eDNA: Movie Fiction or the Real Deal?
Ever watch the futuristic science fiction movie “Oblivion?” Good plot, terrible acting. My ten year old, already a sage movie critic, calls it “Oblivious.” That said, there’s a great scene in the movie where the female antagonist tracks our hero (Tom Cruise) using a futuristic technology that analyzes the wind for Tom’s residual DNA particles, allowing her to “see” the route he took several hours earlier. Made me think of how my labrador tears through our yard, nose to the ground, hot on the trail of a cat that passed by several hours earlier.
Environmental DNA (or eDNA) is real. It’s the DNA left behind in the environment by all creatures – generally from their urine, feces, or shed skin cells. Now, through laboratory analysis of a sample of water, we can conveniently search for the DNA of a species of interest to determine if it swam through the body of water, or if it exists upstream. Use of eDNA has recently been shown to be an innovative way to identify fish species composition and distribution within freshwater habitats using a completely non-invasive approach. The technique has been evolving over the past several years, and with each study the approach becomes more effective and affordable.
Wild Fish Conservancy recently partnered with the Snoqualmie Indian Tribe on a successful proposal to the Environmental Protection Agency’s National Estuary Program to survey and map several tributaries to the Snoqualmie River (King County, WA). The project will also evaluate the use of eDNA techniques to supplement traditional fish species composition and distribution surveys. Instead of using resource-intensive techniques like electrofishing to document fish presence and distribution, genetic material collected in water samples is analyzed in a laboratory to identify the species existing upstream from the collection point. The approach has great potential for identifying the presence of rare and threatened species like ESA-protected Puget Sound Chinook, Steelhead, and Bull Trout. The technique may also prove to be more effective at documenting fish presence when density is low, as it often is at the upstream extent of their range in watersheds. Including eDNA in our sampling design will improve our understanding of the strengths and weaknesses of the tool, and may ultimately increase the effectiveness, accuracy, and reliability of mapping of fish species composition and distribution.
Photo Credits: USFWS & Pilliod D