After hatching, young sea turtles move into the water and disappear. It is several years before they begin to re-emerge to reproduce. The conventional wisdom has long held that they then move into seaweed mats and simply drift with ocean currents during their “lost years” until their swimming skills improve.
Now, new research from the National Oceanic and Atmospheric Administration (NOAA) and the University of Central Florida shows that turtles are strong swimmers from a very early age, as young as 6 – 18 months, and do not float with the current at all.
“All species of sea turtles are endangered or threatened under the Endangered Species Act; knowing their distribution is an essential part of protecting them. With a better understanding of swimming behavior in these yearlings we can make better predictions about where they go and what risks they might encounter,” said Dr. Nathan Putman in a statement.
Pitman is the lead author of the study, published in the journal Current Biology, and sea turtle biologist with NOAA’s Southeast Fisheries Science Center in Miami.
Prior studies have shown that hatchlings swim offshore and are disbursed with the help of ocean currents, and that some reside in mats of seaweed that provide shelter and habitat. However, the turtles are rarely observed between birth and adulthood and little is truly known about their activities during this period.
Pitman, along with Dr. Kate Mansfield of the University of Central Florida’s Marine Turtle Research Group placed placed solar powered tags on 44 turtles. The 24 green and 20 Kemp’s ridley sea turtles were caught in the Gulf of Mexico and tracked for 2-3 months, before the tags came off naturally. Mansfield also tracked small, passive-drifting surface buoys designed to monitor the current.
When the buoy tracks were compared to the turtle tracks it became clear that the turtles were swimming independently. After just a few days the turtle’s positions differed from the current track by as much as 125 miles. According to the researchers the turtles behaviour appears to help them remain in or reach favourable habitats.
“The results of our study have huge implications for better understanding early sea turtle survival and behavior, which may ultimately lead to new and innovative ways to further protect these imperiled animals. What is exciting is that this is the first study to release drifters with small, wild-caught yearling or neonate sea turtles in order to directly test the ‘passive drifter’ hypothesis in these young turtles. Our data show that one hypothesis doesn’t, and shouldn’t, fit all, and that even a small degree of swimming or active orientation can make a huge difference in the dispersal of these young animals,” said Mansfield.
According to the Sea Turtle Conservancy all species of sea turtles are currently endangered or threatened. The list of potential threats to the animals includes over-harvesting by humans for their meat and shells, or as accidental by-catch in the hunt for fish. Pollution, loss of habitat, invasive species and climate change are all also listed as threats.
After hatching most sea turtles are lost to predators, understanding how to improve the odds of the turtles who do reach the water could go a long way to improving their numbers.
