Whether living or extinct, on land or at sea, in literature or in life, large animals have long fascinated people. The largest animals have been hunted since prehistory: whales, walruses, elephants, rhinos, hippos, giraffes, and large fishes. In fact, many species of large animals are endangered or extinct due to overhunting or climate change. One giant animal, however, has remained almost unnoticed and unobserved in its habitat. That animal is the giant squid (Architeuthis). The giant squid is among the largest invertebrates on Earth—with lengths measuring nearly 60 feet (18 m)! They are one of the largest predators that live in the deep sea.
If they are so big, why don’t we know more about them? Conversely, since they live so deep, how do we know anything at all? Here we present the myths that surround this elusive animal and a look at our present understanding of these magnificent and mysterious creatures.
2 Background and mythology
Not so long ago, people imagined fabulous fictional creatures living on Earth— sirens and mermen, leviathans, monsters, serpents and kraken— animals that breach the boundaries between major groups of organisms! Men and women with fish scales and tails, birds with reptilian teeth, animals from the deep and dark places on Earth! These creatures were born in the minds of people and perpetuated through myth and folklore, where they captured the imagination and grew with the re-telling of their existence.
One of these imagined creatures, the kraken, with its immense proportions, terrible grasping arms, thousands of suckers, sharp, powerful jaws, and glaring eyes the size of volleyballs, was based on a real sea animal—the giant squid. Krake, or more commonly, kraken, is the Norwegian word that means “fabulous sea monsters.” Olaus Magnus was the first to publish the term in 1555 and Bishop Erik Pontoppidan added significantly to the story in his Natural History of Norway (1755). Pontoppidan used the term krake to describe a very large sea serpent observed from a ship off the coast of Norway sometime in August 1746. Giant squid also have been featured in the well-known books Moby Dick (1851) by Herman Melville and Twenty Thousand Leagues Under the Sea (1870) by Jules Verne.
The North Atlantic Ocean has revealed an impressive number of these creatures over the centuries, but we now know that they are not serpents or monsters at all, just gigantic squid. Sea serpent, sea monster and kraken all share with the giant squid a long serpentine form. Sea serpent bodies are the same shape as giant squid arms and tentacles. At 30 feet (10 m) or more, a single tentacle easily could be mistaken for a serpent or monster!
Today squid, octopus, cuttlefish, and chambered nautilus are classified as cephalopods. Giant squid are known scientifically as Architeuthis. Scientists who study squid are called teuthologists, after the Greek word for squid, Teuthis.
3 How are giant squid studied? (Sources of information) Whether found floating at sea or washed ashore as flotsam (debris), giant squid have been reported in records dating back to the 16th Century. No doubt, these fabulous creatures have been scattered around the world’s beaches for as long as giant squid have existed. Greek philosopher Aristotle first described giant squid, which he called teuthos, around 350 B.C. In 1857, Jappetus Steenstrup, an eminent Danish biologist, pieced together from stories, ancient drawings, and one beak, the fact that kraken were nothing more or less than squid—giant squid. Steenstrup named these animals Architeuthis after the Greek for “ruling squid”. Professor Addison E. Verrill of Yale University later, in 1873, confirmed Steenstrup’s assignment by examining two specimens that washed up on the Newfoundland coast.
Since then, more than 300 Architeuthis have been found on the beaches and coastlines of the world’s oceans and captured in deep sea fishing nets. Although this number of specimens is substantial, they have not provided enough detailed information for scientists to fully understand the anatomy or infer the biology of these squid. This is because many of the earlier specimens were destroyed and never preserved. Once dead, giant squid decompose rapidly. Other marine organisms frequently are scavengers on dead squid. The eyes, skin and internal organs are usually first to be damaged. Tentacles and arms are commonly missing. In addition, stomachs are usually empty or, if food is present, it is so fragmented from digestion that it is difficult to identify the prey species. So, we must look beyond the flotsam to learn more.
Sperm whales (Physeter catodon) are known to be the major predator of giant squid. Whales stranded on beaches and caught by whaling ships bear circular scars inflicted by the powerful suckers of giant squid. Scientists have used the size of the scars to estimate the size of the squid eaten by the whales. Scars as large as 7.8 inches (20 cm) have been reported and some people believe that it would take a 246-foot (75 m) squid to bear such a sucker! Do not believe it! Scientists have noted that no fresh scars have been measured larger than about 1.97 inches (5 cm), and no giant squid specimens have been examined with suckers larger than 2.05 inches (5.2 cm). In fact, the size of giant sucker scars increases as sperm whales grow. It is also possible that ringworm, a fungal infection that grows in a circular pattern, has been mistaken for old sucker scars. The current scientific conclusion is that adult giant squid suckers are between 0.79-1.97 inches (2-5 cm) in diameter, smaller on arms and largest on the tentacles. No credible reports exist of suckers larger than this. Sperm whales have an interesting way of digesting giant squid. Enzymes in the large whales’ stomach quickly digest the soft tissues of squid. The squid’s hard beak, made of a carbohydrate called chitin, is indigestible. Sperm whales must rid themselves of the thousands of hard, pointy beaks that accumulate in their digestive tracts. To do so, they coat the beaks with a slick, waxy substance called ambergris, then pass the mass of beaks and ambergris through the digestive tract.
The distribution and abundance of giant squid can be roughly estimated from the stomach contents of sperm whales. Sperm whales and giant squid occur in all oceans of the world.
Scientists also learn about these deep-sea creatures from the catch of commercial fishing operations. As commercial fishing nets are dropped to ever-greater depths, they more frequently bring up giant squid. Netted specimens are often in better condition than stranded squid since the netted squid are likely to have been alive before they were caught. While many of these giants are not saved for scientific examination, some that are preserved have enough remains in their stomachs that some prey can be identified. During the 1990s, the greatest numbers of giant squid came from the deep waters of New Zealand where they were caught in the fishery for orange roughy fish. In 2004, Japanese scientists took the first still photographs of a living giant squid on a camera set at almost 3000 feet (900 m) deep. In 2006, these same scientists captured a live giant squid and pulled it to the surface where it was videotaped while still alive. It is now a specimen at the Japanese National Museum. There are now about a dozen giant squid on display in museums and aquaria worldwide including 2 specimens currently on display in the museum's new Sant Ocean Hall. Our hall specimens include a large immature female and a smaller mature male. Both were caught by fishing trawlers.
Imagine your own arms as giant squid tentacles. Stretch them to 33 feet (10 meters). Your hand represents the club with four rows of suckers with sharp, serrated edges that line your palms and suckers along your wrists. Add small knobs and both tentacles can be locked together as you capture your prey. Now that you are equipped like Architeuthis, imagine how well you could catch a baseball!
Although giant squid have eight arms up to 9.8 feet (3 m) long, they are unlikely to be used to grab prey. The two much longer tentacles, 33-40 feet (10-12 m), actually make the catch. At the business end, away from the head, the tentacles expand to resemble clubs. Suckers, round cups lined with sharp, finely serrated rings of chitin, are located on both arms and tentacles. Suckers hold on to prey with powerful suction while the chitinous rings sink into the unlucky prey. Hundreds of suckers are found on the inner surface of the arms and tentacles.
Although giant squid tentacles are very long compared to the arms and mantle, and even proportionately longer than the tentacles of most other kinds of squid, they have the same function—snatching prey at a distance. Giant squid may snatch prey more than 33 feet (10 m) away from the predator’s eye!
Once caught by Architeuthis tentacles, the prey is transferred to the arms. The arms further subdue the prey, pulling it to the strong, sharp beaks. The beaks are operated by a massive set of muscles that allow them to bite through just about anything the squid might capture. The giant squid’s bite-sized pieces of food are pushed down the esophagus to the stomach. To do this, the tongue has a radula, an organ loaded with rows of small, file-like teeth. Pieces of food must be very small because the esophagus passes through the brain.
All squid have more than one way to get around. One way is to cruise at slow speeds using paired fins at the rear of the mantle, combined with gentle, rhythmic pulses of water pushed out of the mantle cavity through the funnel. Squid expand the mantle cavity by contracting sets of muscles within the mantle; water fills the expanded space, then other muscles contract, forcing water out through the funnel, which causes the mantle to return to its original size.
“Squid expand the mantle by contracting sets of muscles”??? How is it possible to make something bigger by making something (muscles) shorter? Muscles get shorter when they contract. Squid mantles are thick. Muscles within the mantle actually compress the thickness without collapsing the skin. The mantle then behaves like a syringe, with water drawn or, or more accurately, pushed in.
The jet of water closes the flaps around the squid’s head so water can exit only through the funnel. This rhythmic flow of water is also the way in which squid breathe. As water passes in and out, the gills are refreshed with oxygen.
The other way squid move is with great bursts of speed and acceleration. They do this by using the muscles in the mantle to make dashes through the water. Basically, they suck more water into the mantle and jet it out more forcefully. For squid, this is like running a 100-meter dash. They can swim at full speed for a short distance before they are worn out. They usually use these quick bursts to evade a speedy predator such as a tuna, shark, or wahoo. Some squid may even leave the water and glide above the surface like flying fish when fast predators chase them. Unfortunately for the squid, this makes them available to squid-eating birds!
By examining the anatomy of giant squid specimens and comparing it to better-known species, scientists can determine how giant squid probably move. It seems that Architeuthis has less well-developed musculature for bursts of speed than some shallow-water squid known to be fast. Nonetheless, the giant squid obviously swims fast enough to be a survivor in its natural deep-sea habitat.
6 Growth and reproduction
How long does it take to become a giant? Like people, large mammals such as elephants, whales, and even gorillas take many years to grow large, mature and reproduce. Most larger fish also require many years to reach adult size. On the contrary, cephalopods actually grow very quickly and die after a short life. Short lives and high rates of reproduction are their hallmarks. The giant octopus, a sizeable animal at 1/20th the weight of a mature giant squid, lives just 2-3 years. Evidence from statoliths (solid calcium carbonate granules) found in the statocyst, the organ responsible for equilibrium (balance and stability), suggests that giant squid live no more than five years. This means that the growth rate of giant squid is extremely rapid. It is one thing to be a fast-growing squid that reaches maturity at 12 inches (30 cm), and quite another to grow to nearly 60 feet (18 m) within a few years! To grow at such a rate, giant squid have to be in areas where there is an abundant supply of food; they would need to eat enormous quantities on a continuous basis. They must be feeding machines!
Unlike most fish, squid have a different strategy for reproduction. In association with a short life span, giant squid reproduce once, releasing millions of eggs, then die.
7 Social organization
Scientists do not know whether giant squid live in groups, or what the size and makeup of those groups might be. They may be solitary hunters. How Architeuthis individuals interact with each other is unknown. This is one of the many aspects of giant squid behavior that intrigues people and is an inspiring factor in the desire to continue to study them.
Only single specimens of Architeuthis are caught in fishing nets at any one time. Furthermore, so few juveniles have ever been captured that we have very little information about growth or social habits. The individual squids observed by the Japanese scientists in 2004 and 2006 were alone. However, others may have been nearby but unseen in the blackness of the deep sea. Whether or not giant squid are solitary, gregarious, or occur in schools only as juveniles, are questions yet to be answered.
Every aspect of Architeuthis anatomy and physiology is a form of adaptation. Foremost is the animal’s size. Is there any reason why Architeuthis grows so much larger than other squid? Perhaps the most obvious aspect of large body size and fast growth rate is that giant squid are able to outgrow rapidly the large number of predators to which they are initially exposed. Even at half-size, giant squid will have outgrown all potential predators except sperm whales and large sharks.
Animal size is associated with the abundance and nutritional qualities of its food items. Larger animals must eat more food than smaller ones. As a rule, the rate of metabolism decreases as animals increase in size. This means that, per kilogram, larger animals eat less than smaller ones, even though they must eat more by quantity.
Architeuthis have the largest eyes in the animal kingdom—at up to 10 inches (25 cm) in diameter; they are the size of a human head! There are vertebrates larger than Architeuthis, but none has eyes of comparable size. Cephalopods are visual animals and are distinguished among invertebrates for their highly complex visual system.
The visual systems of cephalopods and vertebrates are an example of convergent evolution. This means that both groups of animals see in a similar way, but their visual systems (eyes) evolved separately in each group. If we compare human eyes to squid eyes, we find remarkable similarity in the anatomy. Squid and people both have eyes with single lenses, pupils, irises, and retinas. We can only imagine the light gathering capabilities of the giant squid’s enormous retina!
Far longer than the arms, the tentacles seem impossibly long to manage with enough accuracy to snag prey at distances over 33 feet (10 m). They may use quick bursts of speed like other squid, or they may sneak up on their prey with stealthy movements. Without direct observations on feeding behavior, scientists assume that they behave like other squid. The still photographs taken in the sea off Japan showed a giant squid attacking a bag of bait in a similar pattern known for shallow-water squid. There is still much to be learned about these fascinating deep-sea giants!