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Fishery Bulletin 113(4) 
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Locations where the vertebrae of bigeye thresher (Alopias superciliosus) were collected between 
September 2007 and December 2009 for use in estimation of the age and growth of this species 
in the Atlantic Ocean. Open circles represent females and black triangles indicate males. The 
horizontal line at 5°N represents the parallel used by the International Commission for the 
Conservation of Atlantic Tunas (ICCAT) to separate the stocks in the Southern and Northern 
Hemispheres and was, therefore, also used in this study as the boundary between samples of the 
North and South Atlantic Ocean. 
(n=117) were used by Fernandez-Carvalho et al. (2011) 
to estimate initial growth curves, and a relationship 
between size of specimen and size of vertebrae, for 
the region of the Cape Verde Archipelago in the tropi- 
cal northeastern Atlantic Ocean. These samples from 
the Cape Verde Archipelago were also included in this 
study (and used as a reference set to model the growth 
of this species for a wider area in the Atlantic Ocean) 
because the readers were the same, our sample size 
was small, and because it was desirable to increase our 
sample area. 
The sexes of specimens were determined and fork 
lengths (FLs) measured in a straight line (in centime- 
ters) onboard ship. A section of vertebrae was removed 
from the area below the anterior part of the first dorsal 
fin. Each of these samples was kept frozen on the ves- 
sel and during land transport until it was processed in 
the laboratory. One vertebra was removed from each 
sample and processed by following the method de- 
scribed in detail in Fernandez-Carvalho et al. (2011). 
First, scalpels were used to remove the soft tissue, 
and then the vertebrae were immersed in a solution 
of 4-6% sodium hypochlorite (commercial bleach) for 
10-20 min, depending on the size of the vertebrae. The 
vertebrae were mounted on a microscopic slide with ei- 
ther thermoplastic cement or a synthetic polymer glue 
and sectioned sagittally with a Buehler 4 (Lake Bluff, 
IL) low-speed saw, with 2 blades spaced approximately 
0.5 mm apart. For a better visualization of the growth 
band pairs, the sections were stained with crystal vio- 
let solution (Sigma-Aldrich Co., St. Louis, MO) for 5-15 
min depending on the size of the vertebrae (Fig. 2). 
Once dried, the sections were mounted onto microscope 
slides with Cytoseal 60 (Thermo Fisher Scientific Inc., 
Waltham, MA). Finally, growth bands were examined 
under a dissecting microscope with transmitted white 
light. 
Age estimation and comparison of age readings 
A preliminary reading of a reference set (n=117) of ver- 
tebrae (from the full set of 546 vertebrae) was complet- 
ed to familiarize the readers with the banding pattern 
of this species. Then, this reference set was indepen- 
dently read by 2 readers 3 times to maintain quality 
control and precision of the readings (see Fernandez- 
4 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the authors or the National Marine Fisheries Service, NOAA. 
