Sea turtles
Introduction.
Sea turtles belongs to the group of marine reptiles. Like other reptiles, sea turtles are cold-blooded and they breath air by using lungs. Sea turtles have a hard external shell. Though they are similar to the terrestrial tortoises they don’t have the ability to retract head or limbs into the shell. Their limbs have adapted for swimming. Forelimbs are long and they are modified into flippers. Hind limbs are short and they act as rudders in swimming.
There are seven sea turtle species in the world. They can be categorized into two families. They are;
• Cheloniidae.
• Dermochelyidae.
There are six sea turtle species in the family Cheloniidae. Key factor for this classification is that they have a hard shell. Below six species belong to the family Cheloniidae.
• Olive ridley turtle.
• Kemp’s ridley turtle.
• Green turtle.
• Loggerhead turtle.
• Flatback turtle.
• Hawksbill turtle.
Turtles belong to Dermochelyidae don’t have a hard shell. Their shell is just like a hard skin. The below species belongs to the family Dermochelyidae;
• Leatherback turtle.
From above mentioned species five species can be seen in Sri Lankan waters. They are;
• Olive ridley turtle.
• Green turtle.
• Loggerhead turtle.
• Hawksbill turtle.
• Leatherback turtle.
Sea turtles can be seen in pelagic waters to deep waters in every ocean except the polar seas. Some species have the ability to swim long distances. As an example, some species migrate from western beaches of North America to eastern beaches of Japan. They can dive about 200m during one respiratory cycle.
Food habits.
Some sea turtle species are carnivores and others are herbivores. Carnivore species feed on sponges, coelenterates, etc. and herbivore species feed on sea grasses, algae, etc. Sea turtles have strong jaws for their feeding. But leatherback turtles don’t have much strong jaws.
Reproduction.
It takes about 50 years for a sea turtle to become sexually matured. They reproduce by sexual reproduction. Their special feature is that females return to the same beach where they were born to lay eggs even they live any ocean in the world. This behavior of sea turtles was once a problem, but now recent researches found that they use magnetic fields of the earth to find their path. Sea turtles lay eggs in slightly deep pits outside the wave zone of the beach. They use their limbs to dig that pit. They come to the beaches at the night time with moonlight to lay eggs. Their eggs have a leathery shell and that is an adaptation to prevent eggs from drying out. Normally a female turtle lay about 120 eggs at once and they lay eggs three times per year. The sexuality of the eggs is not determined by genetics. It is determined by the temperature of the pit they lay eggs. Female sea turtles come out from the eggs of about 30oC-32oC temperature and male sea turtles come out from the eggs of about 27oC-29oC temperature. Normally these eggs hatch after 45-60 days of laying. This period depends on the species. It is very difficult for the baby sea turtle who dig through the soil to crawl into the sea. Most cases they are vulnerable to predators like dogs and crows during this crawling.
Threats to sea turtles.
• Loss of nesting areas due to coastal construction.
• Fearing to come ashore because of bright artificial beach lights.
• Destruction of eggs by predators.
• Predation of baby turtles after hatching.
• Died after feeding polythene that are disposed to ocean.
• Entangled in fishing nets.
• Consumption and illegal trade of eggs, meat and shells.
Conservation measures for sea turtles.
• Aware the people about the importance of sea turtles.
• Implement and make new laws regarding the conservation of sea turtles.
• Prohibit new constructions and using bright artificial lights in sea turtle nesting areas.
• Prevent the disposal of plastics and polythene to the ocean.
• Establish sea turtle conservation centres.
Sea turtle species found in Sri Lanka.
Caretta caretta
• Local name - “S-Olugedi kesbewa”, “Kannadi kesbewa”
• Size - Maximum length of the shell is 125cm.
Chelonia mydas
• Local names - “S-gal kesbewa”, “Mas kesbewa”, “Weli kesbewa”
• Size - Maximum length of the shell is 120cm.
Eretmochelys imbricata
• Local names - “S-pothu kesbewa”, “Leli kesbewa”, “Pana kesbewa”
• Size - Maximum length of the shell is 100cm.
Lepidochelys olivacea
• Local names - “S-mada kesbewa”, “Eramudu kesbewa”, “Parai
kesbewa”, “Batu kesbewa”
• Size - Maximum length of the shell is 79cm.
Dermochelys coriacea
• FAO name - En-leatherback turtle
• Local names - “S-dara kesbewa”, “Wawulkesbewa”, “Thundara
kesbewa”, “Thale kesbewa”, “Naw kesbewa”
• Size - Maximum length of the shell is 180cm.
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