By Lorraine Boissoneault/Undark
When conservation manager Lindsay Chadderton came to the United States from New Zealand to help monitor the movement of invasive species between the Mississippi River and the Great Lakes, everyone was buzzing about one particular intruder: Asian carp.
The moniker includes four fish imported from China starting in the 1960s – grass carp, black carp, silver carp and bighead carp. Together, they might be the posterchild for invasive species in the U.S.
Bighead and silver dominate large stretches of the Mississippi River, outcompeting many native fish. They breed quickly, eat voraciously, grow much larger than most native fish and, when startled, silver carp catapult out of the water. They are not just an ecological nightmare; they also pose a danger to recreational boaters and fishers. According to the United States Geological Survey, jumping Asian carp have seriously injured boaters, and water skiing on the Missouri River is “now considered exceedingly dangerous.” Scientists say these fish could wreak similar havoc in the Great Lakes.
Part of the problem with Asian carp is the difficulty catching them. When the fish number in the thousands and are actually jumping into boats, it’s easy enough. But things change on the very edge of their territory, where the fish are sparser. At low abundances, they evade nets, as well as the electrical currents biologists sometimes use to temporarily stun and catch the creatures.
Chadderton, who works at the nonprofit Nature Conservancy, and his colleagues, along with the Army Corps of Engineers and other government agencies, all wanted to know how far along the fish had actually traveled – what was the edge of their territory? Chadderton wondered: What if instead of catching the carp, biologists could find some other marker of their presence – something like environmental DNA, or eDNA? All organisms shed genetic material into the environment. In the case of fish, this happens via flaking scales, mucus and feces. Scientists could start by sampling the water and then analyzing it for the presence of the fishes’ genetic material.
Chadderton consulted his colleagues on the project, biologists Andrew Mahon, Chris Jerde and David Lodge. At the time, “there was literally one paper” that had used eDNA techniques to study small ponds in France, says Jerde. The Illinois River and the Chicago Area Waterway System are exponentially larger systems, he explains, so the group didn’t know what to expect. Would their samples be too dilute to capture any carp DNA?
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Posted on March 21, 2020
