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Chapter 1: What is the main topic discussed in this episode?
This week on Consider This, the drama at CBS News. Some of the most respected journalists in America say their corporate ownership is bowing to political pressure. It's intimidation. They've created a climate of fear to make the news organization unwilling to tackle the problem and report the news. Longtime 60 Minutes correspondent Steve Croft, this week on Consider This.
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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.
Or from mud or from slime. So they thought it was not like an animal that was reproducing, which just started to exist spontaneously from something.
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.
Even a big name like Sigmund Freud, he started his career by looking for the gonads of eel, but never found them.
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.
Somewhere in the 1890s, Italians discovered larvae were found in the seas around Italy. And that was basically the starting point for Johannes Schmidt.
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.
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Chapter 2: What mystery surrounds the life cycle of European eels?
We're talking about going to Mars, but in the meantime, we don't know many things of our deep seas.
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.
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So, Arjan, why have scientists still not found a European eel spawning in the Sargasso Sea?
That's a very good question. It may have to do with the fact that they don't have a specific site where they spawn. For instance, Japanese eel that spawns in the Mariana Ridge, we know that they do that near seamounts.
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Chapter 3: How did historical beliefs about eel reproduction evolve?
And they do that in upwelling areas near seamounts and also at a specific time, at noon moon. So if you can pinpoint where you have to be and at what time, then you may be able to catch them in the act of spawning. And Professor Tsukamoto, he has done that already back in the 90s for the Japanese eel. But for European eels, they swim to the Segasu Sea, but not to a specific site.
It seems that they are spawning along an axis, I guess you see, which may be as long as about 2,000 kilometers. So it's not a specific site, but it probably has to do with the Earth magnetic field.
That's awesome.
Yeah.
So the sea is big, but they are just like close to the surface, right?
Well, no, not that close. Well, for European eel, I don't know exactly. For Japanese eel, they're like around 150 meters of depth. So that's still quite deep. And the eels are supposed to spawn even deeper, maybe about 300 meters deep.
So despite these eels being so mysterious, people have learned some things about them. They are weird. Let's talk about some of this weirdness. What do scientists know about their life cycle?
Well, everything that happens on the continent, we know a lot about it. But what I say, the moment that they disappear into the ocean, and like almost a year later, we get small transparent eels back, that was always a black box. So eels are born in the Sargasso Sea. These larvae, they turn into willow leaf-shaped larvae, leptosafely larvae. They're about just a few centimeters.
And by the currents, they're taken to the European continent. There they metamorphose into tiny transparent glaciers, and they swim up the rivers. Actually, the moment that they swim into the freshwater, then they start to pigment. Wow. And then they spend a long life basically growing.
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Chapter 4: What evidence suggests where European eels spawn?
What's the Holy Grail for you then? Like, what would you love to learn about eels?
Yeah, it's not one thing. I'm already intrigued by the fact that at which moment do they start to swim to the Sargasso Sea and why?
Yeah, like what triggers them?
Yeah, that's still a longstanding physiological question. Like, We see what happens, but we don't know why. And if we know why, we can use that information, of course. Well, some people consider it like it should always remain a biological mystery. It's so beautiful. So we should not discover the final truth.
It should be mythical forever.
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Chapter 5: Why is the Sargasso Sea significant for eel reproduction?
Yeah. On the other hand, yeah, there are so many questions. So when are they leaving? Why do some eels get so old? If they don't go to the Sequeso Sea, then it There are stories known of eels becoming 150 years. Imagine that you're 150 years and you're still not even a puber. You're like a Peter Pan. So if you do not reproduce, you have eternal life.
I mean, that's great to know. I would love that. It's too late for me. I already have a kid.
Yeah, for me too.
Arjan, thank you so much for talking to me about eels. I learned so much.
All right. Yeah, thank you.
Short Wavers, we are proud to be part of the public radio ecosystem. Help support us in making the show by following us on the NPR app or wherever you listen from. We can't do this without you. This episode was produced by Burleigh McCoy. It was edited by our showrunner, Rebecca Ramirez, and the facts were checked by Tyler Jones. The audio engineer was Jimmy Keeley. I'm Regina Barber.
Thanks for listening to Short Wave from NPR.
This week on NPR's Newsmakers, former First Lady Jill Biden. She reveals Joe Biden's 2024 debate performance was so alarming, doctors checked him after he got off the stage. I was terrified. I thought, oh my God, what's happening? Is this a stroke? What is this? Inside, the dramatic month that followed, leading to one of the biggest decisions of Biden's presidency, to walk away.
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