A moderately sized marine turtle; largest recorded specimen has a carapace length of 735 mm. Carapace depressed, slightly elongate, smooth; scutes juxtaposed; posterior edge with moderate indentations; with 6-8 coastal scutes; first marginal scute not in contact with first vertebral scute. Head large, triangular, with 2 pairs of prefrontals. Front limbs with a single claw, hind limbs with 2 claws. Males smaller, with longer tails and larger claws. Color of carapace and dorsal sides of limbs and head uniform olive gray. All ventral sides yellowish white.
The Olive Ridley Turtle has a large range within the tropical and subtropical regions in the Pacific and Indian Oceans as well as the Southern Atlantic Ocean. They generally tend to stay within the latitudes of 40° North and 40° South. Around North America it can be found in the waters of the Caribbean Sea and along the Gulf of California. The largest nesting beach for the Olive Ridley Turtle is at the Bhitar Kanika Wildlife Sanctuary on the Bay of Bengal located in Orissa, India.
Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Non-breeding
Global Range: Range encompasses warmer waters of the Pacific, Indian, and Atlantic oceans (Zug and Wilson 1998).
Distribution in Egypt
Vagrant to Egyptian Red Sea waters, where it has been recorded at least three times, all in the 1970s, off the South Sinai coast. Two animals were caught in nets at Dahab and Nuweiba, and 2 animals were observed "off the southern tip of Sinai"
Pan-tropical species, recorded about 5 times in the Red Sea. Nearest breeding site is on Masirah Island, Oman, where some 150 females nest annually.
Distribution: Pacific and Indian oceans from Micronesia, Japan, India, and Arabia south to S Africa; Israel, Eritrea, United Arab Emirates (UAE), Somalia, Madagascar, Seychelles, Andaman Islands, Nicobar Islands, Cameroon Atlantic Ocean off the western coast of Africa; e.g. Gabon; Mauritania, Tanzania, Zanzibar, Principé and São Tomé (Gulf of Guinea), Gambia Australia (North Territory, Queensland, West Australia), Solomon Islands [McCoy 2000], In the eastern Pacific it is found from the Galapagos northward to the USA (Alaska, California, Oregon ?, Washington); Occasionally in the Caribbean Sea as far north as Puerto Rico. Central America: SE Mexico, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama South America: coasts of N Brazil, French Guiana, Surinam, Guyana, Venezuela acording to the 1994 IUCN Red List of Threatened Animals: EC/SE/SW/WC Atlantic Ocean, Indian Ocean, EC-SE-SW-WC Pacific Ocean, Angola, Australia, Bangladesh, Brazil, Costa Rica, El Salvador, French Guiana, Guatemala, Guyana, Honduras, India, Indonesia, Kenya, Madagascar, Malaysia, Mexico, Mozambique, Myanmar (= Burma), Nicaragua, Oman, Pakistan, Panama, Papua New Guinea, Peru, Senegal, South Africa, Sri Lanka, Suriname, Tanzania, Thailand, Trinidad and Tobago, Venezuela
Type locality: Manila Bay, Philippines (fide COGGER 1983).
Circumglobal in tropical and temperate seas
The Olive Ridley Turtle is a large sea turtle that can weigh as much as 45 kg (100 lbs) and have a length of up to 75 cm (30 in). The skin of the turtle is olive gray and the distinguishing feature between male and female turtles is that the male's tail extends past the carapace while the female's does not. The relatively thin shell compared to other turtles is somewhat heart-shaped and is olive in color. Each of the four limbs has two claws.
Other Physical Features: ectothermic ; bilateral symmetry
Length: 71 cm
Catalog Number: USNM 243393
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: Sex unknown;
Locality: Bahia Ventosa, Oaxaca, Mexico
Marismas Nacionales-San Blas Mangroves Habitat
This taxon is found in the Marismas Nacionales-San Blas mangroves ecoregion contains the most extensive block of mangrove ecosystem along the Pacific coastal zone of Mexico, comprising around 2000 square kilometres. Mangroves in Nayarit are among the most productive systems of northwest Mexico. These mangroves and their associated wetlands also serve as one of the most important winter habitat for birds in the Pacific coastal zone, by serving about eighty percent of the Pacific migratory shore bird populations.
Although the mangroves grow on flat terrain, the seven rivers that feed the mangroves descend from mountains, which belong to the physiographic province of the Sierra Madre Occidental. The climate varies from temperate-dry to sub-humid in the summer, when the region receives most of its rainfall (more than 1000 millimetres /year).
Red Mangrove (Rhizophora mangle), Black Mangrove (Avicennia germinans), Buttonwood (Conocarpus erectus) and White Mangrove trees (Laguncularia racemosa) occur in this ecoregion. In the northern part of the ecoregion near Teacapán the Black Mangrove tree is dominant; however, in the southern part nearer Agua Brava, White Mangrove dominates. Herbaceous vegetation is rare, but other species that can be found in association with mangrove trees are: Ciruelillo (Phyllanthus elsiae), Guiana-chestnut (Pachira aquatica), and Pond Apple (Annona glabra).
There are are a number of reptiles present, which including a important population of Morelet's Crocodile (Crocodylus moreletii) and American Crocodile (Crocodylus acutus) in the freshwater marshes associated with tropical Cohune Palm (Attalea cohune) forest. Also present in this ecoregion are reptiles such as the Green Iguana (Iguana iguana), Mexican Beaded Lizard (Heloderma horridum) and Yellow Bellied Slider (Trachemys scripta). Four species of endangered sea turtle use the coast of Nayarit for nesting sites including Leatherback Turtle (Dermochelys coriacea), Olive Ridley Turtle (Lepidochelys olivacea), Hawksbill Turtle (Eretmochelys imbricata) and Green Turtle (Chelonia mydas).
A number of mammals are found in the ecoregion, including the Puma (Puma concolor), Ocelot (Leopardus pardalis), Jaguar (Panthera onca), Southern Pygmy Mouse (Baiomys musculus), Saussure's Shrew (Sorex saussurei). In addition many bat taxa are found in the ecoregion, including fruit eating species such as the Pygmy Fruit-eating Bat (Artibeus phaeotis); Aztec Fruit-eating Bat (Artibeus aztecus) and Toltec Fruit-eating Bat (Artibeus toltecus); there are also bat representatives from the genus myotis, such as the Long-legged Myotis (Myotis volans) and the Cinnamon Myotis (M. fortidens).
There are more than 252 species of birds, 40 percent of which are migratory, including 12 migratory ducks and approximately 36 endemic birds, including the Bumblebee Hummingbird, (Atthis heloisa) and the Mexican Woodnymph (Thalurania ridgwayi). Bojórquez considers the mangroves of Nayarit and Sinaloa among the areas of highest concentration of migratory birds. This ecoregion also serves as wintering habitat and as refuge from surrounding habitats during harsh climatic conditions for many species, especially birds; this sheltering effect further elevates the conservation value of this habitat.
Some of the many representative avifauna are Black-bellied Whistling Duck (Dendrocygna autumnalis), Great Blue Heron (Ardea herodias), Roseate Spoonbill (Ajaia ajaja), Snowy Egret (Egretta thula), sanderling (Calidris alba), American Kestrel (Falco sparverius), Blue-winged Teal (Anas discors), Mexican Jacana (Jacana spinosa), Elegant Trogan (Trogan elegans), Summer Tanager (Piranga rubra), White-tailed Hawk (Buteo albicaudatus), Merlin (Falco columbarius), Plain-capped Starthroat (Heliomaster constantii), Painted Bunting (Passerina ciris) and Wood Stork (Mycteria americana).
Niger Coastal Delta Habitat
The Niger Coastal Delta is an enormous classic distributary system located in West Africa, which stretches more than 300 kilometres wide and serves to capture most of the heavy silt load carried by the Niger River. The peak discharge at the mouth is around 21,800 cubic metres per second in mid-October. The Niger Delta coastal region is arguably the wettest place in Africa with an annual rainfall of over 4000 millimetres. Vertebrate species richness is relatively high in the Niger Delta, although vertebrate endemism is quite low. The Niger Delta swamp forests occupy the entire upper coastal delta. Historically the most important timber species of the inner delta was the Abura (Fleroya ledermannii), a Vulnerable swamp-loving West African tree, which has been reduced below populations viable for timber harvesting in the Niger Delta due to recent over-harvesting of this species as well as general habitat destruction of the delta due to the expanding human population here. Other plants prominent in the inner delta flood forest are: the Azobe tree (Lophira alata), the Okhuen tree (Ricinodendron heudelotii ), the Bitter Bark Tree (Sacoglottis gabonensis), the Rough-barked Flat-top Tree (Albizia adianthifolia), and Pycnanthus angolensis. Also present in its native range is the African Oil Palm (Elaeis guineensis)
Five threatened marine turtle species are found in the mangroves of the lower coastal delta: Leatherback Sea Turtle (Dermochelys coricea, EN), Loggerhead Sea Turtle (Caretta caretta, EN), Olive Ridley Turtle (Lepidochelys olivacea, EN), Hawksbill Sea Turtle (Eretmochelys imbricata, CR), and Green Turtle (Chelonia mydas, EN).
There are a number of notable mammals present in the upper (or inner) coastal delta in addition to the Critically Endangered Niger Delta Red Colubus (Procolobus pennantii ssp. epieni), which primate is endemic to the Niger Delta. The near-endemic White-cheeked Guenon (Cercopithecus erythrogaster, VU) is found in the inner delta. The Endangered Chimpanzee (Pan troglodytes) is also found in the inner delta. The limited range Black Duiker (Cephalophus niger) is fournd in the inner delta and is a near-endemic to the Niger River Basin. The restricted distribution Mona Monkey (Cercopithecus mona), a primate often associated with rivers, is found here in the Niger Delta. The Near Threatened Olive Colobus (Procolobus verus) is restricted to coastal forests of West Africa and is found here in the upper delta.
Some of the reptiles found in the upper Coastal Niger Delta are the African Banded Snake (Chamaelycus fasciatus); the West African Dwarf Crocodile (Osteolaemus tetraspis, VU); the African Slender-snouted Crocodile (Mecistops cataphractus); the Benin Agama (Agama gracilimembris); the Owen's Chameleon (Chamaeleo oweni); the limited range Marsh Snake (Natriciteres fuliginoides); the rather widely distributed Black-line Green Snake (Hapsidophrys lineatus); Cross's Beaked Snake (Rhinotyphlops crossii), an endemic to the Niger Basin as a whole; Morquard's File Snake (Mehelya guirali); the Dull Purple-glossed Snake (Amblyodipsas unicolor); the Rhinoceros Viper (Bitis nasicornis). In addition several of the reptiles found in the outer delta are found within this inner delta area.
Other reptiles found in the outer NIger Delta are the Nile Crocodile (Crocodylus niloticus), African Softshell Turtle (Trionyx triunguis), African Rock Python (Python sebae), Boomslang Snake (Dispholidus typus), Cabinda Lidless Skink (Panaspis cabindae), Neon Blue Tailed Tree Lizard (Holaspis guentheri), Fischer's Dwarf Gecko (Lygodactylus fischeri), Richardson's Leaf-Toed Gecko (Hemidactylus richardsonii), Spotted Night Adder (Causus maculatus), Tholloni's African Water Snake (Grayia tholloni), Smith's African Water Snake (Grayia smythii), Small-eyed File Snake (Mehelya stenophthalmus), Western Forest File Snake (Mehelya poensis), Western Crowned Snake (Meizodon coronatus), Western Green Snake (Philothamnus irregularis), Variable Green Snake (Philothamnus heterodermus), Slender Burrowing Asp (Atractaspis aterrima), Forest Cobra (Naja melanoleuca), Rough-scaled Bush Viper (Atheris squamigera), and Nile Monitor (Varanus niloticus).
There are a limited number of amphibians in the inner coastal delta including the Marble-legged Frog (Hylarana galamensis). At the extreme eastern edge of the upper delta is a part of the lower Niger and Cross River watersheds that drains the Cross-Sanaka Bioko coastal forests, where the near endemic anuran Cameroon Slippery Frog (Conraua robusta) occurs.
The Olive Ridley Turtle spends most of its time within 15 km of shore, preferring shallow seas for is feeding and sunbathing. However this species is observed in the open ocean as well.
Aquatic Biomes: coastal
Habitat and Ecology
Like most other sea turtles, Olive Ridleys display a complex life cycle, which requires a range of geographically separated localities and multiple habitats (Márquez 1990). Females lay their nests on coastal sandy beaches from which neonates emerge and enter the marine environment to continue their development. They remain in a pelagic phase, drifting passively with major currents that disperse far from their natal sites, with juveniles sharing some of the adults’ habitats (Kopitsky et al. 2000) until sexual maturity is reached (Musick and Limpus 1997). Reproductively active males and females migrate toward coastal zones and concentrate near nesting beaches. However, some males appear to remain in oceanic waters and mate with females en route to their nesting beaches (Plotkin et al. 1996, Kopitsky et al. 2000). Their post-breeding migrations are complex, with pathways varying annually (Plotkin 1994) and with no apparent migratory corridors, swimming hundreds or thousands of kilometers over large ocean expanses (Morreale et al. 2007), commonly within the 20°C isotherms (Márquez 1990). In the East Pacific, they are present from 30°N to 15°S and often seen within 1,200 nautical miles from shore although they have been sighted as far as 140°W (IATTC 2004). Western Atlantic Olive Ridleys appear to remain in neritic waters after breeding (Pritchard 1976, Reichart 1993).
Demographic features / Reproduction
The species displays three modes of reproduction: arribada, dispersed nesting, and mixed strategy (Bernardo and Plotkin 2007). The first mode represents a synchronous, mass nesting behaviour that may include hundreds to thousands of females over a period of days and occurs in fewer than a dozen places worldwide. The more common form of nesting is dispersed or “solitary” with no apparent synchronicity between individual events. At some localities, a mixture of these two forms of nesting can also occur. In general, individual Olive Ridleys may nest one, two or three times per season, with approximately 100–110 eggs per clutch (Pritchard and Plotkin 1995). For this assessment we have used an average number of 2.5 nests/female/season and 105 eggs/nest. In contrast to other sea turtle species, the reproductive cycle is nearly annual (over 60% of turtles nest every year; Márquez 1990). Solitary nesters oviposit on 14 day cycles whereas arribada nesters approximately every 28 days (Pritchard 1969, Kalb and Owens 1994, Kalb 1999). Kalb (1999) found that within a nesting season solitary nesters use multiple beaches for oviposition but arribada nesters display nest site fidelity. There are extreme variations in hatching rates between nesting beaches, however, in general they are much higher in solitary nesting beaches where around 80% is common and sometimes even higher (Gaos et al. 2006). It is widely recognized that survivorship is extremely low on high-density arribada nesting beaches because of density-dependent mortality (Cornelius et al. 1991) leading to hatching rates as low as 1 to 8% (Cornelius et al. 1991). Moreover, turtles return approximately every month during a discrete nesting season (three to six months) and nests that remained intact during the previous month are again at risk when new waves of turtles crawl ashore. On solitary nesting beaches, where density-dependent mortality is not a factor, hatching rates are significantly higher (Castro 1986, Gaos et al. 2006). Post-hatching survivorship is unknown and there is no information available on recruitment rates. Presumably, like other sea turtles, Olive Ridleys experience high mortality in their early life stages. Juveniles are believed to occur in similar habitats as the adults (i.e,. pelagic waters) where they forage on gelatinous prey such as jellyfish, salps and tunicates (Kopitsky et al. 2004).
Comments: Habitat includes tropical and subtropical waters, ranging from protected, shallow, marine and estuarine waters, including bays and lagoons, to offshore areas well beyond the continental shelf (NMFS and USFWS 2007). Nesting occurs on upper beaches. Individuals sometimes change to a different nesting beach within a single nesting season (see Eckert et al. 1989).
Water temperature and chemistry ranges based on 11411 samples.
Depth range (m): 0 - 0
Temperature range (°C): 18.880 - 29.382
Nitrate (umol/L): 0.008 - 7.680
Salinity (PPS): 30.295 - 37.158
Oxygen (ml/l): 4.208 - 5.338
Phosphate (umol/l): 0.067 - 0.526
Silicate (umol/l): 0.787 - 8.023
Temperature range (°C): 18.880 - 29.382
Nitrate (umol/L): 0.008 - 7.680
Salinity (PPS): 30.295 - 37.158
Oxygen (ml/l): 4.208 - 5.338
Phosphate (umol/l): 0.067 - 0.526
Silicate (umol/l): 0.787 - 8.023
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Warm tropical and subtropical marine waters, prefers shallow waters.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
At least in the eastern Pacific Ocean this species is nomadic when not nesting; distinct migration corridors apparently do not exist (NMFS and USFWS 2007). Individuals migrate up to thousands of kilometers between nesting and non-nesting habitats. Turtles tagged in Costa Rica have been recovered in Ecuador and Mexico (Cornelius and Robinson 1983).
The Olive Ridley is a chiefly carnivorous species feeding on invertebrates and protochordates such as jellyfish, snails, shrimp and crabs. The Olive Ridley Turtle has a tendency to eat a wide variety of foods which has lead to many attempts on its behalf to ingest trash such as plastic bags and Styrofoam. Surprisingly, in captivity, this species has been observed to be cannibalistic. Most feeding takes place in shallow, soft-bottomed waters. The Olive Ridley Turtle has also been known to principally feed on algae in areas devoid of other food sources.
Comments: Diet includes fishes, jellyfish, tunicates, salps, crustaceans, mollusks, sea urchins, and seaweed.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 - 300
Comments: On a global mapping scale, there are several dozen known nesting areas (NMFS and USFWS 2007).
Comments: This is the most abundant of all sea turtles (more than 1 million adults).
Hatchlings are preyed upon by crabs, birds, and fishes. Humans collect eggs and kill adults. Predation on solitary nests by native mammals in Costa Rica was relatively greater than on arribada nests (Eckrich and Owens 1995, Herpetologica 51:349-354). See Iverson 1991 for a compilation of data on egg survivorship (to hatching and to age 1 year) (variable but not more than 0.60).
Life History and Behavior
Mainly carnivorous, food items include various crustaceans, molluscs, jellyfish, and fish. Nesting often involves huge concentrations of females. Not known to nest in Egypt.
While the exact age at which reproduction occurs is not known, females usually reach a length of 60 cm before becoming reproductively active. Mating usually occurs on beaches during the spring and early summer in North America and is not monogamous. Male sperm is stored within the female for use throughout the entire breeding season. Mating takes place just offshore of the breeding beaches. Females choose to return to their beach of birth and will do this by remembering the smell of the beach through enhanced chemosensors. Nesting takes place during the night with the females riding in on the high tide and usually coincides with the first or last quarter of the moon. The Olive Ridley turtle is well known for its mass nesting, with 300 or more females at a time coming ashore. Situating themselves approximately 50 m from the sea, females will dig a nest 30-55 cm deep, depositing on average 107 eggs, and then return to the sea. This entire process takes the female turtles less then an hour. Since females store sperm in their bodies for later use, a single female can nest multiple months in a row. The eggs resemble white ping-pong balls and hatch within 45-51 days depending on incubation temperatures, which will also determine the sex of the turtle. The turtles face varying degrees of success in each of the clutches that are laid in large groups to increase their success of surviving.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)
Clutch size is about 30-170 (most often 100-110). Incubation lasts about 50 days. Individual females may nest 1-3 (usually 2) times during a single season and may nest in successive years. In the Pacific Ocean, females first nests at an age of 10-18 years (median 13). (see NMFS and USFWS 2007).
Nesting is highly synchronized in some areas; 100s to 10,000s of females may emerge and nest within a period of a few hours or days. Solitary nesting also occurs. In the eastern Pacific, synchronized nesting occurs annually at several beaches in Mexico, Nicaragua, Costa Rica, and Panama from June through December; during the same period, ridleys emerge to nest solitarily along the entire coast from Mexico to Colombia (NMFS and USFWS 2007).
Molecular Biology and Genetics
Barcode data: Lepidochelys olivacea
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Lepidochelys olivacea
Public Records: 5
Specimens with Barcodes: 16
Species With Barcodes: 1
Within the past thirty years the Olive Ridley Turtle has experienced population loss due to hunting at nesting sites for the female's skin and meat. The Olive Ridley Turtle is still the most abundant of all sea turtles, yet it nests at only five beaches in the world. Governments are in the process of protecting these nesting sites and populations. The United States has passed a law requiring that all shrimp sold in the United States must be harvested by companies with "Turtle Excluder Devices" that allow sea turtles to safely escape capture in shrimping nets.
IUCN Red List of Threatened Species: vulnerable
IUCN Red List Assessment
Red List Category
Red List Criteria
In accordance with the IUCN guidelines for Red List Assessments, the focus of this evaluation has been the number of mature individuals (IUCN 2001). For Olive Ridleys, as with other sea turtle species, as it is not possible to survey mature individuals we used an index of abundance in the form of the number of annual nesting females. Although not all females breed every year (see section on Reproduction below) and males are not evaluated, this index is considered to be the most reliable estimator for long-term population trends of marine turtles since the proportion of the total number of females that nest in any given year and the sex ratio is believed to be fairly constant across time within and between subpopulations (Meylan 1982, Limpus 1996).
Direct counts of the number of nesting females (NF) are not always available so we also relied on alternative information that can be converted to NF: number of nests per season, nests/km/yr or number of protected nests per season; annual estimates of hatchling or egg production, or census estimates of nesting females from arribada rookeries. When these proxies were used, the counted units were converted to NF based on the following constants: 105 eggs/nest and 2.5 nests/season/female. Some conservation programs reported annual number of protected nests but did not include the quantity of poached or otherwise destroyed or predated nests. For these cases we extrapolated to the total number of nests based on local estimates of conservation efficiency. All conversions to NF were made under the assumptions that (a) the mean number of eggs/nest and the number of nests/female/season do not differ significantly over the timescales we have used; and (b) the effort and the coverage of the biological parameters we used are reasonably constant through the time frame evaluated. In cases where the different surveys involved different levels of coverage, explicit corrections were made and specified in the result tables.
In spite of the Olive Ridley being the most abundant sea turtle, available quantitative information is extremely scarce and unevenly distributed across regions. We thus relied on a subset of the world’s rookeries which, we assume, exhibit population trends that are representative of the population as a whole or, at least, for each of the regions. We selected 28 Index Sites (see Figure 1 and Table 1 in the attached PDF, see link below) for which reasonably long time series of quantitative data are available. They include all the largest known populations, as well as an assortment of smaller rookeries from almost all of the regions where the species is found. All sites are assumed to be demographically independent. However, although genetic data indicate a high degree of inter-rookery migration between some rookeries (e.g., Brazil-Suriname- Bowen et al. (1998); between México to Central America in the Eastern Pacific- Briseño-Dueñas (1998)) the results reflect events within an evolutionary timescale (many generations). Within the time span relevant to the assessment (two to three generations), available evidence suggests significant demographic independence between the pairs of rookeries in question (e.g., mark-recapture in Nancite and Ostional indicate the vast majority are different turtles- reviewed by Bernardo and Plotkin (2007); absence of exchange by tagged turtles and non-overlapping nesting seasons Brazil vs Suriname/French Guiana- de Silva et al. (in press); and the lack of re-colonization of depleted arribadas in Jalisco and Guerrero in México by the very large Escobilla rookery, 500 to 1,000 km distant in over four decades).
The population abundance estimates were based on raw data or on extrapolations from regressions performed on available data. As the relatively data-rich trends consistently indicated exponential trajectories we relied on these as the method of choice for extrapolations. Some data sets contained a number of trajectories across the time frames employed and in these more than one regression was employed or a combination of regressions and raw data. We have constrained our back extrapolations to time spans close to known historical events that are believed to have defined major abundance changes in order to avoid gross exaggerations with no supporting evidence. This has, however, meant that in some cases the extrapolations have only been performed back two generations (40 years) and could be considered underestimates of decline.
Uncertainties in the assessment process
Calculations based on very different datasets obtained by different workgroups, using multiple survey methods and spanning many decades are fraught with uncertainties. A number of these could be biasing our assessment. (1) Combining abundance information for individual rookeries obtained with a number of different methodologies could provide a source of error. However, we believe that the magnitude of these errors is of minor significance to the final declines estimated. (2) Because of the assessment’s requirement for quantitative information, a very small proportion of the total known rookeries were included, and some regions are not well represented. The bias this introduces is further augmented since it is most likely that rookeries having long time series of data are also the most monitored and hence the better protected. In this case the estimates of decline will be underestimated relative to the true trends for the more numerous and less well monitored/protected rookeries. This is likely the case for regions with little (Indian Ocean and Western Pacific Ocean) or no (entire Eastern Atlantic) representation in our assessment that contribute very little to our global decline values yet where reports with qualitative evidence indicate extensive population declines (reviewed by Frazier et al. 2007, Cornelius et al. 2007). Nonetheless, although ideally a global assessment should incorporate full data from all regions to derive robust evaluations, the available information on the geographic distribution of abundances suggests that the largest rookeries are concentrated in regions with good representation and thus their inclusion will not significantly affect the global results. This is reflected at the regional level and in results for non-arribada rookeries where our sample bias will probably have caused an underestimation of true decline levels. (3) The extent of extrapolations into time past is an aspect that will undoubtedly contribute to the uncertainty of the results, particularly with scarce information. We have avoided extrapolating far beyond the oldest datasets to avoid this type of errors and thus consider that our results are conservative.
Rationale for the Red List Assessment:
In spite of scarcity in historical data, information from diverse sources has made it possible to evaluate a global decline for this widely distributed species over time periods ranging from decades to 2-3 generations. Striking regional differences are observed in the estimations that undoubtedly indicate far lower survival probabilities in some of the regions than what the global results would suggest.
There was also a stark and recurring contrast between the decline estimates for subpopulations grouped according to breeding strategy- arribada or non-arribada (solitary). The global decline rate estimated from non-arribada subpopulations (-63 to -83%) reflects a widespread low conservation status for these types of subpopulations that suggests they haven’t recovered to historical (pre 1960) levels even in regions with long-term protection programs (e.g., over four decades in México) in spite generalized increments over the last decade (Márquez et al. 1998). This needs to be highlighted because rookeries with non-arribada behavior are many times more numerous than those that nest as arribadas (e.g., in México about 98% of Olive Ridley subpopulations are non-arribada). Yet, as their abundances are up to three to four orders of magnitude smaller than arribada rookeries, they have an insignificant influence on the global decline estimates. In fact, the global net decline for the Olive Ridley is driven principally by population trends in just two arribada populations, Escobilla (México) and Ostional (Costa Rica), both in the Eastern Pacific.
The global decline value estimated on the basis of estimated population reductions of the annual number of Olive Ridley nesting females at subpopulations in the Index Sites used ranged between 31 and 36% (see Table 3 in the attached PDF, see link below). As most of the back extrapolations were limited to two generations it is likely that this value is conservative.
When deciding whether to apply Red List decline criterion A1 (the causes of reduction are clearly reversible AND understood AND ceased) or A2 (the causes of reduction may not have ceased OR may not be understood OR may not be reversible) to obtain decline thresholds for the listing process three characteristics of the species’ decline need to be analyzed (SPWG 2006): (1) is the reduction reversible?, (2) are the causes of the reduction identified and understood?, and (3) have the threatening factors ceased? Since the decline estimated is driven by result from arribada rookeries, the questions need to be addressed against what is known for these types of populations. While it would appear that the elimination of large scale commercial exploitation of the Olive Ridley for leather and local consumption has allowed for the stabilization of a significant portion of rookeries, particularly in the Eastern Pacific and in particular facilitated the growth of arribada rookeries such as Escobilla and Ostional, the population growth of Mismaloya, Tlalcoyunque and Chacahua in the same region and under similar conservation circumstances remain at reduced abundances well below an arribada category. This could indicate that under some circumstances, the reduction of arribada rookeries below a certain level can make it impossible or unlikely for it to recover an arribada behavior. The major cause for the reduction in the species is thought to have been the massive commercial over-exploitations, particularly in the Eastern Pacific. Furthermore, we do not yet fully understand nor are able to manage other stressors, some intrinsic or at least due to interactions between the overcrowding of growing populations that equally provoke dramatic declines in arribadas such as that of Nancite in spite of decades of protection (Cornelius et al. 2007). Though commercial exploitation of Olive Ridleys for international markets has effectively been eliminated, at local levels significant factors continue to impact individual rookeries such as excessive egg exploitation (e.g., Isla Caña, Panama) or bycatch (such as in Orissa, India). These examples indicate that Olive Ridleys, under current circumstances, do not meet all of the conditions for A1 and hence should be evaluated under criterion A2.
Under A2, the decline estimations obtained for the Olive Ridley Turtle at a global scale correspond to the Vulnerable IUCN Red List threshold (a decline of >30% but <50%.
- 1994Endangered(Groombridge 1994)
- 1990Endangered(IUCN 1990)
- 1988Endangered(IUCN Conservation Monitoring Centre 1988)
- 1986Endangered(IUCN Conservation Monitoring Centre 1986)
National NatureServe Conservation Status
Rounded National Status Rank: N1N - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G3 - Vulnerable
Reasons: Wide range in the tropical and subtropical Pacific, Indian, and Atlantic oceans; population much smaller than historical level; current trend varies among regions; many populations are declining as a result of incidental take by shrimpers, disturbance and development of nesting beaches, exploitation for meat, leather, and eggs, and other factors.
Intrinsic Vulnerability: Highly vulnerable
Environmental Specificity: Very narrow to narrow.
Date Listed: 07/28/1978
Lead Region: Southeast Region (Region 4)
Where Listed: Mexican nesting pop.
Date Listed: 07/28/1978
Lead Region: Southeast Region (Region 4)
Where Listed: except where endangered
Population location: Breeding colony populations on Pacific coast of Mexico
Listing status: E
Population location: Wherever found except where listed as endangered
Listing status: T
For most current information and documents related to the conservation status and management of Lepidochelys olivacea , see its USFWS Species Profile
For the purposes of Red List assessments, generation length is defined as the “average age of parents” (IUCN 2001). Since this information is not available from direct observation of sea turtle species we derived a comparable value from estimates of age at which 50% of the breeders are expected to have survived, using information for age at sexual maturity and adult survival rates. An important caveat is that, while it is known that different populations of the same species can attain sexual maturity at different ages (Heppell et al. 2003) and therefore different values would need to be taken into account for different regions, the information is only available for a single region and we have had to assume the estimated values are generally applicable on a global scale. The only published study on growth and age for Olive Ridleys (Zug et al. 2006) indicates a mean age at sexual maturity for North-central Pacific Ridley sea turtles of around 13 years (range of 10-18 years). We calculated the time it would take for a cohort of breeders to reach 50% of its original size from Sn =50%, where n is years since age at first reproduction, and S is annual survival. Solving for n, n = ln(0.5)/ln(S). As extensive estimates of annual survival rates for female nesters are only available from the better studied sister taxon, Lepidochelys kempii, (TEWG 2000) we used these, which have a range of 85-92% per year. Thus, n50% = 4-9 yrs and our derived average age of female Olive Ridley parents is 17-22 years. We additionally assumed that this value would be the same for male parents. For simplicity, we have used a value of 20 yrs for the species’ generation length in this assessment.
Global Short Term Trend: Decline of 30 to >90%
Comments: Trend varies among different regions (NMFS and USFWS 2007). Some populations are increasing, some are stable, and others are declining.
The time frame for short-term trend (three generations) probably is at least 40 years and may be much longer, so the coded short-term trend refers to the change since the 1960s or earlier.
Since the ban on the harvest of turtles in Mexico, the primary threat to the Mexican nesting population has been reduced and the population appears to be stabilizing (NMFS and USFWS 1998). At La Escobilla, Mexico, the population increased from around 50,000 nests in 1988 to more than 1 million nests by 2000 (see NMFS and USFWS 2007).
Global Long Term Trend: Decline of 50 to >90%
Comments: Over the long term, likely there has been at least a moderate to substantial range-wide decline in population size and number/condition of occurrences (NMFS and USFWS 2007).
Egg harvest. Olive Ridleys and their eggs have been harvested, mostly unsustainably, worldwide. However, the current impact is difficult to evaluate because of other simultaneous factors such as incidental take in commercial fisheries. Nonetheless, there is documentation of recent egg use causing declines (Cornelius et al. 2007). From México to Colombia, Olive Ridley eggs have been and still are used for personal and commercial use (Lagueux 1989, Arauz 2000, Campbell 2007, Cornelius et al. 2007). Laws regulating turtle egg use vary among countries, and even where laws prohibit egg use, illegal use of Olive Ridley eggs is believed to be widespread because enforcement is either non-existent or insufficient. On unprotected solitary nesting beaches (most are unprotected), egg extraction often approaches 100%. Human use of turtle eggs for consumption and domestic animal consumption historically was widespread in the Indian Ocean and continues today largely wherever Ridleys nest (Cornelius et al. 2007). Egg use has been reported in India, Bangladesh, Myanmar, Sri Lanka, Andaman Islands, Pakistan and Malaysia and is believed to have caused the decline of Olive Ridleys in these countries (Cornelius et al. 2007). Even at monitored beaches a proportion of the eggs are still lost to poaching.
Directed take of adults. In the East Pacific, although Olive Ridley turtle fisheries are now closed, illegal take of adult turtles still occurs widely with an unknown level of impact. There is evidence that thousands of Olive Ridleys are still taken each year along the Pacific coast of México (Frazier et al. 2007). In the West Atlantic, the direct take of adults has diminished over time to negligible levels (Cornelius et al. 2007). In the Indian Ocean, the use of adult Olive Ridleys and their eggs for personal use has been and continues to be widespread (Frazier 1982, Frazier et al. 2007), and market-driven harvesting of eggs and females from nesting beaches are considered the greatest threat (Cornelius et al. 2007). Personal, subsistence use of adult Olive Ridley turtles is widespread worldwide (Cornelius et al. 2007, Frazier et al. 2007). Olive Ridleys and/or their eggs are used along the entire coast of West Africa (including Macaronesia) and sold in local and regional markets (Fretey 2001).
Bycatch in fisheries
The incidental capture of Olive Ridleys occurs worldwide in trawl fisheries, longline fisheries, purse seines, gill net and other net fisheries and hook and line fisheries (Frazier et al. 2007). The impact of the incidental capture of Olive Ridleys in fisheries has been well documented for some regions but not for others. In some locations where by-catch statistics are unavailable from fisheries, cause and effect has been used to implicate a fishery in the decline of Olive Ridleys. The incidental capture of Olive Ridleys in the shrimp trawl fishery in the western Atlantic, is believed to be the main cause of the significant population decline observed there since the 1970s and currently the number of Olive Ridleys by caught in trawl fisheries off the coasts of Surinam and French Guiana is believed to be approximately a couple of thousand turtles annually (Godfrey and Chevalier 2004, Frazier et al. 2007). Gillnets and other fishing methods in this region also capture Olive Ridleys incidentally but to a lesser extent than shrimp trawl fishery (Frazier et al. 2007). Bycatch in trawl fisheries off Sergipe State in Brazil is considered the most pressing threat to that population (Thomé et al. 2003). In the eastern Atlantic, the incidental capture of Olive Ridleys by commercial fisheries is thought to be a significant threat but very little systematic data is available (Frazier et al. 2007). Incidental mortality of Olive Ridleys is worst along the coast of Orissa, India with arribada Olive Ridleys gathering to nest were fishing effort is high. Every year since the early 1980s, thousands or tens of thousands of Olive Ridleys have stranded dead on the Orissa beaches, presumably as a result of incidental capture in shrimp trawls (Pandav 2000). A gill net fishery also operates in the region and contributes to the ridley mortality along this coastline. Incidental capture in fisheries is also believed to be a serious threat in the eastern Pacific (Frazier et al. 2007) where Olive Ridleys aggregate in large numbers off shore from nesting beaches (Kalb et al. 1995, Kalb 1999), but the information available is incomplete (Pritchard and Plotkin 1995, NMFS/USFWS 1998). Incidental capture of Olive Ridleys in this region has been documented in shrimp trawl fisheries, longline fisheries, purse seine fishery and gill net fisheries (Frazier et al. 2007). Incidental capture of sea turtles in shrimp trawls is a serious threat along the coast of Central America, with an estimated annual capture for all species of marine turtle exceeding 60,000 turtles, most of which are Olive Ridleys (Arauz 1996). Recent growth in the longline fisheries of this region are also a serious and growing threat to Olive Ridleys and have the potential to capture hundreds of thousands of Ridleys annually (Frazier et al., 2007). Bycatch of Olive Ridleys is high in Indonesian tuna long-lines and shrimp trawls although mortality appears to be low (WWF Indonesia, unpublished data).
Degradation, transformation and destruction of natural conditions at nesting beaches from coastal developments continue to threaten the long-term survival of many Olive Ridley rookeries. Transformation of nesting habitat comes from the construction of new aquaculture ponds, fishing harbours and tourist facilities, as well as growth of existing coastal villages which are increasing in many parts of the world within the range of the Olive Ridley, particularly along the east coast of India (Pandav and Choudhury 1999) and in some zones in coastal México to Central America (Cornelius et al. 2007). These impacts contribute stress directly through the loss of nesting habitat or indirectly through changes in the thermal profiles of the beach, increased light pollution (Witherington 1992) and sewage effluents.
Global warming has the potential to impact the habitats and ecosystems of Olive Ridley populations worldwide (Hays et al. 2003, Weishampal 2004) but the specific impacts are purely speculative at this time. Most accounts have focused on the impact of global warming on incubation temperatures of eggs, which influence the sex ratio of the embryos (Hays et al. 2003).
Diseases and predation
Extremely little is known about diseases and their effects on Olive Ridley abundance. The only disease identified in the literature for Olive Ridleys is fibropapilloma, a herpes-virus found in sea turtles nearly worldwide (Herbst 1994). The incidence of fibropapilloma is not believed to be high in Olive Ridleys but has been observed in Olive Ridleys nesting in Costa Rica (Herbst 1994) and in México (Vasconcelos et al. 2000). At some individual rookeries, the predation by wild pigs and/or feral dogs can be substantial (e.g., in the Andaman Islands; Andrews et al. 2001). Infestation of developing eggs by fly and beetle larvae can cause significant mortality of embryos. In an extremely worrying case, the beetle larvae (Omorgus suberosus fabricius) has become a plague in the world’s largest arribada rookery in Escobilla, México where it is provoking steep drops in the hatching efficiency of the clutches laid, from a typical 30% for this colony (Márquez 1990) to less than 5% in some areas (López-Reyes and Harfush 2000). When combined with the relatively low hatching rates of high-density arribada beaches and the destruction of eggs laid by previous nesters, this problem could provoke the rookery’s decline.
Degree of Threat: Very high - high
Comments: Extensive over-harvesting of olive ridleys and their eggs caused severe population declines in some parts of the range. Current major threats include incidental take in commercial fisheries (especially shrimp trawl fisheries), harvest in artisanal fisheries, harvest of eggs and turtles, and disturbance and development of neasting beaches.
This species appears to be distributionally flexible at sea and perhaps is not strongly affected by changes is ocean temperatures, although relatively low numbers of nesting turtles on Pacific beaches have been associated with El Nino conditions (see NMFS and USFWS 2007).
On the basis of the species’ classification in the IUCN Red List or in national endangered species lists, local legislatures of range states confer protection to the Olive Ridley. Although this sanctions law-enforcement, the implementation remains patchy at the global scale because of paucity in enforcement capabilities. Successful conservation has usually relied on well-coordinated national programs in combination with local and non-governmental organizations incorporating public outreach. Statutory use and enforcement of the Turtle Excluder Devices in the shrimp trawlers has also proven critical in some areas with high levels of interaction with this fishery.
Despite the legislative efforts to protect the Olive Ridley, human impacts continue to be significant. In some areas (such as West Africa and South East Asia), extensive monitoring needs to be implemented to identify regions and stressors requiring priority actions. Bycatch and illegal take particularly from the coastal, artisanal fisheries need to be evaluated through adequate on-board observer programs and properly addressed. The beetle infestation of the Escobilla rookery must be adequately evaluated and acceptable measures of biological control of the insect need to be implemented. The impact from the increasing development of much of the range state’s coastline has to be evaluated and suitable mitigation measures implemented.
Management Requirements: See "Recovery plan for U.S. Pacific populations of the olive ridley turtle (LEPIDOCHELYS OLIVACEA)" (NMFS 1998).
Global Protection: Many to very many (13 to >40) occurrences appropriately protected and managed
Needs: Frazer (1992) emphasized the primary need for clean and productive marine and coastal environments; installation of turtle excluder devices in shrimp trawl nets and use of low pressure sodium lighting on beaches were suggested as appropriate sea turtle conservation technologies, whereas headstarting, captive breeding, and hatcheries were regarded as ineffective at best.
Greatest management need is protection from excessive commercial exploitation of adults and eggs.
See recovery plan for U.S. Pacific populations of the olive ridley turtle (NMFS and USFWS 1998).
Relevance to Humans and Ecosystems
As with other large sea turtles, the Olive Ridley Sea Turtle is considered somewhat of a pest for commercial fishermen for they often find these turtles caught in their nets.
Since turtle egg harvesting became legal on the Playa Ostional in Costa Rica in 1987, local villagers have been able to sell nearly 3 million eggs collected from the beaches each season. The villagers can legally harvest only eggs laid during the first 36 hours of a nesting period since any turtles nesting after this period would destroy them. Approximately 27 million eggs are left unharvested and are protected from predators such as snakes and birds by the villagers.
Comments: This species is a primary source of skins for commercially produced turtle leather; annual harvest in the 1970s (mainly Mexico & Ecuador) was estimated to be in the 100,000s (Mack et al. 1982).
Olive ridley sea turtle
The olive ridley sea turtle (Lepidochelys olivacea), also known as the Pacific ridley sea turtle, is a medium-sized species of sea turtle found in warm and tropical waters, primarily in the Pacific and Indian Oceans.
The olive ridley is a small sea turtle, with an adult carapace length averaging 60 to 70 cm. The heart-shaped carapace is characterized by four pairs of pore-bearing inframarginal scutes on the bridge, two pairs of prefrontals, and up to 9 lateral scutes per side. Olive ridleys are unique in that they can have variable and asymmetrical lateral scute 6 to 8 counts ranging from five to 9 plates on each side, with six to eight being most commonly observed. Each side of the carapace has 12–14 marginal scutes. The carapace is flattened dorsally and highest anterior to the bridge. It has a medium–sized, broad head that appears triangular from above. The head's concave sides are most obvious on the upper part of the short snout. It has paddle-like forelimbs, each having two anterior claws. The upperparts are grayish green to olive in color, but sometimes appear reddish due to algae growing on the carapace. The bridge and hingeless plastron of an adult varies from greenish white in younger individuals to a creamy yellow in older specimens.
Hatchlings are dark gray with a pale yolk scar, but appear all black when wet. Carapace length ranges from 37 to 50 mm. A thin, white line borders the carapace, as well as the trailing edge of the fore and hind flippers. Both hatchlings and juveniles have serrated posterior marginal scutes, which become smooth with age. Juveniles also have three dorsal keels; the central longitudinal keel gives younger turtles a serrated profile, which remains until sexual maturity is reached.
Olive ridleys rarely weigh over 50 kg (110 lb). A study in Oaxaca, Mexico, reported a sample of adults ranged from 25 to 46 kg; adult females weighed an average of 35.45 kg (n=58), while adult males weighed significantly less, averaging 33.00 kg (n=17). Hatchlings usually weigh between 12.0 and 23.3 g. Adults are somewhat sexually dimorphic. Mature males have longer and thicker tails, which are used for copulation, and the presence of enlarged and hooked claws on the males' front flippers allow them to grasp the female carapace during copulation. Males also have longer, more tapered carapaces than females, which have round, dome-like carapaces. Males also have more concave plastrons, believed to be another adaptation for mating. The plastrons of males may also be softer than females.
The olive ridley turtle has a circumtropical distribution, living in tropical and warm waters of the Pacific and Indian Oceans from India, Arabia, Japan, and Micronesia south to southern Africa, Australia, and New Zealand. In the Atlantic Ocean, it has been observed off the western coast of Africa and the coasts of northern Brazil, Suriname, Guyana, French Guiana, and Venezuela. Additionally, the olive ridley has been recorded in the Caribbean Sea as far north as Puerto Rico. It is also found in the eastern Pacific Ocean from the Galapagos Islands and Chile north to the Gulf of California, and along the Pacific coast to at least Oregon Migratory movements have been studied less intensely in olive ridleys than other species of marine turtles, but they are believed to use the coastal waters of over 80 countries. Historically, this species has been widely regarded as the most abundant sea turtle in the world. More than one million olive ridleys were commercially harvested off the coasts of Mexico in 1968 alone.
The population of Pacific Mexico was estimated to be at least 10 million prior to the era of mass exploitation. More recently, the global population of annual nesting females has been reduced to about two million by 2004, and was further reduced to 852,550 by 2008. This indicated a dramatic decrease of 28 to 32% in the global population within only one generation (i.e., 20 years).
The olive ridley sea turtles are considered the most abundant, yet globally they have declined by more than 30% from historic levels. These turtles are considered endangered because of their few remaining nesting sites in the world. The eastern Pacific turtles have been found to range from Baja California, Mexico, to Chile. Pacific olive ridleys nest around Costa Rica, Mexico, Nicaragua, and the northern Indian Ocean; the breeding colony in Mexico was listed as endangered in the US on July 28, 1978.
Olive ridley turtles are best known for their behavior of synchronized nesting in mass numbers, termed arribadas. In the Indian Ocean, the majority of olive ridleys nest in two or three large groups near Gahirmatha in Odisha. In 1991, over 600,000 turtles nested along the coast of Odisha in one week. Nesting occurs elsewhere along the Coromandel Coast and Sri Lanka, but in scattered locations. However, olive ridleys are considered a rarity in most areas of the Indian Ocean.
They are also rare in the western and central Pacific, with known arribadas occurring only within the tropical eastern Pacific, in Central America and Mexico. In Costa Rica, they occur at Nancite and Ostional beaches. Two active arribadas are in Nicaragua, Chacocente and La Flor, with a small nesting ground in Pacific Panama. Historically, several arribadas were in Mexico, yet only one remains at Playa Escobilla in Oaxaca.
Although olive ridleys are famed for their arribadas, many of the nesting grounds can only support relatively small to moderate-sized aggregations (about 1,000 nesting females). The overall contribution and importance of these nesting beaches to the population may be underestimated by the scientific community.
Some of the olive ridley's foraging grounds near southern California are contaminated due to sewage, agricultural runoff, pesticides, solvents, and industrial discharges. These contaminants have been shown to decline the productivity of the benthic community, which negatively affects these turtles, which feed from these communities. The increasing demand to build marinas and docks near Baja California and southern California are also negatively affecting the olive ridleys in these areas, where an increase in oil and gas will be released into these sensitive habitats. Another threat to these turtles are power plants, which have documented juvenile and subadult turtles becoming entrained and entrapped within the saltwater cooling intake systems.
The olive ridley was first described as Testudo mydas minor, Suckhow, 1798. It was later renamed Chelonian olivacea, Eschscholtz, 1829, and eventually Lepidochelys olivacea Fitzinger, 1843. Because Eschscholtz was the first to propose the specific epithet olivacea, though, he was credited with the valid name Lepidochelys olivacea Eschscholtz, 1829.
The genus name is derived from the Greek words lepidos, meaning scale, and chelys, which translates to turtle. This could possibly be a reference to the supernumerary costal scute counts characteristic of this genus. The etymology of the English vernacular name olive is somewhat easier to resolve, as its carapace is olive green in color. However, the origin of ridley is still somewhat unclear. Lepidochelys is the only genus of sea turtles containing more than one extant species: L. olivacea and the closely related L. kempii (Kemp's ridley). 
Ecology and behavior
Mating is often assumed to occur in the vicinity of nesting beaches, but copulating pairs have been reported over 1,000 km from the nearest beach. Research from Costa Rica revealed the number of copulating pairs observed near the beach could not be responsible for the fertilization of the tens of thousands of gravid females, so a significant amount of mating is believed to have occurred elsewhere at other times of the year.
The Gahirmatha Beach in Kendrapara district of Odisha (India), which is now a part of the Bhitarkanika Wildlife Sanctuary, is the largest breeding ground for these turtles. The Gahirmatha Marine Wildlife Sanctuary, which bounds the Bhitarkanika Wildlife Sanctuary to the east, was created in September 1997, and encompasses Gahirmatha Beach and an adjacent portion of the Bay of Bengal. Bhitarkanika Mangroves were designated a Ramsar Wetland of International Importance in 2002. It is the world's largest known rookery of Olive Ridley sea turtles. Apart from Gahirmatha rookery, two other mass nesting beaches have been located which are on the mouth of rivers Rushikulya and Devi. The spectacular site of mass congregation of Olive Ridley sea turtles for mating and nesting enthralls both the scientists and the nature lovers throughout the world.
Olive Ridley sea turtles migrate in huge numbers from the beginning of November, every year, for mating and nesting along the coast of Orissa. Gahirmatha coast has the annual nesting figure between one hundred to five hundred thousand, each year. there has been decline in the population of these turtles in the recent past due to mass mortality. Olive Ridley sea turtle has found place in Schedule - I of Indian Wildlife (Protection) Act, 1972 (amended 1991). All the species of sea turtles in the coastal water of Orissa are listed as "endangered" as per IUCN Red Data Book. The sea turtles are protected under the 'Migratory Species Convention' and CITES (Convention of International Trade on Wildlife Flora and Fauna). India is a signatory nation to all these conventions. The 'Homing' characteristics of the Ridley sea turtles make them more prone to mass casualty. The voyage to the natal nesting beaches is the dooming factor for the sea turtles. Since Gahirmatha coast serves as the natal nesting beach for millions of turtles, it has immense importance on turtle conservation.
Olive ridleys generally begin to aggregate near nesting beaches about two months before nesting season, although this may vary throughout its range. In the eastern Pacific, nesting occurs throughout the year, with peak nesting events (arribadas) occurring between September and December. Nesting beaches can be characterized as relatively flat, midbeach zone, and free of debris. Beach fidelity is common, but not absolute. Nesting events are usually nocturnal, but diurnal nesting has been reported, especially during large arribadas. Exact age of sexual maturity is unknown, but this can be somewhat inferred from data on minimum breeding size. For example, the average carapace length of nesting females (n = 251) at Playa Nancite, Costa Rica was determined to be 63.3 cm, with the smallest recorded at 54.0 cm. Females can lay up to three clutches per season, but most will only lay one or two clutches. The female will remain near shore for the internesting period, which is about one month. Mean clutch size varies throughout its range and decreases with each nesting attempt.
A mean clutch size of 116 (30–168 eggs) was observed in Surinam, while nesting females from the eastern Pacific were found to have an average of 105 (74–126 eggs). The incubation period is usually between 45 and 51 days under natural conditions, but may extend to 70 days in poor weather conditions. Eggs incubated at temperatures of 31 to 32°C will produce only females; eggs incubated at 28°C or less will produce solely males; and incubation temperatures of 29 to 30°C will produce a mixed sex clutch. Hatching success can vary by beach and year, due to changing environmental conditions and rates of nest predation.
Most observations are typically within 15 km of mainland shores in protected, relatively shallow marine waters (22–55 m deep). Olive ridleys are occasionally found in open waters. The multiple habitats and geographical localities used by this species vary throughout its life cycle. More research is needed to acquire data on and use of pelagic habitats.
The olive ridley is predominantly carnivorous, especially in immature stages of the life cycle. Animal prey consists of protochordates or invertebrates, which can be caught in shallow marine waters or estuarine habitats. Common prey items include jellyfish, tunicates, sea urchins, bryozoans, bivalves, snails, shrimp, crabs, rock lobsters, and sipunculid worms. Additionally, consumption of jellyfish and both adult fish (e.g. Sphoeroides) and fish eggs may be indicative of pelagic (open ocean) feeding. The olive ridley is also known to feed on filamentous algae in areas devoid of other food sources. Captive studies have indicated some level of cannibalistic behavior in this species.
Known predators of olive ridley eggs include raccoons, coyotes, feral dogs and pigs, opossums, coatimundi, caimans, ghost crabs, and the sunbeam snake. Hatchlings are preyed upon as they travel across the beach to the water by vultures, frigate birds, crabs, raccoons, coyotes, iguanas, and snakes. In the water, hatchling predators most likely include oceanic fishes, sharks, and crocodiles. Adults have relatively few known predators, other than sharks, and killer whales are responsible for occasional attacks. Females are often plagued by mosquitos during nesting. Humans are still listed as the leading threat to L. olivacea, responsible for unsustainable egg collection, slaughtering nesting females on the beach, and direct harvesting adults at sea for commercial sale of both the meat and hides.
Other major threats include mortality associated with boat collisions, and incidental takes in fisheries. Trawling, gill nets, ghost nests, longline fishing, and pot fishing, have significantly affected olive ridley populations, as well as other species of marine turtles. Between 1993 and 2003, more than 100,000 olive ridley turtles were reported dead in Odisha, India from fishery-related practices. In addition, entanglement and ingestion of marine debris is listed as a major threat for this species. Coastal development, natural disasters, climate change, and other sources of beach erosion have also been cited as potential threats to nesting grounds. Additionally, coastal development also threatens newly hatched turtles through the effects of light pollution. Hatchlings which use light cues to orient themselves to the sea are now misled into moving towards land, and die from dehydration or exhaustion, or are killed on roads.
However, the greatest single cause of olive ridley egg loss results from arribadas, in which the density of nesting females is so high, previously laid nests are inadvertently dug up and destroyed by other nesting females. In some cases, nests become cross-contaminated by bacteria or pathogens of rotting nests. For example, in Playa Nancite, Costa Rica, only 0.2% of the 11.5 million eggs produced in a single arribada successfully hatched. Although some of this loss resulted from predation and high tides, the majority was attributed to conspecifics unintentionally destroying existing nests. The extent to which arribadas contribute to the population status of olive ridleys has created debate among scientists. Many believe the massive reproductive output of these nesting events is critical to maintaining populations, while others maintain the traditional arribada beaches fall far short of their reproductive potential and are most likely not sustaining population levels. In some areas, this debate eventually led to legalizing egg collection.
Historically, the olive ridley has been exploited for food, bait, oil, leather, and fertilizer. The meat is not considered a delicacy; the egg, however, is esteemed everywhere. Egg collection is illegal in most of the countries where olive ridleys nest, but these laws are rarely enforced. Harvesting eggs has the potential to contribute to local economies, so the unique practice of allowing a sustainable (legal) egg harvest has been attempted in several localities. Numerous case studies have been conducted in regions of arribadas beaches to investigate and understand the socioeconomic, cultural, and political issues of egg collection. Of these, the legal egg harvest at Ostional, Costa Rica, has been viewed by many as both biologically sustainable and economically viable. Since egg collection became legal in 1987, local villagers have been able to harvest and sell around three million eggs annually. They are permitted to collect eggs during the first 36 hours the nesting period, as many of these eggs would be destroyed by later nesting females. Over 27 million eggs are left unharvested, and villagers have played a large role in protecting these nests from predators, thereby increasing hatching success.
Most participating households reported egg harvesting as their most important activity, and profits earned were superior to other forms of available employment, other than tourism. The price of Ostional eggs was intentionally kept low to discourage illegal collection of eggs from other beaches. The Ostional project retained more local profits than similar egg collection projects in Nicaragua, but evaluating egg harvesting projects such as this suffers from the short timeline and site specificity of findings. In most regions, illegal poaching of eggs is considered a major threat to olive ridley populations, thus the practice of allowing legal egg harvests continues to attract criticism from conservationists and sea turtle biologists. Plotkin's Biology and Conservation of Ridley Sea Turtles, particularly the chapter by Lisa Campbell titled "Understanding Human Use of Olive Ridleys", provides further research on the Ostional harvest (as well as other harvesting projects). Scott Drucker's documentary, Between the Harvest, offers a glimpse into this world and the debate surrounding it.
The olive ridley is classified as Vulnerable according to the International Union for Conservation of Nature and Natural Resources (IUCN), and is listed in Appendix I of CITES. These listings were largely responsible for halting the large scale commercial exploitation and trade of olive ridley skins. The Convention on Migratory Species and the Inter-American Convention for the Protection and Conservation of Sea Turtles have also provided olive ridleys with protection, leading to increased conservation and management for this marine turtle. National listings for this species range from Endangered to Threatened, yet enforcing these sanctions on a global scale has been unsuccessful for the most part. Conservation successes for the olive ridley have relied on well-coordinated national programs in combination with local communities and nongovernment organizations, which focused primarily on public outreach and education.Arribada management has also played a critical role in conserving olive ridleys. Lastly, enforcing the use of turtle excluder devices in the shrimp trawling industry has also proved effective in some areas. Globally, the olive ridley continues to receive less conservation attention than its close relative, the Kemp's ridley (L. kempii).
Several projects worldwide seek to preserve the olive ridley sea turtle population. For example, in Nuevo Vallarta, Mexico, when the turtles come to the beach to lay their eggs, some of them are relocated to a hatchery, where they have a much better chance to survive. If the eggs were left on the beach, they would face many threats such as getting washed away with the tide or getting poached. Once the eggs hatch, the baby turtles are carried to the beach and released.
Another major project, in India involved in preserving the olive ridley sea turtle population was carried out in Chennai, where the Chennai wildlife team collected close to 10,000 Olive Ridley turtle eggs along the Marina coast, of which 8,834 hatchlings were successfully released into the sea in a phased manner.
- Chelonioidea ��� the sea turtle superfamily
- Loggerhead turtle
- Green sea turtle
- Leatherback turtle
- Hawksbill turtle
- Flatback turtle
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- "Marine Turtle Newsletter" - Harold A. Dundee
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- Karnad, Divya; Isvaran, Kavita; Kar, Chandrasekhar S.; Shanker, Kartik (1 October 2009). "Lighting the way: Towards reducing misorientation of olive ridley hatchlings due to artificial lighting at Rushikulya, India". Biological Conservation 142 (10): 2083–2088. doi:10.1016/j.biocon.2009.04.004.
- "Over 8000 turtle hatchlings released", Deccan Chronicle, Chennai, 23 May 2014. Retrieved on 23 May 2014.
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