(Caretta caretta )

Note: This section is taken from Ali Fuat Canbolat, Ph.D’s book entitled “Biology, Conservation and Management of Caretta caretta in Belek Tourism Area” without any modification.

Most scientists count 8 species of sea turtles  (Dermochelys coriacea, Eretmochelys imbricata, Lepidochelys kempii, Lepidochelys olivacea, Chelonia mydas, Chelonia agassizi, Natator depressus, Caretta caretta) living on earth today. Five of these species (Caretta caretta, Chelonia mydas, Dermochelys coriacea, Eretmochelys imbricata and Lepidochelys kempii) are found in the Mediterranean. However, the only species nesting regularly in the Mediterranean are Caretta caretta and Chelonia mydas (Groombridge, 1990).

Systematic, Morphology and Distribution

The systematic place of Caretta caretta is as follows:

Phylum- Chordata

   Subphylum- Vertebrata

      Superclass- Tetrapoda

         Class- Reptilia

            Subclass- Anapsida

               Order- Testudines

                  Suborder- Cryptodira

                     Superfamily- Chelonioidae

                        Family- Cheloniidae

                           Genus- Caretta

                              Species- Caretta caretta (Linnaeus 1758)

Carapace is heart shaped and somewhat tapered posteriorly in adult individuals, with a length of 70-75 cm and width of 50-55 cm (for Turkey) The head is relatively large and triangular in shape. General colouration is reddish-brown dorsally and yellowish-white ventrally. Their distinctive characteristics from the other sea turtle species are as follows:

A very strong and hard shell, two pairs of prefrontal scutes between the eyes and nostrils (there might be a fifth scute in the middle of the these other four scutes in some individuals), five pairs of costal scutes on the carapace, three large pairs of inframarginal scutes on the plastron reaching carapace, two claws on each flipper and typical brownish-red colouration.

The distribution of Caretta caretta includes the coastal parts of lagoons, bays, estuaries and the seas in the temperate and subtropical waters of the Atlantic Indian and Pacific Oceans. One of their major nesting areas is Masirah Island of Oman (Ross and Barwani, 1982). Another nesting area that hosts a considerable ratio of the population is in Florida (Dodd, 1988). The major nesting areas of Caretta caretta in the Mediterranean include the coasts of Greece and Turkey. A lower ratio of the population can also be seen in Cyprus. Nesting in Tunus is very rare and it is much less in Israel. There is occasional nesting in Lampedusa (Italy), Sicily and even in Sardinia. Data for Egypt and Libya is not sufficient (Groombridge, 1990). The nesting areas of Caretta caretta in Turkey are Ekincik, Dalyan, Dalaman, Fethiye, Patara, Kumluca, Belek, Kızılot, Demirtaş, Gazipaşa, Anamur and Göksu Delta (Baran and Kasparek, 1989).

Caretta caretta is bisexual and sexual dimorphism is apparent in the adults. Size dimorphism between the sexes cannot be demonstrated clearly. However, males are known to have a longer tail than the females (3:1) and longer claws curved backwards. Sexual distinction of hatchlings, juveniles and sub-adults is not possible via external examination. 

According to Caldwell (1962) and Uchida (1967), estimated age of maturity for Caretta caretta raised in captivity averages about 6-7 years (Nelson, 1988). Studies of wild turtles gave estimates for the age of maturity as 10-15 years according to Mendonca (1981), 14-19 years according to Zug et al. (1983), 22 years according to Frazer (1983) and 12-30 years with the data obtained from the curves of Frazer and Ehrhart (1985)'s study (Nelson, 1988).

Mating of C. caretta occurs along the way to the nesting beach for several weeks prior to the onset of nesting, or in specific aggregation areas. Mating pairs are frequently seen at the surface, although there are reports of submerged copulations (Dodd, 1988 according to Limpus, 1985).

Nesting season in the northern hemisphere is generally from May through August, and it is from October through March in the southern hemisphere. Laying eggs usually takes place at night. However, nesting during daytime can rarely be seen.  The female while approaching the beach to lay eventually raises her head to view the beach. At this stage, the turtle is most sensitive to disturbance and will rapidly turn back and swim away in case of any danger. The female then crawls onto the beach and starts seeking for a suitable spot to lay her eggs. In some instances, the female will wander over considerable distances before nesting or returning back to the sea. A body pit to hide the carapace is usually dug shallowly in sand. Although fore flippers are not used much in nesting process, rear flippers work alternately. One rear flipper digs while the other sweeps away the deposited sand preventing it from tumbling back into the chamber. Following this procedure, the egg chamber is complete. Eggs are dropped singly or in lumps of two or three. While laying eggs, the female is not as sensitive to disturbance. When the female finishes depositing eggs, the eggs are gently covered with the moist sand dug out beforehand and the sand is pressed with the help of rear flippers. Finally, the front flippers begin to throw sand backwards as the turtle slowly moves forward, forming a camouflaged area to hide the egg chamber. After this is completed, the female returns rapidly to the sea.

The emergence of females may result with a nest (nesting emergence) or not (non-nesting emergence). Evaluation of such results might provide important clues about the appropriateness of the beach for nesting and the environmental factors. 

Sea turtles generally nest every 2-3 years. They may also nest more than once in one nesting season. The interval between two nesting in the same season is about 2 weeks.

Freshly laid sea turtle eggs are generally spherical and white, with soft leathery shells coated with a mucous secretion. Sea turtles' eggs are approximately the size of a ping-pong ball (about 40mm in diameter and 40grams). The clutch size in a nest is approximately 100 and the incubation period lasts for 1.5-2 months. 

Predation on sea turtle eggs might be caused by ghost crabs, gulls, racoons, pigs, foxes and stray dogs. Additional mortality during the egg phase may be due to wind erosion, wave erosion, sand lifting and off-road vehicles crushing nests.

After hatching, hatchlings lie still for up to 26 hours to allow their carapaces to straighten. Hatchlings leave the nest in 1-7 days (2,5 days average) after hatching by helping each other to scramble toward the surface (Dodd, 1988 according to Demmer, 1981 and Miller, 1982). Most emergence occur at night when sand temperature decrease. In some cases, hatchlings may not emerge all at the same time and emergence continues in subsequent nights. Hatchlings leaving their nests orient towards the sea by moving towards the brightness of the horizon and the reflection of the moon on the water’s surface. Any artificial lighting behind the beach meanwhile can disorient hatchlings and lead to extensive mortality. Once in the water, the hatchlings swim virtually non-stop for about 20 hours as a result of a phenomenon called the "swimming frenzy" (Salmon and Wyneken, 1987).

Hatchling mortality is assumed to be substantial after emergence and during the first few days of swimming. Ghost crabs, foxes, dogs, racoons, near-shore fishes and sharks are among their major predators. Besides natural predators, hatchlings are exposed to additional mortality resulting by the disorienting effect of beach lights (Dodd, 1988).

There is no life span estimate for C. caretta living in the wild. However, the reproductive life span of adult females is estimated to be 32 years (Frazer, 1983) and time to reach the age of maturity is estimated to be 15-30 years (Frazer, 1986). Under these conditions, the maximum female life span would be 47-62 years (Dodd, 1988).

Hatchling and juvenile C. caretta individuals feed on macroplanktonic prey concentrated in drift lines at the surface (Carr, 1987). The adult Caretta caretta's are primarily carnivorous, feeding on a wide variety of food items including especially molluscs. The large head, strong horny beak and well-developed jaw muscles seem particularly well adopted for crushing hard-shelled prey. 

Because they mostly nest in temperate and sub-tropical regions, C. caretta are assumed to migrate between mating and wintering grounds. Little is known about the migrations of males. Group migration is not reported for C. caretta. They may remain year round in offshore waters. In Florida, some individuals are reported to enter channels with soft bottom mud. Some populations may spend the whole year near the nesting beaches and may dwell in holes and cracks between nesting periods. There is no evidence that C. caretta form "flocks" in the classical sense. They may, however, form local concentrations in the sea or in the vicinity of nesting beaches (Dodd, 1988).

The sex ratio of the C. caretta populations has remained unknown because of the lack of information about males. There is no extensive information on the age and size composition of their populations. Henwood (1987) noted that the composition of the population also varied seasonally that further makes the determination of a population's size more complicated. As a result of the lack of information on the population structure and sex ratios as well as the uncertainty of the limits of biological population, it is very hard to make estimates on the average abundance and population density. However, crude estimates are possible regarding direct counts of nesting females or number of nests.

Factors affecting the reproductive rates of C. caretta appear to vary geographically, and there is considerable variation inside the population as well. These variations make it difficult to assess the reproductive output on specific beaches. General environmental factors prevailing during the nesting season such as heavy rain, wind erosion and temperature affect productivity. Food supply and food quality on the foraging grounds also affect reproduction in terms of the number of eggs laid. Factors affecting hatchling success of the nests are the chemical composition of the sand, moisture, temperature, gas exchange and predators. Human existence and artificial light sources on nesting beaches may disturb female sea turtles causing them to return back to the sea (Dodd, 1988).

C. caretta hatchlings are preyed upon primarily by ghost crabs, sharks, predatory osteichtyes, and a variety of mammals such as racoons, foxes and dogs. A variety of birds also feed on hatchlings that emerge during daytime. Disease, starvation and cold stunning may also cause mortality. However, their effect on particular populations is unknown. Mortality of hatchlings might also occur as a result of ingestion of tar, oil residues and plastic or Styrofoam objects. Juvenile, sub-adult and adult sea turtles are preyed upon primarily by sharks. They may also ingest tar and plastic leading to injury and death. Deaths occurring as a result of malicious hunting, accidental catching by nets and trauma associated with speedboat collisions are also reported.

C. caretta is conserved strictly under enforced prohibitions in Australia, South Africa and the United States. They may be captured wherever they are encountered throughout the year although they are not a priority for fishing industry. C. caretta meat is consumed by coastal inhabitants in India, Madagascar and Mozambique. Although meat, shell and leather of C.caretta are not precious as Chelonia mydas, Eretmochelys imbricata, Lepidochelys kempii and Lepidochelys olivacea, their eggs are consumed in several locations around the world. Usage of their eggs as a protein intake in coastal residents of Mozambique, Madagascar and Oman caused a rapid decline in their population (Dodd, 1988).

Several laws call for the protection of sea turtles, including C. caretta and their habitats via banning their hunt and purchase, as the present situation and importance of these species are slowly recognised. C. caretta is listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This convention is signed by many countries including Turkey. Commercial trade of all species in this list is banned among signatory nations. C. caretta is also listed in Annex II under the provisions of the Convention on Migratory Species. Despite the fact that they are protected under various regulatory measures and laws, incapable or unwilling manner of security watchmen as well as the differences between the economic levels of countries have seriously hampered the application of conservation and management measures. 

In order to ensure the survival of C. caretta populations, it has become a necessity to focus on all important nesting, foraging, migratory and wintering grounds besides the application of conservation measures based on biological data. Different conservation and management alternatives are applied for the conservation of sea turtles in different regions (Mrosovsky, 1983; Dodd, 1988).

As there is no great demand for C. caretta shell or leather, international trade is not improved. However, its meat and eggs are often consumed locally. Provisions of CITES may be effective in obstructing international trade. Trade within nations is controlled with varying degrees of success by laws. For instance, consumption of their eggs has been has been ceased within the United States and Australia by law. Illegal hunting, however, still continues. Complete enforced protection seems obligatory for the survival of these populations.

Female sea turtles should be kept away from any kind of disturbance as they are very vulnerable while depositing eggs, and as they carry a great importance in productivity. This can be accomplished by reducing human access to important nesting beaches and minimising the artificial lights causing disorientation during the nesting season. Nests and nesting females should also be protected from off-road vehicles accessing to nesting beaches since they may compact the sand thereby leaving deep tracks that hatchlings might fall into not being able to come out. Usage of such vehicle at night might also disturb females as they attempt to nest. Highly mechanised beach cleaning devices should either be operated on a very small scale or should not be used on the beaches during nesting season.

In regions where it is difficult to prevent poachers, predators, and erosion, freshly deposited nests may be moved to protected hatcheries where they are either reburied within a nest or kept within Styrofoam boxes filled with moist beach sand. These practices should be planned and held with great care as the method carries some certain risks.

Another method used for the conservation of the sea turtle hatchlings is to raise them to a matured stage able to protect themselves from the predators. Researchers involved with the subject advocate the need of using this method after the conservation of habitat. This method is especially preferred to increase the populations of Chelonia mydas, Eretmochelys imbricata and Lepidochelys kempii in different parts of the world.

In order to conserve sea turtle hatchlings, it is necessary to reduce predation, prevent disorientation from beach lighting, and minimize pollutants and plastic material in the water and drift lines that sea turtles might mistake for food items.

In places where mortality resulting from accidental capture by nets is in question, usage of "Turtle Excluder Devices (TED)" is a method useful for reducing the death ratio caused by fishing activities. This method is especially applied in the USA where the mortality rate caused by shrimp trawls is high.

Photographs

Photos: Ali Fuat Canbolat Ph.D