The Dead Horse Mountains, Sleeping Lion, the Staked Plain — our region's place names are evocative. And some evoke a vanished past. Take the Rio Conchos, the major river that joins the Rio Grande at Presidio-Ojinaga. “Conchos” is Spanish for shells — the name speaks to the abundant freshwater mussels the first Europeans found here in the Rio Grande watershed.
It's a different picture today. In July, the U.S. Fish and Wildlife Service proposed federal protection for the Salina mucket, a Big Bend mussel threatened with extinction. It would join another mussel — the Texas hornshell — on the endangered-species list. What's driven these Big Bend creatures to the brink, and what would it take to save them?
Jeff Renfrow of Terlingua, a river guide since 1990, is founder of Rio Bravo Restoration and a fisheries biologist who's long conducted and supported river research.
“I had been kind of missing being involved with science,” Renfrow said, “and that little project looking for mussels in the national park was probably the first thing that had to do with science.”
In 2003, at Big Bend National Park's request, Renfrow began a native-mussel survey, collecting shells on a 200-mile stretch of the Rio Grande. It gave him a singular acquaintance with these creatures.
“I went from Lajitas all the way through the Lower Canyons to Dryden,” Renfrow said, “and walked every gravel bar on both sides of the river, and I did that a couple of times. It was really fun.”
Renfrow collected 1,500 shells. He passed over an invasive species — the corbicula, or Asian clam — focusing on the Salina mucket, the Texas hornshell and a third native, the Tampico pearlymussel. The method had its limits: There was no way to know when, or precisely where, the mussels had lived — shells could have been carried downstream. But the big picture was unmistakable.
Renfrow found fewer than 20 native shells in the first 95 river miles. But near Rio Grande Village, on Big Bend park's east end, shell numbers began a steady rise.
And that correlates with something important: the presence of springs, which, from the park's east side through the remote Lower Canyons, supplement the river's often-meager flow.
“I think the mussels are a really great indicator of what's going on,” Renfrow said, “and I think the fact that their density increases significantly as you move down through that spring gradient is a really good indicator of the importance of that spring water.”
Renfrow has continued studying the shellfish, joining teams to find live mussels. It's confirmed the connection between the mussels and the springs.
In spring 2022, the Big Bend Rio Grande went dry upstream of the springs. And amidst climate change, and ongoing human demands on the U.S. Rio Grande and Mexico's Rio Conchos, that could become routine. The source of the springs here is little understood, but safeguarding them is clearly vital for the mussels.
A decision on the endangered-species listing will come in 2024. Mexican biologists share their U.S. colleagues' alarm over the river's collapsing ecology, Renfrow said. And he's hopeful that endangered-species status for the Salina mucket could be “another piece of evidence” prompting a binational commitment to leave a little water in the Big Bend Rio Grande.
That's what's required to save not only the Salina mucket, but all the river's aquatic life, and even the river itself.
“People are going to have to decide that it's worthwhile to save it,” Renfrow said, “and they're going to have to manipulate these flows – because the current trajectory without any intervention is not promising.”
