Nearly 500 miles of Rio Grande, other rivers could be deemed critical habitat for endangered mussel

Madlin Mekelburg
Austin American-Statesman
A handfull of Texas hornshell mussels are gathered at the Black River in southern Carlsbad.

Tucked into a crevice in the depths of the lower Rio Grande, the Texas hornshell mussel lies in wait.

In its protected position buried in the sediment, the mud-colored mollusk can avoid being swept away during floods and is in prime position for feeding and reproduction.

These animals are largely immobile as adults, experiencing movement only at an early stage in their life cycle, when as larvae — or glochidia — they attach to the face or gills of a host fish for up to a month to survive.

The mussel beds in the lower Rio Grande where adult Texas hornshells spend their days are one of five known populations of the species, which are also present in the Black River, Pecos River, Devils River and lower canyons of the Rio Grande.

These modern habitats represent 15% of the historical range of the species in the United States, as the Texas hornshell’s population has dwindled in recent decades. In 2018, it was classified as an endangered species. The loss of flowing water, declining water quality and the introduction of barriers to fish movement threaten to further reduce the mussel’s footprint.

Now the U.S. Fish and Wildlife Service has proposed designating nearly 500 miles of the Rio Grande and adjoining rivers as critical habitat for the hornshell, a move that would have implications for future infrastructure projects in the area.

“Critical habitats are areas that are necessary for the recovery of endangered species, not just for survival, but getting them to the point at which they’re no longer in danger of extinction,” said Michael Robinson, a senior conservation advocate at the Center for Biological Diversity, which has pursued protections for the Texas hornshell for more than 20 years. “It’s effective because the federal government is not allowed to take any actions that harm or destroy critical habitat for an endangered or threatened species.”

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Critical habitat designation

A critical habitat designation identifies geographic areas occupied by an endangered species that have physical or biological features essential to species’ conservation and recovery, according to the U.S. Fish and Wildlife Service.

The service is required to identify critical habitats for any species that are federally listed as threatened or endangered. Once approved, the designation requires federal agencies and other entities to consult with the agency on any actions that could affect the critical habitat.

In the case of the Texas hornshell, the proposed designation covers approximately 464 miles of river, including roughly 304 miles of the Rio Grande, 86 miles of the Pecos River, 33 miles of the Devils River, 31.1 miles of the Delaware River and 9.7 miles of the Black River.

This map shows the proposed critical habitat designation for the Texas hornshell, which includes nearly 500 miles of waterways in South Texas.

Clint Robertson, a senior scientist in the river studies program at the Texas Parks and Wildlife Department, said the Texas hornshell is endemic to the Rio Grande basin and is the only freshwater mussel that lives throughout the Devils River system.

“I wouldn’t say it is unique, but anything that has evolved in the Desert Southwest is pretty extraordinary,” he said. “Water is a pretty precious commodity, and so any aquatic organism that has evolved to live there is always interesting.”

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Robertson has handled mussel-related issues and research projects at the state agency for 11 years — including efforts to study and protect the Texas hornshell, which can grow 3 to 4 inches long and live as long as 20 years.

Freshwater mussels generally are considered an “umbrella species,” he said. That means if mussels are protected and thriving in an environment, the entire ecosystem is protected.

“Mussels are kind of like the quintessential canary in the coal mine for aquatic communities,” Robertson said. “If some impact or habitat alterations or things going wrong, because of their complex life history and their sensitivity to water quality and habitat alterations, they’re usually the first to start dying off. That’s when you know you have a problem.”

DEL RIO, TX - MAY 8, 2017 - View from the bluff over the Del Norte Unit of the Devils River State Natural Area.

Water quality is among the primary concerns for the longevity of the Texas hornshell and other freshwater mussels, because the animals are completely dependent on water. Mussels are filter feeders, meaning they pull nutrients from the water for survival, Robertson said, and serve as “the livers of the river or little wastewater treatment plants.”

They also depend on fish for survival in early stages in their life cycle, when as glochidia they attach to the face or gills of a fish to obtain nutrients and to hop a ride to a different area of the river.

Flowing water is also essential to the reproductive cycle of the mussel, as males release sperm into the water and allow it to be carried to a female through the water column. This flow is essential, as Robertson said the Texas hornshell is almost entirely submerged in sediment under the water and does not move as an adult.

Despite their hidden positions, Robinson of the Center for Biological Diversity said they serve an essential role both as a part of the food chain — raccoons and catfish are known predators of the mussel — and as a filter feeder.

“People very naturally may be saying, ‘I went down to the Rio Grande six years ago; it was great, but I went under the water, and I didn’t see Texas hornshells,’” he said. “The key thing to keep in mind is the beauty and direct benefits we get from the natural world depend on complex, complex interactions between a lot of different creatures out there — even the ones underneath the water.”

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Infrastructure impact

After proposing a critical habitat designation, the U.S. Fish and Wildlife Service has one year to finalize the rule. In the case of the Texas hornshell, it has until next summer.

On Tuesday, the agency will host a public informational meeting where officials will outline the proposal and solicit feedback from members of the public. People and organizations may also submit written comments about the proposal.

“We’ll review the information we received and, based on that information and the best available science, we’ll make a determination about what final critical habitat may look like,” said Lesli Gray, a congressional liaison for the service based in Dallas.

If adopted, any federal project that has the potential to affect the designated habitat would have to consult with Fish and Wildlife. This includes projects from federal agencies or any that use federal funds or require federal permits.

The Rio Grande runs alongside FM 170, also known as the River Road, on Tuesday, February 28, 2017. To the left is Mexico and the right the United States.

Unlike protections for endangered species that are specific to the animal itself, critical habitat designations aim to specifically protect the physical environment. In some cases, there is little distinction between protecting the species and its habitat.

“This is an example of where critical habitat really isn’t worth all the trouble,” said Alan Glen, an Austin attorney who specializes in federal environmental law. 

Under the Endangered Species Act, Glen said, federal agencies are prohibited from jeopardizing a species listed as threatened or endangered or from adversely modifying a designated critical habitat. 

“This is one of those species where the jeopardy determination is so similar to the adverse modification of critical habitat,” he said, referencing that the Texas hornshell can only survive in water and under certain river conditions. “That’s why the service’s economic analysis on the impact of this listing is very constrained. They don’t see that there’s a very large increase in cost.”

In a document addressing questions about the designation, the agency wrote that its economic analysis found that “it is unlikely that critical habitat would generate additional requests for conservation efforts beyond what would be required as a result of the” Texas hornshell being listed as an endangered species in 2018. The analysis estimated that no more than eight consultations would be required by a federal agency or federally funded project in a given year, with an estimated annual price tag of $72,000.

Those types of projects could include road or bridge construction, dams and other diversions, oil and gas protection, or possibly border protection initiatives.

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It remains to be seen what impact a finalized designation could have on Gov. Greg Abbott’s plan to build a physical barrier along the U.S.-Mexico border, which he said will be funded through a combination of state dollars and donations.

Until specifics of Abbott’s plan are revealed — including funding sources, the location of the wall and whether federal permits would be required — the impact of a possible critical habitat designation is difficult to assess.

“I’m not aware that any information has been shared with us regarding that, where that would happen, how that would be done,” Gray said. “I would not want to speculate on what it may or may not mean with respect to the hornshell.”

Hearing on Texas hornshell protections

On Tuesday, the U.S. Fish and Wildlife Service will hold a virtual informational meeting from 6 to 7 p.m., followed by a public hearing from 7:30 to 9:30 p.m. Anyone wishing to make an oral statement at the public hearing must register before the hearing at https://zoom.us/meeting/register/tJcpfu6vrDIsG9V8ggbwWStJJz5umZ2DJmVi.

Post and review online comments at regulations.gov. In the Search box, enter FWS-R2-ES-2018-0021 to find the Texas hornshell proposal. You may submit a comment by clicking on ‘‘Comment Now!’’

Send written comments to Public Comments Processing, Attn: FWS-R2-ES-2018-0021; U.S. Fish and Wildlife Service Headquarters, MS: BPHC, 5275 Leesburg Pike, Falls Church, VA 22041-3803.