Sea Turtle Conservation in Greece

A preserved female turtle

This is very late in coming, but here are some interesting turtle facts that I have learned during my time with the Katelios Group and ARCHELON! First of all, there are 7-8 species of sea turtle in the world; the discrepancy in classification arose because some scientists consider the Green (Chelonia mydas) and Black (Chelonia agassizii) turtle to be the same species, while others think they are not. All species of sea turtle are classified as endangered on the World Conservation Union (IUCN) Red List. Only three species of sea turtle are found in the Mediterranean: the Loggerhead (Caretta caretta), Green (Chelonia mydas) and Leatherback (Dermochelys coriacca). The Leatherback is a visiting species that nests in the Atlantic, while the Green turtle nests in the Eastern Mediterranean and the Loggerhead nests primarily in Greece.

Sea turtles are highly migratory and travel long distances between nesting seasons. Sea turtles tagged in Greece have been found as far away as Libya and Tunisia during the winter months. Males and females begin to mate in late April through to early June. Mating sometimes occurs during migration back to nesting beaches but most often sea turtles will mate once they reach the coast where they nest. A female sea turtle will mate with more than one male and she has the capacity to store the sperm, which she uses to individually fertilize her eggs when she wants. This increases the diversity of the turtle population by maximizing the gene pool.

A replica of a turtle's nest

Once nesting season begins in late May or early June, female Loggerheads come onto the beach and lay nests between 20-50 cm deep with an average number of eggs between 100-120 although nests have been found with more or less. Female sea turtles can lay up to five nests per season with an interval between nests of approximately 2 weeks. Once the female lays her eggs, she returns to the sea and never sees her nest again. Male Loggerheads never return to the beach after they hatch.

Since sea turtles are reptiles, they have what is called “Temperature Dependant Sex Determination” or TSD. This means that the sex of a turtle is not defined when the female lays her eggs, but rather is determined by the temperature of the sand during the incubation period (between 50-60 days although nests in the beginning and end of the nesting season can incubate for up to 80 days) and can fluctuate in the early stages. Warm temperatures yield female turtles while cool temperatures yield males.

A close-up of a metal tag

Once a nest hatches, there is usually a hatching success rate of 80%. The eggs that don’t hatch are usually unfertilized, although some eggs don’t make it through the gestation period due to genetic mutations and some eggs hatch but the hatchlings die while still in the nest. Usually, hatchlings will engage in cooperative digging once they hatch. This means that hatchlings will wait in the nest until a few eggs have hatched and then they will all make their way to the surface together, where they wait until they detect a drop in temperature, which alerts them that it is safe and cool enough to make their way to the sea.

The long tail on a male Loggerhead turtle

It takes about 20 years for hatchlings to reach sexual maturity and during that time they grow from 4 cm and 16 grams to an average length of 1 meter and 110-140 kg.  During their juvenile years, birds predate Loggerheads when they come to the surface for air as do large fish, sharks and there are major threats from boats and fishing nets. This is why only 1 or 2 in 1000 sea turtles (approximately) reaches sexual maturity. It is really hard to tell the sex of a sea turtle before it reaches sexual maturity. However, once it does, males have a long, large tail and two long claws on their front flippers, which help them grab onto the females during mating. Female turtles have short tails and very small from claws.

The long front claw of a male Loggerhead turtle

Loggerheads are the omnivores of sea turtles and will eat anything they find available from sea grass to fish and jellyfish although their “favorite” food seems to be crustaceans. The Loggerhead has the capacity to dive up to 200 m deep and hold its breath for hours; sea turtles have been observed to sleep for 8 hours underwater. Their ability to hold their breath for such extended periods of time is attributed to their lack of a diaphragm (making inhaling and exhaling active) and the fact that their heart is divided into two atria and one ventricle, which causes “incomplete double circulation” and allows high levels of carbon dioxide in the blood.

A lot of the information and facts here have been taken from:

Turtle Facts, A publication of ARCHELON the Sea Turtle Protection Society of Greece (Third Edition), 2004