“Actually, 2020 was a good year for something,” he says. He’s talking about American eels. They’re having a good year — a good decade, in fact — continuing their unlikely comeback in the largest river on the East Coast, with help from daily truck rides.
For more than a decade, biologists have been trapping baby eels in the Susquehanna River and trucking them past four hydroelectric dams to release them in freshwater creeks upstream. Dams interrupt the natural migration routes of the eels, which are born in the Chesapeake Bay and then swim upriver, sometimes hundreds of miles, into freshwater streams, where they grow into adulthood before eventually returning to the bay.
The idea of trapping and physically relocating a species — in this case, moving eels around physical obstacles — is gaining new interest as the planet warms and causes some plant and animal species to struggle in their native habitats. Moving them to a more hospitable home, also known as assisted migration, may be one way to save some species as the climate changes.
Minkkinen says his trap and haul program, which he’s dubbed the “eelway,” is reviving the watershed ecosystem.
Mark Schwartz, a conservation biologist at the University of California at Davis, says this type of assisted migration is helping inform similar programs aimed at responding to climate change. “We’ve thought for a century about heavy-handed ways to alleviate the problem of dams,” Schwartz said. “And now it’s led us to heavy-handed things for our other conservation problems.”
At the Conowingo Dam, about nine miles north of the Chesapeake Bay, this summer’s trap and haul operation was on pace to reach a 240,000-eel milestone, more than double last summer’s numbers, despite a three-week delay this summer because of the pandemic.
“I don’t think there would be any eels in the Susquehanna River watershed if we hadn’t done this project,” says Minkkinen, a broad-shouldered federal scientist with a salt-and-pepper goatee.
The movement of eels up river is like the pumping of blood through veins. Stop it and the rest of the body soon deteriorates. That is essentially what happened to the Susquehanna River watershed starting in 1928, when the first and largest of four still-operational dams was constructed.
For millennia, a seasonal wave of baby eels traveling from the Chesapeake Bay to freshwater upriver carried mussel larvae with them, latched on their heads. The freshwater mussels caught rides north to the same headwaters the eels seek in order to grow into adults.
When the Susquehanna River’s main stem became jammed by dams, eel migration stopped. The critical eel-mussel hitchhiking relationship was also interrupted, resulting in upriver streams with almost no thriving young mussel beds, once common in Pennsylvania and New York and critical to keeping waters filtered and clean.
The result was “ghost creeks,” devoid of the mussels that support almost all creek life, Minkkinen said.
To restore some semblance of the eels’ ecological role in the river, Minkkinen came up with an idea in 2008: He would truck them around the dams. It was a last resort, a quick fix until a better solution for reconnecting broken ecological links came along.
Using materials from Home Depot, Minkkinen and his team erected a homemade structure next to the Conowingo Dam. It was a humble sight: a metal chute filled with landscaping cloth ran 10 feet down the riverbank; a common garden hose trickled water down the chute 24 hours a day, enticing eels to crawl up.
The eels and their baby mussel hitchhikers were funneled into a donated 160-gallon royal blue plastic tank and loaded onto a truck for the 200-mile ride north on Interstate 83, across the Maryland border to two Pennsylvania creeks.
In the late 1990s, American shad were also trucked around the Conowingo Dam in a similar effort to reconnect their natural migration paths. That practice was discontinued after mechanical fish “elevators” were installed inside the river’s dam structures to help the shad cross the dam. But it turns out eels can’t take elevators, Minkkinen said.
The first summer of the eelway, Minkkinen and his team made the trip three times a week and trucked 17,504 eels upriver. By 2016, the project reached a 1-million-eel milestone. In 2019, they found the ancient mussel beds in one upriver stocking site had more fish, growing eels, and a thin layer of young mollusks, a pumping and pulsing garden, cleaning the water with each gape.
Unlike salmon, eels migrate back downstream, and out to the ocean waters near Bermuda, where they spawn. But the Conowingo eelway runs in only one direction; trucking eels back to the bay would be a significant commitment as a downriver migrating eel can grow larger than a baseball bat. “That is a major logistics proposition,” Minkkinen said. It’s unclear how many eels survive the return trip down through the four dams’ many turbines.
The notion of humans relocating a species of animals or plants is controversial among conservation biologists. Some warn about the unintended consequences of interfering with nature. Others question whether it makes sense to spend scarce dollars on assisted migration. No U.S. agency has implemented a high-profile assisted migration project. Ecologist Daniel Simberloff compares assisted migration to “reshuffling the deck chairs on the Titanic.”
As the ecological fallout from climate change worsens, though, scientists are thinking more about different ways to help plants and animals survive.
In Mexico, as the climate grows drier and hotter, researchers have relocated oyamel fir trees to higher, cooler elevations where they can thrive and continue to host monarch butterflies that fly south in winter to find refuge in the dense, dark green conifers.
In Wyoming, the changing climate is altering the annual migrations of mule deer, elk and pronghorn, prompting the state to — like bike lanes, but for animals — to help them navigate hazards such as highways.
And in Quebec, fish biologists are studying experimental programs that use trucks to help migrating Atlantic salmon reach colder, more pristine stream reaches, above usually impassible waterfalls.
The notion of moving species to adapt to the challenges of a warming planet is so new that International Union for Conservation of Nature, one of the world’s largest conservation groups, is only at the stage of writing broad “guidelines” for saving climate-threatened species through assisted migration.
One group of Montana-based fish biologists is ahead of the rest, publishing a step-by-step decision-making tool for other freshwater fish scientists considering assisted migration.
Clint Muhlfeld, a fish biologist for the U.S. Geological Survey, led what some consider a radical experiment recently to relocate bull trout, a Western fish that thrives in cold water and is under threat as Western lakes and streams grow warmer.
In 2012, Muhlfeld and a team of federal scientists moved bull trout from one warming lake stocked with invasive predators in Glacier National Park to a lake with cooler temperatures at a higher elevation within the park.
Muhlfeld carried the fish in a bulging, waterproof backpack and hiked through backcountry to the colder lake. The team relocated 111 bull trout to a fishless, cold glacier lake. They published their road map in North American Journal of Fisheries Management: the surveys, risk assessments, planning process, and logistics.
The relocated bull trout are surviving and growing in their new home; the team is waiting to see whether they reproduce.
But scientists appointed to advise the U.S. Department of the Interior were critical of the Glacier National Park program. In a report, they wrote that introducing nonnative fish to a fishless lake could threaten the ecological balance of that lake, noting that fish-transmitted diseases could harm amphibians and reptiles that live there, among other things.
Anna Lampei-Bucharova, a German plant biologist, published a study of assisted migration for European grasses in the journal Ecology and Evolution in 2016 that found it sometimes resulted in negative consequences for the plant.
“There was lots of talk about [assisted migration] … blah, blah, blah. Therefore, it must work, right?” Lampei-Bucharova said. “But this is not a silver bullet.”
Even Schwartz, the UC-Davis conservation biologist who first argued in a seminal 2007 paper that humans may need to help species adapt to climate change by relocating them, has doubts.
“Natural areas are becoming more like influenced zoos,” said Schwartz. “The painful part of this is that many people don’t want that. I don’t want that.”
One rainy night last month, a new group of baby eels were following their ancient rhythms, migrating near Minkkinen’s eelway structure, now run by the dam’s owner, Exelon. This transfer of management from the U.S. Fish and Wildlife Service to the power company is one condition of a new 30-year federal re-licensing agreement that allows Exelon to keep the dam turbines running.
Two pencil-sized eels were crawling up an out-of-use boat ramp, lured by the rainwater streaming off an access road. The pair wasn’t headed for the eelway and so wouldn’t make it onto the trucks. But more than a million have. And today, 10 Pennsylvania creeks receive eel drops and await the rebirth of habitats in glass-clear waters that few living people can remember.