Table 1 Morphometric Data on Small Black Tuna 



Fish taken off Ajiro in Izu, 12-17-37. 



Consequently ring No. 1 (tj) was completed at body length (!« ) 43 cm, ring 

 No, 2 (ro) at 69 cm, ring No. 3 (t^) at 93 cm, r. at 118 era, r^ at 143 cm, and 

 r^ at 168 cm. Furthermore, if the body length increases at the same rate, it is 

 assumed that r^ will be completed at 190 cm, rg at 210 cm, r^ at 230 cm, and r^^ 

 at 250 en. 



The average condition factor for black tuna is 27.8 for fish of the year, 

 26.5 for fish in their 2nd year, and 25.0 for fish in their 3rd year. It is not 

 known for 4th-year fish, but it is 24,0 for the 5th year, 18.6 - 20.4 for the 

 6th year, 18.0 - 19,3 for the 7th year, and 18.6 for the 8th year. The condi- 

 tion factor becomes lower as the age of the fish increases. Taking this change 

 into consideration, an attempt was made to determine the range of length and 

 size and the rate of growth for each age group. (Table 3). The presence or ab- 

 sence in the catch of length and weight groups corresponding to these ranges 

 was used to check the accuracy of the determinations described above. 



The black tuna landed at the Numazu fish market in 1936 comprised three 

 groups, one very small one at 2.2 kq i;i CL8.2 lbs.] , and the others at 1.0 kan 

 (.8.27 lb8,3 and 0.4 kga C3.31 lbs, 3T"( Figure 2). Judging from the monthly 

 changes in the situation, the 2,2 kan (8,2 kg) group are probably in their 3x^ 

 year, the 1.0 kaq (3.75 kg) group are probably in their 2nd year, and the 0.4 

 kan (1.5 kg) group are probably fish of the year. At Numazu from April to June 

 quite a few schools of 6th-year fish which have their modes at 22 Jcgfi (82 kg) and 

 5,3 shaku (161 cm) are fished. The black tuna landed at Numazu in the spring 

 are mostly large fish, while fish of the year and 2nd-year fish predominate in 

 the fall. Fish of the year are taken during approximately half of the year, but 

 they account for U9% of the total catch. The 2nd-year fish which are taken 

 throughout the year account for 47/6, while the fish In their 3rd year which ap- 

 piear in small numbers in the spring comprise only A%» Consequently it is 

 thought that irtien black tuna enter their third year, they go out to pelagic wa- 

 ters and take up a migratory life. 



The black tuna landed at Aburatsu in the spring of 1937 included fish of 

 from 20 }taa C165.4 Ibs.J to over 80 ^ C66l,6 lb8,4 in weight, but the major 

 part of the catch was composed of groups having their modes at 34 kan [280,2 

 lbs.], 48 kaa ["397 Ibs.J , and 63 Jean C 521 Ibs.J , (Table 5), According to length 

 and weight data on the Citih landed in Ttay of that year, the average condition 

 factor can be considered to be 19, and consequently the lengths of the three 



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