Length frequency distributions of Atlantic menhaden, Brevoortia tyrannus, plotted by age, month, and latitude, support the hypothesis of an annual north-south movement. The majority of Atlantic menhaden, wintering in offshore waters south of Cape Hatteras, North Carolina, move northward in early spring. By about mid-June menhaden are distributed in coastal waters from Florida to Maine, their age and size increasing from south to north. A slow northward movement of fish north of False Cape, Virginia, continues throughout the summer. A southward movement, beginning in early September north of Cape Cod, Massachusetts and involving all fish north of False Cape by November, culminates in January when the majority of the population is again south of Cape Hatteras.