"There are two main causes for yearly alewife die-offs. One is warmer water; the other is biological stress. ... Since they are a salt water fish, they have issues regulating their bodies to a fresh water environment.

What happened to the alewives in Lake Michigan?

Most scientists believe the drop has been due to a combination of factors, including invasive zebra and quagga mussels which remove plankton from the lake and reduce the amount of food available for other organisms, as well as predation on forage fish by salmon and trout.

What impact do alewives have on the Great Lakes?

Although alewives serve as a key source of food for Pacific salmon, they also have a down side. The species exerts strong, negative impacts on many fish: they consume the pelagic early life stages of native species such as yellow perch and lake trout and compete with coregonines for zooplankton.