Sea Turtles of the Mediterranean Sea
A loggerhead turtle swims above endemic seagrass (Posidonia oceanica) in the Mediterranean Sea. © KOSTAS PAPAFITSOROS
By SANDRA HOCHSCHEID, MUSTAPHA AKSISSOU, THOMAS ARAPIS, MOULOUD BENABDI, LIZA BOURA, ANNETTE BRODERICK, LUIS CARDONA, CARLOS CARRERAS, FRANÇOISE CLARO, ANDREAS DEMETROPOULOS, WAYNE J. FULLER, IMED JRIBI, YAKUP KASKA, YANIV LEVY, FULVIO MAFFUCCI, DIMITRIS MARGARITOULIS, CARMEN MIFSUD, ALIKI PANAGOPOULOU, JACQUES SACCHI, JESÚS TOMÁS, OĞUZ TÜRKOZAN, and ALAN REES
A SEA OF BOUNTY AND DANGER
The Mediterranean Sea is a bountiful yet dangerous place for sea turtles. In an area bounded by Europe on its northern shores, Asia to the east, and Africa to the south, sea turtles share their relatively small home (2.5 million square kilometers, or about 1 million square miles) with more than 150 million people who live along the coasts of 20 countries and two island nations. On top of that, the Mediterranean basin is by far the largest global tourism destination, attracting almost a third of the world’s international tourists every year. Characterized by beautiful natural and cultural heritage sites and by rich biodiversity, the Mediterranean is also a troubled and overexploited sea, where sea turtles have a hard time coping with high fishing pressure, gas and oil development, major cross-continental maritime traffic, beachfront and other habitat impacts, and widespread marine pollution.
A turtle’s journey around the Mediterranean, following the main counterclockwise surface currents, would begin at the in flow from the Atlantic that passes through the 14-kilometer-wide (less than 9 miles) Strait of Gibraltar, then along the coast of North Africa starting in Morocco, passing between Tunisia and Malta, and moving into the eastern basin. By now our hypothetical Mediterranean sea turtle would have gotten used to the high salinity (over 38 practical salinity units) caused by an imbalance between water gain through river inflow and loss through high evaporation. He would continue past the endless beaches of Libya and go by Egypt, where the Suez Canal allows Lessepsian fauna and flora migrants to enter from the Red Sea.
Now he’d turn north, traveling through the Levant from Israel to Syria, passing zones of human conflict where turtle conservationists must watch out for more than just turtle nests on the beaches. Continuing westward, he’d pass between Cyprus and Turkey to continue along the southern coasts of Crete (Greece). Crossing over the sea’s deepest recorded point of 5,267 meters (3.3 miles) in the Ionian Sea, he would then take a trip to Croatia in the far north of the cold Adriatic Sea and would circumnavigate the Italian peninsula to complete his tour in Spain, having traveled some 11,700 kilometers (7,270 miles).
TURTLE RESIDENTS AND VISITORS
Two of the world’s seven species of sea turtles breed in the Mediterranean, and their nesting distribution is the result of several preglacial and postglacial colonization events. Two sea turtle regional management units (RMUs), or subpopulations, are present (see map). The Mediterranean loggerhead RMU is considered of least concern, though the species (Caretta caretta) is vulnerable globally, and the Mediterranean green RMU is as yet unranked, with the species (Chelonia mydas) considered endangered globally. Mediterranean loggerheads are the smallest specimens of this species in the world, and their nesting areas range from the Western Mediterranean to the Levantine coast in the east, with most of the estimated 8,000 clutches laid annually occurring in the Eastern Mediterranean, especially in Greece (see SWOT Report, vol. X, “A Tale of Two Beaches in Greece”). Green turtle nesting is confined to the easternmost part of the Eastern Mediterranean, mostly in Cyprus and Turkey, where more than 2,200 clutches are laid each year. Juvenile loggerheads forage throughout the Western Mediterranean in deep oceanic and shallow continental shelf regions. In the Eastern Mediterranean, adults tend to frequent the shallow continental shelf of the northern Adriatic and the Tunisian shelf, while juveniles remain more oceanic. Adult green turtles forage in Turkey, on the coasts of the Levant, and on North African shores (to Libya’s western border). Some juvenile foraging has been reported in the Eastern Mediterranean, off the Peloponnesian coast of Greece, and possibly also in the southern Adriatic.
Non-breeding turtles from the Atlantic often enter the Mediterranean as well. They are mainly loggerheads from both sides of the Atlantic, which coexist with their indigenous conspecifics on oceanic foraging grounds. Generally, the Atlantic loggerheads enter the Mediterranean as small juveniles and are unable to depart until they have grown much larger and can confront the strong inward current at the Strait of Gibraltar, though new evidence has revealed that some Atlantic loggerheads are now breeding and nesting within the Western Mediterranean.
A loggerhead turtle swims near seaside homes on the coast of Greece. With more than 150 million coastal residents and one of the world’s highest levels of tourism, the Mediterranean Sea is an environment profoundly shaped by people. © KOSTAS PAPAFITSOROS
Visitors from the Atlantic also include green turtles that frequent the Western Mediterranean. Since indigenous greens are found only in the Eastern Mediterranean, the Atlantic greens do not share foraging grounds with the local greens. Leatherbacks have also been recorded throughout the basin and as far east as Egypt, Israel, and Syria. Though Mediterranean leatherbacks are generally large juveniles and adults of both sexes, no nesting by this species has ever been confirmed. The presence of both Kemp’s and olive ridleys in the Mediterranean is confirmed but rare, with only a handful of records of juvenile Kemp’s ridleys in France, Italy, Malta, and southern Spain and a single record of an olive ridley from Spain. There are several records of hawksbills in the Mediterranean.
MAJOR TURTLE REGIONS
SOUTHERN SHORES (Morocco to Egypt, Including Malta)
The 500 km (311 mi) coastline of Morocco is primarily a foraging habitat for loggerheads; leatherbacks also are regularly observed—and on rare occasions, greens. Most of the knowledge about sea turtles in this zone comes from strandings and animals incidentally captured by fishers. Fisheries interactions are unquestionably the most common threat to Morocco’s turtles. However, until 2007, juvenile loggerheads were also found in markets, not necessarily for consumption but rather for the use of their carapaces and other products.
The 1,622 km (1,007 mi) Algerian coastline is dominated by rocky shores and sandy beaches, and here too sea turtles have been reported since the 1800s as stranding and being caught accidentally by fishers. They are typically loggerheads (70 percent) and some leatherbacks (30 percent). To date, no nesting has been confirmed, but rising temperatures may make nesting possible in Algeria; thus, authorities began to monitor beach temperatures in 2017 to evaluate potential nesting areas.
Three sea turtle species are observed in the waters adjacent to Tunisia’s 1,148 km (713 mi) coastline; greens are rare, leatherbacks are regularly observed, and loggerheads are the most common. The wide continental shelf in southern Tunisia, including the Gulf of Gabès, is one of the most important foraging areas for sea turtles in the whole Mediterranean. The number of accidental captures by trawlers, longlines, and gill nets suggests a high turtle density in that region. Tunisia has an active sea turtle stranding network and a rescue center based in Monastir. Loggerhead turtles also nest regularly in Tunisia, especially on Kuriat Island, which receives about 25 nests each year.
The small (315 sq km, or 122 sq mi) island nation of Malta lies southeast of the Sicily Channel, connecting the Mediterranean’s western and eastern basins. Turtles are frequently found in Maltese waters, with five species being recorded; however, subadult and juvenile loggerheads are the most commonly seen. Malta has three marine NATURA 2000 sites (part of the European Union’s NATURA 2000 network of protected areas) for protection of loggerhead turtles, and since 2001, a rescue center has rehabilitated many of the accidentally caught and stranded turtles, especially those with ingested fishing lines. Malta has also seen some sporadic turtle nesting, although sandy beaches are rare, only 2.5 percent of all beaches.
At 1,770 km (1,000 mi), Libya’s coastline is the longest of any African country bordering the Mediterranean, and long sandy beaches are its predominant feature. It also has the oldest nesting colony for loggerhead turtles in the entire basin. The Libyan Sea Turtle Program, supported by the Regional Activity Centre for Specially Protected Areas (RAC/SPA), which is part of the United Nations Environment Programme’s Mediterranean Action Plan (UNEP-MAP), has been monitoring loggerhead turtles for many years, even during periods of political turmoil. However, the total numbers of nesting females still remain unknown. Post-nesting loggerheads also seem to frequent the Tunisian shelf. No green turtle has been found nesting in the country, but Libyan waters provide ample foraging and overwintering habitats in the Gulfs of Bomba and Sirte for green turtles that nest in Levantine countries.
Egypt’s 1,050 km (652 mi) of Mediterranean coast host potentially important loggerhead and green turtle foraging grounds and migratory corridors. The presence of leatherbacks has also been verified through stranding and bycatch data. Of special interest is Bardawil lagoon, an important foraging and possible overwintering site, which requires further in-water investigation and conservation action, especially with regard to fisheries interactions.
Loggerhead and green turtle nesting in Egypt are low when compared with other Mediterranean sites, though minor diffuse nesting is scattered along the western Egyptian coastline. The main nesting area is a 22 km (14 mi) sandy beach on the North Sinai Peninsula (average nests/year: 67 for loggerheads and 7 for greens). Ongoing surveys by Egyptian authorities with assistance from RAC/SPA are expected to provide updated information in relation to nesting along the western coastline (between Port Said and El Salum). In addition to widespread regional threats like habitat degradation, pollution, and bycatch, illegal trade is particularly acute. Trade in turtle products has been reported since the beginning of the 20th century, and consumption is a tradition that has been documented since at least the 1970s and up through the present, predominantly in Alexandria and Port Said.
LEVANTINE COAST (Israel to Turkey, Including Cyprus)
Israel’s 200 km (124 mi) Mediterranean coastline is largely suitable for loggerhead and green turtle nesting, although light pollution is a problem, and the continental shelf’s moderate slope provides foraging grounds for both species. Since 1993, Israel’s Nature and Parks Authority has surveyed beaches during nesting season; nests are relocated to protected hatcheries, a practice that has increased nest numbers over time. In 1999, a turtle rescue center was founded that today tends to about 100 animals yearly, with 70 percent being returned to the wild. A turtle head-start program that was begun in 2002 is now a captive breeding facility as well. The facility’s volunteers serve the public through lectures, media publications, school programs, and other turtle conservation work, and their research addresses aspects of turtle biology, genetics, movement ecology, husbandry, veterinary care, and endocrinology.
Lebanon’s 200 km (124 mi) coast has only a few sandy beaches suitable for sea turtle nesting. Extensive urban development, sand mining, and litter reduce the available turtle habitat even further. Loggerhead and green turtle nests are found in small numbers in southern Lebanon, an area affected by military operations that is also home to the Tyre Coast Nature Reserve, which is dedicated to the protection of sea turtles.
Loggerhead turtle nesting was first recorded in 1991 on Syria’s 193 km (120 mi) coast by the Mediterranean Association to Save the Sea Turtles (MEDASSET), and a survey in 2004 confirmed that low-level loggerhead nesting occurred at several locations in the country. The survey also declared Syria among the top 10 nesting areas for Mediterranean green turtles, specifically one 12.5 km (8 mi) beach south of Latakia city. Local researchers have monitored turtle nesting there and at other places, though internal turmoil has prevented the acquisition of consistent data. Syria’s coastal waters are home to juvenile green turtles year-round and are part of a migratory corridor for turtles nesting in Cyprus and other areas to the west.
Green and loggerhead turtles nest on the beaches of Cyprus (an island with an area of 9,250 sq km, or 3,571 sq mi). In 2018, well over 1,300 green and 2,200 loggerhead clutches were laid islandwide, making this a noteworthy nesting site for both species. Because of significant long- term conservation efforts, including caging of nests and beach protection, nesting populations appear to be stable or rising, although loss of nesting habitat and predation by dogs and foxes is an ongoing problem.
A green turtle returns to sea after nesting on the island of Cyprus. © LAWRENCE SAMPSON
Large numbers of both species also forage around the shores of Cyprus, with juvenile and subadult green and adult loggerhead turtles being the most common. More than 1,000 turtles are estimated to be accidentally caught by small-scale fisheries each year, with a mortality rate in excess of 50 percent. Ongoing projects are under way to further understand and mitigate this effect. Through long-term monitoring of individual females nesting in Cyprus, researchers have learned a great deal about their life history and behavior. Most notably, females of both species can breed for at least 24 years—maybe longer—according to 27 years of observations. Furthermore, research has demonstrated that females show site fidelity to their winter foraging grounds and that the coast of Cyprus is an important migratory corridor for turtles from both Cyprus and Turkey.
In the north of the Levant, Turkey has a total of 21 nesting beaches along its 1,577 km (980 mi) of Mediterranean coastline. Its western beaches are mainly used by loggerhead turtles, which nest in the highest densities on Amamur, Belek, and Dalyan beaches and represent 65 percent of the country’s nesting activity. With annual numbers of loggerhead turtle nests as high as 6,000, Turkish beaches make a very important contribution of around one-third of the total loggerhead nests in the Mediterranean basin. Green turtles nest mainly on Turkey’s eastern beaches, including Akyatan, Alata, Davultepe, Kazanlı, Samandag, and Sugözü, which represent 88 percent of the country’s nesting and as many as 4,000 nests per year, or nearly two-thirds of the total green turtle nests in the Mediterranean.
The Turkish coast also hosts important feeding grounds for different age classes of both species. Monitoring of 15 of those beaches is carried out by universities, nongovernmental organizations, and government authorities. Turkey also has a turtle rescue center and three first aid stations along the Aegean and Mediterranean shores. Scientific studies in Turkey include sea turtle genetics, temperature-based sex determination, stable isotope analyses, pollution and plastic ingestion, and fisheries bycatch monitoring.
NORTHERN SHORES (Greece, the Adriatic, and West to Spain)
Systematic nest counts that have been conducted since 1984 by the Sea Turtle Protection Society of Greece (ARCHELON) and its contingent of international volunteers have shown that Greece hosts the largest number of loggerhead nests in the Mediterranean (more than 6,000 in 2018). Top nesting sites include Kyparissia Bay in the Peloponnese and Laganas Bay in Zakynthos. Both sites have been protected since 1999, the former by presidential decree and the latter by the establishment of the National Marine Park of Zakynthos.
Other important nesting beaches in the Peloponnese and on Crete are included in the European Union’s NATURA 2000 network of protected areas. Over the years, the total number of nests has remained more or less stable. However, a notable steep increase at Kyparissia Bay, which now exhibits higher nest numbers than Laganas Bay, is a result of long-term nest protection against mammal predators. This increase is offset by severe declines in Rethymno and Chania on Crete, which can be attributed to rising anthropogenic pressures. ARCHELON continues in-water work in Amvrakikos Bay, a notable foraging area for loggerhead turtles, with more than 1,000 juvenile and adult loggerheads—mostly male—now tagged and measured. ARCHELON has also operated a Sea Turtle Rescue Centre in Glyfada since 1994, which rehabilitates injured turtles that are found along the 16,000 km (9,942 mi) Greek shoreline through their Stranding Network.
Entering the Adriatic Sea, loggerheads, greens, and leatherbacks migrate past or reside along Albania’s 362 km (225 mi) coastline. Although there has been evidence of sporadic nesting for some years, the first actual nest was officially confirmed in 2018. Albania’s Drini Bay is potentially an important habitat for overwintering and foraging—and possibly as a developmental habitat for both adult and subadult loggerheads (mostly originating from Greece) and occasionally by greens as well. A systematic study of Albania’s turtle population structure in 2008–2010 showed the presence of a large number of male turtles and a very substantial proportion of subadult animals. Tagging and satellite tracking revealed site fidelity both intra-annually and inter-annually. Apart from the usual hazards found throughout the Mediterranean, illegal fishing techniques, such as the use of dynamite, pose serious threats to Albania’s turtles and other marine life.
North along the Adriatic coast from Albania, Montenegro has 294 km (183 mi) of coastline, and Bosnia and Herzegovina has 20 km (12.4 mi). Croatia has the longest eastern Adriatic coastline, at 526 km (327 mi), though that number becomes 7,368 km (4,578 mi) when including the coastlines of the country’s many islands. Finally, Slovenia has 47 km (29 mi) of coastline. Those countries are similar in that sea turtles do not nest on their beaches, but tens of thousands of turtles, mostly loggerheads, are found year-round in their nearby waters. Genetic research has shown that most of these animals originated in Greece, and satellite and flipper tagging have further confirmed that many loggerheads nesting in Greece migrate to the Adriatic for foraging and overwintering.
Italy, including its many islands, has a coastline of about 7,600 km (4,722 mi) on the Adriatic, Ionian, and Tyrrhenian seas, and it is effectively the dividing line between the western and eastern basins of the Mediterranean. Turtles of all species that roam the Mediterranean Sea inevitably cross Italian waters at some point, whether for foraging or simply moving from one place to another, though the most common species in Italy is the loggerhead in all life stages. There are good neritic foraging habitats off the Tyrrhenian and Adriatic shores; however, those zones are also heavily fished, resulting in bycatch mortality and high stranding rates. High numbers of human-induced strandings have led to a proliferation of more than 20 sea turtle rescue centers, making Italy the country with the highest number of such facilities in the region. Italy has regular nesting along the southern Ionian coast and on nearby pelagic islands, and loggerhead nesting has recently increased on Italy’s western beaches.
The French Mediterranean waters, including Corsica, are frequented mainly by loggerhead turtles and occasional leatherbacks. Leaving the pelagic waters of the Liguro-Provençal current, loggerhead juveniles arrive in the spring for feeding in the Gulf of Lions, but they may remain, as it is also believed to be an overwintering area. Recently the fourth loggerhead nest since 2002 was observed on the Languedoc coast, giving France the northernmost nesting site of this species worldwide. Loggerheads are frequently caught unintentionally by fishermen, and many also wash ashore dead. Annually, these strandings account for 50–110 animals, as recorded by the French observer network, Réseau Tortues Marines de Méditerranée Française (RTMMF) and French rescue centers.
Notwithstanding the tiny peninsula of Gibraltar (UK) with its 4 km (2.5 mi) coastline that witnesses the comings and goings of sea turtles between the Atlantic and Mediterranean through the Strait of Gibraltar, Spain is the final country of this counterclockwise tour around the Mediterranean. Spain reports five sea turtle species in the waters adjacent its 1,670 km (1,037 mi) of coast, yet only loggerheads occur in large numbers. Most of those are juveniles from nesting beaches in the northwest Atlantic, the Mediterranean, and Cape Verde. The loggerheads of Mediterranean origin are predominantly found off eastern Spain in shallow seas; conversely, loggerheads of northwest Atlantic origin are mostly found o the Balearic Islands and are more oceanic. Loggerheads from Cape Verde represent less than 4 percent of the total number of loggerheads in Spanish seas.
Bottom trawling and drifting longline fisheries are the main threats for turtles off mainland Spain and the Balearic Islands. Until 2001, evidence of loggerhead turtle nesting was scarce, but Spain has recorded about 42 nests over the past two decades, and genetic analyses indicate an ongoing and exciting process of colonization from distant nesting beaches.
CONSERVATION
Mediterranean sea turtle conservation started on Cyprus’s nesting beaches in the early 1970s, then in Greece and Turkey in the 1980s, and in Israel by the 1990s. Surprisingly, important turtle nesting rookeries were still being discovered into the 2000s. For countries that host the majority of the Mediterranean’s sea turtle nesting, such as Cyprus, Greece, and Turkey, nest protection has been the principal conservation focus, led by local communities, nonprofit groups, and volunteers. Where turtle nesting is less common, as in Italy, sea turtle rescue and rehabilitation centers are more prevalent and serve as the frontlines of actions to help sea turtles.
The 1980s saw the inauguration of important national and international grassroots turtle conservation organizations in the Mediterranean, including ARCHELON and MEDASSET, in addition to projects supported by the World Wide Fund for Nature (WWF) and others. Meanwhile, on a governmental policy scale, the Parties to the Barcelona Convention for the Protection of the Marine Environment and the Coastal Regions of the Mediterranean, a treaty that began in 1975 as “the Convention for Protection of the Mediterranean Sea against Pollution,” was amended by the Genoa Declaration in September 1985 to include the protection of Mediterranean marine turtles among their priority targets for the period 1985–1995. And in 1989, all the Mediterranean countries adopted an Action Plan for the Conservation of Marine Turtles within the Mediterranean Action Plan (MAP) framework.
In 1990, the Council of Europe (Bern Convention) released one of the first important reports on Mediterranean sea turtles, which described the conservation status and geographical distribution of all species and recommended cost-effective research and realistic conservation measures. Finally, UNEP’s RAC/SPA has been working for more than three decades on marine turtles.
CONCLUSION
The Mediterranean is an exciting place for sea turtle research, with prospects of range expansion and new colonization, and with long-term conservation projects that have achieved stable or even positive population trends. Yet researchers and conservationists still have a long way to go before turtles in the Mediterranean can be called safe. Indeed, many major threats, particularly fisheries bycatch and climate change, still urgently need solutions. To that end, a solid network of conservationists, researchers, and stakeholders must continue to focus their energies on the actions needed to ensure that Mediterranean sea turtles survive and thrive into the future. Fortunately, the community dedicated to the Mediterranean sea turtle, despite its disparity of cultures and languages, is a consolidated and collaborative movement of individuals, institutions, and governments committed to this worthy goal.
FEATURE MAPS: BIOGEOGRAPHY OF SEA TURTLES IN THE MEDITERRANEAN SEA
The maps below display available nesting and satellite telemetry data for sea turtles in the Mediterranean Sea, as well as modeled foraging areas for loggerhead turtles (bottom left). The data include 216 nesting sites and 316 satellite tags, compiled through a literature review and contributed directly to SWOT by dozens of data contributors throughout the Mediterranean region. For metadata and information regarding data sources and contributors, see the data citations here.
Nesting sites are represented by dots that are colored and scaled according to the species present and their relative nesting abundance in the most recent year from which data are available. If multiple species are present at a particular nesting site, the dot for that site is scaled according to the total nesting abundance for both species combined, and the proportion of nesting by each species is indicated by the proportion of each species’ respective color within the dot. For the purposes of uniformity, all types of nesting counts (e.g., number of nesting females, number of crawls) were converted to number of clutches as needed. Conversion factors were as follows: for Caretta caretta, a ratio of 2 nests to each nesting female and 0.68 nests for every crawl; for Chelonia mydas, a ratio of 3 nests to each nesting female and 0.64 nests for every crawl.
Satellite telemetry data are represented as polygons that are colored according to the number of locations and the composition of species they contain. Darker colors represent a higher number of locations, which can indicate that a high number of tracked turtles were present in that location or that turtles spent a lot of time in that location. Telemetry data are displayed as given by the providers, with minimal processing to remove locations on land and visual outliers. As such, some tracks are raw Argos or GPS locations, whereas others have been more extensively filtered or modeled.
The maps on the upper left, “Regional Management Units,” show the two Regional Management Units (or subpopulations) that primarily reside within the Mediterranean Sea. They were defined by Wallace et al. in 2010 by combining telemetry, genetics, tagging, and nesting data. Newer data have shown a wider range for green turtles into the southwestern Mediterranean that is not captured in the boundary of that Regional Management Unit. We are grateful to all of the data contributors and projects that participated in this effort—please see the complete data citations here for details.
Biogeography of Sea Turtles in the Mediterranean Sea (data citations) | SWOT Report, vol. XIV (2019).
This article originally appeared in SWOT Report, vol. 14 (2019). Click here to download the complete article as a PDF.