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Fishery Bulletin 96(3), 1 998 
rable to the results from MI. This finding indicates that 
one band is formed per year by bigeye thresher sharks. 
Chen et al. (1997) estimated PCL at birth for the 
bigeye thresher shark to be 73.7 cm, similar to our 
estimated mean length at the birth mark formation 
(69.6 cm). Because no growth band was found for em- 
bryos, the first band was assumed to be a birth mark. 
For comparison with other literature that reported 
total length (TL), PCL and FL can be converted to 
TL with the following equations: 
female: TL = 15.3 + 1.81PCL 
TL = 13.3 + 1.69FL 
male: TL = 15.1 + 1.76PCL 
TL = 26.3 + 1.56FL 
(r 2 =0.90, n=177); 
(r 2 =0.89, n = 177); 
(r 2 =0.88, n=6 8); 
(r 2 =0.81, ;j=6 8). 
The relations between body weight and total length, 
and body weight and precaudal length are described 
as follows: 
female: W = 6.87 x 10" 5 PCL 2 769 (r 2 =0.88, n=421); 
W = 1.02 x 10~ 5 TL 2 78 (r 2 = 0.90, n=175); 
Figure 4 
Monthly change of marginal increment of male Alopias 
superciliosus. Numbers indicate sample size and vertical 
bars indicate +SE. 
male: W = 9.93 x 10~ 5 PCL 2 685 (r 2 =0.83, n=187); 
W = 3.73 x 10- 5 TL 2 - 57 (r 2 = 0.80, «=65). 
The parameters of VBGE estimated from band counts 
for females and males are given in Table 2 and the 
VBGE in PCL (cm) are 
female: L t = 224.6 ( 1 - e -oo92«+4.2p). 
male: L t = 218.8 ( 1 - e -o.o88<f+4.24)) (Figs. 5j 6) 
With the above equations, the asymptotic PCL can 
be converted to asymptotic TL as 422 cm for female, 
385 cm for male. The VBGE in weight (kg) can be 
expressed as follows: 
female: W t = 222.8 (i-*-o.092(t + 4.2i))2.769; 
male: W, = 190.5 (i^-0.088(t + 4.24) )2 .685. 
Female bigeye threshers are estimated to mature 
between 175 and 180 cm PCL (Chen et al., 1997), 
78% and 80% of asymptotic length, and between 12.3 
and 13.4 yr old. The largest immature female was 
185 cm PCL, 14.6 yr.; the smallest mature female 
was 154 cm PCL, 8.4 yr. Males mature between 150 
and 155 cm PCL (Chen et al., 1997), 69% and 70% of 
asymptotic length, and between 9 and 10 yr old. The 
largest immature male was 171 cm PCL, 13 yr; the 
smallest mature male was 138 PCL, 7 yr (Chen et 
al., 1997). 
The length-frequency histograms for both sexes 
used in the analysis and results of the best data fits 
were plotted in Figures 7 and 8, females and males, 
respectively. In the best fits, age classes 18 and 20 
were obtained for females and males, respectively. 
The estimated modes followed the length-frequency 
line closely and overlay the peaks well (Figs. 7 and 
8). For estimated mean lengths at age of female and 
males see Table 3. The parameters of VBGE were 
estimated as L to = 230.5 cm, K = 0.092/yr, t Q = -3.69 
for females, and L m = 224.4 cm, K = 0.087/yr, t Q = 
-4.61 for males; these parameters were similar to 
those from vertebral band counts (Table 2). 
Table 2 
Comparison of the von Bertalanffy parameters derived from vertebral band count and length-frequency analysis of Alopias 
superciliosus. 
Male 
Female 
Parameters 
K 
to 
n 
L m 
K 
*0 
n 
Vertebral reading 
218.8 
0.088 
-4.24 
107 
224.6 
0.092 
-4.21 
214 
Length-frequency 
224.4 
0.087 
-4.61 
330 
230.5 
0.092 
-3.69 
491 
