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Episode 346: A Colossal and Giant Squid Episode

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An incredibly rare image of a Giant Squid, captured off the coast of Japan. (image from CNN)

This week on the podcast we cover one of the most enigmatic and legendary species of the deep ocean, the Giant Squid. Although their names are pretty close, the Colossal and Giant Squid are actually two different species, and there are some significant differences between them. The Giant Squid belongs to the genus Architeuthidae and is found in most of the world’s oceans, below 1500 feet, although they aren’t usually found in tropical or very cold waters. Both species are monstrously large, but the Giant Squid has a longer body with a thinner mantle, whereas the Colossal Squid has a shorter, wider, heavier body. The Colossal Squid also belongs to another genus, the Mesonychoteuthis, and is only found in the southern and polar seas, deeper than 3000 feet.

A diagram displaying the different sizes of squid and octopus species, including the colossal and giant squid. Here you can see the Colossal squid is much squatter, whereas the Giant Squid is much longer.

Both species are molluscs, close to snails, clams and slugs, which are all classed as molluscs thanks to their soft bodies. Cephalopods have been around for 500 million years, although it is tricky to trace the evolutionary path of Giant and Colossal squid as their DNA is hard to get hold as they are so rarely sighted. Museum samples are generally no use for DNA analysis and the tissues are too degraded and the preservation techniques often destroy the DNA.

When a fisherman caught a dying specimen off the coast of New Zealand, he was able to send a fresh frozen piece of tissue to a research team at the University of Copenhagen. Unfortunately, even this was not of high enough quality for analysis. Instead, the researchers turned to close species and examined their genomes to infer DNA sequences in the giant squid. They found that the Giant Squid has many highly conserved sequences in their genome, meaning natural selection has retained these genes as they are so essential to the survival of the species. In 2020, scientists were able to extract some Giant Squid DNA and create and publish a draft genome, which gave some interesting information about the evolution and biology of the squid. There is even some research into using environmental DNA (eDNA), which is a technique that analyses DNA from the environment, such as from soil or seawater, to identify what species are in the location. This technique is gaining more prominence in conservation and could be an ideal way to determine where squid populations are and how many individuals there may be.

Myth and mystery: the history of the Giant Squid

The famous monster of legend, the Scandanavian Kraken, most likely modelled off the Giant Squid (image from the BBC)

The Giant Squid is behind one of the most famous monster stories in human history; the Kraken, the towering beast of legend that terrified sailors around the world. The Kraken was an integral part of Scandinavian folklore and was likely based on the Giant Squid. The Odyssey has its own squid inspired creature, Scylla, a monstrous woman with six snake heads and rows of sharklike teeth that lurked on the cliffs of a narrow strait and would devour ships that came too close. Until a few hundred years ago, the Giant Squid was believed to be nothing more than myth, the terror of folklore and not a real animal that existed beneath the waves.

This began to change with the sighting of what was suspected to be a Giant Squid by the HMS Daedalus, which was sailing off the Cape of Good Hope in 1848. The sailors claimed to have spotted a sea serpent, something long and tentacled that surfaced beside the boat briefly. Many zoologists ridiculed this, saying it was nothing more than a large seal, but the captain of the ship stood behind his crew, and the debate raged on. In 1861, the French warship Alecton ended much of the controversy around the Giant Squid when they came across a specimen dying on the surface. They hauled the dead squid aboard, accidentally detaching the tentacled head from the rubbery tail sheath, which fell into the water to be lost. However, this was enough to prove that cephalopods of significant size did in fact exist, although none found so far have quite matched the enormous size of the Kraken, capable of bringing warships down.

The first ever photograph of a Giant Squid was taken in 1874 by a Revered from Newfoundland, who bought a dead Giant Squid from a fisherman for just $10! He then displayed the enormous tentacles in his bath! Not a particularly glorious end for the unfortunate squid.

The first known photograph of a Giant Squid ever taken, by a reverend who snagged the dead squid for $10 and displayed it in his bath

In 2002, Japanese scientists caught the first image of a live squid in its deep ocean habitat, a single blurry photograph. The National Science Museum of Japan later caught further images in 2004 after using a deep ocean baited hook on a remotely operated submersible. This was also important in understanding the behaviour of the squid, as it aggressively attacked the bait and lure, showing an impressive speed and vicious hunting behaviour its size doesn’t allude to. In 2006, scientists in the Gulf of California utilised a cleverly designed bait shaped like a Humboldt squid to lure the Giant Squid in. The camera attached to the submersible caught images of the squid engaging in hunting behaviour. In 2012, Japanese scientists again contributed to the field of Giant Squid science, by catching footage of a huge Giant Squid using flashing lights to imitate bioluminescent jellyfish, presumably to draw in their prey. The most recent footage of a Giant Squid was from 2019, caught by a NOAA remote operated vehicle with a probe attached to the front.

The first video footage of a Giant Squid captured by Japanese scientists. The Giant Squid can be seen chasing the baited lure. (image from Science)

There are a few specimens preserved in museums around the world, with arguably the most famous examples at the Smithsonian Museum in Washington. Specialised reinforced tanks had to be built to house the two specimens, and the US Navy and Air Force were involved to move these huge creatures under the right conditions to preserve them, in a project aptly called Operation Calamari.

Amazing Adaptations in the Abyss

The Giant Squid is an apt name given that the largest specimen ever recorded was 43 feet long and weighed almost a ton! Its not just their size that makes them impressive though, they have some incredible adaptations that enable them to survive in the hostile environment of the deep ocean.

The enormous beak of the Colossal Squid (www.tepapa.govt.nz)

The Giant Squid is a textbook example of Abyssal Gigantism, a phenomenon where deep ocean invertebrates are significantly larger than many other species. There are many theories as to why this occurs, such as the extreme cold in the deep ocean leading to much slower metabolism or a general lack of resources and less predation pressure. Not only are their bodies huge, but they have also evolved eyes the size of dinnerplates that are the largest recorded eyes in the animal kingdom. These eyes allow them to absorb as much light as possible down in the depths of the ocean, so they can detect and hunt their prey.

The huge eye of the Giant Squid (image from the Smithsonian)

When they do spot their prey, they can catch them from as far as 33 feet away, using their two huge feeding tentacles to reach out and catch prey using the sharp toothed suckers that line them. They can then feed their prey towards their sharp beak, which slices the prey into small pieces. Behind this beak lurks a structure called the radula, which is a tongue like organ covered in rows of tiny teeth that can ram the bite size chunks of food down the throat. Stomach analyses from washed up squid has revealed that they eat deep sea fish species and other smaller squid, like the Humboldt squid, and from time to time cannibalise members of their own species, as evidenced by beaks found in the stomachs of Giant Squid. There is also evidence that they steal food from each other, in a behaviour called kleptoparasitism. When a female squid was seen alive in the shallows of a Spanish beach, a tourist knew this was important and called the local marine conservation charity. It wasn’t immediately obvious what had killed her; she wasn’t riddled with parasites, which can often be fatal for Giant Squid, but she did have a deep gash in her mantle and two severed tentacles. Only two animals were suspected to be large enough to have killed the Giant squid, the Dana Octopus or the Neon Squid, but the wounds didn’t match either of these animals. The circular shaped marks on the body, left only one suspect: another Giant Squid. Since she hadn’t been partially eaten, it was most likely she has been attacked for her dinner by another, larger squid. Aside from the risk from other Giant Squid, their other predators are sperm whales, killer whales, pilot whales and southern sleeper sharks.

The suckers that cover the tentacles of the Giant Squid (image from the BBC)

For a long time, it was hypothesised that Giant Squid simply floated in the water column with their tentacles extended, passively waiting for food to drift towards them. However, evidence from washed up squid such as the one in Spain, and footage recorded of Squid aggressively chasing after baited hooks revealed that they can actively hunt prey efficiently. To move around with such agility, the Squid have fins on the back of their mantle which they use to change direction, and they propel themselves with jets of water that they pull through their mantle cavity and push through their siphon. To help orient themselves in the water, Giant Squid use organs called statocysts. These organs can actually be used to age Giant Squid, similar how we age trees with the rings in their trunks. Unlike many fish, Giant Squid don’t use a swim bladder to keep their buoyancy, but instead utilise ammonium chloride, a solution which is lighter than water. Giant Squid have a very complex nervous system and interesting behaviours, but there is a great deal more research that is needed in the area.

Deep sea worries: the future of the Giant Squid

Currently, the IUCN lists the Giant Squid and the Colossal Squid as least concern, although their numbers and population trajectories are almost completely unknown. Due to the high amounts of ammonium chloride in their tissues, Giant and Colossal squid are likely to taste incredibly bitter, which fortunately means they won’t be going on a seafood menu any time soon. However, as fisheries expand and plumb ever deeper depths of the ocean, there is a risk to the prey base of the Squid. As large predators near the top of the food chain, there are also concerns that polluting chemicals could build up to lethal levels in the tissues of squid, although this hasn’t been detected in Giant Squid as of yet, although this is likely because they are just so rare it is incredibly hard to study them.

Deep sea mining and fishing are also a concern, as deep sea trawling, a process in which a huge net is dragged across the ocean floor, is hugely destructive to deep sea biodiversity and the food webs the Giant Squid is a part of. Mining for essential minerals for technology puts squid and other deep sea species, including other cephalopods like octopi, at risk from pollution, sedimentation in the water, and noise pollution.

However, the conservation charity the Deep Sea Conservation Coalition is working to protect the often neglected ecosystems of the deep oceans. They aim to limit deep sea mining and ban trawl fishing in certain biodiverse hotspots. You can check out their work at: Protecting the Deep Sea for All of Us – Deep Sea Conservation Coalition (savethehighseas.org)

The Giant Squid needs a great deal more research before we can truly understand this amazing denizen of the deep, and how it will cope with a changing world. Dr Clyde Roper, a zoologist from the Smithsonian, is leading the world with his research on the Giant Squid. He has developed the ‘critter cam’, a specialised camera that can be attached to the heads of Sperm Whales, one of the main predators of the Giant Squid, and used remote operated submersibles to try and film Giant Squid and their behaviours. However, so far, he has little luck in finding this shy giant. Hopefully, with more funding for his research, he will be able to add more science to the sparse repertoire of the Giant Squid. You can learn about the world leading research being conducted at the Smithsonian here: Smithsonian Institution | Home (si.edu)

Dr Clyde Roper, a Smithsonian zoologist, showing off the size of a Giant Squid specimen (image from the Smithsonian)

Awesome videos!



Black, R. (2011) ‘The Giant Squid: Dragon of the Deep.’ Smithsonian Magazine

Da Fonseca et al (2020) ‘A draft genome sequence of the elusive giant squid, Architeuthis dux.’ Giga Science

Nilsson, D.E. Warrant, E.J. Johnsen, S. Hanlon, R. and Shashar, N. (2012) ‘A unique advantage for giant eyes in giant squid.’ Current Biology

Preston, E. ‘The bloody pirate life of one of the oceans most elusive creatures.’ The Atlantic

Wada, T. Doi, H. Togaki, D. Kaida, R. Nagano, M. Katano, I. Suzuki, M. Ohtani, T. and Mitusuhashi, H. (2020) ‘Exploring a legendary giant squid: an environmental DNA approach.’ Marine Biology


July 26, 2023
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