Threeridge
NDGF
Large mussel with a maximum length of 7 inches. Shell is elongated and generally rectangular. Wing present near the umbos. Shell dark green to brown. Nacre is pink.
Status in North Dakota
Year-round resident and can be locally common.
Range Map
Threeridge range in North Dakota.
Reason for SWAP Designation
This species is regionally at risk or declining based on expert review and feedback.
Changes in land use in/around rivers including agriculture and impoundments have impacted this species.
Threats
Impoundment of the Red River and its tributaries have changed the flow regime and increased sediment deposits making many areas in the river unsuitable for the Threeridge.
Impoundments also block host fish movement necessary for this species’ reproduction and dispersal.
Agricultural practices within the basin have reduced suitable habitat in the river.
Runoff from treated fields into the river decreases water quality.
Ditches used to drain wetlands contribute agricultural runoff and sedimentation to the Red River and its tributaries.
The Threeridge is considered a commercially valuable species.
It is presently illegal to collect mussels for commercial use in North Dakota, but this practice may occur in parts of its range, which may contribute to an already declining population.
The release of water from Devils Lake changing the water chemistry of the Sheyenne River is a potential threat.
Research and Monitoring
A monitoring protocol for mussels has been developed by the North Dakota Game and Fish Department (NDGF) under the State Wildlife Grant Program with increased implementation as a future goal.
Additionally, the North Dakota Department of Environmental Quality (NDDEQ) conducts biological monitoring surveys on State waters as part of their Index of Biotic Integrity (IBI) development.
Valley City State University (VCSU) conducted a twophase population survey of mussels in 2008-2010 and began another evaluation in 2024.
Management Recommendations
- Develop/maintain buffers along riparian areas.
- Partner with local, state, and federal entities to limit chemical use in/near aquatic habitats.
- Continue partnering with local, state, and federal entities to maintain instream flows.
- Continue partnering with local, state, and federal entities to reduce wetland drainage.
- Remove river impoundments where possible.
- Encourage efficient use of pesticides.
Primary Geological Regions
Habitat Associations
Habitat Use
Primarily found in medium to large rivers/streams with mud, sand, and gravel substrate.
The Threeridge is Found only in the Red and Sheyenne rivers with the highest concentrations throughout the Sheyenne River in Ransom County.