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Olive Ridley Sea Turtle (Lepidochelys olivacea)

FAMILY: Cheloniidae

STATUS: Breeding colony populations on the Pacific Coast of Mexico are listed as Endangered; all others are listed as Threatened (Federal Register, July 28, 1978).

DESCRIPTION: The olive ridley was named for the olive color of its heart-shaped shell and is one of the smallest of the sea turtles, with adults reaching 2 to 2½ feet in length and weighing 80 to 110 pounds. 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, in nearly all cases some division of costal scutes occurs, so that as many as six to nine pairs may be present. In addition, 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. Existing reports suggest that the olive ridley's diet includes crabs, shrimp, rock lobsters, jellyfish, and tunicates. In some parts of the world, algae has been reported as its principal food.

REPRODUCTION AND DEVELOPMENT: The olive ridley is most noted for its massive nesting aggregations, known as arribadas or arribazones, with literally thousands of females nesting in large simultaneous waves over small stretches of beach. Arribadas may be precipitated by climatic events, such 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. Although not every adult female participates in these arribadas, the vast majority do. Olive ridleys typically nest 1 to 3 times per season, producing about 100 to110 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. Incubation takes about 50 to 60 days. Age at sexual maturity is not known, but if similar to its close relative the Kemp's ridley, it would be 7 to 15 years.

RANGE AND POPULATION LEVEL: The olive ridley occurs within the tropical regions of the Pacific, Atlantic, and Indian Oceans. In the Pacific, it nests primarily on beaches from Mexico south to at least Colombia with major nesting beaches at Escobilla, Mexico; La Flor, Nicaragua; and Ostional and Nancite, Costa Rica. In the Indian Ocean, it nests in great abundance in eastern India and Sri Lanka, although minor nesting also occurs at other localities. A small and declining population nests in the western Atlantic, primarily along the coasts of Surinam and French Guiana. It does not nest in the United States, but during feeding migrations, olive ridley turtles nesting in the Pacific may disperse into waters of the southwestern U.S., occasionally as far north as Oregon.

The olive ridley is widely regarded as the most abundant sea turtle in the world because of the continued existence of several large arribadas. However, since its listing under the U.S. Endangered Species Act, there has been a decline in abundance of this species, and it has been recommended that the olive ridley in the western Atlantic be reclassified as Endangered. The need for this reclassification is based on continued direct and incidental take, particularly in shrimp trawl nets and nearshore gill nets. The western North Atlantic (Surinam, French Guiana, and Guyana) 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 one of the largest nesting populations in the world with an average of 398,000 females nesting in a given year. These populations, however, are suffering high mortality from nearshore gill nets and trawl fisheries.

HABITAT: The olive ridley appear to be more of an open ocean inhabitant than its congener, the Kemp's ridley, which primarily inhabits shallow nearshore coastal waters.

CRITICAL HABITAT: None designated.

REASONS FOR CURRENT STATUS: The decline of this species is primarily due to human activities, including the direct harvest of adults and eggs, incidental capture in commercial fisheries, and loss of nesting habitat.

MANAGEMENT AND PROTECTION: In Mexico, 17 reserve areas were established for the protection of sea turtles in 1986, and a total prohibition on sea turtle harvest was instituted and additional protection camps were established on nesting beaches in 1990. Since the 1990 ban, the take of olive ridleys has been reduced, and the population appears to be stabilizing. U.S. and Mexico government regulations requiring shrimp trawlers to use turtle excluder devices have resulted in reduced mortality from commercial fishing operations in U.S. and Mexico waters. Continued direct and incidental take, particularly in shrimp trawl nets, remains a serious concern in the western Atlantic and Indian Oceans.

SUGGESTED REFERENCES:

Eckert, K.L., K.A. Bjorndal, F.A. Abreu-Grobois, and M. Donnelly (eds.). 1999. Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtle Specialist Group Publication No. 4. 235pp.

Lutz, P.L., and J.A. Musick (eds.). 1997. The Biology of Sea Turtles. CRC Press, Inc., Boca Raton, FL. 432pp.

National Marine Fisheries Service and U.S. Fish and Wildlife Service. 1998. Recovery plan for U.S. Pacific populations of the olive ridley turtle (Lepidochelys olivacea). National Marine Fisheries Service, Silver Spring, MD. 52pp.

National Research Council. 1990. Decline of the sea turtles: causes and prevention. National Academy Press, Washington, D.C. 259pp.

Pandav B., B.C. Choudhury, and C.S. Kar. 1997. Olive ridley sea turtle (Lepidochelys olivacea) and its nesting habitats along the Orissa Coast, India. Wildlife Institute of India, Dehra Dun, India. 48 pp.

Ross, J.P. 1982. Historical decline of loggerhead, ridley, and leatherback sea turtles. Pages 189-195 in Bjorndal, K.A. (ed.). Biology and Conservation of Sea Turtles. Smithsonian Institution Press, Washington, D.C.

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