Migrating Turtles Aren’t As Good At Navigation As We Thought

An international team of scientists tagged 22 hawksbill turtles after they’d finished nesting on the island of Diego Garcia. They then mapped their migratory paths using high-resolution Fastloc-GPS Argos, a marine life tracking system. The expectation was that turtles forced to veer away from a strong undercurrent (accounted for in the study) would course-correct, similar to green turtles when they’ve previously been tracked during lengthier travels.

The team, led by Deakin University professor and marine scientist Graeme Hays, found that “hawksbill turtles only have a relatively crude map sense in the open ocean.” Individual turtles often covered far more ground (er, water?) than necessary, with one in particular traveling 1,306 kilometers when the beeline distance to its destination island was only 176 kilometers. In fact, trips to closer destinations involved more roundabout travel than trips to destinations that were far away.

This may have something to do with the hawksbill turtle’s detection abilities, specifically as they relate to sensing the turtle is off-course. “Often it is only when [the turtles] are well off track that they reorient,” the study reads. Hays told The Guardian that the turtles “almost certainly” use a geomagnetic map as they navigate open waters, though this map appears to have a “coarse resolution.” Scientists have wondered whether sea turtles use smell to detect wind-borne cues as they travel, but this is unlikely given the turtles’ slow rate of travel and rare above-water surfacing.

Despite the erratic nature of the hawksbill turtles’ routes, most of them eventually reached their target destinations. Those that didn’t “gave up,” and returned to mainland foraging sites they were already familiar with and therefore had an easier time finding. Contrary to what one might assume, the researchers did not see any of the 22 tagged turtles give up and settle for an island they weren’t shooting for and had never visited, indicating that this behavior is (while possible) extremely rare.

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