The olive ridley is considered the most abundant sea turtle in the world, with an estimated 800,000 nesting females annually. The olive ridley gets its name from the olive coloration of its heart-shaped top shell (carapace).
Adult turtles are relatively small. The size and morphology of the olive ridley varies from region to region, with the largest animals observed on the Pacific coast of Mexico. There are often only 5 pairs of costal “scutes” on the carapace, but that number varies. Some individuals have been documented having as many as 9 pairs of costal scutes. Each of their four flippers has 1-2 visible claws. The carapace of eastern Pacific olive ridleys is greater in height than other populations. Western Atlantic olive ridleys usually have a darker coloration than eastern Pacific olive ridleys.
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”. During these arribadas, hundreds to thousands of females come ashore 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: Kemp’s ridley sea turtles and olive ridley sea turtles. 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.
Olive ridleys reach sexual maturity around 15 years, a young age compared to some other sea turtle species. Females nest every year, once or twice a season, laying clutches of approximately 100 eggs. Incubation takes about 2 months.
|Weight:||Adult: 100 pounds (45 kg)
Hatchling: <1 ounce (28 g)
|Length:||Adult: 22-31 inches (55-80 cm)
Hatchling: 1.5 inches (4 cm)
|Appearance:||olive/grayish-green (darker in the Atlantic than in the Pacific) with a heart-shaped top shell (“carapace”) and 5-9 pairs of costal “scutes” with 1-2 claws on their flippers; hatchlings emerge mostly black with a greenish hue on their sides|
|Lifespan:||unknown, but they reach sexual maturity at about 15 years|
|Diet:||algae, lobster, crabs, tunicates, mollusks, shrimp, and fish|
|Behavior:||one of the most extraordinary nesting habits in the natural world, vast numbers of olive ridley turtles come ashore and nest in what is known as an “arribada”; females nest every year, once or twice in a season, laying clutches of approximately 100 eggs|
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. Olive ridleys dive to depths of about 500 feet (150 m) to forage on “benthic” invertebrates.
Olive ridleys are globally distributed in the tropical regions of the South Atlantic, Pacific, and Indian Oceans. In the South Atlantic Ocean, they are found along the Atlantic coasts of West Africa and South America. In the Eastern Pacific, they occur from Southern California to Northern Chile.
Olive ridleys often migrate great distances between feeding and breeding grounds. Using satellite telemetry tags, scientists have documented both male and female olive ridleys leaving the breeding and nesting grounds off the Pacific coast of Costa Rica migrating out to the deep waters of the Pacific Ocean.
Solitary nesting occurs extensively throughout this species’ range, and nesting has been documented in approximately 40 countries worldwide.
Arribadas, however, occur on only a few beaches worldwide, in the eastern Pacific and northern Indian oceans, in the countries of:
- Costa Rica
In the eastern Pacific, arribadas occur from June to December on certain beaches on the coasts of Mexico, Nicaragua, and Costa Rica, and on a single beach in Panama.
In the northern Indian Ocean, arribadas occur on three different beaches along the coast of India.
The olive ridley may be the most abundant sea turtle on the planet, but some argue that it is also the most exploited.
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.
In the Western Atlantic Ocean (Surinam, French Guiana, and Guyana), there has, since 1967, been an 80% reduction in certain nesting populations (USFWS 2005).
In the Eastern Atlantic Ocean, lack of data and trends on specific nesting beaches make it difficult to estimate nesting populations. Along the entire west coast of Africa, nesting females and eggs are regularly taken for consumption, except where research stations have been established. This impact is likely extremely devastating to the entire Eastern Atlantic population (Plotkin ed. 2007).
Prior to 1950, an estimated 10 million olive ridleys nested on the Pacific coast of Mexico. In the mid-1960s, an olive ridley fishery developed in Mexico and Ecuador, and the taking of eggs and females also increased, which devasted the population. Only a single arribada nesting beach remains in La Escobilla, Mexico, and more than 20 nesting populations have been severely depleted since the 1960s. The other nesting populations identified in the 1960s have yet to recover despite increased protection.
Gahirmatha, Orissa in India used to be one of the largest arribada nesting sites in the world, though arribada nesting events do not occur every year. Additionally, from 1996 to 2002, the average size of nesting females declined at that site, indicative of a declining population (Plotkin ed. 2007). Declines in solitary nesting of olive ridleys have been recorded in Bangladesh, Myanmar, Malaysia, and Pakistan. In particular, the number of nests in Terengganu, Malaysia has declined from thousands of nests to just a few dozen per year (Limpus 1995).
Still, not all populations are depleted. Some nesting populations are currently stable and/ or increasing. In Sergipe, Brazil, strict nest protection has led to increases of the nesting population over the past 20 years. In La Escobilla, Mexico, conservation measures, such as increased nesting beach protection and closure of the turtle fishery in 1990, have led to a dramatic increase in the once largest nesting population in the world. The number of olive ridley nests has increased from 50,000 in 1988 to over 700,000 in 1994 to over 1,000,000 nests in 2000 (Márquez et al. 2002). At-sea estimates of density and abundance of the olive ridley show a yearly estimate of over 1 million, which is consistent with the increase seen on the eastern Pacific nesting beaches as a result of protection programs that began in the 1990s (Eguchi et al. 2007). This dramatic improvement gives hope that with strict protections the once depleted populations in Mexico have begun to stabilize.
- collection of turtle eggs (historically, though continued in some parts of the world)
- killing turtles (historically, though continued in some parts of the world)
- incidental captures in fishing gear
- longlines, primarily
- gill nets
- purse seines
- hook and line, specifically in Central America and the Indian Ocean
- general threats to marine turtles
The principal cause of the historical, worldwide decline of the olive ridley sea turtle is long-term collection of eggs and killing of adults on nesting beaches. Because arribadas concentrate females and nests in time and space, they allow for mass killing of adult females as well as the taking of an extraordinary number of eggs. These threats continue in some areas of the world today, compromising efforts to recover this species.
In the western south Atlantic Ocean, killing adults and collecting eggs of all nesting sea turtle species is historically widespread in the Guianas and northeastern Brazil. Despite a current prohibition on olive ridley egg harvest in Suriname, an estimated 40% of the olive ridley nests were harvested in 1995 (Hoekert et al. 1996). In the eastern North Atlantic Ocean, nesting olive ridleys are captured along the entire west coast of Africa and sold in local and regional markets. A survey of 27 west African nations indicated that nesting females were killed in 14 of those countries.
In the eastern Pacific Ocean, killing sea turtles and collecting their eggs has occurred for hundreds of years. Little data on historical egg taking in Mexico currently exist, but egg collection has previously reached nearly 100% at solitary nesting sites. In many places, egg collecting currently continues at this level (Plotkin ed. 2007).
Throughout the Indian Ocean, nesting populations of olive ridleys have declined due to both killing of nesting females at solitary nesting beaches and a directed fishery for the species concentrated at the major arribada nesting beach in Orissa, India during the 1970s.
Additionally, incidental captures in fishing gear, primarily in longlines and trawls, but also in gill nets, purse seines, and hook and line, is a serious ongoing source of mortality that adversely affects the species’ recovery.
Incidental capture of sea turtles in shrimp trawls along the coast of Central America is estimated as exceeding 60,000 sea turtles annually, most of which are olive ridleys (Arauz 1996).
Expansion of the shrimp trawling fishery in the eastern Indian Ocean in the mid-1970s has resulted in numerous olive ridley deaths. During the 1982-1983 nesting season, over 7,000 carcasses washed ashore over a 9 mile (15 km) stretch of beach. Between 1993 and 1999, more than 46,200 carcasses were recorded by beach surveyors, with a peak during the 1997-1998 seasons of 13,575 dead olive ridleys. Over 10,000 olive ridley carcasses a year have been counted on the Orissa coast since 1999 (Wright and Mohanty 2006). These carcasses have largely been attributed to the shrimp trawl fishery, but trawling is not the only source of olive ridley mortality in the Eastern Indian Ocean. On February 17, 2002, 205 dead olive ridleys entangled in a section of gillnet were washed ashore at Gundalba Beach, Orissa (Wright and Mohanty 2002).
The highly migratory behavior of sea turtles makes them shared resources among many nations. Thus, conservation efforts for sea turtle populations in one country may be jeopardized by activities in another. Protecting sea turtles on U.S. nesting beaches and in U.S. waters alone, therefore, is not sufficient to ensure the continued existence of the species.
Sea turtles are protected by various international treaties and agreements as well as national laws:
- CITES: listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Flora and Fauna, which prohibits international trade
- CMS: listed in Appendices I and II of the Convention on Migratory Species and are protected under the following auspices of CMS:
- IOSEA: Memorandum of Understanding on the Conservation and Management of Marine Turtles and their Habitats of the Indian Ocean and South-East Asia
- Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa
- SPAW: protected under Annex II of the Specially Protected Areas and Wildlife Protocol of the Cartagena Convention
- IAC: The U.S. is a party of the Inter-American Convention for the Protection and Conservation of Sea Turtles, which is the only international treaty dedicated exclusively to marine turtles
In the U.S., NOAA Fisheries (NMFS) and the U.S. Fish and Wildlife Service (USFWS) have joint jurisdiction for sea turtles, with NOAA having the lead in the marine environment and USFWS having the lead on the nesting beaches. Both federal agencies, along with many state agencies and international partners, have issued regulations to eliminate or reduce threats to sea turtles, while working together to recover them.
In the Atlantic and Gulf of Mexico, we have required measures to reduce sea turtle bycatch in pelagic longline, mid-Atlantic gillnet, Chesapeake Bay pound net, and southeast shrimp and flounder trawl fisheries, such as
- gear modifications
- changes to fishing practices
- time/ area closures
NOAA Fisheries have worked closely with the shrimp trawl fishing industry to develop turtle excluder devices (TEDs) to reduce the mortality of sea turtles incidentally captured in shrimp trawl gear. TEDs that are large enough to exclude even the largest sea turtles are now required in shrimp trawl nets. Since 1989, the U.S. has prohibited the importation of shrimp harvested in a manner that adversely affects sea turtles. The import ban does not apply to nations that have adopted sea turtle protection programs comparable to that of the U.S. (i.e., require and enforce the use of TEDs) or to nations where incidental capture in shrimp fisheries does not present a threat to sea turtles (for example, nations that fish for shrimp in areas where sea turtles do not occur). The U.S. Department of State is the principal implementing agency of this law, while we serve as technical advisor. We provide extensive TED training throughout the world.
We are also involved in cooperative gear research projects designed to reduce sea turtle bycatch in the Gulf of Mexico and Atlantic pelagic longline fisheries, the Hawaii-based deep set longline fishery, the Atlantic sea scallop dredge fishery, the Chesapeake Bay pound net fishery, and non-shrimp trawl fisheries in the Atlantic and Gulf.
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