By Morgan Linn
Investigators are using modern forensic science to hunt down a Great Lakes cold-blooded killer: the sea lamprey.
They’re advancing the use of the DNA that an organism sheds into its environment — called environmental DNA or eDNA for short.
Previously used to locate other invasive species such as Asian carp, eDNA can also help hunt for sea lamprey. A recent study funded by the Great Lakes Fishery Commission says that eDNA is a “highly promising tool for sea lamprey monitoring” and that it could be also used to detect “native lamprey species, which are of conservation concern”.
It could save money and reduce the time spent looking for the parasites, the study said.
Sea lamprey were introduced into the Great Lakes in the 1920s after the Welland Canal opened. They spread and destroyed Great Lakes fisheries in the 1940s and 50s. Those fisheries eventually recovered once ways of controlling the lamprey were developed.
The eel-like organisms have suckers on their mouths, allowing them to clamp onto the sides of fish and “suck the juices out,” much like a tick, said Nick Schloesser, a biologist at the United States Geological Survey.
Nowadays crews survey a stream with “shockers” that stun fish briefly with electricity, allowing scientists to observe them, he said. If enough lamprey appear, they poison the stream to kill them.
That takes a lot of time and effort. But eDNA could make detection faster and cheaper.
Instead of shocking and surveying every stream, a water sample is tested for sea lamprey eDNA, Schloesser said. A lot of sea lamprey eDNA in the sample could mean the stream is worth treating.
The technique could also reduce the number of native lamprey that are harmed by the lampricide used to kill the invaders.
There are four beneficial lamprey species native to the Great Lakes that managers want to avoid killing, said Margaret Docker, a co-author of the eDNA study and biologist at the University of Manitoba.
The best way to kill invasive sea lamprey and protect the native lamprey is to know where each species lives, she said. Areas with high numbers of sea lamprey and low numbers of native lamprey could be targeted, limiting the number of native casualties.
Each lamprey species has a different genetic signature, making eDNA an easy way to tell them apart, Docker said.
With traditional surveying it can be hard to distinguish between the
species, she said. They all look similar, especially in the larval stage, which is when they are best killed before they become parasitic adults, she said.
“It’s a lot easier to take a water sample than to go out with a survey crew looking for larval lampreys that are buried in the mud and sediment and are difficult to assess,” Docker said.
But there are drawbacks to the method.
A stream can become contaminated with sea lamprey eDNA, even if there aren’t any present.
That happens when animals or boats transfer sea lamprey DNA between streams and when sea lamprey were once present but died.
Boaters and anglers can prevent contamination, said Kelly Baerwaldt, the eDNA program coordinator for the U.S. Fish and Wildlife Service.
One is to clean your boat before launching it into a new water body, she said. Even if you can’t, you should always let it dry completely before bringing it to a new area. Another is to avoid dumping bait into other water systems.
Because of potential contamination, “eDNA is not the only thing you should be relying on,” Baerwaldt said. If an eDNA test comes back positive for sea lamprey, it is important to follow up with traditional testing methods.
Researchers are working to distinguish the eDNA of dead lamprey from that of live lamprey, but there’s still a ways to go, Docker said.
“You can’t go out and electrofish all of the Great Lakes, but you can use eDNA to focus on certain areas you might want to take a closer look at,” Baerwaldt said. Using eDNA brings researchers closer to developing a fast way to keep the Great Lakes safe from invasive parasites.