Scientists recently solved the biggest mystery in animal reproduction: eel sex; or at least,
that's what all of the mainstream media and science reporting and press releases would
have you believe.
According to them, in 2022 science finally figured out where eels make babies.
But this discovery was not actually a discovery at all, because more than a century ago, a
decidedly low-tech but ingenious study had already given us the answer.
Hi.
I’m David, and this is MinuteEarth.
Freshwater eels were once so plentiful in European rivers that people pulled them up
by the bushel, baked them into pies and jellies, and ate them nearly every single day because
they were so much cheaper than other meat or fish.
But no one could figure out where all these eels originated from; no one ever saw eel
sex, or eel eggs, or eel babies…no one could even find eels’ reproductive organs.
Aristotle hypothesized that the eels were spontaneously generating in puddles.
Sigmund Freud got obsessed with eel genitalia and dissected hundreds of specimens before
finally finding one that had actual gonads.
But no one was able to make real headway on the so-called “Eel Question” until the
early 1900s.
A Danish scientist named Johannes Schmidt happened to be aboard a marine research vessel
off the Faroe islands when the nets pulled up one of those freshwater eels – one of
the smallest ever documented.
Considering how young the eel was, and the weird fact that it was in saltwater, Schmidt
hypothesized that it must be on its way to its adult habitat – the rivers of Europe
– from somewhere in the Atlantic, where it had presumably been hatched.
But to figure out where, exactly, Schmidt needed a lot more data.
So he asked the captains of Danish trading ships headed to America for a favor: every
few days, they’d trail a net for thirty minutes, and send him whatever they pulled
up, along with the date and location.
This went on for 15 years, during which time Schmidt also made several of his own sampling
journeys.
When he finally plotted the data from this mountain of samples, Schmidt found that as
ships moved West from Europe across the Atlantic, the eels first got smaller and smaller, and
then – as they got closer to America – they got bigger and bigger.
Ships that took a more southern route tended to find even smaller eels throughout their
journey.
The very smallest eels were found in spring and summer in an area about a thousand miles
off the coast of Bermuda, known as the Sargasso Sea.
With this data, Schmidt was able to put together pretty much everything we know – even today
– about the wildly eel-aborate reproductive cycle of the European eel.
The adults make a year-long, multi-thousand mile journey from the freshwaters of Europe
to the Sargasso Sea, developing their reproductive organs along the way (The lone eel with gonads
that Freud found must have gotten started a little early).
Once they get to the Sargasso Sea, the eels mate – probably in very deep water – then
presumably die and sink to the bottom.
Once the eggs hatch, the babies rise to the surface.
The baby eels then spend three years riding the currents back to Europe, arriving as mostly
mature adults.
So what had seemed like spontaneous eel generation was actually the result of one of the longest
animal migrations in the world.
Since Schmidt’s breakthrough, scientists have kept trying to learn more, via hundreds
of research trips to the Sargasso and lots of fancy new equipment.
All the evidence they’ve gathered along the way has essentially supported Schmidt's
theory.
The most recent evidence is the first ever *direct* tracking of a single adult eel’s
entire journey from Europe to the Sargasso sea.
But they’ve turned up almost nothing new; we’ve still yet to find a single wild eel
egg.
When it comes to some mysteries, at least, you don’t need direct evidence or hi-tech
gadgets…
with some ingenuity and a boatload of perseverance, sometimes the truth can be re-veeled.
It was this story in Nautilus – one of the MinuteEarth team’s favorite magazines – that
first got us excited about the weirdness of eels.
Nautilus gets us excited about all sorts of things; it’s basically a delivery device
for wonder and enlightenment that covers everything from astronomy to zoology, and it’s written
by some of the best science writers out there.
You can subscribe as a digital-only member, or add a print subscription to receive 6 beautifully
illustrated, award winning collectible editions every year.
In addition to full access to all the stories in Nautilus, all members receive benefits
like priority access to events, exclusive products and product discounts.
Memberships to Nautilus rarely go on sale, but right now you can go to Nautil.us/minuteearth
(or is it Nautil.us/minuteearth?
I don’t know how you pronounce that, anyway!
go there) to receive 15% off your membership - or just click the link in the description.
Thanks Nautilus!