A small herring, the alewife is important as forage for gameﬁsh in many inland waters and along the Atlantic coast. It is used commercially in pet food and as ﬁsh meal and fertilizer, and it has been a signiﬁcant factor in the restoration of trout and salmon ﬁsheries in the Great Lakes.
IdentificationSmall and silvery gray with a greenish to bluish back tinge, the alewife usually has one small dark shoulder spot and sometimes other small dusky spots. It has large eyes with well-developed adipose eyelids. The alewife can be distinguished from other herring by its lower jaw, which projects noticeably beyond the upper jaw.
SizeAlewives can grow up to a half pound in weight and to 15 inches in length; they usually average 6 to 12 inches in saltwater and 3 to 6 inches in freshwater.
Life history/BehaviorThe alewife is a schooling fish and is sometimes found in massive concentrations detectable on sportﬁshing sonar. In late April through early June, saltwater alewives run up freshwater rivers from the sea to spawn in lakes and sluggish stretches of river.
Landlocked alewives move from deeper waters to nearshore shallows in lakes or upstream in rivers, spawning when the water is between 52° and 70°F. A saltwater female deposits 60,000 to 100,000 eggs, whereas a freshwater female deposits 10,000 to 12,000 eggs.
They deposit the eggs randomly, at night, and both adults leave the eggs unattended. Young alewives hatch in less than a week, and by fall they return to the sea or to deeper waters. Adult landlocked alewives cannot tolerate extreme temperatures, preferring a range of 52° to 70°F—the same temperatures they spawn in.