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Fishery Bulletin 1 13(4) 
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Age (years) 
Age (years) 
Figure 6 
Growth curves estimated for (A) male and (B) female big- 
eye thresher (Alopias superciliosus ), collected between 2007 
and 2009 in the Atlantic Ocean by using models fitted with 
data from readings of vertebrae. Results are presented for 
the regular 3-parameter von Bertalanffy growth function 
(VBGF) model reparameterized to estimate size at birth 
(Lq), the VBGF model with a fixed Lq, the 3-parameter Gom- 
pertz growth function (GGF) model, and the GGF model with 
a fixed Lq (Lq=84 cm in fork length). The bottom panel (C) 
shows the growth curve estimated with the regular VBGF 
model, which was selected on the basis of the statistical 
goodness-of-fit as the best model for describing the growth of 
this species for both males and females and highlighting the 
differences in growth between the sexes. 
Of these studies, only in 3 of them was age verifica- 
tion attempted and in none of them was age validation 
attempted. Liu et al. (1998) verified a periodicity of 
one band (composed of one opaque ring and one hya- 
line ring) per year in bigeye thresher, and Liu et al. 
(1999) verified the same pattern for the pelagic 
thresher, in both cases using marginal increment 
analysis for populations of the northwestern Pa- 
cific Ocean. In the Atlantic Ocean, Mancini (2005) 
attempted marginal increment analysis and cen- 
trum edge analysis that weakly supported an- 
nual growth-band formation. Also in the Atlantic 
Ocean, preliminary centrum edge analysis (with 
limited samples from 6 months of each year) was 
conducted for bigeye thresher, also indicating a 
seasonal pattern in band formation (Fernandez- 
Carvalho et al., 2011). Therefore, although no age 
verification or validation was carried out in the 
study presented here, the assumption of a one- 
band-per-year periodicity for this species is rea- 
sonable in light of the few available studies. 
Furthermore, in age and growth studies of 
other species of lamniform sharks an annual 
band deposition has been validated. Natanson et 
al. (2002), who used vertebrae from recaptured 
oxytetracycline-injected porbeagle ( Lamna na- 
sus), proposed that vertebral band pairs are de- 
posited annually. On the other hand, Francis et 
al. (2007), when performing bomb radiocarbon as- 
says, found that the ages of older porbeagle (>20 
years) were underestimated from vertebral band 
counts, indicating that in some long-lived shark 
species, after a certain age, either growth bands 
are deposited on vertebrae in extremely narrow 
increments (and are impossible to recognize) or 
vertebrae cease to grow altogether. Nevertheless, 
Campana et al. (2002) and Francis et al. (2007) 
found that it was possible to validate that the 
visible growth bands were formed annually, with 
no gaps, for the first 20 years of life in porbeagle. 
The same periodicity of one band per year was 
validated for the shortfin mako (Isurus oxyrin- 
chus), both by bomb carbon chronology and by 
oxytetracycline marking (Ardizzone et al., 2006; 
Natanson et al., 2006). Finally, Wintner and Cliff 
(1999) stated that, although they could not deter- 
mine band periodicity by using marginal incre- 
ment analysis in the white shark ( Carcharodon 
carcharias ) off the coast of South Africa, annual 
deposition was indicated for one specimen that 
had been tagged with oxytetracycline and recap- 
tured. More recently, Hamady et al. (2014), us- 
ing bomb radiocarbon, also observed deposition of 
one band pair per year for white shark from the 
northwestern Atlantic Ocean up to 44 years old. 
On the other hand, Hamady et al. (2014) and An- 
drews and Kerr (2015) suggested that some age 
| underestimation for older white shark resulted 
from change in the rate of deposition of vertebral 
material or from the narrowing of the growth 
bands to the point of becoming unreadable. 
Therefore, there is a growing body of evidence that 
annual banding counts of growth bands in shark ver- 
tebrae may not provide an accurate estimate of maxi- 
mum age, given that long-lived sharks can become con- 
