How do baby sea turtles behave during their first days at sea? This question has been difficult to answer until now, as there have not been adequate ways to link the tracking devices to small, fast-growing marine animals for long periods of time. Researchers have now developed such a technology and used it to monitor 21 young green sea turtles by satellite for about half a year. Thus, animal movement patterns are more complex than previously assumed. Instead of letting themselves passively drift, they actively swim in preferred areas. So the Sargasso Sea in the North Atlantic Ocean is an especially important habitat for endangered species.
As a “green turtle” was hunted to nearly extinct, and today it is threatened by climate change and the destruction of its habitat: the green sea turtle (Chelonia mydas) is endangered and under international protection. Information about how turtles live, migrate and breed is important in efforts to conserve the species. But this data is superficial. In particular, little is known about the early life stage of marine animals. One reason for this: Because young turtles grow quickly, it is difficult to attach satellite trackers to their shell that they will stick to for a long time, but it does not affect the animal’s growth or other well-being. Therefore, the previous findings are mainly based on short-term observations and insights.
New tracking method
A team led by Katherine Mansfield of the University of Central Florida in Orlando developed a tracking method for young green sea turtles and used it to track 21 individuals for up to 152 days. All turtles were collected on the Florida beach immediately after they hatched and reared in large tanks at the university’s marine laboratory for three to nine months, until they weigh at least 300 grams. Then the researchers equipped them with solar-powered satellite trackers and launched them near the beach of their birth on Gulfstream.
Mansfield and colleagues already had experience tracking sea turtles through previous studies with loggerhead turtles (Caretta caretta), which they also observed via satellite as small animals. “The green sea turtle shell has a different structure and waxy surface, so we had to develop a new method for attaching the tracer,” the researchers said. After several failed attempts, during which the trackers fell again a few days later, the researchers found a solution: Before applying the special adhesive, they gently sanded the wax layer onto the tank. Only then did they connect a satellite tracker. According to the researchers, this method could also help, in the future, to monitor green sea turtles for several months.
Lake Sargasso as a breeding ground
“Our data show that green sea turtle behavior is more complex than previously thought,” Mansfield and colleagues say. While it was previously assumed that animals were mainly passively driven, the new data clearly shows that the animals are actively oriented and swim outside large currents such as the Gulf Stream. An apparently popular destination is the Sargasso Sea, a marine region in the Atlantic Ocean east of Florida that takes its name from the abundant brown algae of the genus Sargassum. “Two-thirds of the tracked green sea turtles were in the waters of the Sargasso Sea when their markings stopped broadcasting,” the researchers reported. “This indicates that many green sea turtles in the Atlantic Ocean are using the Sargasso Sea as a breeding habitat.”
The Sargasso Sea provides plenty of food for young turtles, certain protection from predators and a good temperature for growth. “The turtles in this study remained in the ocean surface layer and it is possible that they received thermal benefits from exposure to direct sunlight on the ocean surface,” the researchers said. It remains unclear how long the turtles remain in the Sargasso Sea and why not all but many individuals have swum. It might be conceivable, for example, that smaller and weaker swimmers initially stay in the larger currents. The researchers want to clarify this in future studies with more green sea turtles of different ages.
Species protection results
The researchers also compared their results with previous results on loggerhead turtles from the same area. Accordingly, the paths and movement patterns of both species differ, but the Sargasso Sea is an important station on the early life path. “Now that there is more and more data available on the early years of sea turtles in the North Atlantic, it is clear that the Sargasso Sea is an important development and habitat for marine turtle breeding,” the authors write. That is why it is especially important to conserve this habitat. “Understanding early behavior and identifying early development habitats is critical to the successful management and conservation of this endangered species,” Mansfield and colleagues said.
Cowell: Katherine Mansfield (University of Central Florida, Orlando) et al. Proceedings of the Royal Society B: Biological Sciences, Doi: 10.1098 / rspb.2021.0057