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 huge numbers until the recent past. They have evolved from large, land-living tortoise-like animals. Their body consists of a head, a short neck, a pair of long fore-flippers & a pair of short and rounded hind flippers, and a tail. The upper carapace and lower plastron make a protective structure (box) for internal organs. Unlike tortoises and freshwater terrapins, sea turtles cannot withdraw their head and limbs into their box. Instead of teeth, sea turtles have beak-like sharp jaws that can crush, tear or bite their prey and food items which vary 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 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 ‘’sunbathing’’ 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. Time taken for sexual maturity depends on species. Olive Ridley Turtle, the smallest, takes 7 to 15 years, while herbivorous Green Turtle might take 50 years! The remaining 3 species including the largest Leatherback Turtle take 20 to 30 years. 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 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 the 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 Dermochelyidea remain. All of them are now threatened with extinction due to man’s destructive activities.
Incubation and hatchling behavior
Mother turtles do not care for their young like crocodiles and some other reptiles. Instead, once the eggs are laid the female turtle does not have any further contact with the nest and the eggs are left to incubate by the heat of the surrounding sand that is warmed by the sun. After an incubation period of about 60 days the young turtles or ‘’hatchlings’’ begin to break out of their shells and move about in the nest. After a further 2 days, most of the eggs will have hatched. The movement of all the hatchlings causes sand from the roof and sides of the nest to fall down to the floor and form a platform. This platform rises as more sand falls and the hatchlings are pushed to the surface with an ‘’elevator-like’’ movement. The hatchlings emerge from the nest at night when it is cooler and they are less conspicuous to predators.
This is a particularly dangerous time for the young turtles as there may be many predators such as rats, crabs, dogs, and in the morning, birds. Therefore, they immediately and rapidly crawl towards the brightest, lowest horizon, which under natural conditions is the reflection of the moon and stars on the sea. But even those hatchlings that reach the water are not out of danger. The inshore waters are home to many sharks, large fish, and seabirds. As soon as they reach the sea, hatchlings swim constantly for about 48hours. During this time they do not feed. Instead, they rely on the remains of the egg yolk in their stomachs for nutrition. This is known as the “juvenile frenzy’’ and is an essential behavior that allows the hatchlings to escape the predator-rich inshore waters and be carried away by the open ocean currents. Once they reach these currents, they start feeding on tiny, floating sea animals. Not much is known about their first year, also known as the ‘’lost year’’. It is believed, that when the female turtles reach maturity they will return to their nest on the same beach where they themselves hatched. It has been estimated that under natural conditions only one in a thousand eggs survive eventually to become mature adult turtles.