Leatherback turtles survive or reproduce in the face of the climate challenge?

• Of the seven species of sea turtles, six are now on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.
• Among them, leatherback turtles, ten of which were equipped with an Argos beacon, in June, by scientists from the Multidisciplinary Institute Hubert Curien, helped by Greenpeace. The idea: better follow their migrations, from nesting to food
• Individuals tracked since June have traveled almost twice as far as groups of leatherback turtles seen in past studies. A possible effect of climate change with far-reaching consequences

Their ancestors shared the planet with dinosaurs 100 million years ago, and they have spanned the ages since, occupying a crucial place in the marine ecosystem. “Sea turtles are among the most mysterious and charismatic inhabitants of our oceans, says Damien Chevallier, researcher at the Multidisciplinary Institute Hubert Curien (IPHC-CNRS), specialist in this marine animal. And it is hardly believable to imagine that their time is running out today. "

Of the seven species of sea turtles, six are now on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The pressures they face are multiple. From industrial fishing to plastic pollution, including poaching and climate change.

Nine leatherback turtles tracked since June

A study, carried out by IPHC scientists with the collaboration of the NGO Greenpeace, and the first results of which were published on Thursday, illustrates one of the threats posed by climate change to sea turtles. It began in early June, in the Amana Nature Reserve, in French Guyana, places for leatherback turtles to lay eggs between April and July. The idea was to equip ten leatherback turtles with Argos beacons - the largest of the seven current species of sea turtles - in order to follow their migrations, from nesting sites to feeding areas.

The paths traveled by these animals can always be followed in real time, on an online map. "One, Frida, was found dead on a beach in Suriname, only 120 kilometers from its starting point and only two weeks after having been equipped with a beacon, says Edina Ifticène, in charge of the oceans campaign at Greenpeace France. The traces found on her body show that she was, most certainly, trapped by a drifting fishing net, which illustrates another threat hanging over these leatherback turtles. "

From Guyana to La Rochelle for Lucie

The other nine continue their wanderings. They all went back up to the North Atlantic to find their food. Namely jellyfish, which constitute the main part of their diet, but also salps and sometimes small fish. The vast majority of these leatherback turtles have remained along the American Atlantic coast, San and Charlotte rising very high in northern Canada. And then there is Lucie, who opted for a completely different path by crossing the Atlantic to venture off La Rochelle. It has since turned around and is now in the middle of the Atlantic.

The paths traveled by these leatherback turtles can be followed in real time, on an online map. - Screenshot / my.wildlifecomputers.com

If leatherback turtles are used to traveling thousands of kilometers to find the best feeding sites, Damien Chevallier still notes that their daily distances tended to lengthen. After nesting, the nine turtles ventured far north, into relatively cold waters, in search of areas rich in jellyfish. "They covered an average of 14,000 km in 210 days," said the IPHC researcher. Almost double what an other group of about 15 leatherback turtles did, over a similar period of time, also equipped with Argos beacons in French Guiana and monitored between 1999 and 2005. "

Climate change that shuffles the cards

A consequence of climate change? In any case, this is the fear raised by Damien Chevallier and Greenpeace. "Studies published in Nature in 2018 announced that the ocean current system of the North Atlantic, which includes the Gulf Stream, is weakening, due to climate change," explains the first. This system works like a transmission belt, transporting warm water from the tropics to the north. And when they reach the northern seas, they cool down. A weakening of this system would lead to temperature increases or decreases, depending on the region, by several degrees. "This can affect the distribution of nutrients, oxygen, phytoplankton and zooplankton," says Damien Chevallier. And, by extension, all the species that depend on it in the food chain. »Fish, cetaceans, birds ... and therefore sea turtles.

More energy spent surviving ... less reproducing?

In this context, leatherback turtles could face either a reduced food availability or the need to travel longer distances to find their food. "However, traveling more distance involves greater energy expenditure," explains Damien Chevallier. Leatherback turtles could then invest less energy in reproduction to devote more to their survival. "

In play, therefore, there is a decrease in the number of spawning per season. It has already been observed in the demographic monitoring of leatherback turtles in Guyana for almost thirty years. "There is a significant decline in populations," says Damien Chevallier. We went from almost 50,000 spawning per season in the 1990s to less than 200 in 2018. ”

Why is it important to create marine reserves on the high seas?

If the reason for this decline is multifactorial (fishing, pollution, poaching of eggs, etc.), for the IPHC researcher, “we must also mention the possibility that the turtles never returned to lay because they have invested more in survival only in reproduction, or even they died during their migration for lack of having managed to feed. Hypotheses that the researchers at IPHC intend to dig further, in particular by equipping Argos beacons with other leatherback turtles in French Guiana and other nesting sites in the North Atlantic.

Sea turtles survived the extinction of the dinosaurs, but maybe they won't survive us ... #ProtectTheOceans #TurtleJourney https://t.co/45nuux4aoC

For its part, Greenpeace draws on these first results to remind the importance of creating more marine reserves or marine protected areas, including on the high seas. "These protected areas would provide places for breeding, living and essential food for migratory species like leatherback turtles, Edina Ifticene seaweed. Several already exist along the coasts, created by States within their exclusive economic zones (EEZ). On the other hand, there is none on the high seas, because there is no legal framework that would allow it to be done. This is one of the challenges of the world ocean treaty which the United Nations must adopt this year, and which is still under negotiation. The fourth and final working session, which is expected to lead to the adoption of a text, is scheduled for the spring.

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• science
• Guyana
• Animals
• Climate change
• Ocean
• Tortoise