On August 10, 2016, the U.S. Fish and Wildlife Service (Service) will publish its proposal to list the Texas hornshell, a freshwater mussel species from New Mexico and Texas, as an endangered species under the Endangered Species Act (ESA). The Service will accept comments on the proposed listing until October 11, 2016. The Service requests certain information, including information regarding the mussel, its habitat and requirements for its conservation and notes that, since the determination whether a species is an endangered or threatened species must be made solely on the basis of the best scientific and commercial data available, only comments based upon supporting information will be considered in making the determination. The Service typically makes a final decision to list or withdraw the proposal within a year after proposal.

In addition to the potential direct implications for activities within habitat areas of the Texas hornshell, the Service’s determination to propose listing for the Texas hornshell is important because it provides insight into decisions the Service may make regarding five additional freshwater mussels with ranges that extend across major rivers in central Texas that have been identified by the Service as candidates for listing. The Service is scheduled to make decisions whether to propose those five species for listing sometime after fiscal year 2016.

The Service states that it is proposing to list the Texas hornshell as endangered because it has declined significantly across its historical range that included the Rio Grande River Basin in New Mexico, Texas and Mexico, as well as along Mexican coastal area rivers. The Service asserts that the mussel is now found in only 15% of its historical range in the U.S. and is presently in danger of extinction. In New Mexico, it is now confirmed only in the Black River (a Pecos River tributary) and is the last remaining native mussel in New Mexico. In the Rio Grande, the species is known to be present downstream of Big Bend National Park and near Laredo in Webb County, Texas and the Devil’s River in Val Verde County, Texas.

As noted by the Service, the primary factors affecting the current and future conditions of the Texas hornshell are river fragmentation due to habitat inundation by impoundments and alterations of the natural streamflow regime (by impoundments, drought, groundwater withdrawal and resultant mussel-smothering sediment accumulation), predation and degradation of water quality within its range.