The alewife (Alosa pseudoharengus) is an anadromous marine fish that is native to the east coast of North America from Newfoundland to South Carolina. It feeds and grows to maturity in the ocean, then migrates into freshwater rivers and lakes to spawn. Under certain circumstances it is able to live its entire life cycle in freshwater, and as a result, self-sustaining, landlocked alewife populations have become established in at least nineteen states.

Landlocked alewives typically inhabit pelagic waters (deep open water, not associated with the bottom) of lakes during most of the year, migrating inshore in the spring and early summer to spawn. Inshore migrations and spawning generally take place from April to August, although the exact timing varies geographically. By late August most adults have returned to deep water. Spawning takes place at night over sand or gravel bottom. The young remain on the spawning ground until at least the late larval stage and then slowly move to deeper waters.

Alewives are 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. They are preyed upon by just about all larger piscivorous fish, including northern pike, smallmouth bass, walleye, burbot, bowfin, lake trout, brown trout, rainbow trout, and Great Lakes Pacific salmon; adult rainbow smelt and yellow perch prey on larval and young-of-the-year alewives.

• Ranges from 3 to 10 inches in length.
• Silvery, with a blue-green metallic luster along the back.
• Large black spot behind gill cover.
• Body is deep (i.e., the vertical line distance from just in front of the dorsal fin, straight down through the fish is greater than other species of fish of the same size).
• Lower jaw protrudes beyond upper jaw.
• Underside of belly has a distinct serrated edge where scales from each side of the body meet and overlap.

Non-indigenous, landlocked alewives impact native ecosystems in a number of ways:

• They alter the zooplankton community.
  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. The end result is a zooplankton community dominated by small species. This phenomenon has been reported in a number of lakes, including: Lake Michigan; Lake Ontario; Claytor Lake, Virginia; Black Pond, New York; and seven lakes in eastern Connecticut. This size-selective zooplanktivory may indirectly impact nutrient dynamics and water clarity, resulting in increased algal blooms (i.e., greening).
• They out-compete other fish species for food.
  Alewives are potentially very fierce competitors with other planktivorous fish or life stages of important game fish such as yellow perch, bass, trout, salmon, and walleye. Alewives compete directly for zooplankton with other planktivorous fish, including yellow perch and rainbow smelt, and with the young of many piscivorous species, such as bass, which are dependent on zooplankton during the early parts of their lives. Competition with alewives for zooplankton has been hypothesized as a major cause of the declines of many native fish species in the Great Lakes.
• They feed on the eggs and larvae of other fish.
  Alewives are known to feed on the eggs and larvae of a number of fish species and alewife predation on yellow perch and lake trout larvae appears to be a significant source of mortality in those species. In one study, 30 to 41% of alewives collected over two years from a Lake Ontario yellow perch spawning ground had fed on larval yellow perch. In another study, alewife predation on lake trout larvae in Lake Ontario caused nearly 100% mortality of emergent fry from near-shore spawning areas where alewives were abundant. In Claytor Lake, Virginia, alewives fed on the larvae of largemouth bass, black bass, white bass, sunfish, yellow perch, and golden shiner. Additionally, laboratory studies have shown that alewives readily feed on the larvae of walleye and lake whitefish. Egg and larval predation by alewives is considered a major mechanism by which alewives affect native species, potentially more important than competition for food.
• They cause reproductive failure in trout and salmon.
  Alewives are the cause of major reproductive failures in landlocked Atlantic salmon and lake trout populations. In several of New York's Finger Lakes, a maternally transmitted, non-infectious disease, known as the Cayuga syndrome, has been found to cause up to 100% mortality in the larval offspring of landlocked Atlantic salmon. The syndrome has recently also been documented in landlocked Atlantic salmon from Otsego Lake and Green Pond, New York. Similarly, the swim-up or early mortality syndrome (EMS) has been found to impair the survival of lake trout in Lakes Ontario and Erie. Larval mortality rates range from 33.5-57.9% in Lake Ontario and 25.2% for Lake Erie.

  Recent studies demonstrate that both syndromes are the result of thiamin (vitamin B1) deficiencies resulting from diets consisting principally of alewives. Alewives contain very high levels of thiaminase, a group of enzymes which diminish the ability to store thiamin in tissues. In a laboratory experiment, the progeny of landlocked Atlantic salmon fed thiamin-deficient diets for six months prior to spawning were afflicted with Cayuga syndrome, while Cayuga syndrome was not observed in the progeny of salmon fed thiamin-sufficient diets. Alewives are the principal food of lake trout in both Lake Ontario and Lake Michigan, where EMS has been reported. However, in Lake Huron and Lake Superior, where alewives are much less abundant and therefore only a minor part of the diet, EMS has not been reported. As well, the Cayuga syndrome only occurs in those Finger Lakes containing alewives and alewives are the major prey item of landlocked Atlantic salmon in Otsego Lake and Green Pond.

• They cause declines in native species.
  The alewife has had detrimental effects on many native fish stocks. The establishment of alewives in the Great Lakes was associated with the population collapse of several native planktivorous and minor piscivorous fishes. In Lake Michigan, bloater, yellow perch, and deepwater sculpin have all shown large-scale declines during alewife increases and subsequent increases during alewife declines. Lake herring and emerald shiner in Lake Michigan have also been adversely affected by alewives. The disappearance of native Lake Ontario planktivores such as whitefish and lake herring has been attributed, at least in part, to the introduction of alewives which reduced zooplankton populations. In Cayuga Lake, the alewife appears to have replaced the cisco as the major forage species.
• They undergo periodic mass mortalities.
  Landlocked alewife populations generally undergo annual die-offs and periodic mass mortalities. Catastrophic mid-winter, early spring and summer mortalities have been common in the Great Lakes since the alewife first established itself. In general, alewife populations recover rapidly after such catastrophic mortality events. The causes of these mortality events are unclear, but food limitation, temperature extremes, and temperature fluctuations have been suggested as factors. When these large-scale die-offs occur, several problems arise. First, any predator fish that utilizes alewife populations as a main source of food will have difficulty finding enough to eat. This results is poor growth rates or declines in game fish. This situation is often seen in chinook, coho, brown trout, and lake trout populations in the Great Lakes. Second, the large numbers of alewives that die in these events wash up on beaches, causing foul odors and public health concerns. Stretches of shoreline in the Great Lakes are often closed for weeks at a time after an alewife die-off so that the thousands of fish can be bull-dozed off the beaches, as is often necessary.

A large alewife population was discovered in Lake St. Catherine, in Rutland County, Vermont, in July 1997. How the alewives got into the lake is somewhat of a mystery. One possibility is that alewives migrated naturally into Lake St. Catherine via the Champlain Canal, the Mettawee River, Wells Brook, and Mill Brook from the Hudson River, into which anadromous alewives make yearly spring spawning migrations. However, alewives have not been reported anywhere along this hypothesized migration route, and alewives probably would not have been able to navigate Lake St. Catherine's outflow dam to get into the lake. The only remaining possibility is that alewives were introduced to the lake by human activity, either as accidental bait bucket releases or as a purposeful introduction to the lake. Since no bait shops in the area sell alewives, it is believed that they were transported from out-of-state and purposely released into Lake St. Catherine by a member of the public.

Lake St. Catherine is a mesotrophic (deep, relatively fertile, with vegetated shoreline areas) lake with a surface area of approximately 345 hectares. It is connected to two small ponds, Lily Pond (8 hectares) at the north end and Little Pond (73 hectares) at the south end. It supports a large fish community which includes rainbow smelt, yellow perch, bluegill sunfish, pumpkinseed sunfish, common white sucker, smallmouth bass, largemouth bass, black crappie, northern pike, brown bullhead, and various minnow species including golden shiner and emerald shiner. Lake trout, brown trout and rainbow trout are stocked annually on a put, grow and take basis. Lake St. Catherine has a single outflow over a small concrete dam at the southern end of Little Pond. Water spills over the dam into Mill Brook which flows for approximately 1.8 miles to Wells Brook which in turn flows for 1.2 miles to the Mettawee River. The Mettawee River empties into the Champlain Canal, 24 miles away, just south of Whitehall, New York. The Champlain Canal flows into southern Lake Champlain 1.7 km to the north. Although currently contained within Lake St. Catherine, the direct water connection between Lake St. Catherine and southern Lake Champlain makes migration of alewives to Lake Champlain very possible.

Based on the impacts which exotic alewives have had on native ecosystems in the past, we can predict the specific impacts they are likely to have in Lake St. Catherine. The main impacts of alewives will likely result from competition for zooplankton and predation on eggs and larvae of other fish. We expect declines in rainbow smelt and yellow perch since all life stages are in direct competition with the alewife. Although initial impacts on adult bass could be positive (i.e., increased growth rates due to increased food supply), long-term impacts to larval bass from alewife competition and direct predation during spring spawning could be severe. We could also expect decreased growth rates of rainbow trout due to competition for food. Furthermore, we expect periodic alewife die-offs to occur, the first of which occurred in April 1999.

If alewives were to spread to Lake Champlain, we might expect a huge impact due to thiaminase and serious setbacks for efforts to re-establish self-reproducing populations of native lake trout and Atlantic salmon into the lake. We would also expect impacts due to competition and predation, including declines in yellow perch and rainbow smelt, as well as impacts on bass and walleye due to predation on their early life stages. Due to the size of Lake Champlain, there is potential for alewife abundances to skyrocket and for massive die-offs similar to those documented in the Great Lakes to occur.

The Vermont Department of Fish and Wildlife has considered a variety of management alternatives to address the alewive population in Lake St. Catherine. At the current time it has chosen not to take any specific action, but continues to monitor the situation.

Prevent the spread of alewives and other non-native aquatic species by:

• Learning to identify alewives and know which lakes are infested.
• Understanding the law: it is illegal to use alewives, dead or alive, for bait within the State of Vermont (Title 10, Chapter 2, Section 106).
• Spreading the word not to use or move alewives. Public participation in alewife control and prevention is essential to minimizing the impacts of this aquatic nuisance species.
• Contacting the Department of Fish and Wildlife immediately if you think you have found a new occurrence of alewives (phone: 802-483-2172).

Please direct questions or comments to Shawn Good, District Fisheries Biologist, Pittsford District Office 802-483-2172 or shawn.good@state.vt.us.

• The Alewife in Lake St. Catherine - pamphlet (pdf, 154 KB)
• USGS - Alewife North America Distribution Map & Information

Updated: January 2004