Midway et al : Stock structure of Paralichthys lethostigma inferred from otolith shape analysis 
327 
tinely for age determination purposes, making large 
sample sizes available for shape analyses. Consequent- 
ly, numerous examples of successful discrimination of 
fish stocks based on otolith morphometries and shape 
descriptors exist. 
Campana and Casselman (1993) were among the 
first to use otolith shape as an indicator of stock varia- 
tion. They conducted an exhaustive study of all 3 types 
of otolith pairs in which they found evidence of struc- 
turing among spawning groups of Atlantic cod (Ga- 
dus morhua ) in the Northwest Atlantic, in addition to 
differences in otolith shape among age groups, sexes, 
and year classes. Begg and Brown (2000) used otolith 
shapes to challenge successfully the assumption of a 
single stock of haddock ( Melanogrammus aeglefnus ) 
at Georges Bank, and DeVries et al. (2002) clarified 
previous tag and genetic data when they used oto- 
liths to successfully distinguish stocks of king mack- 
erel (Scomberomorus cavalla) from the Gulf of Mexico 
and the Atlantic that were sampled during their win- 
ter mixing off southern Florida. More recently, otolith 
shape analysis has been done at varying spatial scales 
for dolphinfish ( Coryphaena hippurus [Duarte-Neto et 
al., 2008]), North Atlantic saury (Scomberesox saurus 
saurus [Agiiera and Brophy, 2011]), and anglerfish 
( Lophius piscatorius [Canas et al., 2012]) to help clari- 
fy questions about geographic population structure. 
The southern flounder ( Paralichthys lethostigma ) oc- 
curs in the Northwest Atlantic and Gulf of Mexico from 
North Carolina to Texas; however, this species does not 
occur around the southern tip of the Florida peninsula 
(Gilbert 1 ). Southern flounder in the South Atlantic and 
Gulf of Mexico basins are considered separate genetic 
stocks (Anderson et al., 2012). Management for the 
range of this species occurs generally at the individual 
state level, despite a high likelihood of within-basin 
mixing during offshore spawning migrations of adults 
and the possibility of year-round offshore residents 
(Watterson and Alexander 2 ; Taylor et al. 3 ). 
Southern flounder support important commercial 
and recreational fisheries throughout their range, 
with females contributing most to the landings be- 
cause growth is greater in females than in males. In 
1990-2010, more than 30,000 metric tons were landed 
commercially, and the vast majority (-98%) of these 
1 Gilbert, C. R. 1986. Species profiles: life histories and en- 
vironmental requirements of coastal fishes and invertebrates 
(South Florida) — southern, gulf, and summer flounders. U.S. 
Fish Wildl. Serv. Biol. Rep. 82 (11.54). U.S. Army Corps Eng. 
Tech. Rep. TR EL-82-4, 27 p. [Available from http://www. 
nwrc.usgs.gov/wdb/pub/species_profiles/82_l l-054.pdf.] 
2 Watterson, J., and J. Alexander. 2004. Southern flounder 
escapement in North Carolina. Final performance report 
F-73, Segments 1-3, 41 p. [Available from North Carolina 
Department of Environment and Natural Resources, Division 
of Marine Fisheries, P.O. Box 769, Morehead City, NC 28557.1 
3 Taylor, J. C., J. M. Miller, and D. Hilton. 2008. Inferring 
southern flounder migration from otolith microchemistry. 
Final report for Fishery Resource Grant 05-FEG-06, 27 p. 
[Available from North Carolina Sea Grant, NC State Univ., 
Campus Box 8605, Raleigh, N.C. 27695-8605.] 
landings took place in North Carolina. Over the same 
period, recreational landings were about 50% lower in 
magnitude and were more evenly distributed among 
states between the Gulf of Mexico and South Atlan- 
tic basins (NMFS 4 ). However, recreational harvest may 
be a primary factor that is contributing to population 
declines in the Gulf of Mexico (Froeschke et al., 2011), 
and these declines have prompted a new stock en- 
hancement program in Texas aimed at supplementing 
natural reproduction. 
Because no directed fishery exists for southern 
flounder in offshore habitats and exchange of individu- 
als among states is not well understood, state manage- 
ment agencies assume unit stocks on the basis of state 
boundaries. However, population structure that does 
not coincide with state boundaries has been shown 
with other flounders in the Northwest Atlantic that 
share geographic ranges of a similar size and life his- 
tory characteristics with the southern flounder. These 
flounders include the southern flounder congener sum- 
mer flounder ( P. dentatus [Burke et al., 2000]), winter 
flounder {Pseudopleuronectes americanus [DeCelles and 
Cadrin, 2011]), and yellowtail flounder ( Limanda fer- 
ruginea [Cadrin, 2010]). 
Interestingly, each of these studies reported stock 
structuring at varying scales. Summer flounder were 
found to have structure related to the biogeographic 
boundary of Cape Hatteras in North Carolina, whereas 
evidence indicated that winter flounder and yellow- 
tail flounder had population structures of much finer 
scales, including the existence of up to 3 stocks within 
New England waters. Yet despite evidence for within- 
basin genetic homogeneity (Anderson et al., 2012), 
flounder residency within specific estuaries for the 
first few years of life may create regional phenotypic 
differences that reflect local adaptation. For example, 
estimates of the von Bertalanffy growth coefficient ( K ) 
for female southern flounder vary considerably among 
states. For fish in Texas, Stunz et al. (2000) estimated 
K at 0.75, and Fischer and Thompson (2004) estimated 
K at 0.51 for Louisiana fish. Within the South Atlantic 
basin, estimates of K have been lower: 0.23 for fish in 
South Carolina (Wenner et al. 5 ) and 0.28 for fish in 
North Carolina (Takade-Heumacher and Batsavage 6 ). 
4 NMFS (National Marine Fisheries Service). 2011. Per- 
sonal commun. Fisheries Statistics Division, NMFS, Silver 
Spring, MD 20910. 
5 Wenner, C. A., W. A. Roumillat, J. E. Moran Jr., M. B. Mad- 
dox, L. B. Daniel III, and J. W. Smith. 1990. Investigations 
on the life history and population dynamics of marine rec- 
reational fishes in South Carolina: Part 1. Final report for 
project F-37, 187 p. Marine Resources Research Institute, 
South Carolina Wildlife and Marine Resources Department. 
Charleston, SC. [Available from the Marine Resources Re- 
search Institute, South Carolina Department of Natural Re- 
sources, 217 Fort Johnson Rd., Charleston, SC 29412.] 
6 Takade-Heumacher, H., and C. Batsavage. 2009. Stock 
status of North Carolina southern flounder (Paralichthys 
lethostigma), 91 p. North Carolina Division of Marine Fish- 
eries, Morehead City, NC. [Available from http://00del7f. 
netsolhost.com/fmps/downloads/souflounderSA.pdf] 
