Species Profile

Rocky Mountain Ridged Mussel

Scientific Name: Gonidea angulata
Taxonomy Group: Molluscs
Range: British Columbia
Last COSEWIC Assessment: November 2010
Last COSEWIC Designation: Endangered
SARA Status: Schedule 1, Special Concern

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Quick Links: | Taxonomy | Description | Distribution and Population | Habitat | Biology | Threats | Protection | Recovery Team | National Recovery Program | Documents

Image of Rocky Mountain Ridged Mussel


The taxonomic relationship between the Rocky Mountain Ridged Mussel and other subgroups of the same family is uncertain. Until we know more about this mussel, which does not appear to be closely related to any other species in North America, the Rocky Mountain Ridged Mussel must be classified as a very particular genus of the pearly mussel family.



The Rocky Mountain Ridged Mussel is a large freshwater mussel. Its shell is trapezoidal and up to 12.5 cm long and 0.4 cm wide. It is typically rather thin, but can be up to 6.5 cm high toward the posterior. Like that of all other mussels, the shell of the Rocky Mountain Ridged Mussel is composed of two parts, known as valves, connected by a hinge. This hinge is medium-sized and has small, irregular, indistinct anterior teeth. The surface of the shell is marked by well-defined growth rings, and the dorsal valve is distinguished by a sharp, prominent ridge at the beak. In juveniles of this species, the outside of the shell is greenish or ochre, while adults are typically darker, becoming bluish-black. The inside of the shell is white tinged with coppery blue.


Distribution and Population

The Rocky Mountain Ridged Mussel occurs from southern British Columbia to southern California and eastward to southern Idaho and northern Nevada in the United States. In Canada, this species is limited to the Columbia River system and its tributaries, including the Okanagan and Kootenay rivers. This species is probably also present in other similar areas in southern British Columbia. Currently, there are two distinct, severely fragmented populations of this mussel in British Columbia: one at about eight locations on the Okanagan River, and the other at an undetermined number of locations on the Kootenay River. The size of these populations is not known. The presence of this species has been confirmed recently at only one of the eight locations where it has been observed in the past. This location is Park Rill Creek, a tributary of the Okanagan River, where a dead specimen was collected in 2002 near the town of Oliver. Given the small number of specimens that have been gathered and preserved in collections in Canada, and the decline in water quality, these populations are regarded as being in decline.



The Rocky Mountain Ridged Mussel lives in fresh water. It is found in various sizes of lakes and streams in shallow water where the flow is constant and especially where the bottom is composed of fine material. The species seems to avoid murky, nutrient-rich water. This mussel will attach itself to gravel or firm mud on the bottom so long as this bottom also contains a small amount of fine material such as sand or clay; depending on how fine the bottom is, the mussel may bury itself partially or completely. It is not unusual to see individuals of all non-larval age classes together at a single location.



Little is known about the biology of this species, but it is assumed that, like the other freshwater mussels of North America, it reproduces by the internal fertilization of the female and the production of small larvae called glochidia. After developing in the gills of the female mussel, the larvae are expelled from April to July and drift in the water until they attach themselves to the gills or fins of a host fish. (The species of this host fish is still unknown but, partly because of the large historical range of this mussel, it is believed that a number of different species might actually be involved.) After one to six weeks, the larvae, which have grown into juvenile mussels, drop off the host fish and float freely near the bottom, where they attach themselves once they become adults. The adults generally remain attached to the bottom and cannot move unless disturbed several times. Rocky Mountain Ridged Mussels probably feed on bacteria and algae, which they ingest by filtering the water. As with all freshwater mussels, the survival rate of the larvae is low. According to counts of annual growth rings, it is estimated that the adult can live up to 30 years.



The Rocky Mountain Ridged Mussel is threatened by the destruction and degradation of its habitat. Like all members of this family of mussels, it is highly sensitive to changes in its environment, such as those affecting the temperature or composition of the water. Consequently, several species in this family are endangered in North America. In British Columbia, plans to develop the Okanagan River could have a negative impact on the mussel populations by causing fluctuations in water levels, among other things. In the long term, however, this development could prove beneficial to the species by facilitating its dispersal and creating suitable new habitats. Another threat to the Rocky Mountain Ridged Mussel is the eutrophication of lakes and streams, a process in which increased amounts of nutrients, released largely from agriculture and aquaculture, cause aquatic vegetation to proliferate and reduce the oxygen levels in the water. Also, as filtering organisms, these mussels are generally vulnerable to pollution and particularly to heavy metals, because as the mussels filter large volumes of water in order to feed, the dissolved pollutants from the water build up in their bodies. The proliferation of exotic species such as zebra mussels is also a source of concern.



Federal Protection

The Rocky Mountain Ridged Mussel 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

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.


Recovery Team

South Okanagan Invertebrates at Risk Recovery Team

  • Orville Dyer - Chair/Contact - Government of BC
    Phone: 250-490-8244  Send Email
  • Jennifer Heron - Chair/Contact - Government of BC
    Phone: 604-222-6759  Fax: 604-660-1849  Send Email



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.

12 record(s) found.

Report on the Progress of Recovery Strategy Implementation

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Rocky mountain ridged mussel Gonidea angulata in Canada (2011)

    The freshwater mussel Gonidea angulata, commonly known as the Rocky Mountain Ridged Mussel, was described by Lea in 1839. The shell is up to 125 mm long, 65 mm high, 40 mm wide, and with shell wall up to about 5 mm thick at mid-anterior; variable in form but typically rather thin, trapezoidal in shape, with posterior margin obliquely flattened and relatively broad, and with a sharp and prominent posterior ridge running from the umbo to the angular basal posterior margin of each valve. Juveniles of this species may be greenish/tan in appearance while adults are typically darker, becoming bluish-black.

COSEWIC Assessments

Response Statements

  • Response Statement - Rocky Mountain Ridged Mussel (2004)

    The distribution of this species is limited to southern British Columbia in the Okanagan and Kootenay River systems. This species has likely been impacted by the damming of the Kootenay, Columbia and Okanagan Rivers and the channelization of the Okanagan River and resulted in loss or alteration of the mussel's habitat quality and extent.
  • Response Statement - Rocky Mountain Ridged Mussel (2011)

    This mussel, one of only a few species of freshwater mussel in British Columbia, is restricted in Canada to the Okanagan basin.  Historically, channelization and water regulation in the Okanagan River have affected mussel beds and caused population reduction. Additional sites have been found since the original COSEWIC assessment (2003). Currently, Zebra and Quagga (dreissenid) Mussels are the most serious potential threat to the native mussel. Dreissenid mussels have had devastating effects on native unionid communities elsewhere, such as in the Great Lakes region. A recent assessment of the sensitivity of the Okanagan basin to dreissenid mussels demonstrated that the latter could spread quickly and establish intense infestation on native mussels once introduced. Within the foreseeable future, the introduction of dreissenids into the Okanagan basin is likely because they can survive for days out of water and are known to be transported between water bodies on trailered watercrafts; dreissenid mussels have been intercepted on trailered boats heading to British Columbia in recent years. Ongoing foreshore and riparian development, and some methods of control of invasive Eurasian Watermilfoil reduces habitat and affects water quality.

Management Plans

  • Management Plan for the Rocky Mountain Ridged Mussel (Gonidea angulata) in British Columbia (2011)

    The Rocky Mountain Ridged Mussel is a freshwater mollusc and was listed as a species of special concern under the Species at Risk Act (SARA), in July 2005. This large freshwater bivalve has a trapezoidal shell. The most distinctive feature of the shell is a prominent posterior ridge running almost parallel with the anterior margin, from the umbo to the angular basal posterior margin of each valve. The posterior length of the shell exceeds the anterior length of the shell.


  • Order Acknowledging Receipt of the Assessments Done Pursuant to Subsection 23(1) of the Act (2004)

    The Order acknowledges receipt by the Governor in Council of the assessments of the status of wildlife species done pursuant to subsection 23(1) of the Species at Risk Act (SARA) by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The purpose of SARA is to prevent wildlife species from being extirpated or becoming extinct, to provide for the recovery of wildlife species that are extirpated, endangered or threatened as a result of human activity and to manage species of special concern to prevent them from becoming endangered or threatened.
  • Order Amending Schedules 1 to 3 to the Species at Risk Act (2005)

    The Minister of the Environment is recommending, pursuant to section 27 of the Species at Risk Act (SARA), that 43 species be added to Schedule 1, the List of Wildlife Species at Risk. This recommendation is based on scientific assessments by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and on consultations with governments, Aboriginal peoples, wildlife management boards, stakeholders and the Canadian public.

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2004 (2004)

    2004 Annual Report to the Canadian Endangered Species Conservation Council (CESCC) from the Committee on the Status of Endangered Wildlife in Canada.
  • COSEWIC Annual Report - 2010 - 2011 (2011)

    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”. COSEWIC held two Wildlife Species Assessment Meetings during the past year assessing the status or reviewing the classification of a total of 92 wildlife species.

Consultation Documents

  • Consultation on Amending the List of Species under the Species at Risk Act: November 2004 (2004)

    The Government of Canada proclaimed the Species at Risk Act (SARA) on June 5, 2003 as part of its strategy for the protection of wildlife species at risk. Attached to the act is Schedule 1, the list of the species that receive protection under SARA, hereinafter referred to as the 'SARA list'. Canadians are invited to comment on whether all or some of the species included in this document should be added to the SARA list.
  • Species at Risk Act- Legal Listing Consultation Workbook, Pacific Region (2004)

    Your opinion is being sought to assist the government of Canada in making an informed decision on whether to add the White Sturgeon, Grey Whale, Harbour Porpoise, Steller Sea Lion, and Rocky Mountain Ridged Mussel to the Schedule 1 (the List of Wildlife Species at Risk) of the Species at Risk Act (SARA). Your input on the impacts of adding these species to the List is important. This workbook has been developed to give you an opportunity to provide Fisheries and Oceans Canada with your feedback, advice, and other comments regarding adding these species to Schedule 1 of SARA (Schedule 1 identifies which species are legally protected under SARA).