The alewife is an anadromous member of the herring family. Native populations of this fish exist off the Atlantic coast, and make annual migrations up rivers such as the Connecticut, the Hudson and the Mohawk to spawn. Alewives can, however, survive in freshwater and have established landlocked populations in the Great Lakes and other inland waterbodies such as New York's Finger Lakes and some inland lakes in Maine. Once landlocked populations become established, they cause serious problems in native fish communities. Alewives can establish large populations in inland lakes and they are very efficient feeders, consuming huge quantities zooplankton.
Alewives compete for food with baitfish and young game fish such as yellow perch, bass and trout.
This competition often deprives the native fish species of essential food, and it can ultimately result in the decimation and loss of these native fish populations. This is a very real and serious threat to the smelt and shiner populations of Lake St. Catherine, as well as other species that depend on plankton for food such as yellow perch. Collapses of fish species such as smelt and yellow perch will not only affect game fish but also impact the important recreational and commercial fisheries that they sustain in Vermont. As a forage fish, alewives do not provide a consistent food base for predatory fish such as bass and trout. Aside from the loss of a potential food source for game fish, these alewife population crashes result in literally thousands of dead fish washing up on shore and beaches, creating bad odors and public health concerns.