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Pecos assiminea Assiminea pecos
ESA status: endangered

Pecos_assiminea pc Brian LangBitter Lake National Wildlife Refuge in Chaves County, New Mexico, is a place of unique ecological convergence, where the Chihuahuan Desert meets the shortgrass prairie and the Pecos River flows through the Roswell artesian basin. This wetland refuge is a haven for birds, and heaven for birders, who can seasonally enjoy thousands of migrating lesser sandhill cranes, Ross and snow geese, and about twenty duck species, as well as myriad songbirds and quail. Walking trails lead hikers through wetland thickets and along riverbanks, providing a peaceful getaway. But the Refuge’s most unique offering is available by appointment only...

The diverse waters of the Bitter Lake area—flowing streams, rivers, sinkholes, playa lakes, and brackish waters—shelter an incredible diversity of rare organisms. On the first Saturday of every month from October through May, you can take a guided Endangered Species Tour into parts of the Bitter Lake National Wildlife Refuge that are closed to the public. In these closed sections, you will see Bitter Lake itself, the springs which are the source of the refuge’s lakes and ponds, and around 60 sinkholes, each one a unique habitat. It is on this tour that you may have your only chance to see the tiny, rare Pecos assiminea.

This miniature snail, only 1.5 to 1.9 millimeters in length (a little bigger than a pencil point), belongs to the genus Assiminea, which can be distinguished from other snail genera by its short, stubby eyestalks. The Pecos assiminea is not fully aquatic, preferring a humid habitat in wet mud or beneath mats of vegetation, typically within a few centimeters of running water (a long way for such a tiny creature). This snail likely evolved from one of the snail species that enjoyed a broader distribution during the wetter, cooler Pleistocene around 10,000 years ago. They have a short lifespan, only 9 to 15 months, and reproduce several times during that brief opportunity. They feed on algae, bacteria, and decaying organic material.

The Pecos assiminea is currently found along Bitter Creek and at the edges of a sinkhole in the Sago Springs complex in Bitter Lake National Wildlife Refuge. It is also known from two springs in Texas. It was once found in Coahuila, Mexico, but the status of that population is unknown. Aquifer depletion and contamination from development and oil and gas drilling in the Roswell Basin are the most important threats to the species. There are at least 190 oil wells surrounding Bitter Lake that could contaminate the aquifer that underlies the refuge.

Pecos assiminea are important ecological barometers of water quality. These tiny creatures are very sensitive to oxygen levels, water temperature, sedimentation and contamination. Their disappearance usually indicates the loss of a pristine spring or watercourse. WildEarth Guardians fought to obtain protections this tiny snail now enjoys under the Endangered Species Act, and we will continue to advocate for responsible water use and against the proliferation of oil and gas drilling and unsustainable development that threaten Bitter Lake. Our vision for the whole of the West, not just Bitter Lake, is that of clear streams and springs free of pollution and home to their full complement of unique inhabitants.

photo credit: Brian Lang, New Mexico Department of Fish and Game