The status of the Dwarf Wedgemussel, Alasmidonta heterodon, in Canada

The watershed of the Petitcodiac River, New Brunswick, is the only recorded location of the Dwarf Wedgemussel, Alasmidonta heterodon (Lea 1830), in Ca nada. The species was last collected in the Petitcodiac watershed in 1960, at which time it was considered to be common in the freshwater reaches of t he Petitcodiac River and one of its major tributaries, the North River. Sur veys in 1984, 1997 and 1998 failed to detect any specimens and the Dwarf We dgemussel was classified as Extirpated by the Committee on Status of Endang ered Wildlife in Canada (COSEWIC) in April 1999. The disappearance of the s pecies from Canadian waters was probably caused by the construction of a ca useway across the tidal portion of the Petitcodiac River in 1967-1968 and r esultant exclusion of a diadromous fish species required for completion of the glochidial stage of the Dwarf Wedgemussel's lifecycle. Local extirpatio ns of the Dwarf Wedgemussel from much of its American range have also been linked to dam construction, which blocked migration of anadromous fishes.