Those of you who hike, walk dogs, or birdwatch along sections Putah Creek may be familiar with the small white clam shells that litter sections of the creek bottom and creekside trails. The shells are from an invasive Asian clam called Corbicula fluminea. But on a recent canoe trip down a section of lower Putah Creek, in about two feet of water, I noticed a larger white pearl-colored shell which was easily five times bigger than the Asian clam shells. I had just found the beautiful and fragile shell of -- not a clam -- but the native Western Pearlshell mussel, Margaritifera falcata.
Western Pearlshell mussels can be found from California to Alaska, and east into Wyoming. Like all mollusks, they are filter feeders, consuming plankton, algae and bacteria. They thrive in cool, clean freshwater creeks, preferring undisturbed flatwater and eddies with gravel, sand and boulder bottoms. When they are protected from high water flows and other disturbances, they can live 50 to 60 years or more. Construction of dams, agricultural runoff, sedimentation, erosion, contamination from mining, introduction of nonnative fish, and other disturbances have caused a significant population decline in most areas of their native range. In Putah Creek, Pearlshells thrive in the clean, cool creek waters (45º F to 50º F) above Lake Berryessa, and can be found below the dams, sometimes as far east as the Yolo Bypass Wildlife Area.
A large shell like this one, which measures four inches, means Western Pearlshell mussels are finding suitable habitat to grow and mature and thrive for many many many years in lower Putah Creek. This is very exciting news from a creek restoration point of view!
Although they are not a listed species under the Federal or State Endangered Species Acts, handling of the mussels and their shells, also called “take,” is protected under State scientific collecting permit requirements.