Traces of lost hammerhead sharks discovered in ocean water

A scientist has recently built a radar for critically endangered hammerhead sharks using environmental DNA (eDNA) samples.

Instead of chasing rare animals with nets and cameras, the eDNA method looks for microscopic fragments of genetic material shed by fins, skin, mucus, eggs, or waste in seawater samples. 

Florida International University (FIU) marine biologist Diego Cardeñosa showed the test can pick up three small-bodied, elusive hammerhead sharks: the scalloped bonnethead, the scoophead, and the Pacific bonnethead.

For species that are teetering on the edge, this is not just clever science – it’s a potential lifeline.

“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 said. 

“The short-term goal is to find these three species, as they’re likely among the most critically endangered coastal sharks in the world.”

Why hammerheads vanished from view

These diminutive hammerheads have been squeezed by decades of coastal overfishing. Because they inhabit shallow, often remote shorelines – muddy bays, mangrove-fringed inlets, surf zones – scientific monitoring has lagged precisely where pressures are highest. 

Fisheries oversight is patchy. Reporting is sparse. And when populations crash in places with little research presence, they can effectively disappear from the scientific record.

Cardeñosa thinks it wasn’t always like this. Long before industrial gears ramped up, these sharks were probably common. But across much of their range, encounters have dwindled to almost nothing. 

Some of the last confirmed records are decades old, including the scalloped bonnethead in Mexico in 1994 and the scoophead in 2007. In Honduras, one of these species surfaced again only recently after years without a trace.

“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.”

A last refuge in the water

Colombia’s Uramba/Bahía Málaga National Natural Park, where Cardeñosa tested the method, looks like an outlier – a place where these sharks may still hang on.

“You can drop a hook and line there and, within 10 minutes, catch one or two of these species,” he said.

That density makes it an ideal laboratory: if the test lights up where animals are truly present, scientists can trust negative results in lonelier waters. 

From there, teams can fan out along coasts from Mexico to northern Peru, scanning bays, ports, and estuaries for the genetic fingerprints of species that elude traditional surveys.

How eDNA helps protect hammerheads

The power of eDNA is twofold. First, it’s sensitive: a single bottle of water can betray a shark that passed through hours or days before. Second, it’s gentle: there’s no bycatch, no stress on animals, no disturbance to habitats. 

Once collected, samples can be archived for years, ready to be re-analyzed as new assays are developed for other species in the same waters.

“It’s fascinating that you can take a simple water sample and know whether a species was there or not,” Cardeñosa said.

For managers, eDNA turns a vast coastline into a map of probabilities. It can flag hotspots worth formal protection, inform patrols and gear restrictions, and help target community outreach where it will matter most. 

It can also track whether interventions are working – if genetic signals strengthen as fishing rules tighten, that’s a rare early win you can measure.

Evolution, ecosystems, and time

Conservation arguments often center on ecosystem roles, such as predators structuring food webs or biodiversity stabilizing fisheries.

Cardeñosa adds an evolutionary lens: some of these hammerheads are among the most recently evolved shark lineages. Losing them is not just losing function. It’s erasing a unique branch of the tree of life.

“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.”

That urgency is practical, too. Every additional year of data poverty makes enforcement harder, funding tougher, and local buy-in more elusive. eDNA aims to solve these issues by delivering timely, place-specific evidence that communities and agencies can act on.

Next steps to save hammerheads

Scaling up is the challenge, and the opportunity. With a test that works in hand, teams can build regional sampling grids, standardize protocols across countries, and fold the results into management plans. 

Because the technique is relatively inexpensive and doesn’t require exotic gear, it can be paired with local partners, such as fishers, rangers or students.

Furthermore, thanks to the long shelf life of extracted DNA, each liter of seawater is a time capsule future scientists can reopen to answer new questions as they arise.

The promise is simple: let the water keep the score. If small-bodied hammerheads truly persist beyond a few refuges, eDNA will find them.

If they don’t, the absence will be visible, too, and the next step should thus be bolder protections where sharks still swim, and honest triage where they no longer do.

The study is published in the journal Frontiers in Marine Science.

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