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Why are sea turtles nesting for the first time ever on Mallorca?
The first sea turtle (Caretta caretta) or loggerhead turtle nest ever to be recorded on Mallorca was discovered on 7th June 2023. Environmental changes, such as global warming, mean that it is increasingly common to find sea turtles nesting on the coasts of the western Mediterranean.
Just over a month later, on 10th July, a second nest was found on the same Balearic island. So far this year, a total of 21 nests have been detected on coasts of Spain, a record number.
What is the reason for this change of behaviour among sea turtles?
In all likelihood, the sea turtles are seeking higher latitudes to lay their eggs in order to ensure successful incubation and a more balanced sex ratio that will contribute to maintaining the species, as the incubation temperature will determine the hatchlings’ sex. In the case of this species, temperatures below 29º C will produce more males; if the temperature is higher, more females will be born.
Sea turtles exhibit philopatry: in other words, they nest on the beach where they were born. In this sense, these new nests may be attributable to errors in the turtles’ behaviour or their identification of the beaches, mere chance, or possibly to the turtles’ adaptation and selection of these beaches for nesting. Turtles appear to be able to orient themselves extremely well, using sea currents and temperature gradients, and even magnetic signals and sound.
For this reason, each year, the Balearic Islands’ Wildlife Recovery Consortium (COFIB in its Spanish initials), in collaboration with the Palma Aquarium Foundation, prepares for the arrival of new nesting sea turtles in the Balearic Islands. As the number of turtle nests in the islands is on the rise, we have decided to offer a deeper insight into the life cycle of the various species of sea turtles.
The loggerhead (Caretta caretta) is the most common species of turtle that inhabits our seas. Sea turtles spend practically their entire lives in the sea, and only the females return to the beaches to nest. They are estimated to reach sexual maturity when they are between 20 and 30 years old, which is when they return to the beaches where they were born in order to mate in the water, close to the shore.
The reproductive cycles of sea turtles are sequential. Loggerhead turtles breed every 2 years, although this may vary due to a shortage of food, environmental changes, age or disease, etc.
One or two months after mating, the females return to land to lay their eggs. Xisca Pujol, head of the Balearic Islands’ marine life stranding network at the Palma Aquarium Foundation, explains that “nesting tends to occur in summer on large sandy beaches, and always when the sea surface temperature is above 24 ºC”.
Laying does not take place in a single clutch: on average, the loggerhead turtle lays 4 clutches, once every 10-14 days during a single reproductive period. Females nesting for the first time take advantage of the experience of older females and join them during their migrations. In contrast, the males mate with females in various spawning areas, thereby generating an intense flow of genes between populations.
Laying almost always takes place after dark until the early hours of the morning and lasts between 1 and 3 hours depending on the species. When the females leave the sea, they normally head for the top of the beach, seeking shelter from the high tides. They use their flippers to build their nests several metres from the shore.
Depending on the species, they lay between 70 and 240 spherical eggs with a soft shell and a texture reminiscent of parchment. Loggerhead turtles lay between 90 and 110 eggs. Immediately after laying, the turtles use their rear flippers to cover the nest with sand before returning to the sea.
“Generally speaking, turtles are extremely sensitive to external disturbances when they leave the sea, which may lead them to abandon the nesting process at any time and return to the sea. However, they will never interrupt the laying process once it has begun”, Xisca explains.
For this reason, if you find a sea turtle on the sea shore, or observe turtle tracks or hatchlings, we urge you to call 112 immediately in order to activate the nesting protocol.
If you come across a nesting sea turtle, after calling 112, you must not disturb it. Remember to keep a distance of at least 15 metres and stop other people and/or dogs from approaching the nest. Do not shine lights onto the nest, use flash photography or make a noise. It is important to follow these instructions: if you frighten the animal, it may return to the sea before laying its eggs.
If you find turtle prints, remember not to step on them and prevent other people from doing the same so that the experts can interpret them.
If you see any turtle hatchlings, try to stop them from reaching the sea. Collect them and keep them damp, but not in water. Place them in a shady spot until the specialists in charge of dealing with them arrive.
Over the course of the various clutches, the number of eggs each female lays will gradually decrease. Once the last clutch of the season has been laid, the females will return to the adult feeding zone until the next reproductive season.
Egg incubation takes place with no parental care and lasts between 6 and 13 weeks, depending on the temperature of the nest. In order to ensure the success of the nesting process in the Balearic Islands, a number of eggs have been moved to incubators installed in the Marine and Aquaculture Research Laboratory (LIMIA in its Spanish initials) and Palma Aquarium.
Sea turtles are a natural treasure and their conservation is vital in order to maintain the balance of our marine ecosystems. The Palma Aquarium Foundation works constantly towards this objective and is conducting various projects aimed at the conservation of sea turtles. Examples include the Balearic Islands’ marine life stranding network, the ‘head starting’ project or the Anida (nesting) project, among others.
In all probability, the number of loggerhead turtle nests on our shores will remain steady or even increase in the coming years. So we trust that now you know more about these amazing creatures, you will share our wish to protect and care for them, guaranteeing a promising future for current and future generations.
