A major factor in causing algal blooms is the introduction of phosphorus. When adult alewives migrate into a freshwater pond or lake, there is an influx of phosphorus to the lake. However, the majority of these alewives survive spawning and return to the ocean, taking phosphorus with them. Additionally, young alewives that grow in freshwater ponds and lakes incorporate phosphorus in their bodies, which causes that phosphorus to be removed when the young migrate to the ocean. Typically, there is a decrease in total lake phosphorus due to alewife emigration.
Alewives are important to the ecology of the freshwater, estuarine, and marine environment.
The adults and young provide a food source for striped bass, brown trout, salmonid species, eels, ospreys, eagles, kingfishers, cormorants, and aquatic fur bearing mammals. Adult alewives are a preferred bait for the spring lobster fishery. There are 35 Maine municipalities that have commercial harvesting rights to alewives on 39 coastal streams and rivers. These runs provide revenue to the towns, which lease their fishing privileges to independent fishermen. Many of the fishways built for alewife restoration on some of our small coastal streams were partially funded by these municipalities as they recognized the value of this native fish species.