Colomera was unlucky. This loggerhead turtle (Caretta caretta), a magnificent specimen weighing one hundred kilos, fell three times into the nets of fishing boats off the Valencian coast. But she also had good luck: the fishermen who hooked her were aware of the importance of the species and three times they took her to the recovery center of the Oceanogràfic Foundation of Valencia, where the veterinarians managed to recover her and return her to the sea. The last one was given a satellite tag that allowed them to follow their vital journey. For two years, Colomera managed to avoid more accidents and wandered around the Mediterranean until the device stopped broadcasting.
“This is a case that is symptomatic of the pressure that this species suffers,” explains José Luis Crespo, head of the Conservation and Marine Fauna Area of the Foundation. Threatened by man, by fishing, by its natural predators, by climate change that warms its usual nesting places, the Caretta caretta look for a new home.
The common turtle, or loggerhead, is a highly vulnerable species and one of the two types of turtles, along with the green turtle, included in the EU’s catalog of controlled species. These animals can lay 300 eggs at a sitting, but at the same time they have minuscule success rates: only one specimen in every 500 reaches adulthood. It needs help and, even if it is due to external circumstances, Spain is acquiring a basic role in its conservation due to the changes that the planet is undergoing: it is the only country in the world that produces more males than females, a fundamental value as the species.
It is increasingly common to see these turtles emerging from the sea on a Spanish beach to lay their eggs. Their presence has been relatively normal on the coast, but they came as visitors. In the last two decades, however, the Caretta caretta It is moving to our coasts to nest driven by climate change, explain the scientists at Oceanográfic. This animal reproduces in certain temperature conditions and the warming experienced by countries like Türkiye or Greece is pushing them towards somewhat cooler places. Since 2014, 70 nesting episodes have been detected in the Valencian Community, when 20 years ago they were sporadic. In 2023 alone, 29 nests were located throughout the country and in 2024 they have fallen to 11, but scientists believe that this is due to the fact that each female lays eggs only once every two or three years and this has touched fallow.
An indicator of global warming
Researchers have made the journeys of these turtles a reliable indicator of global warming, says Jesús Tomás, from the Department of Zoology of the University of Valencia, who together with Eduardo Belda, from the Polytechnic University of Valencia, carry out the main research program. and monitoring of the Generalitat Valenciana. “We are seeing the evolution live,” he explains, between enthusiasm and alarm. “We are seeing how an animal with a 20-year life cycle adapts to climate change.” Crespo confirms the idea, established in the scientific community: “It is a serious wake-up call.” The more the Caretta caretta Towards the west, the worse the planet is.
At the moment, the southernmost point in Spain where nests have been found is Marbella (Málaga). Satellite tags, small devices with an antenna that stick to the top of the turtle’s shell, have recorded some roaming the Strait of Gibraltar, perhaps in an attempt to cross the Atlantic, says Tomás, but the surface currents are too strong. for the young specimens and push them back to the Mediterranean.
Tomás and Crespo attend this Friday on Almassora beach (Castellón) the release of 22 specimens recovered by the Fundació Oceanográfic in the presence of a group of journalists invited by the Biodiversity Foundation, of the Ministry of Ecological Transition and Demographic Challenge (MITECO). The release occurs within the framework of the Life Intermares project, which is coordinated by the Foundation and in which various administrations, the CSIC, some universities and organizations such as the Spanish Fishing Confederation or WWF Spain participate. The turtle program is just one of many they manage.
The 22 specimens released on Friday were recovered from a nest on this same beach just a year ago. Weighing between one or two kilos and 30 or 40 centimeters in length, they are in better conditions to survive immersion in a hostile environment after 12 months gaining strength and presence in small tanks in the Oceanogràfic. Under natural conditions they would have entered the sea fresh from the egg, weighing 20 grams and smaller than the palm of the hand. 99% of them would not have made it. In the good scenario.
That is why MITECO, in collaboration with the autonomous communities and various institutions, monitors every turtle that leaves the sea in Spain. When one is sighted or a nest is located (the trail they leave in the sand is characteristic) it is protected, 20% of the eggs are removed to incubate them in recovery centers and their evolution is monitored. Although there is no global data, scientists assure by monitoring those they mark and release that the chances of survival multiply when they enter the sea with a certain size.
“Spanish society has to start getting used” to seeing turtles come out of the water in search of a suitable place to nest, scientists say. Our country has become a preferred place for turtles to nest due to the rise in temperature in their usual habitats.
“Spanish society has to start getting used to seeing turtles come out of the water in search of an appropriate place to nest, says Daniel García, technical director of the Oceanogràfic Foundation. In addition to the displacement that is being recorded, because the species is philopathic: it returns to the place of birth, or where it entered the sea, to look for areas suitable to make nests and lay its eggs. Although it is not yet clear whether philopathy works the same for those raised in captivity as for hatchlings left on the beach, and there are studies that suggest that the return point is incubation, not entering the sea, says Tomás.
In any case, the expectation is that the phenomenon will be recurrent, if it cannot already be considered that way. Not all turtles always return to the same place and there are also some that lay several eggs in different places, explains the researcher on the beach. In their research they have examples of all kinds: there was a turtle that in the same season laid eggs in Catalonia, the Valencian Community and Andalusia, the three places in Spain along with the Balearic Islands where nesting has been recorded. There was another that made three nests on the same beach in Catalunya. The number of clutches and the number of eggs depends on the “energy” (food) that each female has managed to accumulate, explains Tomás.
This Friday’s release is especially relevant because of the 22 turtles, 21 are males. And they are starting to become scarce. The sex of the turtles depends on the temperature at the time of incubation, explains Crespo: when it is around 29 degrees the mixture is around 50%. If it rises, it begins to shift in favor of females. If it goes down, from the males. Global warming is destroying the balance of the species and scientists have identified nests where 90% of the specimens were females. The problem this generates is obvious.
But not in Spain, “the only country in the world where more males than females are born,” says García, from Oceanogràfic. “We need females to come and produce males,” he says.
Recovery programs cannot tell females to come to Spain to nest, but they can improve the survival of the species as a whole so that it happens naturally as a matter of numbers. Work is being done on several fronts, and a good part of them refer to awareness. Awareness of society in general when they see an episode of nesting, but also of fishermen, says Crespo. It is working: more and more specimens are taken to the recovery center. More than a hundred come to the Oceanogràfic a year and they have already served close to a thousand.
“We should not demonize fishermen, but it is true that it is an impactful activity,” explains the veterinarian. The institutions have created agreements and protocols so that when a specimen gets hooked in fishing nets, they take it to a conservation center (in the case of the Valencian Community, the Oceanogràfic) to be treated by experts, as happened three times. times to Colomera. These animals are resilient, and although the nets are devastating and amputate limbs, if cared for they survive. Turtles with three fins have been recorded that have been emitting for years (and that the device stops emitting only means that it has stopped working, not necessarily that the turtle has died).
This care also allowed García and Crespo’s team, from Oceanogràfic, to discover that turtles can suffer gas embolism and decompression syndrome, like divers, something that scientists were unaware of. “It happens to some when they come into contact with fishing equipment,” says García. It is not known whether it was due to stress or why, but they detected that there were turtles that were apparently fine when the fishermen untangled them and after a while they began to worsen until they were almost in a coma despite having no apparent symptoms of injuries.
That led to another discovery, a small pride of the Oceanogràfic team: they discovered that the turtles responded extremely well to the hyperbaric chambers. Like people. And they incorporated one into their work material with a very high success rate. “They are very strong animals, with a very slow metabolism that makes them very tolerant of hypoxia,” says García. In any case, he adds, it is not a realistic solution: the job is to prevent. But in the meantime, a step through the camera, a season in the recovery center, a marking to follow its evolution and collect information and ready to return to the sea. Hopefully, to reproduce.
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