The Olive Ridley Sea Turtle

The Olive Ridley is probably the most abundant of the seven or eight currently recognized species of sea turtles. It inhabits tropical and subtropical coastal bays and estuaries. This sea turtle is found in the Pacific and Indian Oceans, and along the Atlantic coast of West Africa and the Atlantic coast of South America. In the Eastern Pacific it occurs from Southern California, USA to Northern Chile. Large nesting aggregations called "arribadas" still occur in Pacific Costa Rica, primarily at Nancite and Ostionales and Pacific Mexico at La Escobilla, Oaxaca.
The Olive Ridley is the smallest of the sea turtles usually less than 100 pounds and named for the olive color of its heart-shaped shell. Ridleys appear to prefer coastal areas, but large groups have been seen in the open ocean. Their behavior were more like bottom dwellers than others and frequented the shallow water between reef and coast line. In fact, very little is known of the habits of all sea turtles away from the nesting beaches where they have been observed and studied the most.

The phenomenon of synchronized mass nesting (arribadas), where several thousand turtles emerge together, is peculiar to the Ridleys. 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.
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.

During the march up the beach Ridleys plow through the sand with their noses, implying that olfactory sensing may play a role in beach recognition or site selection on the beach. 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.

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.