The Olive Ridley Sea Turtle
Lepidochelys olivacea (Eschscholitz , 1829)

Sea turtles have evolved from land-dwelling reptiles which laid eggs and they have retained this one vital link with life on land. The female turtle comes ashore during the nesting period to dig a pit and lay a nest on a sandy beach above the high tide mark. During incubation many nests are destroyed by predators and the hatching turtles are heavily preyed upon as they enter the sea. Many are lost to predators as they grow , but with each years growth they have fewer enemies, until, when they are adults, only very large sharks can eat them. Less than one in a thousand hatchlings survive to adulthood.

The Olive Ridley is the most common turtle nesting on the Indian Coast. It is the smallest of all the sea turtles and is named for the color of its olive shaped shell. It forages off-shore in surface waters or dives to depths of atleast 150 meters to feed on bottom dwelling shrimp, crabs, sea urchins and other animals. The Ridley was once thought to be a solitary nester in the 1970's however, it was discovered that, like the kemps Ridley some populations of olive Ridley's synchronize their nesting in mass emergences or Arribadas. Tens of thousands of Olive Ridley's nest during Arribadas which continues for several nights. Today most populations have collapsed as a result of over exploitation.

The Olive Ridley is the smallest of all sea turtles , adults being about 60 - 70 cm in carapace length and weighing about 40 kg. In shape the adult is very wide-shelled, the carapace having typically sloping sides and a rather flat top. Hatchlings are uniformly charcoal gray , and immature individuals are gray dorsally and white ventrally. Adult turtles differ from hatchlings and sub-adults in their coloration ,having a dark olive or greenish dorsal surface and light yellow on the plastron and ventral aspects of the soft parts.

Adult turtles appear to migrate from long distances to shallow coastal waters to breed and generally do so in large numbers . Mating takes place on the surface of water , with males holding onto the carapaces of the females with the curved claws of their fore-limbs .Copulating pairs are often seen off nesting beaches prior to nesting .The reproductive habits of the Olive Ridley are rather distinct. The small size and Light weight of this species facilitates its utilization of flat wide beaches which are generally avoided by the heavier ones. They usually come to nest only at night , but are also seen nesting at dawn and dusk. Nesting females spend usually around 45 minutes to an hour on land.The turtle chooses a part of the beach which is free from the action of the tide and excavates a round hole about six feet in diameter called a Body Pit. It is in the body pit that they start to build their nest. A turtle may dig several body pits before building a nest . Any noise or unfamiliar movements may scare them . The nests are shallow and the eggs laid have an average diameter of 3 to 5 cm. After laying the eggs and filling up the nesting cavity , the Olive Ridley usually thumps the sand over the nesting site by means of vigorous , side to side rocking action of the shell. Nesting may occur two to three times in a season and unlike other species of turtles , nesting in successive seasons occurs quite frequently.On the Chennai coast , a clutch comprises of 80 to 160 eggs and incubation periods range between 50 and 63 days. Hatchlings measure between 3.5 centimeters to 6 centimeters.

The greatest and most obvious threat facing the Ridley's on the Chennai coast is the presence of unnatural beach lighting either onshore or off-shore. Artificial lights affect both Nesting females as well as hatchlings . There is evidence to show that females may be discouraged from nesting on heavily lit beaches. Hatchlings become disoriented and suffer high rates of mortality because of bright lights .

The most obvious form of chemical pollution in the nesting habitat is Oil . Fresh crude oil is known to cause significant mortality and morphological changes in the incubating embryos , but weathered oil may not. Untreated Industrial effluence appears to deter nesting turtles in some parts of the Chennai coast . But more research is needed to document the the lethal effects of such chemical pollutants. Eggs , embryos and hatchlings are more vulnerable than adults since volatile and water soluble contaminants can be absorbed into the egg . Both oil spills and resulting clean up operations could have harmful effects at the nesting beach.

Beaches around the world are rapidly becoming polluted by man-made debris . This debris includes light bulbs , styrofoam , plastics , tar , wood , glass cloth , fishing gear and organic wastes .Small objects like these , if abundant enough , could become incorporated into the beach sand , and ultimately alter their thermal properties or patterns of gas diffusion within it.

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