Masters of the open sea

Scientists have long wondered how sharks manage these epic journeys. Many species migrate seasonally, some cross entire ocean basins, and others return to their birthplace after years away. Unlike seabirds or turtles, they do not surface for landmarks or rely on familiar coastlines. So what is their secret?

A magnetic sense

The leading theory is that sharks possess an internal compass tuned to Earth’s magnetic field. Recent experiments suggest they can detect subtle magnetic cues, allowing them to orient themselves, much like sailors with a chart and compass. In one study, young sharks placed in tanks with artificially altered magnetic fields actually tried to swim in the direction where they thought home should be.

Other clues in the water

Sharks are able to integrate their magnetic sense with information from their other senses. They can pick up chemical cues in the water at astonishingly low concentrations, so they could follow scent “trails.” Likely, each island and region of land has a unique chemical signature, carried by its rivers’ waters, that drifts slowly through the ocean, providing reference points for sharks. Sharks are also able to sense currents and thermal boundaries, which may serve as marine highways for them. Over time, repeated journeys could allow them to build a mental map.

Still an unsolved mystery

Despite these discoveries, the exact mechanism of shark navigation is still not fully understood. How do their sensory systems read Earth’s invisible magnetic field? Do different shark species use different strategies? Scientists are only beginning to piece it together.

Why it matters

Unravelling this mystery is not just about curiosity. Understanding shark navigation could help protect these ancient mariners. If we know how they move through the oceans, we can better safeguard their migratory routes, which is critical at a time when coastal and oceanic shark populations are under intense pressure from overfishing and habitat loss.

Nature’s navigators

So the next time you see a shark on a dive, imagine the hidden compass it carries within. Long before humans invented GPS, sharks were already charting courses across the planet’s oceans—mysterious, precise and humbling to behold.

Ethologist Ila France Porcher, author of The Shark Sessions and The True Nature of Sharks, conducted a seven-year study of a four-species reef shark community in Tahiti and has also studied sharks in Florida with shark-encounter pioneer Jim Abernethy. Her observations, the first of their kind, have yielded valuable details about the reproductive cycles, social biology, daily behaviour patterns, roaming tendencies and cognitive abilities of sharks.