MACHIAS, Maine — Lost in the rhetorical fog of the ongoing economic, political and cultural controversies surrounding the netting of glass eels along Maine’s rugged shoreline is the grim fate that awaits the elvers being harvested.

Two prominent naturalists recently interviewed by the Bangor Daily News said they share a fascination with Anguilla rostrata — the scientific name for the American eel. Both also have toured Asian fish farming operations where tons of the tiny, transparent eels will be shipped from Maine to be raised to market size before being processed and packaged for sushi and other culinary concoctions.

Trevor Corson describes such facilities as “very dirty concentration camps,” while fellow author James Prosek terms conditions at the Chinese fish farms he has seen as “disgusting.”

Before that, however, is the curious life cycle of this species of “sea snake” that begins arriving by the millions each spring along Western Atlantic coastlines from Greenland to South America. For centuries, eels have left scientists worldwide with many more questions than answers.

Among those baffled scientists was the “father of psychotherapy,” whose first foray into marine biology did not go well. Sigmund Freud was a 19-year-old medical student when he spent four months in 1876 at an Adriatic Sea laboratory, tasked with dissecting eels in search of male testicles. Not knowing then that eels don’t develop genitals until late in their life cycles, just before they spawn and die, Freud concluded — wrongly — that each of the hundreds of eels he dissected was “of the fairer sex.”

Where life begins

The fabled Bermuda Triangle is shrouded in mysteries that have included unexplained disappearances of ships, aircraft and people within the 500,000-square-mile expanse of western Atlantic ocean bounded roughly by its points at Florida, Bermuda and Puerto Rico. Within it are sections of the massive Sargasso Sea, a vast patch of free-floating seaweed that is dynamically defined by colliding Western Atlantic ocean currents.

The sea’s thick vegetative cover serves as both the birthplace and the final resting place for an eel population that as larvae shaped like willow leaves drift with the currents before actively migrating thousands of miles to estuaries and freshwater rivers and streams from Greenland to South America. Years later, as adults eager to spawn, they slither back to the Sargasso to breed and to die.

“Eels really behave like nothing else on the planet,” said Prosek, a Connecticut-based author, artist and naturalist who spent 12 years traveling the world while researching his 2010 book “Eels: An exploration from New Zealand to the Sargasso of the World’s Most Amazing and Mysterious Fish.”

“They are the only fish that spawn in the middle of the ocean, but spend their adult lives in freshwater,” he said in a recent telephone interview. “They are born as orphaned fishes, as their parents die after spawning, and they make their way to the Gulf Stream and then distribute themselves randomly along the whole coast line, overcoming seemingly insurmountable obstacles. They can even cross over land and climb up a vertical, cement wall if it is even a little bit damp.”

Prosek and other eel researchers seem intrigued by the scientific reality that eels pose so many unanswered questions.

“They do a lot of weird things,” Prosek said. “At some point they make a conscious decision to leave the Gulf Stream to head for their native range. How do they do that? In working with scientists who study eels, I’ve seen that a lot of times the answers to such questions are: ‘We don’t know.’”

Prosek’s fascination with eels is the basis for a documentary film titled, “The Mystery of Eels,” which premieres 8 p.m. Wednesday, April 17, on the PBS program “Nature.” That project, he said, has been a year in production and took him and a production crew to China, New Zealand and to Maine.

Eels in Maine

Gail Wippelhauser, a fisheries biologist with the Sea-run Fisheries and Habitat Division of the Maine Department of Marine Resources, said the amount of time eels that survive migration remain in East Coast freshwater lakes, rivers and streams before returning as adults to the Sargasso to spawn varies widely.

“The research shows that eels that come up the Chesapeake Bay may stay five or six years, while those that migrate up rivers and streams and estuaries in Maine may stay 15 or 16 years,” she said. “In Maine we’ve seen eels as big as three-feet in length, and the oldest one we’ve seen in Maine was 29 years old, which was determined by counting the number of rings in an ear bone, much like you would count the rings of a tree trunk.”

The eel fishery in Maine is related to the species’ three distinct life stages. While the glass eel and elver fishery harvests juvenile eels returning to freshwater rivers, the yellow eel fishery uses nets and baited pots to harvest larger eels that are typically at least 2 years old, but not fully mature. A silver eel season in late summer and fall uses nets to harvest sexually mature eels that are moving downstream in rivers and streams as they return to the Sargasso Sea to spawn.

While eels once may have been found in lakes, rivers and streams in every state east of the Continental Divide, that’s no longer the case, Wippelhauser said. Fewer eels are making the trip up the Mississippi River, she said, and a census project on the St. Lawrence River has shown fewer eels are entering the Great Lakes.

“In the late ‘70s and early ‘80s, those St. Lawrence River fish ladder counts were seeing a million eels,” she said. “Now, maybe a couple of thousand will pass.”

Wippelhauser said DMR utilizes the West Harbor Pond outlet in West Boothbay Harbor as a research and monitoring site for eel migration in Maine, as required by the Atlantic States Marine Fisheries Commission.

“At our West Boothbay Harbor facility we do an annual ‘young of the year’ survey with eels, as do most states,” Wippelhauser said Friday. “We’ve been doing that since 2001, and what we’ve seen — and from the data from other states that I’ve seen — there is a lot of variability. There’s no clear trend, but last year was the highest catch in terms of young eels that came to that site.

“As for the future, it’s hard to see trends,” she said. “A lot will be determined by how many eels spawn, and a lot may have to do with random oceanographic trends. Young eels get caught up in the Gulf Stream, and we really don’t know why they swim out of it. It may be something as random as eddies.”

Landing records reflect the impact of market price on the size of Maine’s recent annual eel harvests. In 2008, Maine’s eel catch weighed in at 6,951 pounds, with a value of $1.5 million, or $216 a pound. By 2010, the take was down to 3,185 pounds with a market value of $585,000, or $184 a pound. Both the harvest and its value spiked in 2012 at 19,000 pounds worth $38 million at a record-high per-pound price of $2,000.

Maine’s Department of Marine Resources is trying to manage the fishery by limiting the number of licenses it issues to people allowed to harvest eels, but the Passamaquoddy Tribe argues that their catch quota approach is better.

Commercial harvesting of glass eels and elvers is legal in only two states — Maine and South Carolina. The tiny eels netted are sold — most recently at hefty prices of $1,700 to $2,000 per pound — with most sent to fish-farming operations in China, Japan and elsewhere. There they are raised in captivity to market size for sale throughout Asia, where eels are not only considered a culinary delicacy but, in places like Japan, an aphrodisiac.

Curiously, Prosek said, eels that wind up being served in sushi bars throughout America may have been netted in Maine, raised in China and then shipped back to the United States.

“I’ve seen farms in China where they are raised, and the conditions are disgusting,” Prosek said. “They feed them these fish meal cakes. They float these big cakes, and the eels chomp on them in tanks that are covered in black plastic, so the internal temperature must be 120 degrees.”

Author Trevor Corson, perhaps best known in Maine for his 2007 best-selling book, “The Secret Life of Lobsters,” shares Prosek’s fascination with eels. Corson’s most recent book, “The Zen of Fish,” traces the origins and cultural traditions of sushi. It includes a chapter titled “Sea Snakes” in which Corson explores the popularity of eels as food over centuries, dating back to the ancient Greeks. It’s a phenomenon now marked by the ongoing proliferation of restaurants throughout the U.S. featuring sushi.

What most intrigues Corson about eels is the mysterious process by which they are born, disperse themselves across thousands of miles and then, in response to some hard-wired urge to procreate, return thousands of miles to the Sargasso Sea to spawn and to die.

“In human terms,” Corson says in his book, “it’s like having just one chance to have sex before you die, but you have to swim from the moon to earth — without stopping to eat — to get it.”

Another way of looking at it, he said in a recent phone interview, is this:

“Suppose everyone in New York City has kids at the same time, so the city is suddenly filled with infants,” he said. “Then four million of these infants start running in different directions, some across the Washington Bridge, others across the Brooklyn Bridge. And they keep running until they get to what was once a parent’s home, although no one told them where to go, whether it’s to Iowa or Argentina.

“So they finally make it to what’s their hometown, where they stay through puberty, when they run all the way back to New York City, for the one chance they have to breed, without eating on the way. So they show up hungry, and the first thing they do is go find a club where they can hook up.”

Not all survive the trip. As Wippelhauser points out, eels have no shortage of predators, both human and marine, including larger eels. Corson points out that young eels netted while migrating face bleak futures as they come of age.

“A lot of these babies who are trying to find their parents’ homes are netted and then shipped to very dirty concentration camps in China, where they are raised in these farming facilities in really nasty conditions before being killed, packaged and sent to thousands of mid-range sushi providers.”

The future of the eel fishery in Maine and elsewhere remains as big a mystery as eels themselves.

“These eels just don’t fit in any neat category in our minds,” Prosek said. “Frankly, we don’t know what to make of them.”