Regina Barber

You're listening to Shortwave from NPR.

Hey Shore Wavers, Regina Barber here with a modern day eel mystery.

To this day, no one knows where they come from.

Well, not entirely.

Centuries ago, people thought that baby eels just sprang up spontaneously from morning dew.

Arjan Palstra is a fish physiologist at Wageningen University and Research in the Netherlands.

He says eventually people started looking for eel reproductive organs like gonads to convince the world that spontaneous generation wasn't happening.

A couple decades later, somebody found an adult eel in the ocean, sex organs and all.

And that part of the mystery was solved.

But still, no one knew where they went to make baby eels.

All they knew was that decades-old eels living in rivers would swim out to sea and never come back.

Over multiple sea voyages, Danish biologist Johannes Schmidt would eventually trace smaller and smaller eel larvae to the Sargasso Sea in the middle of the Atlantic Ocean.

Then a century went by with no major breakthroughs, until the late 2010s, when scientists attached satellite tags to a couple dozen eels by a chain of Portuguese islands in the Mid-Atlantic.

When the trackers were recovered, they showed the first direct evidence that adult European eels go to the Sargasso Sea to spawn.

But to this day, no one has found a mature eel in the act of spawning in the Sargasso Sea, a 2 million square mile area.

That discovery could help explain why eel populations have declined and guide ways to raise them in captivity, which could boost eel numbers in the wild and decrease illegal trafficking.

Today on the show, the hunt for the spawning grounds of the European eel.

Plus, a look at their quirky lives and what solving this mystery would mean for the future of the species.

I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR.

So, Arjan, why have scientists still not found a European eel spawning in the Sargasso Sea?