Six female green sea turtles swam more than 1,000 miles across the Indian Ocean using nothing but Earth's magnetic field as their guide. Researchers tracked them for about a month as they traveled westward, and the data shows the turtles held steady courses without any visual landmarks.
Satellite tags that took five years to build
Scientists from Australia attached custom satellite tags to six green sea turtles. The tags took five years to develop and could measure the turtle's compass heading to within 10 degrees and its location to within 100 meters. The devices recorded both where the turtles went and which direction they faced at each moment. The turtles were tracked as they migrated across open ocean, far from any coast or island that could serve as a visual cue.
A purely observational test of an old idea
Earlier experiments had suggested that sea turtles use geomagnetism to navigate, but those studies were done in controlled settings. This study, published in Science Advances, was purely observational. The researchers did not interfere with the turtles. They simply watched where the animals went and compared their headings to the local magnetic field. The turtles maintained consistent compass directions even when ocean currents pushed them off course, correcting their paths as they went. The study took place in the Indian Ocean, and the turtles covered more than 1,600 kilometers (about 1,000 miles) in roughly a month.
Local people in Australia and across the Indian Ocean region have long known that sea turtles make incredible migrations. But understanding exactly how they do it matters for conservation. If turtles rely on magnetic cues, then changes to the magnetic environment, or obstacles that disrupt their sensing, could threaten their ability to reach feeding grounds and nesting beaches. The study provides the strongest evidence yet that these animals navigate by reading the planet's magnetic field in real time, not by following coastlines or using memory alone.
