Olive ridley sea turtle
Olive ridley sea turtle | |
---|---|
Olive ridley sea turtle at Kélonia, an aquarium in Saint-Leu, Réunion | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Testudines |
Suborder: | Cryptodira |
Superfamily: | Chelonioidea |
Family: | Cheloniidae |
Genus: | Lepidochelys |
Species: | L. olivacea
|
Binomial name | |
Lepidochelys olivacea (Eschscholtz, 1829)
| |
Synonyms[3] | |
|
The olive ridley sea turtle (Lepidochelys olivacea), also known commonly as the Pacific ridley sea turtle, is a species of turtle in the family Cheloniidae. The species is the second-smallest[4][5] and most abundant of all sea turtles found in the world. L. olivacea is found in warm and tropical waters, primarily in the Pacific and Indian Oceans, but also in the warm waters of the Atlantic Ocean.[4]
This turtle and the related Kemp's ridley sea turtle are best known for their unique synchronised mass nestings called arribadas, where thousands of females come together on the same beach to lay eggs.[4][5]
Taxonomy
The olive ridley sea turtle may have been first described as Testudo mydas minor by Georg Adolf Suckow in 1798. It was later described and named Chelonia multiscutata by Heinrich Kuhl in 1820. Still later, it was described and named Chelonia olivacea by Johann Friedrich von Eschscholtz in 1829. The species was placed in the subgenus Lepidochelys by Leopold Fitzinger in 1843.[6] After Lepidochelys was elevated to full genus status, the species was called Lepidochelys olivacea by Charles Frédéric Girard in 1858. Because Eschscholtz was the first to propose the specific epithet olivacea, he is credited as the binomial authority or taxon author in the valid name Lepidochelys olivacea (Eschscholtz, 1829). The parentheses indicate that the species was originally described in a different genus.
The
Description
Growing to about 61 cm (2 ft) in
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 fore limbs, each having two anterior claws. The upper parts are grayish-green to olive in color, but sometimes appear reddish due to
Hatchlings are dark gray with a pale yolk scar, but appear all black when wet.[7] Carapace length of hatchlings ranges from 37 to 50 mm (1.5 to 2.0 in). A thin, white line borders the carapace, as well as the trailing edge of the fore and hind flippers.[12] 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.[7]
The olive ridley sea turtle rarely weighs over 50 kg (110 lb). Adults studied in Oaxaca, Mexico,[7] ranged from 25 to 46 kg (55 to 101 lb); adult females weighed an average of 35.45 kg (78.2 lb) (n=58), while adult males weighed significantly less, averaging 33.00 kg (72.75 lb) (n=17). Hatchlings usually weigh between 12.0 and 23.3 g (0.42 and 0.82 oz).
Adults are sexually dimorphic. The mature male has a longer and thicker tail, which is used for
Distribution
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. A female was found alive on an Irish Sea beach on the Isle of Anglesey, Wales, in November 2016, giving this species its northernmost appearance. It was taken in by the nearby Anglesey Sea Zoo, while its health was assessed.[13] A juvenile female was found off the coast of Sussex in 2020.[14] The olive ridley is also found in the eastern Pacific Ocean from the Galápagos 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.[15] Historically, this species has been widely regarded as the most abundant sea turtle in the world.[7] More than one million olive ridleys were commercially harvested off the coasts of Mexico in 1968 alone.[16]
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,[17] and was further reduced to 852,550 by 2008.[1][18] This indicated a dramatic decrease of 28 to 32% in the global population within only one generation (i.e., 20 years).[15]
Olive ridley sea turtles are considered the most abundant, yet globally they have declined by more than 30% from historic levels.[citation needed] 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.[19]
Nesting grounds
Olive ridley turtles exhibit two different nesting behaviours, the most prevalent solitary nesting, but also the behaviour they are best known for, the synchronized mass nesting, termed arribadas.
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
Although olive ridleys are famed for their arribadas, most of the known nesting beaches are only frequented by solitarily nesting females and support a relatively small quantity of nests (100 to 3,000 nests). The overall contribution and importance of solitary nesting females for the population may be underestimated by the scientific community as the hatching success rate of nests at arribada beaches is generally low, but high at solitary nesting beaches.[7]
Isolated nesting does also sporadically occur.[21]
Foraging grounds
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 decrease the productivity of the benthic community, which negatively affects these turtles, which feed from these communities.[7] 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 more oil and gasoline will be released into these sensitive habitats. Another threat to these turtles is power plants, which have documented juvenile and subadult turtles becoming entrained and entrapped within the saltwater cooling intake systems.[7]
Ecology and behavior
Reproduction
Mating is often assumed to occur in the vicinity of nesting beaches, but
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 100,000 and 500,000 each year. A decline in the population of these turtles has occurred in the recent past due to mass mortality. The olive ridley sea turtle has been listed on Schedule – I of the Indian Wildlife (Protection) Act, 1972 (amended 1991). The species is listed as vulnerable under IUCN.[1] The sea turtles are protected under the 'Migratory Species Convention' and Convention of International Trade on Wildlife Flora and Fauna (CITES). 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 them. 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 their 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.[6] Beach fidelity is common, but not absolute. Nesting events are usually nocturnal, but diurnal nesting has been reported, especially during large arribadas.[7] 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.[7] Females can lay up to three clutches per season, but most only lay one or two clutches.[12] The female remains near shore for the internesting period, which is about one month. Mean clutch size varies throughout its range and decreases with each nesting attempt.[18]
A mean clutch size of 116 (30–168 eggs) was observed in Suriname, while nesting females from the eastern Pacific were found to have an average of 105 (74–126 eggs).[12] 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 produce only females; eggs incubated at 28 °C or less produce solely males; and incubation temperatures of 29 to 30 °C produce a mixed-sex clutch.[12] Hatching success can vary by beach and year, due to changing environmental conditions and rates of nest predation.
Habitat
Most observations are typically within 15 km of mainland shores in protected, relatively shallow marine waters (22–55 m deep).[12] Olive ridleys are occasionally found in open waters. The multiple habitats and geographical localities used by this species vary throughout its lifecycle.[6]
Feeding
The olive ridley is predominantly carnvirous. Common prey items include
Threats
Known predators of olive ridley eggs include raccoons, coyotes, feral dogs and pigs,
Other major threats include mortality associated with boat collisions, and incidental takes in fisheries.
The greatest single cause of olive ridley egg loss, though, 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.
Economic importance
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.[18] 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 of 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.[7]
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,[18] 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.
Conservation status
The olive ridley is classified as vulnerable according to the
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 eggs along the Marina coast, of which 8,834 hatchlings were successfully released into the sea in a phased manner.[26]
In March 2023, in Honnavar, India, local fishers sighted 86 sea turtle nests, with over 5,000 eggs in them, along a 3-km stretch of beach between Apsarakonda and Pavinkorava. The highest number of nests previously recorded in the area, 34, was in 2008.[27]
References
- ^ . Retrieved 12 November 2021.
- ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
- ^ a b c d e f "Olive ridley Turtle". WWF India. Retrieved 24 February 2018.
- ^ OCLC 71006746.
- ^ a b c "Lepidochelys olivacea" at the Encyclopedia of Life. Retrieved 16 April 2013.
- ^ a b c d e f g h i j k l m n o p q r s t u v "Recovery Plan for U.S. Pacific Populations of the Olive Ridley Turtle (Lepidochelys olivacea)". Silver Spring, MD: National Marine Fisheries Service. 1998. Retrieved 16 April 2013.
- ISBN 1597265993.
- ISBN 978-1-4214-0135-5. (Lepidochelys olivacea, p. 221).
- ^ Dundee, Harold A. (2001). "The Etymological Riddle of the Ridley Sea Turtle". Marine Turtle Newsletter. 58: 10–12.
- ^ "Marine Turtle Newsletter" – Harold A. Dundee
- ^ ISBN 1560983469.
- ^ "Scan results 'good news' for health of stranded sea turtle", Retrieved on 26 January 2017.
- ^ "Olive ridley turtle found injured off Seaford beach". BBC News. 19 January 2020. Retrieved 19 January 2020.
- ^ a b "Lepidochelys olivacea – Olive Ridley Turtle, Pacific Ridley Turtle". Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities. Retrieved 16 April 2013.
- ^ Carr, A. (March 1972). "Great Reptiles, Great Enigmas". Audubon. 74 (2): 24–35.
- ISBN 0801880076.
- ^ ISBN 978-0801886119.
- ^ "Forging a Future for Pacific Sea Turtles" (PDF). Oceana. 2007. p. 6. Retrieved 16 April 2013.
- ^ Farhana Parvin (22 May 2023). "Record year for olive ridley turtles in Bangladesh as conservation work pays off". Mongabay. Retrieved 26 May 2023.
- ^ "Rare turtles rescued in Ka'u". 9 February 2021.
- ^ Michael R. Heithaus, Aaron J. Wirsing, Jordan A. Thomson, Derek A. Burkholder (2008). "A review of lethal and non-lethal effects of predators on adult marine turtles" (PDF). Journal of Experimental Marine Biology and Ecology (356). Elsevier: 43–51.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ "Jaguar v. sea turtle: when land and marine conservation icons collide". news.mongabay.com.
- S2CID 17524432.
- .
- ^ "Over 8000 turtle hatchlings released", Deccan Chronicle, Chennai, 23 May 2014. Retrieved on 23 May 2014.
- ^ Kumar H., Pavan (17 March 2023). "The more the merrier: Olive ridleys bring cheer to Karnataka". Deccan Herald. Retrieved 15 May 2023.
Further reading
- Eschscholtz F (1829). Zoologischer Atlas, enthaltend Abbildungen und Beschreibungen neuer Thierarten, während des Flottcapitains von Kotzbue zweiter Reise um die Welt, auf der Russisch-Kaiserlichen Kriegsschlupp Predpriaetië in den Jahren 1823 — 1826. Erstes Heft. Berlin: G. Reimer. iv + 17 pp. + Plates I-V. (Chelonia olivacea, new species, pp. 3–4 + Plate III). (in German and Latin).
- ISBN 0-307-47009-1(hardcover). (Lepidochelys olivacea, pp. 36–37).
- ISBN 978-0-395-98272-3. (Lepidochelys olivacea, p. 259 + Plate 23).
- Tripathy, Basudev. Awaiting Arribadda: protection of Olive Ridley Turtles (Lepidochelys olivacea) and their habitat at Rushikulya Rookery in Orissa. OCLC 824502296.
- "Mass-nesting of turtles begins at Odisha's Gahirmatha". www.downtoearth.org.in. Retrieved 21 September 2021.
External links
- Olive ridley turtle, NOAA Fisheries
- Olive Ridley Project
- Photos of Olive ridley sea turtle on Sealife Collection
- https://theoceanconnection.honavar.com/