Environmental DNA, commonly called eDNA, is DNA that is shed from organisms
in the natural environment. Skin cells, mucus, urine, and feces all contain the
signature DNA of the animal that shed them. Everywhere animals go, they leave a
trail of eDNA behind. As a result, using cutting-edge genetics techniques we
can sample eDNA in streams to determine, with confidence, whether fish species
of interest were present upstream from the sample site, or were there within
the week preceding the sampling event.
This requires having DNA from the target species, against which the sampled eDNA is compared in a laboratory. The DNA ‘library’ from target species in the Pacific Northwest is growing rapidly as eDNA becomes more widely used by researchers to better understand the distribution of fishes.