884 



Abstract.— Genetic population struc- 

 ture in Atlantic croaker (Micropogonias 

 undulatus Linnaeus) was examined by 

 using the polymerase chain reaction 

 (PCR) and restriction fragment length 

 polymorphism (RFLP) analysis of mi- 

 tochondrial DNA (mtDNA). Juvenile 

 croaker from three U.S. Atlantic locali- 

 ties (Delaware. North Carolina, and 

 Florida) and one Gulf of Mexico local- 

 ity (Louisiana) were screened to docu- 

 ment the magnitude and spatial distri- 

 bution of mtDNA variation in M. 

 undulatus; to evaluate the integrity of 

 Cape Hatteras, North Carolina, as a 

 genetic stock boundary; and to estimate 

 levels of gene flow among Atlantic lo- 

 calities to provide an improved basis for 

 future decisions regarding coastwide 

 management of this fishery resource. 



RFLP analysis of the ATPase 6 and 

 D-loop mtDNA regions revealed a total 

 of 15 composite haplotypes in 93 indi- 

 viduals. Monte Carlo simulations re- 

 vealed no geographic heterogeneity in 

 mtDNA haplotype frequencies among 

 Atlantic localities and no evidence that 

 juveniles collected north and south of 

 Cape Hatteras originated from sepa- 

 rate gene pools (net sequence diver- 

 gence=-0.002'7f ). There was significant 

 heterogeneity between Atlantic and 

 Gulf of Mexico samples, suggesting re- 

 stricted gene flow between these two re- 

 gions. Analysis of molecular variance 

 also indicated regional (Atlantic versus 

 Gulf) population structure, but pro- 

 vided no evidence that Cape Hatteras 

 represents a genetic stock boundary. 

 AMOVA indicated relatively high gene 

 flow iN^m = 12-23 effective female mi- 

 grants per generation) among Atlantic 

 localities. These findings are consistent 

 with 1) a single genetic stock of M. 

 undulatus on the Atlantic coast and 2) 

 separate, weakly differentiated stocks 

 in the Atlantic and Gulf of Mexico. 



Mitochondrial DNA analysis of population 

 structure in the Atlantic croaker, 

 Micropogonias undulatus 

 (Perciformes: Sciaenidae) 



Thomas E. Lankford Jr. 

 Timothy E. Targett 



Patrick M. Gaffney 



Graduate College of Marine Studies 



University of Delaware 



700 Pilottown Road 



Lewes, Delaware 19958 



Present address (for T E Lankford Jr) 



E mail address (for T E Lankford Jr) 



Marine Sciences Research Center 

 State University of New York 

 Stony Brook, New York 11794-5000 

 ankford g ccmail sunysb edu 



Manuscript accepted 24 March 1999. 

 Fish. Bull. 97:884-890 (1999), 



Atlantic croaker (Micropogonias 

 undulatus Linnaeus) is an impor- 

 tant commercial and recreational 

 fishery species along the U,S. Atlan- 

 tic and Gulf of Mexico coasts (Chao 

 and Musick, 1977; MercerM, On the 

 Atlantic coast, M. undulatus is com- 

 mon in estuarine and coastal waters 

 from Indian River, Florida, to 

 Chesapeake Bay (Nelson et al., 

 1991; Stone et al., 1994). Current 

 fishery management practices for 

 M. undulatus assume a single or 

 "unit" stock for the entire Atlantic 

 coast (Kline and Speir, 1993) despite 

 indications that two stocks may ex- 

 ist. The two-stock hypothesis is 

 based on variation in life history 

 traits and population dynamics of 

 Atlantic croaker occurring north 

 and south of Cape Hatteras, North 

 Carolina. White and Chittenden 

 (1977) reported lower mortality 

 rates, greater longevity, and larger 

 maximum size for M. undulatus 

 north of Cape Hatteras. Ross ( 1988) 

 concluded that two groups with con- 

 trasting life histories may overlap 

 in the vicinity of Cape Hatteras, 

 with the northern, mainly offshore 

 group exhibiting greater size-at- 

 age, greater longevity, lower annual 

 mortality, and delayed maturation 



compared with southern individu- 

 als. Geographic variation in biologi- 

 cal characteristics of northern and 

 southern M. undulatus implies that 

 these groups may respond indepen- 

 dently to exploitation and may re- 

 quire management as separate 

 stocks; however, the basis for these 

 differences (i.e. genetic or ecopheno- 

 typic) is unclear. 



Identification of Atlantic croaker 

 stock structure was listed among 

 the priority research needs by the 

 1981 Sciaenid Assessment Work- 

 shop sponsored by the Atlantic 

 States Marine Fisheries Commis- 

 sion (ASMFC) and National Marine 

 Fisheries Service ( Wilk and Austin, 

 1981). The Atlantic Croaker Fish- 

 ery Management Plan, prepared 

 under the ASMFC Interstate Fish- 

 ery Management Program, also rec- 

 ommended research to identify 

 croaker stocks along the Atlantic 

 coast (MercerM. In the present 

 study, polymerase chain reaction 

 (PCR) and restriction fragment 

 length polymorphism analysis 



' Mercer, L. P. 1987. Fishery manage- 

 ment plan for Atlantic croaker. Fisheries 

 Management Rep. 10, Atlantic States Ma- 

 rine Fisheries Commission, Washington, 

 DC, 90 p. 



