[LUM#18] Turtles on the Menu
It was on the French islands in the Indian Ocean that Jérôme Bourjea, a researcher atIfremer, has been studying the behavior of sea turtles for more than 15 years. From adult migrations to the coastal habits of juveniles and the impact on their health, biologging is peeling back the shell of these mysterious creatures.
Whether green turtles or hawksbill turtles, the French islands in the Indian Ocean are fortunate to see these large migratory turtles return to their beaches every year. “Réunion, Mayotte, and the Scattered Islands are hot spots for sea turtles that come to breed before heading off to feed elsewhere,” explains Jérôme Bourjea, a researcher at the Marbec marine biology laboratory. To track their feeding grounds, starting in 2010, scientists fitted about a hundred turtles with Argos tags attached to their shells using a heat-activated epoxy resin, and tracked them through thick and thin for nearly a year.
Turtles hide to eat
“The results were impressive,” recalls Jérôme Bourjea. “We were able to watch them spread out like fireworks: Mozambique, South Africa, the Seychelles, Madagascar, Kenya… They’re spread throughout the southwestern Indian Ocean!” This information is invaluable for the conservation of these endangered species. “This allows us to better manage France’s turtle population by cooperating with our neighbors, to whose waters they migrate to feed.”
Building on these initial successes with adult turtles, the researchers used biologging to learn more about juvenile turtles that settle along the coast and feed there during the first ten years of their lives. “We see them, but do they always stay in the same place? Do they circle the island? Do they mix with other groups?” asks the biologist, who this time used GPS trackers to pinpoint their locations to within 5 or 10 meters.
Turtle-Reality
The data collected revealed different feeding strategies among juveniles, varying not only by island but also by individual.“Some turtles are very loyal and will stick to an area no larger than a soccer field, likely because they find plenty of food there,” explains the researcher. “Others are more exploratory and move to different areas after a few weeks.”
The GPS data was then cross-referenced with seafloor maps showing seagrass beds, red algae beds, and other features. “It’s interesting, but GPS doesn’t tell us whether the turtles are eating or sleeping. So we equipped them with cameras, but since each camera has a battery life of only two hours, the data is more qualitative than quantitative.”
Environmental Watchdog
The images, however, provided new insights not only into the turtles’ feeding strategies but also into their social behavior. “We discovered that they engage in social interactions that we previously thought didn’t exist at all,” explains Jérôme Bourjea, who will be heading to Aldabra—an unspoiled island in the Indian Ocean—in a few days to explore the link between the turtles’ diet, their health, and the environment, and to demonstrate “that turtles can serve as true environmental sentinels.”
Check out theUM podcasts,UM available on your favorite platform (Spotify, Deezer, Apple Podcasts, Amazon Music, etc.).