Investigation of congeneric hybridization in and stock structure of weakfish (Cynoscion regalis) inferred from analyses of nuclear and mitochondrial DNA loci

The weakfish (Cynoscion regalis) is ric data (Scoles, 1990), and various distributed along the east coast of the life history characters (Shepherd and United States from Massachusetts to Grimes, 1983, 1984) suggest two or eastern Florida and is most abundant more independent stocks of weakfish. from New York to North Carolina (BigThese characters may be influenced elow and Schroeder, 1953). Historiby environmental differences, however cally there has been some question as (Shepherd and Grimes, 1983), and may to the taxonomic relationship between not reflect genetically distinct (reproweakfish and sand seatrout (Cynoscion ductively isolated) stocks. Genetic arenarius); some suggest they may be analyses of weakfish stock structure separate populations of a single species in the mid Atlantic Bight employing (Moshin, 1973; Weinstein and Yerger, allozyme analysis (Crawford et al., 1976; Cowan, 1985; Ditty, 1989), and 1989) and restriction fragment length others treat them as separate species polymorphism (RFLP) analysis of (Schlossman and Chittenden, 1981). whole molecule mitochondrial (mt) Weakfish support substantial comDNA (Graves et al., 1992) were unable mercial and recreational fisheries to reject the null hypothesis that weakthroughout their range. Precipitous fish along the U.S. east coast comprise a drops in total annual catches between single, genetically homogeneous stock. 1980 and 1994 led to a temporary ban However, the power of both the analy­ on commercial fishing in federal waters ses was limited by low overall genetic in 1995 (Anonymous, 1995), and there variation. is concern that bycatch of juvenile Recent analyses of new molecular weakfish by shrimp trawlers at the markers, including microsatellite southern end of the species’ range DNA loci and nuclear gene intron is adversely impacting abundance regions, have revealed elevated levels (Vaughan et al.1). of genetic variation in relation to traAs water temperatures warm in ditional methods, such as allozymes the spring, weakfish move north and or RFLP analysis of mtDNA (Miller inshore into estuaries to spawn. When and Kapuscinski, 1996; Brunner et inshore temperatures cool in the fall, al., 1998). Although higher levels of juveniles move south to overwinter genetic variation do not necessarily off the coast of North Carolina, and provide greater stock resolution (Seeb older fish are thought to migrate et al., 1998), microsatellite loci have south and offshore (Wilk2). Traditional revealed stock structure for some spe­ studies based on tag and recapture cies, where more traditional molecular data (Nesbit, 1954), scale structure markers have not (Bentzen et al., 1996; (Perlmutter et al., 1956), morphometRuzzante et al., 1996; Patton et al., 1997). Similarly, analyses of variable gene intron regions have revealed stock structure within several marine fishes (Palumbi and Baker, 1994; Moran et al., 1997; Leclerc et al., 1996; Chow and Takeyama, 2000). In this study we em­ ployed analyses of nuclear and mtDNA markers to evaluate stock structure in weakfish along the east coast of the United States and to investigate pos­ sible hybridization between weakfish and other Cynoscion species.