Morphometric Separation Of Annual Cohorts Within Mid-Atlantic Bluefish, Pomatomus Saltatrix, Using Discriminant Function Analysis

Larval and tagging studies neither support nor refute the existence 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. Subsequent studies have suggested either a continuous spawning with two survival 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 discriminant function analysis (DFA) of morphometrics of "spring-spawned" yearling (200-400 mm) and older (>400 mm) bluefish did not classify fish by probable spawning cohort. It did, however separate the yearling fish (200-400 mm) by year class rather than geographic 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 influenced each year by the physical environment during spawning and the early juvenile stages.