In their native range, alewives (Alosa pseudoharengus) are a saltwater fish that swim up freshwater rivers and streams to spawn. Landlocked populations are able to complete their entire life cycle in freshwater and are usually considered invasive. Alewives are found in deep, open waters except during spawning season when they move to shallower waters in bays and tributaries. In Vermont, alewives are established in Lake Champlain and Lake St. Catherine.
The origin of alewife in Lake Champlain is unknown, although they may have entered through the Hudson or Richelieu rivers. The population in Lake St. Catherine was most likely established from a bait bucket release.
Adult alewives are typically 5-8 inches long, though they can reach 11-12 inches in Lake Champlain. They are generally silvery in appearance with a dark, bluish-green back and lighter belly, sometimes marked with dark horizontal stripes. They have a large black spot behind the gill cover and a serrated edge on the belly where scales overlap. Alewives’ lower jaws also protrude past the upper jaw in an underbite.
Alewives are prolific and can rapidly increase their population size when introduced to new waters. Females on average can lay 60,000 to 70,000 eggs each spawning season. Alewife primarily feed on plankton, a major food source for native fish species. Alewives’ voracious feeding behavior allow them to outcompete native fish.
In Vermont specifically, populations of rainbow smelt have declined in Lakes Champlain and St. Catherine due to competition with alewives. Alewives also compete with the juveniles of game fish species such as walleye, salmon, and trout leading to a loss of fishing opportunities for anglers.
Alewives can also impact trout and salmon reproduction. When these species consume alewives, an enzyme in alewives prevents these fish from producing a vitamin necessary for egg development, reducing the amount of young that survive.
Control and Prevention
Control of alewives is difficult. Predation may help but does not have a large enough impact to eradicate a population. Alewife populations are also naturally cyclical with periodic large die-offs, which can help reduce the population. However, the best management option is spread prevention.
Illegal alewife introductions typically occur when anglers transport them from one waterbody to another for use as bait, and then release them when done. Alewives may also spread naturally through connected waters by use of rivers and canal systems.
It is very important to follow Vermont’s baitfish regulations and not transport live fish from one waterbody to another.
For more on spread prevention
VT Department of Environmental Conservation
For volunteer opportunities to help monitor and protect Vermont's waters
VT Fish and Wildlife
For more on baitfish use in Vermont
US Geological Survey Nonindigenous Aquatic Species