How an Invasive Species Populated the Great Lakes

by Julian Medina Ruiz, age 14

The shorelines of Lake Michigan near Milwaukee are covered with a lot of dead fish. These fish are called alewives and have overpopulated the area.

Seventy years ago, the alewives were introduced into the Great Lakes. They spread out lake by lake through the Detroit River. The overpopulation started in the 1950s because there were not enough predators to hunt alewives. Some of the alewives' predators are fish such as salmon and lake trout. Birds, such as herons, and mammals such as otters and minks can also eat alewives.

This invasive species eats zooplankton, small insects, and fish larvae. The problem with this is that when alewives eat too much of the food, other fish will not have access to food. Another problem is that when these fish die, they float to the shoreline where everyone can see. This usually happens during the spring and summer due to the temperature of the water, making the fish pile up on the shoreline. The Great Lakes’ ecosystem has changed because of how many alewives there are now.

The alewives’ overpopulation has caused problems in the Great Lakes and now they are the most common fish in the lakes.

[Sources: Milwaukee Journal-Sentinel ; Wisconsin Sea Grant ]