On August 10, 2016, the U.S. Fish and Wildlife Service (USFWS) issued a proposed rule to list the Texas hornshell (Popenaias popeii), a freshwater mussel, as an endangered species under the Endangered Species Act (ESA). The species has been on the candidate species list for over a decade, and the proposed rule meets a listing determination deadline established by a 2011 multidistrict settlement agreement. In the proposed rule, USFWS determined that the species is in danger of extinction due to habitat loss from loss of water flow, decreased water quality, increased accumulation of fine sediments, and predation, and therefore that listing is warranted. Texas hornshell spawning occurs from March through August, and USFWS cited flowing water needs, water quality sensitivity, drought, climate change, sedimentation, groundwater and surface water withdrawals, and reservoir impoundment impacts on the Texas hornshell in its discussion of the species’ needs and threats. The Texas hornshell is one of a number of Texas freshwater mussel species that face similar threats and remain on the candidate list or are pending status review.
Historically, the Texas hornshell ranged throughout the Rio Grande drainage in New Mexico and Texas in addition to multiple river drainages in Mexico. The species’ current range includes five known populations in the Black River (Eddy County, New Mexico), Pecos River (Val Verde County, Texas), Devils River (Val Verde County, Texas), Lower Canyons of the Rio Grande (Brewster and Terrell Counties, Texas), and Lower Rio Grande near Laredo (Webb County, Texas). While USFWS declined to include a critical habitat designation in the proposed rule, USFWS is seeking information that would inform a future designation as well as other specific information that is currently lacking for the species. Further, the listing proposal recognizes management actions currently underway—including reintroduction into the Delaware River in New Mexico by the New Mexico Department of Game and Fish and management of 200,000 acres of conservation lands in Devils River watershed in Texas by the Texas Parks and Wildlife Department and The Nature Conservancy—and seeks participants for additional recovery efforts in the event of final listing.
In accordance with USFWS policy, the proposed listing identifies certain activities that are unlikely to result in a prohibited “take” of Texas hornshell, including: (1) normal agricultural and silvicultural practices, including herbicide and pesticide use, which are carried out in accordance with any existing regulations, permit and label requirements, and best management practices; and (2) normal residential landscape activities. USFWS further provided a non-comprehensive list of some activities that may result in a “take” violation, including: (1) unauthorized handling or collecting of the species; (2) modification of the channel or water flow of any stream in which the Texas hornshell is known to occur; (3) livestock grazing that results in direct or indirect destruction of stream habitat; and (4) discharge of chemicals or fill material into any waters in which the Texas hornshell is known to occur.
Photo credit: Joel Lusk, USFWS