443 



Investigation of congeneric hybridization in and 

 stock structure of weakfish (Cynoscion regalis) 

 inferred from analyses of nuclear and 

 mitochondrial DNA loci* 



Jan F. Cordes 

 John E. Graves 



School of Marine Science 



Virginia Institute of fv\anne Science 



College of William and Mary 



Gloucester Point, Virginia 23062 



Present address (for J. F, Cordes): Department of Animal Science 



University of California 

 Davis, California 95616 



E-mail address (for J F Cordes): |fcordes@ucdavis edu 



The weakfish (Cynoscion regalis) is 

 distributed along the east coast of the 

 United States from Massachusetts to 

 eastern Florida and is most abundant 

 from New York to North Carolina (Big- 

 elow and Schroeder, 1953). Histori- 

 cally there has been some question as 

 to the taxonomic relationship between 

 weakfish and sand seatrout (Cynosc/on 

 arenarius); some suggest they may be 

 separate populations of a single species 

 (Moshin, 1973; Weinstein and Yerger, 

 1976; Cowan, 1985; Ditty, 1989), and 

 others treat them as separate species 

 (Schlossman and Chittenden, 1981). 



Weakfish support substantial com- 

 mercial and recreational fisheries 

 throughout their range. Precipitous 

 drops in total annual catches between 

 1980 and 1994 led to a temporary ban 

 on commercial fishing in federal waters 

 in 1995 (Anonymous, 1995), and there 

 is concern that bycatch of juvenile 

 weakfish by shrimp trawlers at the 

 southern end of the species' range 

 is adversely impacting abundance 

 (Vaughan et al.'). 



As water temperatures warm in 

 the spring, weakfish move north and 

 inshore into estuaries to spawn. When 

 inshore temperatures cool in the fall, 

 juveniles move south to overwinter 

 off the coast of North Carolina, and 

 older fish are thought to migrate 

 south and offshore (Wilk-). Traditional 

 studies based on tag and recapture 

 data (Nesbit, 1954), scale structure 

 (Perlmutter et al., 1956), morphomet- 



ric data (Scoles, 1990), and various 

 life history characters (Shepherd and 

 Grimes, 1983, 1984) suggest two or 

 more independent stocks of weakfish. 

 These characters may be influenced 

 by environmental differences, however 

 (Shepherd and Grimes, 1983), and may 

 not reflect genetically distinct (repro- 

 ductively isolated) stocks. Genetic 

 analyses of weakfish stock structure 

 in the mid Atlantic Bight employing 

 allozyme analysis (Crawford et al., 

 1989) and restriction fragment length 

 polymorphism (RFLP) analysis of 

 whole molecule mitochondrial (mt) 

 DNA (Graves et al, 1992) were unable 

 to reject the null hypothesis that weak- 

 fish along the U.S. east coast comprise a 

 single, genetically homogeneous stock. 

 However, the power of both the analy- 

 ses was limited by low overall genetic 

 variation. 



Recent analyses of new molecular 

 markers, including microsatellite 

 DNA loci and nuclear gene intron 

 regions, have revealed elevated levels 

 of genetic variation in relation to tra- 

 ditional methods, such as allozymes 

 or RFLP analysis of mtDNA (Miller 

 and Kapuscinski, 1996; Brunner et 

 al., 1998). Although higher levels of 

 genetic variation do not necessarily 

 provide greater stock resolution (Seeb 

 et al., 1998), microsatellite loci have 

 revealed stock structure for some spe- 

 cies, where more traditional molecular 

 markers have not (Bentzen et al., 1996; 

 Ruzzante 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. 



Materials and methods 



Sample collections were restricted to 

 young-of the-year (YOY) fish (less than 

 140 mm SL) that are reported to remain 

 in their natal estuaries during the first 

 several months of growth (Rowe and 

 Epifanio, 1994). YOY were collected 

 in the summers of 1996 and 1997 from 

 five sites along the east coast of the 

 United States (Fig. 1), maintained on 

 ice after capture, transported to the 

 laboratory, and frozen at -80°C. Muscle 

 tissue was excised from each sample 

 and either stored at -80°C or placed 

 in DMSO buffer (25 mM EDTA, 20% 

 DMSO, saturated NaCl) and stored at 

 room temperature. Genomic DNA was 

 isolated by following the protocol of 

 Sambrook et al. (1989), as modified in 

 Cordes (2000). 



Specific identification of individuals 

 was determined by using a molecular 

 key for 16 species of Chesapeake Bay 



* Contribution 2532 of the Virginia Institute 

 of Marine Science. College of William and 

 Mary, Gloucester Point, VA 23062. 



' Vaughan, D. S.. R. J. Seagraves. and K. 

 West. 1991. An assessment of the 

 Atlantic weakfish stock, 1982-1988. Atl. 

 States Mar. Fish. Comm. Spec. Rep. 21. 

 29 p. + tables. Atlantic States Marine 

 Fisheries Commission, 1444 Eve St., NW 

 6"' Floor, Washington, D.C. 20005. 



- Wilk, S. J. 1976. The weakfish— a wide 

 ranging species. Atl. States Mar. Fish. 

 Comm, Mar. Resourc. Atl. Coast Fish. 

 Leaflet 18, 4 p. Atlantic States Marine 

 Fisheries Commission. 1444 Eye St., NW 

 6'*' Floor, Washington. D.C. 20005. 



Manuscript accepted 21 October 2002. 



Manuscript received 9 January 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 101:443-450 (2003). 



