What do giant squid look at with their basketball-sized eyes?

By Seriously Science | February 10, 2014 7:00 am
Photo: flickr/LuzKreativa

Photo: flickr/LuzKreativa

Giant squid have truly giant eyes, in fact they have the largest eyes of any animal. Whether or not their eyes are larger than you might expect for their size is still debated, but nonetheless, they are truly enormous; according to this paper they are three times the size of any other known animal: “In a search for more reliable data on the eye size of the largest deep-sea squid, we were fortunate to obtain a photograph of a freshly caught giant squid (Architeuthis sp.), where the pupil diameter could be reliably determined to be 90 mm [3.5 inches], with the entire eyeball being at least 270 mm [10 inches]. We also had access to an adult colossal squid (Mesonychoteuthis hamiltoni) from New Zealand and determined its eye diameter to be between 270 and 280 mm.” So, why do these deep-sea squid have such giant eyes? Well, if you have read Moby Dick, you might remember that sperm whales feed on giant squid. These researchers propose that the giant squid use their giant eyes to spot sperm whales deep in the sea, where light is a very limited resource, and seeing anything, even a very large whale, is no easy feat.

A unique advantage for giant eyes in giant squid.

“Giant and colossal deep-sea squid (Architeuthis and Mesonychoteuthis) have the largest eyes in the animal kingdom, but there is no explanation for why they would need eyes that are nearly three times the diameter of those of any other extant animal. Here we develop a theory for visual detection in pelagic habitats, which predicts that such giant eyes are unlikely to evolve for detecting mates or prey at long distance but are instead uniquely suited for detecting very large predators, such as sperm whales. We also provide photographic documentation of an eyeball of about 27 cm with a 9 cm pupil in a giant squid, and we predict that, below 600 m depth, it would allow detection of sperm whales at distances exceeding 120 m. With this long range of vision, giant squid get an early warning of approaching sperm whales. Because the sonar range of sperm whales exceeds 120 m, we hypothesize that a well-prepared and powerful evasive response to hunting sperm whales may have driven the evolution of huge dimensions in both eyes and bodies of giant and colossal squid. Our theory also provides insights into the vision of Mesozoic ichthyosaurs with unusually large eyes.”

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CATEGORIZED UNDER: fun with animals, Uncategorized
  • Zirkman

    Hmm, then why do sperm whales have such small eyes in comparison?
    Oh, I should revisit the detecting mates theory. Well, science is about trying .. and publications, right?

    • Robert Johns

      Sperm Whales detect prey using sonar, so their eyes are of limited use in detecting squid. The article even tells you “Because the sonar range of sperm whales exceeds 120 m”.

      • Matthew Slyfield

        Also, look at the eye placement relative to the bulk of their head. Sperm whales are one of only a few vertebrate predators to not have binocular vision. It’s unlikely that vision plays a major role in any aspect of a sperm whales life.

        • WRSI

          Also, sperm whales have been found who lived and thrived over some time despite injured or malformed mandibles. They’re down there hunting in the darkness, possibly both finding their prey and incapacitating it using their enormous noses to amplify sound. Damage to their jaws seems noncritical to them.

          This is the largest known toothed predator, I believe, ever? And it doesn’t seem to particularly use its teeth. Its nose, on the other hand, is absolutely critical, and takes up a third of its body! What a most amazing animal.

          • Matthew Slyfield

            I believe from what I have read, that the bulk of the sperm whales head is actually a resonating chamber for it’s sonar, not it’s nose. It’s possible that they can produce a sonar pulse intense enough to stun their prey.


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