Science Spin July 2008

The colossal squid: An elusive, reclusive giant

It sounds like something from a science-fiction movie but on April 30th this year the thawing out and public autopsy took place of the world's largest knowninvertebrate, a 495kg colossal squid (who remains as yet unnamed).

The colossal squid is a bit of a recluse usually found in the icy, black waters of the Antarctic about 1km from the surface. The squid is mysterious and elusive. Thefirst colossal squid was discovered in 1925 in the stomach of a sperm whale after he had been guzzled for dinner. The sperm whale is a predator of the colossal squid and most sperm whales bear scars on their backs believed to have been inflicted by the hooks of the colossal squid.

Approximately, eight colossal squid carcasses have been discovered since then most of them semi-digested inside sperm whales. Little is known about the colossal squid to date because of it's habitat.

The colossal squid is a type of mollusc called a cephalopod as are it's similar relations the giant squid and the octopus. The colossal squid is believed to be thelargest of the squid species. It is the only know member of the genus Mesonychoteuthis, from Greek Meso (middle), onychos (claw) and teutis (squid).

Caught

This colossal squid was caught accidentally by the crew of a New Zealand fishing boat the "San Aspiring" near Antarctica in 2007. It was only just alive and the crew thought that it would die if they released it. The squid was frozen by the fishing crew and stored in a massive freezer below decks. It was transferred to New Zealandfor thawing and further scientific evaluation in Te Papa Tongarewa museum in Wellington.

The scientists in Te Papa were then posed with a bit of a problem -- how to thaw a 495kg frozen squid? If they thawed it out naturally, there was every chance tha the outer layers of tissue would commence decomposition before inner core was defrosted.

They then considered building the world's largest microwave in order to thaw it out but as the skin of the colossal squid is very soft, it was considered too risky. After sifting 462 suggestions from the public, they came to a decision to thaw it out in a bath full of saline and ice in order to control the rate of thawing using saline toprevent decay of tissue.

Thawing

The thawing began on the 29th April and lasted for three days. Once thawed the scientists had just four hours to record all the anatomical information andmeasurements necessary before the squid would need to be fixed in formaldehyde to prevent decomposition.

On defrosting, the scientists went about the painstaking process of measuring and cataloguing the details of the colossal squid. It was necessary for them to be verycareful as the tissue was very friable. It required six people to turn the squid over. The scientists clambered around in the icy tank in order to gently tease the squidinto its correct shape and unfurl carefully its tentacles. This process was filmed and was broadcast on the web worldwide. The Te Papa website had over 100,000 hits a day from over 180 different countries.

The plan is that the colossal squid will be displayed in Te Papa Tongarewa museum suspended in formaldehyde when the scientists are finished studying it.

Features

The colossal squid has been recorded to have sharp beaks made form a material similar to human fingernails. They also have long tentacles. The tentacles were measured at 4.2m in length in Te Pap's specimen.

The colossal squids tentacles possess two rows of sharp, swivelling hooks and two rows of tiny suckers. The beak and hooks are lethal weapons for catching and holding large fish like the Patagonian tooth fish (thought to be the preferred diet of the colossal squid).

Many squid are cannibalistic so the giant squid may actually eat each other if necessary. The scientists also used an endoscope to see what the squid ate for itslast meal but details of stomach content have not been released yet.

The eyes were measured at greater than 11 inches in diameter, larger than a dinner plate each. The tentacles were measured at 4.2m in length. On close examination, it was discovered that the eyes had two rows of bioluminescent (light-emitting) organs. The small light emitting organs are all that the colossal squid'sprey would be able to see of the large animal.

Colossal squid hunt in total darkness at depth."The prey might well look at [the squid] and think, Well, I can't be bothered with those two tiny little specks of light. And all of a sudden this great big thing lunges in and latches on to it with vicious hooks," said Dr Steve O'Shea, a squid expert from New Zealand.

The light from the glowing organs also help conceal squid as they venture closer to the surface. "The body of the animal is translucent, [but] these very large eyes are anything but translucent.

"If you are a predator approaching from below, you've got two silhouettes of the eyes. So those rows of photophores then beam down light of an equivalent intensity to that from above, so the eyes are rendered invisible," Dr O'Shea said. "It's a very successful cloaking device."

The colossal squid is thought to eat prey that glow also which you would think would perhaps give it's position away, a glowing stomach in a transparent animal butevolution may have solved this problem. The squids mantle, a covering layer just beneath the head is lined with a dense, dark red pigment that would block any light from within.

Despite the advances made in the last couple of weeks that have provided scientists with a new wealth of information on the colossal squid there exists still manyquestions that need to be answered.

Another interesting piece of information that been ascertained is that the beak of this colossal squid was measured at 42.5mm which is smaller than some of thbeaks recovered previously from the innards of sperm whales (up to 49mm) so it is possible that even larger specimens remain lurking in the deep.