Taxonomic name: Alosa pseudoharengus (Wilson, 1811)
Synonyms: Pomolobus pseudoharengus
Common names: alewife (English), bigeye herring (English), branch herring (English), freshwater herring (English), gaspareau (French), gray herring (English), grayback (English), kyack (English), mooneye (English-northwest New York state), sawbelly (English), white herring (English)
Organism type: fish
Alosa pseudoharengus (alewife) is a small, fish species indigenous to the east coast of North America that causes several major effects in aquatic environments. Alewife migrate from the ocean to spawn in fresh water. It can occupy all strata of a land-locked body of water throughout the course of the year. A. pseudoharengus alters the zooplankton community as it is an extremely efficient feeder on zooplankton, competing with other fish species for food. Alewife feed on the eggs and larvae of other fish and thereby can cause other fish species to decline. It is often stocked as a forage fish.
Maine's Department of Marine Resources (1998) states that A. pseudoharengus is an iridescent gray green or violet shade on top that fades down their sides to a silver underbelly. It usually has a distinct dusky spot just behind the upper margin of the gill cover. Its strongly laterally compressed body is three and one-third times as long as it is deep and has a forked tail fin. The midline of their belly is sharp and saw edged. Serrations located on the midline of their belly are much stronger and sharper than the ones found on most other members of their family. Adult alewives normally grow to be 25cms to 28cms (10-11 inches) in length and 230grms- 255grms (8 to 9 ounces) in weight." Alewives in land-locked populations rarely exceed 20cms (8 inches) long and most are 13cms to 18cms (5 to 7 inches) long (O'Gorman et al. 1997).
estuarine habitats, lakes, water courses
In lake habitats Alosa pseudoharengus are known to occupy all strata of a land-locked water body during the course of the year. Alewives have been found to prefer rocky habitats to sand sites along the Wisconsin shoreline. This may be related to their feeding on emerging insects associated with rocky areas (Janssen and Luebke, 2004). The majority of their time is spent in the limnetic zone (inhabiting fresh water). In late spring and summer they move into littoral areas (the region of the shore of a lake or sea or ocean) for spawning and move into deeper water during fall. Alewives have a preference for warmer waters. A. pseudoharengus move in large schools and are attracted to light. They move into shallow areas at night and return to deeper waters during the day. River populations of A. pseudoharengus are anadromous (meaning they migrate from the ocean to spawn in fresh water). They are found in river systems during spring migration, and are known to move further upstream than their close cousin, the American shad (Alosa sapidissima) (Chosid, Undated).
In the Laurentian Great Lakes, the alewife invasion has been associated with declines in abundance of emerald shiner (Notropis atherinoides), yellow perch (Perca flavescens), deepwater sculpin (Myoxocephalus thompsoni), and burbot (Lota lota). Alewives are suspected of interfering with reproduction of these fishes, most likely by preying upon the pelagic fry (Chuck Madenjian pers.comm., 2004).
Multiple impacts have been reported by the Vermont Department of Environmental Conservation (VTDEC, 2002). Alewives are extremely efficient feeders on zooplankton. They feed selectively on the larger species and the larger individuals within a species, causing drastic alterations in zooplankton size, abundance and community structure. A. pseudoharengus out-compete other fish species for food. Alewives compete directly for zooplankton with other planktivorous fish, including yellow perch (Perca flavescens) and rainbow smelt (Osmerus mordax), and with the young of many piscivorous species, such as bass, which are dependent on zooplankton during the early parts of their lives. A. pseudoharengus feed on the eggs and larvae of other fish. Predation on yellow perch and lake trout (Salvelinus namaycush) larvae appears to be a significant source of mortality in those species.A. pseudoharengus are the cause of major reproductive failures in landlocked Atlantic salmon (Salmo salar) and lake trout populations.
A. pseudoharengus undergoes periodic mass mortalities.The large numbers of alewives that die in these events wash up on beaches, causing foul odors and public health concerns. Any predator fish that utilises A. pseudoharengus populations as a main source of food will have difficulty finding enough to eat after an alewife mass mortality. This results in poor growth rates and declines in game fish. Land-locked alewives are high in thiaminase and Atlantic salmon and lake trout that eat mainly alewives produce thiamine deficient eggs which results in high mortality of fry from a syndrome linked to thiamine deficiency (O'Gorman and Stewart 1999).
The Nova Scotia Department of Agriculture and Fisheries (2001) report that "A. pseudoharengus eggs, or roe, are canned and sold as a delicacy. The catch is used for fish meal lobster bait, pet food, or it is smoked, canned, salted, or pickled."
Describing the distribution of alewife is difficult as native and invaded ranges overlap. For example, alewife is native along Atlantic coast of New York, however it is invasive in western New York outside of the Atlantic drainage (Robert O'Gorman., pers. comm 2004)
Native range: A. pseudoharengus is native to the Atlantic coast of North America from Newfoundland to the Carolinas (Fuller et al. 2005).
Known introduced range: Through introduction it has spread to several other states and the Great Lakes (Fuller et al. 2005).
Introduction pathways to new locations
Aquaculture: Fuller et al. (2005) brings up the possibility that alewife were introduced into Lake Ontario with American shad stockings in the 1880s, but he discounts this possibility in favour of the hypothesis that they reached the lake via the Erie Canal from the Hudson River.
Natural dispersal: This species was probably native to Lake Ontario and spread through the Great Lakes via the Welland Canal (Fuller et al. 2005). Canals for commercial navigation allowed alewife to invade the Great Lakes west of Lake Ontario and may have allowed the alewife to invade Lake Ontario. In a review of the history of the alewife in the Great Lakes, O'Gorman and Stewart (1999) concluded that the alewife was not native to Lake Ontario, the easternmost Great Lake.
Other: Alewife were once purposely introduced into land-locked waterbodies to provide prey for piscivores although many such introductions were not sanctioned by management agencies.
Smuggling: Lakes in the Adirondack Mountains and Otsego Lake, New York were illegally stocked with alewives for forage (Fuller et al. 2005)
Local dispersal methods
Aquaculture (local): Fuller et al. (2005) brings up the possibility that alewife were introduced into Lake Ontario with American shad stockings in the 1880s, he discounts this possibility in favour of the hypothesis that they reached the lake via the Erie Canal from the Hudson River.
Natural dispersal (local): This species was probably native to Lake Ontario and spread through the Great Lakes via the Welland Canal (Fuller et al. 2005).
Biological: Several options for alewife management and control have been listed by VTDEC (2002). Population reduction can be achieved by the stocking of alewife predator species such as the brown trout (Salmo trutta) which feed predominately on alewives.
Physical: An aggressive netting project can be undertaken when the alewives are vulnerable. Construction of barriers could prevent the spread of alewives downstream.
Chemical: An extreme measure of using a piscicide which would kill all fish species within a lake is also suggested.
VTDEC (2002) states that A. pseudoharengus "is planktivorous (their main food source is plankton), feeding predominantly on zooplankton as both juveniles and adults. However, large landlocked alewives also feed on the eggs and larvae of other fish species, as well as those of their own species".
The Department of Fisheries and Wildlife Science at Virginia Tech (VT-FIW, 2001) states that "in anadromous populations, females mature a year later than males. A. pseudoharengus matures between the ages of 3 and 5. The fecundity of oceanic female is 48,000 - 360,000 eggs. Landlocked fish mature between 1 and 3 years of age and their fecundity is between 13,200 and 49,200 eggs. Spawning occurs from March to May in tidal freshwater streams and ponds. After spawning, adults return to the sea. Inland populations spawn from April to August in the shallow areas of lakes and streams. Adults pair during spawning and swim in spirals to the surface. The eggs of A. pseudoharengus are non-adhesive and sink to the bottom of calm, still waters." Spawning occurs at night.
Maine's Department of Marine Resources (1998) report that "every spring, adults ascend rivers and streams to spawn in freshwater lake and pond areas. After the eggs hatch, the young-of-the-year spend two to six months in the freshwater environment, growing 4cm to 12.5cms (1½ to 5 inches) in size before they begin to migrate to sea."
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Monday, 21 March 2005