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Researchers studying habits of Iowa’s ‘important, iconic’ shovelnose sturgeon
One piece of study seeks to understand why the prehistoric fish stay in water that’s too warm for them, resulting in fish kills
Nov. 3, 2024 5:30 am, Updated: Nov. 4, 2024 8:36 am
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Shovelnose sturgeon have been around for millions of years. Evidence of the prehistoric fish can be traced back to the age of dinosaurs. Over time, they’ve managed to adapt and survive myriad environmental changes.
But in the last two decades, thousands of the fish have died in Iowa’s rivers. Investigations by the Iowa Department of Natural Resources have reported at least four of the fish kills were the result of shallow water that had become too warm for the fish to survive.
In general, sturgeon “don’t do well in hot water temperatures,” said Mark Flammang, a fisheries management biologist for Iowa Department of Natural Resources.
Flammang has investigated fish kills in the Des Moines River, including one in July 2012 that resulted in the death of more than 37,000 shovelnose sturgeon. As part of his investigation, he measured the temperature of the water, and found that it was 97 degrees.
“You just don't see rivers at 97 degrees, and it was 97 degrees at every site that we sampled,” Flammang told The Gazette in 2012. “I've never seen water at that temperature in Iowa.”
Since 2002, there have been four significant fish kills of shovelnose sturgeon in the Des Moines River that were traced to high water temperatures, according to the DNR’s fish kill database:
- July 31, 2002: About 110 shovelnose sturgeon were found dead between Eldon and Bonaparte. The report notes that the suspected cause was high water temperatures coupled with low flows.
- July 7, 2012: Nearly 57,895 fish — including 37,159 shovelnose sturgeon — were found dead in a 42-mile section of the Des Moines River, from the dam at Eldon to the Farmington bridge on Highway 2. The cause was determined to be water temperature, which measured 97 degrees.
- July 10, 2023: An estimated 20,000 shovelnose sturgeon were found dead in a 60-mile river stretch from near Ottumwa to Farmington in southeast Iowa. Flammang, the investigator, noted that “Water temperatures are in the upper 80s and exceed levels known to cause shovelnose sturgeon mortality.”
- Aug. 28, 2024: An estimated 4,099 shovelnose sturgeon were found dead in the eight miles between Keosauqua and Bentonsport. The cause was “high water temperatures associated with relatively low flows and high daily temperatures.” Water temperatures were reported to be between 85.4 and 90.1 degrees.
Last year, researchers from the DNR and Iowa State University began working together on a study of shovelnose sturgeon. Part of their work seeks to understand why the fish stay in shallow, warmer areas of the Des Moines River, rather than swimming toward the Mississippi River, where the water is deeper and cooler.
Flammang said they’re trying to find out if there’s “any set of conditions that causes them to hang around that part of the river later than perhaps they should, because ultimately they can move back to the Mississippi River and avoid this kind of mortality.”
“We're trying to determine if there are any environmental conditions that cause them to not migrate back downstream after the spring spawn,” he said.
Michael Weber, a professor in the Natural Resource Ecology and Management Department at Iowa State University, said that while the study is looking at the sturgeon fish kills, that’s just one part. More broadly, researchers are seeking to understand the fish’s movements, ecology and reproduction at different times of the year.
An ‘altered habitat’ for an ‘iconic’ fish
Weber said concerns about the shovelnose sturgeon’s ability to adapt to change — and what that may mean for the future of the fish — kick-started the study.
“We've been concerned about sturgeon populations because they're important, iconic native fish to the Midwest, and Iowa [is] one of the strongholds for sturgeon, but it is a species of concern because they are really impacted by a lot of the environmental changes that have occurred on the river,” Weber said. Researchers are “trying to make sure that we have a good knowledge base on what their reproductive and spatial requirements are to help us conserve that species for the future.”
Weber said although sturgeon are abundant in the Des Moines and Cedar rivers, changes to its natural habitat have created challenges for the fish.
“The rivers really have been highly channelized and altered, so they don't meander back-and-forth anymore like they used to,” he said. “The rivers have been disconnected from their flood plain and that's really important habitat for a lot of aquatic species.”
Ryan Hupfeld, a fisheries biologist with the Iowa DNR, said the sturgeon population in Iowa is “pretty stable” now, but historically the fish has experienced periods of decline due to the construction of dams, or because of overharvesting.
He said the state has implemented “pretty strict” regulations to help support sturgeon populations. While other sturgeon in Iowa — including the endangered lake sturgeon — are protected and cannot be harvested, it is legal to catch and keep shovelnose sturgeon in Iowa.
While some data shows an increase in sturgeon reproduction in recent years, Hupfeld said fish kills — particularly those in the Des Moines River — have made it harder for researchers to fully understand the species’ population on a wide level.
How the study works
Weber and his team of researchers are conducting their study during two key times of the year: spring and summer.
Shovelnose sturgeon typically spawn in May and June. Although female sturgeon do not spawn every year, when they do, larger sturgeon can produce up to 50,000 eggs. The researchers also are focusing on summer months to observe the sturgeon’s movements in “stressful” conditions, such as warmer water.
The researchers have anchored 17 “acoustic receivers” — small data-collecting computers — to the bottom of the Des Moines River, from the Red Rock Dam in Knoxville, to Keokuk.
About 50 sturgeon have been tagged with a transmitter that sends a signal to researchers when the fish swim past a receiver.
“As sturgeons flip past those receivers and those tags are pinging, those receivers hear those pings and then tell us which fish are where,” Weber said.
The receiver records the date, time and ID code each time a fish passes.
Not all fish swim past the receivers, so Weber said a student researcher goes out to also conduct manual tracking from a boat. They use a hydrophone to listen for sturgeon while maneuvering up and down the river.
After their initial launch in January 2023, the researchers conducted their first field evaluation from May through mid-October. Weber said it’s still too early to draw results from the data collected this year. Research will continue in future years.
ISU and DNR researchers also are working with the Army Corps of Engineers, which is looking into the shovelnose sturgeon’s response to different water releases from the Red Rock Dam.
“We are very excited to participate in this study as it helps identify ways that [the Army Corps of Engineers] can operate existing infrastructure such as dams and reservoirs in a positive, environmentally beneficial manner,” said Perry Thostenson, who is involved in the Environmental Stewardship & Sustainable Rivers Program with the Army Corps.
Related research also is being conducted on the Iowa and Cedar rivers, Weber said.
Replacing sturgeon takes more time, costs more money
The loss of sturgeon — especially in mass events like a fish kill — can be especially impactful because they grow so slowly and are difficult to replace.
“We know that many of these [sturgeon] are in excess of 40 or 50 years old, and they grow so slowly that it would be very difficult for them to recover as a population if they consistently die off like that,” Flammang said.
To bolster some fish populations in the state, the DNR operates hatcheries where different species are raised before being released into Iowa’s rivers and lakes. However, shovelnose sturgeon are not one of them. The state does not raise sturgeon and it does not stock sturgeon raised by other states or federal agencies.
Because they grow slowly and live for so long, sturgeon are a more expensive fish. That means the financial impact of fish kills of shovelnose sturgeon also is bigger.
The 4,099 shovelnose sturgeon who were found dead in August were valued at $1.2 million. And the nearly 38,000 sturgeon who died in the Des Moines River in 2012 had a value of around $9.86 million.
“The reason that shovelnose sturgeon come out as such an expensive individual fish is because they do grow so slowly; to replace that fish would take a lot of money and a lot of time,” Flammang said. “That's why sturgeon kills tend to ramp-up in terms of cost so quickly.”
Despite the kills, DNR Fisheries Biologist Chris Mack said shovelnose sturgeon are not an endangered or threatened species, but are in fact, “plentiful” in Iowa.
But he said studies like the one being conducted on the Des Moines River and the DNR’s annual May sturgeon count on the Cedar River are helping the species continue to thrive, if not grow stronger in Iowa.
Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.
Comments: (319) 398-8370; olivia.cohen@thegazette.com
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