Center for Biological Diversity

For Immediate Release, August 9, 2016

Contact: Michael Robinson, (575) 313-7017,

Vanishing Rio Grande Mussel Proposed for Endangered Species Protection

Texas Hornshell Barely Hangs On in Texas, New Mexico

SILVER CITY, N.M.— Following a landmark settlement with the Center for Biological Diversity requiring consideration of protection for 757 species, the U.S. Fish and Wildlife Service today proposed endangered species protections for the Texas hornshell, a species of mussel from the Rio Grande and its tributaries. The last surviving native freshwater mussel in New Mexico, the hornshell is severely threatened by plans for a new dam, pollution and destruction of its river habitat. 

“The plight of the Texas hornshell reflects the unchecked pollution, overuse and damming of the once-mighty Rio Grande,” said the Center’s Michael Robinson. “The remarkable survival of this unassuming creature spotlights the critical importance of protecting our last clean, flowing rivers — and doing right by mussels and people alike.”

The Texas hornshell, sporting a dark green or brown shell up to 4 inches long, was once found in rivers and streams throughout the Rio Grande watershed. It is now confined to six isolated stretches, including just two tributaries of the Pecos River in southeastern New Mexico, an 8.7-mile stretch of the Black River and a recently reintroduced and not-yet-established population in the Delaware River.

The largest Texas hornshell population, in the Rio Grande near Laredo, Texas, is immediately threatened by plans for a new dam. Another Texas population, in the Pecos River, is declining steeply as a result of increasing salinity caused by excessive diversion of river water for irrigation.

The Texas hornshell is also imperiled due to groundwater pumping and stream-diversions for municipalities and agriculture, global warming that reduces surface water, pollution from oil and gas drilling and sedimentation, and loss of riparian vegetation from grazing by livestock.

This is the final year of the 757 species settlement agreement between the Center and the Fish and Wildlife Service. To date 147 species have been granted endangered species protection under the agreement, and another 35, including the hornshell, have been proposed for protection. 

The Texas hornshell typically occur in narrow areas of rivers and streams with sand, clay or gravel bottoms. They prefer undercut big boulders where the current slows, allowing the mussels to get a safe foothold and not be washed away in times of high water. They also anchor themselves in crevices and undercut riverbanks.

Male Texas hornshells release their sperm into river currents, and females downstream inhale them to fertilize their eggs. Embryos develop in specialized portions of the females’ gills, growing into sand-grain-sized creatures called “glochidia,” which are released into the current and attach themselves to fish gills. The glochidia grow to maturity and then drop to the bottom of the river.

The Center for Biological Diversity is a national, nonprofit conservation organization with more than 1.1 million members and online activists dedicated to the protection of endangered species and wild places.

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