Sea monsters on record: which giant creatures are real?

What the phenomenon is

"Sea monster" covers three very different kinds of claim, and keeping them apart matters. Some are large, real animals that scientists have now filmed alive in the deep ocean: the giant squid and the colossal squid. Some are folklore, like the kraken, built from centuries of sailors' half-glimpses rather than from any single species. And some are ordinary animals, such as sharks and oarfish, that looked monstrous only because of how they decomposed or how briefly they were seen.

The popular claim

Popular retellings often flatten these three categories into one dramatic story: giant, tentacled monsters lurking in the deep, sinking ships, almost mythical. That framing makes it easy to assume giant squid are exaggerations too, on the same footing as the kraken, since for centuries nobody could produce a live one. It also runs the other way: a strange carcass or a distant sighting gets treated as proof of an undiscovered species, when it is often a known animal in an unfamiliar state.

The giant squid, documented

The giant squid, Architeuthis dux, settles the exaggeration question: it is real, and it has been directly observed. Japanese researchers Tsunemi Kubodera and Kyoichi Mori took the first photographs of a live giant squid in its natural habitat on September 30, 2004, off the Ogasawara Islands, using a baited camera line. The animal that attacked the bait was estimated at eight meters long from the tentacle it left behind, which DNA testing confirmed as Architeuthis.

Video of a live giant squid in the deep sea followed in the summer of 2012, when Kubodera worked with oceanographer Edith Widder in the same Ogasawara waters, using a submersible and a camera system called Medusa, built around a dim red light invisible to deep-sea animals. The team recorded five separate giant squid over 285 hours underwater. In June 2019, a NOAA-backed expedition filmed one in the Gulf of Mexico, 10 to 12 feet long, after thousands of earlier submersible dives in the same waters had failed to find one.

The colossal squid, filmed for the first time in 2025

The colossal squid, Mesonychoteuthis hamiltoni, is a separate, heavier-bodied species living in Antarctic waters at depths beyond 3,200 feet. Adults are estimated to grow to 23 feet and weigh up to 1,100 pounds, making them the heaviest invertebrates known. Until recently, everything scientists knew about them came from remains pulled from the stomachs of whales and seabirds; nobody had filmed one alive in the wild.

That changed on March 9, 2025, when the Schmidt Ocean Institute's remotely operated vehicle SuBastian, diving near the South Sandwich Islands in the South Atlantic, recorded a live colossal squid on camera for the first time: a juvenile just under a foot long. The sighting fell during the hundredth anniversary of the species being formally identified and named, closing a gap in direct observation that had lasted a century.

Where the legends come from

The kraken is not a documented species; it is Scandinavian folklore describing a creature large enough to wrap its arms around a ship in a crushing embrace. Giant squid, which can grow to around 13 meters, are the most likely real animal behind the story: large enough to be terrifying, encountered rarely enough to become legend, and, before 2004, never observed alive by the people describing them.

The sea-serpent reports common in older sailors' logs have a different, better-documented candidate: the oarfish, a real fish that can stretch to about seven meters, with a flame-red crest running down a long, shimmering silver, ribbon-shaped body. Folklore holds that oarfish beaching themselves signals an imminent earthquake or tsunami, but there is no scientific proof behind that claim.

When a "monster" turns out to be a shark

Not every carcass is a new species. On April 25, 1977, the Japanese trawler Zuiyo Maru netted a decomposing, 10-meter carcass off New Zealand, with what looked like a long neck and small head, and early coverage speculated it was a plesiosaur, a marine reptile extinct for tens of millions of years. Researchers who examined preserved tissue samples found otherwise.

A 1978 Japanese research team ran amino acid analysis on the carcass's fibrous tissue and matched it to elastoidin, a protein found in the fins of sharks and rays, with microscopic and thermal tests pointing the same way. Their conclusion was that the animal was a badly decomposed basking shark: decay strips away a shark's jaw and gills first, which can leave the remaining carcass looking, to an untrained eye, like a small head on a long neck.

What is still debated

The identification of giant and colossal squid is not in question; both have been photographed, filmed and DNA-tested. What remains genuinely open is how many of each exist, and how large the biggest living individuals actually get, since most measurements come from dead or dying specimens rather than healthy adults in the wild, along with how these animals behave when no camera or bait line is there to disturb them.

Verdict

Real or Legend has filed the giant squid and the colossal squid as confirmed real: both are documented species, now photographed and filmed alive in their own deep-sea habitat, with dates, names and locations on record. The kraken is filed separately, as legend inspired by real encounters rather than a species of its own, and the 1977 Zuiyo Maru carcass is filed as a solved case: a basking shark, not a sea monster.