Scientists at NOAA's Northeast Fisheries Science Center (NEFSC) are using environmental DNA (eDNA) to identify fish communities and monitor ecosystems by collecting a water sample and analyzing the DNA found in it, identifying the species that left it behind without capturing a single animal. As animals swim, they shed scales, tissue, and waste, leaving traces of DNA in the water. A water sample is first collected from the ocean and filtered to concentrate DNA in it. NOAA scientists then make millions of copies of a target DNA region through polymerase chain reaction (PCR) to make enough genetic material for high throughput sequencing. The metabarcoding process described above for eDNA analysis allows scientists to look for many species in the same sample. The final step is like a matching game, in which the DNA sequences are compared with a reference library of known species to find a match. The eDNA method is particularly useful for detecting species that are not easily captured, including rare or migratory species. It can also help in areas that are difficult to sample because of challenging ocean conditions, sensitive habitats, or a rugged seafloor. An eDNA analysis provides a snapshot of the community of species at the time of sampling and over time. This can help us detect shifts in marine ecosystems. eDNA samples have been collected on NOAA Ecosystem Monitoring (EcoMon) surveys since 2019. These samples will help develop best eDNA practices using metabarcoding, an innovative way to determine what fish species live in what parts of the ocean without actually seeing any fish.