Western Freshwater Mussels

By Celeste Mazzacano

A handful of western freshwater mussels. Photo: Celeste Mazzacano

Freshwater mussels are experiencing a dramatic decline; 72% percent of North American freshwater mussels are considered extinct or imperiled, representing one of the most at-risk groups of animals in the United States (learn more about mollusks in general here). The decline of freshwater mussels has been well studied in eastern North America but has received very little attention in states west of the Rocky Mountains. To better understand the status and distribution of these animals, the Xerces Society in partnership with the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) Mussel Project has completed extinction risk assessments for four of the six species of western freshwater mussels using the methods and criteria of the IUCN Red List of Threatened Species™: the western pearlshell (Margaritifera falcata), the western ridged mussel (Gonidea angulata), the winged floater (includes both Anodonta nuttalliana and previously-recognized A. californiensis), and the Oregon floater (includes both Anodonta oregonensis and previously-recognized A. kennerlyi). Too little information was available to assess the Yukon floater (Anodonta beringiana) or the woebegone floater (Anodonta dejecta). We concluded that declines have occurred in parts of each species’ range, and both the western ridged mussel and the winged floater are Vulnerable to extinction; the western pearlshell is Near Threatened. Although populations of the Oregon floater have also declined, they are ranked Least Concern. Evidence suggests that these animals are experiencing population declines due to habitat alteration or destruction, and mussels have been relatively neglected in western aquatic conservation efforts.

Native freshwater mussels have immense ecological and cultural significance. As filter-feeders, they can substantially improve water quality by filtering out harmful pollutants, which benefits both humans and aquatic ecosystems. Freshwater mussels can benefit native fish by making food more visible and bioavailable to the fish. These animals can be highly sensitive to environmental changes and thus have great potential to be used as indicators of water quality. Freshwater mussels have been historically important sources of food, tools, and other implements for many Native American tribes. Native Americans in the interior Columbia Basin have harvested these animals for at least 10,000 years, and they remain an important cultural heritage for tribes today.

Have you seen or worked with western freshwater mussels? We’re seeking information on observations for the Western Freshwater Mussel Database (see below), tracking mussel relocation projects, and documenting observations of mussel die-offs. Please share your observations with us by contacting us at mussels@xerces.org.



Western Freshwater Mussel Database

The Xerces Society and the Confederated Tribes of the Umatilla Indian Reservation have compiled a database of western freshwater mussel records for the following species and clades: Anodonta californiensis/nuttalliana, A. oregonensis/kennerlyi, Gonidea angulata, and Margaritifera falcata. Copies of this database are available to researchers upon request. For a full list of contributors and data sources used for this database, click here.

PNW Native Freshwater Mussel Workgroup

Visit the Pacific Northwest Native Freshwater Mussel Workgroup website, Facebook page, or Freshwater Mussels of the Western US iNaturalist project for more information.


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