| Summary: | Scup Stenotomus chrysops, a commercially important marine species, are distributed from Nova Scotia to south Florida, and may represent morphologically distinct populations across their range. It was determined whether there were morphological differences between a North Atlantic Bight (NAB) population (41°N) and two South Atlantic Bight (SAB) populations (30°N and 32°N) of this species from April 2005 to July 2005, when the populations had formed spawning groups. Morphology was compared among populations by means of a geometric, landmark-based analysis of morphological and meristic traits for 180 individuals that were sexed and staged to maturity. A backward, stepwise discriminant functions analysis (DFA) produced a model that generated DFA scores that differed significantly between the NAB and SAB populations. Forehead and body depth dimensions differed among populations but not sexes. The DFA model predicted similar scores for 32 new NAB individuals and 31 new SAB individuals; however, scores were consistently underpredicted for the NAB individuals and overpredicted for the SAB individuals. We concluded that distinct northern and southern populations support a two-stock or two-species hypothesis; however, it is unclear whether this stock structure is related to reproductive or other life history traits. Either phenotypic plasticity or divergent selection may explain the morphological dissimilarities among these populations, but their influence on individual fitness remains unknown.
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