Status of freshwater mussels (unionidae) of the Río Conchos basin, Chihuahua, Mexico

Before this study, researchers had not systematically surveyed the Rió Conchos, a tributary of the Rio Grande located in northern Mexico, for freshwater mussels. The Texas hornshell, Popenaias popeii, an endangered species under the United States Endangered Species Act, occurs in the main stem of the Rio Grande near its confluence with the Rió Conchos. The Texas hornshell's proximity to the Rió Conchos prompted us to survey to determine whether P. popeii also occurs within the Conchos basin. Additionally, previous researchers described the Conchos disk, Disconaias conchos, from the Rió Conchos but, to date, no one has reported live individuals of this species. The goal of this study was to determine the status of mussels within the Rió Conchos basin and to provide a baseline for future monitoring efforts. We qualitatively surveyed 11 sites within the Rió Conchos basin in May 2018. In total, we found two live individuals of the paper pondshell, Utterbackia imbecillis, at one site in the Rió San Pedro, a tributary of the Conchos River, and as shells of recently live individuals at two sites in the Rió Conchos. We found D. conchos as relict shells only at three sites, two in the Rió Conchos and one in a tributary of the river at Coyame. The lack of live or fresh-dead material suggests that D. conchos is extinct. We also found live individuals of nonnative Asian clams (Corbicula spp.) at 10 sites. Sand and gravel mining, high organic pollution, and inadequate instream flows were evident throughout the basin and might explain the general absence of mussels.