Origin

Alewives are native to much of the eastern U.S., and were historically found from the Atlantic coast of Florida to the rivers of eastern Maine. Before their introduction into landlocked systems, all alewife populations in North America were anadromous, meaning they would spend most of their lives in saltwater and migrate into freshwater systems to spawn. Habitat degradation and other factors have threatened alewives in much of their native range, and there are efforts to restore alewives to East Coast rivers where spawning populations are now a fraction of what they once were. Introduced populations of alewives have been deemed invasive in landlocked systems in the East and Midwest, including the Great Lakes.

Habitat

Anadromous alewives are found along the east coast in various ocean depths, but usually are not found in areas exceeding 110 meters in depth. In landlocked systems where alewives can be problematic, they typically form dense schools in pelagic (open water) zones of lakes. 

LifeCycle

In systems where they have been introduced, such as the Great Lakes, Lake Champlain and various other systems in the East and Midwest, alewives complete their entire life cycle in fresh water. In native populations on the East Coast, alewives spawn in freshwater but live most of their lives in the ocean, similar to Atlantic salmon.