Scientific Name: Alasmidonta heterodon
Taxonomy Group: Molluscs
COSEWIC Range: New Brunswick
COSEWIC Assessment Date and Status Change: December 2021
COSEWIC Status: Extirpated
COSEWIC Status Criteria:
COSEWIC Reason for Designation: This freshwater mussel was previously known in Canada from only the Petitcodiac River drainage in New Brunswick. It disappeared after construction of a causeway across the river in 1967/68, presumably because of the loss of the host fishes which are required for completion of the mussel species life cycle. The species has not been found since, despite intensive systematic searches of its former habitat. The causeway has been partially removed, and is no longer fully blocking access to the river for the host fishes. Some host fishes have been observed in the river but the mussel remains Extirpated in Canada.
COSEWIC History of Status Designation: Extirpated by 1968. Designated Extirpated in April 1999. Status re-examined and confirmed in May 2000, November 2009, and December 2021.
SARA Status: Schedule 1, Extirpated
Date of Listing (yyyy-mm-dd): 2003-06-05
Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.
Image of Dwarf Wedgemussel
This freshwater mussel is small (< 55 mm long) and roughly trapezoidal in shape. The outside of the shell is brown or yellowish-brown, with greenish rays visible in young or pale-coloured specimens. The nacre is bluish or silvery white and is iridescent in the posterior part of the shell. The hinge teeth are small but distinct. This species is unique in that it has two lateral teeth in the right valve and one in the left; other species have two lateral teeth in the left valve and one in the right.
Distribution and Population
The only recorded Canadian location for the Dwarf Wedgemussel is the Petitcodiac River drainage of New Brunswick. A specimen was last collected there in 1960, at which time the species was classified as being common. It became extirpated in 1968, following construction of a causeway. The species has been declared endangered in the U.S., where it occurs in coastal rivers from North Carolina to the Connecticut River in Vermont.
The mussel is found in small streams to medium-sized rivers with slow to moderate current and fine sediment, sand or gravel substrates. It appears to have poor tolerance for suspended silt. Stream-side vegetation seems to be required.
The parasitic larvae (glochidia) are released in the spring. The host fish species for the glochidia in the wild are not known, but five species of fish are able to serve as hosts in the laboratory. Of these, only Atlantic Salmon (Salmo salar) occurred in the Petitcodiac watershed. The maximum life span of the mussel is believed to be 12-18 years.
Reasons for extirpation
The species requires the presence of host fish species for the parasitic larval stage of development. It is vulnerable to pesticide and metal contamination, and to low oxygen levels. Impoundment of rivers has been a major negative factor on continued persistence of this species throughout its range, due to dams blocking movements of host fish species. In 1967/68, a causeway was built across the tidal part of the Petitcodiac River, which has severely restricted the passage of fish into the freshwater stretches of the river and its tributaries.
The Dwarf Wedgemussel is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.
Provincial and Territorial Protection
Status of Recovery Planning
Recovery Strategies :
Name Recovery strategy for the Dwarf Wedgemussel (Alasmidonta heterodon) in Canada
Status Final posting on SAR registry
PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.
7 record(s) found.
- COSEWIC Status Reports (1 record(s) found.)
- Response Statements (1 record(s) found.)
- Recovery Strategies (1 record(s) found.)
- COSEWIC Annual Reports (1 record(s) found.)
- Permits and Related Agreements (3 record(s) found.)
COSEWIC Status Reports
Response Statement - Dwarf Wedgemussel (2010-12-02)This freshwater mussel is small (< 55 mm long) and roughly trapezoidal in shape. The outside of the shell is brown or yellowish-brown, with greenish rays visible in young or pale-coloured specimens. The nacre is bluish or silvery white and is iridescent in the posterior part of the shell. The hinge teeth are small but distinct. This species is unique in that it has two lateral teeth in the right valve and one in the left; other species have two lateral teeth in the left valve and one in the right.
COSEWIC Annual Reports
COSEWIC Annual Report - 2010 (2010-09-03)Under Canada’s Species At Risk Act (SARA), the foremost function of COSEWIC is to “assess the status of each wildlife species considered by COSEWIC to be at risk and, as part of the assessment, identify existing and potential threats to the species”. During the past year, COSEWIC held two Wildlife Species Assessment Meetings and reviewed the status of 79 wildlife species (species, subspecies, populations). During the meeting of November 2009, COSEWIC assessed or reviewed the classification of the status of 28 wildlife species. COSEWIC assessed or reviewed the classification of an additional 51 wildlife species (species, subspecies and populations) during their April 2010 meeting. For species already found on Schedule 1 of SARA, the classification of 32 species was reviewed by COSEWIC and the status of the wildlife species was confirmed to be in the same category (extirpated - no longer found in the wild in Canada but occurring elsewhere, endangered, threatened or of special concern). The wildlife species assessment results for the 2009-2010 reporting period include the following: Extirpated: 6 Endangered: 39 Threatened: 16 Special Concern: 17 Data Deficient: 1 This report transmits to the Minister the status of 46 species newly classified as extirpated, endangered, threatened or of special concern, fulfilling COSEWIC’s obligations under SARA Section 24 and 25. A full detailed summary of the assessment for each species and the reason for the designation can be found in Appendix I of the attached report. Since its inception, COSEWIC has assessed 602 wildlife species in various risk categories, including 262 Endangered, 151 Threatened, 166 Special Concern and 23 Extirpated. In addition, 13 wildlife species have been assessed as Extinct. Also, to date, 46 wildlife species have been identified by COSEWIC as Data Deficient and 166 wildlife species were assessed as Not at Risk. This year has been a particularly productive year for COSEWIC’s Aboriginal Traditional Knowledge (ATK) Subcommittee. In April 2010 COSEWIC approved the Aboriginal Traditional Knowledge Process and Protocol Guidelines, providing clear and agreed principles for the gathering of Aboriginal Traditional Knowledge to carry out COSEWIC functions as required under Section 15(2) of SARA (See Appendix III of the attached report). We are grateful for the rich and enthusiastic contribution made by community elders and experts in helping the ATK Subcommittee prepare the ATK protocols.