Sea Turtles

Where do baby sea turtles go?

Mansfield KL, Wyneken J, Luo J. 2021 First Atlantic satellite tracks of ‘lost years’ green turtles support the importance of the Sargasso Sea as a sea turtle nursery. Proc. R. Soc. B 288: 20210057. https://doi.org/10.1098/rspb.2021.0057

The lost years

Three images stacked vertically, the first showing a baby green sea turtle with greenish limbs/head and a brown shell, the second showing a gloved hand gluing a piece of technology to the turtle's shell, and the third showing a small sea turtle swimming in a pool with the tag stuck to it's back and an antenna sticking up.
This figure from Mansfield et al 2021 shows a juvenile Green sea turtle with a satellite tag attached with marine adhesives.

Beneath the light of the moon, a hundred baby sea turtles burst from the sand where they hatched from their eggs. Waving their limbs about, these tiny creatures make their way towards the water, where they can find safety amidst the waves. Once underwater, these little turtles swim through the shallow, coastal waters, away from land. But where do they go next?

For years, scientists have tried to answer this question. Researchers and beachgoers alike have marveled at sea turtles hatching on the beach and swimming out into coastal waters. But where exactly these baby sea turtles go to grow and develop has been a mystery, leading this life stage to be termed “the lost years” by some scientists.

Previous research has led to educated guesses about the life and habitats of juvenile sea turtles, but no explicit observations of their movement patterns have been made. It is important to understanding where animals, like sea turtles, go at different life stages for conservation efforts; it’s impossible to protect an animal if you don’t know where to go to protect it.

Now, thanks to advancements in animal-borne tracking technology, scientists can monitor the movements and behavior of marine animals, from whales and sharks to seabirds and itty bitty turtle hatchlings.

A sticky situation

In a recent paper led by Dr. Katherine Mansfield, a research team developed a new method for attaching solar-powered tags to the shells of green sea turtle hatchlings so that the tags would stay on for at least a few months, transmitting GPS coordinates and other information back to the lab via satellite. Their method involves careful cleaning of a turtle’s shell before using store-bought marine adhesives to carefully secure a tag which was originally intended for use with seabirds.

To develop and test their method, the research team caught sea turtle hatchlings on a beach in Florida and then raised them in a lab for 3 to 9 months. Once the tag attachment had been perfected, these turtles were released off the coast of Florida and the data started pouring in. Twenty-one turtle hatchlings were tagged and tracked, in total.

Life in the weeds

A picture of brown seaweed, or sargassum, which has spindly brown branches with small round spheres.
A photo of a species of Sargassum seaweed taken near the Bahamas. Photo credit: James St. John

Baby sea turtles love brown seaweed, known scientifically as sargassum. Drifting amongst mats of sargassum provides hatchlings with lots of food and a warm, safe place to hide. Sargassum drifts about in the North Atlantic Ocean, accumulating at the center of four major currents, forming a region known as the Sargasso Sea. Unlike other seas, the Sargasso Sea is not formed by surrounding land masses and is instead named for the mass of seaweed that swirls around in the gyre created by the surrounding currents. A variety of organisms, like fish, crabs, and shrimp, also call this region home, and it is especially important for other juvenile animals as well.

A map of the Eastern US and the North Atlantic Ocean, with a circle representing the Sargasso Sea and lines extending Northeast from Florida showing the tracks of tagged sea turtles.
A figure from Mansfield et al 2021 showing the tracks of tagged sea turtles (white lines) as they traveled out into the North Atlantic Ocean from the coast of Florida.

Many of the tagged sea turtle hatchlings made their way to the Sargasso Sea, where their tags eventually fell off. This was contrary to prior hypotheses, which considered the Sargasso Sea important for these turtles but which described juvenile turtle movement as restricted to areas within the currents surrounding the sea.

It appears that the Sargasso Sea is an important nursery habitat for both green sea turtles and loggerhead sea turtles, which were similarly tracked with satellite tags in a previous study. This detailed information about the migratory routes and destinations of juvenile turtles across species raises questions about turtle behavior and emphasizes the importance of protecting this key habitat.

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