Nonetheless, scattered populations of alewives still spawn in Lake Superior's bays and nearshore waters during the early summer. By fall, they disappear to the central depths of the lake, where they spend the winter feeding on zooplankton before migrating shoreward again in late spring. After sea lampreys had eliminated most of Lake Michigan's large predator fish, the population of alewives exploded throughout Lake Michigan. During the early summer, these small fish spawn in harbors and nearshore waters, disappearing by late fall to feed off the bottom in the central depths of the lake. They migrate shoreward again in mid-March and April, completing the yearly cycle.
Alewives swim in dense schools and have been the major prey of the Lake Michigan's trout and salmon.
The alewives found off of the Atlantic Coast are larger and meatier and have been used for human consumption for years. Scientists are currently working on ways to make a smoked or sardine-like food product from Great Lakes alewives. While Lake Superior's alewives remain essentially a forage fish for trout and salmon, tons of the thin, bony fish are already being harvested in Lake Michigan for animal food.