Dive deep deep down into the ocean, long past the point where the sun’s rays can penetrate, and you will enter the realm of the ghost sharks.
Also called chimaeras, ghost sharks are dead-eyed, wing-finned fish rarely seen by people. Relatives of sharks and rays, these deep-sea denizens split off from these other groups some 300 million years ago.
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Even though ghost sharks have been gliding through the depths since long before the dinosaurs, we still know very little about them. Now, video recently released by the Monterey Bay Aquarium Research Institute in California has shined new light on these mysterious creatures.
In 2009, the institute sent a remotely operated vehicle, or ROV, on several dives to depths of up to 6,700 feet in waters off California and Hawaii. They weren’t looking for ghost sharks: “The guys doing the video were actually geologists,” says Dave Ebert, program director for the Pacific Shark Research Center at Moss Landing Marine Laboratories. (See more amazing shark pictures.)
“Normally, people probably wouldn’t have been looking around in this area, so it’s a little bit of dumb luck,” he says.
One fish the ROV kept running into looked like a new ghost shark, since it did not resemble ghost shark species known to frequent either of these regions.
To find out its identity, the institute reached out to Ebert and other chimaera experts. The team analyzed the video and now believe it's a pointy-nosed blue chimaera (Hydrolagus trolli), a species usually found near Australia and New Zealand, according to a recent study in the journal Marine Biodiversity Records.
Though the ghost shark is not new to science, it's still exciting: The video is the first time the pointy-nosed blue chimaera has been seen alive in its natural habitat.
UNCOVERING LOST SHARKS
If Ebert and colleagues are correct, the video is also the first discovery of this species in the Northern Hemisphere.
But they can't be sure unless they get DNA from an actual specimen, which is not easy. Ebert will scour local fish markets for new specimens, but one of the best—and only—ways is to use a trawling boat to scrape the depths. (The fish is usually dead by the time it makes it back up to the surface.)
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Even without a physical specimen, the video has provided a wealth of information. First, unlike many creatures of the deep, pointy nosed blue chimaera seemed to be a ham for the ROV's camera and its bright lights.
“It’s almost a little comical,” says Ebert. “It would come up and bounce its nose off the lens and swim around and come back.”
In addition, rocky outcrops in the background of the video suggest that pointy-nosed blue chimaeras prefer this habitat to the flat, soft-bottom terrain that's usually the domain of other ghost shark species, says Ebert, a specialist in what he calls lost sharks, or species that don’t tend to garner the attention of great white sharks and hammerheads.
Unlike those more well-known sharks, chimaeras don’t have rows of ragged teeth, but instead munch up their prey—mollusks, worms, and other bottom-dwellers—with mineralised tooth plates.
A pattern of open channels on their heads and faces, called lateral line canals, contain sensory cells that sense movement in the water and help the ghost sharks locate lunch.
And perhaps most fascinating, male chimaeras sport retractable sex organs on their foreheads. (Also see a rare two-headed shark in the Mediterranean.)
At least three other species of chimaera likely live across the world's oceans, so it's not that surprising that the pointy-nosed blue would as well, says Dominique Didier, a marine biologist and chimaera expert at Millersville University in Pennsylvania.
“The only way we can collect these species is by trawling,” she says. “So, it's like a snapshot. Imagine trying to understand species distribution in Lake Michigan and you sample the lake using a Dixie cup. Trawling the ocean is like that.”
“I suspect many species are wide-ranging—we just don't have the data.”
Whether you call them chimaeras, ghost sharks, ratfish, or even “water bunnies”—which is what Hydrolagus roughly means in Greek—the fish “are just one of the many beautiful and poorly studied species that shares this planet with us," Didier says.