To learn more about rare lake sturgeon, Iowa researchers turn to another prehistoric fish

This is the second installment of Nature’s Alarm, a series about endangered and threatened species and research in Iowa.

The rippling Cedar River reflected an overcast sky, painting the murky water shades of gray. An 18-foot electrofishing boat slowly glided through the center of the waterway. Orange droppers dangled off the front of the watercraft, sending pulses of electricity into the river that stunned curious fish into calm obedience.

Seasonal worker Trevon Zeman stood at the bow of the boat, armed with a net. Shocked fish floated to the water’s surface; he watched closely for his target species. “Got ‘em,” he’d murmur, scooping them out of the water — sometimes two or three at a time — and dumping them into a large holding tank on the boat. He averaged three catches per minute.

“This is not even a good day,” said Chris Mack, the Iowa Department of Natural Resources fisheries management biologist who expertly maneuvered the boat that day. “I’ve seen 10 a minute … I’ve seen six or eight (fish) in a net at a time.”

The creatures were prehistoric: Several fins protruded from their small body covered in tones of tan and olive. Whisker-like appendages — called barbels, which are sensory features that supplement the fish’s tiny, beady eyes — poked out from underneath their oblong shovel-shaped snouts. Their mouths pulsated on their underbellies. On average, they weighed between 1 and 4 pounds.

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The fish, called shovelnose sturgeon, creep over from the Mississippi River, where they’re harvested by the tens of thousands every year, to spawn in Iowa waterways. Their abundant numbers make them relatively easy to study — much more so than their much larger, much rarer cousin: lake sturgeon.

Lake sturgeon are river giants that can grow upward of 100 pounds. Their bodies — which can be more than 6 feet long — are adorned in lines of ridged scales and shades of gray. Like the shovelnose, lake sturgeon harbor barbels under their upturned snouts that help them find food. But, unlike the shovelnose, their population in Iowa is at risk.

After decades of decline, lake sturgeon are listed as endangered in Iowa. Very little is known about their population status or reproductive habits in the state. And, because they’re so rare, it’s hard to learn more about them. That’s why Iowa Department of Natural Resources researchers are leaning on shovelnose sturgeon studies to create effective management plans for lake sturgeon.

“Sometimes you can't study the fish — but you study the next closest species,” said Scott Gritters, an Iowa DNR fisheries management biologist. “We just can't come across the lake sturgeon in enough numbers to do any meaningful research on it right now … They’re out there, though.”

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Decline of a river giant

Lake sturgeon are one of 25 known species of sturgeon — fish that have persisted since the Cretaceous period when dinosaurs roamed Earth.

The fish can live to be 100 years old and swim thousands of miles. They inhabit the depths of large rivers, dig around river bottoms and vacuum up their food. Since lake sturgeon need clean water to spawn and survive, they are indicators for healthy aquatic ecosystems.

In Iowa, lake sturgeon are concentrated in the Mississippi and Missouri Rivers and likely found in major tributaries like the Des Moines, Iowa and Cedar Rivers. The species’ native range spreads throughout the Midwest and into the Northeast.

Lake sturgeon populations started declining as early as 1900. Habitat loss was a big contributor: Major dams fragmented rivers, separating the fish from their spawning grounds and migration routes. Remaining aquatic habitat was often so altered or polluted that it became unsuitable.

Poaching and overharvesting were also major factors in their decline. Historical records show prolific take of lake sturgeon, largely to use their eggs for caviar.

“Those folks are going to make some money,” Gritters said about the still-growing caviar industry, which could prompt illegal take of the fish, “but they're going to rob from all of us.”

Once impacted, lake sturgeon populations are difficult to recover.

A female sturgeon takes about 25 years to sexually mature. They often die without getting the chance to reproduce. They also only spawn every two to six years — not annually, like many other fish species.

“You just don't replace a big old animal like that overnight,” Gritters said. “It takes another 50 to 100 years to get that back. That is part of the problem.”

Species listings for lake sturgeon vary nationwide. They are listed as endangered in several states, including Iowa, Indiana, Missouri and Pennsylvania. They are listed as threatened or special concern in other states. But in other states, including Wisconsin and Minnesota, people are allowed to fish for lake sturgeon.

The Center for Biological Diversity, a national nonprofit conservation organization, petitioned in 2018 for lake sturgeon to be federally listed as threatened under the Endangered Species Act. The U.S. Fish and Wildlife Service will make a determination by 2024.

Fish helping fish

Seasonal worker Zeman reached his gloved hands into the 100-gallon container on the boat and pulled out a shovelnose sturgeon.

He laid it flat against a ruler, measuring its length. He noted its fat belly and determined it was female. After he weighed the squirming fish, he brought it to Mack, who clipped a tag to one of the sturgeon’s pectoral fins, then implanted one into its cheek.

“She is locked and loaded for the rest of her life,” Mack said as he gave Zeman the go-ahead to release the fish back into the river.

Mack’s research pinpoints variables that influence shovelnose sturgeon spawning, including timing, water temperature and flow. It’s just one slice of a larger Iowa DNR project that started studying the species as early as 2005. Since shovelnose sturgeon aren’t protected under state or federal law, long-term population data helps researchers monitor if they’re being over-harvested, said Iowa DNR fisheries biologist Ryan Hupfeld.

On the surface, shovelnose sturgeon and lake sturgeon appear very different. Their sizes alone are stark contrasts, along with their respective abundances in Iowa rivers. But they share several similarities. They are both slow-growing, have long lifespans and swim upstream to spawn. Their fish eggs are coveted for caviar, and they both roam around river bottoms.

The species overlap just enough that they may be useful to each other one day: Techniques perfected in shovelnose sturgeon research could be mimicked on lake sturgeon, creating a foundation for future studies of the endangered fish.

“They are different species and have different life history traits, but the problems with managing them are very similar,” Hupfeld said. “There’s definitely a parallel there.”

For instance, the Iowa DNR is already studying how water movement at Red Rock Dam on the Des Moines River impacts shovelnose sturgeon reproduction. Teams are adjusting dam operations to better mimic natural river flows. Baby sturgeon have been recorded after each pulse, indicating that the extra flow is helping the fish reproduce.

The project’s success is encouraging — and could be adjusted for other species. In the future, water pulses may be released earlier in the year to target lake sturgeon populations, which spawn at colder water temperatures than shovelnose sturgeon.

Researchers in Iowa and beyond are also analyzing sturgeon bones for traces of nuclear bombs. Each detonation released a unique carbon signature that was absorbed into a bone in sturgeons’ heads. Scientists can match the carbon signature to the detonation date to accurately estimate how long the fish can live.

The innovative technique, called bomb radiocarbon dating, is only being done on shovelnose sturgeon in Iowa currently. But it also could be applied to lake sturgeon to learn more about their life history, Hupfeld said.

A brighter future

Lake sturgeon show up infrequently. But, when they have been caught, they’ve appeared in different sizes and ages — good signs that reproduction is happening.

“I think their numbers are pretty stable, potentially increasing,” Hupfeld said. “But we just don't have the hard data for that currently.”

That may change soon, though.

Over the next two years, the Iowa DNR will develop a management plan for lake sturgeon. The plan will establish goals for the species, outline monitoring strategies, identify data gaps and make recommendations for habitat improvements.

It also calls for more research on the endangered species. Biologists must develop baselines for current lake sturgeon populations to gauge how future work impacts the species.

Thanks to the ongoing shovelnose sturgeon research, there’s already a path there.

“We need to manage these species. We're developing ways to get at that with shovelnose sturgeon, which could lead to methodology to do that for lake sturgeon as well.” Hupfeld said. “It’s pretty in-depth. It's gonna take a bit of time. But it's really important.”

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How we reported this series

Nature’s Alarm started as a question this spring: On the 50th anniversary of the Endangered Species Act, what do we know about threatened and endangered species in Iowa? Can we highlight some of these species and the researchers studying them?

Members of The Gazette’s newsroom have spent the last four months planning and reporting this series, which began July 16 and will publish weekly over the next two months.

Reporter Brittney J. Miller started with background interviews in search of active research occurring for at-risk species in Iowa. Once she identified target species — each representing a different fauna group — she coordinated with researchers to accompany them into the field with photojournalist Jim Slosiarek and social video producer Bailey Cichon. Digital editor John McGlothlen built graphics to accompany the stories online.

The Gazette team clambered through vegetation in search of bumblebees, worked by the light of headlamps to spot bats, and floated along rivers to catch a glimpse of fish, amphibians and mussels to report this series.

Brittney J. Miller is the Energy & Environment Reporter for The Gazette and 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; brittney.miller@thegazette.com