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Comment by ubermonkey | Hacker News Reader

Look, it's not really on point for the article, but I just want to say that you probably have NO IDEA how fucking WEIRD European eels are. Because of their insanely convoluted life cycle, really smart people thought they spontaneously generated for FAR FAR LONGER than you'd think is reasonable.

There's really great and fairly short book about eels and eel-fishing mixed in with a memoir called THE BOOK OF EELS by Patrik Svensson that I cannot recommend highly enough.

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I ended up studying European Eels a lot recently and my mind was blown by how prolific they are, and how culturally and historically important they are, and yet how little we know about them. My favourite one is that we’ve known they reproduce in the Sargasso Sea since the early 20th century, due to finding larvae there, but their breeding has never been observed in the wild, and up until February THIS YEAR, an adult European Eel had never been observed to be arriving at the sea. This has now been achieved with satellite tagging https://www.nature.com/articles/s41598-022-19248-8

Seems like the kind of thing that has perhaps been witnessed, but no one has yet lived to tell the tale.

Stay away from the eels. They keep their secrets.

New Zealand short and long fin eels are also quite interesting. They live in rivers and go far inland, able to climb even 20m waterfalls, but breed only once right at the end of their life cycle somewhere in the sub-tropic Pacific, probably in deep trenches, but it is not known where.

The longfin eels are 2m in length, can weight up to 25kg and live 40-70 years.

https://www.doc.govt.nz/nature/native-animals/freshwater-fis...

https://www.rnz.co.nz/national/programmes/ourchangingworld/a...

Due to that convoluted life cycle, we are not sure why the population is declining drastically. The numbers of young eels arriving in Europe in recent years is only 10% what it was in the 80s.

We don't know how long wild eels live (again, the life cycle) but this is much shorter than a single lifetime of captive fish.

Isn’t impassable dams/hydro stations a huge issue for them?

One of many issues. The European eel gets hit by just about every possible thing due to its many and varied life cycles. Larval stage is subject to disrupted ocean currents due to climate change, juveniles are subject to an enormous illegal fishing trade (as the most prolific remaining Anguilidae, they are used to supply eel demand in many areas where local species aren’t doing as hot) as they reach European coast, young adults struggle to navigate up waterways due to dams and whatnot, adults spend their lives being fat in the mud and absorb lots of pollutants, then when ready to breed they face the dams again going back out to sea. They’re also under immense pressure from an invasive swim bladder parasite brought over when Japanese eels were introduced to Europe sometime in the 20th century.

And these are just the headline threats for each stage, there’s myriad smaller ones. The reason for their decline is almost certainly a case of lots of small threats overcoming their ability to adapt, rather than one discrete cause.

Smuggling also. In the last decade some cargo of alive eels had been found inside lugagges in airports flying to Asia.

There is an american Nematode parasite also that castrate the European eels.

Plus, overfishing, contamination, invasive species of fishes, drough, engineering of rivers, by-caught, propellers in dam pipes that cut them in chunks while swimming... And can't be breed in captivity.

The animal will go extinct in this century by greed, as usual.

They can now be induced to mate in captivity, after a long course of hormone treatments and a 2000km trip on a “water treadmill” to mimic their migration. The current problem is that the larvae don’t survive past the first week. If I recall correctly, the current hypothesis is nutritional, and there’s work being done on understanding the phytoplankton makeup of the Sargasso Sea to determine how the larvae should be fed.

I spoke to Patrik not too long ago about a newly formed stream where eels have started showing up. I dint know how they get up there from the sea, but spontaneous generation would seem more likely than swimming there :D.

Was out looking at them earlier today and this year must be a population record in this small stream.

YOU KNOW SVENSSON? Oh, that's cool.

Similar (though not quite as extreme) case: https://en.m.wikipedia.org/wiki/Barnacle_goose_myth

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