Detecting the presence or absence of a species of interest is a common challenge for scientists and fisheries managers. Whether you’re interested in protecting an endangered species or removing an invasive species, knowing where they are or are not is crucial. Many techniques can be time-consuming or damaging to the local environment, and they don’t always work on more cryptic species. An emerging technique has the potential to address some of these pitfalls: environmental DNA, or eDNA.
eDNA is DNA fragments found in the environment (usually in soil or water) that come from an animal. Animals shed cells from their bodies through routes such as mucous, feces, or skin flakes. Each cell contains a full set of nuclear DNA and many copies of mitochondrial DNA. As these cells break down, the DNA is released into the environment. A researcher can collect samples (such as water or soil samples) and analyze any DNA present (typically mitochondrial DNA) for a match with the target species.
A useful application of this technology is to learn when and where endangered/threatened salmonids are present. Knowing which drainage systems these fish spawn and rear in is essential to managing and restoring their populations. Scientists can take water samples along river and creek systems where they suspect salmon will be. They then analyze the water samples for salmon DNA, and generate maps of fish distribution. If sampling is repeated over time, temporal trends along with spatial trends in salmon populations can be mapped, providing powerful information to managers and policy-makers.
In the future, eDNA may also help determine how many of each species of interest are in a given area. Research into the relationship between quantity of eDNA obtained and population numbers is ongoing.
For more information on eDNA methodologies, see this USGS factsheet.