490 
Fishery Bulletin 96(3), 1 998 
length-frequency data were analyzed independently 
to derive estimates of the von Bertalanffy growth 
parameters for the bigeye thresher shark. Param- 
eter estimation with MULTIFAN was based on the 
maximum likelihood method which has been success- 
fully applied to various marine animals (Fournier et 
al., 1990; Haist and Porter, 1993; Bigelow et al., 1995; 
Pagavino and Gaertner, 1995). Growth curves de- 
rived from MULTIFAN and vertebral band counts 
are in good agreement for females but the former 
method yields larger size at age than the latter for 
males (Figs. 5 and 6). In addition, the similar values 
of VBGE parameters derived from MULTIFAN and 
vertebral band counts suggest that the age and 
growth estimation for bigeye thresher sharks in this 
study is reliable. The age classes (20 and 18) sliced 
by MULTIFAN from length-frequency data are less 
than those from vertebral reading (21 and 20). Small 
sample size and overlapping lengths at older ages 
may obscure length modes (Ernizi, 1990), and length- 
frequency estimates may be somewhat biased because 
of limitations of data and properties of length-frequency 
methods (Majkowski et al., 1987; Shepherd et al., 1987; 
Natanson and Cailliet, 1990). Thus, the vertebral 
method is considered more robust and the length-fre- 
quency analysis is used for verification only. 
Acknowledgments 
We thank S. J. Joung and two anonymous reviewers 
for helpful comments and suggestions and L. F. Chen 
for assistance in sample collection. The study was 
supported by the National Science Council, Repub- 
lic of China on contract NSC87-2313-B-019-021. 
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