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Small ponds in Minnesota’s prairies can save species

LUVERNE, MINN. – Nick Utrup sat in the tall grass with a team of biologists, trying to see through the ripples of a small, nameless pond. An approaching rainstorm from the west, already over the red cliffs of nearby Blue Mounds State Park, had stirred the wind across the prairie. But Utrup and the others remained focused on finding signs of an elusive roach.

The Topeka shiner, a rare and endangered fish, is found only in the few remaining prairies of Minnesota and a handful of other Midwestern states. Ten years ago it seemed well on its way to extinction. But a group of scientists from a poorly funded branch of the U.S. Fish and Wildlife Service, along with nonprofit conservationists from the Nature Conservancy, may have discovered the secret to bringing back this life, as well as a host of other prairie life. And it all depends on little nameless ponds called oxbows.

“The wind makes it very difficult to see,” Utrup said.

When people think of prairie restoration, they almost always think of the grasses, the bison, the birds and the soil, says Marissa Ahlering, science director for the Nature Conservancy.

“But it’s also the water and the wetlands,” Ahlering said. “These are the veins of the entire prairie system.”

Oxbow ponds get their name from the horseshoe shape that resembles the old yokes used on ox teams. They arise from the bends of streams and rivers that run through grasslands. Over time, some of those bends naturally separated from the larger flow, leaving small puddles behind. Once a year, or every few years, the stream reconnects with these orphan pools when the water is high enough, allowing fish to move briefly from one to the other.

The isolation and shallow water of an oxbow pond provide a nice little refuge and breeding ground for an array of small fish, such as Topeka shiners, protected from swift currents and predators, said Utrup, the Fish and Wildlife Service’s lead biologist for fish recovery the Topeka Shiner. .

But dynamic streams and flooded ponds also make it difficult to farm and build roads.

Many of the region’s oxbows have been removed or filled. Streams and rivers have been made straighter and stronger by extensive agricultural drainage systems, restricting their natural meander. By the late 1990s, it was clear that Topeka standouts were on the brink of extinction and were added to the endangered species list. But they still had a few strongholds in South Dakota, Minnesota, and Iowa.

In 2010 and 2012, the Minnesota Department of Natural Resources began seeing massive declines in the already small number of Topeka shiners remaining in the state. For example, Utrup thought it wouldn’t be long before they left Minnesota.

But ten years ago, things changed suddenly and remarkably. The Fish and Wildlife Service got a small federal grant in 2014 to try a simple plan: Find some of those old oxbows that had been filled in, bring in some heavy equipment and dig them out again.

Even if filled in, the oxbows would have left clear impressions on the land that made them easy to find, said Scott Ralston, a wildlife biologist with Fish and Wildlife working on the project.

Much of the work was done on private property, Ralston said. The drained oxbows never provided good farmland, and many farmers were happy to see the ponds restored as watering holes for livestock, for duck hunting, as feeding wells or just for the view, he said.

The results were immediate. Within a year or two of an oxbow restoration, the Topeka blinkers not only returned, but exploded. The four-inch minnows turned out to be much stronger than anyone expected, Ralston said.

They can survive in waters with little oxygen, rich in nutrients and agricultural chemicals.

When federal funding dried up, the Nature Conservancy stepped in. The conservation group received grants to buy land or pay farmers for easements to permanently protect oxbows with money from Minnesota’s Outdoor Heritage Fund, a sales tax approved by voters. Together they have now restored more than 130 oxbows across the state.

In 2019, the Conservancy purchased 160 acres of restored prairie along Champevelden Creek, just outside Luverne in far southwestern Minnesota, and gave the land to Fish and Wildlife. The agency excavated several old oxbows that year, all about four feet deep and less than 300 feet long.

Last week, as rain clouds rolled in, biologists returned to the Champe paths oxbows for the first time to see if any fish had returned. Conditions at the site were almost terrible; Since it was dug out, the state has suffered one of the most severe and prolonged droughts in decades. There have been few opportunities for the pools to reconnect with the creek.

“There,” Utrup said suddenly, pointing out several small shadows swarming around a much larger moonfish. ‘There they are. Do you see them?’

Topeka shiners like to use sunfish nests when breeding and lay their own eggs in them. Angelfish then protect the shine eggs together with their own eggs.

The biologists saw dozens of shiners circling the angelfish nests.

The crew dragged a seine net over another nearby arch to confirm what was now clear: the Topeka shiners were back. The drought didn’t seem to bother them at all.

“Ooh, there’s one right away,” said habitat biologist Heidi Keuler as soon as the net came out of the water. She picked up a healthy, wriggling, shiny silver specimen with bright orange fins. The orange glows brightly in June, at the peak of their breeding colors. The fish’s skin will turn a duller gray again in the fall. The crew counted and measured a total of 85 Topeka shiners and quickly released them back into their small sanctuary.

They have now returned to virtually every oxbow that Fish and Wildlife has recovered.