The eel, the drop, and the whistle

The first real map of the mystery was drawn by a Danish biologist named Johannes Schmidt, who spent the better part of two decades, from about 1904 to 1921, dragging fine nets across the Atlantic. The eel larvae he caught grew steadily smaller the farther west he sampled, and the smallest of all turned up over the Sargasso Sea, the warm, still gyre of the western North Atlantic. That was as close to the birthplace as anyone could get. No adult had ever been followed there, and the spawning itself stayed unseen.[2]

The gap finally began to close in 2022. A team fitted twenty-six mature female eels with pop-up satellite tags, floats programmed to detach on a set date and radio their position home, and released them from the Azores over two years. Several of the tags surfaced inside the Sargasso Sea, and one reached the very stretch of ocean where the larvae suggest the eels breed. It was the first direct evidence that the adults actually complete the journey people had inferred for a hundred years.[1]

The life behind that journey is a sequence of near-total transformations. An eel begins as a transparent, leaf-shaped drifter called a leptocephalus, riding the currents toward Europe for months. Near the coast it becomes a slender see-through juvenile, the glass eel, then a pigmented elver climbing into rivers, then a yellow eel that can spend a decade or two in fresh water, and at last a silver eel that stops eating, and swims some five to seven thousand kilometres back to the sea it has never seen.[2]

All of which is why no one has learned to farm it properly. Every eel raised for the table starts as a wild glass eel, scooped from an estuary, because the species has never been bred through its full cycle at any commercial scale. The cues that ripen an eel and hatch its eggs remain, for this fish, mostly guesswork.[3]

The wild supply that the whole trade leans on is in freefall. The European eel is listed as critically endangered, and the count of glass eels returning to Europe has fallen to a low single-digit percentage of what it was in the nineteen-sixties and seventies, so that fisheries scientists now advise catching none at all.[4][5] Into that scarcity has grown one of the largest wildlife crimes on the planet by sheer number of animals. Europol has put a single season’s smuggling at roughly a hundred tonnes of glass eels leaving the European Union for farms in Asia, and since a kilogram is about three thousand of the near-weightless young, that traffic runs into the hundreds of millions of living creatures.[6][7] Europe has protected the eel under international trade rules since 2009 and banned its export outright since 2010, and enforcement crackdowns still seize the animals by the tonne.[6][7]

The experiment was set up in 1927 by Thomas Parnell, the first professor of physics at the university, to make a slow truth visible to students. He heated a sample of pitch, the brittle residue left from distilling tar, poured it into a sealed funnel, and let it settle for three years. When he cut the stem in 1930 the pitch began, imperceptibly, to flow.[1]

Nine drops have fallen in the near-century since, about one every decade. The ninth came in April of 2014, a tenth is gathering at the lip of the funnel now, and the custodians expect it to fall sometime this decade.[2] Pitch is the reason the wait is so long. At room temperature it looks and shatters like a solid, yet it is a fluid of staggering thickness, measured at something like two hundred and thirty billion times the viscosity of water.[3]

There is a quiet sadness folded into the record. John Mainstone looked after the experiment for about fifty-two years, from 1961 until his death in 2013, and in all that time he never once caught a drop in the act of falling. He was away for one, stepped out for a drink and missed another, and in 2000 a camera set up expressly to record the event failed at the crucial moment. Parnell, who started it, died in 1948 without seeing a drop fall either.[4]

It was a younger rival that finally caught one on film. A pitch drop set up at Trinity College Dublin in 1944 was being watched by a webcam when, in July 2013, it recorded a drop falling cleanly away, the first time the thing itself had ever been filmed, with Queensland beaten to its own headline moment.[6]

Queensland has its consolations. The experiment holds the record as the world’s longest continuously running laboratory experiment, and in 2005 it earned Parnell and Mainstone an Ig Nobel Prize, the award for research that makes people laugh and then think. What it really keeps is a kind of time the rest of the lab cannot hold, the slow clock of a material that behaves like a solid across a human afternoon and like a liquid across a human life.[5][1]

The whistled speech is called Silbo Gomero, and it grew up as a practical answer to the island’s terrain, whose deep barrancos make a short walk a long climb. More than twenty thousand islanders can still use it, and a good whistle travels perhaps ten times as far as a raised voice, clearing a valley that ordinary speech would die in.[1][4]

What the whistler does is strip speech to its bones. The rich texture of vowels and consonants is thrown away, and what remains is pitch and the breaks in it, a melody line that rises, dips, and stops. A pair of whistles has to stand in for all the vowels and a handful more for the consonants, so a great many spoken words collapse onto the same whistled shape, and the listener leans hard on context to tell them apart. In careful tests of a whistled language, isolated words were guessed right around seven times in ten, and far more reliably once a sentence gave them somewhere to sit.[1][5]

La Gomera is not alone in this. Whistled forms of speech have been documented in at least eighty cultures, almost always in mountains or thick forest, wherever the land pulls people apart and a voice will not reach.[4] In the Pontic mountains of northern Turkey, the village of Kuşköy keeps a whistled Turkish that some ten thousand people in the surrounding valleys still understand.[2][4]

That Turkish variety gave neuroscientists a rare natural experiment. Ordinary spoken language leans mostly on the brain’s left hemisphere, a lopsidedness that shows up cleanly in listening tests. When researchers ran the same tests on fluent whistlers hearing whistled Turkish, that bias vanished, and both hemispheres pulled their weight, the acoustic melody of the whistle recruiting the right side of the brain that plain speech leaves largely idle.[3]

Most whistled languages are quietly going silent, their work now done by the phone in every pocket, and UNESCO lists the Turkish one as needing urgent safeguarding. Silbo Gomero is the exception that shows the way back. La Gomera made it a required school subject in 1999, and in 2009 UNESCO recognised it as heritage worth keeping, so the island’s children now learn to speak across the valleys their grandparents did.[2][1]