Tuesday, 26 October 2010

Colossal Squid: World's Largest Squid

Image of the largest colossal squid ever caught
The Colossal squid caught in 2007
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Teuthida
Family: Cranchiidae
Genus: Mesonychoteuthis
Species: Mesonychoteuthis hamiltoni
Conservation Status: Not assessed
Common Name(s): Colossal Squid, Antarctic Squid, Giant cranch squid

The Colossal squid is the largest known extant squid and the sole member of the genus Mesonychoteuthis.

Surely, it's one the most frightening predators found in the deep sea. Very little is known about the species, since only a handful of specimens have ever been captured, analyzed and studied.

In February 22 2007, a New Zealand fishing boat captured the largest ever recorded specimen, somewhere in Antarctica. It had an approximate length of 10 meters and weighted 495 kg!

Where do they live?
The species' habitat is believed to range among thousands of kilometres northward from Antarctica to southern South America, southern South Africa, and the southern tip of New Zealand. Thus we can say it inhabits the entire circumantarctic Southern Ocean.

Based on the capture depths of a few specimens, as well as beaks recovered from sperm whale stomachs,  it is assumed that adults inhabit depths of up to 2200 meters (7217 ft) deep, whereas juveniles inhabit depths of at least 1000 meters (3280 ft).

Current data indicate that the Colossal Squid can reach a maximum length of 12 to 14 meters (39–46 feet). The tentacles are equipped with suckers (lined with small teeth) and have sharp hooks. Some of these hooks are swiveling while others are three-pointed. It has the largest beak among all squid species, exceeding even the one the giant squid has (Architeuthis sp.), both in size and robustness.

Image of the Colossal Squid's Beak
Colossal Squid Beak

The Colossal Squid also holds the Guinness world record for having the biggest eyes among animals, terrestrial and marine alike.

It is assumed that the species is sexually dimorphic, with females being larger than males, something very common among invertebrates.

The squid’s massive size is attributed to a phenomenon known as abyssal gigantism or deep-sea gigantism.

In general, gigantism is the tendency for certain species to display an abnormally larger size than their close relatives. Some notable examples that the Strange Animals blog has covered, include the giant isopod and the Japanese spider crab.

Graphic comparison between colossal squid and a human diver
A graphic comparison between a diver and an adult colossal squid

What do they eat?
Most scientists agree that the colossal squid primarily feeds on:
  • Chaetognatha (also known as arrow worms, a phylum of small predatory marine animals)
  • Various large fish like the Patagonian tooth fish (Dissostichus eleginoides)
  • Other smaller squids
It is believed that the colossal squid has a low metabolic rate allowing it (despite its large size) to consume only about 30 g of prey on a daily basis in order to survive.

It is assumed that the main predator and antagonist is the sperm whale (Physeter macrocephalus). This is due to the many sightings of sperm whales with scars made from colossal squids. Moreover, approximately 14 % of the beaks found in the stomachs of sperm whales belong to Colossal Squids, meaning that about 75 % of the total biomass they consume is from eating colossal squids!

Other common colossal squid predators include:
  • Beaked whales such as bottlenose whales
  • Patagonian tooth fish
  • Pilot whales
  • Sleeper sharks
  • Southern elephant seals
  • Albatrosses (like the Wandering and Sooty albatrosses)
    It should be noted though, that the majority of the aforementioned predators only hunt and kill small, juvenile and immature individuals. Beaks from adults have only been found inside large aquatic animals like the sperm whale and the sleeper shark.

    Image of a captured Colossal squid in New Zealand
    Image of the specimen caught in 2007
    ( on display in Te Papa Museum Wellington New Zealand)

    How do they reproduce?
    No one has ever observed how the species reproduces, however we can assume a few things from its anatomy. The fact that males don't have a hectocotylus (an organ that other male cephalopods utilize for transferring their spermatophore to the female) indicates that males use a penis for introducing the sperm directly into females.

    Largest colossal squid ever caught
    In February 22, 2007 the New Zealand authorities announced that the largest ever known Colossal Squid had been captured. It had a weight of 495 kilos (1.091 pounds) and a length of 10 meters (33 feet). Initially, it was thought to be male, however it was later revealed to be a female. The squid was caught by the fishermen of the San Aspiring boat, belonging to the Sanford seafood company.

    The capture was made in the Antarctic waters of the Ross Sea. The ship's crew froze the squid in a cubic meter of water and transferred it to New Zealand's national museum (Te Papa Tongarewa). The largest ever Colossal Squid specimen caught before has a weight of only 195 kilos (~ 450 pounds).

    Quick Interesting Facts
    - The species holds the Guinness world record for biggest eyes among all animals. The 2007 specimen eyes were 27 cm (11 in) wide, with a lens 12 cm (4.7 in) across. This is the largest eye ever recorded on any known animal. These measurements were taken from the partly collapsed specimen. When alive, the eyes were probably 30 to 40 cm (12 to 16 in) wide!
    - The beak found in the 2007 specimen was considerably smaller than some recovered by the stomachs of sperm whales, suggesting that colossal squids may reach much larger sizes.
    - The Colossal Squid was first identified in 1925, using the remains found in the stomach of a dead sperm whale. It took many decades until 1981, for one to be captured alive in a net.

    References & Further Reading
    - Rui Rosaa, Brad A. Seibela (2010). Slow pace of life of the Antarctic colossal squid Journal of the Marine Biological Association of the United Kingdom DOI: 10.1017/S0025315409991494
    - Nilsson DE, Warrant EJ, Johnsen S, Hanlon RT, & Shashar N (2013). The giant eyes of giant squid are indeed unexpectedly large, but not if used for spotting sperm whales. BMC evolutionary biology, 13 PMID: 24010674
    - Anderton, H.J. 2007. Amazing specimen of world's largest squid in NZ. New Zealand Government website.
    - Cherel Y, & Hobson KA (2005). Stable isotopes, beaks and predators: a new tool to study the trophic ecology of cephalopods, including giant and colossal squids. Proceedings. Biological sciences / The Royal Society, 272 (1572), 1601-7 PMID: 16048776
    - "New giant squid predator found". BBC News. January 8, 2004. Retrieved 14 February 2007.

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