Five Iowa lakes will be treated to eliminate gizzard shad within the next few weeks using a low level chemical application that will not require eliminating the entire fishery.
The Iowa Department of Natural Resources will use cooler water temperatures and a smaller amount of the fish toxicant, Rotenone, to kill gizzard shad, while sparing most of the game fish.
Lakes receiving treatment are Don Williams in Boone County, Badger Creek in Madison County, Lacey Keosauqua State Park Lake in Van Buren County, Humeston Reservoir in Wayne County, and Lake Fisher in Davis County.
Lake Fisher is a water supply and the application rate of Rotenone is 85 percent below the limit of what is allowed for a water supply. The city of Bloomfield uses chlorination treatment which will deactivate any remaining traces of Rotenone before entering the water supply system.
Gizzard shad were illegally introduced recently in the lakes, with the exception of Lake Fisher, where they have been present for some time. They cause problems in Iowa lakes by over populating and squeezing out game fish. As a filter feeder, gizzard shad remove important food from the water necessary for survival for newly hatched bluegills, bass and other species. It is illegal to possess live gizzard shad in Iowa.
Gizzard shad are susceptible to low levels of Rotenone and the cooler water temperature allows the chemical to stay active a little longer than normal to draw out the targeted fish kill.
“In the past, once gizzard shad were in a lake, it was only a matter of time before we would have to eliminate the entire fish population to make sure we got all of the shad. With this new method, we can preserve most of the game fish so the fishery can rebound more quickly,” Flammang said. “We will monitor the lakes during 2012 to see if we were successful or not.”
Low dose treatments have worked to varying degrees in the past and the process continues to be refined.
At Lake Sugema in Van Buren County, the treatment worked for shad, but also for the walleye population. At Badger Creek, some shad made it through the treatment.
“We are partnering with Iowa State on some experiments to find the exact dosage that kills shad with minimal impacts to the game fish. These trials are part of a proactive approach to preserve fishing where it would otherwise eventually be lost,” Flammang said.
Media Contact: Mark Flammang, Fisheries Biologist, Iowa Department of Natural Resources, 641-647-2406.