The Natural History of American Shad(Alosa sapidissima)
American shad (shad) is the largest member of the herring family, averaging between 17 and 24 inches in length and between 3 and 6 pounds in weight at sexual maturity. It is a schooling species and highly migratory. Shad are found along the Atlantic seaboard from Labrador to Florida. Most abundant on the East Coast from Connecticut to North Carolina, shad have spawned, historically, in almost every major river along the Atlantic Coast. Shad are river- specific; each major river along the Atlantic Coast appears to have a discrete spawning stock.
Shad spawning can occur as early as November in southern states and as late as July in New England and Canada. Shad that spawn in the northern part of the range may survive to spawn again. Spawning begins in the spring as rising water temperatures signal a return to freshwater. Water temperature at the time of upstream migration is typically 56-66 oF. Males arrive at the spawning grounds first, soon followed by the females. A female shad may produce from 100,000 to 600,000 eggs, depending on size, each spawning season.
The transparent, fertilized eggs measure one-tenth to two-tenths of an inch in diameter and range from pale pink to amber. Carried along by the current, the eggs hatch in about four to twelve days, depending on water temperature. Shad spend their first summer in tributary and river nursery areas. By autumn, when they are three to five inches long, most juveniles migrate to near-shore coastal wintering areas. Immature shad remain in the ocean before returning to spawn. Males are smaller than females and generally mature earlier.
After spawning, adult shad return to the sea and migrate northward to summer feeding grounds in the Gulf of Maine, feeding primarily on zooplankton and small fishes. As water temperatures decline in the fall, particularly October and November, shad migrate southward and offshore. Overwintering occurs along the Mid-Atlantic coast, particularly from Maryland to North Carolina.