The Iowa Department of Natural Resources says their most recent survey found the number of gizzard shad in the Iowa Great Lakes is up.
Fisheries biologist Andrew Carlson says the fish have been in the Little Sioux River drainage to the south, but until recently hadn’t move as far north as the lakes. “Last year, we observed gizzard shad at the narrows in East Okoboji. This year, we observed them in the same location in greater numbers. We also saw them at the north end of East Okoboji Lake by the fish hatchery,” Carlson says.
He says they’ve been found in rivers throughout the midwest, but they are susceptible to large die offs in cold conditions on iced over lakes. “Increasingly in a warming climate, they’ve started to move north and northwest. They’re even found up into Lake Oahe in South Dakota now and Lake Sharp in Pierre. I’ve seen them up there around 20 to 25 inches long, so they can get really big and grow fast up there,” he says.
Carlson says gizzard shad eat zooplankton in the lakes that other more desirable species rely on. That’s why they are keeping an eye on the population. “There’s plenty of zooplankton to go around. That’s one reason why we’ve stocked paddlefish, which are another zooplanktivore. So, you know, it’s a potential concern, but it’s certainly not something negative that we’ve seen so far,” Carlson says.
Carlson says the positive is smaller gizzard shad can be a food source for the top game fish. “Perfect forage for largemouth bass, for walleyes. A lot of fishing baits are meant to mimic shad,” he says, “so there are some benefits of having shad expand their range as well, providing a high energy food source for our valued predator species.”
Carlson says the gizzard shad may have entered the Great Lakes in the 2024 flood. “It’s too early to make a call on either benefits or downside of this particular species. But it does underline the need for monitoring,” Carlson says. He says the DNR has been doing shoreline surveys on Spirit Lake, East Okoboji and West Okoboji at fixed standardized sites every year since 1989.