Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Olive ridley turtles are the smallest and most numerous of the seven sea turtle species. The ‘olive’ in their common name comes from the coloration of the adults. Males usually spend their entire lives at sea while females characteristically only leave the water to lay their eggs, usually on the beach where they themselves hatched (nest site fidelity). Over the years, purposeful and accidental depredations have seriously reduced populations of this species in selected geographic areas.
At the Aquarium
The habitat for our olive ridleys is the Tropical Reef and the Soft Coral Gardens in the Tropical Pacific gallery.
Pacific and Indian Oceans, along south Atlantic coast of east Africa and South America.
Breeding: Pacific Ocean, principally from Mexico, south to east Colombia, with major beaches in Mexico, Nicaragua, and Costa Rica. Most common in the Indian, eastern Pacific, and southern Atlantic Oceans, but distributed worldwide in tropical and subtropical ocean waters. Occasionally seen along the southern California coast.
Olive ridley turtles prefer tropical and subtropical waters, but they can be seen in colder waters as well. Post hatchlings and young juveniles are most commonly observed in surface waters of open oceans. Adults may be seen in both the open ocean and in shallower waters near the shore in the eastern Pacific or in small parts of their range elsewhere.
When viewed from above, the hard, relatively thin carapace of the olive ridley sea turtle appears broadly oval and without ridges. It is composed of a series of five to nine transverse bony plates called scutes. The number of scutes may vary relative to the geographical location of the turtle. The upper shell is relatively high in the eastern Pacific population of this species. There are two claws on each of the four flippers and there is sometimes an extra claw on the front flipper. Males and females differ in the length of the tail. The tail of a female is short and barely, if at all, visible from under the carapace. The male’s tail is much longer and can be seen beyond the margin of the carapace.
Newly hatched turtles are black whereas adults are a dark greenish-olive color on the upper surfaces of the shell, head, and flippers. The ventral side is light yellow.
Turtles are commonly measured by carapace length. In the case of olive ridleys, the length of the carapace is 56 to 78 cm (1.8-2.6 ft). The turtles weigh 36 to 45 kg (80 to 110 lb).
These turtles, which are equipped with powerful jaws, are omnivores, feeding mostly on a wide variety of invertebrates such as shrimp, sea jellies, lobsters, and crabs. They will also prey on fish. Algae is a source of food if their usual preferred diet items are in short supply. They use multiple feeding grounds, typically foraging offshore to depths of 150 m (500 ft) on bottom dwelling crustaceans.
Olive ridley’s make use of many different nesting sites around the world, varying in size and population. Three major populations are recognized—Indian Ocean, eastern Pacific Ocean, and western Atlantic Ocean. The site where most eggs are laid is probably the one in Orissa, India where as many as 398,000 eggs are laid.
Although not definitely known, the age of sexual maturity is estimated to be 7 to 15 years of age or when they reach a carapace length of about 60 cm (23.6 in). Nesting frequency varies, but probably does not take place more than every two to three years. Breeding takes place in the water. The females store sperm through the reproductive season with the result that one to three clutches of eggs may be produced at intervals.
Most commonly a female will nest on the same beach where she hatched (nest site fidelity).Females ready to nest may appear individually or in large groups that may be made up of thousands of turtles. These large gatherings are called arribadas, a Spanish word for “arrival”. Where and when arribadas will occur is unpredictable at all sites. They appear to be precipitated in part by climatic events, such as a strong offshore wind, or by certain phases of the moon and tide. Solitary nesters lay a clutch at intervals of 14 days whereas the interval for those in arribadas is 28 days.
Nesting primarily takes place at night at a high tide period. The female leaves the water and laboriously crawls to a place of her liking above the high tide mark where she digs a nesting hole with her hind flippers. She deposits 50 to 200 eggs, (average 100+), that look like ping pong balls. She uses her hind flippers to cover the eggs with sand, tamping it down to remove all traces of the nest. She then returns to the ocean. The process usually takes from one to three hours.
The eggs incubate for about 50 to 58 days, but the number of days varies depending on temperature of the sand. The temperature of the sand also determines the ratio of male to female turtles hatching.Most eggs in a clutch hatch at the same time. The hatchlings use an egg tooth to open the egg shell. Once out they dig their way out of the nest. Guided by the light, they quickly make their way to the water. Predation is heavy as they crawl to the water and swim into the shallows. There is no parental care.
These turtles are migratory, sometimes traveling several thousand kilometers (miles) between feeding grounds and nesting sites. They are excellent divers spending a great deal of time underwater foraging for food. Trawlers on the east coast of Australia reported that most turtles caught in their nets were taken at depths between 11 to 40 m (36 to 131 ft). It is believed that foraging depths to over 100 m (328 ft) are not uncommon.
In cooler waters, ridleys may be seen, sometimes in small groups, sunning themselves on the water surface to warm themselves. In warmer waters this behavior is rarely noticed.
Sea turtles as a group are well adapted to their watery environment. They are, with one exception, cold blooded which permits them to adapt within limits to changing temperatures. The rather streamlined shape of the head and carapace reduces the amount of energy required to move through the water. The long, sturdy, fore flippers are efficient “propellers” and the rear flippers are effective “rudders” for steering.
The blood of sea turtles can absorb a relatively large quantity of oxygen. With a rapid exhalation and inhalation, almost all of the air in the lungs can be quickly renewed. The olive ridley can quietly rest or sleep underwater for up to about two hours. Activity or stress increases the need for oxygen and substantially reduces the time a turtle can stay submerged.
The lifespan of the olive ridley is believed to be 50 to 60 years.
The US Endangered Species Act lists the breeding colony on Mexico’s Pacific coast as endangered. All other populations are listed as threatened. The IUCN Red List lists all populations as endangered. Continuing and serious efforts are needed if this species is to survive.
The olive ridley’s life is fraught with many dangers. It is estimated that only one of a thousand hatchlings reaches maturity. The mortality rate in newly hatched and juveniles is extremely high. Predators such as small, carnivorous land animals, birds, and sharks and other fishes, contribute to a serious reduction in turtle population. As is so often the case of animal safety, man is the worst offender when it comes to loss of animal life. Although the ridley is legally protected in most areas where it occurs, frequently little or no enforcement of laws and regulations takes place.
There are many ways in which humans affect sea turtle populations. These include encroachment on nesting areas by commercial and residential development, placement of lights that confuse hatchlings trying to find the water, interference to nesting sites and egg-laying females, ghost nets and other dangerous debris, and boat-turtle collisions. In areas where the turtles have been plentiful, residents have traditionally harvested adults for meat and emptied the nests of eggs for subsistence and for sale. Thousands of turtles are killed yearly as bycatch by commercial fishing boats such as fish and shrimp trawlers and the long line fisheries. Newly developed turtle exclusion devices (TEDS) and circular fish hooks are effective in minimizing the accidental taking of turtles, but the fishing industry in general, with some exceptions, has been slow in adopting the new techniques.
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. US and Mexico government regulations requiring shrimp trawlers to use turtle excluder devices have resulted in reduced mortality from commercial fishing operations in US and Mexico waters. Continued direct and incidental take, particularly in shrimp trawl nets, remains a serious concern in the western Atlantic and Indian Oceans.
Male sea turtle embryos can’t stand the heat. The temperature of the sand in which the eggs are incubated determines the sex differentiation of hatchlings. Warmer temperatures yield more female offspring; cooler temperatures yield more males. Temperature rise due to global climate change may cause male turtles to lose their cool.
In the United States protection of marine animals is usually the responsibility of NOAA’s National Marine Fisheries Service (NMFS). However, because sea turtles nest on land, the US Fish and Wildlife Service, the protector of terrestrial animals, shares responsibility with NMFS.
Olive ridley arribadas are believed to be a ‘safety in numbers’ natural technique to conserve the loss of newly hatched young. So many hatchlings appear in such a short period of time as a result of the great number of eggs laid, a number of hatchings can escape the predators searching for food. Even so predation of hatchlings is heavy.