Condini et al.: Age and growth of Epinephelus marginatus in the southwestern Atlantic 
315 
A 
Summer Autumn Winter Spring 
Figure 3 
Seasonal variation (A) in the mean marginal increment 
(solid lines) and sea-surface temperature (dashed line) 
and (B) in the frequency of occurrence of opaque (black 
bars) and translucent edges (gray bars) of otoliths 
of dusky groupers ( Epinephelus marginatus) caught 
at Carpinteiro Bank in the southwestern Atlantic by 
small-scale fisheries from 2008 to 2011 (summer: n=91; 
autumn: 48; winter: 10; and spring: 39). Error bars in 
panel A indicate ±1 standard error of the mean. 
for K when males (n=ll) were removed from the analy- 
sis (n=178, L to = 851.1 mm TL, A=0.153, to= _ l-06 years). 
The von Bertalanffy curve had the typical exponential 
asymptotic shape and allowed us to estimate that 70% 
of the asymptotic length of a fish was achieved at ap- 
proximately 8 years of age (Fig. 4; Table 1). 
A comparison of fish sizes at ages 3-6 between litto- 
ral sites and offshore sites showed that dusky groupers 
from the offshore Carpinteiro Bank were significantly 
larger than fish from the inshore rocky jetties locat- 
ed at the mouth of Patos Lagoon in the Rio Grande 
(F- 22.39, P<0.001; Fig. 5), with mean differences of 
11.7%, 19.6%, 16.7%, and 11% per year, respectively. 
Significant differences, however, were not observed for 
age 7. 
Discussion 
For otoliths to be used as reliable age indicators, they 
must display an internal structure of increments 
formed on a regular and predictable time scale. In 
dusky groupers, otoliths present well-defined growth 
increments that allow for age estimation at a relatively 
high precision. Translucent and opaque bands typically 
were formed during winter and summer, respectively, 
as determined through the analysis of marginal incre- 
ments. Marginal increment analysis, however, is not 
considered the most trustworthy technique for valida- 
tion of growth increments in otoliths (Campana, 2001), 
particularly where the temporal variation in environ- 
mental temperature is not strong enough to signifi- 
cantly influence fish metabolism. Therefore, to help in- 
crease confidence in validation, the seasonality of SST 
also was examined (Beckman and Wilson, 1995; Fablet 
et ah, 2011). As expected, the results from marginal in- 
crement analysis closely followed the seasonal fluctua- 
tions in SST — a finding that supports the hypothesis 
that opaque and translucent increments in the otoliths 
of dusky groupers may be formed on an annual basis. 
Moreover, the annual deposition of growth incre- 
ments in otoliths has been reported previously for the 
dusky grouper (Fennessy, 2006; Rehones et al., 2007) 
and other grouper species, such as the yellowedge 
grouper (E. flavolimbatus [Manickchand-Heileman and 
Phillip, 2000]), yellowmouth grouper (Mycteroperca in- 
terstitialis [Manickchand-Heileman and Phillip, 2000]), 
leopard grouper (M. rosacea [Diaz-Uribe et al., 2001]), 
orange-spotted grouper (E. coioides [(Grandcourt et 
al., 2005)], and island grouper (M. fusca [Bustos et 
ah, 2009]), indicating that it is an usual characteris- 
tic in epinephelids. The same pattern also was found 
for other long-lived fish species, such as the white- 
mouth croaker (Micropogonias furnieri [Haimovici and 
Umpierre, 1996]) and wreckfish ( Polyprion americanus 
[Peres and Haimovici, 2004]), that inhabit the south- 
western Atlantic. 
The first finding on the growth of the dusky grou- 
per in this study was the absence of males younger 
than 20 years or smaller than 760 mm TL — probably a 
result of protogynous hermaphroditism in this species 
(Heemstra and Randall, 1993; Andrade et al., 2003; Re- 
nones et al., 2010; Condini et ah, 2013). Under that 
reproductive strategy, dusky groupers are expected to 
first mature as females (at approximately 5 years old) 
and then change sex into males after approximately 7 
years old (Renones et ah, 2010). Results from the few 
studies that have examined age and gonads simultane- 
ously in dusky groupers indicate that males first ap- 
pear in dusky grouper populations at diverse sizes and 
ages. For example, younger sampled males varied from 
7 years (and -580 mm TL) in the Mediterranean Sea 
(Renones et al., 2007) up to 9 years (and -810 mm TL) 
off southeast Africa (Fennessy, 2006). We recognize that 
variables like sampling selectivity, environmental con- 
ditions, intraspecific competition, and fishing pressure 
may be related to the age and size at which sexual 
transition occurs. However, at this point, we have no 
further evidence to explain the very low abundance of 
male dusky groupers found in our study. 
