remain in 

 southern water Sj (2) their survival rate can be considered to be 

 about o5U and their catch i5ate between olO - o30o 



*mt According to Kimura V "the average numbers of fish caught 

 1937-39 were ^jUiO^OOO in Satsunan^ 6j,590yOOO in Kinan, 

 ^yliliOjOOO in Izu=Ogasawaras and 29 $066,000 in the Northeast, 

 so the proportions for the fishing grounds Sat sunang Kinan j 

 Izu-OgasawarasNortheast are 5UU ? 6$9 j Skk s 2,906 - o t t c^ 



But the proportion caught on the fishing grounds from Ogasawara 

 south is ol3ii 30 that from the waters adjacent to Japan., 

 including the Northeast, is ol3U x 9 .| „3o<, if an inference 



U 



is drawn on the basis of the Satsunan and Izu=Ogasawara areas, 

 leaving out Kinan, where so few fish were released^ o03i4- x 



£ k olOo Consequently, if we assume that the skipjack in 

 3 " 



the waters adjacent to Japan move northward from Satsunan to 

 the Northeast, it means that the catch rate in the waters 

 adjacent to Japan proper is ,10 - o30o 



31 



