A fish kill involving gizzard shad which occurred in southeast Michigan is a natural event due to harsh winter weather conditions and a large year-class, according to the state's Department of Natural Resources and Environment.

The department received reports of fish die-offs in southern Michigan beginning shortly after the New Year. The reports are coming from the St. Clair River, Lake St. Clair, the Detroit River and Lake Erie.

Gizzard shad are native to the Great Lakes with the exception of Lake Superior. Shad can be seen concentrated at warm water discharges of industrial plants.

Gizzard shad are an important forage fish, providing a high-energy food resource for predator species such as walleye, muskellunge, smallmouth bass and northern pike. Like many forage fish species, annual abundance of gizzard shad can vary drastically between years.

Shad are filter feeders, feeding on both zooplankton and phytoplankton, and can reach a size of 19 inches. However, most of the gizzard shad involved in the fish die-offs are five to six inches long. There was a very large hatch of shad this spring throughout the St. Clair system, resulting in large schools of these young shad.

Anglers along Lake St. Clair have reported seeing large schools of these fish passing through their ice holes while perch fishing. According to the department, the public should expect to see more shad die-offs through the winter and into spring.
 

source: Michigan Department of Natural Resources and Environment