How Do Sea Turtles Navigate in the the Ocean?
By CATHERINE M. F. LOHMANN & KENNETH J. LOHMANN
Sea turtles live life on the move. Most migrate to open-sea nursery habitats as hatchlings and then migrate back to coastal waters as juveniles (learn more about the sea turtle life cycle). Some migrate seasonally. Adults migrate repeatedly between feeding and breeding areas. So the question naturally arises: How do turtles guide their journeys across vast expanses of water without landmarks or a GPS? Thirty years of work with turtles along the eastern U.S. coast has provided a framework for understanding those remarkable travels.
A sea turtle’s first migration seems a straightforward task: swim toward the open ocean and away from shore. Hatchlings start this trip in the dark; they cannot see the direction of the open ocean, but they can use wave direction to find it. When hatchlings enter the sea, they dive beneath the surface and use water motion to determine the direction that waves are moving. They then swim directly into the approaching waves and thus inevitably swim away from land and toward open water.
Sea turtles are born with the remarkable ability to use Earth’s magnetic field to navigate across the vast ocean. © Ben Hamilton
Sea turtles can also maintain a course in one direction using biological compasses based on the sun or Earth’s magnetic field. For young turtles, however, a compass alone is not enough to keep them safe within the boundaries of their nursery habitat. Fortunately, Earth’s magnetic field provides turtles with a map. Several magnetic features vary geographically so that most locations have unique combinations of magnetic characteristics. Essentially, every place has its own magnetic address.
Hatchling loggerheads emerge from their nests programmed to recognize specific magnetic addresses in the ocean and to swim innately in directions that keep them safe; thus, for example, Florida turtles do not stray too far north into fatally cold waters. As the turtles age, they move beyond those innate responses and learn to use the spatial patterns of Earth’s magnetic field as a map, thereby allowing them to sense their current magnetic addresses and set course for the magnetic addresses of their destinations. It seems likely that once juvenile turtles return to coastal waters, they can use their magnetic map to guide travel between different feeding sites, such as during the seasonal migrations of turtles along the U.S. coast. Sea turtles also use magnetic cues to migrate to their natal beaches; as hatchlings, they are thought to learn or imprint on the magnetic address of the beach where they hatched and, as adults, swim back to it years later to breed.
The remarkable magnetic navigation of turtles has important conservation implications. Conservationists need to ensure that turtles can imprint on their natal beach in a natural magnetic environment, and they need to understand that turtle populations are probably not interchangeable. Animals programmed to migrate in the Atlantic Ocean are unlikely to navigate appropriately in the Pacific and vice versa. If researchers keep such needs in mind, it seems likely that the same skills that guided turtles for the last 120 million years will keep them on track for the next 120 million.
Sea turtles can elicit tricky questions from those curious about their mysterious lives and natural histories. And even sea turtle specialists can struggle to answer some of the most seemingly basic questions about sea turtle biology and conservation. If you are among the many specialists who have stumbled to concisely answer things such as “How many sea turtles are there?,” “How old do turtles get?,” or “Where do baby turtles go?,” then this feature is for you. Our hope is to set the record straight about often-asked questions with answers written by top experts who will prepare you to respond like an expert yourself. Moreover, we hope that for those questions about sea turtles that may still have no firm answers, this series can pique SWOT readers’ curiosity and drive them to conduct the research needed to solve the mysteries.
This article originally appeared in SWOT Report, vol. 16 (2021). Click here to download the complete article as a PDF.