E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Preferred habitats include shallow muddy or sandy habitats in slow rivers and lakes, though they are also known from some reservoirs. They can inhabit streams and rivers but usually are found in stable areas with fine sedi­ments and little shear stress.

Given the recent taxonomic work suggesting that A. californiensis and A. nuttalliana belong to a single clade, it is difficult to denote the range of these “species” in western North America. The native range of what has been called A. californiensis extended from Baja California to southern British Columbia, and east to western Wyoming, eastern Arizona, and Chihuahua (Mexico). It was originally widespread in California, but its distribution is now greatly reduced. It was once distributed throughout six major drainages in Arizona, but today only remnant populations are thought to exist in portions of the Black River drainage and Little Colorado River. In Washington, recent records are mainly from the Columbia River drainage. A. nuttalliana had been considered the least common western Anodonta. Even before the recent genetic work was published, people had difficulty identifying this species and historical data are difficult to assess because A. nuttalliana was often called by other names. One reason for the confusion is that specimens of A. nuttalliana with a low dorsal wing are nearly indistinguishable from A. californiensis.

In British Columbia this species is known from the lower mainland to the east Kootenays and north to Lac la Hache (Gelling 2008).

Mussels rely on fish to reproduce and replenish populations; and therefore changes in the West’s fish fauna have threatened the region’s mussel fauna. This species has historically been affected by water diversion for irrigation, water supply, and power generation. They have been found in reservoirs, but many reservoirs experience severe annual water level fluctuations that decimate the standing crop of mussels during low-water periods. Non-native fish may compete with a mussel’s host fish, or eat young mussels (e.g., common carp), and nonnative mollusks can compete with mussels for food and space (e.g., Asian clams, zebra mussels, and quagga mussels). Mussels are sensitive to water quality changes, habitat changes as well as changes in the fish fauna.

The Unionidae are distributed throughout the world, but are most diverse in eastern and central North America, and in China and Southeast Asia.