The Beacon

Recent Studies Provide Insight on Sea Turtle Migration and Future Trends

A loggerhead (Caretta caretta) sea turtle hatchling makes its way to the ocean. (Photo: Florida Fish and Wildlife / Flickr Creative Commons)

Sea turtles are some of the oceans’ most charismatic species, but there’s still much to be learned about them. Since May 23 is World Turtle Day, we’re spotlighting two recent studies on sea turtles. Read more below to find out more about their migration patterns and how climate change will affect future populations.

Where do sea turtles spend their “lost years”?

When sea turtle nests hatch, dozens of palm-sized baby sea turtles emerge from the sand at once and scurry towards the open ocean. Decades later, female sea turtles often return to their natal beach to nest, this time much larger after feasting on jellyfish, crabs, and sea grasses for years. But, scientists have long wondered where sea turtles go during this time – commonly called the “lost years” – and why some sea turtles migrate to certain feeding grounds, while others don’t at all.

This has long been a gray area for scientists, but a soon-to-be-published study, titled “Ontogeny of Long Distance Migration,” shows that turtles’ drifting patterns as little hatchlings imprints their behavior as adults.  After combining all available satellite tracking data with sea water movement patterns, the researchers found adult sea turtles migrated to and chose their feeding grounds based off areas they visited as hatchlings.

“Hatchlings’ swimming abilities are pretty weak, and so they are largely at the mercy of the currents. If they drift to a good site, they seem to imprint on this location, and then later actively go there as an adult; and because they're bigger and stronger they can swim there directly,” explained lead researcher Rebecca Scott in a press release. “Conversely, if the hatchlings don't drift to sites that are suitable for adult feeding, you see that reflected in the behavior of the adults, which either do not migrate or they feed in the open ocean, which is not the normal strategy for most turtle species.”

These findings come at the heels of a study published this past March that defines the nursery grounds and habitat for Loggerhead sea turtles during the “lost years,” too.

How will climate change affect sea turtle sex determination?

Climate change poses a wide range of threats to sea turtles, from stronger storms flooding sea turtle nests to rising sea levels eroding nesting habitat. Now, a recent study published online in the journal Nature Climate Change, “Effects of Rising Temperature on the Viability of an Important Sea Turtle Rookery,” sheds light on how climate change could throw the ratio of male to female sea turtles off balance.

Sea turtles practice temperature-dependent sex determination, meaning sea turtle hatchling gender is determined by the average incubation temperature. Hotter sands caused by a warming climate could cause more females to hatch, the study warns, which could have long-term consequences of a predominantly female population. The pivotal temperature for sea turtles is 82.4 degrees Fahrenheit – meaning nests above that temperature generally produce females, and cooler nests produce males. 

The researchers carried their study out at the Cape Verde Islands in the Atlantic, one of the world’s largest sea turtle rookeries. They combined sand temperature measurements, air temperature records since 1850, and predicted warming scenarios from the Intergovernmental Panel on Climate Change (IPCC) to develop their predictions.

“Over the next 20 to 30 years, it’s not going to create problems,” Graeme Hays, one of the lead authors of the study, told the Guardian. “But ultimately, if you extrapolate long enough into the future … once you get 100 years or more into the future, then things start to look serious. You have so few males left that it’s likely to be a problem. There will be heaps of female but not enough males to fertilize all those eggs.”

The researchers also noted that sand color plays a role in sex determination, with darker beaches producing more females than light-colored sand beaches.

Oceana is working to protect sea turtles around the planet, campaigning to protect their habitat, reduce sea turtle bycatch from industrial fisheries, and combat poaching. Learn more about our efforts by clicking here


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