Olive Ridley Sea Turtles
Olive ridley sea turtles, Lepidochelys olivacea (Eschscholtz, 1829), aka Pacific ridleys, are small, hard-shelled marine turtles, one of the two species of the genus Lepidochelys, and a member of the Family Cheloniidae. It is closely related to the Kemp’s ridley, with the primary distinction being that olive ridleys are found only in warmer waters The olive ridley sea turtle was named after H.N Ridley FRS, who was on the island of Fernando de Noronha, and in Brazil in 1887.
General Description
The olive ridley gets its name from the olive coloration of its heart-shaped top shell (carapace) and is one of the worlds smallest of the sea turtles, with adults reaching up to 60 centimetres in length and weighing anything from 36 to 49 kilograms. The species may be identified by the uniquely high and variable numbers of vertebral and costal scutes along its carapace which is bony, without ridges and has large scutes (scales). In addition, the vertebral scutes also show frequent division, as do the scales on the dorsal surface of the head. The prefrontal scales, however, usually number two pairs.
Their smooth shells and paddle-like flippers help them speed through the water as fast as 24 kph. These long-distance travelers have been known to swim up to 4,828 km in one year.
Males have longer thicker tails than females and well-developed curved claws on the forelimbs.
Although olive ridley sea turtles cannot withdraw their heads into their shells, the adults are protected from predators by their shells, and thick scaly skin on their heads and necks.
The turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, olive ridleys can quickly replace the air in their lungs. The lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. The blood of olive ridley sea turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving.
Eating olive ridley sea turtles and their eggs, anywhere, can cause severe illness and even death, especially to children. The flesh has been found to contain chelonitoxin which may cause a number of symptoms including nausea, vomiting, diarrhea, burning sensation of lips, tongue and mouth, chest tightness, difficulty swallowing, hypersalivation, skin rash, coma and even death.
Behavior
The species can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or while escaping predators. Breath-holding ability is affected by activity and stress, which is why sea turtles drown in shrimp trawls and other fishing gear within a relatively short time.
Although olive ridley sea turtles move swiftly in the ocean, they are slow and defenseless on land. Male sea turtles almost never leave the water. Female sea turtles leave the ocean only to lay eggs and, for most species, nest only at night. Females of most species may nest every two to three years.
Feeding Habits
The olive ridley is omnivorous, meaning it feeds on a wide variety of food items, including algae, lobster, crabs, tunicates, mollusks, shrimp, and fish. They can dive to depths of about 150 metres, to forage on benthic invertebrates. and they possess powerful jaws that crush their prey which enables the turtle to swallow their meal.
Reproduction
The olive ridley has one of the most extraordinary nesting habits in the natural world. Large groups of turtles gather offshore next nesting beaches. Then, all at once, vast numbers of turtles come ashore and nest in what is known as an arribada. During these arribadas, hundreds to thousands of females come ashore to lay their eggs. At many nesting beaches, the nesting density is so high that previously laid egg clutches are dug up by other females excavating the nest to lay their own eggs.
There are many theories on what triggers an arribada, including offshore winds, lunar cycles, and the release of pheromones by females. Despite these theories, scientists have yet to determine the actual cues for ridley arribadas. Not all females nest during an arribada, instead some are solitary nesters. Some employ a mixed nesting strategy. For example, a single female might nest during an arribada, as well as nest alone during the same nesting season.
Females nest every year, once or twice a season, laying clutches of approximately 100 eggs on average. Incubation usually takes between 50 to 60 days.
Nesting can take between one and three hours. After a female turtle drags herself up the beach, she hollows out a pit with her back legs and deposits anything from 50 to 200 eggs the size of golf balls. When the last egg is laid, the turtle covers the eggs with sand, tamps down the sand with her tail and flings more sand about with her flippers to erase any signs of the nest.
After about two months, the hatchling turtles emerge at night. The light reflected off the water from the sky guides them to the sea. These days, car headlights, street lamps, or lights on buildings near the beach cause some hatchlings to travel in the wrong direction. Waiting herons make fast meals of other hatchlings. Any babies still on the beach in the morning are easily picked off by predators or die in the hot sun. It is thought that when the surviving hatchlings reach sexual maturity, at about 15 years of age, they return to the beach where they hatched to lay their eggs.
Distribution
he olive ridley is mainly a pelagic sea turtle, but has been known to inhabit coastal areas, including bays and estuaries. Olive ridleys mostly breed annually and have an annual migration from pelagic foraging, to coastal breeding and nesting grounds, back to pelagic foraging.
They are found worldwide in tropical and warm temperate ocean waters, and is usually an open ocean inhabitant, commonly found in protected, relatively shallow bays and lagoons and the shallow water between reefs and the shore
Wicked Diving is lucky enough to experience these turtles in most places we dive. However, the numbers are very low in the Similan Islands so it warrants a special day when we see one. They are spotted in the area around Komodo park and on our expeditions.
Ecological Considerations
The olive ridley sea turtle is listed as endangered by the IUCN. Degradation of nesting beaches, ongoing directed harvest, and bycatch in fisheries have all contributed to the decline of the species. The olive ridley may be the most abundant sea turtle on the planet, but some argue that it is also the most exploited.
According to the Marine Turtle Specialist Group (MTSG) of the IUCN, there has been a 50% reduction in population size since the 1960s. Although some nesting populations have increased in the past few years, the overall reduction is greater than the overall increase.
The principal cause of the historical, worldwide decline of the olive ridley sea turtle is long-term collection of eggs and killing of adults on nesting beaches. Because arribadas concentrate females and nests in time and space, they allow for mass slaughters of adult females for their meat and skin, as well as the removal of an excessive number of eggs. These threats continue in some areas of the world today, compromising efforts to recover this species.
Additionally, incidental captures in fishing gear, primarily in longlines, but also in trawls, gill nets, purse seines, and hook and line, frequently snag and drown these turtles and is therefore a serious ongoing source of mortality that adversely affects the species’ recovery.
Though the olive ridley is widely considered the most abundant of the marine turtles, by all estimates, it is in trouble. Rough estimates put the worldwide population of nesting females at about 800,000.
Olive ridley sea turtles are protected by various international treaties and agreements as well as national laws. Many governments have protections for olive ridleys, but still, eggs are taken and nesting females are slaughtered.
This species is also threatened by human impact. Pesticides, heavy metals and PCBs have been detected in turtles and eggs, but their effect is currently unknown. Oil spills cause respiratory, skin, blood and salt gland problems. Marine debris such as plastic bags, plastic and styrofoam, tar, balloons and plastic pellets have been discovered in dead olive ridley stomachs. Consumption of synthetic materials interferes with metabolism and harms the animal through absorption of toxic byproducts. Marine recreation, boating, and ship traffic also threatens this species due to propeller and collision injuries.
