Flatback Sea Turtles: Description and Behavior
The flatback sea turtle (Natator depressus), also called the Australian flatback, is named for its flattened, elliptical carapace with slightly upturned edges. The shell is olive-gray on top and pale yellow on the underside. Measuring 102–125 centimeters in length and weighing around 84 kilograms, these medium-sized turtles are easily recognized by their smooth, thin, and waxy shells, which are more delicate compared to other species.
Like other sea turtles, flatbacks are built for long-distance swimming. Their streamlined shells and paddlelike flippers allow them to reach speeds of up to 24 kilometers per hour and travel thousands of kilometers across the ocean. While they cannot retract their heads into their shells, adults are well-protected by their large size, sturdy shells, and tough, scaly skin.
Breathing and Diving
Though sea turtles spend nearly all their lives submerged, they rely on air for survival. With a quick exhalation and rapid inhalation, they replace lung air in seconds. Their lungs are adapted to exchange oxygen efficiently and prevent gas trapping during deep dives. Typically, green and loggerhead turtles dive for 4–5 minutes and resurface briefly for just 1–3 seconds. Remarkably, one female loggerhead was recorded making up to 500 dives in 12 hours.
Sea turtles can rest underwater for hours, though their breath-holding capacity shortens under stress or during active foraging. Unfortunately, this makes them vulnerable to drowning in fishing gear such as shrimp trawls. Scientists now use radio transmitters attached to nesting turtles to track their movements, shedding light on their elusive lives at sea.
World Range and Habitat
Flatbacks are unique among sea turtles because they prefer turbid, inshore waters rather than clear, open seas. They are found exclusively in Australian waters, inhabiting coastal regions of Western, Northern, and Eastern Australia. Unlike other sea turtle species with global ranges, the flatback’s distribution is entirely limited to this region.
Feeding Behavior
The diet of flatbacks is diverse, consisting of squid, sea cucumbers, soft corals, and various mollusks. Their feeding habits support growth and may contribute to their relatively fast maturity compared with other sea turtle species.
Life History and Nesting
On land, sea turtles are slow and defenseless, and males rarely leave the water. Females emerge only to lay eggs, usually every two to three years, with nesting taking place at night. After laboriously dragging themselves ashore, females dig a pit with their back flippers and lay 50 to 200 eggs, each the size of a golf ball. They then cover the nest with sand, disguising it from predators.
Flatback nesting occurs during Australia’s summer, in November and December, on steep beaches and sand dunes along the northeast coast. Each female may lay four clutches in a season. Eggs hatch within 47–58 days, producing hatchlings larger than those of most sea turtles. Guided by natural light, the young instinctively head toward the sea, though artificial lighting often disorients them. Predation by birds and other animals also takes a heavy toll, and only a small fraction survive. Those that do eventually return to their natal beaches to lay eggs, continuing the cycle of survival unique to the flatback turtle.
