[LUM#18] Turtle Specials
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 over 15 years. From adult migrations and the coastal habits of juveniles to the impact on their health, biologging is shedding light on these mysterious creatures.
Whether green turtles or hawksbill turtles, the French islands in the Indian Ocean are fortunate to see these great migratory creatures return to their beaches every year. “Reunion, Mayotte, and the Scattered Islands are hotspots 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 migration routes, starting in 2010 scientists fitted about a hundred individuals 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 scattered all across 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 others?” asks the biologist, who this time used GPS tags to pinpoint their location 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 seabed maps showing areas of seagrass, red algae, and so on. “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 only has a battery life of two hours, the data is more qualitative than quantitative.”
Environmental Watchdog
The images nevertheless provided new insights into the turtles’ feeding strategies as well as their social behavior. “We discovered that they engage in social interactions that we previously thought were nonexistent,” explains Jérôme Bourjea, who will be heading to Aldabra, an unspoiled island in the Indian Ocean, in a few days to establish the link between diet, turtle health, and the environment, and to demonstrate “that turtles can serve as true sentinels of the environment.”
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