Flatback Sea Turtles, Natator depressus
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Description & Behavior
Flatback sea turtles, Natator depressus (Garman, 1880), aka Australian flatbacks, are named for their flattened carapace (shell). Synonym: Natator depressa. The flatback's olive gray shell is elliptical in shape with upturned edges. The ventral (under) side, or plastron, is pale yellow. Their shell measures between 102-125 cm long, and these turtles weigh about 84 kg. The flatback's smooth, waxy shell is quite thin and easily damaged. Australian flatbacks are medium sized turtles.
Sea turtles are some of the largest and most endangered turtles in the world and live in almost every ocean of the world. Their smooth shells and paddlelike 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.
Although sea turtles cannot withdraw their heads into their shells, the adults are protected from predators by their shells, large size, and thick scaly skin on their heads and necks.
Sea 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, sea turtles 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 sea turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds. A female loggerhead tracked at sea made up to 500 dives every 12 hours.
Sea turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles drown in shrimp trawls and other fishing gear within a relatively short time.
Because sea turtles are difficult to study in the open ocean, scientists are just beginning to learn about the life history of sea turtles. Today, radio transmitters, attached to nesting turtles, help track the sea creatures on their travels and provide valuable information.
World Range & Habitat
Flatbacks are unique in many ways including their choice of habitat. Instead of clear, coastal waters, flatbacks live in turbid, inshore waters.
Flatback sea turtles are indigenous to Australian waters and are not found anywhere else in the world. They inhabit the coastal waters of Western, Northern and Eastern Australia.
Feeding Behavior (Ecology)
Like many sea turtles, flatbacks have a varied diet that includes squid, sea cucumbers, soft corals, and a variety of mollusks.
Although 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. A female may nest every two to three years.
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 from fifty to two hundred 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 plastron, 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 maturity, they return to the beach where they hatched to lay their eggs.
Nesting for flatbacks takes place in November and December (Australia's summer) on steep, sloping beaches and sand dunes along the northeast coast of Australia. Females lay about four times per season. The eggs hatch in 47-58 days. When the hatchlings emerge, they are larger than most species. They also reach sexual maturity earlier than other turtles. This may be a result of their high protein diet.
Conservation Status & Comments
Flatback sea turtles are preyed upon by saltwater crocodiles, dingos, foxes, rats, and monitor lizards attack hatchlings. Inshore, herons and sea eagles are known to prey upon them as well.
WARNING: Eating 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 death. See the following for more information:
Chelonitoxism: new case reports in French Polynesia and review of the literature
Turtle meat kills six in Micronesia
Tainted Turtle Meat Suspected in Chuuk Deaths
References & Further Research
Great Barrier Reef Marine Park Authority, Flatback Turtles - Natator depressus
SEATURTLE.ORG - Dedicated to providing online resources and solutions in support of sea turtle conservation and research
The State of the World's Sea Turtles (SWoT)
IUCN/SSC Marine Turtle Specialist Group
IUCN Red List of Threatened Species
Research Natator depressus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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