Western Pearlshell Mussel
Category
Native Bivalve (Family Margaritiferidae)
Common Name
Western Pearlshell Mussel
Species Name
Margaritifera falcata
Distribution / Status (Tahoe)
Native to western North America; present in the Truckee River and tributaries but not confirmed in Lake Tahoe; populations declining regionally
Diagnostic Features
Thick, dark shell with smooth concentric lines; elongated “falcate” shape; pearly white nacre interior
Commonly Confused Species
Quagga Mussel (Dreissena bugensis), Zebra Mussel (Dreissena polymorpha), Golden Mussel (Limnoperna fortune)
Shell Shape / Form
Elongate, elliptical to slightly curved (“falcate”) shell with rounded anterior and posterior ends
Shell Size
60–130 mm long; older individuals can exceed 140 mm
Shell Thickness
Thick, heavy, and durable; becomes thicker with age
Hinge Features
Strong hinge with small pseudocardinal teeth; lateral teeth long, slightly curved; hinge plate robust
Shell Sculpture / Texture
Smooth, with fine concentric growth lines; lacks obvious ridges or spines
Color / Patterning
Exterior dark brown to black (may appear olive in juveniles); interior nacre (pearly layer) white to bluish or pinkish
Umbonal Position
Slightly anterior; raised above hinge line; worn and eroded in older individuals
Periostracum Condition
Thick and dull in adults; glossy in juveniles
Soft Body Features
Pale to gray body; large muscular foot; paired siphons for filter feeding and respiration
Habitat Type
Cold, clear, well-oxygenated rivers and streams
Substrate Preference
Coarse sand, gravel, or cobble substrates; avoids silt
Depth Range
Typically <1 m; embedded partially in substrate with posterior end exposed
Temperature Range
Prefers cold water (<18 °C); sensitive to temperature and sedimentation increases
Association / Behavior
Sedentary; adults largely immobile once buried
Ecological Role / Impact
Native species important for water filtration, nutrient cycling, and as an indicator of cold, unpolluted streams; filter feeder; juveniles interstitial and feed on bacteria; adults filter phytoplankton and detritus
Reproduction
Long-lived (often 50–100+ years); larvae (glochidia) are parasitic on salmonid fish (e.g., trout, salmon)
Growth Lines / Rings
Prominent annual growth rings; distinct concentric rings mark annual growth and can be used to estimate age (individuals often >50 years). Rings visible on shell surface and internal cross-sections.
References
Frantz, T.C., and A.J. Cordone. (1996). Observations on the macrobenthos of Lake Tahoe, California-Nevada. California Fish and Game 82:1–41.
Gould, A.A. (1850). [Shells from the United States Exploring Expedition]. Proceedings of the Boston Society of Natural History 3(19):292–296.
Howard, J. (2010). Sensitive Freshwater Mussel Surveys in the Pacific Southwest Region: Assessment of Conservation Status (pp. 1–60). USDA Forest Service.
Hovingh, P. (2004). Intermountain freshwater mollusks, USA (Margaritifera, Anodonta, Gonidea, Valvata, Ferrissia): geography, conservation, and fish management implications. Monographs of the Western North American Naturalist, 2(1), 109–135. doi:10.3398/1545-0228-2.1.109
Nedeau, E. J., Smith, A. K., Stone, J., & Jepsen, S. (2009). Freshwater Mussels of the Pacific Northwest (pp. 31–35).
U.S. Forest Service. (n.d.). Western pearlshell mussels in the Tahoe Basin. U.S. Department of Agriculture, Forest Service, Lake Tahoe Basin Management Unit. Retrieved from https://www.fs.usda.gov/r05/laketahoebasin/animals-plants/exotic-invasives/western-pearlshell-mussels-tahoe-basin
Supporting Partners
The Martis Fund, a collaborative project of Martis Camp landowners, DMB/Highlands Group (the developers of Martis Camp), Mountain Area Preservation (MAP), and Sierra Watch. (See martisfund.org for more information)
The Community Impact Fund, Ashley Quinn Fund & the Foresight Fund held at the Tahoe Community Foundation
Additional thanks to the Tahoe Regional Planning Agency for providing specimens for studio filming
