Alewife

Alosa pseudoharengus

Invader Images

    • Alewife collected from a die-off event in Lake Champlain
      Alewife collected from a die-off event in Lake Champlain
    • Adult alewife
      Adult alewife
    • Alewife populations are cyclical, and are prone to massive die-offs
      Alewife populations are cyclical, and are prone to massive die-offs
    • Certain conditions can cause large mortality events among alewives
      Certain conditions can cause large mortality events among alewives

Identification

Alewives are small members of the herring family with a dark, bluish to greenish dorsal side (top), a lighter colored ventral side (bottom) with darker horizontal stripes. In inland systems, rarely do they exceed 10 inches in length, with most adults in the 5-8 inch range. Other notable characteristics are a black spot on the upper portion of the back behind the gill cover, and a lower jaw that protrudes past the upper jaw, which gives this species the appearance of having a slight underbite. Also, if you were to run your finger on the underside of an alewife, starting from the tail and working towards the head, you would notice that the belly is serrated in a manner similar to a steak knife.

Identification diagram of an alewife

 

Biology

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 that they spend most of their lives in saltwater but run up into freshwater systems to spawn. Habitat degradation and other factors, however, 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 those not exceeding 110 m. 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.

Management Options

Like many aquatic invaders, management of alewives is difficult, and eradication is rarely attainable without drastic measures. Alewife populations are cyclic in nature, however, and massive die-offs will occur when environmental conditions and other factors dictate.

Alewives are a preferred food source for many predatory fish, although predation rarely has an impact on populations as a whole.

Vermont Distribution

Alewives are currently present in two Vermont waterbodies: Lake Champlain and Lake St. Catherine (Wells/Poultney).

Outside of Vermont, alewives are found in much of the Midwest, as well as the Atlantic coast where they are indigenous.

Alewife distribution map

How You Can Help

For alewives, the most likely means of spread from one waterbody to another is via transfer of baitfish. Never take bait from one waterbody to another, and follow Vermont's baitfish regulations. You should also take the following steps to ensure you are not unknowingly transporting other invasive pests.

BEFORE MOVING BOATS BETWEEN WATERBODIES:

  • CLEAN off any mud, plants, and animals from boat, trailer, motor and other equipment. Discard removed material in a trash receptacle or on high, dry ground where there is no danger of them washing into any water body.

  • DRAIN all water from boat, boat engine, and other equipment away from the water.

  • DRY anything that comes into contact with the water.  Drying boat, trailer, and equipment in the sun for at least five days is recommended. If this is not possible, then rinse your boat, trailer parts, and other equipment with hot, high-pressure water.

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