Juvenile loggerhead turtles don't just passively drift through life, they swim into oncoming ocean currents, according to a new study.

After loggerhead turtle hatchlings leave nesting beaches, they live in the ocean for 7-12 years before migrating to coastal habitats. Juvenile loggerhead turtles have good swimming abilities, but scientists aren't sure if they passively drift in ocean currents or actively swim. Combining turtle movement data with ocean circulation models aids scientists in understanding how juvenile turtles orient themselves in response to a current flow.

In the new study, scientists compared the daily movement over the course of 13 to 350 days of ~40 juvenile loggerhead turtles tracked by satellite with oceanic circulation data from various sources off New Caledonia.

Generalized additive model for u-component (east/west) of oceanic juvenile loggerhead turtle swimming direction estimated from HYCOM shallow currents. Credit: 
doi:10.1371/journal.pone.0103701

The authors found that the turtles were swimming against the prevailing current in a statistically significant pattern at a rate of 30 cm/sec, which indicates an ability to detect the current flow and orient themselves to swim into the current flow direction. The authors suggest that the turtles likely use multiple sensory cues that enable them to orient and offset displacement due to wind and ocean currents. Additional factors could be taken into consideration for future studies to provide more information about why this swimming pattern exists, to further explore turtle ecology in ocean currents.

"This study provides evidence that these oceanic stages of loggerhead sea turtles studied with satellite tags do not necessarily get passively transported with ocean currents and, further, provides compelling evidence that these turtles are able to resist such transport using some mechanism not yet fully understood. They are apparently able to detect the direction of current flow and swim against the prevailing current," Dr. Kobayashi added.