A Deep Sea Mystery: The Tale of the Giant Squid
The giant squid, Architeuthis dux, is thought to be the largest known amongst the cephalopods and perhaps more importantly, the largest invertebrate to have ever existed, secondly only to the possibly mythical colossal squid. The largest found giant squid was measured at 18 metres in length and weighing in at 900kg, however this includes the length of their feeding tentacles, and hence without, the length of a giant squid is typically 13m – the length of an average bus. The picture below compares the size of a giant squid with that of the average human and a giraffe to emphasise its size. So if such a large and overwhelming creature exists… why is so little known about it?
So what do we know?
The giant squid has a typical body structure to that of its smaller relatives; it has two eyes (which can be the size of a beach ball), eight arms combined with two feeding tentacles, which can often double the length of the squid, a beak, siphon and mantle. The giant squid lives in the deep ocean and is typically found at depths between 300 metres and 600 metres, although in an extreme case one was found to be living at a depth of 1175 metres, and hence the only known predator of the giant squid is the sperm whale. It is found globally, though they are rarely found in tropical and polar regions. Due to life at these depths, giant squid have been the subject of myths and legends for centuries because of few and irregular sightings. The deep nature of their habitat has made them intensely difficult to study, and hence extremely little is known about them.
Lights, camera, action!
Due to the depth at which the giant squid lives, there has been minimal research into their lifestyle, feeding and behaviour. However, there have been two notable sightings of the giant squid and in the world of extreme marine invertebrates, both sightings have been scientific breakthroughs. The species was first recorded in 2006 by a team of researchers working with Japan’s National Science Museum, which caught a female using a smaller squid as bait, and brought both to the surface as shown in the video below. However, the research ended there as the specimen died of injuries sustained during resurface.
The next, and most important sighting of the giant squid, occurred due a combined effort between leading squid researchers; Tseneumi Kubodera, Steve O’Shea and Edith Widder, in 2013. This footage is the leading in its area as it provides an access all areas point of view to the giant squid in its natural habitat, as opposed to it being captured or dragged to the surface. Each researcher took a different approach to capture; the use of mimicking bioluminescence in atolla, using flashing LED’s in a glass orb was one and funnelling chemicals collected from the body parts of other squid, creating pheromones, into the ocean while flashing the lights in the submersible were both trialled. However, the most effective method inevitably was using a diamond squid, Thysanoteuthis rhombus, as bait and removing any source of vibration and light from the submersible, to attract the squid. The researchers experienced 23 minutes of giant squid action while in the submersible, a summary of which is shown in the video below, and from this footage the cephalopod speaking world gained the majority of its knowledge of the giant squid.
And what did we learn?
The first question to be answered regarded the hunting behaviour of the giant squid – is it an aggressive and agile hunter, or is it, on reflection of its size, a lethargic and limp hunter? Both hypothesis were confirmed on viewing of the footage.
The giant squid aggressively darted around its prey and then used its feeding tentacles to grip and attach itself to the prey, becoming lazy once attached. On the ends of the feeding tentacles are serrated like suckers, known as tentacle clubs, and the squid uses these to bring the prey to its beak where a radula system on the tongue shreds the prey, allowing digestion. The footage showed researchers however that the giant squid is not afraid to catch prey much larger than previously thought, as the diamond squid is much larger than the deep sea fish thought to be the preferred food of the giant squid.
The next question was locomotion – how does the giant squid move through water, and how can it know where it’s going with such scarce or no light? Located at the rear of the mantle, the giant squid has small fins which gently push water through the funnel and out of the mantle cavity, pushing the squid through the water column. The squid locates prey and guides itself using its two eyes, the largest eyes in the world, maximised in diameter for optimal light capture.
So… What’s the mystery?
The extent of the knowledge we have about the giant squid is limited to 23 minutes of footage in their natural habitat, bringing a specimen to the surface only for it to die and relating knowledge of smaller species to the giant squid. The depth at which they live has made them difficult to study, as it has been shown that they cannot be brought up to the surface, worsened by the fact that the level of light at the depths in which they live also makes them nearly impossible to find. The giant squid has gained fame in its notoriety for being difficult to catch, being the subject of many myths, and for this reason the scientific community should endeavour to learn more about this creature.