Loggerhead turtle
Caretta caretta

Identifying a sea turtle from a deck or kayak requires knowing a few precise criteria. The loggerhead sea turtle (Caretta caretta) has distinctive visual characteristics, usable even from a distance.

The Large Head and Jaws: Criterion Number One

The loggerhead's head is disproportionately wide compared to its body, much larger than in other sea turtles found in Europe. This morphology reflects very powerful jaws adapted to crushing hard prey. Seen from the front or profile from a boat, this massive head is the first identification criterion.

Heart-Shaped Carapace, Color, and Adult Size

The carapace, called the carapace or dorsal scute, has a slightly elongated heart shape. Its color ranges from reddish-brown to orange-brown, sometimes covered with epibionts (algae, barnacles, acorn barnacles). An adult measures between 70 and 95 cm in carapace length and weighs between 80 and 200 kg (UICN, 2015). The five pairs of costal scutes on the carapace distinguish it from the green turtle (Chelonia mydas), which has only four.

Differentiating the Loggerhead from Other Sea Turtles in Europe

In the Mediterranean, the loggerhead accounts for the vast majority of sea turtle sightings.

Surface Behaviors Visible from a Boat

The loggerhead regularly surfaces to breathe, every 20 to 40 minutes during normal activity. It often shows itself at the surface during thermoregulation phases: the animal exposes itself to the sun, with a flipper or carapace out of the water. Floating rest ("logging") is a common behavior in calm weather: the turtle remains motionless at the surface, making it vulnerable to collisions with vessels.

The loggerhead sea turtle is often presented as a Mediterranean species. This image is incomplete. Caretta caretta is a cosmopolitan species with a wide distribution, present in all temperate and tropical oceans.

The Mediterranean Basin: Core of the Eastern Atlantic Population

The Mediterranean hosts the most important breeding population of the eastern Atlantic. The main nesting beaches are in Greece (Zakynthos, Crete), Turkey, Cyprus, and Libya. This population is genetically distinct from western Atlantic populations (Florida, Antilles). Mediterranean waters offer rich feeding areas, particularly seagrass meadows and rocky bottoms.

Northeast Atlantic: Seasonal Presence up to the Bay of Biscay and Breton Coasts

Individuals, mainly juveniles and sub-adults, leave the Mediterranean and travel up the northeast Atlantic carried by the North Atlantic current. Sightings are regularly reported in the Bay of Biscay, off the Basque and Landes coasts, and more rarely in Brittany, especially in summer and autumn. Data from the INPN platform and the Obs-MAM network document these French sightings outside the Mediterranean. These individuals are often in poor physiological condition as winter approaches, victims of cold stunning (hypothermia) when temperatures drop below 15°C.

Global Populations: Western Atlantic, Pacific, Indian Ocean

The largest global populations are concentrated in Florida (USA), Brazil, Oman, and Australia. The Florida population is the world's largest, with tens of thousands of nests recorded each year (UICN, 2015). Each population shows strong genetic fidelity to its nesting beaches.

Why Does the Mediterranean Population Remain Sedentary?

Part of the Mediterranean individuals migrate between feeding areas and nesting beaches but stay confined to the Mediterranean basin. The Strait of Gibraltar acts as a partial barrier: currents and bathymetry limit exchanges, although tagged individuals from the Mediterranean have been found in the Atlantic (ARCHELON report, 2021).

The life cycle of the loggerhead sea turtle is marked by remarkable slowness: late maturity, high longevity, and an unwavering attachment to the birth beach.

Nesting: Beach Choice, Nest Digging, Number of Eggs

Females nest at night on fine-sand beaches they have frequented since birth. They dig a cylindrical nest about 50 cm deep with their rear flippers, deposit an average of 100 to 120 eggs per clutch, then carefully cover the nest. A female can nest 2 to 5 times per season, with an interval of 12 to 15 days between clutches. She then reproduces only every 2 to 3 years.

Incubation and Thermosensitive Sex Ratio

Incubation lasts between 45 and 65 days depending on sand temperature. Sex determination in sea turtles is entirely thermosensitive: below 29°C, eggs produce mostly males; above, mostly females. This mechanism, called TSD (Temperature-dependent Sex Determination), makes the species particularly vulnerable to climate warming. Recent studies on Greek beaches show a growing imbalance in favor of females (Zbinden et al., 2007; updated ARCHELON data, 2022).

The First Meters: Predation and Oceanic Drift of Juveniles

At hatching, the newborns (about 4 cm) head to the sea in groups, guided by the natural luminosity of the ocean horizon. Crossing the beach is the deadliest phase: birds, crabs, and foxes take a significant portion of the clutch. Survivors enter a pelagic drift phase lasting several years, carried by major ocean gyres.

Late Sexual Maturity and Natal Philopatry

Sexual maturity is reached between 17 and 33 years depending on populations (UICN, 2015). Adult females return to lay eggs on the exact beach where they were born: this is natal philopatry, a behavior documented by tagging and photo-ID programs since the 1980s. This fidelity to the natal site is valuable for conservation but also makes the species highly sensitive to degradation of its nesting beaches.

The loggerhead sea turtle's diet is directly linked to its cephalic morphology. Its wide, powerful jaws allow it to crush prey that other predators cannot exploit.

Benthic Diet: Mollusks, Crustaceans, Echinoderms

The adult diet is primarily benthic: the loggerhead dives to the bottom to capture bivalve mollusks (mussels, cockles), crustaceans (crabs, lobsters), echinoderms (sea urchins), and gastropods. This diet explains its frequenting of rocky areas and posidonia seagrass meadows in the Mediterranean, where these prey are abundant.

Jellyfish and Fish: Opportunistic Diet Component

The loggerhead also consumes jellyfish, sponges, cephalopods, and occasionally fish. This opportunistic component is more important in pelagic-phase juveniles. It is precisely this tendency to ingest translucent floating objects that exposes the species to plastic pollution.

The Loggerhead as a Floating Reef: Epibionts and Associated Biodiversity

The loggerhead's carapace is often colonized by an epibiont community: algae, barnacles, acorn barnacles, anemones, and sometimes small crustaceans. Some individuals carry dozens of different species. The turtle thus becomes a mobile habitat, contributing to the dispersal of marine organisms over long distances.

Impact of Plastic Waste: Confusion with Natural Prey

Plastic bags and transparent films floating resemble jellyfish visually. Stomach content studies show that over 50% of loggerheads examined in the Mediterranean have ingested plastic (Campani et al., 2013). Ingestion causes intestinal blockages, false satiety signals, and reduced buoyancy. This direct link between diet and anthropogenic threat justifies special attention to marine debris management.

The loggerhead sea turtle is classified as Vulnerable on the IUCN Red List globally (UICN, 2015). In the Mediterranean, the population is considered Endangered by some regional assessments. Threats are multiple and amplify each other.

IUCN Vulnerable Status Globally

Despite significant protection efforts since the 1990s, population trends remain concerning in several basins. The slow sexual maturity and low juvenile survival rate make populations highly sensitive to any additional adult mortality.

Bycatch: Longlines and Trawls

Bycatch is the leading cause of direct adult mortality in the Mediterranean. Bottom longlines and pelagic trawls capture thousands of individuals each year. Turtles caught in longlines can drown if not released quickly. Turtle exclusion devices (TEDs) have been developed for trawls, but their adoption remains insufficient (WWF Mediterranean report, 2020).

Plastic Pollution and Waste Ingestion

As detailed in the diet section, confusion between floating plastics and natural prey is documented in more than half of individuals examined in the Mediterranean. Chronic ingestion weakens animals and reduces their reproductive capacity.

Coastal Development of Nesting Beaches and Light Pollution

Urbanization of the Mediterranean coastline directly destroys or degrades nesting beaches. Light pollution from beach resorts disrupts nesting females and disorients hatchlings, who follow artificial light instead of heading to the sea. Studies on Turkish and Greek beaches show a direct correlation between light density and emergence failure rates (Kamrowski et al., 2012).

Climate Change: Northward Shift and Sex Ratio Imbalance

Warming of Mediterranean waters is gradually extending the nesting range northward and westward. This is an opportunity for colonizing new beaches but also a major risk: rising sand temperatures imbalance the sex ratio in favor of females, which could eventually reduce population reproductive capacity. Climate change also amplifies vulnerability to other threats by stressing individuals already affected by pollution and bycatch.

The loggerhead sea turtle is strictly protected in France. Observing it without disturbing it is possible, provided a few precise rules are followed.

French Regulations: Strictly Protected Species

The order of October 14, 2005 prohibits in France the capture, holding, transport, intentional disturbance, and habitat degradation of all sea turtles, including Caretta caretta. The loggerhead is also listed in Annex II of the Barcelona Convention (Mediterranean protection) and Annex I of CITES (international trade ban). Violations incur criminal penalties.

Recommended Minimum Distances from a Boat or Kayak

No French regulation sets a specific numerical minimum distance for sea turtles, unlike cetaceans. Recommendations from marine protected areas and conservation associations converge on 50 meters minimum from a motorized boat, and 20 meters from a kayak or paddleboard. Cut the engine or reduce speed to under 3 knots when approaching. Never circle the animal or cut off its path to the surface.

What to Do with a Stranded or Distressed Turtle: Numbers to Call

Faced with a stranded or distressed turtle at sea, the priority is to not return it to the water immediately: a hypothermic or injured animal can drown. Call 196 (maritime CROSS) or contact the OFB (French Biodiversity Office). In the Atlantic, the CESTM (Center for Sea Turtle Studies and Care) at La Rochelle Aquarium is the national referent. Staying near the animal to guide rescuers is helpful.

Report a Sighting: INPN, Obs-MAM, Local Networks

Any at-sea sighting deserves to be reported. The INPN platform (inpn.mnhn.fr) and Obs-MAM app accept sea turtle reports. Specifying GPS position, estimated size, observed behavior (resting, feeding, active swimming), and attaching a photo greatly increases the scientific value of the report. Mediterranean marine protected areas also have dedicated forms.

Metropolitan France holds a peripheral position in the loggerhead's nesting range, but recent data show an accelerating dynamic, particularly since 2020.

Regular Feeding Sites: Posidonia Seagrass and Rocky Areas

French Mediterranean waters offer quality feeding habitats. Posidonia (Posidonia oceanica) seagrass meadows in Var and Corsica host the mollusks and crustaceans that the loggerhead feeds on. Rocky areas along the Corsican coast and Hyères Islands are regularly frequented feeding sites. The Port-Cros National Marine Park and the Cap Corse and Agriate Marine Nature Park include the loggerhead in their monitoring protocols.

Nestings in France: History and Recent Data (2020-2024)

The first documented nestings in metropolitan France date back to the 1990s, but they remained anecdotal. Since 2020, the phenomenon has accelerated. In 2023, 11 nests were recorded on French beaches, mainly in Corsica, according to CARI network data (Conservation of Amphibians and Reptiles of Italy and Mediterranean, shared with French partners). Nestings have also been reported on the Var coast. These figures remain modest compared to Greece or Turkey, but the trend is clearly upward.

Role of Marine Protected Areas in Species Monitoring

French marine protected areas coordinate nesting beach surveillance protocols and at-sea sighting reports. They train field agents in species recognition and nest protection (caging, signage). These structures play a central role in uploading data to national (INPN, OFB) and European databases.

Citizen Science Programs for Reporting Sightings

The CARI network, in partnership with French entities, coordinates nesting reports around the Mediterranean. At sea, Obs-MAM centralizes sea turtle sightings reported by recreational boaters, fishermen, and whale-watching operators. These participatory data complement professional scientific monitoring and refine knowledge of the species' distribution in France.