By Jim Robbins
A U.S. Forest Service technician heads out to the Blackfoot River in western Montana and pumps water through a small filter, five liters every time she stops. In a single day, she gathers dozens of samples, bringing back to the lab each of the fine mesh filters that the river water passed through.
U.S. Forest Service biologist Michael Schwartz gathers water to be sampled for eDNA from Rattlesnake Creek in Montana.
U.S. Forest Service biologist Michael Schwartz gathers water to be sampled for eDNA from Rattlesnake Creek in Montana. Kellie Carim/U.S. Forest Service
The filters contain DNA for species — whether brook trout, stone flies, wood ducks, or river otters — that have swum in that stream in the last day or two, up to a kilometer above the sample site. Every insect, fish, or animal continually sloughs off bits of its DNA — in its feces or from its skin — and just a single cell of the invisible, free-floating genetic material can tell researchers which species are present in a river or other water body.
Environmental DNA, or eDNA, is at the center of a brand new kind of fish and wildlife biology, and it is such a powerful tool that it’s transforming the field. eDNA was first used to detect invasive bullfrogs in France a decade ago. It was used in North America for the first time in 2009 and 2010 to detect invasive Asian carp in and around the Great Lakes. Since then, its use has grown exponentially, primarily in marine and freshwater environments.
“You can’t manage a species if you don’t know where it is — even 80-pound Asian carp, because you can’t see them underwater,” said Cornell University biologist David Lodge, who participated in the Asian carp study. “So eDNA is particularly powerful in aquatic systems.”
The DNA is so easy and inexpensive to gather and assay — $50 to $150 to test each sample — that the U.S. Forest Service has launched a project to collect DNA from all rivers and streams across the western U.S. to create an Aquatic Environmental DNA Atlas.
“Environmental DNA is turning out to be an amazing tool in allowing us to detect the distribution of species, a distribution that has been invisible to us in the past,” said Michael K. Schwartz, director of the Forest Service’s National Genomics Center for Wildlife and Fish Conservation in Missoula, Montana. “It has remarkable efficiency.”