Environmental DNA is an effective tool to track recolonizing migratory fish following large‐scale dam removal

Abstract

Environmental DNA (eDNA) has emerged as a potentially powerful tool for use in conservation and resource management, including for tracking the recolonization dynamics of fish populations. We used eDNA to assess the effectiveness of dam removal to restore fish passage on the Elwha River in Washington State (USA). Using a suite of 11 species‐specific eDNA polymerase chain reaction (PCR) assays, we showed that most targeted anadromous species (five Pacific Salmon species and Pacific Lamprey) were able to pass upstream of both former dam sites. Multiscale occupancy modeling showed that the timing and spatial extent of recolonization differed among species during the four years of post‐dam removal monitoring. More abundant species like Chinook Salmon and Coho Salmon migrated farther into the upper portions of the watershed than less abundant species like Pink Salmon and Chum Salmon. Sampling also allowed assessment of potamodromous fish species. Bull Trout and Rainbow Trout, ubiquitous species in the watershed, were detected at all sampling locations. Environmental DNA from Brook Trout, a non‐native species isolated between the dams prior to dam removal, was detected downstream of Elwha dam but rarely upstream of the Glines Canyon Dam suggested that the species has not expanded its range appreciably in the watershed following dam removal. We found that eDNA was an effective tool to assess the response of fish populations to large‐scale dam removal on the Elwha River.

Development of a Quantitative PCR Assay for Four Salmon Species Inhabiting the Yangyangnamdae River Using Environmental DNA

“…Furthermore, the sensitivity test, including the LOD and LOQ determination, is required in the eDNA surveillance guidelines since many eDNA studies can detect low-abundance species within ecosystems. Previous species-specific eDNA studies in Pacific salmon do not contain adequate information regarding sensitivity tests, except that of Duda et al [ 73 ], who studied five Pacific salmon in the Columbia River (USA). Xia et al [ 74 ] reported that two of three eDNA studies consisted of newly developed markers, whereas only 88 of 165 studies determined the LOD of the marker.…”

The future of biodiversity monitoring and conservation utilizing environmental DNA

“…To advance its use in this arena, Duda et al. (2021) used multiple species‐specific real‐time PCR assays to monitor over four years the fish distribution after a dam removal project in Elwha River, Washington, USA. Indigenous salmon species expanded their migrating area to the upstream side of removed dam sites whereas a non‐native Brook Trout has been suggested not to expand its range due to the dam removal.…”

Resumption of Anadromy or Straying? Origins of Sockeye Salmon in the Elwha River

“…The removal of the two dams occurred between 2011 and 2014; full fish passage was restored at Elwha Dam in spring 2012 and at Glines Canyon Dam in fall 2014. Since dam removal, Chinook Salmon, steelhead, and Bull Trout have ascended to the headwaters of the Elwha River, Coho Salmon and Pink Salmon have passed the former Glines Canyon dam site, and Chum Salmon have passed the former Elwha Dam location (McMillan et al 2019; Duda et al 2020).…”