Scientists synthesized 22 hawksbill turtles (Eretmochelys imbricata) using GPS trackers to see which ways they will return to their original hunting grounds after mating and breeding. These trackers revealed that the routes taken were somewhat crooked.
A single turtle traveled a total distance of 1,306 kilometers (812 miles) to find an island 176 kilometers (109 miles) from its starting point, for example. The researchers found that, in general, there was a lot of swimming in circles before the animals were able to settle on land again.
“Our results provide compelling evidence that hawksbill turtles have only a relatively false sense of the map in the open ocean,” the researchers wrote in their published paper.
“The presence of extensive search and breeding areas in isolated ocean sites suggests that targeted search in the final stages of migration is common in sea turtles.”
Sea turtles are famous for their ability to migrate great distances across the ocean, often landing on small, isolated islands far from anywhere else – so the question is how they find these remote spots surrounded by open water.
While previous research has demonstrated that these turtles have some sense of the Earth’s magnetic field, which can help plot their path, until now it’s not clear how accurate or precise this magnetic mapping technique is.
Tagged turtles typically swim twice as far as they would have to to find foraging sites. Compared to other turtle species, these hawksbill turtles have relatively short migratory distances to cover.
Many species use changes in the strength and direction of the magnetic field around the Earth in order to tell which way to go. In the case of these turtles, this navigation aid appears to be working, but only to a certain extent.
“It doesn’t allow for precise determination of migration in straight lines, but it does tell them when they get away from the long way,” said marine ecologist Graeme Hayes, of Deakin University in Australia. Watchman.
The researchers report that there is some evidence of course correction in both open water and shallow water closer to land. Several of the findings in this study are consistent with what has been previously observed in green turtles (Chelonia Midas).
As far as researchers can tell, ocean currents have not affected the way the turtles travel from point A to B. And the turtles don’t seem to wait for a certain set of local weather conditions before setting out on their flights – they just start right after breeding.
Turtles’ behavior and navigation contrast starkly with some seabirds, which usually find their destination quickly, and likely use wind-borne scents to do so. Sea turtles seem to have no such signals to make decisions from.
“Our findings suggest that sea turtles’ navigational abilities are far from perfect, but may simply be as good as possible within the limitations of their sensory ability,” the researchers wrote.
The search was published in Royal Society Interface Magazine.