In the Age of Sail, when much of the world’s oceans were still uncharted, the mythical Kraken, a gigantic tentacled sea monster with a taste for human flesh, was a sailor’s worst nightmare. “Below the thunders of the upper deep; Far, far beneath in the abysmal sea; His ancient, dreamless, uninvaded sleep; The Kraken sleepeth: faintest sunlights flee…” wrote Lord Alfred Tennyson in his 1830 poem titled The Kraken.
But the Kraken was not just a product of superstition. Today, it is well-known that its descriptions were probably based on sightings of real animals, namely the giant squid (Architeuthis dux) and colossal squid (Mesonychoteuthis hamiltoni), the largest cephalopods (class of marine animals including octopii and cuttlefish), and possibly the largest invertebrates in the world.
Despite their size, these deep-sea squid remain elusive. Until very recently, a century after it was first identified and named, there was still no image of the colossal squid in its natural environment.
Illustration of the Kraken monster. (Wikimedia Commons)
This changed last month when a team of scientists, on board a research vessel in the South Atlantic, recorded a juvenile colossal squid, only a foot long, 2,000 feet under the ocean’s surface. The footage taken near the South Sandwich Islands was released on April 15.
Why the colossal squid has remained an enigma
Colossal squid have been nearly impossible to spot, especially on camera. This is due to their large, sensitive eyes, which probably makes them stay away from research equipment that can be bright and loud, Dr Kat Bolstad, an associate professor at the Auckland University of Technology, told NPR.
As a result, researchers have very little idea about the diet, lifespan or reproductive traits of the colossal squid. Most of our understanding of the creature comes from dead or dying specimens found within the stomachs of whales and seabirds, or when younger ones turn up in trawl nets.
The cephalopod was first discovered in 1925 when scientists found arm fragments from two squid in the belly of a sperm whale. Until last month, humans had not seen it in the depths of the Southern Ocean, its natural habitat.
Although also elusive, more is known about the giant squid, which was identified in 1857. A live specimen was captured on camera only in 2004, and on video in 2016. Giant squid also live in the frigid depths of the ocean, between 600 to 3,000 feet under the surface, in tropical and temperate waters. They are known to eat deep-sea fish and other species of squid.
Archie’ the giant squid (Architeuthis dux) in the Tank Room of the Natural History Museum, London. (Wikimedia Commons)
What explains their huge size?
Beyond their habitat, the two massive squid differ in shape and size. However, reports have often exaggerated just how big they are.
Experts believe that colossal squid can be as long as seven metres or 23 feet, and weigh up to 500 kg. The giant squid is thought to grow up to 13 metres or 43 feet, and typically weighs up to 275 kg.
“Colossal squid have a huge body but relatively short arms and tentacles, which means their body plan is in some ways opposite to giant squid,” said Jon Ablett, a curator at the Natural History Museum, London, according to a report on the museum’s website.
Researchers suggest their massive size increases the number of animals that they can prey on, and reduces the number of species that can prey on them. Once fully grown, the only animal that can eat them is the sperm whale, the largest toothed predator in the world. The massive eyes of the two squid, roughly the size of a basketball, are meant to help them spot their primary adversary, according to some experts.
But unlike many other squid species, giant and colossal squid likely take years to mature. “Most squid live fast and die young,” Ablett said in the report. Researchers believe giant squid live anywhere between two and 12 years. There is no clear agreement on the average life span of the colossal squid.
Why this was a significant sighting
The high-resolution video footage of the colossal squid can help resolve several mysteries around the animal, from where these animals spend their time to where they travel to mate or spawn, and how long they live.
Speaking about the observed juvenile colossal squid, Dr Aaron Evans, an independent researcher who was not part of the expedition, told CNN: “For us to see this kind of midrange size in between a hatchling and an adult is really exciting because it gives us the opportunity to fill in some of those missing puzzle pieces to the life history of this very mysterious animal.”
Researchers highlighted that the sighting of rarely seen colossal squid can also inform decisions about human activities such as deep-sea mining, which is known to directly harm marine life.
This is the first confirmed live observation of the colossal squid, Mesonychoteuthis hamiltoni, in its natural habitat. (Via Schmidt Ocean Institute) 
Illustration of the Kraken monster. (Wikimedia Commons)
Archie’ the giant squid (Architeuthis dux) in the Tank Room of the Natural History Museum, London. (Wikimedia Commons)
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