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
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 ProtectionThe 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
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.
11 record(s) found.
- COSEWIC Status Reports (1 record(s) found.)
- COSEWIC Assessments (1 record(s) found.)
- Response Statements (2 record(s) found.)
- Management Plans (1 record(s) found.)
- Orders (2 record(s) found.)
- COSEWIC Annual Reports (2 record(s) found.)
- Consultation Documents (2 record(s) found.)
COSEWIC Status Reports
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.
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