411 



Abstract.— Larval and tagging stud- 

 ies neither support nor refute the ex- 

 istence of two mid-Atlantic stocks of 

 bluefish, Pomatomus saltatrix, one that 

 spawns just south of Hatteras. North 

 Carolina, in the spring, and the other 

 off New England in the summer Sub- 

 sequent studies have suggested either 

 a continuous spawning with two sur- 

 vival events, or two distinct spawning 

 events, one in spring south of Hatteras, 

 NC, and a second in mid-summer from 

 Long Island to New England. Genetic 

 studies have supported a single stock 

 because they show the existence of a 

 single gene pool. A stepwise linear dis- 

 criminant function analysis (DFA) of 

 morphometries of "spring-spawned" 

 yearling ( 200-400 mm ) and older ( >400 

 mm) bluefish did not classify fish by 

 probable spawning cohort. It did, how- 

 ever separate the yearling fish (200- 

 400 mm) by year class rather than geo- 

 graphic or seasonal spawning. Older 

 fish (>400 mm) showed less separation 

 because multiple (2-10) year classes 

 were present. The DNA studies have 

 revealed genetic homogeneity among 

 these fish. This finding suggests that 

 the morphological characteristics are 

 phenotypically plastic and are influ- 

 enced each year by the physical envi- 

 ronment during spawning and the early 

 juvenile stages. 



Morphometric separation of annual cohorts 

 within mid-Atlantic bluefish, 

 Pomatomus saltatrix, 

 using discriminant function analysis* 



Herbert M. Austin 

 Daniel Scoles 



Allison J. Abell 



School ol Marine Science 



Virginia Institute of Marine Science 



College of William and Mary 



Gloucester Point, Virginia 23062 



Email address (for H M Austin) Haustin a'vims edu 



Manuscript accepted 14 August 1998. 

 Fish. Bull. 97:411-420 (1999). 



The question of bluefish (Pomatomus 

 saltatrix) stock composition along 

 the east coast of the United States 

 has been of considerable interest to 

 fisheries scientists for 30 years and 

 has recently (since 1986) become the 

 focus of discussion by management 

 agencies, primarily the Atlantic 

 States Marine Fisheries Commis- 

 sion (ASMFC) and Mid-Atlantic 

 Fisheries Management Council 

 (MAFMC) (Anonymous, 1989). The 

 problems of managing fisheries 

 when the stock composition and 

 boundaries are unclear have ham- 

 pered effective management of 

 weakfish, Cynoscion regalis. sum- 

 mer flounder, Paralichthys den- 

 tatus, surf clam, Spisula solidis- 

 sima. and striped bass, Morone 

 saxatilis by the ASMFC or MAFMC 

 (or both) because current manage- 

 ment practices manage by unit (ge- 

 netic) stock. Interstate manage- 

 ment is further hampered when a 

 unit stock exhibits differential spa- 

 tial reproduction and migration pat- 

 terns (e.g. weakfish, Scoles, 1990). 

 The stock structure of the blue- 

 fish (Pomatomus saltatrix) in the 

 western mid-Atlantic region is not 

 well understood. Lund (1961) re- 

 corded meristic counts of gill rak- 

 ers along the first bralnchial arch of 

 young fish and suggested that six 

 separate stocks of bluefish occur 



along the western north Atlantic 

 coast of the United States. He later 

 suggested the occurrence of several 

 races in this region on the basis of 

 results of two mark-recapture stud- 

 ies (Beaumariage and Wittich, 

 1966; Lund and Maltezos, 1970). 

 These results were not supportive 

 of Lund's original six stock concept 

 because they suggested that there 

 might be a "Florida" or "South At- 

 lantic Bight" and a "northern" or 

 "mid-Atlantic Bight" stock. Subse- 

 quent analyses of temporal and spa- 

 tial distributions of bluefish in the 

 ichthyoplankton, and spawning 

 times, suggested two north Atlan- 

 tic stocks (Norcross et al, 1974; 

 Kendall and Walford, 1979), in ad- 

 dition to a south Atlantic or Florida 

 Stock (Collins and Stender, 1987). 

 Chiarella and Conover ( 1990), on 

 the other hand, using back calcula- 

 tions of scales, demonstrated that 

 most spawning in the north mid- 

 Atlantic Bight (MAB ) occurs dur- 

 ing mid-summer (July) and is com- 

 posed of spring-spawned fish, both 

 of which suggest a single stock. 

 They also found from back calcula- 

 tions that most yearling fish (260 

 mm) collected in waters along Long 



' Contribution 2143 from the Virginia Insti- 

 tute of Marine Science, College of William 

 and Mary, Gloucester Point, VA. 



