The high-tech hunt for one of the world's most elusive sharks
- Oops!Something went wrong.Please try again later.
OFF THE COAST OF CORSICA - Nicolas Tomasi has never laid eyes on it. He has worked these waters for years without seeing one but has heard the tales from old-timers - of a patient predator, hiding under the sand off this French island's shores, waiting for the right moment to strike.
The angel shark does not want to be found. But it can hide no longer.
On a hot August afternoon, Tomasi lowered a long, plastic tube attached to a weight over the edge of a dinghy and into the indigo water.
With the push of a few buttons, an electric pump began sucking up a small portion of the Mediterranean Sea - and with it, the ocean's secrets.
The thin stream of siphoned water looked ordinary, but floating in it were microscopic particles laden with DNA from dozens of ocean animals. If an angel shark was below, this device could detect it.
Today, said Tomasi, a project manager with the Natural Marine Park of Cap Corse and Agriate, we can find rare sea life "sans avoir à plonger." Without having to dive.
This is environmental DNA, or eDNA, a revolutionary technology that is helping scientists detect the treasure trove of genetic information animals leave in their wake and understand the breadth of life on Earth like never before.
Before, biologists had to drag nets through the sea or run electric currents through the water to incapacitate and count animals. Now, they can tally biodiversity simply by sampling water, soil or even air for the DNA animals shed in their environments daily.
Around the world from the Arctic to the Amazon, eDNA is rewriting the way biologists do conservation, allowing them to spot invasive pests entering ecosystems before anyone has seen them and to follow animals' migration fueled by climate change without deploying an army of people to track them.
But the most promising place for deploying eDNA may be Earth's oceans, where many species remain unknown and many threats, such as warmer waters and ocean acidification, are mounting.
In the case of France's elusive angel shark, eDNA helped scientists rediscover an animal many thought to be lost for good, and gave ocean managers key information about where it lives so that they can protect it.
"They are always surprised that from a sample of water, you can detect the species," said Stéphanie Manel, a professor at the École Pratique des Hautes Études who was showing Tomasi how to collect DNA.
"But this is DNA," she said. "DNA is there. So it's not magic."
Her ambitions extend beyond the angel shark. Her goal is nothing short of "a map of the biodiversity in the Mediterranean."
- - -
Fallen angel
It used to be easy to find an angel shark.
A 19th century zoologist in the British Isles wrote it "haunts our coasts in abundance." Once widespread from Scandinavia to the Western Sahara, it was so plentiful in Europe's seas that the crystal-blue water off Nice in the French Riviera is named Baie des Anges, or the Bay of Angels.
With a flattened body and eyes on top of its head, the common angel shark, or squatina squatina, lies on the bottom of the ocean, burying its body in the sand. For hours it waits in shallow waters until - whoosh! - it pops its head up, opens its jaws and sucks an unsuspecting fish into its mouth.
For as long as humans have known about the shark, they have exploited them. The Roman naturalist Pliny the Elder lauded its rough skin for its ability to polish ivory and wood.
But it was the advent of modern fishing that really did the carnivorous fish in. That lie-and-wait strategy for ambushing prey also made it easy for fishermen to scoop it up in trawls scraping the sandy sea bottom, even when trying to catch other fish.
Slow to grow and reproduce, the fish's population plummeted and the Mediterranean lost a key predator. Today, the common angel shark is no longer common, with the International Union for Conservation of Nature listing the species as critically endangered.
By 2015, its last stronghold appeared to be the Canary Islands off northwestern Africa. The shark had disappeared everywhere else. Or so scientists thought.
But locals in Corsica knew better. "I've seen the bite," Sébastien Leccia said. As a teenager, he remembered a man showing him a scar on his arm. "We knew," said Leccia, now an official with the Office of the Environment of Corsica. "But it wasn't studied."
Until in 2019, a fisherman shared pictures of the odd, flat fish caught off the northeastern coast with biologists. Some were juveniles, suggesting a hidden shark nursery. Another series of photos from a diver further confirmed Corsica's angel sharks were no myth.
But those fleeting images only painted a partial picture. Where else around Corsica did the angel shark swim? Did these sharks stay put, or mingle around the Mediterranean? In 2020, during covid lockdowns, the sharks started "to come back to the shore," said David Mouillot, a University of Montpellier professor collaborating with Manel. Had the decline in beach and boat activity during the pandemic made angel sharks less shy?
"We don't know whether it's covid, climate" or something else, he said.
For the past several years, Manel and Mouillot's team have been siphoning water along the Corsican coast to find its genetic finprint and map its whereabouts. In late August, a 56-foot trimaran named the Victoria IV cut a course along the island's northwestern shoreline to continue the search.
After dropping the tube into the blue water on that hot August afternoon, the eDNA team waited as a pump whooshed water through a fist-sized amber capsule. Inside, an accordion-shaped filter collected tiny DNA-laden particles.
After half an hour running the pump, Tomasi snapped on rubber gloves and poured a bottle of clear solution into the amber capsule, preserving the genetic material so it could be sent to a lab onshore.
There, the snippets of DNA would be multiplied using a polymerase chain reaction, or PCR - a technique also used for detecting covid in humans - and then compared to DNA from a database to see what species were swimming below. The plunging cost of analyzing DNA over the past decade opened the door for this work.
So far, the team has used eDNA to find at least seven spots along the Corsican coast where angel sharks were still patrolling, according to a paper the team published in May. But more may be lurking undetected.
"Because it is endangered, the DNA is rare," Manel said.
- - -
'A young science'
Manel first got interested in eDNA after geneticists found invasive frogs in French wetlands. Much of the first eDNA work, in fact, was done in freshwater ecosystems, where DNA lingers in abundance.
More recently, scientists have refined ways of extracting strands of genetic material from saltwater, soil and air. Depending on conditions, DNA can last for days in the ocean after an animal has shed it.
"When we started nobody believed it would work," Mouillot said of their marine eDNA work as the boat chugged along Corsica's rocky coast lined with modern steel wind turbines and medieval stone towers once used to watch for pirates.
"Everyone thought we are crazy. It's a waste of money."
In the Mediterranean, the team was on the lookout for another invader: the rabbitfish.
The rabbitfish doesn't look much like a rabbit. But it shares with its land counterpart one crucial and devastating trait: It reproduces like crazy, overwhelming ecosystems. The fish has infiltrated the eastern Mediterranean through the Suez Canal, one of some 3,500 harmful invasive species costing society more than $423 billion a year. It hasn't been spotted near Corsica. But it's only a matter of time, scientists say.
"It's inevitable at some point," said Rick Stewart-Smith, a marine biologist from the University of Tasmania in Australia who joined Manel and Mouillot on the Victoria IV.
But biologists are doing more than just tracking endangered and invasive species. Today they use eDNA to diagnose infections in insects and reconstruct entire food webs by combing through feces.
"We got to the point where we could detect one or two molecules," said Colin Simpfendorfer, a shark scientist at James Cook University in Australia conducting his own eDNA work. "That's how powerful those sorts of techniques can become."
"What eDNA can deliver for conservation is massive," he said. "It is revolutionizing a lot of the work that we do."
Yet the field is still new, and going through growing pains.
DNA is the blueprint for life, made up of four bases - adenine, thymine, guanine and cytosine - strung together in an order distinctive to every type of organism. To match DNA collected from the environment to a specific species, researchers must check samples against a reference database.
Yet the databases available right now are incomplete and disjointed. To confirm that particular sequence of A's, T's, G's and C's came from angel sharks, for instance, Manel and Mouillot's team had to test their method on angel shark tissue provided by fishers in Corsica and by an aquarium in Spain.
There is also a lack of standardization for filtration methods as well as a lack of communication with other scientific disciplines, said Louis Bernatchez, editor in chief of the scientific journal Environmental DNA. Many of the scientists sampling tissue from animals and sequencing DNA don't focus on the parts of the genome that eDNA methods are good at detecting.
"It's still a young science," said Bernatchez, a professor at Laval University in Canada. "It just keeps improving."
Then there are the privacy concerns. Wild animals aren't the only ones shedding DNA everywhere. Humans do, too. Spikes in the viral genetic signatures in sewer water, for instance, are allowing health officials to predict covid outbreaks.
In a paper this year, University of Florida biologist David Duffy and colleagues showed sleuths can recover medical and family information from genetic traces left in the environment by humans, suggesting one day police departments and insurance companies may be able to spot genetic disorders and surveil populations using eDNA.
"Essentially what we have shown is that humans are not really very different," Duffy said. "The same technologies that can allow us to recover a tiger's DNA from the environment actually can recover human DNA as well."
- - -
Going deep
And eDNA still can't capture some vital information. It can't say much yet about the quantity or body size of fish - though researchers are working on linking the amount of DNA they find in the water to the abundance of a species. And there are other fish that don't shed a lot of DNA to begin with, making eDNA detection difficult.
Some fish "don't piss a lot," Stewart-Smith said. "They don't have soft skin or mucus."
Finding some creatures requires taking a plunge. Stewart-Smith bobbed his head up and down and side to side, letting out big puffs of glistening air bubbles from his scuba gear. In one hand he held a pencil and in the other, a piece of special waterproof paper.
Swimming along a 50-meter tape measure laid along the seafloor, he counted every rainbow wrasse, painted comber and other vibrant fish he could spot. His colleague Graham Edgar passed him going the opposite direction, snapping pictures of the seafloor.
Once Stewart-Smith got to the end of the tape measure, he spun around to swim the line again - this time gently brushing away seagrass with his hand and plunging headfirst into crevices to get a better look at the life on this stretch of rocky seafloor near the small island of Giraglia at the northern tip of Corsica.
In one of the cracks he spotted a cardinal fish, a neon-orange animal that looks like a living piece of gummy candy.
"Nothing out of the ordinary," Stewart-Smith, who is also co-founder of the Reef Life Survey, said back aboard the Victoria IV.
This is a tried-and-true method for surveying sea life. For the past 16 years, the Reef Life Survey has trained professional scientists and amateur divers alike to conduct underwater surveys the same standardized way. Their catalogues, which include not only the species but also the abundance and body sizes of different reef fish at thousands of sites around the world, has provided marine managers with crucial baseline data.
This old-school approach can complement eDNA analysis. Visual surveys, for instance, aren't very good at spotting sea creatures swimming in deep waters or hiding under rocks. And other fish simply flee at the first sight of divers.
"The first thing to recognize when you're surveying marine life is that no method is perfect," said Edgar, also a University of Tasmania marine biologist.
Back on the deck, the pair enter data into their laptops. No angel sharks. No fish, in fact, bigger than 6 inches. In other areas off the coast of Corsica where Stewart-Smith went diving, fish were also small and skittish, a sign of overfishing even in areas that are supposed to be protected. Both eDNA and visual surveys can let government agencies know if fishing restrictions are working, or being ignored by poachers.
"They were all very shy," he said. "If it's meant to be no entry, the fish are telling me no."
- - -
One last look
As the Victoria IV clipped up a stretch of dry coastline, Mouillot drew in a breath of ocean air. "I'm very excited to swim," he said. "Do you smell the angel shark?"
Sure, eDNA is the shiny new technology. But there is nothing quite like seeing a shark face to face.
Snapping on flippers and swim caps, Moullot and Manel plunged into the water near a smattering of beachgoers enjoying the last days of summer. This sandy cove is near one of the spots the eDNA team had detected the shark in two years ago.
To find an angel shark, look for its silhouette. Often, the only thing to see is its outline in the sand. "You don't see the angel shark," said Jose A. Sanabria-Fernandez, another reef diver looking for the shark. "You see the shape of the angel shark."
The pair swam at a brisk pace along the coast, overhead strokes and eyes down, scanning for the outline of the shark under the sand. After several minutes of searching, Mouillot stopped.
"Many beautiful fish," he said, bobbing in the water. "But no angel shark."
The eDNA samples collected on the trip may reveal the sharks once they are analyzed in the coming weeks. But he and Manel care about more than just the angel shark. Their latest survey involves an eDNA method called metabarcoding that can detect not just one species, but whole groups of animals.
"People need to be aware that you need to protect species," Manel said. "The angel shark is maybe an emblematic species."
The pair want not just to measure biodiversity but bolster it, by someday moving some of Corsica's sharks to the French mainland coast and giving Nice's Baie des Anges its angels back.
Mouillot acknowledged the political and legal hurdles. "It's a very controversial idea," he said.
"It would be the greatest challenge of the end of my career," he added, "because it means that we can reverse the decline of biodiversity."
Related Content
Biden, Trump visits fall flat for autoworkers girding for long strike
Inside the tactics that won Christian vendors the right to reject gay weddings
Home schooling today is less religious and more diverse, poll finds
