County eDNA sampling finds salmonid DNA at multiple sites, highlights invasive-species detection and further monitoring needs

County environmental staff on Monday presented results of a December 2024–May 2025 environmental-DNA (eDNA) survey intended to map fish and other taxa across the ferry-served islands and inform conservation priorities.

Tyler Davis, a county scientist, said crews collected 383 samples at 123 sites and sent them to the Washington Department of Fish and Wildlife molecular genetics lab for meta-barcoding analysis. The laboratory results returned identifications across roughly 121 taxonomic groups, of which about 49 were fish taxa. Davis reported salmonid eDNA at 31 unique sites, and the team produced a public web dashboard to allow partners and residents to review detections by species and location.

Davis described several limitations and caveats: about 113 of the 383 samples failed laboratory processing (likely due to sediment, turbidity and contaminants), some detections appeared to reflect secondary transport (for example, marine fish DNA detected inland likely resulting from predators or material transport), and taxonomy resolution in some cases returned genus-level or higher identifications rather than definitive species calls. He said a small subset of surprising records (for example, taxa that appear biogeographically unlikely) will be subject to further scrutiny.

The project was funded through a mix of Salmon Recovery Funding Board / Recreation and Conservation Office grants and reallocated local funds; Davis said the project had been budgeted near $100,000 and ultimately ran under that budget because the team collected fewer visits than planned. He emphasized that nondetection in a given sample does not prove absence and that the county plans additional targeted sampling, particularly at sites where prior monitoring suggests salmonids should be detectable.

Councilors and staff discussed next steps: sharing the dataset with state and local partners, where it will add to existing sampling efforts and help prioritize culvert replacement and restoration work; seeking additional funding for more targeted, seasonally timed sampling; and using the dashboard in partnership planning. Davis also noted the survey provided useful absence data for a priority invasive species (northern pike was not detected in sampled sites outside the historically affected lake), a useful early-detection outcome.

Council members praised the work and asked staff to bring a formal plan for future sampling and use of the data to guide funding and prioritization decisions.