The colonisation of sea turtles on the Spanish Mediterranean coasts continues

• The 2024 season has already begun, with at least six female turtles visiting the beaches of the Valencian Community, Catalonia, Murcia, the Balearic Islands and Andalusia. 
• 2023 was a record year and 29 loggerhead nests were detected on the Spanish coasts, 19 of them in Catalonia and Valencia, as well as another 17 unsuccessful nesting activities.
• The increase in the surface temperature of the water in the Mediterranean Sea and the sand on its beaches due to climate change, contributes to this phenomenon being repeated year after year with an apparently increasing trend.
• Nesting females have started to be detected in different years, as well as fidelity to certain beaches when laying their eggs.
• The results of InGeNi-Caretta, a project funded by Fundación Biodiversidad, indicate that the colonisation process of this sea turtle species on our coasts is consolidating.

In the last decade, beaches along the Spanish coastline and the rest of the western Mediterranean have been experiencing an increase in the detection of loggerhead turtle (Caretta caretta) nests. The increase in the number of nests in these areas is due to the fact that sea turtles are beginning to colonise new areas as a result of climate change. This colonisation is of great importance for the species, as it is predicted that in areas where they used to nest, climate change could prevent males from hatching and reduce the survival of hatchlings.

The nesting season runs from the beginning of June to the end of August, and hatchlings can be found as late as October. Despite increased vigilance by volunteers, awareness campaigns and training, the nesting detected so far has been scattered, although we are beginning to see a concentration of nesting events in some coastal areas. Some nests are detected when the turtles have already hatched, suggesting that the actual number of nests may be higher.

Moreover, this emergent colonisation occurs in areas with a high human occupation, such as the Spanish coastline, which is why appropriate management is necessary to favour the success of these nestings in a non-natural environment. The lack of public knowledge of the phenomenon, the scarcity of scientific information on the factors that regulate it, the alteration of beach conditions due to recreational use, and the lack of knowledge on the effectiveness of nest and hatchling management measures by beach managers can compromise the success of nest incubation and hatchling survival.

Start of the InGeNi-Caretta project

Given this reality, it is necessary to increase surveillance of beaches and collaboration with local, regional and national authorities to protect nests and make the high level of tourist activity compatible with the conservation of sea turtles in the summer months. Citizen involvement is also essential for the detection of females that come out to the beaches to build their nests, the location of their tracks to find their nests, the discovery of hatchlings or their traces. It is important for the public to be aware of these events for the conservation of sea turtles in our environment. The growing trend observed, and the presence of females nesting in different years, suggests that sea turtle nesting on the Spanish Mediterranean coasts has entered a new stage in which migrants from distant populations could coexist with some individuals already resident on our coasts.

This multidisciplinary and collaborative project started in May 2023 thanks to funding from the Biodiversity Foundation. InGeNi-Caretta is a consortium formed by the BETA Technology Centre of the University of Vic-Central University of Catalonia, the Biodiversity Research Institute (IRBio)-University of Barcelona, the Polytechnic University of Valencia with the collaboration of the University of Valencia, and the Doñana Biological Station. The objectives of the project are the detection and study of nests on the beaches of the Spanish coast, evaluation of the quality of beaches through the study of temperatures, telemetry monitoring, genetic analysis and monitoring of stable isotopes of females and hatchlings (to identify their origin). The project also aims to study and evaluate management actions in order to refine action protocols.

The research team is made up of sea turtle specialists, who generate the scientific knowledge necessary to understand this unique colonisation phenomenon in the world. They also transmit it to the authorities to facilitate decision-making in the planning and management of the Spanish coastline. The set of results of InGeNi-Caretta provides relevant scientific information to improve the nesting and management of the species.

InGeNi-Caretta’s field actions started in 2023, during which data and samples were collected from 29 nests. During the project, nine adult females have been tagged to track their movements by satellite telemetry. The information analysed by the InGeNi-Caretta consortium, especially that obtained from genetic studies of nest hatchlings and satellite telemetry of the females, has made it possible to detect turtles loyal to the same area and exploratory turtles nesting in different regions and in different years.

Actions will continue during the 2024 nesting season, which began in early June. So far this year, the activity of at least six females has been recorded, some of which had already visited Spanish beaches in previous years. In addition, three nests have been located and protected. It is expected that nesting activity will increase during the month of July, as seawater temperatures rise.

InGeNi-Caretta is supported by the Biodiversity Foundation of the Ministry for Ecological Transition and the Demographic Challenge (MITECO) within the framework of the Recovery, Transformation and Resilience Plan (PRTR), funded by the European Union – NextGenerationEU.