National Geographic

Giant Squid – From Sea Monster to Conservation Icon

When I was five years old, shortly after my dinomania hit a fever pitch, my parents took me to New York City’s grand American Museum of Natural History. The towering, tail-dragging Tyrannosaurus and low-slung, wrong-headed “Brontosaurus” were the species I most wanted to see on my fossil safari, but I didn’t only have eyes for the Mesozoic. Anything suitably large and monstrous shocked my imagination, including the dim diorama of a sperm whale tussling with a giant squid.

The life-scale model was artificial – I can’t even imagine how anyone would go about mounting an authentic giant squid – but the fantastic scene drew me in because there was the distinct possibility that such an epic battle was actually taking place at that very moment. The dinosaurs in the upper halls were all gone. They only lived where speculation and science melded together. But the giant squid and sperm whale didn’t need me to try to revive them. That dark, static vision was a three-dimensional snapshot of a living truth.

As a child, I was convinced that the squid had as much a chance of winning the battle as the whale. The toothed cetacean had brute strength, certainly, but I believed that the slippery squid was crafty enough to ensnare and drown its attacker. The giant squid was a real sea monster, after all, and only a foolish predator would trifle with a 50 foot cephalopod. Only later did I face the ugly fact that the squid was not an equal in combat, but prey. Sperm whale stomach contents leave no doubt that giant squid are little more than tasty morsels for the marine mammals. All that’s usually left of the titanic cephalopods are their tough, keratinized beaks.

So if giant squid don’t actually hunt sperm whales, sink ships, or devour rum-soaked pirates, what do they eat? And how do they catch their food? Discovery’s Monster Squid: The Giant Is Real, due to air this Sunday, might offer a few clues through the first video footage of Architeuthis dux in its deep sea haunts, but marine biologists actually know quite a bit about the feeding habits of this elusive cephalopod thanks to stranded specimens and beaks.

Outlining the giant squid menu isn’t quite so simple as cutting open the rare specimens that wash ashore. This is because there usually isn’t very much left in their guts. In some cases, such as a squid that washed up on Fuengirola beach near the Strait of Gibraltar in 1997, there might be nothing inside the mollusk’s stomach. And even when stranded giant squid retain parts of their last meals, the fact that the squid use their beaks to tear prey into tiny pieces obscures the identities of their meals.

But zoologist Bruce Deagle and colleagues proposed an ingenious workaround. By screening torn morsels and slurry inside squid stomachs, marine biologists can pick out genetic markers that identify prey species. When Deagle and coauthors sifted through the messy gut contents of a squid that had been caught in 1999 by a trawler off Tasmania’s west coast, they found the genetic markers for a fish called the blue grenadier and giant squid.

The squid sequences could represent the cephalopod itself, cannibalism, or even the squid’s own arms. The fact that parts of a giant squid tentacle were found in another specimen caught off New Zealand, described the year before Deagle’s study, hint that giant squid either consume each other or eat their own tentacles. The fish material, however, made sense of why trawlers around Australia and New Zealand sometimes catch giant squid. The squid in this region are probably feeding on the same fish that the trawlers are targeting, an interaction that researchers had speculated about but never documented before.

The distribution of giant squid around the world. Image created by NASA, from Wikipedia.

Not all giant squid feed on blue grenadier, though. The huge cephalopod is widely distributed through the global ocean, and squid elsewhere in the world target different prey. Three giant squid caught in the waters of Ireland, for example, had a varied diet of small fish such as blue whiting and Atlantic horse mackerel, in addition to Norway lobster and curled octopus. That assessment was based on gut contents, but researchers can also get an idea for how giant squid diets shift by looking at chemical traces in their beaks.

As giant squid feed and digest their prey, isotopes of carbon and nitrogren from their food become embedded in their bodies. These isotopes are signatures of particular kinds of prey that researchers can detect in squid tissues and, therefore, reconstruct diet. (Paleontologists use the same techniques to study the feeding habits of extinct species.) After sampling four beaks from giant squid found in the Bay of Biscay and off Namibia, marine biologist Ángel Guerra and coauthors found that giant squid targeted different prey as they aged. Younger squid, as might be expected, went after smaller prey, while more mature squid were able to handle larger prey. But the traces also indicated that the squid probably stayed in a relatively small area during their lives, hinting that giant squid tend to inhabit places where there is a great deal of food to fuel their quick growth.

Much as the truth may disappoint Kraken fans, the giant squid seems to target relatively small fish and cephalopods, possibly including other giant squid. How giant squid go about catching their victims, however, isn’t quite so clear. Some cephalopod experts have suggested that Architeuthis are sluggish ambush predators that sit still in the water column until inattentive prey just happens to blunder into the sucker-lined trap. Rare observations of giant squid in the wild, however, suggest that the predator is capable of striking with speed. In a 2005 paper, marine biologists Tsunemi Kubodera and Kyoichi Mori reported that a giant squid attacked a baited line by rapidly propelling its tentacles at the morsel and then coiling the appendages “in an irregular ball in much the same way that pythons rapidly envelop their prey within coils of their body immediately after striking.” We still don’t know exactly how squid hunt actively-swimming prey, but squid’s swiftness in this instance hints that the huge cephalopods are not so slothful as had been assumed.

A modest-sized giant squid found off New Zealand. Photo by NASA, image from Wikipedia.

As mysterious and odd as the giant squid seems, the mollusk is not a monster. Truly, the massive invertebrate is one of the “endless forms most beautiful and most wonderful” that Charles Darwin rhapsodized about, and is a reason for us to keep searching the alien marine realm that makes up so much of our own planet. And as we learn more about the giant squid, the creature is slowly transforming from a deep sea terror into a symbol of conservation.

In 2011, Ángel Guerra and colleagues proposed that the giant squid be raised up as “an emblematic invertebrate that can represent concern for the conservation of marine biodiversity.” Or, as Craig McClain put it, we should make the giant squid the panda of the deep. The enigmatic invertebrate is undoubtedly affected by climate change, overfishing, pollution, and damage caused by seismic surveys, and we risk losing this strange beastie just as we’re starting to understand how it lives. The giant squid might not look quite as cuddly as a panda, but it’s still an abyssal representative of wild, wonderful habitats that we are damaging even if we can’t directly see the stretch of our influence.

The leviathan that fired my imagination so many years ago is not an aberration to be feared. The giant squid is a creature so wondrous that it was initially easier to believe it as a legend than a reality. The charismatic cephalopod is still a powerful symbol of the deep, but one that should inspire stewardship rather than fear. Our world would be so much poorer without many-armed giants to inspire us to keep venturing fathoms down, to glimpse a different world that we can only briefly visit.

References:

Bolstad, K., O’Shea, S. 2004. Gut contents of a giant squid Architeuthis dux (Cephalopods: Oegopsida) from New Zealand waters. New Zealand Journal of Zoology. 31, 1: 15-21

Deagle, B., Pemberton, J., Gales, N. 2005. Genetic screening for prey in the gut contents from a giant squid (Architeuthis sp.). Journal of Heredity. 96,4: 417-423

González, M., Fernández-Casado, M., Rodríguez, M., Segura, A., Martín, J. 2000. First record of the giant squid Architeuthis sp. (Architeuthidae) in the Mediterranean Sea. Journal of the Marine Biological Association of the UK. 80, 4: 745-746

Guerra, A., Rodriguez-Navarro, Gonzalez, A., Romanek, C., Alvarez-Lloret, P., Pierce, G. 2010. Life-history traits of the giant squid Architeuthis dux revealed from stable isotope signatures recorded in beaks. ICES Journal of Marine Science. 67: 1425-1431

Guerra, A., Gonzalez, A., Pascual, S., Dawe, E. 2011. The giant squid Architeuthis: An emblematic invertebrate that can represent concern for conservation of marine biodiversity. Biological Conservation. 144: 1989-1997

Kubodera, T., Mori, K. 2005. First-ever observations of a live giant squid in the wild. Proceedings of the Royal Society B. 272, 1581: 2583-2586

Lordan, C., Collins, M., Perales-Raya, C. 1998. Observations on morphology, age and diet of three Architeuthis caught off the west coast of Ireland in 1995. Journal of the Marine Biological Association of the United Kingdom. 78, 3: 903-917

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