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Study: Range Of Western Freshwater Mussels Declines By One-Fifth, Could Impact Stream Health
Posted on Friday, November 03, 2017 (PST)

The historic range – Mexico to Alaska – of freshwater mussels has declined by 18 percent, according to a recent study that surveyed over 700 watersheds in western states.


Surveying 708 watersheds, thought to have at one time hosted a variety of mussel species as far back as 1834, the study found that just 580 of the watersheds still contain some species of mussel. In addition, mussel richness, or diversity of types of mussels found, declined by 35 percent.


“When watersheds with higher past mussel richness (containing three or four species or clades) were considered independently, 48 percent of these historic ‘hot spots’ have declined in richness in the recent time period,” the study says.


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


There are more than 300 species of freshwater mussels in North America, mostly east of the Rocky Mountains, but 74 percent of those are considered imperiled, according to Xerxes Society information. That means that they either have disappeared from some areas, persist in only small population or are extinct.


Western species, such as western pearlshell, western ridged and several species of floater mussels are fewer in number and receive less attention than eastern mussels or other aquatic species that share the same waters with mussels.


“Freshwater mussels are profoundly important to creek health, filtering the water as they feed and keeping it clean and clear for people as well as fish and other wildlife,” said Matthew Shephard of the Xerces Society.


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.


The scientists also assessed the health of individual species, finding that the western ridged mussel and winged floater are “vulnerable” to extinction; they have disappeared from more than 30 percent of their range.


The western pearlshell is “near threatened,” having disappeared from more than 15 percent 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 of “least concern,” the report concludes.


“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 provided their observations or collection information to the Western Freshwater Mussel Database ( The database is a project of the Xerces Society and the Confederated Tribes of the Umatilla Indian Reservation’s mussel project.


Members of the Pacific Northwest Native Freshwater Mussel Group ( contributed thousands of records to the database, often revisiting mussel populations repeatedly over the ten-year study to document their observations. In some cases, the project used crowdsourcing to gather information.


The study, Extinction risk of Western North American freshwater mussels: Anodonta Nuttalliana, The Anodonta Oregonensis/KennerlyI Clade, Gonidea Angulata, and Margaritifera Falcata, was published online October 27 in Freshwater Mussel Biology and Conservation,


In addition to Blevins and Jepsen, co-authors are Jayne Brim Box, Donna Nez and Alexa Maine with the Department of Natural Resources Fisheries Program, Freshwater Mussel Project of the Confederated Tribes of the Umatilla Indian Reservation; Jeanette Howard of the Nature Conservancy; and Christine O’Brien of Browns River Consultants.


“Many conservation and research priorities identified in the Freshwater Mollusk Conservation Society’s national strategy (2016) would benefit western freshwater mussels,” the study concludes. “These strategies include improving understanding and increasing accessibility of taxonomy and distribution information, addressing past, ongoing, and emerging stressors and their impacts, improving understanding of habitat and conserving habitat, improving understanding of mussel population ecology, and restoring abundant mussel populations.”


Established in 1971, the Xerces Society is a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat (


Also see:


--CBB, September 4, 2015, “Umatilla Tribes Use BPA Funds To Acquire Acreage To Improve Spawning, Rearing For Endangered Salmon,”


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