Nature Notes; Return of the Rio Grande Silvery Minnow

U.S. Fish & Wildlife Service. The Rio Grande silvery minnow was once the most abundant fish in the river, but had disappeared from Texas by the 1960s. Now, biologists are trying to reintroduce the minnow in the Big Bend.

Photo by Aimee Roberson

Fish – not what leaps to mind when you think of the native wildlife of the Southwest. But the Rio Grande historically has been home to dozens of fish species – including some not found in any other river system.

The Rio Grande silvery minnow was once the most abundant fish species in the river. But by the 1960s, it had vanished from Texas.

Now, wildlife specialists are working to reintroduce this endemic, native creature.

The Rio Grande silvery minnow once flourished in the river, from the southern Rockies to the Gulf of Mexico. Three to 5 inches long, it was at the base of the food chain.

But flows in the Rio Grande have declined in the last century, as water demands from agriculture and cities have increased. And with the construction of dams like Elephant Butte in southern New Mexico, snowmelt floods no longer surge downstream.

The changes have decimated fish populations. The silvery minnow is now found only between Albuquerque and Elephant Butte – just five percent of its former range. In 1994, the minnow was added to the endangered species list.

Since 2000, wildlife managers have worked to protect the fish. Minnows are spawned in fisheries in New Mexico, and reintroduced there in an effort to boost populations.

And in 2005, Texas biologists joined the effort.

Mike Montagne is project leader with the U.S. Fish and Wildlife Service in Austin. His office is working with Texas Parks and Wildlife and Sul Ross State University to return the minnow to the Big Bend.

“What we’re doing right now is kind of a small-scale effort to try to show them, that if we have some success, we can be valuable,” Montagne said. “We’d like them to start helping us to find these answers faster.”

The work hasn’t been easy.

Biologists initially released fish in Big Bend National Park and Big Bend Ranch State Park. But there was no evidence the minnows were taking hold there.

Now, the biologists are focused on the Lower Canyons of the Rio Grande. The 140-mile stretch between La Linda and Langtry is famed for its beauty, and its inaccessibility. The remote canyons are also lined with springs, which add water to the river and improve water quality.

The minnows appear to be responding to those conditions, and the biologists are finding more survivors than they did in releases upstream.

Yet it remains to be seen if the altered river can support the minnow. The release of the minnow’s eggs is “cued” to the pulse of spring snowmelt. That snowmelt no longer reaches West Texas.

Young minnows need floodplains and backwaters in which to hatch and grow. And those features are now scarce.

“It’s a big experiment,” Montage said. “We don’t know if it’s going to work or not. We might be able to keep them alive down in the canyon, but if we can’t get them to reproduce, it doesn’t really matter. First steps first – we’ve got to get a place where we can find them consistently, so that we can make those kinds of decisions and really start applying our science to them so we can come up with some answers.”

In the West, habitats have been often altered or destroyed before they’ve been understood. Montagne said the silvery minnow is just one of many creatures that have vanished from the Rio Grande in West Texas.

“The fish is just an indicator of what’s going on in that river,” he said. “We have other species we don’t see out there anymore, but they’re not listed as endangered. Once something’s gone, it never comes back. There are probably things going away that we don’t even know about.”

The Uvalde National Fish Hatchery, in Uvalde, Texas, is working with Montagne to raise minnows for the project. In contrast to the restoration effort in New Mexico, the Texas project is defined as “experimental” – meaning private landowners face no restrictions on the use of their land or water.

The silvery minnow can be removed from the endangered species list if there are three self-sustaining populations. If the Texas biologists succeed in establishing a breeding population in the Lower Canyons, they could receive funding to expand their work.

Montagne said he and his colleagues are committed to trying to return the Rio Grande silvery minnow to its West Texas home.

Nature Notes is underwritten by the Dixon Water Foundation and is produced by Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Andrew Stuart.

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