(Lepidochelys olivacea) Threatened species throughout its range, except the population on the Pacific coast of Mexico where it is considered endangered, listed by the US Endangered Species Act (ESA) There is a ban on all olive ridley products under the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES)

The olive ridley turtle was listed as endangered for the "Mexican nesting population" and threatened for all other populations on July 28, 1978. Since listing, there has been a decline in abundance of this species, and it has been recommended that the olive ridley for the Western Atlantic be reclassified as endangered. The need for this classification is based on continued direct and incidental take, particularly in shrimp trawl nets. The western North Atlantic (Surinam and adjacent areas) nesting population has declined more than 80 percent since 1967. Declines are also documented for Playa Nancite, Costa Rica, however other nesting populations along the Pacific coast of Mexico and Costa Rica appear stable or increasing. 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. Direct harvest of adults and eggs, incidental capture in commercial fisheries and loss of nesting habitat are main concerns regarding the recovery of this species.

Physical Characteristics

In size, female olive ridleys in Surinam range in carapace length from 62 to 74 cm; in Pacific Honduras from 58 to 74 cm; and in Pacific Mexico from 56 to 78 cm. The carapace is olive brown in color and the plastron is yellowish white.

Identifying Characteristics

The olive ridley is a small, hard-shelled marine turtle, one of the two species of the genus Lepidochelys , and a member of the family Cheloniidae. The species may be identified by the uniquely high and variable numbers of vertebral and costal scutes. Although some individuals have only five pairs of costals (the number shown by almost all individuals of the congener Lepidochelys kempii), in nearly all cases some division of costal scutes occurs, so that as many as six to nine pairs may be present. Division of the "standard" scutes occurs from the rear of the carapace, so that a specimen with, say, seven pairs of costals shows division of the homologs of costals IV and V. Asymmetry in the number of costal scutes is frequent.

In addition to the division of the costal scutes, the vertebral scutes also show frequent division, as do the scales on the dorsal surface of the head. The prefrontal scales, however, typically number two pairs. The carapace is wide in subadults and adults, although less so than that of L. kempii. In anterior profile it is typically elevated and flat-topped, with flat, sloping sides. The plastron is large, with the usual six pairs of large scutes and sometimes a small intergular and interanal also. The inframarginals typically number four on each side, each of which is perforated by a pore located towards its posterior margin. The head is relatively large, as compared with that of Chelonia or Eretmochelys, but is smaller than that of adult Caretta, and slightly smaller than that of L. kempii.

The skull of L. olivacea differs from that of L. kempii in many ways. The orbit is consistently larger, the width across the pterygoids is consistently less, and the alveolar ridges are sharp and are only evident on the rhamphothecae, not on the underlying maxillary-palatine sutural area. There are also numerous differences between the lower jaws of the two species.

1. The entire bony alveolar surface of L. olivacea is flat (rather strongly concave in L. kempii)
   
   
2. The overall depth of the jaw of L. olivacea is somewhat less than that of L. kempii
   
   
3. The tip of the coronoid bone, that provides attachment for the temporal muscle closing the jaw, is rounded off in L. olivacea (bluntly pointed in L. kempii)
   
   
4. The dorsal mandibular vacuity is relatively larger in L. olivacea that in L. kempii
   
   
5. The articular surfaces of the mandible of L. olivacea tend to be directed upward (directed more posteriorly in L. kempii)
   
   
6. The bones comprising the articular surfaces (the articular, pre-articular, and angular) are loosely sutured in adult L. olivacea.

Geographic variation in olive ridleys is subtle, and no subspecies are currently recognized. However, the number of costal scutes apparently varies from one area to another, specimens with only five pairs of costals being somewhat more abundant in the eastern Pacific than elsewhere. In addition, overall carapace coloration is typically somewhat lighter in the western Atlantic than in the eastern Pacific. and the shell is typically more elevated in the eastern Pacific than elsewhere.

The most dramatic aspect of the life history of the olive ridley is the habit of forming great nesting aggregations, generally known as "arribadas," sometimes as "arribazones" or "morriÛas". Although not every adult olive ridley participates in these arribadas, the vast majority of them do. Formerly these nesting concentrations occurred at several beaches along the Pacific coast of Mexico, including Piedra del Tlacoyunque, Bahia Chacahua, and El Playon de Mismaloya, but in recent years the Mexican arribadas have been largely restricted to La Escobilla, although smaller nesting concentrations have been reported from Morro Ayuta. In Costa Rica, a major nesting aggregation is found at Ostional, on the Nicoya Peninsula, and smaller arribadas occur at Nancite, in the Santa Rosa National Park. Smaller arribadas also occur in Nicaragua at La Flor and Chacocente and at several localities in Panama. In the Indian Ocean, four arribada sites have been reported in the Indian State of Orissa, the most important being Gahirmatha Beach. In the Atlantic, only small arribadas, numbering at most a few hundred animals per night, have been reported from a single locality.

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 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.

Individual olive ridleys may nest one, two or three times per season, typically producing 100-110 eggs on each occasion. The internesting interval is variable, but for most localities it is approximately 14 days for solitary nesters and 28 days for arribada nesters. The genus is also unique in that ridleys of both species commonly, and probably typically, nest each year, without intervening non-breeding seasons as shown by dermochelyids and other cheloniids. The ridleys nesting in an arribada could not be sustained by the productivity of immediately adjacent marine ecosystems, and the species is indeed migratory. Recent investigations show that olive ridleys reside in oceanic habitats of the eastern Pacific Ocean during the non-reproductive portion of its life cycle.

The overall distribution of the olive ridley shows interesting parallels with that of the utterly different leatherback turtle (Dermochelys coriacea). Both occupy oceanic habitats and both nest primarily on Pacific shores of the American tropics and in the Guianas, in moderate numbers in tropical West Africa, and in relatively small numbers elsewhere, both being extremely rare, for example, throughout Australia, or Pacific oceanic islands.

Despite its abundance, there are surprisingly few data relating to the feeding habits of the olive ridley. However, those reports that do exist suggest that the diet in the western Atlantic and eastern Pacific includes crabs, shrimp, rock lobsters, jellyfish, and tunicates. In some parts of the world, it has been reported that the principal food is algae.

Range

The range of the olive ridley is essentially tropical. In the eastern Pacific nesting takes place from southern Sonora, Mexico, south at least to Colombia. Non-nesting individuals occasionally are found in waters of the southwestern United States. They occur abundantly in Pacific Colombia and Ecuador, but only in small numbers in Peru and Chile.

The olive ridley has been recorded occasionally from Galapagos waters, but it is essentially very rare throughout the islands of the Pacific, and indeed even in the western Pacific it is scarce everywhere, although widespread low-density nesting occurs. In the Indian Ocean it only achieves abundance in eastern India and Sri Lanka, although minor nesting occurs alongside the green turtles at Hawke's Bay, Pakistan, and some nesting also occurs in New Britain, Mozambique, Madagascar, peninsular Malaysia, and various other localities.

In the Atlantic Ocean, the olive ridley occurs widely, but probably not in great abundance, in waters of West Africa, from about Mauritania southward at least to the Congo. In the western Atlantic, nesting formerly occurred abundantly in eastern Surinam, as well as in western French Guiana and northwestern Guyana. Non-nesting individuals occur regularly as far west as Isla Margarita and Trinidad, but they rarely penetrate any further into the Caribbean than this. The species occurs in Brazil, and nests in the states of Bahia and Sergipe, but it seems to be rare.

Feeding

The olive ridley is omnivorous, eating shrimp, jellyfish, crabs, snails, fish, algae, and sea grasses.

Population Status

Because of the continued existence of several large arribadas, it is probable that the olive ridley is, in terms of absolute numbers of adult individuals in existence, the most abundant sea turtle species in the world. Nevertheless, there is evidence of downward trends at several arribada beaches. The various populations are under considerable stress, and the concentration of such a large proportion of the reproductive animals into a few arribadas may be a liability, not only in that such aggregation facilitates industrial-scale exploitation, as it has in Mexico as well as on the feeding grounds in Ecuador, but also because arribadas do not seem to be an efficient method of guaranteeing maximum reproductive efficiency. Indeed, at the relatively undisturbed arribada beach of Nancite, within Santa Rosa National Park, Costa Rica, it has been estimated that only about 5 % of eggs laid actually produce hatchlings.

The number of ridleys nesting during an arribada is difficult to count, although methodologies to estimate arribada size have been developed that are useful if nesting is well supervised by competent biologists. On the other hand, estimates by laymen of numbers of turtles in a given arribada are probably so inaccurate as to be useless. Because nesting in successive years is commonplace for olive ridleys, and may well be the norm for the species, the erratic nesting population trend lines often shown by loggerhead or green turtle populations, that very rarely nest in successive years, are not shown by olive ridley populations. It is thus much easier and more justified to draw conclusions about overall ridley population trends from a few years of comprehensive nest counts than it is for those species with multi-year nesting cycles.

Human Impacts on Olive Ridley Sea Turtles

1. Pesticides, heavy metals and PCB's have been detected in turtles and eggs, but the effect on them is unknown.
   
   
2. Marine turtles are at risk when encountering an oil spill. Respiration, skin, blood chemistry and salt gland function are affected.
   
   
3. Olive ridley turtles eat a wide variety of marine debris such as plastic bags, plastic and styrofoam pieces, tar balls, balloons and raw plastic pellets. Effects of consumption include interference in metabolism or gut function, even at low levels of ingestion, as well as absorbtion of toxic byproducts.
   
   
4. In areas where recreational boating and ship traffic is intense, propeller and collision injuries are not uncommon.