'It Was Like Seeing a T. Rex in the Water': Ancient, Deep-Sea Shark Up to 20 Feet Long Filmed by Florida Scientists

A team of researchers has managed to tag and film an ancient type of deep-sea shark—which can grow up to 20 feet in length and weigh more than a ton—in its native habitat.

The bluntnose sixgill is one of the largest sharks in the world, characterized by six pairs of long gill slits—most sharks have five—a long tail, a rounded snout, big green eyes and comb-like teeth.

They are distributed across tropical and temperate waters around the world usually living at depths of between 650 and 3,300 feet in the so-called "Twilight Zone" of the ocean, although they have been spotted up to 5,000 feet below the surface.

The shark can be traced back 180 million years in the fossil record—before the evolution of many dinosaurs—and in that time it has changed relatively little, retaining several primitive body features.

"It was like seeing a T. rex in the water," Gavin Naylor, one of the scientists from the Florida Program for Shark Research at the Florida Museum of Natural History, said in a statement. "This lineage has been around for 100 times as long as Homo erectus—the ancient ancestor of humans—and these sharks haven't changed that much."

Part of the reason that the team—led by Florida State University ecologist Dean Grubbs—wanted to tag a bluntnose sixgill is that researchers know very little about these sharks.

"[They] have had almost zero attention in terms of research," Grubbs said in the statement. "When I said I wanted to study them, other scientists said there was no way to do so. I took that as a challenge to prove them wrong."

While Grubbs has tagged around 20 individuals since 2005, he had never managed to achieve the feat in the shark's deep-sea home. Tagging them nearer the surface has its drawbacks because it can stress the animals and increase the time it takes them to recover from the ordeal.

In an attempt to address this problem, Grubbs and Naylor—in collaboration with Cape Eleuthera Institute researchers Brendan Talwar and Edd Brooks—worked with ocean exploration initiative OceanX to develop a system that could tag the sharks in the deep-sea.

"So much money has been expended on tagging great whites, and here we have a comparably sized predator, and we know almost nothing about it," Grubbs said. "Are they really rare? The answer may be that not many people are looking for them."

The tags enable scientists to collect data on various factors, including the shark's depth, temperature and the amount of ambient light the animal is exposed to, providing fascinating insights into their behavior.

After three months, the tags remove themselves from the shark and float to the surface in order to beam back the data they have collected to scientists via a satellite link.

To tag a sixgill in the deep-sea for the first time, the researchers used a submersible known as Nadir provided by OceanX. However, the process was not easy. It required three expeditions, more than 2,000 pounds of bait and over 12 attempts before the successful shot with the spear gun was made on June 29 at a depth of around 1,600 feet below sea level during the crew's very last dive.

"Any mission conducted 1,600 feet under the surface is challenging," Naylor told Newsweek. "Most of the challenges are infrastructural: having a submarine, an appropriately fitted research vessel and expertise on hand to solve all of the unexpected contingencies takes a lot of resources, careful planning and organization."

"Modifying the submarine to carry a pair of solenoid-triggered spear guns that operate effectively at depth is another challenge—one that had never been tried before and was carried out by our sub-pilot Lee Frey," he said. "Finding a sixgill shark at depth turned out to be much less of a challenge than many had imagined. They seem reasonably common."

To confirm that the shot had hit its intended target, the scientists then captured video footage of the shark, which showed that the tag was sticking out of its side.

"Approximately half of all living species of sharks on the planet live their entire lives in the deep-sea," Grubbs told Newsweek. "Yet we know virtually nothing about their biology and ecology. Contrast this with the volumes of scientific information on species like white sharks and tiger sharks. Yet as commercial fisheries globally move deeper, deep sea sharks are being increasingly caught, particularly as bycatch."

"It is often assumed that these deep-sea sharks would die if released and so in some cases the sharks or their livers are retained," he said. "We began this project in 2005 to begin investigating whether deep-sea sharks caught and brought to the surface survive if released. We began this work with the bluntnose sixgill sharks because they are a large species that occurs many places around the world and it is the largest predatory shark in the habitats where it occurs."

Currently, the worldwide population of bluntnose sixgills is unknown but they are listed as "Near Threatened" on the International Union for Conservation of Nature's Red List.

The shark is thought to be primarily a carrion feeder but it is also an effective predator which feeds on a wide variety of fish—including rays and other sharks—and invertebrates such as squid, crab, sea cucumbers and shrimp, when the opportunity arises, according to the IUCN.

This article was updated to include additional comments from Gavin Naylor and Dean Grubbs.

Bluntnose sixgill
On the last dive of the expedition, the team inside OceanX’s submersible Nadir encountered several bluntnose sixgill sharks, including this large female that paused to look through the glass at the researchers. Gavin Naylor/Florida Museum