Olive Ridley Sea Turtle

The olive ridley sea turtle may have been first described as Testudo mydas minor by Georg Adolf Suckow in 1798. It was later described and named Chelonia multiscutata by Heinrich Kuhl in 1820. Still later, it was described and named Chelonia olivacea by Johann Friedrich von Eschscholtz in 1829. The species was placed in the subgenus Lepidochelys by Leopold Fitzinger in 1843. However, the origin of "ridley" is unknown, perhaps derived from "riddle". Lepidochelys is the only genus of sea turtles containing more than one extant species: L. olivacea and the closely related L. kempii (Kemp's ridley).

The olive ridley turtle has a circumtropical distribution, living in tropical and warm waters of the Pacific and Indian Oceans from India, Arabia, Japan, and Micronesia south to southern Africa, Australia, and New Zealand. In the Atlantic Ocean, it has been observed off the western coast of Africa and the coasts of northern Brazil, Suriname, Guyana, French Guiana, and Venezuela. Additionally, the olive ridley has been recorded in the Caribbean Sea as far north as Puerto Rico. A female was found alive on an Irish Sea beach on the Isle of Anglesey, Wales, in November 2016, giving this species its northernmost appearance. It was taken in by the nearby Anglesey Sea Zoo, while its health was assessed. A juvenile female was found off the coast of Sussex in 2020. The olive ridley is also found in the eastern Pacific Ocean from the Galápagos Islands and Chile north to the Gulf of California, and along the Pacific coast to at least Oregon. Migratory movements have been studied less intensely in olive ridleys than other species of marine turtles, but they are believed to use the coastal waters of over 80 countries. Historically, this species has been widely regarded as the most abundant sea turtle in the world. The population of Pacific Mexico was estimated to be at least 10 million prior to the era of mass exploitation. More recently, the global population of annual nesting females has been reduced to about two million by 2004, and was further reduced to 852,550 by 2008. This indicated a dramatic decrease of 28–32% in the global population within only one generation (i.e., 20 years).

Olive ridley turtles exhibit two different nesting behaviours: solitary nesting (the most prevalent) and synchronized mass nesting, termed arribadas. 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 occur at Nancite and Ostional beach, and a third arribada beach seems to be emerging at Corozalito. Two active arribada beaches are located in Nicaragua, Chacocente and La Flor, with a smaller arribada beach of unknown status on the Pacific coast of Panama. Historically, arribadas happened at several beaches in Mexico, but in the present arribadas are only observed at Playa Escobilla and Morro Ayuda in Oaxaca, and Ixtapilla in Michoacan.

Some of the olive ridley's foraging grounds near Southern California are contaminated due to sewage, agricultural runoff, pesticides, solvents, and industrial discharges. These contaminants have been shown to decrease the productivity of the benthic community, which negatively affects these turtles, which feed from these communities. The increasing demand to build marinas and docks near Baja California and Southern California are also negatively affecting the olive ridleys in these areas, where more oil and gasoline will be released into these sensitive habitats. Another threat to these turtles is power plants, which have documented juvenile and subadult turtles becoming entrained and entrapped within the saltwater cooling intake systems.

Mating is often assumed to occur in the vicinity of nesting beaches, but copulating pairs have been reported over 1,000 km from the nearest beach. Research from Costa Rica revealed the number of copulating pairs observed near the beach could not be responsible for the fertilization of the tens of thousands of gravid females, so a significant amount of mating is believed to have occurred elsewhere at other times of the year. Beach fidelity is common, but not absolute. Nesting events are usually nocturnal, but diurnal nesting has been reported, especially during large arribadas. Exact age of sexual maturity is unknown, but this can be somewhat inferred from data on minimum breeding size. For example, the average carapace length of nesting females (n = 251) at Playa Nancite, Costa Rica, was determined to be , with the smallest recorded at . Females can lay up to three clutches per season, but most only lay one or two clutches. The female remains near shore for the internesting period, which is about one month. Mean clutch size varies throughout its range and decreases with each nesting attempt. A mean clutch size of 116 (30–168 eggs) was observed in Suriname, while nesting females from the eastern Pacific were found to have an average of 105 (74–126 eggs). The incubation period is usually between 45 and 51 days under natural conditions, but may extend to 70 days in poor weather conditions. Eggs incubated at temperatures of produce only females; eggs incubated at or less produce solely males; and incubation temperatures of produce a mixed-sex clutch. Hatching success can vary by beach and year, due to changing environmental conditions and rates of nest predation.

The olive ridley is predominantly carnivorous. Common prey items include tunicates (salps and sea squirts), starfish, sea urchins, bryozoans, squid, bivalves, snails, barnacles, shrimp, crabs, rock lobsters, and sipunculid worms. Additionally, consumption of jellyfish and both adult fish (e.g. Sphoeroides) and fish eggs may be indicative of pelagic (open ocean) feeding. The olive ridley is also known to feed on filamentous algae in areas devoid of other food sources. Captive studies have indicated some level of cannibalistic behavior in this species.

within the Maldives]] Known predators of olive ridley eggs include raccoons, coyotes, feral dogs and pigs, opossums, coatimundi, caimans (Caiman, Paleosuchus), ghost crabs, and the sunbeam snake. On land, nesting females may be attacked by jaguars. Notably, the jaguar is the only cat with a strong enough bite to penetrate a sea turtle's shell, thought to be an evolutionary adaption from the Holocene extinction event. In observations of jaguar attacks, the cats consumed the neck muscles of the turtle and occasionally the flippers, but left the remainder of the turtle carcass for scavengers as most likely, despite the strength of its jaws, a jaguar still cannot easily penetrate an adult turtle's shell to reach the internal organs or other muscles. In recent years, increased predation on turtles by jaguars has been noted, perhaps due to habitat loss and fewer alternative food sources. Sea turtles are comparatively defenseless in this situation, as they cannot pull their heads into their shells like freshwater and terrestrial turtles. Females are often plagued by mosquitos during nesting. Humans are still listed as the leading threat to L. olivacea, responsible for unsustainable egg collection, slaughtering nesting females on the beach, and direct harvesting adults at sea for commercial sale of both the meat and hides. In addition, entanglement and ingestion of marine debris is listed as a major threat for this species. Coastal development, natural disasters, climate change, and other sources of beach erosion have also been cited as potential threats to nesting grounds. Hatchlings which use light cues to orient themselves to the sea are now misled into moving towards land, and die from dehydration or exhaustion, or are killed on roads. The greatest single cause of olive ridley egg loss, though, results from arribadas, in which the density of nesting females is so high, previously laid nests are inadvertently dug up and destroyed by other nesting females. In some cases, nests become cross-contaminated by bacteria or pathogens of rotting nests. For example, in Playa Nancite, Costa Rica, only 0.2% of the 11.5 million eggs produced in a single arribada successfully hatched. Although some of this loss resulted from predation and high tides, the majority was attributed to conspecifics unintentionally destroying existing nests. The extent to which arribadas contribute to the population status of olive ridleys has created debate among scientists. Many believe the massive reproductive output of these nesting events is critical to maintaining populations, while others maintain the traditional arribada beaches fall far short of their reproductive potential and are most likely not sustaining population levels. In some areas, this debate eventually led to legalizing egg collection.

Historically, the olive ridley has been exploited for food, bait, oil, leather, and fertilizer. The meat is not considered a delicacy; the egg, however, is esteemed everywhere. Egg collection is illegal in most of the countries where olive ridleys nest, but these laws are rarely enforced. Harvesting eggs has the potential to contribute to local economies, so the unique practice of allowing a sustainable (legal) egg harvest has been attempted in several localities. Numerous case studies have been conducted in regions of arribadas beaches to investigate and understand the socioeconomic, cultural, and political issues of egg collection. Of these, the legal egg harvest at Ostional, Costa Rica, has been viewed by many as both biologically sustainable and economically viable. Since egg collection became legal in 1987, local villagers have been able to harvest and sell around three million eggs annually. They are permitted to collect eggs during the first 36 hours of the nesting period, as many of these eggs would be destroyed by later nesting females. Over 27 million eggs are left unharvested, and villagers have played a large role in protecting these nests from predators, thereby increasing hatching success. Most participating households reported egg harvesting as their most important activity, and profits earned were superior to other forms of available employment, other than tourism. The price of Ostional eggs was intentionally kept low to discourage illegal collection of eggs from other beaches. The Ostional project retained more local profits than similar egg-collection projects in Nicaragua, but evaluating egg-harvesting projects such as this suffers from the short timeline and site specificity of findings. In most regions, illegal poaching of eggs is considered a major threat to olive ridley populations, thus the practice of allowing legal egg harvests continues to attract criticism from conservationists and sea turtle biologists. Plotkin's Biology and Conservation of Ridley Sea Turtles, particularly the chapter by Lisa Campbell titled "Understanding Human Use of Olive Ridleys", provides further research on the Ostional harvest (as well as other harvesting projects). Scott Drucker's documentary, Between the Harvest, offers a glimpse into this world and the debate surrounding it.

]] The olive ridley is classified as vulnerable according to the International Union for Conservation of Nature and Natural Resources, and is listed in Appendix I of CITES. These listings were largely responsible for halting the large-scale commercial exploitation and trade of olive ridley skins. In March 2023, in Honnavar, India, local fishers sighted 86 sea turtle nests, with over 5,000 eggs in them, along a 3-km stretch of beach between Apsarakonda and Pavinkorava. The highest number of nests previously recorded in the area, 34, was in 2008.