The bigeye thresher, Alopias supercilious,
is commonly caught as bycatch in pelagic longline fisheries targeting
swordfish. Little information is yet available on the biology of
this species, however. As part of an ongoing study, observers sent
aboard fishing vessels have been collecting set of information that
includes samples of vertebrae, with the aim of investigating age
and growth of A. supercilious. A total of 117 specimens
were sampled between September 2008 and October 2009 in the tropical
northeastern Atlantic, with specimens ranging from 101 to 242 cm
fork length (FL) (176 to 407 cm total length). The A. supercilious vertebrae
were generally difficult to read, mainly because they were poorly
calcified, which is typical of Lamniformes sharks. Preliminary trials
were carried out to determine the most efficient band enhancement
technique for this species, in which crystal violet section staining
was found to be the best methodology. Estimated ages in this sample
ranged from 2 to 22 years for females and 1 to 17 years for males.
A version of the von Bertalanffy growth model (VBGF) re-parameterised
to estimate L0, and a modified VBGF using a fixed L0 were fitted
to the data. The Akaike information criterion (AIC) was used to
compare these models. The VBGF produced the best results, with the
following parameters: Linf = 293 cm FL, k = 0.06 y–1 and L0 = 111 cm
FL for females Linf = 206 cm FL, k = 0.18 y–1 and L0 = 93 cm FL
for males. The estimated growth coefficients confirm that A. supercilious is
a slow-growing species, highlighting its vulnerability to fishing
pressure. It is therefore urgent to carry out more biological research
to inform fishery managers more adequately and address conservation
issues.