The life cycle of sea turtles is a fascinating journey. From day dot they’re up against it, battling out of the sand and madly flapping to the water before they get scooped up by a predatory bird. It's thought only one in 1,000 survive. What happens next has been something of a mystery for marine science, as young turtles aren't often spotted at sea and seem to disappear until they return to the same beach they hatched on to lay their eggs as adults. It's thought an unusual bacteria may enable them to do this, using the Earth's magnetic field to navigate.
New research published in the journal Proceedings of the Royal Society B shines some light on the “lost years” of green turtles, as researchers used tracking devices to try and keep tabs on where the baby turtle party was at. Their results showed that ocean-stage green turtles exit the Gulf Stream and North Atlantic Subtropical Gyre currents and head for the surface waters of the Sargasso Sea.
While it may sound like a simple solution, the researchers on the study soon found out that attaching a tracking device to a fledgling turtle is far easier said than done. "Historically, these young turtles were too small to be able to carry older satellite tags," lead author Kate Mansfield told IFLScience. "These older tags had large batteries that were needed to help the tags communicate with overhead, orbiting satellites. The tags we used were developed. The main issue with these small turtles is that they are growing quickly and their shells are changing as they grow. With loggerheads, their shells peel as they grow and anything we glued to their shells would slough off within about 1-2 weeks."
Curious as to whether the connection between turtle shells and human nails might hold the solution (both contain keratin), co-author Jeanette Wyneken called a manicurist to see what they might use when peeling nails. The unusual consult proved to be useful for the tracking of loggerhead, Kemp’s Ridley, and hawksbill turtles but was unsuitable for the green turtles. Here, the search turned into something of a marine scientist’s Goldie Locks and the Three Bears as the team moved through a range of glues in search of the perfect fit. A flexible glue that could stretch to match the turtle’s growth couldn’t be used as it flaked off the shell. The researchers next checked in with a dentist to enquire about what adhesives were used for crowns, but that wasn’t quite right either.
Finally, they found a marine adhesive that was just right and would keep the tracker on a young turtle’s shell before falling off at around the three-month mark. Armed and ready, they fitted the gluey tracker backpacks to 21 young green turtles and sat back to see where the adventure would take them. Their tracking data revealed that the Gulf Stream was a popular ride taking many of the study’s turtles north, but 14 of the 21 peeled off to make their way to the Sargasso Sea. So, why is it such a sweet spot?
"The Sargasso Sea is named for the large mats of brown, floating algae (called Sargassum) that aggregates there," said Mansfield. "Young, oceanic stage loggerhead and green sea turtles are known to associate with Sargassum. This habitat provides them with a bit of protection from predators (young turtles and loggerheads in particular blend in well with this algae due to their coloration) and plenty of available food. Larval and juvenile fish live in the Sargassum, as do little crustaceans (crabs, etc,), some algae, etc. All things that these little turtles likely eat. It also provides warmth – the brown algae traps some water and the sun helps warm things up a bit relative to the open ocean. So, for little cold-blooded turtles, this may give them an advantage in terms of their metabolism and growth."
While a curious find, a rook of 21 turtles is of course a small sample but the significance of their open ocean playpen demonstrates that the high seas shouldn’t be missed out from talks around Marine Protected Areas. It also demonstrates the ongoing theme of research surrounding ocean surface ecosystems, and the danger “scooping” plastic retrieval technologies pose to younger generations of marine life.
“As more data become available for the sea turtle ‘lost years’ in the North Atlantic, it is clear that the Sargasso Sea is emerging as an important developmental habitat and nursery for sea turtles,” wrote the study authors. “Our work highlights the importance of the high seas in the early developmental life stages of sea turtles, and we empirically show that oceanic-stage green turtles from Florida's nesting beaches enter into the shared nursery habitat of the NASG and Sargasso Sea. We encourage the future study of this region to better understand its role in the early life history of Atlantic sea turtles.”