Freshwater Mussel eDNA Surveys
Background
The Western Ridged Mussel was petitioned for ESA-listing by the Xerces Society in August 2020 citing a 43% reduction in its native range and sudden and unexplained die-offs in Washington and Oregon. In July 2021 the US Fish and Wildlife Service (USFWS) published a positive 90-day finding with potential threats including habitat destruction, modification, and curtailment of range; impacts to water quantity, water quality, and natural flow and temperature regimes; aquatic invasive species (Factor A); and disease (Factor C) present substantial information indicating that the petitioned actions may be warranted and are initiating an ESA status review. The Xerces Society maintains a database of all three genera of freshwater mussel records in the Pacific Northwest (PNW) : Floaters (Anodonta spp.), the Western Pearlshell (Margaritifera falcata), and the Western Ridged (Gonidea angulata). Baseline information on freshwater mussel distribution remains a critical need to assess the species status in the Pacific Northwest and within the Yakima Basin. The Xerces Society database has only seven occurrences of the species in the Yakima River Basin (YRB) dating back to 1900 (Figure 1). The US Fish and Wildlife Service received Candidate Conservation Funds in 2022 to inform the ongoing ESA-listing determination by characterizing the range of the Western Ridged and other freshwater mussels using environmental DNA (eDNA).The focus was on the Western Ridged Mussel and sampling occurred within the range of previous observations, but the three other freshwater mussel species possibly present (California Floater, Oregon Floater, and Western Pearlshell) were also evaluated. Field surveys are labor intensive and can be limited by stream depth, turbidity, flow, and the training of surveyors in identifying mussels, but eDNA sampling can identify species and their concentrations (DNA copies/L) using quantitative PCR (qPCR; Tronstad et al. 2021). Results can be challenging to interpret when eDNA is collected from flowing water because it can be transported downstream 8 km or more from its origin (Deiner and Altermatt 2014; Preece et al. 2021), but despite its inability to precisely locate freshwater mussel beds in flowing water, eDNA sampling provides a cost-efficient means to direct future visual surveys.
References
Beals, T. 2019. Summary of Freshwater Mussel Sightings within the Yakama Nation Ceded Lands during Larval Lamprey Habitat Surveys (2014-2018). Confederated Tribes of the Yakama Nation, 2008-470–00, Toppenish, Washington. 15 pp.
Deiner, K., and F. Altermatt. 2014. Transport Distance of Invertebrate Environmental DNA in a Natural River. PLoS ONE 9(2):e88786.
Preece, E. P., M. Bryan, S. M. Mapes, C. Wademan, and R. Dorazio. 2021. Monitoring for freshwater mussel presence in rivers using environmental DNA. Environmental DNA 3(3):591–604.
Tronstad, L., M. Crawford, and T. Rodgers. 2021. Using eDNA to estimate the distribution of California Floater (Anodonta californiensis/nuttalliana clade) and Western Pearlshell (Margaritifera falcata) mussels in the Bear River Basin of Wyoming. Wyoming Game and Fish Department. 21 pp.