EL PASO, Texas— The U.S. Fish and Wildlife Service proposed today to protect 463 miles of the Rio Grande and its tributaries in Texas and New Mexico as critical habitat for the endangered Texas hornshell, a large brown and green mussel.

“Critical habitat will ensure water availability and purity for this sensitive animal,” said Michael Robinson at the Center for Biological Diversity. “Survival of the Texas hornshell in a clean and ever-flowing Rio Grande will help sustain the whole ecosystem as well as our communities.”

Pollution, water impoundments and depletion, along with low flows due to global warming, have fragmented the range and reduced the number of the Texas hornshell, which was once common in streams and rivers throughout the Rio Grande watershed.

Under the Endangered Species Act, other federal agencies will have to consult with the Service over any actions, including permitting and funding, that would destroy or harm areas of critical habitat once the designation is finalized, which must occur within a year. A 60-day public comment period on today’s proposed rule will begin soon.

Today’s proposed rule identifies the aquatic features that the Texas hornshell requires: swift water to move sediment, but not so fast as to dislodge the mussels from their crevices beneath boulders and within undercut banks; low levels of contaminants including ammonia and salinity; and high levels of dissolved oxygen.

The rule also notes the need for three native fish species that the hornshells parasitize by implanting their young within their gills: river carpsucker, red shiner and gray redhorse.

The critical habitat proposed in Texas includes 304.1 miles in four segments of the Rio Grande, 85.7 miles of the Pecos River almost to its confluence with the Rio Grande, and 33 miles of the Devil’s River. The proposal also includes 31.1 miles of the Delaware River flowing from West Texas into southeastern New Mexico, and 9.7 miles of the nearby Black River in New Mexico.

In 2004 the Center and eminent scientists and authors filed a scientific petition to protect the Texas hornshell and more than 200 other imperiled species under the Endangered Species Act. Subsequent litigation by the Center led to the listing in 2018 and today’s proposal.

Background

Texas hornshells 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 ingest 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.