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Updated: Aug 5, 2026

Standardizing a Non-Lethal Method for Characterizing the Reproductive Status and Larval Development of Freshwater Mussels (Bivalvia: Unionida)
Published on: October 4, 2019
Range extension and natural history notes on Rocky Mountain Ridged Mussel Gonidea angulata (Lea, 1838) (Mollusca,
Jennifer Heron1, Roxanne Jessome2, Kihan Yoon-Henderson3
1British Columbia Ministry of Water, Land and Resource Stewardship, Surrey, Canada British Columbia Ministry of Water, Land and Resource Stewardship Surrey Canada.
Abstract:
Rocky Mountain Ridged Mussel (Gonidea angulata (Lea, 1838)) is a freshwater bivalve with a global range in North America that extends from British Columbia, Canada, south to central California and east through Nevada and Idaho in the United States. In Canada, this mussel is of conservation concern and is currently assessed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and recommended for listing as such under the federal Species at Risk Act (SARA). Until recently, the species distribution in Canada was restricted to south-central British Columbia within the Okanagan watershed, with historical, yet vague records from the Kootenays, Cache Creek and Vancouver Island areas of the province. In 2023, a photograph of a Rocky Mountain Ridged Mussel shell from the confluence of the Pitt and Fraser rivers in the lower Fraser Valley of British Columbia was posted to the online citizen-science forum iNaturalist (https://www.inaturalist.ca/). The Fraser River watershed has no present-day aquatic linkages with the Okanagan watershed and the potential range extension for this mussel within a new watershed prompted targeted field surveys within the Pitt River and surrounding waterways to confirm the presence of live mussels. In 2023, 2024 and 2025, we completed surveys and confirmed a subpopulation of live Rocky Mountain Ridged Mussels within the Pitt River. This newly-confirmed subpopulation of mussels in the Fraser River watershed is of significant conservation interest, opens the door to important future research and new opportunities for monitoring and stewardship.
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