Statement as issued Thursday by the Indiana Department of Natural Resources:
Although last winter’s prolonged cold weather killed thousands of gizzard shad in several northeast Indiana lakes, DNR fisheries biologists hoped even more of the nuisance fish would have died.
Gizzard shad, a silver-colored forage fish, can over-populate a lake and compete with popular sport fish. Where abundant, shad can also indirectly reduce water clarity by feeding on microscopic animals that normally eat algae.
“The fewer shad we have in our glacial lakes, the better,” said Neil Ledet, the DNR district biologist who covers several counties that border Ohio and Michigan.
According to Ledet, gizzard shad do not occur naturally in most lakes within his district; however, shad have appeared in more lakes throughout the state in recent years due to unauthorized stockings.
Case in point: Royer Lake, a 69-acre natural lake in LaGrange County.
During sampling for largemouth bass at Royer Lake in mid-May, Ledet noted hundreds of 9-10 inch gizzard shad were present despite numerous shad having died last winter. Shad can be sensitive to cold temperatures.
“Because shad are not native to Royer Lake, we were hoping the winterkill removed them all,” Ledet said. “That obviously didn’t happen.”
Ledet said he hopes that bass will keep shad numbers in check.
“We will do a complete fish survey of Royer Lake in June,” Ledet said. “We’ll then be able to better assess how many shad are still there.”
Based on data compiled from hundreds of DNR fish surveys, shad occur in about one third of Indiana’s natural lakes. Most of the lakes are in the Tippecanoe River watershed, where shad have a natural connection to the Wabash River. Lakes in the Lake Michigan watershed such as Royer never previously contained shad.
Shad got into Royer Lake sometime around 2008 according to reports from local residents. None were detected in fish surveys conducted by Ledet in prior years.
To deal with large shad populations, biologists use several management options. For example, an entire 600-acre lake in southern Indiana will be drained, treated this fall with a fish toxicant, and restocked due to an over-population of shad.
In other lakes, biologists have applied selective pesticides that target gizzard shad without affecting other fish. Success of this technique has varied. Where use of chemicals to control shad is not an option, the DNR has stocked walleyes, muskies, striped bass, and other predator fish to feed on shad.
“The weather can also help us sometime. Maybe we should hope for more winters like the last one,” teased Ledet.