Fernandez-Carvalho et al.: Age and growth of Alopias superciliosus in the Atlantic Ocean 
469 
bigeye thresher in the Atlantic Ocean, recently pro- 
hibited the retention and commercialization of bigeye 
thresher caught in tuna fisheries, recommending the 
release of live specimens when they are accidentally 
captured and requiring that both incidental catches 
and live releases be recorded in accordance with IC- 
CAT data reporting requirements (ICCAT 1 ). However, 
simply releasing caught specimens may not be enough 
to protect this species because 51% of bigeye thresher 
that are caught in the pelagic swordfish longline fish- 
ery have been estimated to have been released dead 
(Coelho et ah, 2012). 
Although pelagic sharks are affected by fishing, they 
remain among the least studied elasmobranchs because 
of their highly migratory nature and because the lack 
of information on these species poses particular diffi- 
culties for their management and conservation (Pikitch 
et ah, 2008). Knowledge of the life history of a species 
is essential for successful management of that species. 
In particular, age and growth studies provide informa- 
tion for estimating important biological variables, such 
as growth rates, natural mortality, productivity, and 
longevity of a species (Campana, 2001; Goldman, 2004, 
Goldman et ah, 2012). Understanding these biological 
parameters is important for assessment of the current 
status of shark populations and for prediction of how 
their population size and structure may change over 
time (Goldman et ah, 2012). In fact, it is crucial that 
age determinations be precise and accurate because an 
erroneous understanding of the population dynamics of 
a species may lead to serious bias in stock assessment, 
bias that frequently results in overexploitation (Gold- 
man et ah, 2012). 
Because elasmobranch species are characterized by 
slow growth rates (e.g., Coelho and Erzini, 2002) and 
a low reproductive potential (e.g., Coelho and Erzini, 
2006), they are extremely vulnerable to fishing pres- 
sure, and overexploitation occurs with even relatively 
low levels of fishing-induced mortality (Smith et al. , 
1998). Therefore, study of their life history, including 
age and growth, is more critical than it is for more 
resilient species (Goldman et al., 2012). 
In most age and growth studies of teleost fishes, 
otoliths or scales are used; however, vertebrae are 
the most widely used structures for age determina- 
tion in elasmobranch fishes, but dorsal spines (usually 
in Squalidae) and caudal thorns (in skates) have also 
been used (Campana, 2001; Caillet and Goldman, 2004, 
Goldman, 2004; Coelho and Erzini, 2007; Moura et al., 
2007; Coelho and Erzini, 2008). In general, an annual 
vertebral growth ring is composed of one opaque band 
(representing faster summer growth) and one translu- 
cent band (representing winter growth), although the 
periodicity of deposition may be different for some elas- 
1 ICCAT (International Commission for the Conservation of 
Atlantic Tunas). 2009. Recommendation by ICCAT on the 
conservation of thresher sharks caught in association with 
fisheries in the ICCAT convention area. ICCAT Recomman- 
dation 09-07, 1 p. [Available at website.] 
mobranchs (Cailliet and Goldman, 2004; Caillet et al., 
2006). It should be noted that the opacity and trans- 
lucency of these bands varies depending on the light 
source used (transmitted versus reflected) and method 
of preparation of the vertebrae (Goldman et al., 2012). 
Because the pattern of calcification can vary greatly 
within and among taxonomic groups of elasmobranchs, 
a species-specific approach is necessary for studies of 
their age and growth; it cannot be assumed that the 
banding pattern of one species is representative of an- 
other (Ridewood, 1921; Goldman, 2004). 
In the case of bigeye thresher, little biological in- 
formation is currently available, especially for this 
species in the Atlantic Ocean, probably because of its 
low prevalence numbers in longline catches (Mejuto 
and Garces 2 ; Mejuto 3 ; Castro et al., 2000; Berrondo et 
al., 2007; Mejuto et ah, 2009). Gruber and Compagno 
(1981) explored the age and growth of this species 
on the basis of a limited data set of mostly museum 
specimens captured in the Pacific and Atlantic oceans. 
Fernandez-Carvalho et al. (2011) estimated growth 
parameters for a specific region of the tropical north- 
eastern Atlantic Ocean. Mancini (2005) studied the age 
and growth of bigeye thresher caught by longliners in 
the southwestern coast of Brazil. In the Pacific Ocean, 
an extensive age and growth study was carried out by 
Liu et al. (1998) in the western central Pacific region 
(Taiwan). In addition, some reproductive parameters 
have been reported for the Pacific Ocean (Gruber and 
Compagno, 1981; Gilmore, 1993; Chen et al., 1997) and 
Atlantic Ocean (Moreno and Moron, 1992; Mancini, 
2005). The objective of this study was to improve the 
biological information for bigeye thresher by providing 
new knowledge about the age and growth parameters 
for this species throughout the Atlantic Ocean. 
Materials and methods 
Sampling and processing 
All samples were collected by fishery observers, from 
the Portuguese Institute for the Ocean and Atmosphere 
onboard Portuguese commercial longline vessels that 
targeted swordfish in the Atlantic Ocean. Vertebral 
samples were collected only from bigeye thresher 
specimens that were retrieved already dead when the 
longline was hauled aboard. From September 2007 
to December 2009, vertebral samples from 546 shark 
were collected throughout the Atlantic Ocean, between 
latitudes 38°N and 35°S (Fig. 1). Some of these samples 
2 Mejuto, J., and A. G. Garces. 1984. Shortfin mako, Isurus 
oxyrinchus, and porbeagle, Lamna nasus, associated with 
longline swordfish fishery in NW and N Spain. ICES Coun- 
cil Meeting (C.M.) Documents 1984/G:72, 10 p. 
3 Mejuto, J. 1985. Associated catches of sharks, Prionace 
glauca , Isurus oxyrinchus , and Lamna nasus, with NW and 
N Spanish swordfish fishery, in 1984. ICES Council Meet- 
ing (C.M.) Documents 1985/H:42, 16 p. 
