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Fishery Bulletin 105(2) 



0.01 



59 



64 



93 

 92 



SL 



cc 



LL 

  UL 



SA 

 — LA 



GB 



MB 



EM 



AB 



FT 



65 



86 



FC 



FS 



Figure 3 



Cavalli-Sforza and Edwards (1967) chord distance neighbor-joining phe- 

 nogram calculated for 13 spatial samples of spotted seatrout iCynoscion 

 nebulosus). Values along branches indicate bootstrap values as percent- 

 ages of replicates, based on locus (above line) or individual (below line). 

 Letter codes are defined in Table 1. 



Microsatellites are assumecl to be selectively neutral, 

 whereas the allozyme and mtDNA markers used in 

 earlier studies are potentially subject to selection and 

 thus may present different patterns for the same region 

 (Hellberg et al., 2002). King and Zimmerman (1993) 

 suggested the cline in AAT-2 observed by King and 

 Pate (1992) may reflect adaptation to temperature or 

 salinity gradients along the Texas Coast. Microsatellite 

 markers would not, in the absence of linkage to loci 

 affected by selection, be subject to such processes. It is 

 also possible, as Gold et al. (2003) suggested, that the 

 earlier allozyme and mtDNA studies provided evidence, 

 not of genetic differentiation of populations inhabiting 

 neighboring bays, but rather of a general confirmation 

 of the isolation-by-distance model, where greatest ge- 

 netic differences are found between the most peripheral 

 sampling sites. 



Currently, about 5 million fingerling spotted seat- 

 rout are stocked per year into Texas bays and estuar- 

 ies. Neither Florida nor the other states of the eastern 

 Gulf of Mexico have implemented large-scale spotted 

 seatrout stocking programs; however such efforts are 

 being considered. The genetic population structure ob- 

 served in studies of allozymes (Weinstein and Yerger, 

 1976; Ramsey and Wakeman, 1987; King and Pate, 

 1992) and mtDNA (Gold et al., 1999) argue for a cau- 

 tious policy concerning the stocking of spotted seatrout. 

 Gold et al. (2003) suggested the gene flow observed 



in microsatellite markers argued against the current 

 Texas policy of stocking only into the bay from which 

 broodfish were procured. Allowing stocking into both 

 the bay of broodfish origin and into adjacent bays would 

 meet this suggestion of simulated gene flow and still 

 protect the putative population subdivision detected by 

 the earlier studies. Should stocking programs in Florida 

 or elsewhere in the northeastern Gulf be implemented, 

 it is critical, considering the level of population subdi- 

 vision observed in the present study and that of Wiley 

 and Chapman (2003), that fine-scale genetic surveys 

 in the eastern Gulf be accomplished. It is also obvious 

 that inter-regional transfers of spotted seatrout should 

 be strictly avoided. 



Acknowledgments 



This research was partially funded by the Federal Aid 

 to Sportfish Restoration Program, project F-36-R. Sam- 

 ples were provided by staff of the Coastal Fisheries 

 Division of Texas Parks and Wildlife Department, the 

 Florida Fish and Wildlife Conservation Commission, 

 and A. Landry and W. Dailey of Texas A&M University, 

 Galveston. I. Blandon, W. Karel, and J. Burr provided 

 laboratory assistance. A debt of gratitude is owed L. 

 McEachron and R. Colura of Texas Parks and Wildlife 

 Department, who supported and guided this work. 



