ITS–The olive ridley sea turtle (Lepidochelys olivacea), also known as the Pacific ridley, is a species of sea turtle. The olive ridley is a small extant sea turtle, with an adult carapace with a length averaging 60 to 70 cm. Its heart shaped carapace is characterized by four pairs of pore bearing inframarginal scutes on the bridge, two pairs of prefrontals, up to nine lateral scutes per side. Olive ridleys are unique in that they can have a variable and asymmetrical lateral scute count ranging from five to nine plates on each side, with six to eight being the most commonly found. Each side of the carapace has 12–14 marginals. The carapace is flattened dorsally and highest anterior to the bridge. It has a medium–sized, broad head that appears triangular in planar view. Its head has concaved sides, most obvious on the upper part of its short snout. It has paddle like forelimbs, each having two anterior claws. The upperparts are gray-green to olive in colour, but sometimes appear red due to algae growing on the carapace. The bridge and hingeless plastron of an adult varies from green to white (younger) to a creamy yellow on older specimens.
Hatchlings are dark gray with a pale yolk scar, but appear all black when wet. The Carapaces length ranges from 37–50mm. A thin white line borders the carapace, as well as the trailing edge of the fore and hind flippers. Both hatchlings and juveniles have serrated posterior marginals, which become smooth with age. Juveniles also have three dorsal keels; the central longitudinal keel gives younger turtles a serrated profile, which remains until sexual maturity is reached.
Olive ridleys rarely weigh over 50 kilograms. A study in Oaxaca, Mexico reported an adult sample ranging from 25 to 46 kilograms. Adult females weighed an average of 35.45 kg (n=58), while adult males weighed significantly less averaging 33.00 kg (n=17). Hatchlings usually weigh between 12.0 to 23.3 grams. Adults are somewhat sexually dimorphic. Mature males have a longer and thicker tail than females, which is used for copulation. The presence of an enlarged and hooked claw on the front flipper of males allows them to grasp the female carapace during copulation. Males have a longer, tapered carapace than females, which have a round, dome like carapace. Males also have a more concave plastron, believed to be another adaptation for mating. The plastra of males may also be softer than the females.
Olive ridley turtles are best known for their behavior of synchronized nesting in mass numbers, termed arribadas. In the Indian Ocean, the majority of olive ridleys nest in two or three large bundles near Gahirmatha in the Orissa. In 1991, over 600,000 turtles nested along the coast of Orissa in one week. Nesting occurs elsewhere along the Coromandel Coast and Sri Lanka, but in scattered locations. However, olive ridleys are considered a rarity in most areas in the Indian Ocean. They are also rare in the western and central Pacific with known arribadas occurring only within the tropical eastern Pacific, in Central America and Mexico. In Costa Rica, they are found at the Nancite and Ostional beaches. There are two active arribadas in Nicaragua; Chacocente and La Flor; and a small nesting ground in Pacific Panama. Historically, there were several arribadas in Mexico, yet only one remains at Playa Escobilla in Oaxaca.
Although olive ridleys are famed for their arribadas, many of the nesting grounds can only support relatively small to moderate-sized aggregations (e.g. 1,000 nesting females). The overall contribution and importance of these nesting beaches to the population may be underestimated by the scientific community.