PORTLAND, Ore. October 30, 2017 – Freshwater mussels filter water, keeping it clean and clear for salmon and other aquatic wildlife. A study published Friday shows that these important animals have been lost from 1 in 5 watersheds in which they occurred in western North America, and more than one third of watersheds in which they remain have lost one or more species of mussels.

Researchers compiled a comprehensive database of mussel records from research and museum collections, historical publications, and public agency and personal records dating as far back as 1834, allowing scientists for the first time to understand the true picture of mussel distribution in western North America.

What they found was not good news: freshwater mussels are being lost from Mexico to Alaska. Mussels have disappeared from 18% of the watersheds they once inhabited, and fewer species are now found in 35% of watersheds.

“The results from this work are depressing,” said Emilie Blevins, conservation biologist with the Xerces Society and lead author on the new study. “But it until now there wasn’t a solid foundation for planning conservation efforts. With this information we can now get on with protection efforts.”

The scientists also assessed the health of individual species, using the criteria of the IUCN Red List. The western ridged mussel and winged floater are “vulnerable” to extinction; they have disappeared from more than 30% of their range. The western pearlshell is “near threatened,” having disappeared from more than 15% of its range and suffered large declines in abundance elsewhere. The Oregon floater and western floater appear to be suffering the least, and are together classified as “least concern.”

“This was a joint project of the Xerces Society and Confederated Tribes of the Umatilla Indian Reservation Mussel Project,” said Sarina Jepsen, director of aquatic programs for the Xerces Society. “The project took nearly ten years and the Confederated Tribes’ continued engagement has been essential to its long-term success.”

More than 160 people and nearly 100 institutions generously provided their observations or collection information to the Western Freshwater Mussel Database, a project of the Xerces Society and Confederated Tribes of the Umatilla Indian Reservation Mussel Project. Members of the Pacific Northwest Native Freshwater Mussel Workgroup have contributed thousands of records to the database, often revisiting mussel populations repeatedly over the years and documenting their observations.