Liu et al.: Age and growth of Alopias superciliosus 
487 
Age (yr) 
Figure 5 
The von Bertalanffy growth curve for female Alopias super- 
ciliosus. ( — = vertebral reading, — = length frequency. 
Discussion 
Joung (1993) noted that the ultimate band shown on 
the x-radiograph was difficult to read with a magni- 
fier. In our study, an image processing system was 
used to solve this problem. 
According to Branstetter (1990), growth coeffici- 
ents ( K) in VBGEs falling in the range of 0.05-0. 10/yr 
is a slow-growing species; 0.1-0.2/yr is a moderate- 
growing species; and 0.2-0.5/yr is a fast-growing spe- 
cies. In this study, K was estimated as 0.092/yr for 
females, 0.088/yr for males; these are in the slow- 
growth category. Cailliet et al. (1983) estimated the 
growth rate of the California common thresher shark 
(. Alopias vulpinus ) to be 0.108/yr, comparable to our 
study. Other slow-growing species include the great 
white shark ( Carcharodon carcharias) (K- 0.058/yr, 
Cailliet et al., 1986), bull shark (Carcharhinus 
leucasMK- 0.039/yr, Hoenig, 1979), dusky shark (C. 
obscurus) (K=0. 038-0. 039/yr, Natanson et al., 1995), 
sandbar shark (C. plumbeus) (K= 0.046/yr, Casey and 
Natanson, 1992, K=0. 057-0. 089/yr, Sminkey and 
Musick, 1995), scalloped hammerhead ( Sphyrna 
lewini) (K= 0.054/yr, Hoenig, 1979; i£=0.073/yr, Bran- 
stetter, 1987), and Squalus acanthias (A=0.037/yr, 
Jones and Geen, 1977). 
Most sharks form a vertebral band once each year 
i.e. Triakis semifasciata (Smith, 1984 ), Carcharhinus 
limbatus, C. brevipinus (Branstetter, 1987), C. 
plumbeus (Casey and Natanson, 1992), C. falciformis, 
Rhizoprionodon terraenovae, Galeocerdo cuvieri 
(Branstetter and Stiles, 1987), and Carcharodon 
carcharias (Cailliet et al., 1986). Some sharks form 
two vertebral bands per year, i.e. Sphyrna lewini 
Figure 6 
The von Bertalanffy growth curve for male Alopias super- 
ciliosus. ( — = vertebral reading, — = length frequency. 
(Chen et al., 1990), Galeorhinus japonicus (Tanaka 
and Mizue, 1978), Isurus oxyrinchus (Pratt and 
Casey, 1983), and Cetorhinus maximus (Parker and 
Stott, 1965). In the present study, although the time 
of band formation fell within a greater time range, 
the hypothesis of one band per year was validated 
by MI and Tanaka and Mizue’s (1979) method. Simi- 
lar results were reported for other species in 
Alopiidae, i.e. the common thresher sharks (Cailliet 
et al., 1983) and pelagic thresher sharks (Liao, 1996). 
Formation of shark vertebral bands may be related 
to water temperature, change of prey (Steven, 1975), 
shark migration, and mating (Pratt and Casey, 1983). 
Because bigeye thresher sharks have no fixed spawn- 
ing season, the band formation may not be closely 
related to mating. Elevated water temperatures in 
spring and summer are a possible factor in band for- 
mation. Jones and Geen (1977) documented that 
highly calcified bands represent summer growth of 
vertebral centra. The first vertebral band was as- 
sumed to be a birth mark in this study. Similar find- 
ings were reported for other species in Alopiidae, i.e. 
the common thresher sharks, Alopias vulpinus , 
(Cailliet et al., 1983) and pelagic thresher sharks, A. 
pelagicus, (Liao, 1996). 
In the present study, ages at maturity were esti- 
mated to be 12.3-13.4 yr for females (332-341 cm 
TL), and 9-10 yr for males (270-288 cm TL). How- 
ever, Gruber and Compagno ( 1981) reported younger 
ages at maturity but similar sizes in the Atlantic 
Ocean, 4.5 yr (356 cm TL) and 3.5 yr, females and 
males, respectively. Gruber and Compagno (1981) 
counted vertebral bands of a 287-cm-TL female and 
reported 8-11 bands, 2 + yr. This length falls in the 
