The Alewife (Alosa pseudoharengus) is a species of small shad, of which there are anadromous and landlocked forms. The landlocked form is also called a Sawbelly or a Mooneye. The use of the name “mooneye”, however, should be discouraged as that name is more properly applied to the mooneye, Hiodon tergisus. The front of the body is deep and larger than many other species, prompting the comparison with a corpulent alewife, a female tavernkeeper.

Alewives are an ocean species but can survive in fresh water. They are perhaps best known for their invasion of the Great Lakes in North America by using the Welland Canal to bypass Niagara Falls. Alewives colonized the Great Lakes and became abundant mostly in lakes Erie, Huron and Michigan. They reached their peak abundance by the 1950s and 1960s. Alewives grew in number unchecked because of the lack of a top predator in the lakes (lake trout were essentially wiped out around the same time by overfishing and the invasion of the exotic sea lamprey). For a time, Alewives, which often exhibit seasonal die offs, washed up in windrows on the shorelines of the Great Lakes. Their control was the impetus for the introduction of various Pacific Salmon species (first Coho, and later the Chinook salmon) to act as predators on them. This caused the development of a salmon/Alewife fish community, popular with many sport anglers. Alewives, however, have been implicated in the decline of many native Great Lakes species through competition and predation.

In Atlantic Canada it is known as the “gaspereau”. More locally, in southwestern Nova Scotia it is called a “kayak”. This fish has, in the past, been used as a baitfish for the lobster fishing industry. It is also used for human consumption, usually smoked. It is caught (during its migration) using large hand-held “dip” nets to scoop the fish out of shallow, constricted areas on its migratory streams and rivers.