The olive ridley is the smallest of all the sea turtle species. It gets its name from the olive green colouration of its carapace (shell). Olive ridleys are known for their arribadas or synchronised mass nesting during which time tens of thousands of female ridleys come ashore to nest in the span of a few days. And when the eggs hatch, millions of olive ridley turtle hatchlings emerge and return to the sea.
An adult typically measures between 62 and 70 cm in length and weighs about 35-45 kg. It has a smaller head and smaller shell than the Kemp’s ridley, to which it is closely related. Both the front and rear flippers of an adult ridley have 1 or 2 visible claws. There is sometimes an extra claw on the front flippers. Juveniles are charcoal grey in colour, while adults are a dark greyish green. Hatchlings are mostly grey (and black when wet) with a greenish hue on the sides.
Track marks are about 70 -80 cm wide, are light and have asymmetrical, oblique marks that are made by forelimbs. There is no tail drag mark or is mostly inconspicuous.
Olive ridley turtles have powerful jaws which enable them to feed on a variety of crustaceans such as shrimp and crabs, molluscs, tunicates and fish.
These turtles nest solitarily and in arribadas, sometimes twice in each season. Arribadas may be precipitated by such climatic events as a strong offshore wind, or by certain phases of the moon and tide, but there is a major element of unpredictability at all arribada sites. This unpredictability and the apparent ability of gravid females (distended with or full of eggs) to wait for weeks while holding fully-shelled eggs, may be an important aspect of the survival advantage of arribada-formation, a phenomenon usually interpreted as one that evolved as a predator-saturation device.
Orissa houses the world’s largest mass nesting sites for the olive ridley turtle. The turtles mate in offshore waters during the breeding season, from October to February. Reproductive aggregations or patches occur off the mass-nesting beaches, and are between 50 and 60 sq. km in size. After successful mating, males return to their feeding grounds. The females come on to the beach to nest. Females nest every year, and often more than once in a season. Clutch sizes are usually about 100 to 120 eggs per nest and eggs measure about 4 cm in diameter. The eggs hatch after 45 to 50 days of incubation after which the hatchlings emerge and find their way to the ocean. Hatchlings weigh less than 30g and measure about 3.8 cm in length. Once hatchlings reach the sea, they are carried by currents across ocean basins for several years till they move to nearshore developmental habitats, and eventually to adult feeding grounds.
Olive ridleys are the most abundant of sea turtle species in the world. They are generally found in coastal bays and estuaries and can be very oceanic over some parts of their range. They typically forage offshore in surface waters or dive to depths up to 150 m. to feed on bottom dwelling crustaceans. Olive ridleys inhabit tropical and subtropical waters of the Pacific, Indian and Atlantic Oceans.
In the Indian Ocean, Gahirmatha located in the Bhitarkanika Wildlife Sanctuary, India, supports perhaps the largest nesting population with an average of 398,000 females nesting in a given year. This population continues to be threatened by nearshore trawl fisheries.
Olive ridleys are found throughout the mainland and in the Andaman and Nicobar Islands and to a lesser extent in the Lakshadweep Islands. In the Andaman and Nicobar Islands, olive ridley and leatherback turtles often share nesting beaches, while hawksbill and green turtles share beaches.
The olive ridley is very oceanic in the Eastern Pacific and probably elsewhere too. Large arribadas of olive ridleys still occur in Pacific Costa Rica, primarily at Nancite and Ostional and Pacific Mexico at La Escobilla, Oaxaca.
Olive ridleys have been internationally categorised as an endangered species. The direct harvest of adults and eggs, incidental capture in commercial fisheries and loss of nesting habitat are the main threats to this species. In India, olive ridleys were taken in tens of thousands for the markets of West Bengal in the late 1970s and early 1980s, after the advent of mechanization in the fishing sector. This declined after the implementation of the Indian Wildlife (Protection) Act, 1972 enforced by the forest department and coast guard. It has been listed as a Schedule I species in the Act, thereby being offered maximum protection. However, rapid development of Orissa’s coastline threatens one of the only three arribadas that occur in the world. Nesting and nearshore habitats of ridleys in other parts of the subcontinent also face mounting threats, although these sites tend to receive less attention.
Indian Wildlife (Protection) Act: Schedule I
IUCN Red list: Vulnerable (http://www.iucnredlist.org/apps/redlist/details/11534/0)