Marine Turtles in Sri Lanka

Introduction

Marine Turtles are a successful group of animals that have witnessed the rise and fall of the dinosaurs. They have inhabited the earth for over 100 million years and survived in great numbers until recent past. They have evolved from large, land living tortoise-like animals. Their body consists of a head, short neck, pair of long fore flippers, pair of short and rounded hind flippers and a tail. Upper carapace and lower plastron make a protective structure (box) for internal organs. Unlike tortoises and freshwater terrapins they are unable to withdraw their head and limbs into their shell. Marine turtles do not have teeth but their sharp, beak-like jaws can crush, tear or bite depending on their diet, which varies according to species.Turtles are reptiles (Class: Reptilia, Order: Chelonia) hence cold-blooded animals. Therefore, the environment determines their body temperature. In the morning, marine turtles "sunbathe" at the surface of the sea to increase their body temperature. They have lungs to breathe air. Turtles rise to the surface to breathe every 5 - 30 minutes. Over millions of years they have become very well adapted to living in a marine environment. With their long and muscular oar-like fore flippers, rudder-like hind flippers and their flattened, streamlined shells, marine turtles are fast and agile swimmers.

The only time marine turtles leave the ocean is when the females come ashore to nest. In some areas they can be seen having their "sunbathe" on beaches or rocks. The males spend all their time at sea and little is known about their habits. Most species are highly migratory, moving between nesting and feeding grounds, which can be thousands of kilometers apart. We do not know exactly how long turtles live, but they are generally assumed to have a life span greater than 80 years. It is thought that marine turtles reach sexual maturity between 15 - 50 years of age depending on the species. Until maturity it is difficult to distinguish between male and female turtles. When they reach maturity, male turtles develop a long claw on each fore flipper and a long tail. The way that an egg-burdened female finds her way to her nesting beach is still a mystery! Some scientists believe that marine turtles are sensitive to earth's magnetic field and use it for navigation. They are often found using not only the same sandy beach but also the very same stretch of beach they used in previous years. Hybrids and Albino specimens could be seen among the marine turtle species. Today seven species of these ocean dwelling reptiles representing two families, Cheloniidae and Dermochelyidae remain. All of them are now threatened with extinction due to man's destructive activities.

Species of marine turtles found in Sri Lanka

Loggerhead Turtle (Caretta caretta):

Loggerheads grow to 1 meter in length and weigh up to 180 kg This species nests on tropical beaches and also on beaches in some temperate locations such as the Mediterranean and the South-East coast of the U.S.A. Although this species is one of the commonest species in the world, it is the most rare nesting species in Sri Lanka. From the Indian sub continent, they only nest in Sri Lanka and they show unique colouration suggesting a unique population with unique genes. Therefore, it is very important to take immediate conservation measures to protect the Loggerhead turtles in Sri Lanka. Loggerheads are primarily carnivorous and feed on mollusks and crustaceans. The name "Loggerhead" refers to the large head which accommodates a large, muscular set of jaws, ideal for crushing mollusks and crustaceans. Loggerhead turtles are now considered as "Endangered".

Green Turtle (Chelonia mydas):
Green turtles have an average length of 1 metre and can weigh up to 230 kg. They are migratory and can be found in all tropical and sub-tropical seas such as the Indian, Atlantic, Caribbean and Pacific Oceans. Green turtles are caught and killed to make "turtle soup" which is a delicacy in many parts of the world. Their English name refers to the colour of the fat found under their shells, which is used to make the soup. Young green turtles are mainly carnivorous. The adults however are herbivorous, feeding only on marine vegetation such as sea grass and marine algae. . Green turtles are considered as "Endangered" species today.

Leatherback Turtle (Dermochelys coriacea):

The Leatherback turtle is the largest of all the marine turtles . They can grow more than 2 metres in length and usually weigh about 500 kg. The largest Leatherback ever found weighed 916 kg! They have a predominant dorsal black colour with variable degrees of white or paler spotting. Spots may be pinkish on the neck. Leatherbacks feed exclusively on jellyfish and will travel long distances in search of their prey. They have been seen feeding on jellyfish in the waters of Arctic Circle. Leatherbacks can survive in the extreme cold because, unlike other turtles, they can regulate their own body temperature because layers of fatty tissue insulate their bodies. The English name "Leatherback" refers to their unique carapace. Leatherback turtles can dive to depths of 1500 metres in search of deep-sea jellyfish. At these depths the Leatherback's body is subjected to tremendous water pressure, but its flexible shell does not break and so the turtle can feed safely. Today, Leatherback turtles are considered as "Critically Endangered".

Olive Ridley Turtle (Lepidochelys olivacea):

The Olive Ridley turtle is the smallest of the marine turtles. The adults weigh less than 40 kg and measure up to 65 cm in length. They are found mostly in the tropical Indian, south Atlantic and Pacific Oceans. They are omnivorous, eating crustaceans, fish and some marine vegetation . Olive Ridley turtles are considered as "Endangered" species today. Arribada - In a few countries, Olive Ridley turtles nest on a beach in a huge congregation known as an "arribada". This Spanish word means "the arrival". For example, in India, 600,000 Olive Ridley turtles have been recorded nesting on the same beach over a period of a few weeks. Despite the apparently large populations Olive Ridley turtles are endangered. This is because so many individuals of this species depend on the security of a small number of important beaches for nesting.

Hawksbill Turtle (Eretmochelys imbricata):

Hawksbills are also relatively small turtles; adults commonly weigh about 60 kg and measure up to 90 cm. They inhabit tropical coastal waters around coral reefs and are mostly carnivorous. They prey on a large variety of animals including jellyfish, sponges and crustaceans. The Hawksbill turtle gets its English name from its narrow birdlike beak, which it uses to catch animals hiding in small crevices. Hawksbill turtles sometimes eat toxic sponges. Instead of being poisoned, Hawksbills can actually store the toxins in their own flesh. If a human eats the flesh of a Hawksbill turtle he can die from acute food poisoning. The Hawksbill turtle is now highly endangered because for centuries, people around the world have killed them for their shell. Once cleaned and polished, the shell is crafted into "tortoiseshell" ornaments. Today, Hawksbill turtles are considered as "Critically Endangered".

Turtle Nesting Beaches in Sri Lanka

Turtle hatching can be seen in the coastal area from Mt. Lavinia to Galle and Tangalle to Arugam bay.

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Threats To Marine Turtles

1. Natural Threats
   
2. Killing for Their Meat
3. Killing for Shell
4. Egg Collection
5. Turtle by-catch
6. Non-Scientific turtle hatchery practices
7. Habitat Destruction
8. Coral mining
9. Beach erosion
10. Beach front development
11. Marine pollution

Conservation Of Marine Turtles

Both in-situ and ex-situ conservation programmes are used for the conservation of marine turtles in the world today

Resource : Turtle Conservation Project