I Helped a Slovenian Park Find Elusive Alien Fish

A National Park Service scientist visits Crater Lake’s European sister park to share a new DNA technique for detecting hard-to-find species.

By David Hering

A man in a white shirt and baseball cap dips a sampling cup into a blue lake. he is surrounded by mountains, trees, and blue sky.
Collecting and filtering water for eDNA analysis from Lake Krn in Triglav National Park, Slovenia. Lake Krn and other lakes I sampled were naturally devoid of fish until exotic minnows and char were introduced. Exotic fish now threaten the ecology of some alpine lakes.

Image credit: NPS / David Hering

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In 2019, I traveled to Triglav National Park, Crater Lake’s Slovenian sister park. Slovenia is a small, beautiful country in central Europe, rich with native forests, lakes, and rivers. I was there to help park biologists sample environmental DNA (eDNA) from lakes high in the Julian Alps. We were looking for DNA from non-native minnows and Arctic char that disrupt the park’s aquatic ecosystems. My work demonstrated eDNA techniques used in the U.S. and provided baseline data about fish DNA present in Slovenian lakes. Parks in both countries seek to reverse the negative effects of invasive fish, and it was useful to share ideas about how to accomplish that goal.

Although fish biologists working in Triglav National Park were aware of eDNA, they had not used the technique before my visit. Our collaboration demonstrated the method’s utility and encouraged the Slovenian fisheries agency to develop its own eDNA protocols. After my visit, Triglav began removing non-native fish from Dvojno Jezero (“Double Lake”).

Two men stand in front of a green meadow with stony gray cliffs, evergreen trees, and distant pink and blue mountains
My Slovenian colleagues, Miha Ivanc (front) of the Fisheries Research Institute of Slovenia and Boštjan Podgornik of Triglav National Park.

Image credit: NPS / David Hering

eDNA analysis is revolutionizing our ability to find out where organisms occur in the environment. This is particularly true for species that are rare or hard to capture. eDNA analysis can be more sensitive than conventional survey techniques such as netting or electrofishing. It is thus well suited for early detection of invasive species and for evaluating the success of eradication projects.

In Slovenia, I filtered lake water from several sites, including Dvojno Jezero. Back in the States, colleagues at the U.S. Forest Service used quantitative polymerase chain reaction, or qPCR, to measure the amount of non-native fish DNA present per liter of water. This year, I will return to Slovenia to conduct follow-up work through a Fulbright Specialist grant. We will repeat these measurements to record the reduction in non-native DNA after exotic fish removal.

A panoramic image of a blue-green lake surrounded by rocky gray mountains, green meadows, green trees, and blue skies.
Triglav National Park has stunningly beautiful scenery. This is a view of Jezero v Ledvicah, or "Lake at Ledvicah." As far as I could tell, it does not yet have non-native fish.

Image credit: NPS / David Hering

David Hering

About the author

David Hering is an aquatic ecologist at Crater Lake National Park. Image credit: NPS

Crater Lake National Park

Last updated: November 19, 2022