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00:00You know what I find genuinely strange?
00:01The deep ocean has almost no food,
00:03and below a certain depth, sunlight can't even reach.
00:06Which means photosynthesis stops.
00:09Which means the base of the food chain as we know it just doesn't exist down there.
00:13Most animals are surviving on what drifts down from above.
00:17Dead plankton, decaying matter, the ocean's leftovers.
00:22That's it.
00:23And the conditions down there are brutal.
00:25Below 3,300 feet, light is completely gone,
00:28and temperatures sit somewhere between 28 and 39 degrees Fahrenheit,
00:32below the freezing point of fresh water.
00:34The pressure is already 100 times what we feel at the surface.
00:38It is, by every measure, one of the most hostile environments on the planet.
00:43And yet, some of the largest animals we've ever found live down there.
00:48Not just large for deep sea creatures,
00:50animals so enormous and so strange
00:52that sailors who encountered them at the surface
00:55came home convinced they'd seen a sea monster.
00:58That's not supposed to happen.
00:59In an environment with almost nothing to eat,
01:02animals should be getting smaller, not bigger.
01:05But the deep ocean doesn't follow that logic.
01:07It has a completely different one.
01:10And once you understand it,
01:11these animals stop looking like exceptions
01:13and start looking exactly like what this environment was always going to produce.
01:19In this video, we're going to look at five of the largest deep sea creatures ever discovered
01:24and uncover the mystery behind why life in the deep ocean involves such giants.
01:30I want to start with the heaviest invertebrate on the planet.
01:33We're talking, of course, about the colossal squid.
01:36And I want to be very clear that this is not the giant squid which we'll dive into next.
01:40People mix these up constantly.
01:43The giant squid is longer.
01:44The colossal squid, however, is heavier, more robust,
01:47and in my opinion, considerably more terrifying.
01:50The colossal squid lives in the southern ocean surrounding Antarctica,
01:54down to depths of around 6,500 feet.
01:57The largest confirmed specimen pulled up by a New Zealand fisherman
02:01in the Ross Sea in 2007 weighed a whopping 1,000 plus pounds.
02:06That's a squid with a mantle, just the main body, not even the arms and tentacles,
02:11and it's about 10 feet long.
02:13The full animal with tentacles is estimated at up to 23 feet,
02:17but it's the mass that gets me.
02:19This is the single heaviest invertebrate ever recorded on Earth.
02:23And the eyes.
02:24The colossal squid has the largest eyes of any animal alive today,
02:29confirmed measurements of up to 11 inches across.
02:32To give you some context, a basketball is about 9 inches in diameter.
02:36These eyes evolve specifically to detect bioluminescent flashes
02:41in complete and utter darkness at depth across distances
02:45that would otherwise be invisible.
02:47So how does a 1,000-pound animal even survive on ocean leftovers?
02:52The answer is something that completely flips the logic of the deep sea on its head.
02:56Scientists have measured the colossal squid's metabolic rate,
03:00and it burns just 45 calories in a day.
03:04Just 45.
03:05That is less than you get from a single boiled egg.
03:08A 1,000-pound predator running on the energy equivalent of a light snack.
03:13Because at that size, the body becomes so efficient at conserving what it takes in
03:17that it barely needs to feed at all.
03:20The deep sea doesn't reward the animal that finds the most food.
03:23It rewards the one that needs the least.
03:26And the colossal squid, somehow, has gotten so large that it's cracked that equation entirely.
03:33And here's what I find so incredible about this animal.
03:36Until March of 2025, nobody had ever filmed a colossal squid alive in its natural habitat.
03:42Not once.
03:44This is the heaviest invertebrate on Earth, and we had never actually seen it living.
03:48The first footage came from an ROV near the South Sandwich Islands, and it was a juvenile barely a foot
03:55long.
03:55We know they grow to over 1,000 pounds, as I've mentioned,
03:58because we found dead ones, and we found their beaks inside sperm whale's stomachs.
04:02But the living animal at depth, going about its life, that is almost entirely a mystery.
04:08For something that weighs over half a ton, that is remarkable, and we have barely scratched the surface.
04:13So that's the colossal squid, but its cousin, the giant squid, deserves its own moment.
04:19It is longer, more widespread, and has one of the most extraordinary relationships in the ocean.
04:24The largest confirmed giant squid measured close to 43 feet long.
04:29The arms and tentacles make up the bulk of that length.
04:32The feeding tentacles alone can extend to around 30 feet when extended.
04:37The mantle is more compact than the colossal squid, but the total length is staggering.
04:42Some researchers, using beak size as a proxy, have suggested individual giant squid could theoretically reach up to 65 feet,
04:51though nothing that large has ever physically been documented.
04:54And here's the thing about giant squid that I think people don't fully appreciate.
04:58For most of human history, we thought they might be myth.
05:02The kraken.
05:03Ancient mariners weren't just making things up.
05:05They were encountering real giant squid at the surface when the animals were dying or disoriented,
05:10and those things are 40 feet long.
05:13Of course they became sea monsters.
05:15We didn't photograph a living giant squid in its natural habitat until 2004.
05:20That is how recently we confirmed that one of the most iconic animals on the planet
05:24actually behaves the way we thought it did.
05:27And down at that depth, its size isn't just extraordinary.
05:30It's the reason it's still alive.
05:32In shallow water, growing this large would make you a target.
05:36A conspicuous, slow, high-calorie meal for anything fast enough to take you.
05:42But in the deep sea, once you cross a certain size threshold, the list of things that can actually hunt
05:47you starts to collapse.
05:49The giant squid is so large that only one predator in the ocean regularly takes it on.
05:54The sperm whale, which has to dive over a mile down to do it.
05:58We know those battles are real.
06:00We've found sperm whales with deep circular scars across their heads, the unmistakable mark of squid suckers,
06:06each one lined with sharp serrated edges from arms that fought back.
06:10Two enormous animals in complete darkness at the bottom of the ocean, neither one guaranteed to win.
06:17That is happening right now somewhere in the deep sea, and we have never once seen it.
06:23Alright, if the squid are the monsters of the deep, the Pacific Sleeper Shark is something different.
06:28Something quieter, and somehow even more unnerving.
06:31The Pacific Sleeper Shark is possibly the largest predatory fish in the entire ocean.
06:36It can reach up to 23 feet in length and weigh close to 2,000 pounds.
06:41It lives throughout the North Pacific, diving to depths of over 6,500 feet, where temperatures barely move above 30
06:48degrees.
06:48And that cold is the engine the whole animal runs on.
06:52It slows the metabolism down to almost nothing.
06:56The shark ages so slowly that a 14-foot female caught in the Aleutians was found to be at least
07:0135 years old and still reproductively immature.
07:05For context, a great white is considered fully mature adult at around 30.
07:09The Pacific Sleeper at 35 is still a juvenile.
07:12The same cold that makes this environment almost uninhabitable is the exact thing keeping this animal alive.
07:19Stretching every biological process out so far that it barely needs to eat, barely needs to hunt, and barely needs
07:27to do anything except exist.
07:29And in the deep sea, that turns out to be enough.
07:32It swims with barely any body movement and almost no hydrodynamic noise.
07:37No pregnant female has ever been caught or examined.
07:39The vast majority of individuals we've seen have been juveniles, including the one that I caught and got to swim
07:45with.
07:46Scientists believe that mature adults live in the abyssal habitats, depths of 10,000 to 20,000 feet, so far
07:54down and so inaccessible that we have essentially never met one.
07:57The largest predatory fish on the planet, and we don't know where it gives birth, how long it lives, or
08:03what its full adult size actually is.
08:05When I was working in Alaska, we set lines down in the Prince William Sound looking for these incredible sharks.
08:12And I was actually lucky enough to be one of the only people in history to bring one of these
08:17sharks up from the depths and get to get in the water and interact and dive with it, even putting
08:22a Pacific sleeper shark into tonic immobility.
08:26Now, getting to document this footage and work with this shark was a true dream come true.
08:30And you can even see those copepods that I mentioned in its eyes making it completely blind.
08:35But getting to swim with an animal like this was incredible, and I certainly wouldn't want to swim with our
08:39next one.
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09:15Let's get back to the video.
09:16Okay, this next one is the one I have the hardest time convincing people is real when I describe it
09:21out loud.
09:22The lion's mane jellyfish is not a deep-sea animal in the way the others are.
09:26It spends most of its life in the upper layers of cold subarctic water.
09:30But it belongs in this build.
09:32More muscle to move it.
09:33More heart to pump blood to the extremities.
09:36Size on land has a cost attached to every centimeter.
09:39But this animal is 95% water suspended in water.
09:44Gravity barely registers.
09:46There's no skeleton to engineer.
09:47No weight to carry.
09:49No internal infrastructure demanding energy.
09:51The ocean is holding it up entirely.
09:53And when there's no biological bill to pay for getting bigger, there's nothing left to stop it.
09:59The cold water it lives in slows its biology just enough to let that growth keep accumulating quietly.
10:05And 120 feet later, here we are.
10:09And those tentacles are not passive.
10:11They're arranged in clusters of up to 150 per group.
10:15Eight groups total, each armed with stinging cells called nematocysts that fire neurotoxins on contact.
10:21The jellyfish positions itself above prey, spreads its tentacles net wide, and then slowly sinks through them.
10:28A slow, silent, 120-foot curtain of venom descending through the water.
10:34And even the detached tentacle fragments retain their ability to sting.
10:38You can encounter a fragment of lion's mane jellyfish on a beach with no jellyfish in sight and still get
10:44stung.
10:45This animal lives about one year.
10:46That is the full lifespan, from egg to fully formed giant jellyfish with 120-foot-long tentacles in about 12
10:53months.
10:54It grows to a size that rivals the largest animal that has ever lived in a year, and then it's
11:00gone.
11:00That is one of the most extraordinary biological facts that I know.
11:05And then there's this, the giant oarfish.
11:08And I genuinely believe this animal is responsible for more sea monster legends than anything else in history.
11:14Because when you see one, especially if you see one at the surface when it's dying,
11:18the only reasonable response, if you don't know what it is, is to believe you've seen something impossible.
11:25The giant oarfish is the longest bony fish alive.
11:28It grows to confirmed lengths of 26 feet, with reports and unverified accounts pushing towards 36 feet.
11:35It is silver, with a brilliant crimson dorsal fin running the entire length of its body,
11:40with an elaborate red crest above its eyes.
11:42It has no scales, it moves by undulating that dorsal fin while its body stays almost entirely rigid,
11:49and it has been filmed swimming vertically in the water, perfectly upright,
11:53which is an image that looks like nothing else in nature.
11:56It lives in the mesopelagic zone, around 650 to 3,300 feet down.
12:01And despite its size, it feeds almost entirely on small crustaceans and krill,
12:06a filter feeder with a toothless, protrusable mouth.
12:09The longest animal in the bony fish world eats some of the smallest prey in the ocean.
12:14There's something almost philosophically uncomfortable about that.
12:18Local traditions hold that the appearance of oarfish near the surface signals an approaching earthquake or disaster.
12:24Now, this might seem silly, but six oarfish appeared before a deadly earthquake in the Philippines in 2017.
12:31Dozens washed up before the 2011 Tohoku earthquake and tsunami.
12:35Science doesn't support this idea, but there are just simply two people.
12:40In the cold, the dark, and the scarcity of the deep ocean, bigger is the winning strategy.
12:45More efficient, harder to eat, and better equipped to outlast the gaps between meals that would kill anything smaller.
12:51Which leaves one final question.
12:54If the fraction of the ocean that we've explored has already given us a squid that burns 45 calories a
13:00day and wasn't filmed alive until last year,
13:03a shark whose adults we've essentially never met, and a jellyfish longer than a blue whale,
13:08what is waiting in the parts we haven't reached yet?
13:12If you want to go deeper on any of these animals, drop it in the comments, subscribe if you're not
13:16already,
13:17and I'll see you on the next one.
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