Giant squid

Giant squid

The giant squid (genus: Architeuthis) is a deep-ocean dwelling squid in the family Architeuthidae, represented by as many as eight species. Giant squid can grow to a tremendous size: recent estimates put the maximum size at for females and for males from caudal fin to the tip of the two long tentacles (second only to the colossal squid at an estimated , one of the largest living organisms). The mantle is about long (more for females, less for males), and the length of the squid excluding its tentacles is about . There have been claims reported of specimens of up to , but no animals of such size have been scientifically documented.

On September 30, 2004, researchers from the National Science Museum of Japan and the Ogasawara Whale Watching Association took the first images of a live giant squid in its natural habitat. Several of the 556 photographs were released a year later. The same team successfully filmed a live giant squid for the first time on December 4, 2006.

Anatomy

Like all squid, a giant squid has a mantle (torso), eight arms and two longer tentacles. The arms and tentacles account for much of the squid's great length, so giant squid are much lighter than their chief predators, sperm whales. Scientifically documented specimens have weighed hundreds, rather than thousands, of kilograms.

The inside surfaces of the arms and tentacles are lined with hundreds of sub-spherical suction cups, in diameter, each mounted on a stalk. The circumference of these suckers is lined with sharp, finely serrated rings of chitin. The perforation of these teeth and the suction of the cups serve to attach the squid to its prey. It is common to find circular scars from the suckers on or close to the head of sperm whales that have attacked giant squid. Each arm and tentacle is divided into three regions — carpus ("wrist"), manus ("hand") and dactylus ("finger"). The carpus has a dense cluster of cups, in six or seven irregular, transverse rows. The manus is broader, close to the end of the arm, and has enlarged suckers in two medial rows. The dactylus is the tip. The bases of all the arms and tentacles are arranged in a circle surrounding the animal's single parrot-like beak, as in other cephalopods.

Giant squid have small fins at the rear of the mantle used for locomotion. Like other cephalopods, giant squid are propelled by jet — by pushing water through its mantle cavity through the funnel, in gentle, rhythmic pulses. They can also move quickly by expanding the cavity to fill it with water, then contracting muscles to jet water through the funnel. Giant squid breathe using two large gills inside the mantle cavity. The circulatory system is closed, which is a distinct characteristic of cephalopods. Like other squid, they contain dark ink used to deter predators.

Giant squid have a sophisticated nervous system and complex brain, attracting great interest from scientists. They also have the largest eyes of any living creature except perhaps colossal squid — over in diameter. Large eyes can better detect light (including bioluminescent light), which is scarce in deep water.

Giant squid and some other large squid species maintain neutral buoyancy in seawater through an ammonium chloride solution which flows throughout their body and is lighter than seawater. This differs from the method of floatation used by fish, which involves a gas-filled swim bladder. The solution tastes somewhat like salmiakki and makes giant squid unattractive for general human consumption.

Like all cephalopods, giant squid have organs called statocysts to sense their orientation and motion in water. The age of a giant squid can be determined by "growth rings" in the statocyst's "statolith", similar to determining the age of a tree by counting its rings. Much of what is known about giant squid age is based on estimates of the growth rings and from undigested beaks found in the stomachs of sperm whales.

Size

The giant squid is the second largest mollusc and the second largest of all extant invertebrates. It is only exceeded in size by the Colossal Squid, Mesonychoteuthis hamiltoni, which may have a mantle nearly twice as long. Several extinct cephalopods, such as the Cretaceous vampyromorphid Tusoteuthis and the Ordovician nautiloid Cameroceras may have grown even larger.

Yet, giant squid size, particularly total length, has often been misreported and exaggerated. Reports of specimens reaching and even exceeding in length are widespread, but no animals approaching this size have been scientifically documented. According to giant squid expert Dr. Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands.

Based on the examination of 130 specimens and of beaks found inside sperm whales, giant squid's mantles are not known to exceed in length. Including the head and arms, but excluding the tentacles, the length very rarely exceeds . Maximum total length, when measured relaxed post mortem, is estimated at for females and for males from caudal fin to the tip of the two long tentacles. Giant squid exhibit reverse sexual dimorphism. Maximum weight is estimated at for females and for males.

Reproductive cycle

Little is known about the reproductive cycle of giant squid. It is thought that they reach sexual maturity at about 3 years; males reach sexual maturity at a smaller size than females. Females produce large quantities of eggs, sometimes more than 5 kg, that average long and wide. Females have a single median ovary in the rear end of the mantle cavity and paired convoluted oviducts where mature eggs pass exiting through the oviducal glands, then through the nidamental glands. As in other squid, these glands produce a gelatinous material used to keep the eggs together once they are laid.

In males, as with most other cephalopods, the single, posterior testis produces sperm that move into a complex system of glands that manufacture the spermatophores. These are stored in the elongate sac, or Needham's sac, that terminates in the penis from which they are expelled during mating. The penis is prehensile, over 90 centimeters long, and extends from inside the mantle.

How the sperm is transferred to the egg mass is much debated, as giant squid lack the hectocotylus used for reproduction in many other cephalopods. It may be transferred in sacs of spermatophores, called spermatangia, which the male injects into the female's arms. This is suggested by a female specimen recently found in Tasmania, having a small subsidiary tendril attached to the base of each arm.

Post-larval juveniles have been discovered in surface waters off New Zealand, and there are plans to capture more and maintain them in an aquarium to learn more about the creature.

Ecology

Feeding

Recent studies show that giant squid feed on deep-sea fish and other squid species. They catch prey using the two tentacles, gripping it with serrated sucker rings on the ends. Then they bring it toward the powerful beak, and shred it with the radula (tongue with small, file-like teeth) before it reaches the esophagus. They are believed to be solitary hunters, as only individual giant squid have been caught in fishing nets. Although the majority of giant squid caught by trawl in New Zealand waters have been associated with the local hoki (Macruronus novaezelandiae) fishery, the fish themselves do not feature in the squid's diet. This suggests that giant squid and hoki prey on the same animals.

Adult giant squids' only known predators are sperm whales and possibly Pacific sleeper sharks, found off Antarctica, but it is unknown whether these sharks hunt squid, or just scavenge squid carcasses. It has also been suggested that pilot whales may feed on giant squid. Juveniles are preyed on by deep sea sharks and fishes. Because sperm whales are skilled at locating giant squid, scientists have tried to observe them to study the squid.

Range and habitat

Giant squid are very widespread, occurring in all of the world's oceans. They are usually found near continental and island slopes from the North Atlantic Ocean, especially Newfoundland, Norway, the northern British Isles, and the oceanic islands of the Azores and Madeira, to the South Atlantic around southern Africa, the North Pacific around Japan, and the southwestern Pacific around New Zealand and Australia. Specimens are rare in tropical and polar latitudes.

Species

The taxonomy of the giant squid, as with many cephalopod genera, has not been resolved. Lumpers and splitters may propose as many as eight species or as few as one. The broadest list is:

  • Architeuthis dux, "Atlantic Giant Squid"
  • Architeuthis hartingii
  • Architeuthis japonica
  • Architeuthis kirkii
  • Architeuthis martensi, "North Pacific Giant Squid"
  • Architeuthis physeteris
  • Architeuthis sanctipauli, "Southern Giant Squid"
  • Architeuthis stockii

It is probable that not all of these are distinct species. No genetic or physical basis for distinguishing between them has been proposed, as evidenced by the placenames — of location of specimen capture — used to describe several of them. The rarity of observations of specimens and the extreme difficulty of observing them alive, tracking their movements, or studying their mating habits militates against a complete understanding.

In the 1984 FAO Species Catalogue of the Cephalopods of the World, C.F.E. Roper, M.J. Sweeney and C.F. Nauen wrote:

"Many species have been named in the sole genus of the family Architeuthidae, but they are so inadequately described and poorly understood that the systematics of the group is thoroughly confused."

Kir Nazimovich Nesis (1982, 1987) considered that only three species were likely to be valid.

In 1991, Frederick Aldrich of the Memorial University of Newfoundland wrote:

"I reject the concept of 20 separate species, and until that issue is resolved, I choose to place them all in synonymy with Architeuthis dux Steenstrup."

In a letter to Richard Ellis dated June 18, 1996, Martina Roeleveld of the South African Museum wrote:

"So far, I have seen nothing to suggest that there might be more than one species of Architeuthis."

In Cephalopods: A World Guide (2000), Mark Norman writes the following:

"The number of species of giant squid is not known although the general consensus amongst researchers is that there are at least three species, one in the Atlantic Ocean (Architeuthis dux), one in the Southern Ocean (A. sanctipauli) and at least one in the northern Pacific Ocean (A. martensi)."

Timeline

Aristotle, who lived in the fourth century B.C., already described a large squid, which he called teuthus, distinguishing it from the smaller squid, the teuthis. He mentions that "of the calamaries the so-called teuthus is much bigger than the teuthis; for teuthi [plural of teuthus] have been found as much as five ells long.

Pliny the Elder, living in the first century A.D., also described a gigantic squid in his Natural History, with the head "as big as a cask", arms long, and carcass weighing .

Tales of giant squid have been common among mariners since ancient times, and may have led to the Norwegian legend of the kraken, a tentacled sea monster as large as an island capable of engulfing and sinking any ship. Japetus Steenstrup, the describer of Architeuthis, suggested a giant squid was the species described as a sea monk to the Danish king Christian III c.1550. The Lusca of the Caribbean and Scylla in Greek mythology may also derive from giant squid sightings. Eyewitness accounts of other sea monsters like the sea serpent are also thought to be mistaken interpretations of giant squid.

Steenstrup wrote a number of papers on giant squid in the 1850s. He first used the term "Architeuthus" (this was the spelling he chose) in a paper in 1857. A portion of a giant squid was secured by the French gunboat Alecton in 1861 leading to wider recognition of the genus in the scientific community. From 1870 to 1880, many squid were stranded on the shores of Newfoundland. For example, a specimen washed ashore in Thimble Tickle Bay, Newfoundland on November 2, 1878; its mantle was reported to be long, with one tentacle long, and it was estimated as weighing 2.2 tonnes. In 1873, a squid "attacked" a minister and a young boy in a dory in Bell Island, Newfoundland. Many strandings also occurred in New Zealand during the late 19th century.

Although strandings continue to occur sporadically throughout the world, none have been as frequent as those at Newfoundland and New Zealand in the 19th century. It is not known why giant squid become stranded on shore, but it may be because the distribution of deep, cold water where squid live is temporarily altered. Many scientists who have studied squid mass strandings believe that they are cyclical and predictable. The length of time between strandings is not known, but was proposed to be 90 years by Architeuthis specialist Frederick Aldrich. Aldrich used this value to correctly predict a relatively small stranding that occurred between 1964 and 1966.

The search for a live Architeuthis specimen includes attempts to find live young, including larvae. The larvae closely resemble those of Nototodarus and Moroteuthis, but are distinguished by the shape of the mantle attachment to the head, the tentacle suckers, and the beaks.

Twenty-first century

The first footage of live larval giant squid ever captured on film was in 2001. The footage was shown on Chasing Giants: On the Trail of the Giant Squid on the Discovery Channel.

As of 2004, almost 600 giant squid specimens had been reported.

The first photographs of a live giant squid in its natural habitat were taken on September 30, 2004, by Tsunemi Kubodera (National Science Museum of Japan) and Kyoichi Mori (Ogasawara Whale Watching Association). Their teams had worked together for nearly two years to accomplish this. They used a five-ton fishing boat and only two crew members. The images were created on their third trip to a known sperm whale hunting ground south of Tokyo, where they had dropped a line baited with squid and shrimp. The line also held a camera and a flash. After over 20 tries that day, an giant squid attacked the lure and snagged its tentacle. The camera took over 500 photos before the squid managed to break free after four hours. The squid's tentacle remained attached to the lure. Later DNA tests confirmed the animal as a giant squid.

On September 27, 2005, Kubodera and Mori released the photographs to the world. The photo sequence, taken at a depth of off Japan's Ogasawara Islands, shows the squid homing in on the baited line and enveloping it in "a ball of tentacles." The researchers were able to locate the likely general location of giant squid by closely tailing the movements of sperm whales. According to Kubodera, "we knew that they fed on the squid, and we knew when and how deep they dived, so we used them to lead us to the squid." Kubodera and Mori reported their observations in the journal Proceedings of the Royal Society.

Among other things, the observations demonstrate actual hunting behaviors of adult Architeuthis, a subject on which there had been much speculation. The photographs showed an aggressive hunting pattern by the baited squid, leading to it impaling a tentacle on the bait ball's hooks. This may disprove the theory that the giant squid is a drifter which eats whatever floats by, rarely moving so as to conserve energy. It seems that the species has a much more belligerent feeding technique.

In December 2005, the Melbourne Aquarium in Australia paid AUD$100,000 (around £47,000GBP or $90,000US) for the intact body of a giant squid, preserved in a giant block of ice, which had been caught by fishermen off the coast of New Zealand's South Island that year.

In early 2006, another giant squid, later named "Archie", was caught off the coast of the Falkland Islands by a trawler. It was long and was sent to the Natural History Museum in London to be studied and preserved. It was put on display on March 1, 2006 at the Darwin Centre. The find of such a large, complete specimen is very rare, as most specimens are in a poor condition, having washed up dead on beaches or been retrieved from the stomach of dead sperm whales.

Researchers undertook a painstaking process to preserve the body. It was transported to England on ice aboard the trawler; then it was defrosted, which took about four days. The major difficulty was that thawing the thick mantle took much longer than the tentacles. To prevent the tentacles from rotting, scientists covered them in ice packs, and bathed the mantle in water. Then they injected the squid with a formol-saline solution to prevent rotting. The creature is now on show in a long glass tank at the Darwin Centre of the Natural History Museum.

On December 4, 2006, an adult giant squid was finally caught on video by Kubodera near the Ogasawara Islands, south of Tokyo. It was a small female about long and weighing . It was pulled aboard the research vessel but died in the process.

The dead giant squid found on shorelines in the Southern Hemisphere have thought to be linked to possible mercury poisoning, as mercury being a very dense metal will sink in water to the deepest of depths. The food sources of the giant squid could possible contain mercury, leading to bioaccumulation. All research into the matter has ended inconclusively.

Cultural depictions

The elusive nature of the giant squid and its terrifying appearance have firmly established its place in the human imagination. Representations of the giant squid have been known from early legends of the Kraken through books such as Moby-Dick and Twenty Thousand Leagues Under the Sea to modern animated television programs.

In particular, the image of a giant squid locked in battle with a sperm whale is a common one, although the squid is, in fact, the whale's prey and not an equal combatant.

See also

References

External links

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