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Alewife (Alosa pseudoharengus)

Common names for the alewife are gaspereau, river herring, sawbelly, or kiack.


The alewife is found in rivers and lakes along the eastern coast of North America, from Newfoundland to North Carolina, and the adults live in coastal marine waters 56 to 110 m (180 to 350 ft) deep. Landlocked populations exist in several Ontario and New York lakes. Since the Welland Canal was built in 1824, the alewife has spread throughout the Great Lakes.

Physical Characteristics

The alewife is a member of the herring family. Here are some things to note:

  • a slender, laterally compressed fish coloured greyishgreen on the back, and silvery on the sides and belly;
  • gaspereau entering freshwater often have a copper sheen colour;
  • a single black spot is present on each side, just behind the head;
  • each eye is relatively large and has an obvious eyelid;
  • a row of scales, known as scutes, form a sharp edge along the mid-line of the belly which is how the alewife came to be called "sawbelly."
  • The alewife in Nova Scotia is usually 25 to 30 cm (10 to 12 in) long and weighs up to 340 g (1 2 oz). There is no lateral line.
  • Another species known as the blueback herring is very difficult to distinguish from the alewife. They inhabit the same watersheds and have similar natural histories. Any reports of alewife probably include the blueback herring as well.
Facts on Alewife

Alewife eggs, or roe, are canned and sold as a delicacy.

Despite the many thousands of eggs laid by spawning alewife, very few offspring actually survive. In some populations, as few as three young-of-the-year fish migrate downstream for each female that spawned.

Fishing Facts
  • During the spawning runs, commercial fishermen set large trap nets or enclosures called weirs in coastal rivers and estuaries to catch migrating alewives. Major Canadian fisheries are on the Shubenacadie, Miramichi, and Saint John Rivers.
  • The catch is used for fish meal lobster bait, petfood or it is smoked, canned, salted or pickled. Although tasty, alewives are not favoured locally for human consumption because they are bony.

Natural History

Alewife eggs are about 1 mm in diameter and are left to lie on the bottom or float with the current. Depending on the water temperature, the eggs hatch in about a week. After the yolk-sac is absorbed the tiny, larval fish stay near the spawning grounds preferring shallow, warm, and sandy areas. They feed on tiny zooplankton.

From August to October young-of-the-year (32 to 152 mm (1.25 to 6 in) in length) migrate downstream in large schools to live in estuaries and coastal areas. Adults overwinter at sea in the George's Bank, Gulf of Maine or Nantucket Shoals. Alewives can live at least 10 years. Alewives are eaten by many species of fish and birds including striped bass, salmonids, smallmouth bass, eels, perch, bluefish, weakfish, terns, eagles, ospreys, great blue herons, and gulls.

In the Maritimes the alewife spends most of its life growing in salt water, feeding mainly on zooplankton (tiny invertebrates that live in the water column). Beginning each spring, from April to July, large runs of adult alewives migrate up coastal rivers to spawn in freshwater lakes, ponds and streams (this movement from sea to freshwater makes the alewife an anadromous fish).

Alewives also spawn in brackish water. Like trout and salmon, alewives use their sense of smell to return to the streams and lakes where they hatched. Female alewives usually begin spawning at age 4. Male alewives often mature a year earlier than females. About 75% of alewives entering Nova Scotia rivers are repeat spawners. Alewives can move into coastal areas in late winter but will not migrate into fresh water until river temperatures begin to warm. Males enter the river first. Alewives only migrate into freshwater during daylight hours. However, spawning occurs at night and can occur in lakes or in slow moving or fast mid-river water. A single female can lay as many as 200,000 eggs. After spawning many alewives die. However, those that survive return to the sea within a few days.

For more information contact your local federal or provincial Department of Fisheries, or write to:

For more information contact your local federal or provincial Department of Fisheries, or write to:
Fisheries & Oceans Canada
PO Box 550
Halifax, Nova Scotia
B3J 2S7
Facsimile: (902) 426-1489
OR: Nova Scotia Fisheries and Aquaculture, Inland Fisheries Division
PO Box 700
Pictou, Nova Scotia
B0K 1H0
Facsimile: (902) 485-4014
Email: Inland Fisheries

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On to the next Species Sheet Published With Funding from the Canada-Nova Scotia Cooperation Agreement on Economic Diversification, Resource Competitiveness Program.
  Last Update: May 1, 2007