Western Ridged mussel survey in the Main Salmon River, 2021 [Excel spreadsheet]

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In early September 2021, biologists from Idaho Fish & Game (Joel Sauder, Diane Evans-Mack, Tempe Regan, and Betsy Wagner) coordinated a survey for Western Ridged Mussels along the Main Salmon River from Corn Creek to Carey Creek. With assistance the USFWS (Ryan Blackadar) and Montana Biological Survey (David Stagliano), we conducted a series of transect surveys (8), quadrat frames (22) and spot checks (25) roughly every 2-3miles along an 80-mile section of river. We use a variety of techniques, including view buckets, snorkels, diving, and quadrats with excavation; preliminary results from these surveys are as follows. We found Western Ridged Mussels to be more or less continuously distributed along the river and were essentially able to find them at will. While individuals were found in a variety of habitats, preferred habitat appeared to be characterized by 5-40% sand, stabilized by 20-50% cobble or boulders, with water velocities low enough to allow organic depositional material to settle out. Angular boulder and cobbles instead of rounded appear to signify more stable areas of the river and were also preferred, as were inside bends and benches to the side of the main river channel. Western Pearlshell Mussels were also regularly encountered along this whole section of river, but at much lower densities. The abundance of Western Ridged Mussels increased as we moved down the river, transitioning from normally encountering singles and small clusters (2-5 individuals) to regularly encountering moderate (10-20 individuals) to large clusters (>30 individuals). At the highest density site we encountered, there were 2982 Western Ridged Mussels (not included those likely buried) in a ~8m by ~3m section of river edge. We collected length measurements on over 1400 Western Ridged Mussels, with the vast majority being between 55mm and 85mm in length. There was no obvious trend or pattern in length along the river or between sites. At sites where we excavated quadrates, we generally found 20-50% of mussels were buried, but saw no difference in mussel length between surface and buried mussels. While empty shells were sporadically encountered, we did not detect any evidence of mass die-off events. Overall, we handled >1000 Western Ridged Mussels, physical counted >10,000, suggesting the population along this section of river is robust and thriving.