671 
Preliminary genetic population structure of 
southern flounder, Paralichthys lethostigma, 
along the Atlantic Coast and Gulf of Mexico 
Ivonne R. Blandon 
Rocky Ward 
Perry R. Bass Marine Fisheries Research Station 
Coastal Fisheries Division 
Texas Parks and Wildlife Department 
Palacios, Texas 77465 
E-mail address (for I R Blandon): ivonne.blandon@tpwd.state.tx.us 
Tim L. King 
U.S. Geological Survey-Biological Resource Division 
Leetown Science Center 
Aquatic Ecology Laboratory 
1700 Leetown Road 
Kearneysville, West Virginia 25430 
William J. Karel 
Perry R. Bass Marine Fisheries Research Station 
Coastal Fisheries Division 
Texas Parks and Wildlife Department 
Palacios, Texas 77465 
James P. Monaghan Jr. 
North Carolina Division of Marine Fisheries 
3441 Arendell Street 
Morehead City, North Carolina 28557 
Southern flounder, Paralichthys letho- 
stigma , inhabit coastal waters from 
Albemarle Sound, North Carolina to 
the Baja Laguna Madre del Sur in 
northern Mexico, but they are appar- 
ently absent from southern Florida 
(Ginsburg, 1952). This species inhab- 
its coastal bays, sounds, and lagoons 
from spring to fall and migrates off- 
shore to spawn in late fall and winter 
(Stokes, 1977). Valuable sport and com- 
mercial fisheries for southern flounder 
exist in both the northern Gulf of 
Mexico (Warren et al. 1 ; Robinson et 
al. 2 ) and the western North Atlantic 
(Monaghan 3 ). 
Declines in southern flounder ab- 
solute abundance in some regions 
(e.g. Texas during the 1980s; Fuls 
and McEachron 4 ) have prompted some 
management agencies to institute re- 
strictions on recreational and commer- 
cial fisheries including reductions in 
bag limits and minimum size. Should 
these measures fail to recover this fish- 
ery, other measures may be considered 
by managers, including further restric- 
tions on harvest, or artificial propaga- 
tion and stocking, or both. Implemen- 
tation of such enhancement programs 
requires that genetic surveys be con- 
ducted to determine genetic variabili- 
ty and stock structure of managed fish 
populations (King et al., 1995). Fail- 
ure to understand underlying genetic 
structure prior to implementing stock- 
ing programs places the genetic re- 
sources of target species at risk (Al- 
lendorf et al., 1987) and may result in 
the reduction or loss of among-popula- 
tion variability and changes in within- 
population genetic characteristics. Ge- 
netic analyses of population structure 
may also provide insight into manage- 
ment options that do not require stock- 
ing (Nelson and Soule, 1987). 
The objective of our study was to 
characterize population structure of 
southern flounder in coastal regions of 
the northern Gulf of Mexico and north- 
western Atlantic Ocean and to test the 
null hypothesis of no genetic differen- 
tiation within the region surveyed. If 
this hypothesis was rejected, a number 
of processes would operate to structure 
southern flounder population(s). Ge- 
netic differentiation in some nearshore 
organisms in the northern Gulf of Mex- 
ico (e.g. Sciaenops ocellatus\ Gold and 
Richardson, 1999) has been explained 
as isolation by distance (Wright, 1943). 
This model describes a population 
structured by isolation caused by lim- 
ited individual migration potential in 
relation to the size of the species’ dis- 
tribution (Kimura and Weis, 1964). The 
hypothesis of isolation by distance is 
supported when geographic distance 
and genetic distance are positively cor- 
related. Alternatively, differentiation 
may arise as an adaptive response 
to localized environmental conditions 
(King and Zimmerman, 1993) or from 
the operation of physical barriers, such 
1 Warren, T. A., L. M. Green, and K. W. Spiller. 
1994. Trends in finfish landings of sport- 
boat anglers in Texas marine waters May 
1974-May 1992, 259 p. Manage. Data 
Ser. 109, Texas Parks and Wildlife (TPW), 
Coastal Fish. Div., Austin, TX 78744. 
2 Robinson, L., P. Campbell, and L. Butler. 
1995. Trends in Texas commercial fish- 
ery landings, 1972-1994, 133 p. Manage. 
Data Ser. 117, Texas Parks and Wildlife 
(TPW), Coastal Fish. Div., Austin, TX 
78744. 
3 Monaghan, J. P, Jr. 1996. Migration of 
paralichthid flounders tagged in North 
Carolina. Study 2 in Life history aspects 
of selected marine recreational fishes in 
North Carolina, 44 p. Completion Rep. 
Grant F-43, Segments 1-5, North Carolina 
Division of Marine Fisheries, 3441 Aren- 
dell Street, Morehead City, NC 28557. 
4 Fuls, B., and L. W. McEachron. 1997. 
Trends in relative abundance and size 
of selected finfishes and shellfishes along 
the Texas coast: November 1975-Decem- 
ber 1995, 108 p. Manage. Data Ser. 137, 
Texas Parks and Wildlife (TPW), Coastal 
Fish. Div., Austin, TX 78744. 
Manuscript accepted 9 February 2001. 
Fish. Bull. 99:671-678 (2001). 
