Deep-water sightings of rare giant-finned squid reveal a strange bizarre

An extensive study of the deep waters off the coast of Australia resulted in a mine of bigfin squid sightings. And by treasure we mean the detection of five individuals – these deep-sea creatures are exceptionally rare, so any new sightings are of great value to scientists.

“Deep sea cephalopods are very diverse and widespread but often shrouded in mystery”, opens a new study published today in PLOS ONE.

The deepwater cephalopod in this case is a strange and poorly understood marine animal known as the bigfin squid. The new article, co-authored by marine biologist Deborah Osterhage of CSIRO Oceans and Atmosphere in Tasmania, Australia, describes a recent deep-water study in which five of these animals were captured on camera. The resulting data fills some important gaps in bigfin squid, such as their distribution, physical characteristics and behavior.

Sightings of this strange squid, a member of the Magnapinnidae family, are rare and little is known about them. To date, there have only been three confirmed sightings in the southern hemisphere, all in the eastern Pacific. Dead specimens, mostly juveniles, sometimes appear, but they are often severely damaged by trawling. What we do know, however, is that these squids have large fins and extraordinarily long “worm-like” arms and tentacle filaments that hang down behind them like impossibly long spaghettini strands.

Osterhage and his colleagues recorded bigfin squid on Great Australian Bight Deepwater Marine program expeditions. From 2015 to 2017, the team traveled this region to learn about the geology and ecology of the Great Australian Bight (GAB), a large open bay off the continent’s southern coast. They did it with a remotely operated vehicle (ROV) called Investigator, which was equipped with a high-definition video camera, twin lights and lasers. A camera towed behind the boat was taking pictures every five seconds.

The researchers managed to cover 281 square kilometers during the investigation, collecting 75 hours of video and more than 10,000 still images. The towed camera scanned depths between 3,104 and 10,689 feet (946 to 3,258 meters). All of this resulted in five bigfin squid sightings, more than doubling the number of sightings in the southern hemisphere. Additionally, this is the first time that big-finned squids have been seen in Australian waters.

Interestingly, these animals have been observed close together. In one case, two squids were seen within 12 hours of each other, and in another only 6 km from each other. In all, the Big Five were only seen in two areas, two in one and three in the other. The clustering of these individuals is likely due to “specific environmental needs” and / or “increased breeding opportunities,” according to the document.

As for their preferred habitat, the squid seemed to like areas with soft sediment, lower slopes of erosion channels, and upper sections of submarine canyons. The animals have been spotted at depths between 6,562 and 9,834 feet (2,000 to 3,000 meters). Whether the relatively high number of individuals seen in this part of the GAB amounts to a bigfin squid hotspot “remains to be seen,” the authors write.

The authors ruled out the possibility that some observations were from the same individual, noting physical differences between the specimens. Because squids were often filmed or photographed without a frame of reference, researchers turned to a technique in which paired lasers were pointed at their bodies, giving an impression of scale. They were able to measure, for example, the length of their single filaments, the longest of which was 183 cm (72 inches).

The researchers also got a feel for their behavior. During one of the sightings, a squid swam away from the camera and settled in an upright position just slightly above the seabed. Three of its filaments then coiled, in what is hitherto unknown behavior in squid, say the authors. The squid moved its body in the water by flapping its fins and performing oscillating back and forth movements (ie, sine waves).

Another behavior reported by researchers is known as “elbow pose”. Here, the squids assume an upright posture, with their appendages spread outward while the ends of the filaments hang downward at an acute angle, in some cases close to 90 degrees, toward the seabed. A previously unknown variation of this pose, in which the squid’s body is horizontal to the seabed, was documented during the expedition. The authors aren’t quite sure what this is all about, but they think it could be a fishing posture used to catch prey.

The squids were generally pale, with tints of pink, orange, and dark reddish brown. In some cases, the mantle (the main part of the squid’s body) and fins appeared slightly translucent. And in fact, the orange color may actually correspond to an internal organ (possibly a digestive gland), say the authors.

“These observations add to our knowledge of this elusive and intriguing genre, and reinforce the value of imagery as a tool in deep-sea squid research,” the scientists conclude.

Australian wildlife continues to surprise. At the end of last month, for example, researchers described the discovery of an exceptionally high coral reef measuring 500 meters high sheltering a unique ecosystem. Stranger creatures will surely be discovered and described in the months and years to come, so stay tuned for more exciting discoveries from this part of the world.