DNA in seawater reveals lost hammerhead sharks

This innovative method identifies traces of the sharks' presence without catching or disturbing them. Acting like faint biological footprints left in the sea, it detects fragments of genetic material floating in the water to reveal where the sharks have been. In a recent study published in Frontiers in Marine Science, FIU marine biologist Diego Cardeñosa, who works with FIU's Institute of Environment and the Global Forensic and Justice Center, demonstrated how the new test can help scientists locate and protect endangered shark species.

Tracking Elusive and Endangered Species

Smaller hammerhead species such as the scalloped bonnethead, scoophead, and Pacific bonnethead have been devastated by overfishing, leaving so few that researchers struggle to find or study them. Their habitats and movements remain poorly understood, making conservation difficult. Cardeñosa's new environmental DNA (eDNA) technique could finally change that by helping scientists pinpoint where these critically endangered sharks still live.

"Just by screening different locations along their distribution range from Mexico to Northern Peru, we can identify high-priority areas where conservation resources might be needed," Cardeñosa explained. "The short-term goal is to find these three species, as they're likely among the most critically endangered coastal sharks in the world."

Searching for the Last Refuges

Cardeñosa believes these species were once common before decades of overfishing drastically reduced their populations. They now survive mostly in shallow, remote coastal regions that are difficult to monitor and where fishing regulations are weak. His research focuses on Colombia's Uramba/Bahía Málaga National Natural Park, one of the few places where these sharks might still be found.

"You can drop a hook and line there and, within 10 minutes, catch one or two of these species," he said. In most other places, sightings are nearly nonexistent. The scalloped bonnethead was last seen in Mexico in 1994, while the scoophead was last documented in 2007. In Honduras, one of these species was recently rediscovered after decades without a single record.

"That's how hard it is to find them," Cardeñosa said. "It's on us if we want to act to protect them or if we just let them slip away."

Preserving a Piece of Evolutionary History

For Cardeñosa, the mission is about more than conservation.

"A lot of these are some of the most derived or newest shark species on the evolutionary scale," he said. "If they disappear, we're also losing a piece of our planet's evolutionary history. Extinction is forever, and that's enough reason for me to do something."

A Powerful Tool for the Future of Marine Science

Cardeñosa hopes his work will inspire greater awareness and appreciation for these often-overlooked sharks and demonstrate the power of environmental DNA.

"It's fascinating that you can take a simple water sample and know whether a species was there or not," he said.

By revealing where hammerheads still exist, this research helps guide conservation priorities and maximize the impact of protection efforts. Beyond hammerheads, the same water samples can hold genetic information about other marine life. Once collected, the DNA can be preserved in laboratories for years, allowing future scientists to study additional species that once swam through the same waters.