Lurking in the murky gloom of the twilight zone some 200 to 1000 metres below the ocean’s surface, is a blue-blooded, triple-hearted, donut-brained enigma of a predator. The inspiration behind countless sea monster tales, the giant squid has long been a glorious mystery for scientists and armchair marine biologists. The sizeable cephalopods owe much of that mystery to their deep-sea lifestyles, which makes it very difficult to study them in their natural habitat.

Enter technology. In a new study, researchers outline how they were able to use an innovative platform equipped with a camera to capture unique footage of squid on the hunt, revealing for the first time how the creatures stalk and seize their prey.

A giant squid attacking a lure attached to a submerged platform in the Gulf of Mexico.

Studying animals that dwell in deep pelagic ecosystems usually involves the crude use of nets which are only effective for “the slow, the stupid, the greedy and the indestructible,” the authors of the paper point out, quoting Peter Herring’s book The Biology of the Deep Ocean. Giant squid are none of those things. So unsurprisingly, it’s not a tactic that turns up too many krakens.

Remotely operated underwater vehicles are also not particularly effective at recording the legendary behemoths, possibly because they require “some form of propulsion that creates a mix of sound and vibrations,” the authors explain in the study. This – combined with bight lights required for navigation that may be a bit harsh for the dinner-plate-sized eyes of the giant squid – is likely enough to send the creatures scooting away before the ROV can film them.

To overcome these challenges, a team of scientists led by Nathan Robinson of the Oceanographic Foundation in Spain experimented with a different approach: a camera mounted on a stationary or passively drifting deep-sea platform. “Without the need for active propulsion, these devices do not require moving parts and can thus create minimal noise,” wrote the researchers. “Also lacking the need to navigate, these devices can use lighting at a lower intensity.” To further minimise the impact of the device, the team used red light, which has a wavelength that is believed to be less obtrusive to deep-sea animals that have monochromatic visual systems adapted to blue light.

Researchers experimenting with the use of a submerged, deep-sea platform recorded their first large squid back in 2004.

And now the clincher: a fake jellyfish mounted to the platform. Dubbed E-jelly and equipped with blue flashing lights designed to mimic the pin-wheel bioluminescence of Atolla jellyfish, the pseudo cnidarian proved an effective lure for ocean giants. The E-jelly itself was unlikely to be the main attraction for giant squid that are not known to dine on jellies, but rather the flashing lights were meant to signal a jelly in distress – possibly because it’s being preyed on by something that a squid will fancy for dinner.

In 2004, just 86 seconds after firing up the E-jelly in the Gulf of Mexico, a squid was recorded “rapidly approaching” the platform. Tentatively, though not conclusively, identified as Promachoteuthis sloani, the squid was spotted in a brine pool at a depth of 647 metres. A year later, a second possible Promachoteuthis sloani had a go at the E-jelly (also a short while after the device was activated).

After some updates to the system, another large squid was recorded in the Bahamas in 2013. This time the squid was filmed approaching a group of giant isopods converged on a bait cage:

But the real “Holy Grail” of squidness came in 2019 while the platform was tethered to a buoy and passively floating some 750 metres below the surface of the Gulf of Mexico. A giant squid (Architeuthis dux) with a mantle length of about 1.7 metres (excluding tentacles), was filmed stalking and striking at the E-jelly.

Sequential video stills of the giant squid approaching and attacking the E-Jelly. Image: Robinson, et al.

Perhaps the most interesting takeaway from the study is the evidence that giant squid are visual hunters that track their prey by movement rather than smell. The hefty cephalopod was recorded cautiously contemplating its attack on the E-jelly while ignoring some nearby bait. The new footage also shows that these ocean giants are active hunters. Previously thought to be ambush predators that lie and wait for any potential meals to stray within striking distance, we now know that giant squid use visual cues to actively stalk their prey.

The researchers recommend that more studies be carried out using low-light, unobtrusive systems with optical lures to learn more about these fascinating deep-sea cephalopods. Who knows what we’ll see next ...