Gerard and Muhling: Variation in the isotopic signatures of juvenile Lut/anus griseus 
99 
before juvenile gray snapper make an on- 
togenetic shift to the nearby Florida reef 
tract. We examined variation in the otolith 
stable isotopic chemistry (6 13 C and b 18 0) of 
juvenile gray snapper among various regions 
of southern Florida, and among sites within 
these regions, over four years. Differences 
in isotopic composition of the otoliths for re- 
gions and sites were used to determine if, 
and at what spatial scale, specific nursery 
grounds for juvenile gray snapper exist. 
Materials and methods 
Sample collection 
A total of 317 juvenile gray snapper were col- 
lected between 2001 and 2005 from 27 sites 
within five geographical regions of Southern 
Florida: Ten Thousand Islands, Biscayne Bay, 
Florida Bay, Lower Florida Keys, and Dry 
Tortugas (Fig. 1). Eight to ten fish per site 
collected in 2002 and 2003 were used for an 
analysis of spatial variation and ten each 
from two sites collected in 2001, 2002, 2004, 
and 2005 were used for an analysis of tempo- 
ral variation. The fish sampled ranged from 
50 to 210 mm SL. For consistency, only gray 
snapper measuring 100 mm SL or larger, 
collected between May and September, were 
used in statistical analyses. Habitats at the 
sites varied from seagrass beds to mangrove 
islands and mangrove-lined coastlines. All 
samples were obtained by using traditional 
hook-and-line gear, baited with fresh shrimp, 
except for the collection of gray snapper from 
the Ten Thousand Islands region that was 
obtained from bycatch of crab traps. Juvenile 
gray snapper were collected between March 
and November. Samples remained frozen 
until dissection for removal of otoliths. 
Sample analysis 
According to Campana (1999), there is no significant 
difference in the chemical composition between the left 
or right otolith of a fish; therefore either otolith was 
randomly chosen. All dissection, cleaning, and drying of 
otoliths were conducted in a class-100 laminar flow clean 
hood by using acid-washed glass knives and probes. 
After the removal of all extraneous tissue, the otoliths 
were rinsed with milli-Q water. 
Otoliths are composed of 96% calcium carbonate in 
the form of aragonite, 3% protein, and 1% inorganics 
(Arslan and Paulson, 2003); therefore, deproteination 
procedures were conducted on all otoliths. During de- 
proteination, the mass of the whole otolith was obtained; 
then whole otoliths were crushed to a fine powder with 
an agate mortar and pestle and transferred to a 15 ml 
Longitude 
Figure 1 
Collection sites for juvenile gray snapper (Lutjanus griseus) 
from five southern Florida regions: Ten Thousand Islands, 
Florida Bay, Biscayne Bay, Lower Keys, and Dry Tortugas. 
Gray snapper were collected in the summer of 2002 and 2003 
for analysis of otolith microchemistry in order to identify indi- 
viduals to specific nursery sites. 
plastic centrifuge tube. For otoliths larger than 17 mg, 
only one half or one quarter of the crushed whole otolith 
powder was used. Depending on the otolith mass, vari- 
ous volumes of 10% sodium hypochlorite were added to 
the crushed otolith and the mixture was allowed to sit 
for 48 hours. Samples were rinsed with milli-Q water 
and centrifuged for 1.5 minutes between rinses before 
being dried in an oven at 60°C for six hours (Gaughan 
et al. 2 ). Stable isotope analyses were carried out at the 
University of Miami Stable Isotope Laboratory, Miami, 
2 Gaughan, D. J., G. A. Baudains, R. W. D. Mitchell, and 
T. I. Leary. 2001. Pilchard (Sardinops sagax) nursery 
areas and recruitment process assessment between differ- 
ent regions in southern Western Australia. Fish. Res. Rep. 
Dep. of Fish 131:1-44. Government of Western Australia, 
Dep. Fisheries, Fisheries Research Division, WA Marine 
Research Laboratories, PO Box 20 North Beach, Western 
Australia 6920. 
