'Monster' Shark Bigger Than a Submarine Filmed by Scientists As It Tries to Eat Their Gun
A team of researchers has captured incredible footage of a close encounter with an ancient species of shark known as the bluntnose sixgill.
The team, led by Dean Grubbs, from Florida State University, were conducting dives in a submersible called "Nadir" as part of an expedition organized by OceanX to tag one of the sharks in their deep-sea environment.
During one of the dives, the team were fortunate to come up close and personal with a huge female bluntnose—=one of the largest sharks in the world—which one of the researchers in the video can be heard describing as "definitely bigger than the sub is long."
The sub crew were left in a state of awe by the encounter: "My goodness that is amazing," one of the team comments, while another can be heard saying, "This is a monster. She is huge." At one point the shark even tries to nibble on the spear gun attached to Nadir.
The bluntnose (Hexanchus griseus) is part of an old lineage of sharks that can be traced back 180 million years in the fossil record. In fact, it represents perhaps the oldest living lineage of sharks in the world, the researchers say. They are highly distinctive due to the fact that they have six large conspicuous gill slits, hence the name. Most sharks only have five.
"They have a single dorsal fin that is placed far back on the midline near the tail," Gavin Naylor, one of the scientists on the expedition from the Florida Program for Shark Research at the Florida Museum of Natural History, told Newsweek. "They are reported to grow to over 5 meters [16 feet] long and weigh more than a ton. They are live bearing. Females can have over 80 pups in a litter. They are likely primarily carrion feeders, but may also take live prey when the opportunity arises. Females are larger than males."
Bluntnose sixgills are distributed across tropical and temperate waters around the world usually living at depths of between 650 and 3,300 feet, although they have been spotted up to 5,000 feet below the surface. However, researchers know very little about this mysterious species. Tagging them could enable scientists to learn more about their biology and behavior, and protect them from threats.
"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," he said. "We began this project in 2005 to begin investigating whether deep sea sharks caught and brought to the surface survive if released. Since this time we have tagged more than 20 bluntnose sixgill sharks with archiving satellite tags and another 50 with simple identification tags. But all of these were tagged by bringing the sharks to the surface and tagging them alongside the boat or even bringing them onto the deck of ship."
This tagging revealed to the researchers that nearly all bluntnose six gills survive being caught and brought to the surface. Furthermore, the data showed, intriguingly, that these sharks vertically migrate every day and night.
"At dusk they come up the slope sometimes in the water column to shallower depths where water temperature are about 62 degrees Fahrenheit, remaining there overnight, and then at dawn they return to deeper depths where temperatures are 41 degrees Fahrenheit," Grubbs said. "In Exuma Sound [the Bahamas,] this corresponds to coming up to 400-500 meters [1,312-1,640 feet] deep at night and remaining at 900-1200 meters [2,952-3,937 feet] during the day. This is a beautifully consistent vertical pattern the sharks undergo every day."
"However, one of the things we noticed is that across all of these sharks there was an initial period of about two days after tagging where the sharks did not show this pattern and seemed to behave a bit more erratically, and then they settled into that distinct vertical migration every day after that," he said. "We interpreted that erratic phase as a possible recovery period due to short term physiological stress associated with being captured and brought to the surface."
This stress could be enough to temporarily alter this behavior, even though the sharks seemed to tolerate being brought to the surface. This finding is what led to team to try and tag a bluntnose in the deep-sea instead.
"So how do we test the theory that this initial difference in behavior represents recovery from capture?" Grubbs said. "We go directly to the sharks in their natural habitat and tag them at depth. This drove our efforts to attempt to tag these sharks at depth. We made three expeditions and many dives spending many hours sitting on the bottom trying to get the sharks to come in and then trying to tag them. We came very close numerous times but never quite had the right shot, or in one case, the shark knocked the spear off the gun and dislodged the tag! But finally on the last dive on this last expedition [in Exuma Sound,] my colleague Gavin Naylor successfully tagged a sixgill from the sub!"
This tag will remain on the shark for 3 months, before detaching, floating to the surface and uploading the data it has collected via satellite link to a processing center where it can be analyzed.
"If our theory is correct, we expect to see the same vertical migration behavior as the other sharks demonstrated but without the initial two days of erratic behavior," Grubbs said. "Unfortunately, we have to wait impatiently to hear from that tag!"
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. Nevertheless, the researchers suggest that they are perhaps more common than previously appreciated.
"Finding a six-gill shark at depth turned out to be much less of a challenge than many had imagined," Gaylor said. "They seem reasonably common. Finding a marine biologist willing to go down in a submarine to try to tag a six-gill at depth was the easiest part!"