The unmistakable fluted T-shape of a scalloped hammerhead shark slides by, followed by a diver holding his breath and a metal spear like an extra-long snooker cue. The spear hits the fish behind its dorsal fin and the 2-metre shark darts away, disgruntled but otherwise unharmed.
Carlos Robalino, a marine biologist from the Galápagos Islands, trained as a shark researcher in Mexico but is now back home and working as a junior researcher at the Charles Darwin Foundation. When we meet in March, he is one of the divers on the foundation’s research expedition to Darwin and Wolf, the most northerly islands in the Galápagos marine reserve.
For three or four hours each morning and afternoon, Robalino is in the sea, honing his freediving skills so he can get close enough to the sharks to take samples of their skin.
“Scalloped hammerheads are super-sensitive, very nervous,” says Simon McKinley, an ecologist with the dive team. “The trick is to wait for the shark to pass by under me to the point where they can’t possibly see me above them. Then I can dive down.”
The plug of skin from the tip of Robalino’s spear is added to a decade’s worth of biopsies collected from scalloped hammerhead sharks, which visit the islands in huge numbers. The species is critically endangered, having declined by at least 80% globally, largely due to overfishing, although you would not guess it diving at Darwin and Wolf.
On most dives during the trip, dozens of the sharks swim by. Later in the year, in the cold season when there is more food in the seas around Darwin and Wolf, more sharks migrate to the archipelago and the population quadruples.
At its peak, about 150 lion-sized scalloped hammerheads roam each hectare of sea – roughly the area of London’s Trafalgar Square. There can be so many they blot out the sun.
Despite their local abundance, studying scalloped hammerheads in Galápagos is not easy. Researchers cannot catch these sensitive sharks because the stress of being handled could kill them.
The foundation team has developed less invasive techniques, including deploying underwater cameras to monitor shark numbers. Chemical analysis of skin biopsies shows, among other things, what the sharks are eating without needing to cut open their stomachs to see the contents.
From twice-yearly visits to Darwin and Wolf, the team is building a long-term picture of the sharks’ lives and how they are responding to changing conditions, including the heatwaves linked to El Niño, such as the big one forecast for 2026.
More immediately, the team is tracking where these sharks go after leaving Galápagos. Scalloped hammerheads are not resident here but set off on long migrations, and to learn about this part of their lives requires another diving technique.
Away from the freedivers at Wolf Island, Pelayo Salinas de León waits silently on the seabed. He uses a closed-circuit rebreather, a device which recycles his exhalations, removes carbon dioxide and adds more oxygen as needed, so he can dive for hours in bubble-free tranquillity without scaring off the hammerheads. Like Robalino and McKinley, he uses a spear, but at the end of his is a satellite transmitter tag worth close to $2,000 (£1,500).
Working as a senior marine ecologist at the Charles Darwin Foundation for the past 14 years, Salinas de León has experimented with different methods to perfect the trick of using rebreathers to sneak up on sharks while they are swimming freely.
This was how he deployed a satellite tag in 2023 that tracked, for the first time, a scalloped hammerhead swimming all the way from the Galápagos Islands to the coast of Panama – an 800-mile (1,300km) journey – then embarking on a westerly migration of a farther 1,800 miles.
Since then, he has tagged dozens more scalloped hammerheads in the archipelago. Eight out of 10 have swum to Panama. Judging by their bulging bellies, most are probably pregnant females nearing the end of their nine-month gestation. They give birth in the sheltered waters of mangrove forests, which are in shorter supply along the mostly rocky shores of the Galápagos.
Uncovering these birthing migrations is proving crucial for conserving the species. Signals from the satellite tags deployed on the latest expedition show some of the sharks had already left Galápagos and were on their way to Panama at the same time that measures to protect the species were dialled up.
In March, Salinas de León took his findings to a meeting of the Convention on the Conservation of Migratory Species (CMS) in Brazil, where a vote was taken to decide whether to recategorise scalloped hammerhead sharks into Appendix I, giving them the highest level of protection under the convention.
“Our science has shown that these are highly migratory sharks, their migrations are periodical, cyclical and predictable,” he says, which ticks all the boxes for an endangered species getting an Appendix I listing on CMS. The vote went through and now signatory countries have to introduce laws within their waters to fully protect the species.
Throughout their migrations from the Galápagos Islands, scalloped hammerheads pass through numerous jurisdictions and encounter countless fishing nets and lines. Their perilous journey starts in the waters of Galápagos. Even though Darwin and Wolf Islands lie within a marine reserve, illegal longline fishing still happens there.
During the March 2026 expedition, the diving team found multiple illegal longlines. One line, tens of metres long with dozens of hooks attached, got tangled around their research boat. Another was threaded around the iconic sea stack, Darwin’s Arch, and had hooked two green turtles. Last year, they released a scalloped hammerhead shark from an artisanal longline inside the marine reserve.
Between Galápagos and Panama there are no-fishing zones where the hammerheads should be safe, including in the Hermandad marine reserve, which extends eastwards from Galápagos and Isla del Coco national park.
But there are gaps along the way where industrial and semi-industrial fisheries operate. “There is a free-for-all,” says Salinas de León. “There are hundreds of thousands of fishing boats that are legally fishing.”
If they can reach the birthing waters of Panama, pregnant scalloped hammerhead sharks are still at risk. Panama recently banned the international shark trade but artisanal fishing is still permitted.
“Baby hammerheads, and even females when they go to give birth, are being caught,” says Salinas de León. “They’re being sold and consumed as ceviche and other products in local markets.”
The Charles Darwin Foundation team is now working closely with authorities in Panama to introduce greater protections for scalloped hammerhead sharks. “The Panama nurseries are key,” says Salinas de León. “It is vital to implement additional management there to reduce the catch of baby sharks and migrating females.”
This breeding season, after the surviving hammerhead mothers have given birth in Panama, they will turn tail and head due west. They will pass Galápagos and continue another 1,200 miles to a region of the high seas called the Pacific equatorial front where yet more troubles await.
Here, mixing currents stir up a profusion of ocean life, which attracts not only female sharks that feed and restore their energy reserves, but industrial fishing fleets that come to exploit the rich waters. This is where Salinas de León hopes to take his research team next, to work out if seasonal closures or changes to fishing gear could help protect the sharks there.
“You can have a false impression of security when you dive in Darwin and Wolf, and you see hundreds of [scalloped] hammerheads, but that’s one aggregation site that has been protected from industrial fishing since 1998,” he says.
“Galápagos represents this bubble frozen in time, where you can still see the ocean of the past, where sharks are common. [But] they’re still dying, so we need to do more, we need to do better.”
This story was supported by the Pulitzer Center