Abstract.— Restriction-fragment 

 length polymorphism analysis of mito- 

 chondrial DNA (mtDNA) was used to 

 investigate the genetic basis of stock 

 structiire of the bluefish Pomatomus 

 saltatrix along the U.S. mid-Atlantic 

 coast, and to determine the degree 

 of genetic differentiation between 

 mid- Atlantic bluefish and Australian 

 conspecifics. A total of 472 young-of- 

 the-year (YOY) and yearling bluefish 

 collected in New Jersey, Virginia, 

 and North Carolina over a period of 

 3 years, and 19 YOY bluefish col- 

 lected in New South Wales, Australia 

 were analyzed with 9 informative re- 

 striction endonucleases. Despite con- 

 siderable mtDNA variation within 

 samples of U.S. mid-Atlantic blue- 

 fish, no significant genetic differen- 

 tiation was detected among spring- 

 spawned and simimer-spawned (YOY) 

 bluefish, YOY and yearling bluefish 

 from different geographic locations 

 along the mid- Atlantic coast, or year- 

 ling bluefish collected at the same 

 location in different years. Mid- 

 Atlantic bluefish differed from their 

 Australian conspecifics by three or 

 more restriction site differences, or 

 a mean nucleotide sequence diver- 

 gence of 1.96%. In addition, Austra- 

 lian bluefish demonstrated greatly 

 reduced levels of mtDNA variation 

 relative to the mid- Atlantic samples. 

 The results of this study suggest that 

 bluefish along the mid- Atlantic coast 

 comprise a single genetic stock and 

 that significant differentiation oc- 

 curs among geographically disjunct 

 populations of this widely distributed 

 marine fish. 



Stock structure of the bluefish 

 Pomatomus saltatrix along 

 the mid- Atlantic coast* 



John E. Graves 

 Jan R. McDowell 

 Ana M. Beardsley 

 Daniel R. Scoles 



Virginia Institute of Marine Science, School of Marine Science 

 College of William and Mary, Gloucester Point, Virginia 23062 



The bluefish Pomatomus saltatrix is 

 broadly distributed in temperate and 

 warm-temperate coastal waters of 

 the world's oceans (Briggs 1960), 

 although it is absent from the eastern 

 Pacific (Smith 1949). In the United 

 States, bluefish occur along the At- 

 lantic and Gulf coasts, supporting 

 large recreational and commercial 

 fisheries. 



The movements and biology of the 

 bluefish, like many fishes along the 

 Atlantic coast, are closely tied to 

 large seasonal fluctuations in water 

 temperature (reviewed in Wilk 1977). 

 Spawning appears to be concentrated 

 in two spatially and temporally dis- 

 tinct events: a spring spawn at the 

 inside edge of the Gulf Stream in the 

 south Atlantic bight, and a summer 

 spawn in the shelf waters of the mid- 

 Atlantic bight (Kendall and Walford 

 1979). However, the presence of eggs 

 and larvae indicates that some spawn- 

 ing occurs throughout the year, espe- 

 cially in the southern portion of the 

 south Atlantic bight (Kendall and 

 Walford 1979, Collins and Stender 

 1988). Presumably, eggs and larvae 

 are transported by cross-shelf cur- 

 rents to estuaries along the Atlantic 

 coast which serve as nursery grounds 

 for the young bluefish. 



The discrete temporal nature of the 

 two spawning events is evidenced by 

 a bimodal size distribution of juvenile 



Manuscript accepted 29 July 1992. 

 Fishery Bulletin, U.S. 90:703-710 (1992). 



•Contribution 1750 of the Virginia Institute 

 of Marine Science. 



bluefish within the estuaries during 

 the middle and late summer (Nyman 

 and Conover 1988, McBride 1989), a 

 difference that is still evident in year- 

 ling fish and may persist until fish 

 reach 4 years of age (Lassiter 1962). 

 The extent to which each of the 

 major spawning events contributes 

 juveniles to specific areas appears to 

 vary annually (Chiarella and Conover 

 1990). 



A general mixing of bluefish from 

 different coastal areas may occur at 

 the end of the first summer. Tagging 

 studies indicate that as water tem- 

 peratures cool, young bluefish move 

 out of the estuaries in a southerly 

 direction and probably overwinter in 

 the south Atlantic bight (Lund and 

 Maltezos 1970, Wilk 1977), while 

 adults move further offshore (Wilk 

 1977). As temperatures along the 

 mid-Atlantic coast warm in the 

 spring, there is a general movement 

 of bluefish up the Atlantic coast, with 

 larger bluefish making more exten- 

 sive migrations into northern waters 

 (Wilk 1977). 



Although the seasonal movements 

 of bluefish may be conducive to a 

 mixing offish from different coastal 

 areas, mark and recapture studies 

 suggest that a large fraction of blue- 

 fish are recaptured in the same 

 general area in which they were 

 tagged (Lund and Maltezos 1970, 

 Wilk 1977). The degree to which this 

 fidelity affects stock structure is not 

 known. 



703 



