For a freshwater American eel in the Hudson Valley’s Black Creek, it all begins in a domain 1750 nautical miles long in the Atlantic Ocean called the Sargasso Sea — the only known spawning place in the entire world for this eel and its European cousin.
In this technologically advanced, hyper-surveilled age of eavesdropping cellphones and orbiting satellites, these eels have stubbornly resisted revealing all their secrets. No one has ever seen these eels mate. No one has ever seen them reproduce.
To delve into the mystery, Laurel Sutherlin, naturalist and host of the Saturday morning Radio Kingston program Nature Nuggets, says that the eel’s mysterious provenance had been one of the more enduring curiosities of the scientific record.
To begin at the beginning, Sutherlin name-checks an ancient Greek polymath. “Aristotle couldn’t figure it out,” he said. “Nobody knew where they came from. He thought that they were spontaneously generated. And then the other big mystery was, what gender are they? They would dissect them and they couldn’t find male parts or female parts.”
Two thousand years passed. The scientists remained baffled.
Larvae, glass eels and elvers
It was only through the miracle of satellite tagging in 2022 that the world learned all the freshwater eels in America and in Europe originated in the Sargasso Sea.
“Somehow American eels know how to go east when they are just tiny little things out on the open ocean,” said Sutherlin. “Then they ride the ocean currents up across the Atlantic Seaboard, under the Verrazano Bridge, past the skyline of Manhattan, and then up the Hudson River.”
The leaf-shaped larvae drift with the plankton over the open sea currents for up to three years before their second phase of life begins. Their body shortens and conforms to a more cylindrical shape six inches long. Called glass eels, they can now swim.
“They look like they’re made out of cellophane or plastic or something,” Sutherlin said. “You can see right through them, and at this point they are genderless.”
Driven on by some hard-wired instinct to seek out lower water temperatures, they trade the salt water for the silt and muddy banks of their preferred fresh-water streams, brooks, creeks and lakes. Again, the eels change their form, another phase in their life cycle during which they are referred to as elvers.
”They turn kind of a brown-green opaque color,” said Sutherlin. “They get a little bit bigger and they look more like what you think of an eel looking like. When they arrive, they’re literally transparent, but for most of the rest of their life, they’re nocturnal and they live in the mud.”
The eels find their way
To follow the shape-shifting creatures deeper into the eel hole, Sutherlin suggests speaking with “a contagiously enthusiastic naturalist and scientist,” named Chris Bowser. Bowser is the estuary education coordinator for the New York State Department of Environmental Conservation. Generously, Bowser was willing to talk.
“Although eels have that sort of snaky look to them, or when they’re little babies a wormy look, they are absolutely 100 percent bony fish,” Bowser said. “Just like a trout, or a guppy or a perch, they even have scales. It’s just that they’re very, very small.”
In a pinch, the eels can slither and writhe their way up over rocks, branches and other obstacles, and even leave the water if need be. Though they breathe air through their gills, they can also breathe through their skin while crossing over dry land. In some tributaries, clever limnologists — those who study inland freshwater systems — provide eel ladders resembling tubes with a grippy substratum for the eels to climb.
“For the entire eastern half of North America, they’re getting into basically every river from the Canadian Maritimes down to Mexico and even the Caribbean Islands,” he said. “Eels are going to find their way above waterfalls. They’ll find their way above dams. Here at the Black Creek they’ll basically go all the way up the Black Creek watershed.”
Not all of them will make it. Many will become ocean-flavored snacks for all the other creatures that live in the Black Creek. “Part of the beauty of the eel is that in most river systems nutrients, carbon, food energy, flow downstream with the water,’’ Bowser said. “Eels, like salmon or herring, represent this very rare case where nutrients are actually traveling upstream into all of these tributaries. Now, hopefully a bunch of those energy packets survive to adulthood and keep the eel generations going. But some serve a role feeding the other fish and wildlife of Black Creek and the Hudson River.”
Research at Black Creek
To track and count the number of young eels in tributaries of the Hudson River, the Department of Environmental Conservation began a community science eel-monitoring program in 2008 led by department’s Hudson River Estuary Program and National Estuarine Research Reserve. Part of the effort is expended in maintaining fyke nets, long funnels made out of fine mesh that the eels swim into and can’t get out from.
“We’re not trying to catch every eel that comes into Black Creek,” Bowser said. “We’re just trying to catch a representative sample to compare year over year.”
The nets are checked for ensnared eels every day. Whatever eels they find are taken out, counted and transported above difficult rocky patches, or dams and culverts.
“We’ve been doing the Hudson River eel project now for many years and the numbers fluctuate greatly, but it’s safe to say that thousands of glass eels come into Black Creek every year,” Bowser said. “And then they continue upstream until they find a spot and then they’ll stay there in a small creek, up in the Catskills or in the mountains around here.”
Decades can pass while the eels hunt in the darkness of the night, slithering through the mud along the tributaries, growing larger and longer. And then at a signal no one has identified, though the light of a full moon unfailingly accompanies the decision, the eels abandon New York.
“Whatever the trigger is,” said Sutherlin, “at some point they start to transform and their digestive organs turn into reproductive organs, and then they turn around and they repeat the journey the other direction. They swim down the creek, into the Hudson, past New York City, back into the open ocean, down the whole of North America and complete the circle, back into the tropical Sargasso Sea.”
Free event on May 31
“Catadromous” is the word that describes creatures that start and end in salt water, with the largest part of their lives spent in fresh water — the mirror opposite of anadromous species like salmon, which begin and end their lives in fresh water.
Here in May the annual invasion of the eels is under way. For a chance to see the eels in the flesh and to celebrate the opening of a new section of the Black Creek Preserve, which is owned by Scenic Hudson, the public is invited to attend a free event on May 31.
“Otherwise,” noted Sutherlin, “for most of the rest of their life they’re nocturnal and they live in the mud, so it’s just very unlikely that you’re ever going to actually encounter one.”The festivities, Sutherlin said, in which Bowser is expected to play a part, will run from 11 a.m. to 5 p.m. Representatives of the John Burroughs National History Society and Scenic Hudson will preside over the occasion.
Tables will be set up along the trails, and people can borrow binoculars to look at birds, or they can go to the station where the eels are.
The exact number of American eels left in the wild is thought to be decreasing. The Atlantic States Marine Fisheries Commission considers their population “depleted.” Through the efforts of citizen scientists, conscientious volunteers and state agencies in New York, it’s hoped that the population of eels swimming and slithering along the waterways of the Hudson Valley will increase.
Correction:
“The article incorrectly provided the number of American eels left in the wild at 700,000. No one knows how many American eels are left in the wild. In 2015, at least 4.7 million eels* were estimated to have spawned in the Sargasso Sea.”
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