Sea turtles have the remarkable ability to make long annual migrations over thousands of miles. A new study published by Cell Press reveals that sea turtles navigate over long distances with nothing more than a “crude map” that is often very misleading.
“By satellite tracking turtles traveling to small, isolated oceanic islands, we show that turtles do not arrive at their targets with pinpoint accuracy,” said study lead author Graeme Hays.
“While their navigation is not perfect, we showed that turtles can make course corrections in the open ocean when they are heading off-route. These findings support the suggestion, from previous laboratory work, that turtles use a crude true navigation system in the open ocean, possibly using the Earth’s geomagnetic field.”
Even though sea turtle navigation has been studied extensively, the researchers recognized that many important details were lacking.
To investigate, the team used satellite tags to track the movements of nesting green turtles on the island of Diego Garcia to their foraging grounds across the western Indian Ocean.
Using models that incorporated ocean currents, the experts analyzed the individual migration tracks of 33 turtles.
The analysis showed that 28 of the 33 turtles did not re-orient themselves daily. As a result, the turtles sometimes wandered up to several hundred kilometers off of the direct paths to their destination before re-routing themselves.
According to the researchers, the turtles frequently failed to reach their small island destinations with pinpoint accuracy. They often went too far or continued to search during the final stages of migration.
“We were surprised that turtles had such difficulties in finding their way to small targets,” said Hays. “Often they swam well off course and sometimes they spent many weeks searching for isolated islands.”
“We were also surprised at the distance that some turtles migrated. Six tracked turtles traveled more than 4,000 kilometers to the east African coast, from Mozambique in the south, to as far north as Somalia. So, these turtles complete round-trip migrations of more than 8,000 kilometers to and from their nesting beaches in the Chagos Archipelago.”
The findings support the theory that migrating sea turtles use a true navigation system in the open ocean. The fact that they can re-orient themselves in deep waters implies that they have an instinctive map, but it lacks fine details. By using this crude map, the sea turtles use up a lot of extra energy and often do not arrive at their precise targets.
Considering that sea turtles travel broadly across the open ocean after nesting season, Hays said that “conservation measures need to apply across these spatial scales and across many countries.”
The study is published in the journal Current Biology.