Deep in the depths of the azure Mediterranean, an Angelshark (Squatina squatina) lies in wait on the seafloor. Its tan, flat body is dappled with grays and blacks, rendering it virtually invisible to unsuspecting prey. As soon as a fish swims above, the shark jolts up and—CHOMP—snatches its meal in just a fraction of a second.
These animals are just as invisible to researchers as they are to fellow sea dwellers—not only are they tricky to spot, but years of overfishing have resulted in a conservation code red.
But something strange kept happening off the coast of Corsica, France: Angelsharks were appearing in fishing nets, confusing fishermen who had heard of their scarcity. And, in 2020, one lucky diver at Andromède Océanologie (a French research and consulting organization) managed to capture a photo of an Angelshark in the Mediterranean Sea. It was an incredible discovery: this once thought-to-be-lost species had taken refuge in the waters off of Corsica. This promising new knowledge showed researchers that small populations persisted in the area and understanding why they persisted could be used for conservation efforts to help Angelsharks bounce back.
However, researching this critically endangered species poses a particular problem. How do you study an animal that is so rare and far from your grasp?
eDNA To The Rescue
The answer lies in the water itself. Nothing is truly untraceable in the ocean: shed skin, scales, blood, and even feces are surefire indicators of the creatures dwelling below. From these bodily castoffs, genetic information known as environmental DNA (or eDNA), can be used to study animals in a less invasive manner. Previously, most information about Angelshark distribution came from fisheries that relied on netting and angling, methods that could be disruptive and potentially fatal—not the best choice for a species that is already facing extinction. But with eDNA, scientists do not need to come face-to-face with an organism to collect its genetic information. This is a revolutionary step in conservation. Now, essential data from rare animals like the Angelshark can be collected quickly and efficiently, increasing the success of conservation initiatives.
Traditional genetic sampling requires the collection of body parts or tissues of an individual organism, but with eDNA, the sample may include traces of everything present in the water. This makes it a lot easier to get more data from a sample, allowing researchers to get a complete picture of the other organisms in the ecosystem as well as the Angelsharks themselves.
However, the method is not completely foolproof. DNA is a fragile thing—especially when it’s in a turbulent environment like the ocean. Water temperature can affect the amount of eDNA present—in cold water animals are less active, reducing the amount of bodily fluids or skin shed. On the other hand, DNA tends to degrade faster in warm water. eDNA can last from only a couple hours up to several weeks; it’s a relatively new and sensitive science, but so far results have been overwhelmingly positive.
In the spring of 2021, Centre D’Ecologie Fonctionelle et Evolutive PhD. student Nadia Faure and her team boarded an Andromède Océanologie catamaran with the goal of accessing the Mediterranean’s genetic treasure trove. As the boat sped across the waters off of Corsica, a hefty filtration set-up was towed along in its wake. Eight gallons (30 L) of water were siphoned up and filtered at a time, leaving behind the precious item they were looking for: Angelshark eDNA. A second boat with a dive team hoped to spot these animals in the wild, but with no luck. It was all up to eDNA to reveal the presence of Angelsharks.
Taking the samples back to the University of Montpellier, the researchers used a laboratory technique called qPCR to amplify the DNA fragments, enabling machinery to detect even the smallest bits of DNA. Researchers then compared the amplified DNA to pre-existing Angelshark DNA stored in a library.
Sure enough, the results confirmed that Angelsharks were present along the Corsican coast. A single photograph and whispers of the sharks’ presence were no longer the only things scientists had to go off of. Now, tangible genetic material was in their hands—material that was the key to identifying the distribution and movement of Angelsharks.
An Unexpected Surprise
Out of 76 samples, seven had Angelshark DNA. But these results also contained something unexpected: one of the samples had been taken from waters in a protected marine area on the northern coast, indicating that Angelsharks were present in more areas than previously thought. Seeing the immediate results of this research was particularly exciting for Faure, especially since she had never seen the sharks with her own eyes. “I detected the DNA in the lab only a few days after sampling, and then I directly told the results to the scuba diver team that was still on the boat. And so they came back to the site where I detected the highest concentration of DNA and they observed several individuals,” she said. “It was a good feeling to have these results and a direct application in a few weeks.”
Additional data suggested a correlation between Angelshark presence and the nesting sites of picarels, a small fish native to the Mediterranean. During the early spring when these fish breed, the ocean floor turns into a craterous landscape of sandy nests as far as the eye can see. These breeding grounds are nothing short of a buffet for sea creatures. With nests along the eastern coast of Corsica, it's no wonder Angelsharks were quick to flock to those areas—a feast of several million fish eggs awaited them.
Steps for the Future
Faure’s team put special emphasis on informing the local community about the plight of the sharks. Short videos and comic strips were created and distributed to local schools in order to raise awareness about the sharks and inform fishermen about ways to avoid disturbing sensitive species.
The data obtained through eDNA was also essential to understanding the distribution and movement of the Angelsharks along the coast of Corsica. Now, action can be taken to help protect Angelsharks, with special measures during important periods of pupping and feeding, for example.
“These results can identify key areas in Corsica in which we can implement protection measures. For example, we know that Angelsharks have seasonal migrations; during the spring they aggregate around the coasts. So, we could imagine a protection measure saying to stop fishing during this season and at these specific sites,” elaborated Faure.
Faure thinks her Angelshark research wouldn’t have been possible without eDNA techniques. Divers searched every day for a week to no avail, and catching the shark was disruptive—traditional methods would be a no-go to study this elusive creature. “It was the only solution,” she said.
According to NOAA, only 5% of our ocean has been discovered—we’ve barely scratched the surface of what it has to offer. But, new technologies like eDNA are key players in discovering more of the ocean than ever before. Without it, this critically endangered species may have completely disappeared from the ocean. eDNA is an extremely important tool for scientists to have in their arsenal—it may be the ticket to discovering the presence of new species, or perhaps more importantly, saving the ones we already know.