AGE AND GROWTH OF YELLOWFIN TUNA 



141 



tills to be true, the month of June may be selected 

 to represent the mean spawning period; thus, 

 the period from Juno A'— III to June A"— II 

 represents age group 0, or fish in their first year 

 of life, June A^— II to June N — I, age group I, 

 and so on. Owing to possible error in extrapolat- 

 ing the curves downward to the origin, the ages 

 thus assigned may not be quite correct. It is 

 felt, however, that ages through group IV cannot 

 be more than 1 year in error. 



Sella (1929) states that bluefin tuna hatched in 

 June weigh 300 to 500 grams by September. This 

 is a weight of approximately 1 pound and would 

 fall very close to our growth curve as calculated. 

 Kishinouye (1923) says of the common tunny 

 {Thunnus orientalis), "such small individuals are 

 found in August and in September. Some of them 

 grow to a length of 30 cm. or more. By next spring 

 they grow to a length of ca 60 cm. When 2 years 

 old they are about 1 meter in length and 1 1 kg. 

 in weight." These values when plotted on our 

 curve are not much in disagreement. Specimens 

 of yellowfin tuna have been taken during the 

 month of December in Hawaiian waters weighing 



2 pounds; these weights when plotted, also fail 

 very close to the curve of figure 9. Lengths and 

 weights by age groups may also be assigned from 

 figures 8 and 9 as has been done in table 2. 



Table 2. — Lengths and weights hy age groups of yellowfin 

 tuna taken in Hawaiian waters determined hy the method 

 of growth analysis of Walford (1946) 



DISCUSSION 



In fairly close agreement with this study are the 

 observations of Schacfer (1948) of the yellowfin in 

 the waters off Central America, where modes in 

 length-frequency distributions were observed at 

 approximately 60 cm., 85 cm., and 115 cm. These 

 modes, when plotted against the assumed age and 

 the month at which the fish were taken, showed a 

 close similarity to the age-length curve of the 

 Hawaiian yellowfin (fig. 10). The conclusion of 



AGE GROUP 



200 



150 





X 



o 



-J 



100 



L_„ 



5 10 



-m — 



20 



N-n- 



25 



30 35 40 



MONTHS 



N-I ! N 



MODAL GROUPS 



45 



50 55 60 

 N+I L 



65 70 

 N + H 



Figure 8.- 



-Cirowth curve of yellowfin tuna taken in Hawaiian waters fitted to lengths witli actual modal values in 



length superimposed. 



