(Spirit Lake)– Officials with the Department of Natural Resources are closely monitoring a recent increase in the population of gizzard shad in the Iowa Great Lakes. Andrew Carlson, a DNR Fisheries Management Biologist, says the breed is native to the Little Sioux River drainage to the south and were unknown this far north in the watershed until just within the past few years…
“They tend not to get very big, they’re a few inches long, they’re a good forage species for our predators but occasionally they get really large. I’ve seen them up to 20, 25 inches up in Lake Oahe in South Dakota. So they’re a plantifore. They can be concerning because they eat what young game fish eat. But it’s a very sensitive fish. They don’t like cold water, so our harsh winters here in Iowa may contain them.”
He says some recent seining operations performed as part of annual assessment of the Iowa Great Lakes fishery turned up a significant increase in gizzard shad populations in an area of East Lake Okoboji…
“We’re about half way done with our assessments this year and one of our nets up in the north end of East Okoboji yielded really high catches of gizzard shad where we didn’t have any last year, so we were concerned with those numbers. One adult, 23 sub adults and 1,846 young of the year in that particular site. So that was definitely high and confirms that there is a reproducing population of gizzard shad in that part of East Okoboji.”
Carlson has a theory as to how gizzard shad got here…
“So this could have been from the 2024 flood, a riverine population of fish moving in to open water. That’s a fairly reasonable explanation but we don’t really have a smoking gun.”
Carlson adds the fact those fish were able to survive and reproduce is an indication of the milder winters we’ve been experiencing…
“Certainly the reproduction that we observed this year is a result of a winter that wasn’t severe enough to kill off that species, so. They’re a pretty adaptable fish. They’re found in lots of rivers throughout the Midwest, so we’re definitely going to continue monitoring them and we’ll see how the population changes from one year to the next through our seining activity.”
And Carlson says whether or not gizzard shad remain anything to be overly concerned about is still uncertain…
“There are positives and negatives to this fish, this species, but right now we don’t have a firm conclusion from the overall effects. We’ll be monitoring those, though.”
In the meantime Carlson continues to emphasize the importance of not transferring live fish or bait between different water bodies. Instead he recommends disposing unwanted bait in the trash.
Carlson again reminds everyone to clean, drain and dry all boats, trailers and gear before entering another body of water.
