482 
Age and growth estimates of the 
bigeye thresher shark, 
Alopias superciliosus, 
in northeastern Taiwan waters 
Kwang-Ming Liu 
Po-Jen Chiang 
Che-Tsung Chen 
Department of Fishery Science 
National Taiwan Ocean University 
Keelung 20224, Taiwan 
E-mail address (for K.-M. Liu): kmiiu@ntou66.ntou.edu.tw 
Abstract.-A g e and growth of Alo- 
pias superciliosus in waters off north- 
eastern Taiwan were determined from 
vertebral band counts on 321 specimens 
(214 females and 107 males) and veri- 
fied with a length-frequency analysis 
of 821 specimens (491 females and 330 
males). Growth bands formed once a 
year according to marginal increment 
analysis and numbered up to 21 and 
20 bands for females and males, respec- 
tively. The parameters of von Berta- 
lanffy growth equations estimated from 
vertebral readings were the following: 
asymptotic precaudal length (L^) = 
224.6 cm, growth coefficient ( K) = 0.092/ 
yr, age at zero length (f 0 ) = -4.21 yr for 
females; and = 218.8 cm, K = 0.088/ 
yr, t 0 = -4.24 yr for males. The ages at 
maturity were estimated to be 12.3- 
13.4 yr for females, 9-10 yr for males. 
The largest female aged from vertebrae 
was 20 yr old, the largest male 19 yr old. 
Length-frequency analysis supported our 
vertebral ageing estimates. 
Manuscript accepted 13 November 1997. 
Fishery Bulletin 96:482-491 (1998). 
The bigeye thresher shark, Alopias 
superciliosus (Lowe), is circumtrop- 
ical and subtropical in distribution 
(Compagno, 1984). It is found over 
the continental slope around Taiwan 
and is abundant at depths of 40- 
100 m in waters off northeastern Tai- 
wan (Fig. 1). Based on daily catch 
data (1989-1994) from Nan Fan Ao 
fish market, near Suao, estimates of 
annual landings of bigeye threshers 
in number of fish are about 3300, and 
220 metric tons (t) in weight, 13% of 
the total annual shark catch. 
Biological information, particu- 
larly on reproduction, for bigeye 
thresher is abundant (Nakamura, 
1935; Cadenat, 1956; Bass et ah, 
1975; Stillwell and Casey, 1976; 
Gruber and Compagno, 1981; Gil- 
more, 1983, 1993; Moreno and Mo- 
ron, 1992; Chen et al., 1997) but 
little is known about age and 
growth. Other than Gruber and 
Compagno’s (1981) preliminary es- 
timation on the age and growth of 
bigeye threshers, no studies have 
been published. Accurate age struc- 
ture of stocks is essential for stock 
assessment and fishery manage- 
ment. This study provides the first 
information concerning age and 
growth of bigeye threshers from 
waters off northeastern Taiwan. 
Age and growth, from vertebral band 
counts, were verified with length- 
frequency analysis. 
Materials and methods 
Thresher sharks caught in north- 
eastern Taiwan waters by commer- 
cial longlines were sampled at Nan 
Fan Ao fish market, from Septem- 
ber 1993 to October 1994. 
Precaudal length (PCL), fork 
length (FL), and total length (TL) 
(in cm) were measured and weighed 
at the fish market. Because caudal 
fins of bigeye thresher sharks are of- 
ten damaged, PCL is used through- 
out this paper, unless otherwise 
noted. After specimens were gutted, 
a total of 371 (245 females and 126 
males) precaudal vertebrae were 
removed for age determination. Ver- 
tebrae located under the first dor- 
sal fin are often used for age deter- 
mination (Casey et al., 1985; Bran- 
stetter and Stiles, 1987; Chen et al., 
1990); samples from two specimens 
( 166 cm and 171 cm PCL) were used 
to compare variations in banding 
patterns from centra at different 
locations along the vertebral col- 
umn. Precaudal vertebrae had the 
same band counts as those under 
