The deep sea may be the largest ecosystem in the world, but to Dean Grubbs it’s more like exploring deep space.
Scientists know very little about both, said the Florida State University ecologist.
Grubbs’ team is trying to change that, and they’ve made one giant leap for marine biology: They figured out a way to tag deep-sea sharks in their natural habitat — using a submarine.
No longer will researchers have to tag sharks on the surface. The tracking technique will help researchers twofold: They’ll be able to better understand the food chain, and they’ll find out if tagging sharks at the surface actually traumatizes the species, disrupting their behavior.
“It’s one of those bucket list sort of things for a deep sea biologist,” said Grubbs, an elasmobranch ecologist with the Florida State University Coastal Marine Laboratory. Elasmobranchs are sharks, skates and rays.
“All of my work with deep sea animals has been at the surface, bringing them to me rather than me going to them. This was a once in a lifetime chance.”
Grubb’s team from OceanX and the Cape Eleuthera Institute made their mark on scientific history off the coast of the Bahamas on June 29. They tagged a bluntnose sixgill shark, a deep-sea shark that has changed so little over hundreds of millions of years that it is essentially a living fossil.
The team took a research submarine down to a depth of about 1,800 or so feet, then laid in wait on the ocean floor with tuna, hoping that would lure the sharks toward the sub.
Grubbs has tagged close to 20,000 sharks in three decades, but he said this was the first time one had ever been tagged by submarine.
His research started by exploring whether bluntnose sixgills ensnared in commercial fisheries’ nets can survive the stress of getting caught, then getting thrown back. The sharks do survive, his research found, but their normal pattern of going to shallow water at night and diving deeper during the day was disrupted for several days.
That’s where the submarines come in.
If sharks were tagged in their natural habitat instead of enduring the trauma of being reeled onto a boat and tagged, would they still behave erratically? When the team gets the data back in a couple of months, they hope to be able to answer that question.
Grubbs toyed with the idea of tagging via submarine as early as 2009, but funding didn’t materialize until 2018 thanks to OceanX. That is the ocean exploring initiative founded by Ray Dalio, the billionaire who runs the world’s largest hedge fund, Bridgewater Associates.
The team made two dives, first in August and later in February, before the successful deep-sea shark tag in June.
Grubbs worked with OceanX engineers to develop a spear gun that could be mounted and fired from the front of a research submarine. The researchers installed two spear guns and loaded each with satellite tracking tags and a dart to anchor them to the shark’s thick musculature.
Then, researchers dove down to about 1,800 feet with bait strapped to the submarine to lure the sharks into position. But they learned that getting the sharks into the right position isn’t easy.
Eventually, the researchers figured out how to do it: park on the ocean floor with a wall or rock to the left of the submarine, forcing the shark to come from the right, giving them a better chance to safely tag them.
In their last chance to tag the sharks on the June mission, Gavin Naylor, program director of the Florida Program for Shark Research, hit the mark. A roughly 13-foot long male sixgill shark popped up right in position. About 30 seconds later, Naylor successfully tagged it.
“When the target appears in front of the laser, you squeeze the trigger,” Naylor said. “It doesn’t take much skill.”
The shark didn’t react aggressively, Naylor said, and actually appeared curious about the sub. After tagging it, the shark swam away, kicking up a lot of dust.
“It was quite magical. I would have been delighted just to see the different types of plankton,” Naylor said. “To see a … sixgill shark exploring the sub was probably the most exciting thing I’ve ever done in my life.”
Researchers know very little about bluntnose sixgills, Grubbs said. Tooth fossil records for six-gill sharks date back to at least 200 million years ago.
“The first time I caught one it was as if I caught a T-Rex just because they’re so old,” Grubbs said. “In reality, T-Rex wasn’t even on the scene yet when these guys showed up.”
The tagging likely marks the end of Grubbs’ project involving sixgill sharks. Once the temperature, depth, and light level data comes back from the tags, he and his team will likely write a research paper based on the tagging dozens of sharks.
“A lot of people might think we’re meddling (by tagging),” Naylor said. “There should be very little detrimental effect on the shark but there is a huge gain that we get from understanding the life cycles of these animals in deep water.”
Contact Ben Leonard at firstname.lastname@example.org or (727) 893-8421. Follow @Ben___Leonard.