Rocky Mountain Ridged Mussel

Gonidea angulata

SARA Status
No Status
NS
Special Concern
SC
Threatened
TH
Endangered
EN
Extirpated
EX

SARA Status

  • No Status NS
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX
COSEWIC Status
Not at Risk
NR
Special Concern
SC
Threatened
TH
Endangered
EN
Extirpated
EX

COSEWIC Status

  • Not at Risk NR
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX

Description

The Rocky Mountain Ridged Mussel (Gonidea angulate) is a large freshwater mussel. The species' shell surface is marked by well-defined ridges. These ridges can be counted as rings to estimate an individual's age. Rocky Mountain Ridged Mussels have been recorded to live up to 60 years. 

The Rocky Mountain Ridged Mussel shell is trapezoidal. The shell dimensions can be up to 12.5 centimetres long, 0.4 centimetres wide and 6.5 centimetres high. Like all other mussel shells, the shell is composed of two parts (known as valves) connected by a single hinge. The dorsal valve has a sharp and prominent ridge. Juvenile Rocky Mountain Ridged Mussel shells are greenish or ochre coloured on the outside, while adults are a darker bluish-black colour. The inside of the shell is white with coppery-blue colour.

Habitat

Globally, this freshwater species occurs from southern British Columbia to southern California. It can also be found eastward to southern Idaho and northern Nevada in the United States. In Canada, the Rocky Mountain Ridged Mussel is only found in the Okanagan Basin. Records for this species have been verified in the Okanagan Lake, Skaha Lake, Okanagan River, Vaseux Lake, Park Rill Creek, and Osoyoos Lake.

At present, all Rocky Mountain Ridged Mussels found in Canada are a part of one population.  Species abundance estimates exist for three sites in the Okanagan River watershed. However a total population size is unknown because the species' density varies and not all suitable habitat has been surveyed.

The Rocky Mountain Ridged Mussel can be found in various sizes of freshwater lakes and streams. The species seems to prefer areas with stable habitat conditions. The mussel is not often found in areas with shifting substrate, water level fluctuations, seasonal low oxygen levels, or murky water. In the Okanagan Basin, the Rocky Mountain Ridged Mussel lives in large cobble, gravel and sand, mud with vegetation, and cobble and gravel over sand. It may attach itself to gravel or firm mud, or bury itself into the substrate.

Threats

The Rocky Mountain Ridged Mussel is particularly vulnerable to threats because the species occurs in small isolated populations. The introduction of aquatic invasive species, such as the Zebra and Quagga Mussels, is the largest current threat to this species. These invasive mussels have had devastating effects on native freshwater mussel communities. They take over and alter habitat, compete for food resources, and smother native species. The Zebra and Quagga Mussels could spread quickly once introduced in the Okanagan Basin. Introduction of these species is likely because they can survive for days out of water and are known to be transported between water bodies on trailered watercrafts.

Other threats to the Rocky Mountain Ridged Mussel are habitat-related. Like all members of this family of mussels, this species is very sensitive to changes in its environment. The Canadian range of the species is within an area of rapid change due to urban development. Some of the specific threats include foreshore/riparian development, historic riverbed channelization, and hydrograph modification and regulation. These all result in habitat fragmentation and habitat loss through direct development of the species' habitat or ecosystem modifications. Several other threats exist to the species as well. These include host fish availability for completion of the life cycle, pollution, direct harm and climate change.

Further Information

Several achievements contributing to the management of the Rocky Mountain Ridged Mussel have occurred in recent years. In 2017, a five-year progress report was published for the implementation of the Management Plan for the period 2011 to 2016.  Over this time period, Fisheries and Oceans Canada and its collaborators have addressed knowledge gaps about the species' life history, including the identification of possible host fish species, have undertaken juvenile and adult abundance surveys, and have conducted preliminary juvenile recruitment and habitat suitability studies. During this time, considerable efforts were made to inventory potential littoral habitat within the known distribution and range. Another key activity has been the identification of potential threats including host fish availability, introduction of invasive plant and aquatic animal species and habitat destruction.

Significant efforts have been made by Fisheries and Oceans Canada, the Province of British Columbia and their collaborators to increase public awareness of the species, decrease incidence of habitat destruction and increase engagement.  This has been achieved through the development and installation of interpretive signage in popular public areas, the production of posters and presentations.  In addition, the known locations of Rocky Mountain Ridged Mussels have been incorporated into land use planning – such as for the Okanagan Large Lakes Foreshore Protocol, the Okanagan Fish Water Management Tool and the Okanagan Water Board Eurasian Water Milfoil rototilling treatment plan – to inform threat mitigation and land use protection.

This work contributes to the management of the species, fills in knowledge gaps, and provides the framework for habitat and population monitoring.

This species is protected under the federal Species at Risk Act (SARA). It is under consideration for listing as Endangered under SARA. More information about SARA, including how it protects individual species, is available on the Species at Risk Public Registry.

To find out more on how this species is protected by provincial or territorial laws, consult the provinces' and territories' website.

Rocky Mountain Ridged Mussel

Photo credit: Canadian Museum of Nature, Ottawa, Canada

Photo credit: Canadian Museum of Nature, Ottawa, Canada

Scientific name: Gonidea angulata
SARA Status: Special Concern, Schedule 1
COSEWIC Status
: Endangered (November 2010)
Region: British Columbia

Region map

Region map, British Columbia

Did You Know?

Freshwater mussels play an important role in aquatic ecosystems and are often used as indicators for an ecosystem’s health. They filter organic matter from the water and their waste can be used as food for algae and other invertebrates. They are also known to increase water and oxygen content in sediment, which is beneficial to other species living in the sediment.

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