Condini et al : Age and growth of Epinephelus marginatus in the southwestern Atlantic 
313 
colonized by bryozoans, sponges, crustaceans, poly- 
chaetes, and coralline algae (Buchmann et al., 2001). 
Located approximately 30 km offshore from the city of 
Rio Grande (32° S), this bank is likely the most aus- 
tral region where the dusky grouper is commercially 
exploited. 
Otolith processing 
The sagittal otoliths were dissected from all samples 
and stored dry. The otoliths were then embedded in ep- 
oxy resin and sectioned through the core with an Isom- 
et 1 low speed saw (Buehler, Lake Bluff, IL) coupled to a 
diamond watering blade to obtain sections 0.4-0. 6 mm 
thick. These sections were glued to histological glass 
slides, polished with fine sandpaper (grits of 2000- 
8000), embedded in Entellan mounting medium (Merck 
KGaA, Darmstadt, Germany), covered with thin glass 
slides, and, finally, examined under a stereomicroscope 
coupled to a computerized imaging system. All sections 
were photographed under transmitted light so that 
translucent and opaque bands in the otoliths could be 
appear as white and dark bands in the digital photo- 
graphs, respectively. Each otolith was read 3 times at 
intervals of one month by an experienced reader with 
no prior knowledge of either fish size or previous read- 
ing results. Only those otoliths with at least 2 corre- 
sponding increment numbers were used in our study. 
The precision of otolith readings was evaluated 
through analysis of average percent error (APE; Cam- 
pana, 2001) with the following equation: 
APE = 100% x — i fa — A ID 
R x j 
where xy = the ith age determination of the jth fish; 
xj = the mean age estimate of the jth fish; and 
R = the number of times that each fish is aged. 
Validation and growth 
The timing of otolith incremental deposition was es- 
timated through marginal increment analysis (MIA) 
following Manickchand-Heileman and Phillip (2000), 
with the extra growth expressed as a proportion of the 
previous year’s growth: 
MIA = (R t - R t - 1) / (R t -1 - R t - 2), (2) 
where R t - the distance measured from the core to 
the otolith’s edge; 
J?t _ l = the distance between the core and the 
distal margin of the last opaque band; 
and 
R t - 2 = the distance between the core and the 
distal margin of the penultimate opaque 
band. 
1 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
Growth increment measurements were conducted with 
otolith images by using the free software ImageTool 
(University of Texas Health Science Center, San An- 
tonio), which was calibrated with a micrometric scale 
glass. For MIA, 188 otoliths (from fish of sizes from 277 
to 1160 mm TL) were used. During summer, autumn, 
winter, and spring, 91, 48, 10, and 39 otoliths, respec- 
tively, were obtained,. Marginal increment values were 
averaged over the summer ( January-March), autumn 
(April-June), winter ( July-September) and spring (Oc- 
tober-December). These averages were compared by 
using the nonparametric Kruskal-Wallis and Mann- 
Whitney tests (Zar, 1999) because the data were not 
normally distributed. 
To estimate average growth, the number of otolith 
increments was modeled against TL by fitting a von 
Bertalanffy (Eq. 3) curve and by using a nonlinear 
least squares method (Ricker, 1975). 
TL = L ao ( 1 - e-^-'o'), (3) 
where TL 
to 
K 
the TL corresponding to age /; 
the mean theoretical maximum TL; 
the theoretical age at zero length; and 
the growth coefficient, the rate at which the 
curve approaches the asymptote. 
These parameters were estimated both on the basis of 
all samples (male+female) and on the basis of females 
only. Growth parameters were not estimated for males 
because of their small sample size (n=ll). 
Sea-surface temperatures 
Data on sea-surface temperatures (SSTs) were ana- 
lyzed from a 40-year time series measured in the re- 
gion neighboring the Carpinteiro Bank (specifically, 
between 32-32°50'S and 50-52°W) made available by 
the Coastal and Estuarine Oceanography Laboratory 
of Rio Grande Federal University. SST data were aver- 
aged by season. Data on subsurface temperature were 
not available for this site. 
Framework for habitat comparison 
The hypothesis that offshore habitats may provide bet- 
ter environmental conditions for growth of dusky grou- 
pers than inshore habitats was tested by comparing 
mean sizes between fish from both sites. Specifically, 
the mean sizes at ages 3, 4, 5, 6, and 7 of fish collected 
offshore at the Carpinteiro Bank (depths of 15-25 m) 
were compared with the mean sizes of fish collected 
from the inshore rocky jetties of Rio Grande (depths <5 
m) from 2007 to 2009 that were previously reported by 
Seyboth et al. (2011). These age groups were selected 
on the basis of the simultaneous availability of 10 or 
more individuals per age group at both sites. Length- 
at-age data of inshore dusky groupers (Seyboth et ah, 
2011) were made available by those authors. Otoliths 
in this study and in Seyboth et al. (2011) were read 
