Midway et al.: Stock structure of Paralichthys lethostigma inferred from otolith shape analysis 
329 
North 
Carolina 
■35°N 
South 
Carolina 
Georgia 
(n= 28) 
Texas 
Missis- 
sippi 
Alabama 
(n= 52) 
• 30° N 
Louisiana 
Florida 
(n= 20) 
i (n= 45) 
Gulf of Mexico 
(n= 65) 
• 25°N 
95°W 
90°W 
I 
85°W 
I 
80°W 
I 
| (n=144) 
300 km 
Basin level 
State level 
75°W 
I 
Figure 1 
Map with sample sizes by state and basin for collections of age-1 female southern flounder (Paralichthys 
lethostigma) used in this study of the population structure of this species in the South Atlantic and 
Gulf of Mexico. Sample collections occurred in state waters in these 2 basins, the South Atlantic (North 
Carolina, South Carolina, Georgia, and Florida) and the Gulf of Mexico (Florida, Alabama, Mississippi, 
Louisiana, and Texas) in 1996 and in 2009-12 as part of state or federal agency sampling programs and 
from seafood dealers. Basin sample sizes are the sum of state sample sizes within each respective basin. 
Although we collected fish from both Georgia and Florida, in order to increase sample size, the samples 
from these 2 states were combined on the basis of their close geographic proximity. 
Florida during the fall of 2012 through purchases from 
licensed seafood dealers and participation in directed 
commercial trips. Southern flounder were collected 
from the Gulf of Mexico in the fall of 1996 from inshore 
and offshore locations in the vicinity of Panama City, 
Florida, as part of sampling conducted by the NOAA 
Southeast Fisheries Science Center. Additional Gulf of 
Mexico samples were collected in Corpus Christi and 
Aransas bays, Texas, during 2009 and 2011 as part of 
a separate research program. 
Because the age of fish and recent growth histo- 
ries can have a considerable influence on otolith shape 
(Campana and Casselman, 1993), the analysis in this 
study focused on fish captured only during October, No- 
vember, and December to reduce variability associated 
with fractional ages (although additional mathematical 
size corrections are detailed in the Statistical procedure 
subsection of the Materials and methods section). Fur- 
thermore, assuming a 1 January birthday for all fish, 
fall sampling meant that fish had completed the major- 
ity of their growth for the most recent year. Therefore, 
the translucent zone closest to the otolith edge was ap- 
proaching maximum width and thus would allow con- 
fident annuli identification for aging purposes. Lastly, 
because the vast majority of individuals collected were 
age-1 females, our analysis of otolith shape focused on 
this sex-age group. 
Otolith preparation and image analysis 
Otoliths were extracted at the time of collection when 
additional data were also collected (e.g., TL in millime- 
ters, mass in grams, and sex). After excision, otoliths 
were cleaned with isopropyl alcohol to remove any loose 
tissue, and then dried and stored in paper envelopes. 
All Atlantic-basin otoliths were aged whole with the 
NCDMF aging protocol (originally described in Wenner 
et al. 5 ). Otoliths from the Gulf of Mexico had been aged 
previously, and those ages were provided for use in this 
study (Fitzhugh 9 ; Nims 10 ). Otoliths were first scanned 
on an Epson Perfection V500 * 11 photo scanner (Epson 
America Inc., Long Beach, CA) at high resolution (1200 
9 Fitzhugh, G. 2011. Personal commun. Panama City Lab, 
Southeast Fisheries Science Center, National Marine Fisher- 
ies Service, NOAA. Panama City, FL 32408. 
10 Nims, M. 2012. Personal commun. Univ. Texas Austin, 
Port Aransas, TX 78373. 
11 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. 
