AMA Mexico

Live Olive Ridley Sea Turtles nest all year on the Pacific Coast of Mexico.

They are the species most frequently seen in Nuevo Vallarta’ and in the State of Nayarit.

Geographic Distribution

Olive Ridleys are globally distributed in the tropical regions of the South Atlantic, the Pacific, and Indian Oceans. In the Eastern Pacific, they occur from Southern California to the Baja California Coast, the Sea of Cortez, the Pacific Coast of Mexico, all of Central America, and the Pacific Coast of South America to Northern Chile.

Olive Ridleys often migrate great distances between feeding and breeding grounds. In two separate satellite telemetry studies, both male and female Olive Ridleys leaving the breeding and nesting grounds off the Pacific coast of Costa Rica migrated out to the deep waters of the Pacific Ocean.  Both sexes migrated to waters deeper than 9800 ft (3000 m). The results did not indicate a directed migration to a specific foraging area; instead it appears the Olive Ridley forages opportunistically in deep ocean waters.

Physical Features, Size, and Biological Classification

The heart-shaped Olive Ridley (Lepidochelys olivacea) is one of the smallest sea turtles.  The adults do not usually weigh over 100 pounds, and they measure between 22 and 31 inches in length.  The largest of this species nest on the Pacific Coast of Mexico.

The Olive Ridley has a high-domed hard shell.  The top shell (carapace) is made up of five pairs of costal scutes, a number which can vary with up to 9 divisions per side. The carapace is a dark olive green in color with a yellowish underside.  Each of its four flippers has one or two nails or claws.  The head is relatively large.

Life History and Ocean Behavior

The Olive Ridley is mainly a “pelagic” sea turtle, but has been known to inhabit coastal areas, including bays and estuaries. Olive Ridleys mostly breed annually and have an annual migration from pelagic foraging, to coastal breeding and nesting grounds, back to pelagic foraging. Trans-Pacific ships have observed Olive Ridleys over 2,400 miles (4,000 km) from shore.

The Olive Ridley is omnivorous, meaning it feeds on a wide variety of food items, including algae, lobster, crabs, tunicates, mollusks, shrimp, and fish. They can dive to depths of about 500 feet (150 m), to forage on “benthic” invertebrates.

Age

Olive Ridleys reach sexual maturity at between 8 and 10 years, a young age compared to some other sea turtle species.  It is believed that they live well in excess of 50 years although little is known about the age of sea turtles.

Nesting

The Olive Ridley has one of the most extraordinary nesting habits in the natural world. Large groups of turtles gather off shore of nesting beaches. Then, all at once, vast numbers of turtles come ashore and nest in what is known as an “arribada” (arrival). During these arribadas, hundreds to thousands of females arrive on the beach to lay their eggs. At many nesting beaches, the nesting density is so high that previously laid egg clutches are dug up by other females excavating the nest to lay their own eggs.

There are many theories on what triggers an arribada, including offshore winds, lunar cycles, and the release of pheromones by females. Despite these theories, scientists have yet to determine the actual cues for ridley arribadas. Not all females nest during an arribada, instead some are solitary nesters. Some Olive Ridleys employ a mixed nesting strategy. For example, a single female might nest during an arribada, as well as nest alone during the same nesting season. Arribada nesting is a behavior found only in the genus Lepidochelys. Although other turtles have been documented nesting in groups, no other turtles (marine or otherwise) have been observed nesting in such mass numbers and synchrony.

Eggs and Incubation

Olive Ridley females nest every year, up to three times a season, laying clutches of between 80 and 120 eggs. Incubation takes 45-60 days. After incubation, hatchlings emerge weighing less than an ounce (< 28 g) and measuring about 1.5 inches (3.8 cm). The hatchlings are mostly black with a greenish hue on the sides.

Studies of Olive Ridleys indicate that temperature affects sex determination during the approximate middle third of incubation.  The warmer the temperature the more potential for producing females, and the cooler the temperature the more potent it is for producing males.

Predation

The principal cause of the historic worldwide decline of the Olive Ridley is long-term collection of eggs and killing of adults on nesting beaches. Though it is a natural behavior of the Olive Ridley,  “arribadas” concentrate females and nests in time and space and makes possible the mass killing of adult females as well as the taking of an extraordinary number of eggs. In the eastern Pacific Ocean, killing sea turtles and collecting their eggs (poaching) have occurred for hundreds of years. Though little historic data on Mexico exist, poaching reportedly reaches nearly 100% at many solitary nesting sites currently. This is not true in the area protected by the Nuevo Vallarta Conservation Program.

Predators such as raccoons, skunks, opossums, cats, coatis, and dogs eat the eggs. Hatchlings are preyed upon by mammals, sea birds, crabs, and carnivorous fishes. Predation continues until the turtles are big enough to avoid being swallowed

Also the incidental capture of Olive Ridleys in shrimp trawl nets and by long line fishing hooks is believed to be one of the principal causes of their decline.  This, along with injuries sustained by collisions with boats, account for many of their deaths along the Pacific Coast of Mexico and Central America.

Endangered Status

The Olive Ridley, though it may be the most abundant sea turtle on the planet, is endangered nevertheless.  It is listed as endangered by the World Conservation Union (IUCN) with degradation of nesting beaches, ongoing directed harvest, and by catch in fisheries listed has having contributed to the decline of the species.

According to the Marine Turtle Specialist Group (MTSG) of the IUCN, there has been a 50% reduction in population size since the 1960s. Although some nesting populations have increased in the past few years, the overall reduction is greater than the overall increase. (View the IUCN “red listing” for the Olive Ridley Sea Turtle.)

An estimated ten million Olive Ridleys nested on the Pacific coast of Mexico prior to 1950.  In the mid-1960s, owing to urban demand, the taking of eggs and females increased, which devastated the population. Over 20 nesting populations were severely depleted and since then only a single “arribada” nesting beach remains at La Escobilla, Oaxaca, Mexico.  Elderly and middle age residents of coastal Nayarit remember seeing “arribadas” of hundreds, and even thousands, of nesting turtles on local beaches. These nesting populations of 40 years ago have yet to recover despite increased protection.

Conservation Efforts

Owing to the highly migratory behavior of Olive Ridleys, efforts to protect them in one country may be jeopardized by activities in another. Protecting Olive Ridleys in U.S. and Mexican waters alone is important but not sufficient to ensure the continued existence of the species.

Various international treaties and agreements as well as national laws do protect the Olive Ridley but the Inter-American Convention for the Protection and Conservation of Sea Turtles is the only binding international treaty that includes them.  Even though our own beach in Nuevo Vallarta is seeing a significant increase in the number of Olive Ridley nests it is important to remember that this is a highly migratory animal which is subject to threats far beyond the waters and shores of Mexico.

The nesting process takes approximately one hour during which the adult female comes ashore.  She excavates a pit with her fore and rear flippers to remove the upper layer of dry sand. Then, using her rear flippers, she digs a flask-shaped egg chamber in moist sand.  The chamber can be as deep as 24 inches.

After laying from 45 to 120 white ping-pong ball-sized eggs, she covers the nest with sand and returns to the water.

Sea turtle eggs incubate for 50 to 70 days.  Nearly all the eggs hatch together, usually at night. After working their way to the surface of the nest the hatchlings scurry toward the water.  Because of the loss of so many hatchlings to animal predators during this journey across the beach, Sea Turtle Conservation Programs often protect the babies in safe relocated nests and release them to the sea under supervised conditions.

Beaches used for nesting are often lost to beachfront development or are disturbed by beach maintenance and recreation.  Sea turtle reproduction is reduced when adult females are unable to nest, nest in poor habitats, or when eggs and hatchlings die from human or other predator activity. At night, both adult female sea turtles and hatchlings may be disoriented by artificial light, including street and hotel lights, flash cameras, and even campfires, all of which attract them away from the sea.

Some are injured or die when they are hit by ships, boats, and jet skis.  Many are drowned after being caught in fishing nets or by long lines. Plastic bags, Styrofoam pieces, balloons, and other trash that floats on the ocean are often mistaken for food and eaten by sea turtles. Ingested trash blocks digestion and can cause death.