Notre Dame researcher speaks of eDNA testing reliability, future improvements

Testing method is decades old, reliable

by T.W. Budig
ECM Capitol Reporter
Although some warn against overacting to the recent eDNA-positive test results for silver Asian carp in the St. Croix and Mississippi rivers, a research professor from the University of Notre Dame warns against ignoring them.
Christopher Jerde, research assistant professor at the Environmental Change Initiative at the University of Notre Dame, said while the application of the eDNA testing used to detect Asian carp — a protocol pioneered by the university — is new, the basic technology is actually decades old.
One Notre Dame professor compares the DNA testing to the testing routinely conducted at crime scenes. It’s reliable, Jerde explained.
He described a meticulous process which identifies and cross-checks known genetic “markers,” using genetic information from specie tissue samples plus the knowledge of the genetic makeup of living things.
Not that the testing is without limitations.
While tests conducted by Notre Dame researchers have successfully identified four-day-old eDNA in water, a threshold of two days has been suggested.
Exactly how the chemical makeup of water — acidity levels, for instance — affects the speed at which DNA disintegrates is currently at the forefront of research.
Additionally, current eDNA testing cannot identify the numbers of a given species. In reporting eDNA test results for Asian carp, local officials often note a certain number of test results — say, 19 out of 48 — registering positive for Asian carp eDNA.
To an extent, the numbers are almost meaningless — at least can be misleading, Jerde argued. All the positive hits, after all, could have come from a single Asian carp, he explained.
Researchers at Notre Dame and elsewhere are trying to improve eDNA testing. “We are very much working on it,” Jerde said.
In the future, not only will the test provide evidence of the presence of Asian carp but indicate the numbers of fish in the area. Such a refinement should become available within five years, Jerde believes.
A hyper-caution towards eDNA test results for Asian carp has found its way into the media, he argues. In part it has been instilled by the U.S. Army Corps of Engineers, one “stakeholder” group that has a vested interest in the Asian carp debate, Jerde’s believes.
Some biologists have theorized that Asian carp eDNA can be spread by other means than swimming fish.
Perhaps it can move by air.
It’s been suggested that birds can spread Asian carp eDNA by consuming Asian carp in one place and depositing the carp DNA in their droppings elsewhere.
Indeed ospreys, birds that live primarily on fish, nest within a 100 yards of the Mississippi River on the Hennepin County side of the Mississippi River near the Coon Rapids Dam.
And Minnesota Department of Natural Resources officials recently expressed a degree of puzzlement over recent positive eDNA testing results for silver Asian carp from water samples taken above the dam.
Jerge doesn’t wholly dismiss the possibility of birds transmitting Asian carp DNA.
Still, in the ospreys at the Coon Rapids Dam scenario, the odds of an osprey catching a rare, juvenile Asian carp and seeding its DNA about the dam are exceedingly slim, he explained. The logic of the thing just doesn’t hold up, he argues.
(One Minnesota DNR official, Tim Schlagenhaft, the agency’s Asian carp point man, holds a similar view.)
Additionally, many birds, like ospreys, migrate and are entirely absent from their summer ranges for months at a time, Jerge noted.
That the commercial fishermen the DNR has dispatched to the St. Croix and Mississippi rivers to fish for Asian carp have come up with empty nets doesn’t surprise Jerge. “Asian carp are notoriously difficult to catch,” he said.
If the commercial fishermen would catch one, Minnesota  DNR officials should be very concerned, he said. It would suggest a sizeable population of Asian carp has already established itself, Jerge said.
Jerge is upbeat about the chances of halting the spread of Asian carp. Even slowing the spread of invasive species can save money, he said.
If a power company is spared the need of scraping zebra mussels from its water intake pipes for a several  years, that’s money saved, Jerge said.
Testing for Asian carp was one topic discussed at Gov. Mark Dayton’s third Asian carp summit at the State Capitol on Dec. 20.
“We really don’t know what it’s telling us,” said Rep. Jean Wagenius, DFL-Minneapolis, of eDNA testing.
Wagenius suggested that eDNA test analysis should be conducted in Minnesota rather than sending samples to Indiana for analysis. She also suggested the University of Minnesota should be called on to do basic Asian carp research.
“We don’t know our enemy,” she said of Asian carp.

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