Lurking in the darkness with large green eyes, sixgill sharks kept their genetic secrets hidden amid the ocean depths since before the age of the dinosaurs.
Toby Daly-Engel, a shark biologist at the Florida Institute of Technology, has helped solve a taxonomic puzzle and spearhead the discovery of a new deepwater species: the Atlantic sixgill shark.
How so? Daly-Engel and a team of researchers determined that bigeye sixgill sharks in the Atlantic Ocean — specifically Belize, the northern Gulf of Mexico and the Bahamas — differ genetically from their counterparts in the Pacific and Indian oceans.
“This is like discovering a brand new living fossil,” Daly-Engel said during an interview in her office at Florida Tech’s Shark Conservation Laboratory.
“What’s exciting about this is that we’re still discovering cryptic species of shark. And not just little sharks. And there are lots of little sharks out there. But big sharks — sharks that are 5-, 6- even 7-feet long — that have been around for hundreds of millions of years, since before the dinosaurs, and yet have not been identified by science,” she said.
Daly-Engel headed a group of shark scientists from the Florida State University Coastal and Marine Laboratory, NOAA’s Southeast Fisheries Science Center in Panama City, and MarAlliance in Belize. Their findings were published Feb. 13 in the online edition of Marine Biodiversity, a peer-reviewed international journal.
Using longlines baited with tuna heads up to 8677 feet deep, the researchers caught sixgill sharks, then collected tissue samples and satellite-tagged the elusive apex predators.
“They look exactly like the other sixgill sharks except on the genetic level, where they look very, very different. And we were incredibly surprised, because we weren’t expecting this result,” Daly-Engel said.
The Atlantic sixgill (Hexanchus vitulus) is a newly discovered variety of the bigeye sixgill (Hexanchus nakamurai).
The bigeye sixgill shark evaded discovery until 1962 near Taiwan. In the Atlantic, the species was first recorded in 1969 in the Bahamas, Daly-Engel said.
Bigeye sixgill sharks can reach about 6 feet in length and have narrow, pointed heads, according to the Florida Museum of Natural History in Gainesville.
“They have these huge green eyes, like a cat eye — but much, much bigger. They’re so well adapted to the dark, deep ocean,” Daly-Engel said.
Modern sharks have five gill slits, while the last remaining primitive sharks have six and seven gill slits.
“They are basically living fossils. There used to be a lot more sixgill and sevengill sharks out there, but they’re all extinct because they’ve been around for so long. And they’re just dinosaurs, compared with the newer version,” Daly-Engel said.
“You know, it’s like the Model T versus the Corvette,” she said.
Florida anglers are prohibited from harvesting bigeye sixgill sharks in state waters.
Daly-Engel has studied sixgill sharks since 2005, and she joined the Florida Tech faculty last fall as an assistant professor of biological sciences.
“I think it’s really exciting that we are still finding out new things about animals that have been around since before the dinosaurs. Sharks are popular. They’re in the media. They’re exciting to people. And yet, we know very, very little about them as scientists,” she said.