(Eschscholtz, 1829)
Olive ridley turtle
Recognition
A small (to 73.5 cm) sea turtle with six to eight (occasionally five to nine) pleurals on each side. The heart-shaped olive carapace is flattened dorsally, highest anterior to the bridge, and serrated posteriorly. The 1st vertebral is usually slightly broader than long, the 2nd to 4th are longer than broad, and the 5th is much broader than long. Often the original five vertebrals subdivide to produce up to nine. The 1st pair of pleurals touches the cervical, and there may be more pleurals on one side of the carapace than on the other; in specimens from the eastern Pacific, at least, the higher number usually is found on the left side. Twelve to 14 marginals occur on each side of the carapace. Both bridge and plastron are greenish white or greenish yellow. Two longitudinal ridges are present on the plastron, and the plastral formula is: an > fem > gul > abd > pect > hum. The skin is olive above and lighter below. The head is wide, with concave sides, especially on the upper part of the short, broad snout. The bony alveolar surface of the upper jaw may have a gentle elevation extending parallel to the cutting edge, but it lacks a conspicuous ridge.
The diploid chromosomes number is 56: 24 pairs of macrochromosomes (12 metacentric, 2 submetacentric, 2 subtelocentric, and 8 telocentric) and 32 acrocentric microchromosomes (Bhunya and Mohanty-Hejmadi, 1986).
Males have long, thick tails, which extend well beyond the rear carapacial margin; females' tails usually do not reach the margin. Males have concave plastra, a more gently sloping lateral profile, and a strongly developed, curved claw on each front flipper.
Distribution
Lepidochelys olivacea occurs in the tropical waters of the Pacific and Indian oceans from Micronesia, Japan, India, and Arabia south to northern Australia and southern Africa; in the Atlantic Ocean off the western coast of Africa and the coasts of northern Brazil, French Guiana, Surinam, Guyana, and Venezuela in South America; and, occasionally, in the Caribbean Sea as far north as Puerto Rico. In the eastern Pacific it is found from the Galápagos northward to California. Márquez (1990) stated that L. olivacea may even reach the Gulf of Alaska during El Niño years.
Nesting occurs on beaches in the Marianas, northern Australia, Indonesia, Malaysia, Sarawak, the Bonin Islands, southern Japan, Vietnam, Pakistan, the Seychelles, India, Sri Lanka, East Africa, Mozambique, northern Madagascar, western Mexico to Panama and possibly Colombia, and in the Atlantic from Senegal to the Democratic Republic of Congo, Brazil, French Guiana, Surinam, Guyana, Trinidad, and Venezuela (Pritchard, 1979; Márquez, 1990).
Geographic Variation
No subspecies are recognized, but the possibility exists that the eastern Pacific and southern Atlantic populations are distinct. Variations in carapace width and numbers of pleural scutes occur between populations (Pritchard and Trebbau, 1984). However, breeding populations of Lepidochelys olivacea from Surinam in the Caribbean Sea and from the Pacific coast of Costa Rica, 25,000 km apart, were indistinguishable in assays of their mitochondrial DNA (Bowen et al., 1991; Avise et al., 1992).
Habitat
Most records are from protected, relatively shallow marine waters, but the olive ridley occasionally occurs in the open sea. Deraniyagala (1939) reported the habitat to be the shallow water between reefs and shore, larger bays, and lagoons.
Natural History
The complete sexual cycle, size, and age at which males mature are unknown. However, two males with curved carapace lengths of 101-107 cm collected in late April off Nicaragua had mature sperm in their epididymides and their testes seemed to be in early to peak spermiogenesis; a third 72.3 cm males was immature (Owens, 1980). Three other males (curved carapace lengths 62.3-69.0 cm) collected in late October off a nesting beach in Oaxaca, Mexico had epididymides packed with sperm and testes in spermiation (Owens, 1980).
Most nesting females are over 60 cm carapace length (Van Buskirk and Crowder, 1994, reported the average size to be 66 cm), but Cornelius (1983) reported females mature at 55 cm in 7-9 years in Costa Rica. Hughes and Richard (1974) observed a 54 cm female nest in Costa Rica, and Pritchard (1969) found that some matured at 58 cm in Surinam. The ovary of reproductive females has a distinct hierarchy of follicles. October reproductive females from Oaxaca, Mexico, with curved carapace lengths of at least 62 cm had ovaries that weighed 200-845 g, with four to many large follicles that averaged 27 mm in diameter, a second set of smaller follicles about 11 mm in diameter, 17-52 corpora lutea representing recently ovulated eggs, up to 69 smaller corpora lutea representing a still earlier ovulated clutch, and 0-51 oviducal eggs (Owens, 1980).
Mating probably occurs offshore from the nesting beaches at the time of nesting. Females can store sperm from a single mating for future fertilizations (Owens, 1980; Gist and Jones, 1989). However, some mating probably also occurs in the open ocean at other times of the year (Hubbs, 1977). Males probably depart the waters off nesting beaches by mid-season because most of the females have already mated (Plotkin et al., 1996). During mating, the male holds his place on the female's carapace with his forelimb claws, and possibly his tail.
Nesting occurs in almost every month of the year, but usually in the spring and early summer. Females start to emerge from the sea with a rising tide in late afternoon and are finished nesting by the advent of low tide at night. During the peaks of activity many nest on the same stretch of beach; Pritchard (1969) saw 97 nesting simultaneously on a 230-yard stretch of beach in Surinam, and 115 were present on the entire beach. The nesting arribadas may be very large; over 100,000 nest each year at Orissa, India. Not all females nest in arribadas; a few are solitary nesters, but these suffer a higher rate of nest predation (Eckrich and Owens, 1995). The complete nesting, from emergence to re-entering the sea usually takes less than one hour to complete. The average duration between successive nestings is probably 15-17 days (Pritchard, 1969; Minarik, 1985), but females in Costa Rica retained oviducal eggs for 63 days during a period of heavy rainfall that prevented nesting, and then emerged synchronously in an arribada to oviposit after the rain had ceased (Plotkin et al., 1997). Nesting often occurs during periods of strong winds, and Pritchard felt that the interval between nestings was controlled more by environmental factors, such as the tide and weather, than by physiologic factors. Some females may nest annually, but the average female cycle is every 1.70 years (Van Buskirk and Crowder, 1994). The flask-shaped nests are 30-55 cm deep (commonly 38-42 cm; Zwinenberg, 1976); the egg chamber may be 17-30 cm wide (Carr, 1952).
Females may oviposit 1-3 times a year (average, 2.21; Van Buskirk and Crowder, 1994). Clutches contain 30-168 eggs (average, 109.9; Van Buskirk and Crowder, 1994), and the number of eggs laid decreases with each successive clutch during a season. The oval to spherical, white eggs have soft, leathery shells and are 32.1-45.4 mm in diameter. Natural incubation takes a minimum of 45-51 days, but possibly up to 70 days if conditions are unfavorable.
The relatively elongated, oval carapace (31-45 cm; mean 43.3; Van Buskirk and Crowder, 1994) of the hatchling usually has well-developed pale keels on the vertebrals and pleurals. There are four longitudinal ridges on the plastron. Hatchlings are gray black to olive black, with a small white mark at each side of the supralabial scale, another on the hind part of the umbilical protuberance, and several where the ridges of the plastron cross the abdominal and femoral scutes. Both skin and plastron may be dark grayish brown. A fine white line borders the carapace and trailing edge of the fore and hind flippers.
Lepidochelys olivacea is highly carnivorous, feeding predominantly on fish, crabs, snails, oysters, sea urchins, and jellyfish. Seaweeds are occasionally eaten. Captives eat fish, meat, and bread, and may be cannibalistic.
Remark
The pleural scutes of Lepidochelys olivacea are clearly divisible into whole and half scutes, the whole scutes being homologous with the five pleurals of L. kempii. Displacement of homologues of the seams of L. kempii usually is slight, although in cases of extreme splitting (to eight or nine pleurals) the seams become displaced to lessen the size of the small 1st pleural and large last vertebral. In almost every case division takes place in the posterior pleurals; for example, a 6-6 count is produced by division of the 5th pleurals on each side or an 8-8 count by division of the 3rd, 4th, and 5th pleurals.
IUCN Red List Status (1996)
Endangered (A1abd). The taking of nesting females and the gathering of eggs has contributed to decline in L. olivacea. Strict conservation laws must be passed to safeguard this species, especially while nesting.