Migratory turtles aren’t as good at navigation as we thought
An international team of scientists have tagged 22 hawksbill turtles after they finished nesting on the island of Diego Garcia. They then mapped their migratory routes using high-resolution Fastloc-GPS Argos, a marine life tracking system. Turtles forced away from a strong undercurrent (accounted for in the study) were expected to correct their course, like green turtles when previously tracked on longer trips.
The team, led by Deakin University professor and marine scientist Graeme Hays, found that “hawksbills have only relatively crude cartographic 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 straight-line distance to its destination island was only 176 kilometers. In fact, trips to closer destinations involved more diverted trips than trips to distant destinations.
This may have something to do with the hawksbill’s detection abilities, specifically in regards to detecting that the turtle is off-road. “Often it’s only when [the turtles] are well on the right path that they are redirecting,” the study reads. Hay Told The Guardian that turtles “almost certainly” use a geomagnetic map when navigating in open waters, although this map appears to have a “coarse resolution”. Scientists have wondered if sea turtles use scent to detect wind-borne signals as they move, but that’s unlikely given how slow the turtles move and the sparse surface area above. some water.
Despite the erratic nature of the hawksbill routes, most of them eventually reached their target destinations. Those who didn’t ‘give up’ and returned to the mainland feeding sites they already knew and were therefore easier to find. Contrary to what one might assume, the researchers did not see any of the 22 tagged turtles abandon and settle on an island they did not shoot for and had never visited, indicating that this behavior is (although possible) extremely rare.