The Galápagos is a wildlife haven. But is that enough to protect the rare scalloped hammerhead shark?

A scalloped hammerhead off the Galápagos. The females swim nearly 1,000 miles to Panama to give birth, facing the threat of the heavily fished high seas. Photograph: Pelayo Salinas de León

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.