[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.84,0:00:10.14,Default,,0000,0000,0000,,From Ancient Greece to the 20th century,
Dialogue: 0,0:00:10.14,0:00:14.24,Default,,0000,0000,0000,,Aristotle, Sigmund Freud,\Nand numerous other scholars
Dialogue: 0,0:00:14.24,0:00:17.33,Default,,0000,0000,0000,,were all looking for the same thing:
Dialogue: 0,0:00:17.33,0:00:19.78,Default,,0000,0000,0000,,eel testicles.
Dialogue: 0,0:00:19.78,0:00:25.92,Default,,0000,0000,0000,,Freshwater eels, or Anguilla Anguilla,\Ncould be found in rivers across Europe,
Dialogue: 0,0:00:25.92,0:00:28.90,Default,,0000,0000,0000,,but no one had ever seen them mate.
Dialogue: 0,0:00:28.90,0:00:31.26,Default,,0000,0000,0000,,And despite countless dissections,
Dialogue: 0,0:00:31.26,0:00:37.73,Default,,0000,0000,0000,,no researcher could find eel eggs\Nor identify their reproductive organs.
Dialogue: 0,0:00:37.73,0:00:43.51,Default,,0000,0000,0000,,Devoid of data, naturalists proposed \Nvarious eel origin stories.
Dialogue: 0,0:00:43.51,0:00:48.76,Default,,0000,0000,0000,,Aristotle suggested that eels \Nspontaneously emerged from mud.
Dialogue: 0,0:00:48.76,0:00:53.56,Default,,0000,0000,0000,,Pliny the Elder argued eels \Nrubbed themselves against rocks,
Dialogue: 0,0:00:53.56,0:00:57.39,Default,,0000,0000,0000,,and the subsequent scrapings \Ncame to life.
Dialogue: 0,0:00:57.39,0:01:02.75,Default,,0000,0000,0000,,Eels were said to hatch on rooftops,\Nmanifest from the gills of other fish,
Dialogue: 0,0:01:02.75,0:01:06.74,Default,,0000,0000,0000,,and even emerge \Nfrom the bodies of beetles.
Dialogue: 0,0:01:06.74,0:01:12.40,Default,,0000,0000,0000,,But the true story of eel reproduction\Nis even more difficult to imagine.
Dialogue: 0,0:01:12.40,0:01:15.10,Default,,0000,0000,0000,,And to solve this slippery mystery,
Dialogue: 0,0:01:15.10,0:01:19.27,Default,,0000,0000,0000,,scholars would have to rethink \Ncenturies of research.
Dialogue: 0,0:01:19.27,0:01:25.68,Default,,0000,0000,0000,,Today, we know the freshwater eel \Nlifecycle has five distinct stages:
Dialogue: 0,0:01:25.68,0:01:32.89,Default,,0000,0000,0000,,larval leptocepheli, miniscule glass eels,\Nadolescent elvers,
Dialogue: 0,0:01:32.89,0:01:37.40,Default,,0000,0000,0000,,older yellow eels, and adult silver eels.
Dialogue: 0,0:01:37.40,0:01:41.32,Default,,0000,0000,0000,,Given the radical physical differences \Nbetween these phases,
Dialogue: 0,0:01:41.32,0:01:45.20,Default,,0000,0000,0000,,you’d be forgiven for assuming \Nthese are different animals.
Dialogue: 0,0:01:45.20,0:01:49.77,Default,,0000,0000,0000,,In fact, that’s exactly what \NEuropean naturalists thought.
Dialogue: 0,0:01:49.77,0:01:54.18,Default,,0000,0000,0000,,Researchers were aware of leptocepheli\Nand glass eels,
Dialogue: 0,0:01:54.18,0:01:58.28,Default,,0000,0000,0000,,but no one guessed they were related\Nto the elvers and yellow eels
Dialogue: 0,0:01:58.28,0:02:01.14,Default,,0000,0000,0000,,living hundreds of kilometers upstream.
Dialogue: 0,0:02:01.14,0:02:06.85,Default,,0000,0000,0000,,Confusing matters more, eels don’t \Ndevelop sex organs until late in life.
Dialogue: 0,0:02:06.85,0:02:09.81,Default,,0000,0000,0000,,And the entirety of their time \Nin the rivers of Europe
Dialogue: 0,0:02:09.81,0:02:12.75,Default,,0000,0000,0000,,is essentially eel adolescence.
Dialogue: 0,0:02:12.75,0:02:17.88,Default,,0000,0000,0000,,So when do eels reproduce, \Nand where do they do it?
Dialogue: 0,0:02:17.88,0:02:23.08,Default,,0000,0000,0000,,Despite its name, the life \Nof a freshwater eel actually begins
Dialogue: 0,0:02:23.08,0:02:26.60,Default,,0000,0000,0000,,in the salty waters \Nof the Bermuda Triangle.
Dialogue: 0,0:02:26.60,0:02:29.30,Default,,0000,0000,0000,,At the height of the annual \Ncyclone season,
Dialogue: 0,0:02:29.30,0:02:32.42,Default,,0000,0000,0000,,thousands of three-millimeter eel larvae
Dialogue: 0,0:02:32.42,0:02:34.94,Default,,0000,0000,0000,,drift out of the Sargasso Sea.
Dialogue: 0,0:02:34.94,0:02:39.44,Default,,0000,0000,0000,,From here, they follow migration \Npaths to North America and Europe—
Dialogue: 0,0:02:39.44,0:02:41.52,Default,,0000,0000,0000,,continents that were \Nmuch closer
Dialogue: 0,0:02:41.52,0:02:46.23,Default,,0000,0000,0000,,when eels established these routes \N40 million years ago.
Dialogue: 0,0:02:46.23,0:02:52.33,Default,,0000,0000,0000,,Over the next 300 days, Anguilla Anguilla\Nlarvae ride the ocean currents
Dialogue: 0,0:02:52.33,0:02:56.52,Default,,0000,0000,0000,,6,500 km to the coast of Europe—
Dialogue: 0,0:02:56.52,0:03:00.67,Default,,0000,0000,0000,,making one of the longest \Nknown marine migrations.
Dialogue: 0,0:03:00.67,0:03:05.60,Default,,0000,0000,0000,,By the time they arrive, they’ve grown \Napproximately 45 mm,
Dialogue: 0,0:03:05.60,0:03:09.98,Default,,0000,0000,0000,,and transformed into semi-transparent \Nglass eels.
Dialogue: 0,0:03:09.98,0:03:12.41,Default,,0000,0000,0000,,It’s not just their appearance \Nthat’s changed.
Dialogue: 0,0:03:12.41,0:03:16.16,Default,,0000,0000,0000,,If most marine fish entered \Nbrackish coastal waters,
Dialogue: 0,0:03:16.16,0:03:21.18,Default,,0000,0000,0000,,their cells would swell with freshwater\Nin a lethal explosion.
Dialogue: 0,0:03:21.18,0:03:23.56,Default,,0000,0000,0000,,But when glass eels reach the coast,
Dialogue: 0,0:03:23.56,0:03:26.44,Default,,0000,0000,0000,,their kidneys shift to retain more salt
Dialogue: 0,0:03:26.44,0:03:29.19,Default,,0000,0000,0000,,and maintain their blood’s \Nsalinity levels.
Dialogue: 0,0:03:29.19,0:03:34.47,Default,,0000,0000,0000,,Swarms of these newly freshwater \Nfish migrate up streams and rivers,
Dialogue: 0,0:03:34.47,0:03:39.89,Default,,0000,0000,0000,,sometimes piling on top of each other\Nto clear obstacles and predators.
Dialogue: 0,0:03:39.89,0:03:44.62,Default,,0000,0000,0000,,Those that make it upstream develop\Ninto opaque elvers.
Dialogue: 0,0:03:44.62,0:03:47.43,Default,,0000,0000,0000,,Having finally arrived \Nin their hunting grounds,
Dialogue: 0,0:03:47.43,0:03:51.43,Default,,0000,0000,0000,,elvers begin to eat everything \Nthey can fit into their mouths.
Dialogue: 0,0:03:51.43,0:03:55.03,Default,,0000,0000,0000,,These omnivores grow in proportion\Nto their diets,
Dialogue: 0,0:03:55.03,0:03:59.86,Default,,0000,0000,0000,,and over the next decade they develop\Ninto larger yellow eels.
Dialogue: 0,0:03:59.86,0:04:04.39,Default,,0000,0000,0000,,In this stage, they grow \Nto be roughly 80 cm,
Dialogue: 0,0:04:04.39,0:04:07.90,Default,,0000,0000,0000,,and finally develop sexual organs.
Dialogue: 0,0:04:07.90,0:04:13.48,Default,,0000,0000,0000,,But the last phase of eel life— \Nand the secret of their reproduction—
Dialogue: 0,0:04:13.48,0:04:15.70,Default,,0000,0000,0000,,remains mysterious.
Dialogue: 0,0:04:15.70,0:04:21.85,Default,,0000,0000,0000,,In 1896, researchers identified \Nleptocepheli as larval eels,
Dialogue: 0,0:04:21.85,0:04:26.09,Default,,0000,0000,0000,,and deduced that they had come \Nto Europe from somewhere in the Atlantic.
Dialogue: 0,0:04:26.09,0:04:29.24,Default,,0000,0000,0000,,However, to find this mysterious \Nbreeding ground,
Dialogue: 0,0:04:29.24,0:04:32.84,Default,,0000,0000,0000,,someone would have to perform \Nan unthinkable survey of the ocean
Dialogue: 0,0:04:32.84,0:04:36.76,Default,,0000,0000,0000,,for larvae no larger than 30mm.
Dialogue: 0,0:04:36.76,0:04:39.10,Default,,0000,0000,0000,,Enter Johannes Schmidt.
Dialogue: 0,0:04:39.10,0:04:42.70,Default,,0000,0000,0000,,For the next 18 years, \Nthis Danish oceanographer
Dialogue: 0,0:04:42.70,0:04:45.34,Default,,0000,0000,0000,,trawled the coasts of four continents,
Dialogue: 0,0:04:45.34,0:04:49.27,Default,,0000,0000,0000,,hunting down increasingly \Ntiny leptocepheli.
Dialogue: 0,0:04:49.27,0:04:53.77,Default,,0000,0000,0000,,Finally, in 1921, he found \Nthe smallest larvae yet,
Dialogue: 0,0:04:53.77,0:04:58.01,Default,,0000,0000,0000,,on the southern edge \Nof the Sargasso Sea.
Dialogue: 0,0:04:58.01,0:05:00.95,Default,,0000,0000,0000,,Despite knowledge \Nof their round trip migration,
Dialogue: 0,0:05:00.95,0:05:04.34,Default,,0000,0000,0000,,scientists still haven’t observed \Nmating in the wild,
Dialogue: 0,0:05:04.34,0:05:06.89,Default,,0000,0000,0000,,or found a single eel egg.
Dialogue: 0,0:05:06.89,0:05:09.84,Default,,0000,0000,0000,,Leading theories suggest \Nthat eels reproduce
Dialogue: 0,0:05:09.84,0:05:12.91,Default,,0000,0000,0000,,in a flurry of external fertilization,
Dialogue: 0,0:05:12.91,0:05:17.37,Default,,0000,0000,0000,,in which clouds of sperm \Nfertilize free-floating eggs.
Dialogue: 0,0:05:17.37,0:05:21.59,Default,,0000,0000,0000,,But the powerful currents \Nand tangling seaweed of the Sargasso Sea
Dialogue: 0,0:05:21.59,0:05:24.80,Default,,0000,0000,0000,,have made this theory \Ndifficult to confirm.
Dialogue: 0,0:05:24.80,0:05:27.47,Default,,0000,0000,0000,,Researchers don’t even know where to look,
Dialogue: 0,0:05:27.47,0:05:29.92,Default,,0000,0000,0000,,since they’ve yet to successfully\Ntrack an eel
Dialogue: 0,0:05:29.92,0:05:32.59,Default,,0000,0000,0000,,over the course of its return migration.
Dialogue: 0,0:05:32.59,0:05:34.100,Default,,0000,0000,0000,,Until these challenges can be met,
Dialogue: 0,0:05:34.100,0:05:40.50,Default,,0000,0000,0000,,the eel’s ancient secret will continue\Nto slip through our fingers.