Fernandez-Carvalho et al.: Age and growth of Alopias superciliosus in the Atlantic Ocean 
479 
Piercy et al., 2007; Coelho et al., 2011; Gervelis and 
Natanson, 2013). Therefore, it is advisable to use the 
growth parameters obtained specifically for each sex, 
instead of the parameters obtained for the sexes com- 
bined. The growth curves of both sexes were similar 
until age 10, after which males exhibited a consider- 
able reduction in growth rate, and females showed a 
straighter growth curve. 
Future studies of this species should include more 
samples from the South Atlantic Ocean, and especially 
of the smaller and larger length classes, because some 
difficulties occurred when comparing results for sam- 
ples from the 2 hemispheres. These difficulties were 
due to not only the relatively smaller sample size for 
the Southern Hemisphere but also the fact that most 
samples from the North Atlantic Ocean were collected 
around the Cape Verde Archipelago, where the majority 
of the specimens tended to be small (size distribution: 
North Atlantic Ocean, 102-242 cm FL; South Atlantic 
Ocean, 128-265 cm FL). The differences observed in 
the growth of bigeye thresher samples from the North 
and South Atlantic Ocean, especially for females, indi- 
cate slower growth rates for the southern population. 
However, because this species seems to be segregated 
by size and sex, the differences in the VBGF parame- 
ters may also be caused by the possibility that we mod- 
eled 2 parts of the same population. The differences 
do not necessarily indicate the existence of 2 distinct 
populations. Future studies of this species should ad- 
dress the genetic structure and population delimitation 
in the Atlantic Ocean. 
Accurate age information is vital for obtaining qual- 
ity estimates of growth, which in turn are essential for 
successful and sustainable fisheries management. The 
growth parameters determined in this study and pre- 
sented here are the first estimates for bigeye thresher 
that cover an extensive area in the Atlantic Ocean, and 
they now can be incorporated into stock assessment 
models to improve science-based fishery management 
and conservation initiatives. The slow growth rates de- 
termined in our study indicate a high susceptibility to 
fishery-induced mortality for this species and, there- 
fore, the importance of protecting it. Although the big- 
eye thresher is managed currently and some conserva- 
tion measures are already in place (ICCAT 1 prohibits 
onboard retention), its slow growth rates, together with 
its high mortality at haulback, indicate the need for 
further studies to help implement additional conser- 
vation measures designed to prevent increased fishing 
mortality and population declines. 
Acknowledgments 
This study was funded by projects THRESHER (Por- 
tuguese Foundation for Science and Technology [FCT] 
proj. PTDC/MAR/1099 15/2009), SELECT-PAL (PRO- 
Mar proj. 31-03-05-FEP-l), and the EU Data Collection 
Framework. We thank the skippers and crews of sev- 
eral Portuguese longliners, as well as the technicians 
(S. Amorim, M. Cerqueira, S. Gois, I. Ribeiro, J.R. Tata, 
and C. Barbosa) for collecting samples. We are grateful 
to G. Burgess and A. Piercy (Florida Museum of Natu- 
ral History) for their help with processing vertebrae 
and to J. Hoenig (Virginia Institute of Marine Science) 
for providing the R code and helping with the inter- 
pretation of the hexagon plots. J. Fernandez-Carvalho 
was supported with a doctoral grant from FCT (grant 
ref: SFRH/B D/60624/2009), and R. Coelho was support- 
ed by an Investigador-FCT contract funded by the EU 
European Social Fund and Programa Operacional Po- 
tencial Humano (ref: IF/00253/2014). We also thank A. 
Andrews (NOAA Fisheries) and 2 anonymous review- 
ers for their comments and suggestions that greatly 
improved this manuscript. 
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