Fish Die-Off in Southeast Michigan is Natural Occurrence
Published: Saturday, February 12, 2011 7:00 am
By: Department of Natural Resources and Environment
A fish die-off involving the species gizzard shad occurring in southeast Michigan is a natural event due to harsh winter weather conditions and a large year-class, according to the Department of Natural Resources and Environment.The department has 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 -- but they are at the northern extent of their range. Severe winters limit the northern distribution of gizzard shad. 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, small mouth bass, and northern pike. Like many for age fish species, annual abundance of gizzard shad can vary drastically between years.
Shad are filter feeders, feeding on both zoo plankton 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 reporting seeing large schools of these fish passing through their ice holes while perch fishing.
Annually, the DNRE gets reports of dead shad, but these are usually involve larger fish taking place in late winter/early spring. Some shad do not have enough fat reserves to make it through the winter and usually run out of energy during this time. The die-offs are likely happening earlier and more frequently this year due to two factors -- the combination of an exceptionally large year-class of shad this year and the early appearance of ice due to the cold fall.
"People get concerned when they see dead fish and want to be sure contamination is not the cause," said Jim Francis, a DNRE Fisheries Division biologist stationed in southeast Michigan. "When fish are poisoned, you see a variety of species and size ranges of dead fish. Given that these fish kills have been only one species, five- to six-inch gizzard shad, the DNRE believes these are the result of temperature stress."
Given the large number of young gizzard shad present and the fact that winter is only part way over, the public should expect to see more shaddie-offs through the winter and into spring, Francis added.
For more information on fish in Michigan, go to www.michigan.gov/dnrfishing.
The DNRE is committed to the conservation, protection, management, and accessible use and enjoyment of the state's environment, natural resources, and related economic interests for current and future generations. For more information, go to www.michigan.gov/dnre.
