What the analysis of the largest squid ever captured has revealed so far

May 5, 2008 18:06 GMT  ·  By

The analysis of the largest colossal squid ever caught (and largest invertebrate ever captured) has provided some first spectacular results - this is also the largest invertebrate species known to have ever existed. In February 2007, a New Zealand fishing crew off the coast of Antarctica (in the northern Ross Sea), that was out fishing Patagonian toothfish (Chilean sea bass), accidentally caught the 1,089-pound (490 kg), 26-ft (8.6 m) long colossal squid, which is also the sixth ever captured.

The colossal squid, Mesonychoteuthis hamiltoni, usually roams to depths of 6,500 ft (2,160 m) in the ocean and is believed to be an aggressive predator. Because of its habitat, it is the most mysterious of the huge squids. The species was first detected in 1925, in the form of two tentacles spat out by a sperm whale. Colossal squid could grow bigger, to up to 46 ft (15.3 m) long, as this specimen has confirmed thus far.

The squid has been preserved in ice so, since thawing it in a giant microwave oven would have damaged its tissues, the the animal was left to defrost in a salty bath. Tissue samples have been collected for DNA analysis, while an endoscope will analyze the animal's inner anatomy with minimum damage to the organs.

A female juvenile

The animal captured and now analyzed seems to be a female, as it lacks hectocotylus, the copulating organ specific for cephalopods (squids, cuttlefish and octopuses), which can be at least of 6.5 ft (2 m) in colossal squids.

"From its size and from its color, I would presume that it's generally [found] at about 3,200 feet [1,000 meters]. When it's alive, it's a deep pink color, and the red-light wavelength is the first to disappear at that depth, so the predator would be essentially invisible in its natural environment," said Carol Diebel, natural environment director of the New Zealand's Te Papa Museum, where the animal is being kept.

"The new specimen is probably not fully grown, meaning that even bigger colossal squid may be lurking in the deep. When we first examined colossal squid specimens, we predicted that they might grow to 1,100 pounds (500 kilograms). This specimen shows that they can grow larger still, to maybe 1,600 pounds (750 kilograms)," said Te Papa projects manager Chris Paulin.

"The size of the squid's beak estimated at between 1.6 and 1.7 in (4.3 and 4.5 cm)-suggests the giant was not fully grown. We know from beaks recovered from the stomachs of sperm whales that squid grow considerably larger. So although [the new specimen is] very large, it's certainly not the maximum size," said biologist Steve O'Shea of the Auckland University of Technology in New Zealand.

Largest eye and cloaking device

Another hit that might confirm the above mentioned theory is that the animal has the world's biggest eyes (10.6-in (27-cm) in diameter) and light-emitting organs functioning like cloaking devices. "They are clearly the largest eyes ever recorded from any animal. About the size of a soccer ball," said biologist Dan-Eric Nilsson, of the University of Lund in Sweden.

Blue whales, the largest living animals (up to 33 m (110 ft) long and 180 tonnes heavy), have eyes the size of those of a cow. The eye lens of the colossal squid is as big as an orange and it was found intact in one of the eyes. "This is the largest eye ever recorded in history and studied. It has a huge lens the size of an orange and captures an awful lot of light in the dark depths in which it hunts." said Eric Warrant of Sweden's University of Lund, who specializes in vision in invertebrates.

"The squid's pupils would reveal more about the sensitivity of squid eyes. That will tell us everything we need to know about how much light they can actually pick up down there. But the massive size indicates the animal is very visual," said Nilsson. "And underneath those eyes? around the outside, are two rows of beautiful bioluminescent [light emitting] organs. The small dots of light generated by these organs are all the squid's prey would be able to see of the giant", O'Shea added

Colossal squid seem to hunt in total darkness at 3,300 ft (1,000 m) depths. The bioluminiscent organs may thus be used to attract prey.

"(But) the light from the glowing organs (photophores) might also help conceal squid as they venture near 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. It's a very successful cloaking device," explained O'Shea.

The squid's prey can also be bioluminiscent, an issue for a semi-transparent animal. "You don't want to fill your stomach up with things that are glowing, because you're sending out a bright signal to all your predators. The inner lining of the squid's mantle-the large covering just above the head is filled with dense, dark red pigment, which would block any light from within," added O'Shea.

The colossal squid also has sharp swiveling hooks at the tips of its tentacles.

Colossal squid is unrelated to the giant squid (Architeuthis dux), which has suckers lined with small teeth. Colossal squid is found in Antarctic waters. Still, the best known of the huge squids is the giant squid, which is much less massive and a little shorter. The giant squid is the common species observed to battle with sperm whales, as it inhabits temperate waters around the world.

Colossal squid are "active predators of fish. But at this size, they eat pretty much whatever they like," Paulin added.

Human impact

This squid is not a "perfect" specimen, as its body still has scars from the fishing net in which it got entangled. Researchers even tasted the meat of a colossal squid from a smaller individual.

"It's edible, but the texture and smell? [the flesh] contains ammonia (resembling urine), so it's nearly the same taste as giant squid, but it's much more muscular - tougher. It tastes very bitter. Not so good for humans, but sperm whales like the taste very much." said squid specialist Tsunemi Kubodera of Japan's National Museum of Nature and Science.

"We are now fishing waters that we never used to fish, at depths that we didn't used to reach. So we are now competing with the squid for its food," said Diebel.

"As the fishing continues to increase around Antarctica, it is possible more colossal squid will be caught unintentionally. It's too early to say whether fishing techniques? are going to impact on the populations of these squid. But if it turns out that we get more and more of these squid being caught, I think that would be the time to make a [conservation] policy about them," said Warrant.