506 
Fishery Bulletin 99(3) 
Table 2 
Observed and back-calculated mean fork length (FL, cm) at age for the western Pacific bigeye tuna, Thunnus obesus. (“ — ” means 
there were no data owing to vascularization at core area). Numbers in normal print represent the mean back-calculated fork 
lengths; numbers in parentheses represent the number of specimens for which the specified ring was readable. 
Age 
(yr) 
n 
Observed 
mean FL 
(cm) 
Annulus number 
I 
II 
III 
IV 
V 
VI 
VII 
VIII 
IX 
X 
1 
8 
67.9 
57.0 
(8) 
2 
79 
93.7 
50.0 
80.8 
(29) 
(79) 
3 
329 
115.3 
52.4 
85.8 
102.9 
(69) 
(265) 
(329) 
4 
413 
131.7 
51.9 
82.7 
107.1 
121.2 
(19) 
(162) 
(384) 
(413) 
5 
188 
145.9 
— 
80.9 
112.1 
122.8 
135.8 
(14) 
(77) 
(184) 
(188) 
6 
59 
158.4 
— 
— 
115.5 
126.6 
138.2 
149.5 
(3) 
(36) 
(58) 
(59) 
7 
11 
169.3 
— 
119.5 
130.1 
142.6 
152.1 
161.8 
(1) 
(5) 
(9) 
(11) 
(11) 
8 
6 
174.7 
— 
— 
— 
123.8 
139.6 
150.8 
161.0 
172.1 
(1) 
(5) 
(6) 
(6) 
(6) 
9 
3 
178.5 
- 
— 
— 
121.0 
129.2 
142.0 
154.2 
169.2 
174.2 
(1) 
(2) 
(2) 
(3) 
(3) 
(3) 
10 
2 
188.5 
- 
— 
— 
— 
138.2 
148.4 
162.5 
174.1 
180.6 
186.2 
(1) 
(2) 
(2) 
(2) 
(2) 
(2) 
Total 
1098 
(125) 
(520) 
(794) 
(640) 
(263) 
(80) 
(22) 
(11) 
(5) 
(2) 
Weighted back-calculated 
mean FL (cm) 
52.1 
83.9 
105.9 
122.0 
136.6 
149.8 
160.6 
171.7 
177.4 
186.2 
Growth increment (cm) 
- 
31.9 
21.9 
16.2 
14.6 
13.1 
10.9 
11.1 
5.7 
8.7 
Table 3 
Growth parameters obtained by the Ford-Walford plot method and the nonlinear regression method for the bigeye tuna from the 
western Pacific Ocean. 
Parameter 
Ford-Walford plot 
Nonlinear regression 
Male 
Female 
Pooled 
Total 7 
Total 7 
n 
278 
180 
458 
1098 
1098 
K 
0.1789 
0.191 
0.1842 
0.185 
0.2011 
220.6 
211.4 
216.1 
226.4 
208.7 
*0 
-0.5566 
-0.4592 
-0.5266 
-0.4465 
-0.9906 
1 Male, female, and sex-unknown combined. 
lucent rings to slower growth periods, whereas the wide, 
opaque rings were attributed to periods of fast growth. The 
spawning season of bigeye tuna in the western Pacific is 
between February and September and peaks from March 
to June (Sun, et al. 4 ), the period that we found to coincide 
4 Sun, C. L., S. L. Chu, and S. Z. Yeh. 1999. Note on reproduc- 
tion biology of bigeye tuna in the western Pacific. SCTB12/WP/ 
BET-4, 6 p. Twelfth meeting of the standing committee on tuna 
and billfish; Tahiti, French Polynesia, June 14-23, 1999. Oce- 
anic Fisheries Programme, Secretariate of the Pacific Commu- 
nity, B.P.D5, 98848 Noumea, New Caledonia. 
