FISHERY BULLETIN: VOL. 87, NO. 1 



1977), but the presence of null heterozygotes seems 

 the most likely explanation. The low number of in- 

 dividuals observed to be homozygous for the null 

 allele suggests that it may be lethal for these in- 

 dividuals (Speiss 1977). 



Previous investigators have suggested that two 

 or three distinct stocks of weakfish occur in the Mid- 

 dle Atlantic region (Nesbit 1954; Perlmutter et al. 

 1956; Seguin 1960). Nesbit (1954) examined dis- 

 tances between circuli on scales and conducted a 

 marking study using celluloid belly tags. He tagged 

 5,789 fish and 7.5% were returned when the fish 

 were eviscerated. Thirty-six percent of the returned 

 tags were from retail dealers and consumers pro- 

 viding little information regarding actual recapture 

 location. Nesbit concluded that the fishery consisted 

 of two stocks. Perlmutter et al. (1956) examined 

 intercirculi distances, fin rays, age, and growth data 

 as well as Nesbit's (1954) data and concluded that 

 there were northern and southern spawning weak- 

 fish populations. 



Seguin (1960) performed a univariate analysis of 

 morphometric and meristic data on juvenile weak- 

 fish and separated Middle Atlantic weakfish into 

 three segments: 1) New York, 2) Delaware (and 

 possibly Virginia), and 3) North Carolina. She re- 

 ported "a north-south trend in regression coeffici- 

 ents" which may have been associated with environ- 

 mental gradients (e.g., temperature) and clinal 

 variation in the characters. Meristic characters, 

 however, may be influenced by temperature (Barlow 

 1961) and intercirculi distances are related to 

 growth rates that can vary geographically (Lux 

 1972; Shepherd and Grimes 1983; Harris and Gross- 

 man 1985). Because growth is affected by many en- 

 vironmental factors (e.g., temperature and food 

 availability), it may not be indicative of genetic dis- 

 continuity (Joseph 1972). 



Our results suggest that weakfish populations in 

 the Middle Atlantic are not sufficiently distinct, 

 genetically, to be considered as separate stocks (i.e., 

 reproductively isolated). Weakfish perform exten- 

 sive spring and fall migrations that could permit am- 

 ple gene flow between populations. There are no ob- 

 vious isolating mechanisms and only a small number 

 of migrants would be needed to cause allelic fre- 

 quencies to converge and make the population 

 homogenous (Hartl 1980). 



In conclusion, the results of this investigation do 

 not support the findings of earlier studies that 

 distinct stocks of weakfish are present in the Mid- 

 dle Atlantic. Even though there do not appear to 

 be genetically discrete weakfish populations, there 

 are variations in the population parameters (Shep- 



herd and Grimes 1983, 1984). The ability of a pop- 

 ulation to sustain a harvest is largely dependent 

 upon its growth, mortality, and fecundity. These life 

 history parameters are used in fishery assessments 

 (e.g., dynamic pool and stock-recruitment models). 

 Use of northern weakfish growth parameters would 

 predict overly optimistic yields for southern fish- 

 eries, and an incorrect stock-recruitment relation- 

 ship. Therefore, as a practical matter it is probably 

 best to manage weakfish as discrete northern and 

 southern units. These units may not be reproduc- 

 tively independent, and the effects of fishing (par- 

 ticularly recruitment overfishing) are likely to be 

 imposed upon the entire population. 



ACKNOWLEDGMENTS 



The authors thank all the people who helped out 

 in sampling including Jess Hawkins at the North 

 Carolina Department of Natural Resources, Division 

 of Marine Fisheries, the scientists at the Virginia 

 Institute of Marine Sciences, Ichthyological Asso- 

 ciates, the personnel at NMFS, Woods Hole, MA, 

 and many commercial fishermen. We are grateful 

 to Bob Vrijenhoek for his advice and use of his 

 laboratory for the electrophoresis. Special thanks 

 to Ken Able of Rutgers University and Brad Brown 

 and Ambrose Jearald, Jr. at NMFS, Miami, FL and 

 Woods Hole, MA respectively. We also thank two 

 anonymous reviewers for their comments. We 

 will not forget the support and encouragement of 

 Steve Turner, Russ Schenk, Deb Shalders, Bob 

 Palmer, Peter Hood and Rhett Lewis. We thank 

 G. Shepherd, G. Grossman, M. Freeman, M. Flood, 

 J. Barrett, D. Stouder, and J. Hill for their com- 

 ments on the manuscript. Funding for this project 

 was provided by NMFS (contract No. NA-79-FAC- 

 00041). 



LITERATURE CITED 



Barlow, G. W. 



1961. Causes and significance of morphological variation in 

 fishes. Syst. Zool. 10:105-117. 

 BiGELOW. H., AND W. SCHROEDER, 



19.53. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv. 

 Fish. Bull. 53:1-577. 

 Crawford, M. K. 



1 984 . Stock identification of the weakfish (Cynoscion regalis) 

 in the Middle Atlantic region. M.S. Thesis, Rutgers Univer- 

 sity, New Brunswick, NJ, 60 p. 

 Clayton, J. W., and D. W. Tretiak. 



1972. Aminecitrate buffers for pH control in starch gel elec- 

 trophoresis. J. Fish. Res. Board Can. 29:1160-1172. 

 Green, D. M. 



1979. A BASIC program for calculating indices of genetic 



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