197 



Abstract — Variation in the allele 

 frequencies of five microsatellite loci 

 was surveyed in 1256 individual spot- 

 ted seatrout (Cynoscion nebulosus) 

 obtained from 12 bays and estuaries 

 from Laguna Madre. Texas, to Char- 

 lotte Harbor. Florida, to St. John's 

 River on the Florida Atlantic Coast. 

 Texas and Louisiana collection sites 

 were resampled each year for two to 

 four years (1998-2001). Genetic dif- 

 ferentiation was observed. Spotted 

 seatrout from Florida waters were 

 strongly differentiated from spotted 

 seatrout collected in Louisiana and 

 Texas. The greatest genetic disconti- 

 nuity was observed between Tampa 

 Bay and Charlotte Harbor, and Char- 

 lotte Harbor seatrout were most simi- 

 lar to Atlantic Coast spotted seatrout. 

 Texas and Louisiana samples were not 

 strongly structured within the north- 

 western Gulf of Mexico and there was 

 little evidence of temporal differentia- 

 tion within bays. These findings are 

 contrary to those of earlier analyses 

 with allozymes and mitochondrial 

 DNA (mtDNA) where evidence of 

 spatial differentiation was found for 

 spotted seatrout resident on the Texas 

 coast. The differences in genetic struc- 

 ture observed among these markers 

 may reflect differences in response 

 to selective pressure, or may be due 

 to differences in underlying genetic 

 processes. 



Genetic variability in spotted seatrout 

 iCynoscion nebulosus), determined with 

 microsatellite DNA markers 



Rocky Ward (contact author) 



Kevin Bowers 



Rebecca Hensley 



Brandon Mobley 



Ed Belouski 



Email address for R. Ward: rward@usgs.gov 



Texas Parks and Wildlife Department 

 Coastal Fisheries Division 

 4200 Smitti School Road 

 Austin, Texas 78744 

 Present address for R. Ward 



Northern Appalachian Research Laboratory 

 USGS/Leetown Science Center 

 176 Straight Run Rd. 

 Wellsboro, Pennsylvania 16901 



Manuscript submitted 23 February 2006 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



11 September 2006 by the Scientific Editor. 



Fish. Bull. 105:197-206 (2007). 



Spotted seatrout (Cynoscion nebulo- 

 sus) support an important recreational 

 fishery in the northern Gulf of Mexico 

 and along the U.S. Atlantic Coast. 

 Management of this fishery is multi- 

 jurisdictional, employing a variety of 

 strategies including reduction or elim- 

 ination of commercial exploitation, 

 adjustments of recreational fish-size 

 limits and bag limits, closed seasons, 

 and artificial spawning and stock- 

 ing of fish (Vanderkooy and Muller, 

 2003). Effective management requires 

 an understanding of the ecology, life 

 history, and genetic structuring of a 

 species. Understanding genetic popu- 

 lation structure is important to every 

 aspect of fishery management but is 

 especially critical when stocking fish 

 is the chosen management strategy. 

 Stocking without regard for existing 

 genetic variability within and among 

 populations places the genetic integ- 

 rity of the targeted species at risk 

 (Allendorf et al., 1986). Genetic popu- 

 lation structuring may be evidence 

 of adaptation to past environmental 

 differences, whereas genetic variabil- 

 ity may enable a population to meet 

 future environmental challenges. 



Evidence of population structuring 

 in spotted seatrout has been gained 

 through morphological, physiological, 

 and genetic examinations. Regional 

 differences have been found in oto- 



lith and scale structure, growth rate 

 (Iverson and Tabb, 1962; however, see 

 Murphy and Taylor, 1994 for a differ- 

 ent interpretation), and in reproduc- 

 tive physiology (Brown-Peterson et 

 al., 2002). Each of these studies found 

 evidence of biologically significant re- 

 gional differentiation — a finding con- 

 sistent with observations of limited 

 movement within and between bays 

 (Music, 1981; Overstreet, 1983; Baker 

 and Matlock, 1993) and between bays 

 and adjacent nearshore waters (Baker 

 et al., 1986). 



Studies of genetic markers general- 

 ly support the existence of population 

 structuring among spotted seatrout 

 in the northern Gulf of Mexico. Stud- 

 ies examining protein variation found 

 evidence of weak (Ramsey and Wake- 

 man, 1987; King and Pate, 1992) to 

 strong (Weinstein and Yerger, 1976) 

 population subdivision. The King 

 and Pate (1992) study found indi- 

 cations of clinal variation in mean 

 heterozygosity and in alleles of the 

 aspartate aminotransferase-2 locus, 

 indicating possible adaptation to en- 

 vironmental gradients on the Texas 

 coast (King and Zimmerman, 1993). 

 In each of the allozyme studies indi- 

 cations of isolation by distance were 

 found, as was found in a survey in 

 which mitochondrial DNA was used 

 (mtDNA; Gold et al., 1999). In the 



