474 



Fishery Bulletin 90(3). 1992 



significant differentiation between the two populations 

 (an uncorrected percent mean sequence divergence of 

 0.75). The lack of significant population structuring 

 within the weakfish relative to the black sea bass is 

 evidenced in a comparison of the ratio of between- 

 group to within-group sequence divergences: For the 

 black sea bass the ratio is 24, while for the weakfish 

 it is ~1. 



The results of our investigation suggest that weak- 

 fish comprise a single genetic stock throughout the 

 species' range. No significant genetic differentiation 

 was found among geographic samples or among 

 samples taken at the same site over several years. Con- 

 sequently, at the level of genetic resolution we em- 

 ployed, we cannot disprove the null hypothesis that 

 weakfish share a common gene pool. The inference that 

 gene flow occurs throughout the species' range is sup- 

 ported by the homogeneous distribution of rare mtDNA 

 genotypes. 



The genetic homogeneity found within the weakfish 

 in this study and in the allozyme analysis of Crawford 

 et al. (1989) contrast with the geographical variation 

 of morphological and life-history characters reported 

 in other studies (Perlmutter et al. 1956, Seguin 1960, 

 Shepherd and Grimes 1983 and 1984, Scoles 1990). The 

 degree of plasticity of weakfish morphological and life- 

 history characters to different environmental condi- 

 tions has not been determined, but in light of research 

 on other fishes (Barlow 1961), it would not be surpris- 

 ing if much of the geographic variation previously 

 described among weakfish is ecophenotypic. 



Our inference that there is sufficient gene flow 

 among weakfish along the mid-Atlantic coast to pre- 

 vent even minor genetic differentiation from occurring 

 has several management implications. There is clear- 

 ly some interdependence among areas, a conclusion 

 also supported by the tagging data of Nesbit (1954). 

 To obtain a meaningful estimate of the magnitude of 

 the interdependence between these areas would require 

 a tagging study much more extensive than that of 

 Nesbit (1954), which would involve considerable time 

 and expense. Until such information is available, it 

 would be best to manage the weakfish resource con- 

 servatively, as a single interdependent stock. 



Acknowledgments 



This study would not have been completed without the 

 assistance of several individuals along the mid- Atlantic 

 coast. The perseverance and efforts of all those who 

 collected weakfish samples are gratefully acknowl- 

 edged, especially Alice Webber, New York Department 

 of Environmental Conservation; Rich Seagraves, 

 Delaware Division of Fish and Wildlife; and Charlie 



Wenner, South Carolina Wildlife and Marine Re- 

 sources. A portion of this project was initiated by Herb 

 Austin and Brian Meehan, Virginia Institute of Marine 

 Science. Ana Beardsley provided technical assistance. 

 Carol Furman and John Gold kindly shared unpublished 

 data. Dan Scoles, Herb Austin, and Mark Chittenden 

 critically read the manuscript. Funding for this study 

 was provided by the Atlantic States Marine Fisheries 

 Commission (88-lWSID), the U.S. Fish and Wildlife 

 Service (F-60-R), and the Commonwealth of Virginia. 

 M. Lisa Jones was supported by a Howard Hughes 

 Summer Fellowship in Molecular Biology. 



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