The Magnetic Personality of Sea Turtles
Posted on May 1, 2018
By Jason Frye
The stars are a little brighter on Bald Head Island. Step out onto the beach any night and you’ll see the difference that little or no light pollution makes; the sky is swimming with constellations. It’s this darkness, and the wild, natural side of Bald Head Island, which make it an ideal place to reconnect with the earth, sky and sea. At night you can spot deer and fox, eerie bioluminescent creatures in the surf, and one of the island’s most iconic visitors, the Loggerhead sea turtle.
Each summer scores of Loggerhead turtles return to the beaches and dunes of Bald Head Island to lay a clutch of eggs. A few months later, those nests “boil” and erupt, sending up to 100 hatchlings to the sea. Of these siblings, a handful of females will reach adulthood, mate, and, decades after they hatch, return to their birth beach— here on Bald Head Island—to continue the cycle and lay their own clutch of eggs.
The Bald Head Island Conservancy (BHIC) has led the charge in protecting the nesting turtles, nests and hatchlings (along with all the flora and fauna on the island) for more than three decades.
“We’ve been keeping records [on sea turtles] since 1980,” said Emily Hardin, Coastal Specialist and Sea Turtle Program Coordinator for the BHIC. “Field data sheets for nesting, hatching and stranding events from 1983 to present take up 28 two inch binders in the Barrier Island Study Center’s library.”
BHIC naturalists and interns collect data including the date, time and tide of each nesting; nest location; measurements of the carapace (shell); PIT microchip and flipper tag numbers; and, now, DNA samples. With all the sea turtle data collected and analyzed by BHIC and similar research and conservation groups the world over, it may come as a surprise that we have no definitive answer on just how sea turtles know their birth beach, the place they lay their own nest.
One researcher and Ph.D. candidate from the University of North Carolina Chapel Hill has a theory. As a child, J. Rogers Brothers saw a sea turtle nest emergence on Holden Beach, N.C., and it started a lifelong fascination with the ocean and with how migratory animals navigate over long distances. Sea turtles became a particular focus.
“Successful nesting requires a combination of different environmental features that are rare: soft sand, the right temperature for egg incubation, few predators, and an easily accessible beach. These factors are impossible to assess from far away, so for a turtle in the open ocean, selecting a nesting beach is no trivial task,” Brothers said. “The only way a female turtle can be sure that she is nesting in a favorable place is to nest on the same beach where she hatched.”
In a paper published in Current Biology, “Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles,” which Brothers co-authored with his advisor, Dr. Kenneth Lohmann, Brothers posits that sea turtles essentially have an inborn GPS that allows them to mark their birth beach using the Earth’s magnetic field.
“While our work does not exclude the possibility that turtles use additional sensory information (olfactory or visual) during the final approach to the beach, no known cue, other than magnetism, provides the information necessary to locate a specific nesting beach over a long distance.”
Brothers goes on to say that once a turtle locates her beach, she may be deterred from nesting by bright lights or the scent of a predator. Once she finds her beach, sand grain size, moisture content, and other factors will determine whether that’s the place for her nest.
Throughout the summer, the Conservancy’s turtle interns patrol the beach, looking for turtle tracks leading from the sea to the dunes, signs of a nesting turtle. Once they locate the turtle, they’ll watch her from a distance until she’s nesting, at which time it’s safe for them to approach and begin collecting data. After the nest is laid, they mark it, install an anti-predator cage, and monitor the nest until it hatches.
The Conservancy makes a number of efforts to educate Bald Head Island’s residents and visitors on sea turtle protection. From simple actions like turning off beach-facing lights and shading beach-facing windows, packing away any beach equipment at the end of the day, and keeping dogs on leashes, to more involved efforts like Turtle Walks and Adopt-A-Turtle or -Nest programs, it’s easy to make a difference in sea turtle conservation.
Hardin says that over the course of nearly 30 years and through the efforts of the Conservancy and its members and volunteers, “about 170,000 turtles have hatched from nests on our beaches.” In 25-30 years, as these turtles reach sexual maturity, they’ll return to lay their eggs here.
“If we look at [records from] the last 10 years, we see an increase in the number of nests per year,” said Hardin. “It’s possible that the conservation efforts made by volunteers and supporters of the Conservancy in its infancy are beginning to show.”
Brothers spent the summer of 2015 on Bald Head Island and said he was “extremely impressed” with their turtle program. “The BHIC has developed a model program that excels at monitoring the nesting population and conserving sea turtles, while simultaneously helping people understand and enjoy them,” said Brothers.
That said, there’s still work to do in protecting these creatures and there’s still research to be done. As far as Brothers’ hypothesis about magnetic fields goes, it raises questions about the metal cages conservation groups use to protect nests. When does the magnetic imprinting happen? If it happens while turtles are in the nest, will the metal cages be detrimental to the imprinting process? If turtles imprint when they leave the nest, how do manmade factors (like power lines and metal structures) impact imprinting? As researchers like Brothers continue their work, and as groups like the Bald Head Island Conservancy continue their preservation, protection and education efforts, we will become better equipped to help keep sea turtles safe.
The Bald Head Island Conservancy makes it easy to get involved. Visit www.bhic.org or stop in at Turtle Central or the Barrier Island Study Center on the island for a full list of adoption and donation programs, to join the Conservancy, and to participate in Turtle Walks and additional volunteer and educational programs.
This article originally appeared in Haven 2016.