Abstract

Freshwater mussels are valuable components of intact salmonid ecosystems and are culturally important to Native Americans. An inventory of the freshwater mussels in the Umatilla and Middle Fork John Day rivers in Oregon was conducted in the summer of 2003. Freshwater mussels were found at all sites surveyed in the Middle Fork John Day River, but at less than 10% of the sites sampled in the Umatilla River system. All three genera of freshwater mussels known to occur in the western United States were found in the Middle Fork John Day River, and co-occurred at almost 50% of the sites sampled. In the Umatilla River, two genera were found, Anodonta and Gonidea, but only in the lower main stem and one tributary. Live Margaritifera were not found in the Umatilla River, although historically they occurred in the system. Shell material collected in the current survey suggests Margaritifera occurred in the Umatilla River main stem until very recently. Habitat degradation, including active channel change and the decline of salmonid and other native fish populations may have contributed to the extirpation of freshwater mussels from historical locations. The data collected in this survey will be used to provide essential information for designing a recovery plan for freshwater mussels in the Umatilla River system, as part of ongoing efforts to rebuild ecosystem function and diversity.