|Hawksbill Sea Turtle
Green Sea Turtle
|Olive Ridley Sea Turtle
Loggerhead Sea Turtle
Kemp’s Ridley Sea Turtle
- Named for it’s green/gray carapace
- The most abundant sea turtle in the world
- Omnivorous, feeds on a wide variety of foods
- Nests in a mass-nesting event called an arribada. Nests two times a season.
- Pelagic yet also inhabits coastal areas and estuaries
- Small by sea turtle standards, measuring only 2 to 2 ½ feet and weighing between 75 and 100 pounds.
- Widely distributed across the globe in the tropical and sub-tropical oceans of the world
- Main threats to survival are egg gathering and killing of nesting females, shrimp trawling and other fishing practices
- Listed as endangered. The overall population has been reduced drastically in the last 60 years.
Nesting: The Grand Arrival
The most remarkable characteristic of the Olive Ridley is their nesting strategy. Hundreds to thousands of females converge in coastal waters then come ashore simultaneously in a spectacular mass-nesting event known as an arribada (Spanish meaning “arrival by sea”). Lepidochelys, which includes the Kemp’s Ridley, is the only genus of sea turtles to lay their eggs in arribadas.
How does the female know that the time is right for the arribada? Scientists have conducted research in order to find the answer to this question and have offered several theories. One theory suggests that females may release a hormonal scent or pheromone that queues the beginning of the event. There is also evidence that these mass-nesting events coincide with certain phases of the lunar cycle. So far, there is no definitive answer and the arribada continues to remain one of nature’s great mysteries.
The Olive Ridley nests two times a season and deposits an average of 105 eggs per nest.
Major Arribada Beaches in Costa Rica
Playa Ostional and Playa Nancinte in Costa Rica are two of the world’s major arribada sites. The annual nesting population at these two beaches has been calculated to be from 600,000 to 750,000. The largest arribada at Ostional was documented in 1995. In that one arribada (lasting about 10 days) approximately 500,000 sea turtles emerged from the sea to lay their eggs (Quirós, du Toit, Phd., 2000).
Not all females participate in the arribada. At Ostional and Nancinte beaches, in Costa Rica. it has been calculated that as many as 5000 of the total population of Olive Ridleys may nest individually. Females have been observed utilizing both individual and mass-nesting strategies.
Hatchlings emerge after incubating in the nest from 50 to 60 days. New hatchlings are only 1 ½ inches in size and weigh less than an ounce. Their coloration is primarily a dull black or charcoal with a greenish cast along the sides. They face the same odds as all other newly hatched sea turtles and many will never make it to sea, let alone adulthood. If they do make it to the water, they will continue to face threats from predation in lessening degrees as they grow larger. Once fully grown, their primary threats at sea are large sea predators and of course, humans.
The Olive Ridley derives its name from its green/gray shell. They are small among sea turtle species, weighing between 75 and 100 lbs and measuring in at 2 to 2 ½ feet along the length of carapace. Variations in size occur region to region and the largest Olive Ridleys are found on the pacific coast of Mexico. They can be differentiated from the Kemp’s Ridley by their small heads and a greater number of scutes. Their scutes are large and smooth and the have least 6 laterals on each side and as many as nine costals.
Habitat and Migration
Although Olive Ridleys spend time in the open ocean, they also forage in coastal waters and estuaries. They inhabit three oceans, the Atlantic, Pacific and Indian and nest on many continents around the globe. The highest density of nesting sites is found on the pacific side of Mexico.
Annually, the Olive Ridley migrates from pelagic foraging areas to coastal waters (for breeding, nesting and shallow water foraging) and back again to the open ocean.
Olive Ridleys are omnivorous, meaning that they consume a varied diet from both plant and animal sources. Their jaws are powerful enough to enable them to consume mollusks such as sea snails and clams. They also eat crustaceans (crabs, lobsters and shrimp) as well as fish, jelly fish, tunicates and various algae.
To be an omnivore is to assume one of natures more successful dietary strategies. This adaptation means a species is less dependent on the availability any single food source and therefore, more able to adapt to extinctions or depletions of dietary resources. This may be contributing factor to the fact that the Olive Ridley is the most abundant sea turtle species on the planet.
Threats to Survival
Despite the relative abundance of the Olive Ridley today, their numbers have diminished by an astounding fifty percent during the last several decades. In the United States, they are labeled threatened or likely to come under danger of extinction in the foreseeable future. The International World Conservation Union (IUNC) has listed the species as endangered.
A primary threat to the Olive Ridley comes from human predation in the nesting habitat. The arribada with its large congregation of nesting females makes it possible for humans to collect huge quantities of eggs and kill or collect (to sell at market) hundreds or even thousands of turtles in one night. This practice of mass harvesting and killing over the past sixty years has caused local populations to plummet in many areas of the globe. Another form of human intrusion that threatens sea turtles is the permanent destruction of the nesting habitat through coastal degradation and development.
Thousands of Olive Ridley are killed annually at sea, becoming collateral damage to the practices of shrimp trawling and commercial fishing. It is estimated that 60, 000 sea turtles—mostly Olive Ridley —die every year as incidental bycatch in shrimp trawls along the coast of Central America (Arauz 1996). These losses could be avoided if regulations requiring turtle excluder devices (TEDs) were enforced. Other fishing practices such as the use of longlines and gill nets also contribute to the decimation of the Olive Ridley and other sea turtles in the open ocean.
We gratefully acknowledge the following resources:
Arauz, R.M. 1996. A description of the Central American shrimp fisheries with estimates of incidental capture and mortality of sea turtles. Pages 5-9 in Keinath, J.A., D.E. Barnard, J.A. Musick, and B.A. Bell (compilers). NAOO Fisheries http://www.nmfs.noaa.gov/pr/species/turtles/oliveridley.htm
Carribean Conservation Corportation http://www.cccturtle.org
Costa Rica, the Land of Pure Life from the PBS series The Living Edens http://www.pbs.org/edens/costarica/ridley.html
Gore, Kedar: photographer of Olive Ridleys’ photos from www.seaturtle.org image library.
Mr. Bhau Katdare: photographer of Olive Ridley hatchlings from www.seaturtle.org image library.
Ostinal National Wildlife Refuge, http://www.costarica-nationalparks.com/ostionalwildliferefuge.html
NOAA FISHERIES, Office Of Protected Resources
NOAA Fisheries, Pacific Islands Regional Office, http://www.fpir.noaa.gov/PRD/prd_olive_ridley.html
Red List Standards & Petitions Subcommittee 1996. Lepidochelys olivacea. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>.
Quirós, Anny Chaves & Leslie A. du Toit, Ph.D, Douglas Robinson, Marine Turtle Research Center (documentary video, Costa Rica, Land of Pure Life) http://www.pbs.org/edens/costarica/ridley.html